Category: invasive plants

What will replace hemlocks? Intractions with other plants & introduced pathogens complicate the situation

eastern hemlocks in Cook Forest State Forest Pennsylvania; photo by F.T. Campbell

As Eastern hemlock (Tsuga canadensis) suffers high levels of mortality across nearly all its range due to hemlock woolly adelgid (HWA; Adelges tsugae),  scientists scramble to determine what the successor forests will look like. The transformation will be stark: from deeply shaded evergreen coniferous forest with a sparse understory to something very different. As this process takes place, most scientists expect cascading effects on not only terrestrial and aquatic wildlife but also onecosystem functions, including soils and nutrient and hydrologic cycles (Dharmadi et al. 2019 Plotkin et al. 2024).

New England

In southern New England, hemlock groves are being replaced by stands of deciduous hardwood forests dominated by black birch (Betula lenta). While birch are expected to continue to dominate, other species comprise at least one third of seedlings in the Harvard Forest experimental sites, primarily eastern white pine (Pinus strobus) and red maple (Acer rubrum). Plotkin et al. (2024) note that conversion of hemlock forests to pine forests would be a less dramatic ecosystem shift since both are evergreen conifers.

symptoms of beech leaf disease; photo by the Ohio State University

In both southern New England and farther north, in Vermont and New Hampshire, maples and American beech have increased in prominence. In the latter case, this is despite the prevalence of beech bark disease and managers’ efforts to suppress beech. I have noted that beech leaf disease now threatens to disrupt this process.

Landowners in the region often seek to get some financial return from their forests before a pest kills the trees. About a quarter of the almost 9,000 ha of hemlock stands in the southern Connecticut River Valley have been harvested as HWA spread into the area. To test the effect of pre-mortality logging of hemlock stands, Plotkin et al. tried to mimic HWA-caused mortality by girdling all the hemlocks in some plots in Harvard Forest. In other plots they harvested most hemlocks and some of the other tree species. The girdled plots had a dramatic increase in standing and downed deadwood and a longer period of elevated understory light levels than the logged plots. They note that standing snags and on-ground dead wood provide critical ecosystem functions. Many wildlife and microbial species depend on dead wood for nutrition and a variety of micro habitats. Plotkin et al. found that the slowly decomposing dead wood also stored a large amount of carbon: girdled plots stored 18% more above-ground carbon than logged sites, even after accounting for carbon stored in harvested wood products.

a beech snag with nesting cavities; photo by F.T. Campbell

The magnitude of these differences might be even larger than demonstrated in this experiment. In New England, hemlocks infested with HWA die over a decade, not the two years seen after girdling. The delayed mortality provides a longer window of opportunity for succeeding vegetation to adapt and preserve higher levels of biodiversity. Plotkin et al. (2024) suggest that logging pest-threatened hemlock forests might remove structural resources that would support forest response to ongoing climate stress and future disturbances.

Considering the disturbed plots’ invasibility by non-native plants, Plotkin et al. (2024) found that more non-native shrubs invaded the girdled plots than the logged plots. They suggest that birds that disperse the shrubs’ fleshy fruits were attracted by perch sites provided by the standing dead trees.

Southern Appalachians

In the Southern Appalachians, post-HWA forests will apparently be quite different. At the USDA Forest Service’ Coweeta Hydrologic Laboratory in the Nantahala Mountain Range of western North Carolina, eastern hemlock died much faster than in New England. Hemlocks comprised more than 40% of the basal area before arrival of HWA (detected in 2003). Within two years all hemlock trees were infested. Half were dead by 2010, 97% by 2014 (Dharmadi et al. 2919).

In some part of the southern Appalachian forests the shrub layer is dominated by Rhododendron maximum (rosebay rhododendron). This dense shrub layer is preventing recruitment of deciduous tree species that had been expected to replace the dead hemlocks. Tree seedlings died rather than grew into saplings. Scientists working in the Coweeta experimental forest attribute the seedlings’ demise to limited access to key resources, e.g., water, nutrients (especially inorganic nitrogen), and light (Dharmadi, Elliott and Miniat 2019).

In the Coweeta Basin, hemlock loss is the most recent of a series of severe disturbances that have apparently led to a cascade of responses in the overstory, midstory, and soil that have promoted expansion of rhododendron. (The earlier disturbances were widespread logging in the 19th Century and the loss of American chestnut to chestnut blight in the first part of the 20th Century. Therefore, the response of future forests to changes in temperature and rainfall might now depend on these novel tree-shrub interactions .

R. maximum hampers succession by forming a dense subcanopy layer that greatly limits light reaching the forest floor and reduces soil moisture and temperature. These changes impede seed germination and seedling survival. In addition, rhododendron leaves that fall to the ground create a thick organic soil layer that decomposes very slowly. This affects soil chemistry, specifically availability of the key nutrient nitrogen.

The rhododendron shrubs in the region are younger than the deciduous trees now making up the canopy above them (Dharmadi, Elliott and Miniat 2019). The dense rhododendron stands resulted from the widespread mortality of American chestnut (Castanea dentata) in the early 20th century and of hemlock in the first years of the 21st Century. What’s more, even the mature deciduous trees appear to be suppressed by dense rhododendron stands. Canopy trees above rhododendrons are on average 6m shorter than those growing on sites without rhododendron thickets (Dharmadi, Elliott and Miniat 2019). In fact, by 2014, 10% of standing trees other than hemlocks had died. The tree suffering the highest level of mortality was flowering dogwood (Cornus florida). The authors do not mention a probable factor, the introduced disease dogwood anthracnose. Other species experiencing high levels of mortality are not, to my knowledge, under attack by non-native pests, so their demise seems more clearly linked to resource competition with rhododendron. These were striped maple (Acer pennsylvanicum), pitch pine (Pinus rigida), witch hazel (Hamamelis virginiana), and that staple of New England aftermath forests, black birch (Betula lenta).

Dharmadi, Elliott and Miniat (2019) suggested that managers should step in to increase recruitment in both understory and overstory layers. They proposed active management: removing rhododendrons and the soil organic layer. USFS scientists are applying these ideas experimentally at the Coweeta research station. I am unclear as to whether there is one study or more. In any case, rhododendronplants have been removed with the goal of restoring vegetation structure and composition – presumably both understory plant diversity and recruitment of tree species capable of growing into the canopy. In at least some cases, the rhododendron removal is followed by prescribed fire. One study is looking also at whether this action increased water yield.

Apparently this lack of tree regeneration is extensive – although published data are not easily accessible. Staff of the North Carolina Hemlock Restoration Initiative report they encounter similar issues (O.W. Hall, Hemlock Restoration Initiative, pers. comm.)

Several experiments have demonstrated that even in the southern Appalachians, where there are abundant moisture and rainfall, the trees and shrubs compete for water and other nutrients. However, Dharmadi et al. (2022) found that removal of the rhododendron shrub layer is unlikely to significantly alter streamflow, atr least during the growing season. In winter, when deciduous trees lack leaves, reduction in interception of precipitation might result in increased streamflow (Dharmadi et al. 2022). I ask whether increasing stream flow in winter is a goal? I thought the concern was stream flow levels in summer.

Nor is removal of the rhododendron shrub layer likely to alter stream chemistry during the growing season.

Removal of living Rhododendron and leaf litter apparently can help restore forest structure through improving tree seedling survival and recruitment as well as increasing growth of established trees.

Removing Privet

However, other management actions might bring about desired changes more effectively or broadly. Specifically Dharmadi and colleagues mentioned removal of privet (Ligustrum) – a very widespread invasive shrub in forests of the Southeast. (Fifteen years ago it was estimated that just one privet species, Chinese privet, occupied more than a million hectares in 12 southeastern states [Hanula 2009].)

Chinese privet

I ask also whether prescribed fire to remove the rhododendron-dominated soil organic layer is useful. Dharmadi and colleagues found that such fires reduced leaf litter temporarily, but annual leaf-fall replaced the litter layer the next year, so this management effort is unlikely to affect plot evapotranspiration rates.

Supporting Pollinators

Another study (Ulyshenet al. 2022) examined whether removing rosebay rhododendron would benefit bees and other pollinators. They found that removal of Rhododendron alone (without fire) did not dramatically improve pollinator habitat in the southern Appalachians. In fact, about a quarter of the bee species studied visited R. maximum flowers and might decline if the shrub’s population is reduced. Ulyshen and colleagues suggest that some factors that correlate with fire severity probably promotes growth of insect-pollinated plants. They suggest specifically the greater presence of downed woody debris, which provides nesting sites and other resources used by insects. They recommended creation of open areas to support wildflowers as a more effective way to benefit bees in this region. Again, rhododendron removal pales in effectiveness compared to eradication of privet.

SOURCES

Dharmadi, S.N., K.J. Elliott, C.F. Miniat. 2019. Lack of forest tree seedling recruitment and enhanced tree and shrub growth characterizes post-Tsuga canadensis mortality forests in the southern Appalachians. Forest Ecology and Management 440 (2019) 122–130.

Dharmadi, S.N., K.J. Elliott, C.F. Miniat. 2022.  Larger hardwood trees benefit from removing Rhododendron maximum following Tsuga canadensis mortality. Forest Ecology and Management

Hanula, J.L., S. Horn, and J.W. Taylor. 2009. Chinese Privet (Ligustrum sinense) Removal and its Effect on Native Plant Communities of Riparian Forests. Invasive Plant Science and Management 2009 2:292–300.

Plotkin, A.B., A.M. Ellison, D.A. Orwig, M.G. MacLean. 2024. Logging response alters trajectories of reorganization after loss of a foundation tree species. Ecological Applications. 2024;e2957.

Ulyshen, M., K. Elliott, J. Scott, S. Horn, P. Clinton, N. Liu, C.F. Miniat, P. Caldwell, C. Oishi,  J.  Knoepp, P. Bolstad. 2022. Effects of Rhododendron removal and prescribed fire on bees and plants in the southern Appalachians. Ecology and Evolution. 2022;12:e8677.

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at  https://treeimprovement.tennessee.edu/

or

www.fadingforests.org

APHIS funding for pests that kill trees (& cacti)

emerald ash borer; some of PPA grants are funding evaluation of biocontrol efficacy

USDA APHIS has released information about its most recent annual allocation of funds under the Plant Pest and Disease Management & Disaster Prevention Program under §7721 of the Plant Protection Act. (Also see Fading Forests II and III; links provided at the end of this blog.) These funds support both critical needs and opportunities to strengthen the nation’s infrastructure for pest detection, surveillance, identification, and threat mitigation. Since 2009, this USDA program has provided nearly $940 million to more than 5,890 projects.

For FY25 APHIS allocated $62.725 million to fund 339 projects, about 58% of the proposals submitted. About $10 million has reserved for responding to pest and plant health emergencies throughout the year.

According to APHIS’ press release, the highest amount of funds (almost $16 million) is allocated to the category “Enhanced Plant Pest/Disease Survey.” Projects on “Enhanced Mitigation Capabilities” received $13.6 million. “Targetting Domestic Inspection Efforts to Vulnerable Points” received nearly $6 million. “Improving Pest Identification and Detection Technology” was funded at $5 million. Outreach & education received $4 million.  I am not sure why these do not total $63 million.

Funding for States and Specific Pests

Wood-boring insects received about $2.3 million. These included more than $869,800 to assess the efficacy of biocontrol for controlling emerald ash borer (EAB) Agrilus planipennis, $687,410 was provided for various detection projects, and $450,000 for outreach efforts related to various pests. Ohio State received $93,000 to optimize traps for the detection of non-native scolytines (bark beetles).

Biocontrol efficacy will also be assessed for hemlock woolly adelgid, invasive shot hole borers, cactus moth, and several invasive plants (including Brazilian pepper). (Contact me to obtain a copy of CISP’s comments on this biocontrol program.)

Opuntia basilaris in Anza Boreggo; one of flat-padded Opuntia vulnerable to the cactus moth; photo by F.T. Campbell

Funding for other pests exceeded $1 million for spotted lanternfly (nearly $1.4 million), Asian defoliators ($1.2 million) and box tree moth (just over $1 million).

$630,000 was provided for detection surveys and studies of the sudden oak death pathogen Phytophthora ramorum, especially how it infects nursery stock. Nursery surveys are funded in Alabama, Louisiana, North Carolina, Ohio, Oklahoma, Pennsylvania, South Carolina, Tennessee, Virginia, and West Virginia. Most of these states are in regions considered most at risk to SOD infection of wildland plants.    

sudden oak mortality of tanoak trees in southern Oregon; photo by Oregon Department of Forestry

Oregon received much-deserved $41,000 to evaluate the threat of the NA2 and EU2 lineages of P. ramorum to nurseries and forests Oregon also received $104,000 to respond to the detection of Phytophthora austrocedri in nurseries in the state. The Oregon outbreak has been traced to Ohio, but I see no record of funds to assist that state in determining how it was introduced.

Asian defoliator (e.g., Lymantrid moths) surveys have been funded for several years. This year’s projects are in Alaska, Arkansas, California, Kentucky, Maryland, Massachusetts, Mississippi, Montana, Nevada, North Carolina, Oregon, Tennessee, Texas, Washington, and West Virginia. While I agree that the introduction risk is not limited to coastal states with maritime ports, I don’t what criteria were applied in choosing the non-coastal states which are funded to search for these insects

Spotted lanternfly surveys (including technological improvements) or related outreach are funded in Alabama, Connecticut, Delaware, Kentucky, New Hampshire, New Jersey, North Carolina, Oregon, Pennsylvania, and Tennessee. California’s project is focused on postharvest treatments.

The Don’t Move Firewood project continues to be funded by APHIS. Several states also direct attention specifically to the firewood pathway: Kentucky, Maine, and Michigan.

I applaud the precautionary funding of the Agriculture Research Service to generate of high-quality genomic resources for managing the causal agent of Japanese oak wilt Dryadomyces quercivorous

Florida Department of Agriculture, North Carolina State University, and West Virginia University each received more than $100,000 to improve detection and management of invasive hornets.

Tennessee State University got $100,000 to continue efforts to detect and understand Vascular Streak Dieback in redbud Cercis canadensis.

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at  https://treeimprovement.tennessee.edu/

or

www.fadingforests.org

Again – analysts of changing forests leave out key factors

oak & beech seedlings; photo by F.T. Campbell

Yet again, studies focusing on issues of regeneration and mortality failing to consider all aspects.

Two studies focused on persistence of oak forests – a topic of great concern because of economic and ecological importance of oak-dominated forests. Since they dominate forests covering 78.5 million ha (51% of all forestland in the eastern United States) (Dey 2013), oaks shape stand structure and composition; their extensive crowns support many bird and arboreal mammal species; their acorns and leaf litter are the foundation of complex food webs; they live in symbiotic relationships with mycorrhizal fungi that enhance nutrient cycling and uptake within forest ecosystems. Deep roots prevent soil erosion. Oaks play a pivotal role in carbon sequestration (Khadka, Hong, and Bardhan 2024).

Until recently concern has focused on mortality of species in the red oak group (Section Lobatae). Now there is increasing concern about white oak (Quercus alba) mortality. Forest managers reported elevated mortality not just in resource-limited sites,e.g., those characterized by drought conditions, poor drainage, and soil nutrient deficiencies. Deaths are also occurring in higher-quality mesic sites, especially in forests with high stand density and advanced maturity stages. While white oaks go through a self-thinning phase – when dense stands of younger trees compete intensely for limited resources –it appears that some of the concern is focused on this stage (Khadka, Hong, and Bardhan 2024).

I think much of the concern is driven by economic rather than ecological considerations. None of oak species mentioned by Duana et al. (2024) is considered at risk by the authors of the recent conservation gap analysis (Beckman et al. 2019). (This is not surprising since presumably these species are sufficiently numerous to support commercial harvests). Furthermore, complaints about forest regeneration in the East are broader than oaks. A multi-author examination of the future of the northern forest projected decreases for four forest types = aspen-birch, elm-ash-cottonwood, oak-hickory, and spruce-fir. One type –maple-beech-birch – was expected to expand (Shifley and Moser 2016).

Regarding oaks specifically, Khadka, Hong, and Bardhan (2024) found that 30% of FIA plots in ten states composed primarily of white oak met their criteria for considering white oaks to be “declining”. However, higher mortality was limited to scattered areas (see map in Fig. 2B in the article). They suggested that contributing factors included higher elevation and distance from water in the north, intense competition in central regions, and drought stress in oak-hickory forests in the south. They also mentioned mature stands which are not replacing themselves in the southern region. Khadka, Hong, and Bardhan (2024) noted that oak decline complex is a factor in the southern region, and localized non-native insect pests (apparently spongy moth) in the northern region. (I will discuss both regeneration failures and the impacts of non-native pests below.) Still, these authors focus most attention to environmental stresses, e.g., droughts or water logging, poor soils, extreme weather events; and to human management, e.g., fire suppression, logging intensity, edge effects. They suggest strategies for mitigating these factors.

A second study, published by Duana et al. (2024), considered stocking levels of several species of oaks (Q. alba, Q. coccinea, Q. prinus, Q. rubra, and Q. velutina) but limited themselves to a large, temperate hardwood forest landscape in southeastern Ohio. Their purpose was to evaluate the efficacy of two levels of silvicultural intervention in sustaining oaks and restraining maples over the long-term, defined as 150-years (to 2060).

red oak (Quercus rubra); photo by F.T. Campbell

Their model suggested that continuing “business as usual” management would result in oaks shrinking from 22.8% dominance in 2010 to 12% dominance in 2160. Many of the remaining oaks would be large — in the 70 cm DBH class. The undesired maples would rise from 23% of total relative dominance in 2010 to 58% in 2160. The maples grew to almost the same size as the oaks: 50–65 cm DBH. As a result of these developments, the maple basal area increase by more than five times. The basal area of early successional species, e.g., poplars and aspens, decreased from 25% dominance to 11% dominance by 2160. Shade-tolerant species like elms, hickories, beech, and hemlock were suppressed by more competitive maples, occupying 17% of the total dominance.

Under the more manipulative alternative management strategy, oaks’ relative dominance on private land would stay above 20% of total relative dominance; all ages and sizes would be present. Maples would hold steadier at 23% to 33%. Shade-tolerant species would also rise, reaching a quarter of relative dominance on private some site (private public lands).

Duana et al. (2024) explained the outcome of “business as usual” management on maples’ ability to thrive in shaded conditions while oak regeneration requires sunlight to reach the forest floor. Another factor is the prevalence of high-grading harvesting practices. These factors result in a significant absence of oak trees in the sapling and midstory sizes, reflecting challenges to both oak seedlings and saplings. In other words, despite the continued growth of mature overstory oaks, the trees cannot reproduce. As Duana et al. (2024) point out, these results are supported by other field-based studies — including ones I have blogged about. Duana et al. (2024) discuss barriers and incentives to private landowners adopting more active management.

However, as I pointed out above, many tree species are regenerating poorly, not just oaks. Indeed, none of the eastern species fulfilling Potter and Riitters’ (2022) criteria for species threatened by poor regeneration was an oak. See Table 2 in Potter and Riitters (2022).

American sycamore (Platanus  occidentalis) – one of the tree species not regenerating adequately; photo by F.T. Campbell

Hanberry et al. (2020) found that actual changes in forest species composition and density do not conform to expectations arising from three factors proposed as drivers: increased precipitation, increased white-tailed deer densities, and functional extinction of American chestnut. They found disappearance of frequent low-intensity fires to be determinative.  However, Hanberry et al. (2020) also do not mention invasive plants or non-native pests other than chestnut blight.

Here I review others’ discussion of browsing by overabundant deer and competition from non-native plants as factors widely recognized as impeding regeneration of canopy trees, including oaks.

Deer

There is widespread agreement that browsing by overabundant deer is a major cause of poor regeneration of deciduous forests, especially but not limited to oaks (Quercus species.). Sources cited in my previous blogs include most studies discussed at the 2023 Northern Hardwood research forum (USDA, FS 2023b Proceedings),  Spicer et al. (2023), Miller et al., and two studies based in either Ohio (the location of the study by Duana et al. [2024]) or neighboring Pennsylvania: Yaccuci et al. (2023) and Reed et al. 2023. Yacucci et al. reported that stem density of red (Q. rubra) and pin oaks (Q. palustris) was 13 times higher in canopy gaps located in areas with low densities of deer than in gaps in high-deer-density locations. In these gaps, oak saplings were growing into the subcanopy. Reed et al. said deer herbivory might be one of the most important drivers of forest composition and canopy structure over long time-scales.

Deer might be less important in New England. Stern et al. (2023), working in Vermont, focused on the importance of changing precipitation patterns in shifting numbers of red maple (Acer rubrum), sugar maple (Acer saccharum), American beech (Fagus grandifolia), and yellow birch (Betula alleghaniensis). Northern red oak was described as a common co-occurring dominant species in their plots, but was not discussed. In New Hampshire, Ducey et al. reported changing species composition as the forest ages but did not mention deer.

Some of these authors advocated wide-scale efforts to reduce deer populations in order to restore forest ecosystems. Yacucci et al. proposed enlisting those military posts that regularly cull deer into efforts to conserve and regenerate native plants. Otherwise, they say, the prognosis for regeneration is poor. Blossey et al. urged creation of a nation-wide lethal removal program.

Some of these studies indicated that additional biological entities were also important. Miller et al. stressed the role of invasive plants in suppressing forest regeneration in National parks from Virginia to Maine. Reed et al. focused on invading earthworms. One study – again, conducted in Ohio – Hovena et al. (2022), found that interactions between non-native shrubs and soil wetness overshadowed even the impact of deer herbivory on the species richness and abundance of seedlings.

Invasive Plants

FIA data indicate that 46% of forests in the eastern United States are invaded by alien plant species (Oswalt et al. 2016). Across the region, hundreds of non-native plant species are established in forests and woodlands. (See lists compiled by the Southeast Exotic Pest Plant Council, Mid-Atlantic Invasive Plant Council, Midwest Invasive Plants Network). Forests of the northern Midwest are among the most heavily invaded; in Ohio specifically, two studies found that more than 90% of FIA plots harbor at least one invasive plant species (Oswalt et al. [2016] and Kurtz (USDA NRS 311).

Many of these invaders are herbs, shrubs, or trees which can invade shaded environments. I remind you that a high proportion of these invasive plant species have been deliberately planted either directly in “natural” areas or in yards and gardens throughout the region.

Invasive plants can reduce native diversity, alter forest structure, suppress tree regeneration, alter nutrient cycling, and modify disturbance regimes (Miller et al. 2023).

Japanese stiltgrass (Microstegium vimineum) is widespread in forests of both Northeast (Oswalt et al. (2016) and Southeast. Stiltgrass invasions can suppress oak regeneration – at least as part of interactions with herbivore browsing and harvest history (Johnson et al. 2015).

Amur honeysuckle; via Flickr

Several non-native shrub and vine species are also widespread. For example, multiflora rose (Rosa multiflora) is the most frequently recorded invasive plant, present on 16.6% of surveyed plots in 39 states and five Canadian provinces. Again, the state with the highest proportion of plots invaded is Ohio – 85% (USDA Forest Service NRS-109). A study in central Ohio found that the presence of Amur honeysuckle (Lonicera mackii) had a stronger influence on tree species diversity than on the size or number of trees. Removing honeysuckle from heavily invaded areas promoted native tree growth (e.g., the height of tallest trees) and increased the tree canopy’s structural complexity for up to 10 years. Forest recovery began within two years of honeysuckle removal Fotis et al. (2022). (To access earlier blogs, visit www.nivemnic.us; scroll below “archives” to “categories”, click on “invasive plants.)

This impediment to forest regeneration is expected to get worse: non-native plant species are already more widely distributed than native species although the average invasive plant inhabits only about 50% of its expected range (Bradley, Early and Sorte 2015). From Virginia and West Virginia north to Maine, 80% of National Park units have experienced a significant increase in at least one trend measuring abundance of invasive plants in recent decades. In 10 parks (a quarter of all parks studied), total invasives increased significantly in two of three metrics (Miller et al. 2023).

Non-native Pests

Another set of biological factors affecting forest persistence and possibly regeneration is non-native pests that kill North American trees. I have complained that too few of the studies of regeneration discuss implications of these bioinvasions. So Khadka, Hong, and Bardhan (2024), Duana et al. (2024), and Hanberry et al. (2020) continue a tradition that I think is most unfortunate.

American elm in full glory; photo by F.T. Campbell

In Ohio specifically, Hovena et al. and Yacucci et al. did not mention loss of canopy elms, or ash, or the impending threat from beech leaf disease. All these trees are – or used to be – quite common in Ohio. More understandable, perhaps, is lack of attention to laurel wilt disease, which is just now at the state’s southern border. It might decimate an important native shrub, Lindera benzoin. American chestnut was also present in Ohio before its near disappearance following introduction of the chestnut blight fungus early in the 20th Century.

Another possibly damaging pest that has recently turned up in Ohio is the elm zigzag sawfly Aproceros leucopoda. This Asian insect was first detected in North America in 2020 in Ontario. It quickly became apparent that it was more widespread. The Ohio detection came in 2023 – too recent to be discussed by Hovena et al. or Yacucci et al. Its impact several elm species is currently unknown.

There are exceptions. Both Stern et al. (2023) and Ducey at al. (2023) reported robust growth rates of American beech (Fagus grandifolia) despite decades-long establishment of beech bark disease. DMF Neither mentioned beech leaf disease – to be fair, this bioinvader is just starting to appear in New England. Stern et al. (2023) did not discuss hemlock woolly adelgid although Eastern hemlock (Tsuga canadensis) is also a common co-occurring dominant species in their plots. Ducey et al. did anticipate pest-driven reversals of increased numbers of eastern hemlock (Tsuga canadensis) and of white ash (Fraxinus americana). Stern et al. (2023) also did not mention oak wilt, despite a vulnerable host — northern red oak — being a common co-dominant species in his study site in Vermont. To be fair, oak wilt is not yet established in New England, although it is in New York and in western Ontario.

The most complete discussion of non-native pests is by Payne and Peet, working in the Piedmont of North Carolina. They state that several “specialist” pathogens have caused loss of important tree species, resulting in drastic and long-lasting shifts in community dynamics. They mention elms and dogwoods plus impending insect-caused widespread mortality of ash.

flowering dogwood (Cornus florida); photo by F.T. Campbell

Miller et al. describe the impact of EAB on ash resources in the National parks and express concern that BLD will cause considerable damage to some units of the system.

I think the failure of scientists to integrate invasive species’ impacts into assessments of changes in forest tree composition will mean that recommendations for management will be – at best – incomplete; at worst – wrong.

SOURCES

Beckman, E., Meyer, A., Denvir, A., Gill, D., Man, G., Pivorunas, D., Shaw, K., and Westwood, M. (2019). Conservation Gap Analysis of Native U.S. Oaks. Lisle, IL: The Morton Arboretum.

Blossey. B., D. Hare, and D.M. Waller, 2024. Where have all the flowers gone? A call for federal leadership in deer management in the US. Front. Conserv. Sci. 5:1382132. doi: 10.3389/fcosc.2024.1382132

Bradley, B.A., R. Early and C. J. B. Sorte. 2015. Space to invade? Comparative range infilling and potential range of invasive and native plants. Global Ecology and Biogeography

Dey, D.C. 2013. Sustaining Oak Forests in Eastern North America: Regeneration and Recruitment, the Pillars of Sustainability. For. Sci. 60(5):926–942 October 2013. http://dx.doi.org/10.5849/forsci.13-114  

Duana, S., H.S. He, L.S. Pile Knapp, T.W. Bonnot, J.S. Fraser. 2024. Private land management is more important than public land in sustaining oaks in temperate forests in the eastern U.S. Journal of Environmental Management 352 (2024) 120013

Ducey, M.J, O.L. Fraser, M. Yamasaki, E.P. Belair, W.B. Leak. 2023. Eight decades of compositional change in a managed northern hardwood landscape. Forest Ecosystems 10 (2023) 100121

Fotis, A., Flower, C.E.; Atkins, J.W. Pinchot, C.C., Rodewald, A.D., Matthews, S. 2022. The short-term and long-term effects of honeysuckle removal on canopy structure and implications for urban forest management. Forest Ecology and Management. 517(6): 120251. 10 p. https://doi.org/10.1016/j.foreco.2022.120251

Hanberry, B.B., M.D. Abrams, M.A. Arthur & J.M. Varner. 2020. Reviewing Fire, Climate, Deer, & Foundation Spp as Drivers of Historically Open Oak & Pine Forests & Transition to Closed Forests. Front. For. Glob. Change 3:56. doi: 10.3389/ffgc.2020.00056

Hovena, B.M., K.S. Knight, V.E. Peters, and D.L Gorchov. 2022. Woody seedling community responses to deer herbivory, intro shrubs, and ash mortality depend on canopy competition and site wetness. Forest Ecology and Management. 523 (2022) 120488

Johnson, D.J., S.L. Flory, A. Shelton, C. Huebner and Keith Clay. 2015 Interactive effects of a non-native invasive grass Microstegium vimineum and herbivore exclusion on experimental tree regeneration under differing forest management. Journal of Applied Ecology 2015, 52, 210–219 doi: 10.1111/1365-2664.12356

Khadka, H.S. Hong,  S. Bardhan. 2024. Investigating the Spatial Pattern of White Oak (Q. alba L.) Mortality Using Ripley’s K Function across the Ten States of the eastern United States. Forests 2024, 15, 1809. https://doi.org/10.3390/f15101809

Miller, K.M., S.J. Perles, J.P. Schmit, E.R. Matthews, and M.R. Marshall. 2023. Overabundant deer and invasive plants drive widespread regeneration debt in eastern United States national parks. Ecological Applications. 2023;33:e2837. https://onlinelibrary.wiley.com/r/eap  Open Access

Oswalt, C.M., S. Fei, Q. Guo, B.V. Iannone III, S.N. Oswalt, B.C. Pijanowski, K.M. Potte. 2916. A subcontinental view of forest plant invasions. NeoBiota. 24: 49-54 http://www.srs.fs.usda.gov/pubs/48489

Payne, C.J. and R.K. Peet. 2023. Revisiting the model system for forest succession: Eighty years of resampling Piedmont forests reveals need for an improved suite of indicators of successional change. Ecological Indicators 154 (2023) 110679

Pinchot, C.C., A.A. Royo, J.S. Stanovick, S.E. Schlarbaum, A.M. Sharp, S.L. Anagnostakis. YEAR

Deer browse susceptibility limits c’nut restoration success in northern hardwood forests PUBLIC

Potter, K.M and Riitters, K. 2022. A National Multi-Scale Assessment of Regeneration Deficit as an Indicator of Potential Risk of Forest Genetic Variation Loss. Forests 2022, 13, 19.

https://doi.org/10.3390/f13010019.

Reed, S.P., D.R. Bronson, J.A. Forrester, L.M. Prudent, A.M. Yang, A.M. Yantes, P.B. Reich, and L.E. Frelich. 2023. Linked disturbance in the temperate forest: Earthworms, deer, and canopy gaps. Ecology. 2023;104:e4040. https://onlinelibrary.wiley.com/r/ecy

Shifley, S.R. and W.K. Moser, editors. 2016. Future Forests of the Northern United States

Simpson, A., and Eyler, M.C., 2018, First comprehensive list of non-native species established in three major regions of the United States: U.S. Geological Survey Open-File Report 2018-1156, 15 p., https://doi.org/10.3133/ofr20181156.

ISSN 2331-1258 (online)

Spicer, M.E., A.A. Royo, J.W. Wenzel, and W.P. Carson. 2023. Understory plant growth forms respond independently to combined natural and anthropogenic disturbances. Forest Ecology and Management 543 (2023) 12077

Stern, R.L., P.G. Schaberg, S.A. Rayback, C.F. Hansen, P.F. Murakami, G.J. Hawley. 2023.

Growth trends and environmental drivers of major tree species of the northern hardwood forest of eastern North America J. For. Res. (2023) 34:37–50 https://doi.org/10.1007/s11676-022-01553-7

Stout, S.L., A.T. Hille, and A.A. Royo. 2023. Science-Management Collaboration is Essential to Address Current and Future Forestry Challenges. IN United States Department of Agriculture. Forest Service. 2023. Proceedings of the First Biennial Northern Hardwood Conference 2021: Bridging Science and Management for the Future. Northern Research Station General Technical Report NRS-P-211 May 2023

United States Department of Agriculture, Forest Service. 2023a. Proceedings of the First Biennial Northern Hardwood Conference 2021: Bridging Science and Management for the Future. Northern Research Station General Technical Report NRS-P-211 May 2023

USDA Forest Service Northern Research Station Rooted in Research ISSUE 18 | SEPTEMBER 2023

Kurtz, C.M. 2023. An assessment of invasive plant species in northern U.S. forests. Res. Note NRS-311. http://doi.org/10.2737/NRS-RN-311

United States Department of Agriculture Forest Service General Technical Report NRS-109.  An Assessment of Invasive Plant Species Monitored by the Northern Research Station

Forest Inventory and Analysis Program, 2005 through 2010.

Yacucci, A.C., W.P. Carson, J.C. Martineau, C.D. Burns, B.P. Riley, A.A. Royo, T.P. Diggins, I.J. Renne. 2023. Native tree species prosper while exotics falter during gap-phase regeneration, but only where deer densities are near historical levels New Forests https://doi.org/10.1007/s11056-023-10022-w

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at  https://treeimprovement.tennessee.edu/

or

www.fadingforests.org

Hawaiian Efforts to Restore Threatened Trees

ʻŌhiʻa trees killed by ROD; photo by Richard Sniezko, USFS

Several Hawaiian tree species are at risk due to introduced forest pests. Two of the Islands’ most widespread species are among the at-risk taxa. Their continuing loss would expose watersheds on which human life and agriculture depend. Habitats for hundreds of other species – many endemic and already endangered – would lose their foundations. These trees also are of the greatest cultural importance to Native Hawaiians.

I am pleased to report that Hawaiian scientists and conservationists are trying to protect and restore them.

Other tree species enjoy less recognition … and efforts to protect them have struggled to obtain support.

1) koa (Acacia koa)

Koa is both a dominant canopy tree and the second-most abundant native tree species in Hawai`i in terms of areas covered. The species is endemic to the Hawaiian archipelago. Koa forests provide habitat for 30 of the islands’ remaining 35 native bird species, many of which are listed under the U.S. Endangered Species Act. Also dependent on koa forests are native plant and invertebrate species and the Islands’ only native terrestrial mammal, the Hawaiian hoary bat. Finally, koa forests protect watersheds, add nitrogen to degraded soils, and store carbon [Inman-Narahari et al.]

Koa forests once ranged from near sea level to above 7000 ft (2100 m) on both the wet and dry sides of all the large Hawaiian Islands. Conversion of forests to livestock grazing and row-crop agriculture has reduced koa’s range. Significant koa forests are now found on four islands – Hawai’i, Maui, O‘ahu, and Kauaʻi. More than 90% of the remaining koa forests occur on Hawai`i Island (the “Big Island) [Inman-Narahari et al.]

In addition to its fundamental environmental role, koa has immense cultural importance. Koa represents strength and the warrior spirit. The wood was used traditionally to make sea-going canoes. Now Koa is widely used for making musical instruments, especially guitars and ukuleles; furniture, surfboards, ornaments, and art [Inman-Narahari et al.]

Koa timber has the highest monetary value of any wood harvested on the Islands. However, supplies of commercial-quality trees are very limited (Dudley et al. 2020). Harvesting is entirely from old-growth forests on private land. [Inman-Narahari et al.]

Koa forests are under threat by a vascular wilt disease caused by Fusarium oxysporum f. sp. koae (FOXY). This disease can kill up to 90% of young trees and – sometimes — mature trees in native forests. The fungus is a soil-dwelling organism that spreads in soil and infects susceptible plants through the root system (Dudley et al. 2020).

Conservation and commercial considerations have converged to prompt efforts to breed koa resistant to FOXY. Conservationists hope to restore native forests on large areas where agriculture has declined. The forestry industry seeks to enhance supplies of the Islands’ most valuable wood. Finally, science indicated that a breeding program would probably be successful. Field trials in the 1990s demonstrated great differences in wilt-disease mortality among seed sources (the proportion of seedlings surviving inoculation ranged from 4% to 91.6%) [Sniezko 2003; Dudley et al. 2009].

In 2003, Dudley and Sniezko outlined a long-term strategy for exploring and utilizing genetic resistance in koa. Since then, a team of scientists and foresters has implemented different phases of the strategy and refined it further (Dudley et al. 2012, 2015, 2017; Sniezko et al. 2016]

First, scientists determined that the wilt disease is established on the four main islands. Having obtained more than 500 isolates of the pathogen from 386 trees sampled at 46 sites, scientists tested more than 700 koa families from 11 ecoregions for resistance against ten of the most highly virulent isolates (Dudley et al. 2020). 

The Hawaiian Agricultural Research Center (HARC), supported by public and private partners, has converted the field-testing facilities on Hawai`i, Maui, and Oahu into seed orchards. The best-performing tree families are being grown to maturity to produce seeds for planting. It is essential that the seedlings be not just resistant to FOXY but also adapted to the ecological conditions of the specific site where they are  to be planted [Dudley et al. 2020; Inman-Narahari et al. ] Locally adapted, wilt-resistant seed has been planted on Kauaʻi and Hawai`i. Preparations are being made to plant seed on Maui and O‘ahu also. Scientists are also exploring methods to scale up planting in both restoration and commercial forests [R. Hauff pers. comm.].  

koa; photo by David Eickhoff via Flickr

Restoration of koa on the approximately half of lands in the species’ former range that are privately owned will require that the trees provide superior timber. Private landowners might also need financial incentives since the rotation time for a koa plantation is thought to be 30-80 years. [Inman-Narahari et al.]

Plantings on both private and public lands will need to be protected from grazing by feral ungulates and encroachment by competing plants. These management actions are intensive, expensive, and must be maintained for years.

Some additional challenges are scientific: uncertainties about appropriate seed zones, efficacy of silvicultural approaches to managing the disease, and whether koa can be managed for sustainable harvests. Human considerations are also important: Hawai`i lacks sufficient professional tree improvement or silvicultural personnel, a functioning seed distribution and banking network — and supporting resources. Finally, some segments of the public oppose ungulate control programs. Inman-Narahari et al.

Finally, scientists must monitor seed orchards and field plantings for any signs of maladaptation to climate change. (Dudley et al. 2020).

2) ʻŌhiʻa Metrosideros polymorpha)   

ʻŌhiʻa  lehua is the most widespread tree on the Islands. It dominates approximately 80% the biomass of Hawaii’s remaining native forest, in both wet and dry habitats. ʻŌhiʻa illustrates adaptive radiation and appears to be undergoing incipient speciation. The multitude of ecological niches and their isolation on the separate islands has resulted in five recognized species in the genus Metrosideros. Even the species found throughout the state, Metrosideros polymorpha, has eight recognized varieties (Luiz et al. (2023) (some authorities say there are more).

Loss of this iconic species could result in significant changes to the structure, composition, and potentially, the function, of forests on a landscape level. High elevation ‘ohi‘a forests protect watersheds across the state. ʻŌhiʻa forests shelter the Islands’ one native terrestrial mammal (Hawaiian hoary bat), 30 species of forest birds, and more than 500 endemic arthropod species. Many species in all these taxa are endangered or threatened (Luiz et al. 2023). The increased light penetrating interior forests following canopy dieback facilitates invasion by light-loving non-native plant species, of which Hawai`i has dozens. There is perhaps no other species in the United States that supports more endangered taxa or that plays such a geographical dominant ecological keystone role [Luiz et al. 2023]

For many Native Hawaiians, ‘ōhi‘a is a physical manifestation of multiple Hawaiian deities and the subject of many Hawaiian proverbs, chants, and stories; and foundational to the scared practice of many hula. The wood has numerous uses. Flowers, shoots, and aerial roots are used medicinally and for making lei. The importance of the biocultural link between ‘ōhi‘a and the people of Hawai`i is described by Loope and LaRosa (2008) and Luiz et al. (2023).

In 2010 scientists detected rapid mortality affecting ‘ōhi‘a on Hawai‘i Island. Scientists determined that the disease is caused by two recently-described pathogenic fungi, Ceratocystis lukuohia and Ceratocystis huliohia. The two diseases, Ceratocystis wilt and Ceratocystis canker of ʻōhiʻa, are jointly called “rapid ‘ōhi‘a death”, or ROD. The more virulent species, C. lukuohia, has since spread across Hawai`i Island and been detected on Kaua‘i.  The less virulent C. huliohia  is established on Hawai`i and Kaua‘i and in about a dozen trees on  O‘ahu. One tree on Maui was infected; it was destroyed, and no new infection has been detected [M. Hughes pers. comm.] As of 2023, significant mortality has occurred on more than one third of the vulnerable forest on Hawai`i Island, although mortality is patchy.  

 [ʻŌhiʻa is also facing a separate  disease called myrtle rust caused by the fungus Austropuccinia psidii; to date this rust has caused less virulent infections on ‘ōhi‘a.]

rust-killed ‘ōhi‘a in 2016; photo by J.B. Friday

Because of the ecological importance of ‘ōhi‘a and the rapid spread of these lethal diseases, research into possible resistance to the more virulent pathogen, C. lukiohia began fairly quickly, in 2016. Some ‘ōhi‘a survive in forests on the Big Island in the presence of ROD, raising hopes that some trees might possess natural resistance. Scientists are collecting germplasm from these lightly impacted stands near high-mortality stands (Luiz et al. 2023). Five seedlings representing four varieties of M. polymorpha that survived several years’ exposure to the disease are being used to produce rooted cuttings and seeds for further evaluation of these genotypes.

ʻŌhiʻa flowers

Encouraged by these developments, and recognizing the scope of additional work needed, in 2018 stakeholders created a collaborative partnership that includes state, federal, and non-profit agencies and entities, ʻŌhiʻa Disease Resistance Program (‘ODRP) (Luiz et al. 2023). The partnership seeks to provide baseline information on genetic resistance present in all Hawaiian taxa in the genus Metrosideros. It aims further to develop sources of ROD-resistant germplasm for restoration intended to serve several purposes: cultural plantings, landscaping, and ecological restoration. ‘ODRP is pursuing screenings of seedlings and rooted cuttings sampled from native Metrosideros throughout Hawai`i while trying to improve screening and growing methods. Progress will depend on expanding these efforts to include field trials; research into environmental and genetic drivers of susceptibility and resistance; developing remote sensing and molecular methods to rapidly detect ROD-resistant individuals; and support already ongoing Metrosideros conservation. If levels of resistance in wild populations prove to be insufficient, the program will also undertake breeding (Luiz et al. 2023).

To be successful, ‘ODRP must surmount several challenges (Luiz et al. 2022):

  • increase capacity to screen seedlings from several hundred plants per year to several thousand;
  • optimize artificial inoculation methodologies;
  • determine the effects of temperature and season on infection rates and disease progression;
  • find ways to speed up seedlings’ attaining sufficient size for testing;
  • develop improved ways to propagate ʻōhiʻa from seed and rooted cuttings;
  • establish sites for field testing of putatively resistant trees across a wide range of climatic and edaphic conditions;
  • establish seed orchard, preferably on several islands;
  • establish systems for seed collection from the wide variety of subspecies/varieties;
  • if breeding to enhance resistance is appropriate, it will be useful to develop high-throughput phenotyping of the seed orchard plantings.

  [See DMF profile for more details.]

Developing ROD-resistant ‘ōhi‘a is only one part of a holistic conservation program. Luiz et al. (2023) reiterate the importance of quarantines and education to curtail movement of infected material and countering activities that injure the trees. Fencing to protect these forests from grazing by feral animals can drastically reduce the amount of disease. Finally, scientists must overcome the factors there caused the almost complete lack of natural regeneration of ‘ōhi‘a in lower elevation forests. Most important are competition by invasive plants, predation by feral ungulates, and the presence of other diseases, e.g., Austropuccinia psidii.

Hawaii’s dryland forests are highly endangered: more than 90% of dry forests are already lost due to habitat destruction and the spread of invasive plant and animal species. Two tree species are the focus of species-specific programs aimed at restoring them to remaining dryland forests. However, support for both programs seems precarious and requires stable long-term funding; disease resistance programs often necessitate decades-long endeavors.

naio in bloom; photo by Forrest & Kim Starr via Creative Commons

1) naio (Myoporum sandwicense)

Naio grows on all of the main Hawaiian Islands at elevations ranging from sea level to 3000 m. While it occurs in the full range of forest types from dry to wet, naio is one of two tree species that dominate upland dry forests. The other species is mamane, Sophora chrysophylla. Naio is a key forage tree for two endangered honeycreepers, palila (Loxioides bailleui) and `akiapola`au (Hemignathus munroi). The tree is also an important host of many species of native yellow-face bees (Hylaeus spp). Finally, loss of a native tree species in priority watersheds might lead to invasions by non-native plants that consume more water or increase runoff.

The invasive non-native Myoporum thrips, Klambothrips myopori, was detected on Hawai‘i Island in December 2008 (L. Kaufman website). In 2018 the thrips was found also on Oahu (work plan). The Myoporum thrips feeds on and causes galls on plants’ terminal growth. This can eventually lead to death of the plant.

Aware of thrips-caused death of plants in the Myoporum genus in California, the Hawaii Department of Lands and Natural Resources Division of Forestry and Wildlife and the University of Hawai‘i began efforts to determine the insect’s distribution and infestation rates, as well as the overall health of naio populations on the Big Island. This initiative began in September 2010, nearly two years after the thrips’ detection. Scientists monitored nine protected natural habitats for four years. This monitoring program was supported by the USFS Forest Health Protection program. This program is described by Kaufman.

naio monitoring sites from L. Kaufman article

The monitoring program determined that by 2013, the thrips has spread across most of Hawi`i Island, on its own and aided by human movement of landscaping plants. More than 60% of trees being monitored had died. Infestation and dieback levels had both increased, especially at medium elevation sites. The authors feared that mortality at high elevations would increase in the future. They found no evidence that natural enemies are effective controlling naio thrips populations on Hawai`i Island.

Kaufman was skeptical that biological control would be effective. She suggested, instead, a breeding program, including hybridizing M. sandwicensis with non-Hawaiian Myoporum species that appear to be resistant to thrips. Kaufman also called for additional programs: active monitoring to prevent thrips from establishing on neighboring islands; and collection and storage of naio seeds.

Ten years later, in February 2024, DLNR Division of Forestry and Wildlife adopted a draft work plan for exploring possible resistance to the Myoporum thrips. Early steps include establishing a database to record data needed to track parent trees, associated propagules, and the results of tests. These data are crucial to keeping track of which trees show the most promise. Other actions will aim to hone methods and processes. Among practical questions to be answered are a) whether scientists can grow even-aged stands of naio seedlings; b) identifying the most efficient resistance screening techniques; and c) whether K. myopori thrips are naturally present in sufficient numbers to be used in tests, or – alternatively – whether they must be augmented. [Plan]

Meanwhile, scientists have begun collecting seed from unaffected or lightly affected naio in hotspots where mortality is high. They have focused on the dry and mesic forests of the western side of Hawai`i (“Big”) Island, where the largest number of naio populations still occur and are at high risk. Unfortunately, these “lingering” trees remain vulnerable to other threats, such as browsing by feral ungulates, competition with invasive plants, drought, and reduced fecundity & regeneration.

Hawai`i DLNR has secured initial funding from the Department of Defense’s REPI program to begin a pest resistance project and is seeking a partnership with University of Hawai`i to carry out tests “challenging” different naio families’ resistance to the thrips [R. Hauff pers. comm.]

wiliwili; photo by Forrest & Kim Starr

2) wiliwili (Erythrina sandwicensis)

Efforts to protect the wiliwili have focused on biological control. The introduced Erythrina gall wasp, Quadrastichus erythrinae (EGW) was detected on the islands in 2005. It immediately caused considerable damage to the native tree and cultivated nonnative coral trees.

A parasitic wasp, Eurytoma erythrinae, was approved for release in November 2008 – only 3 ½ years after EGW was detected on O‘ahu. The parasitic wasp quickly suppressed the gall wasp’s impacts to both wiliwili trees and non-native Erythrina. By 2024, managers are once again planting the tree in restoration projects.

However, both the gall wasp and a second insect pest – a bruchid, Specularius impressithorax – can cause loss of more than 75% of the seed crop. This damage means that the tree cannot regenerate. By 2019, Hawaiian authorities began seeking permission to release a second biocontrol gent, Aprostocitus nites.Unfortunately, the Hawai’i Department of Agriculture still has not approved the release permit despite five years having passed. Once they have this approval, the scientists will then need to ask USDA Animal and Plant Health Inspection Service (APHIS) for its approval [R. Hauff, pers. comm.]

SOURCES

www.RapidOhiaDeath.org

Dudley, N., R. James, R. Sniezko, P. Cannon, A. Yeh, T. Jones, & Michael Kaufmann. 2009? Operational Disease Screening Program for Resistance to Wilt in Acacia koa in Hawai`i. Hawai`i Forestry Association Newsletter August 29 2009

Dudley, N., T. Jones, K. Gerber, A.L. Ross-Davis, R.A. Sniezko, P. Cannon & J. Dobbs. 2020. Establishment of a Genetically Diverse, Disease-Resistant Acacia koa Seed Orchard in Kokee, Kauai: Early Growth, Form, & Survival. Forests 2020, 11, 1276; doi:10.3390/f11121276 www.mdpi.com/journal/forests

Friday, J. B., L. Keith, and F. Hughes. 2015. Rapid ʻŌhiʻa Death (Ceratocystis Wilt of ʻŌhiʻa). PD-107, College of Tropical Agriculture and Human Resources, University of Hawai‘i, Honolulu, HI. URL: https://www.ctahr.HI.edu/oc/freepubs/pdf/PD-107.pdf  Accessed April 3, 2018.

Friday, J.B. 2018. Rapid ??hi?a Death Symposium -West Hawai`i (“West Side Symposium”) March 3rd 2018,  https://vimeo.com/258704469 Accessed April 4, 2018 (see also full video archive at https://vimeo.com/user10051674)

Inman-Narahari, F., R. Hauff, S.S. Mann, I. Sprecher, & L. Hadway. Koa Action Plan: Management & research priorities for Acacia koa forestry in Hawai`i. State of Hawai`i Department of Land & Natural Resources Division of Forestry & Wildlife no date

Kaufman, L.V, J. Yalemar, M.G. Wright. In press. Classical biological control of the erythrina gall wasp, Quadrastichus erythrinae, in Hawaii: Conserving an endangered habitat. Biological Control. Vol. 142, March 2020

Loope, L. and A.M. LaRosa. 2008. ‘Ohi’a Rust (Eucalyptus Rust) (Puccinia psidii Winter) Risk Assessment for Hawai‘i.

Luiz, B.C. 2017. Understanding Ceratocystis. sp A: Growth, morphology, and host resistance. MS thesis, University of Hawai‘i at Hilo.

Luiz, B.C., C.P. Giardina, L.M. Keith, D.F. Jacobs, R.A. Sniezko, M.A. Hughes, J.B. Friday, P. Cannon, R. Hauff, K. Francisco, M.M. Chau, N. Dudley, A. Yeh, G. Asner, R.E. Martin, R. Perroy, B.J. Tucker, A. Evangelista, V. Fernandez, C. Martins-Keli’iho.omalu, K. Santos, R. Ohara. 2023. A framework for establishlishing a rapid ‘Ohi‘a death resistance program  New Forests 54, 637–660. https://doi.org/10.1007/s11056-021-09896-5

Additional information on the koa resistance program is posted at http://www.harc-hspa.com/forestry.html 

Sniezko, R.A., N. Dudley, T. Jones, & P. Cannon. 2016. Koa wilt resistance & koa genetics – key to successful restoration & reforestation of koa (Acacia koa). Acacia koa in Hawai‘i: Facing the Future. Proceedings of the 2016 Symposium, Hilo, HI: www.TropHTIRC.org , www.ctahr.HI.edu/forestry 

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at  https://treeimprovement.tennessee.edu/

or

www.fadingforests.org

Forest Regeneration — Need to See Holistic Picture

red maple; via Pixabay

Research scientists in the USFS Northern Region (Region 9) – Maine to Minnesota, south to West Virginia and Missouri – continue to be concerned about regeneration patterns of the forest and the future productivity of northern hardwood forests.

The most recent study of which I am aware is that by Stern et al. (2023) [full citation at the end of this blog]. They sought to determine how four species often dominant in the Northeast (or at least in New England) might cope with climate change. Those four species are red maple (Acer rubrum), sugar maple (Acer saccharum), American beech (Fagus grandifolia), and yellow birch (Betula alleghaniensis). The study involved considerable effort: they examined tree ring data from 690 dominant and co-dominant trees on 45 plots at varying elevations across Vermont. The tree ring data allowed them to analyze each species’ response to several stressors over the 70-year period of 1945 to 2014.

In large part their findings agreed with those of studies carried out earlier, or at other locations. As expected, all four species grew robustly during the early decades, then plateaued – indicative of a maturing forest. All species responded positively to summer and winter moisture and negatively to higher summer temperatures. Stern et al. described the importance of moisture availability in non-growing seasons – i.e., winter – as more notable.

snow in Vermont; Putnypix via Flickr

The American Northeast and adjacent areas in Canada have already experienced an unprecedented increase of precipitation over the last several decades. This pattern is expected to continue or even increase under climate change projections. However, Stern et al. say this development is not as promising for tree growth as it first appears. The first caveat is that winter snow will increasingly be replaced by rain. The authors discuss the importance of the insulation of trees’ roots provided by snow cover. They suggest that this insulation might be particularly necessary for sugar maple.

The second caveat is that precipitation is not expected to increase in the summer; it might even decrease. Their data indicate that summer rainfall – during both the current and preceding years – has a significant impact on tree growth rates.

Stern et al. also found that the rapid rise in winter minimum temperatures was associated with slower growth by sugar maple, beech, and yellow birch, as well as red maple at lower elevations. Still, temperature had less influence than moisture metrics.

Stern et al. discuss specific responses of each species to changes in temperatures, moisture availability, and pollutant deposition. Of course, pollutant levels are decreasing in New England due to implementation of provisions of the Clean Air Act of 1990.

They conclude that red maple will probably continue to outcompete the other species.

In their paper, Stern et al. fill in some missing pieces about forests’ adaptation to the changing climate. I am disappointed, however, that these authors did not discuss the role of biotic stressors, i.e., “pests”.

They do report that growth rates of American beech increased in recent years despite the prevalence of beech bark disease. They note that others’ studies have also found an increase in radial growth for mature beech trees in neighboring New Hampshire, where beech bark disease is also rampant.

For more specific information on pests, we can turn to Ducey at al. – also published in 2023. These authors expected American beech to dominate the Bartlett Experimental Forest (in New Hampshire) despite two considerations that we might expect to suppress this growth. First, 70-90% of beech trees were diseased by 1950. Second, managers have made considerable efforts to suppress beech.

Stern et al. say specifically that their study design did not allow analysis of the impact of beech bark disease. I wonder at that decision since American beech is one of four species studied. More understandable, perhaps, is the absence of any mention of beech leaf disease. In 2014, the cutoff date for their growth analysis, beech leaf disease was known only in northeastern Ohio and perhaps a few counties in far western New York and Pennsylvania. Still, by the date of publication of their study, beech leaf disease was recognized as a serious disease established in southern New England.

counties where beech leaf disease has been confirmed

Eastern hemlock (Tsuga canadensis) and northern red oak (Quercus rubra) are described as common co-occurring dominant species in the plots analyzed by Stern et al. Although hemlock woolly adelgid has been killing trees in southern Vermont for years, Stern et al. did not discuss the possible impact of that pest on the forest’s regeneration trajectory. Nor did they assess the possible effects of oak wilt, which admittedly is farther away (in New York (& here) and in Ontario, Canada, west of Lake Erie).

In contrast, Ducey at al. (2023) did discuss link to blog 344 the probable impact of several non-native insects and diseases. In addition to beech bark disease, they addressed hemlock woolly adelgid, emerald ash borer, and beech leaf disease.

Non-native insects and pathogens are of increasing importance in our forests. To them, we can add overbrowsing by deer, proliferation of non-native plants, and spread of non-native earthworms. There is every reason to think the situation will only become more complex. I hope forest researchers will make a creative leap – incorporate the full range of factors affecting the future of US forests.

I understand that such a more integrated, holistic analysis might be beyond any individual scientist’s expertise or time, funding, and constraints of data availability and analysis. I hope, though, that teams of collaborators will compile an overview based on combining their research approaches. Such an overview would include human management actions, climate variables, established and looming pest infestations, etc. I hope, too, that these experts will extrapolate from their individual, site-specific findings to project region-wide effects.

Some studies have taken a more integrative approach. Reed, Bronson, et al. (2022) studied interactions of earthworm biomass and density with deer. Spicer et al. (2023) examined interactions of deer browsing and various vegetation management actions. Hoven et al. (2022) considered interactions of non-native shrubs, tree basal area, and forest moisture regimes.

See also my previous blogs on studies of regeneration in New Hampshire, North Carolina, National parks in the East, Allegheny Plateau and Ohio, and the impact of deer.

SOURCE

Stern, R.L., P.G. Schaberg, S.A. Rayback, C.F. Hansen, P.F. Murakami, G.J. Hawley. 2023. Growth trends and environmental drivers of major tree species of the northern hardwood forest of eastern North America. J. For. Res. (2023) 34:37–50 https://doi.org/10.1007/s11676-022-01553-7

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at  https://treeimprovement.tennessee.edu/

or

www.fadingforests.org

Disappearing Floristic Diversity – Should Some of the Attention to Extinctions be Refocused on Invasive Plants?

Sakhalin knotweed (Fallopia (Reynoutria) sachalinensis) – an invasive plant widespread in Europe; photo by Katrin Schneider [korina.info] via Wikimedia

There is growing evidence that invasive plants – as distinct from invasive species of animals, microbes, etc. – play a significant role in causing the loss of floristic uniqueness at the local or regional level. I provide full citations of all sources at the end of this blog.

Less Diversity. More Similarity

Several studies show that plant invasions have a bigger impact than extinction in the homogenization of Earth’s flora. A major driver is sheer numbers. Daru et al. point out that 10,138 plant species have become naturalized to a region outside their native ranges while only 1,065 species have gone extinct. Even under a scenario in which all species currently included in IUCN Red List as “threatened” become extinct, non-native plant species naturalizations are by far the stronger contributor to biotic reorganization.

Winter et al. report that in Europe since AD 1500, plant invasions have greatly exceeded extinctions, resulting in increased taxonomic diversity (i.e., species richness) on the Continent but increased taxonomic and phylogenetic similarity among European regions. In other words, floras of individual European countries became phylogenetically and taxonomically impoverished. This situation is likely to worsen in the future because introductions continue.

Winter et al. conclude, more broadly, that a focus on species richness can be misleading because it does not capture the important effects of taxonomic or phylogenetic distinctiveness.

Yang et al. (2021) considered the situation globally. They divided most of Earth’s ice-free land surface into 658 regions. They found that introduction of non-native plants has increased the taxonomic similarity between any two of these regions in 90.7% of the time. Introductions increased phylogenetic similarity in 77.2% of those pairs. Australasia illustrates the situation. The region has a large proportion of endemic species, reflecting its unique evolutionary history and exhibiting high floristic diversity. However, the region has also received large numbers of non-native plants from other regions. The result is that the Australasian flora has lost much of its original uniqueness.

rubbervine (Cryptostegia madagascariensis) – one of the worst invasive plants in Australia; photo by Tatters via Flickr

Introduced plant species rarely cause outright extinction of members of the native flora of the receiving ecosystem – at least at the scale of a continent. Winter et al. found that in Europe, extinction usually occurs to plant species with small numbers that are limited to localized habitats. Often, however, the same species continue to thrive elsewhere on the continent. The “losing” country finds its flora becoming more similar to that of other European countries. It loses some uniqueness because it lost one or more components of its flora. However, for Europe as a whole, there is no loss. The homogenization of the “losing” country’s flora is exacerbated by the fact that more than half of plant species listed as invading a particular European country are from other European regions. Winter et al. say a similar pattern has been found in North America.

The picture is more complex for small isolated ecosystems. Carvallo and Castro (2017), writing about isolated volcanic islands in the southeastern Pacific Ocean, introduction of large numbers of non-native plant species has not caused extinction of native plant species. It has, however, resulted in the homogenization of the islands’ floras.

These authors worry that this reduction in phylogenetic diversity could have detrimental impacts for ecosystem function and ecosystem services.  (Interestingly, at the level of order or family rather than species or genus, the combined effects of species introductions and extinctions did not change the islands’ taxonomic diversity. They don’t explicitly say whether that fact might mitigate effects on ecosystem function.)  

What is the situation in Hawai`i? The Islands are the “capital” of both extinction and invasion. I know the Hawaiian flora has very high levels of endemism and of endangerment. In addition, naturalized non-native plant taxa constitute up to 54% of the archipelago’s flora (Potter et al. 2023). However, it is probably extremely difficult to distinguish the impacts of introduced plants separate from the impacts of the many non-native animals, e.g., feral hogs. 

Extinction by Introduction

It has been reported that invasive species have caused the extinction of at least seven species of plants on the Cape of Good Hope and endangered another 14% (Houreld 2024). Unfortunately, the report doesn’t specify whether the non-native species are plants or animals. Either way, this is a tragedy. I remind you that the Cape Floral Kingdom is Earth’s smallest Plant Kingdom in geographic size (78,555 km2), and extremely important in uniqueness. According to the article in The Washington Post, two-thirds of the 20,400 plant species growing in South Africa are endemic – found nowhere else on Earth.

Nearly a decade ago, Downey and Richardson objected to measuring the impact of introduced plant species by considering only total extinction of native plant species. They complain that this approach fails to recognize that plants experience a long decline before reaching extinction. They divide this decline into six “thresholds”. Downey and Richardson say there is abundant evidence of invasive plants driving native plants along this extinction trajectory. For example, increases in non-native plant cover or density that result in decreased native plant species diversity or richness equates, under their hierarchy, to the native species crossing from the first to second threshold. They note there are also examples of species causing “extinction debts”. That is, the extinction occurs long after the invader is introduced and initiates a native species’ decline. They call for conservationists to intervene earlier in that trajectory.

The Global Assessment on Biodiversity and Ecosystem Services was recently published by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services.  This report notes that there are at least 1,061 invasive plants on Earth. In terrestrial systems, invasive plants are the taxonomic group most frequently reported as having negative impacts, especially in cultivated areas, plus temperate and boreal forests. As I have noted above, non-native plant taxa constitute a particularly high proportion of the flora on islands. The assessment found that the number of non-native plants exceeds the total number of native plants on more than one quarter of the Earth’s islands. However, this report does not distinguish the number of species endangered by plant invasions from the number of species endangered by invasive species of all taxonomic groups.

Tiburon mariposa lily (Calochortus tiburnensis) – a federally Threatened species in California; photo by T.J Gehring via Flickr

None of the experts denies the impact of extinction on biodiversity. Extinction represents the loss of phylogenetically and taxonomically unique organisms. This loss is exacerbated if some taxonomic groups are at disproportionately higher risk of extinction. Introduced non-native species compensate for these losses only to a point (Daru et al.). In Europe, Winter et al. found that extinctions usually befall specialized endemic or rare species, often from species-poor families. On the other hand, successful invaders are often ecological generalists with large ranges, often belonging to species-rich families. This results in the pronounced decrease of phylogenetic and taxonomic ß-diversity within and between regions to which the rare species are unique.  

All these experts agree that species declines — short of extinction — have severe impacts on ecosystem functions, and even evolution.

Yang et al. emphasize that the rapid and accelerating loss of regional biotic uniqueness changes biotic interactions and species assemblages, with probable impairment of key ecosystem functions. Daru et al. stress that biotic homogenization— declining ß-diversity—reduces trait and phylogenetic differences between regions. Conceding that the consequences of this global biotic reorganization on ecosystems are poorly understood, Daru et al. cite increasing evidence that biotic heterogeneity provides insurance for the maintenance of ecosystem functioning in a time of rapid global change. They assert that declining ß-diversity is a more characteristic feature of the Anthropocene than species loss.

Winter et al. also state that the phylogenetic structure of a species assemblage represents the evolutionary history of its members and reflects the diversity of genetic and thus morphologic, physiologic, and behavioral characteristics. High phylogenetic diversity might enable rapid adaptation to changing environmental conditions.

According to Daru et al., the loss of 14 billion years of evolutionary history has affected some regions particularly. The most disturbed biotas include those of California and Florida; Mesoamerica; the Amazon; the Himalaya-Hengduan region; Southeast Asia; and Southwest Australia. These are regions that experienced spectacular taxonomic radiation over time, and now have both high levels of threat and also species invasion.  

Carvallo and Castro, focused on the Pacific islands, call for integrating the two parallel channels of conservation that currently operate separately: those focused on reversing plant extinctions and those focused on reducing invasions. They call for a biogeographical approach that addresses all causes of phylogenetic homogenization.

Tetragonia tetragonoides – the most widespread invasive plant on these Pacific islands; photo by Jake Osborn via Flickr

I believe all these experts, in all their papers, have made the case for such integration world-wide.

Invasive plants’ impact on non-plant species

While I have focused here – and in most of my blogs more broadly — on impacts on wild, native plant communities, it is clear that alterations to floristic communities influence other taxonomic groups. A couple of years ago I summarized findings by Douglas Tallamy and colleagues on what happens to insects – and their predators – when a landscape is dominated by introduced plant species.

In short, domination by non-native plants – whether invasive or just widely planted – suppresses the numbers and diversity of native lepidopteran caterpillars. One study cited in the blog found that 75% of all lepidopteran species were found exclusively on native plant species. Non-native plants in the same genus as native plants often support a similar but depauperate subset of the native lepidopteran community. Tallamy and colleagues conclude that a reduction in the abundance and diversity of insect herbivores will probably cause a concomitant reduction in the insect predators and parasitoids of those herbivores – although few studies have measured this impact beyond spiders, which are generalists. Tallamy focuses on birds.

In the same blog I reviewed publications by Lalk and colleagues, which examined interactions between invasive woody plants and arthropod communities more broadly. They decried the insufficient data about most of these interactions.

A few weeks ago I saw a report of an unexpected impact of invasive plants: roots of beach naupaka [beach cabbage or sea lettuce] (Scaevola sericea) are penetrating sea turtle nests so aggressively that they kill the unhatched turtles. Apparently this is happening at several sites in the Caribbean, where the plant is not native (Houreld 2024). I could find no scientific reports of this phenomenon. One reference noted that a related species (S. taccada) can form large, dense stands that might prevent adult sea turtles’ access to nesting areas (Swensen et al. 2024).

Sources:

Daru, B.H., T.J. Davies, C.G. Willis, E.K. Meineke, A. Ronk, M. Zobel, M. Pärtel,  A. Antonelli,  and C.C. Davis. 2021. Widespread homogenization of plant communities in the Anthropocene. NATURE COMMUNICATIONS (2021) 12:6983. https://doi.org/10.1038/s41467-021-27186-8 

www.nature.com/naturecommunications

Downey, P.O. and D.M. Richardson. 2016. Alien plant invasions and native plant extinctions: a six-threshold framework. AoB Plants, 2016; 8: plw047 DOI: 10.1093/aobpla/plw047; open access, available at http://aobpla.oxfordjournals.org/

Houreld, K. 2024. “Parched Cape Town copes with climate change by cutting down trade.”. The Washington Post. February 29, 2024.

Potter, K.M., C.Giardina, R.F. Hughes, S. Cordell, O. Kuegler, A. Koch, and E. Yuen. 2023. How invaded are Hawaiian forests? Non-native understory tree dominance signals potential canopy replacement.  Landsc Ecol https://doi.org/10.1007/s10980-023-01662-6

Swensen, S.M., A. Morales Gomez, C. Piasecki-Masters, N. Chime, A.R. Wine, N. Cortes Rodriguez, J. Conklin, and P.J. Melcher. 2024. Minimal impacts of invasive Scaevola taccada on Scaevola plumieri via pollinator competition in Puerto Rico. Front. Plant Sci. 2024; 15: 1281797.

Yang, Q., P. Weigelt, T.S. Fristoe, Z. Zhang, H. Kreft, A. Stein, H. Seebens, W. Dawson, F. Essl, C. König, B. Lenzner, J. Pergl, R. Pouteau, P. Pyšek, M. Winter, A.L. Ebel, N. Fuentes, E.L.H. Giehl, J. Kartesz, P. Krestov, T. Kukk, M. Nishino, A. Kupriyanov, J.L. Villaseñor, J.J. Wieringa, A. Zeddam, E. Zykova. and M. van Kleunen. 2021. The global loss of floristic uniqueness. NATURE COMMUNICATIONS (2021) 12:7290.

https://doi.org/10.1038/s41467-021-27603-y

Winter, M., O. Schweiger, S. Klotz, W. Nentwig, P. Andriopoulos, M. Arianoutsou, C. Basnou, P. Delipetrou, V. Didz.iulis, M. Hejdah, P.E. Hulme, P.W. Lambdon, J. Pergl, P. Pys.ek, D.B. Roy, and I. Kuhn. 2009. Plant extinctions and intros lead to phylogenetic and taxonomic homogenization of the European flora  PNAS Vol 106 # 51 December 2009

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm

or

www.fadingforests.org

Forest Regeneration Again … Deer!

photo by Eli Sagor via Flickr

I have recently recent blogged several times about threats to regeneration of eastern forests. Most of the underlying studies stress the role of deer browsing as a major driver of suppression of native plant species and proliferation of non-native ones. Most studies discussed at a recent Northern Hardwood research forum (USDA, FS 2023b Proceedings) found that deer browsing overwhelms other disturbances, such as fire and canopy gaps that typically promote seedling diversity. Miller et al. also stressed the importance of the deer-invasive plant complex in interrupting regeneration in National parks. Reed et al. found that, on the Allegheny Plateau of western Pennsylvania, high deer densities at the time stands formed reduced tree species diversity, density, and basal area – changes that were still detectable decades later.

On the other hand, Hovena et al. found that at their study sites in Ohio, interaction between non-native shrubs and soil wetness overshadowed even the impact of deer herbivory on the species richness and abundance of seedlings.

Unlike the others, Ducey et al. don’t mention deer as a factor in their analysis of regeneration in a forest in the northern half of New Hampshire. They focus on the minimal impact of silvicultural management. Its effect is secondary to overall forest development as the forest ages. Is it possible that overabundant deer are not a factor in the Bartlett Experimental forest.

American elm (Ulmus americana); photo by F.T. Campbell

Some of the studies acknowledge the impacts of non-native insects and pathogens. The most thorough discussion is in Payne and Peet. They note that specialist pathogens have caused the loss of important tree species, specifically elms and dogwoods plus the impending widespread mortality of ash. Such mortality is resulting in drastic and long-lasting shifts in community dynamics.

Ducey et al. anticipate pest-driven reversals of increases over the decades of eastern hemlock (Tsuga canadensis) and American beech (Fagus grandifolia). Also, they expect that white ash (Fraxinus americana), which has a minor presence, will disappear.

Miller et al. also stressed the importance of emerald ash borer-induced suppression of ash regeneration in some National parks . The authors also noted the threat to beech trees from beech leaf disease in other parks. Hovena et al. state that the interaction between non-native shrubs and soil wetness was more influential than ash mortality in shaping woody seedling communities.

Reed et al. considered the role of non-native earthworm biomass on plant species’ growth.

But too many of the studies, in my view, make no mention of the probably significant role of non-native insects and pathogens.

It is perhaps understandable that they don’t address emerging pests that either have not yet or have barely reached their study sites. For example, Hovena et al. and Yacucci et al. [see below] noted growth of one native shrub, Lindera benzoin, in the face of the challenges presented by deer and invading plants. Neither acknowledges the approach of laurel wilt disease, which has not yet become established in Ohio (it has been detected on the Kentucky-Indiana border). Similarly, neither mentions beech leaf disease, although some of the plots studied by Hovena et al. are just east of Cleveland – where BLD was first detected. The location of the Yacucci et al. study is less than 50 miles away. The North Carolina forests studied by Payne and Peet are apparently too far east to be affected by beech bark disease and beech leaf disease is not yet established nearby.

Less understandable is the failure to mention loss of elms – which were abundant in riparian areas until killed off by Dutch elm disease – which was first detected in Cleveland!); or to discuss the impact of dogwood anthracnose. Their focus on the deciduous forest might explain why they don’t mention hemlock woolly adelgid – which is just now invading the area discussed by Reed et al. I suppose the demise of American chestnut was so many decades ago that it is truly irrelevant to current forest dynamics.

A new study raises anew these questions about whether inattention to the role of non-native pests has skewed past studies’ results. Yacucci et al. compared regeneration in a military installation (Camp Garfield), to the results in the surrounding second-growth forest. This choice allowed them to overcome one drawback of other studies: using deer exclosures that are small and of short durations. The military facility covers 88 km2. Inside it, deer populations have been controlled for 67 years at a density of 6.6 – 7.5 deer/km2. Outside, deer have been overabundant for decades. Populations have grown to densities estimated (but not measured) to be at least 30 deer/km2 – more than four times as high.

These authors established 21 experimental gaps in the low-deer-density area and 20 gaps outside the installation where deer densities are high. Some of the gaps in both low- and high-deer-density environs were located on wetter, seasonally flooded soils, some on drier sites. None of the forest sites had experience fire in recent decades.

Their findings support the importance of deer browsing as driver of changes to forest regeneration.

northern spicebush (Lindera benzoin); photo by R.A. Nonemacher via Wikimedia

They found that at low deer densities, gaps develop a vigorous and diverse native sapling layer, including oaks. Total stem density of red and pin oaks was 13 times higher in these gaps than in gaps in high-deer-density locations. Oak saplings were growing into the subcanopy – that is, above deer browse heights. Saplings of other species – i.e., tuliptree (Liriodendron tulipifera), red maple, and ash (Fraxinus spp.) were also flourishing. Also present were dogwood (Cornus florida) and two native shrubs — Lindera benzoin and Rubus allegheniensis. One non-native shrub, buckthorn (Rhamnus frangula), also thrived at low deer densities. Other non-native plant species were far fewer; their cover was 80% lower. Overall, abundance, richness, and diversity of native herbaceous and woody species were 37–65% higher at the low-deer-density study sites. On average tree species were more than twice as tall as in high-deer-density plots.

In high-deer-density plots, non-native species were six times more abundant while native species richness was 39% lower. Diversity was 27% lower. Most native tree species were short in stature and in low abundance. The one exception was black cherry (Prunus serotina), which deer avoid feeding on. The cherry was 95% more abundant in these high-deer-density plots.

There were several surprising results. In most cases, neither years since gap formation nor habitat type (wet vs. dry) had a significant impact on plant diversity, richness, or abundance. The exception was that non-native plant species were more abundant in older gaps where deer densities were high. Yacucci et al. warn that this phenomenon is a potential threat to biodiversity since high deer density is now the norm across eastern forests.

The authors also note that fire has probably never been a factor in these forests, which are primarily beech-maple forests. Certainly there have been no fires over the past 70 years, either inside or outside the military installation.

Yacucci et al. did not discuss past or possible future impacts of non-native insects or pathogens. They did not mention emerald ash borer or dogwood anthracnose – both of which had been present in Ohio for at least two decades when they completed their study. Although they said their study forest was a beech-maple forest, they did not discuss whether beech are present and – if so – the impact of beech bark disease or beech leaf disease. Both of these are spreading in Ohio. The latter was originally detected in 2012 near Cleveland, just 50 miles from the location of Camp Garfield (between Youngstown and Cleveland, Ohio). As noted above, they also did they mention that Lindera benzoin is susceptible to laurel wilt disease.

beech seedlings in Virginia; photo by F.T. Campbell

Proposed solutions to deer over-browsing

Given the combined threat from widespread deer overpopulation and invasions by non-native plants, Yacucci et al. propose enlisting those military posts that regularly cull deer into efforts to conserve and regenerate native plants. Otherwise, they say, the prognosis for regeneration is poor.

Bernd Blossey and colleagues propose a more sweeping solution: implementation of a national policy to reduce deer populations on all land ownerships. They point out that overabundant deer:

  • disrupt the plant communities of affected forests – from spring ephemerals to tree regeneration;
  • promote disease in wildlife and people; and
  • lead to miserable deaths of deer on our highways, through winter starvation, and disease.

They call for federal leadership of coordinated deer-reduction programs. I discuss their proposal in detail in a separate blog.

SOURCES

Ducey, M.J, O.L. Fraser, M. Yamasaki, E.P. Belair, W.B. Leak. 2023. Eight decades of compositional change in a managed northern hardwood landscape. Forest Ecosystems 10 (2023) 100121

Hovena, B.M., K.S. Knight, V.E. Peters, and D.L Gorchov. 2022. Woody seedling community responses to deer herbivory, intro shrubs, and ash mortality depend on canopy competition and site wetness. Forest Ecology and Management. 523 (2022) 120488

Payne, C.J. and R.K. Peet. 2023. Revisiting the model system for forest succession: Eighty years of resampling Piedmont forests reveals need for an improved suite of indicators of successional change. Ecological Indicators 154 (2023) 110679

Miller, K.M., S.J. Perles, J.P. Schmit, E.R. Matthews, and M.R. Marshall. 2023. Overabundant deer and invasive plants drive widespread regeneration debt in eastern United States national parks. Ecological Applications. 2023;33:e2837. https://onlinelibrary.wiley.com/r/eap  Open Access

Reed, S.P., D.R. Bronson, J.A. Forrester, L.M. Prudent, A.M. Yang, A.M. Yantes, P.B. Reich, and L.E. Frelich. 2023. Linked disturbance in the temperate forest: Earthworms, deer, and canopy gaps. Ecology. 2023;104:e4040. https://onlinelibrary.wiley.com/r/ecy

United States Department of Agriculture, Forest Service. 2023a. Proceedings of the First Biennial Northern Hardwood Conference 2021: Bridging Science and Management for the Future. Northern Research Station General Technical Report NRS-P-211 May 2023

Yacucci, A.C., W.P. Carson, J.C. Martineau, C.D. Burns, B.P. Riley, A.A. Royo, T.P. Diggins, I.J. Renne. 2023. Native tree species prosper while exotics falter during gap-phase regeneration, but only where deer densities are near historical levels New Forests https://doi.org/10.1007/s11056-023-10022-w

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm

or

www.fadingforests.org

Planting Trees to Sequester Carbon – Beware the Wrong Places!

Greater prairie chicken – denizen of the Tallgrass Prairie; NPS photo

In August 2022 I blogged about unwise planting of trees in New Zealand as a warning about rushing to ramp up tree planting as one solution to climate change.

New Zealand has adopted a major afforestation initiative (“One Billion Trees”). This program is ostensibly governed by a policy of “right tree, right place, right purpose”. However, Bellingham et al. (2022) [full citation at end of blog] say the program will probably increase the already extensive area of radiata pine plantations and thus the likelihood of exacerbated invasion. They say the species’ potential invasiveness and its effects in natural ecosystems need more thorough consideration given that the pines

  • have already invaded several grasslands and shrublands;
  • are altering primary succession;
  • are climatically suitable to three-quarters of New Zealand’s land
North American Tallgrass Prairie; photo by National Park Service

A new study by Moyano et al. [full citation at the end of the blog] tackles head-on the question of whether widespread planting of trees to counter climate change makes sense. They focus on plantings in naturally treeless ecosystems, i.e., grasslands, shrublands and wetlands. They find that:

  • relying on tree planting to significantly counter carbon change in the absence of reducing carbon emissions would require converting more than a third of Earth’s of global grasslands into tree plantations.
  • Reforestation of areas previously forested has the potential to produce a net increase in carbon sequestration more than twice as great as can be done by afforesting unforested areas.

Moyano et al. conclude that conservation and restoration of degraded forests should be prioritized over afforestation projects. This recommendation confirms points made in an earlier blog. Then I reported that Calders et al. (2022) said temperate forests account for ~14% of global forest carbon stocks in their biomass and soil. They worried that ash dieback link will kill enough large trees that European temperate deciduous forests will become a substantial carbon source, rather than sink, in the next decades. In my blog I pointed out that other tree taxa that also formerly grew large – elms, plane trees, and pines – have either already been decimated by non-native insects and pathogens, or face severe threats now.

Moyano et al. also point out that naturally treeless ecosystems are often at risk to a variety of threats, they provide numerous ecosystem services, and they should be conserved.

Loss of Biodiversity

Tree planting in naturally treeless areas changes ecosystems at the landscape scale. Moyano et al. say these changes inevitably degrade the natural biodiversity of the affected area. For example, grasslands provide habitats for numerous plant and animal species and deliver a wide range of ecosystem services, including provisioning of forage for livestock, wild food and medicinal herbs, + recreation and aesthetic value. Already 49% of Earth’s grassland area is degraded. Restoration of herbaceous plant diversity in old growth grasslands requires at least 100 years.

These obvious impacts are not the only losses caused by conversion of treeless areas to planted forests.

Ambiguous Carbon Sequestration Benefits

Grasslands store 34% of the terrestrial carbon stock primarily in the soil. Tree planting in grasslands can result in so much loss of carbon stocks in the soil that it completely offsets the increment in carbon sequestration in tree biomass. The underlying science is complicated so scientists cannot yet predict where afforestation will increase soil carbon and where it will reduce it. Important factors appear to be

  • Humid sites tend to lose less soil carbon loss than drier sites;
  • Soil carbon increases as the plantation ages;
  • Tree species: conifers either reduce soil carbon or have no effect; broadleaf species either increase soil carbon or have no effect.
  • Sites with higher initial soil carbon tend to lose more carbon during afforestation.
  • Afforestation has greater impacts on upper soil layers.

Moyano et al. assert that appropriate management of grasslands can provide low cost, high carbon gains: a potential net carbon sequestration of 0.35 Gt C/ year at a global level, which is comparable to the potential for carbon sequestration of afforestation in all suitable dryland regions (0.40 Gt C/year).

Changes in Albedo

Trees absorb more solar energy than snow, bare soil or other life forms (such as grasses) because they reflect less solar radiation (reduced albedo). Moyano et al. say the resulting warmer air above the trees might initially offset the cooling brought about by increased carbon sequestration in the growing trees’ wood. Only after decades does the increase in carbon sequestration compensate for the reduction in albedo and produce a cooling effect. Furthermore, they say, the eventual cooling effect that afforestation could create is slight, reducing the global temperature only 0.45°C by 2100 if afforestation was carried out across the total area actually covered by crops. As they note, replacing all crops by trees maintained to sequester carbon is highly unlikely.

Eucalyptus-pine plantation burned in Portugal; photo by Paolo Fernandez via Flickr

Increased fire severity

Planting trees in many treeless habitats – deserts, xeric shrublands, and temperate and tropical grasslands – increases fire intensity. This risk is exacerbated when managers choose to plant highly flammable taxa, e.g., Eucalyptus.Already the fire risk is expected to increase due to climate change. These fires not only threaten nearby people’s well-being and infrastructure; they also release large portions of the carbon previously sequestered, thus undermining the purpose of the project. Moyano et al. note that the carbon stored in the soil of grasslands is better protected from fire.

Water supplies reduced

Afforestation changes the hydrological cycle because an increase in carbon assimilation requires an increase in evapotranspiration. The result at the local scale is decreased water yield and increased soil salinization and acidification. Water yield losses are greater when plantations are composed of broadleaf species. Moyano et al. point out that these water losses are more worrying in areas where water is naturally scarce, e.g., the American southwest, including southern California. On the other hand, increased evapotranspiration can enhance rain in neighboring areas through a redistribution of water at the regional scale and increased albedo through the formation of clouds.

Moyano et al. say planting trees also alters nutrient cycles. To my frustration, they don’t discuss this impact further.

Bioinvasion risk

Moyano et al. cite several experts as documenting a higher risk of bioinvasion associated with planting trees in naturally treeless systems. These invasions expose the wider landscapes to the impacts arising from tree plantations, e.g., increased plant biomass carbon sequestration, reduced soil carbon, reduced surface albedo, increased fuel loads and fuel connectivity, reduced water yield, and altered nutrient cycles. Even native ecosystems that are legally protected can be threatened. Thickets of invading trees can exacerbate some of the impacts listed above since the invading trees usually grow at higher densities. On a more positive side, invading stands of trees often are more variable in age; in this case, they can be more like a natural forest than are even-aged stands in plantations. Because of these complexities, the effect of tree invasions on ecosystem carbon storage becomes highly context dependent. This is rarely evaluated by scientists. See  Lugo below.

Moyano et al. say woody plant invasions can exacerbate human health issues by providing habitat for wildlife hosts of important disease vectors, including mosquitoes and ticks. I ask whether plantations using unwisely chosen tree species might raise the same risks. They decry the minimal research conducted on this issue.

Assessing the tradeoffs

The goal is to remove CO2 from the atmosphere by fixing more carbon in plant biomass. Moyano et al. say careful consideration of projects’ potential impacts can minimize any negative consequences. An integrated strategy to address climate change should balance multiple ecological goals. Efforts to increase carbon storage should not compromise other key aspects of native ecosystems, such as biodiversity, nutrient and hydrological cycles, and fire regimes. First, they say, planners should avoid the obvious risks:

  • don’t plant fire-prone/flammable tree species; do adopt fuel- and fire-management plans.
  • don’t plant potentially invasive species.
  • don’t plant forests in vulnerable environments where negative impacts are likely.

In order to both minimize that certain risks will arise and ensure counter measures are implemented if they do, Moyano et al. suggest incorporating into carbon certification standards two requirements:

  • that soil carbon be measured throughout the whole soil depth.
  • that plantation owners be legally responsible for managing potential tree invasions.

The authors praise a new law in Chile, which prohibits planting monospecific tree plantations as a natural climate solution.

Furthermore, they advocate for regulators conducting risk analyses rather than accepting groundless assumptions about carbon storage and climate cooling effects.

Recognizing the uncertainty about some effects of introducing trees into naturally treeless areas, and interactions between these effects and the key role of the ecological context, Moyano et al. call for increased study of plant ecology. They specify research on the above-mentioned highly variable impacts on soil carbon as well as albedo.

Role of NIS trees in sequestering /storing carbon in U.S.

According to Lugo et al. (2022; full citation at the end of this blog), in the Continental United States, non-indigenous tree species contribute a tiny fraction of the forests’ carbon storage at the current time:  about 0.05%. This is because non-native trees are widely scattered; while individuals can be found in more than 61% of forested ecosections on the continent, they actually occupy only 2.8% of the forested area.

However, non-native tree species are slowly increasing in both their area and their proportion of species in specific stands. Consequently, they are increasingly important in the forest’s carbon sink – that is, the amount of additional carbon sequestered between two points in time. In fact, non-native trees represent 0.5% of new carbon sequestered each year. This is ten times higher than their overall role in carbon storage. In other words, the invasive species play increasingly important ecosystem roles in the stands in which they occur.

neem tree – considered invasive in the Virgin Islands; photo by Miekks via Wikimedia

On the United States’ Caribbean and Pacific islands, non-native tree species are already much more common, so they are more important in carbon sequestration. On Puerto Rico, 22% of the tree species are non-native; link to blog 340 they accounted for 38% of the live aboveground tree carbon in forests. On the Hawaiian Islands, an estimated 29% of large trees and 63% of saplings or small trees are non-native. link to blog 339 Consequently, they store 39% of the mean plot area-weighted live aboveground tree carbon.

SOURCES

Bellingham, P.J., E.A. Arnst, B.D. Clarkson, T.R. Etherington, L.J. Forester, W.B. Shaw,  R. Sprague, S.K. Wiser, and D.A. Peltzer. 2022. The right tree in the right place? A major economic tree species poses major ecological threats. Biol Invasions Vol.: (0123456789) https://doi.org/10.1007/s10530-022-02892-6  

Calders, K., H. Verbeeck, A. Burt, N. Origo, J. Nightingale, Y. Malhi, P. Wilkes, P. Raumonen, R.G.H. Bunce, M. Disney.  Laser scanning reveals potential underestimation of biomass carbon in temperate forest. Ecol Solut Evid. 2022;3:e12197. wileyonlinelibrary.com/journal/eso3  

Lugo, A.E., J.E. Smith, K.M. Potter, H. Marcano Vega, and C.M. Kurtz. 2022. The Contribution of NIS Tree Species to the Structure and Composition of Forests in the Conterminous US in Comparison with Tropical Islands in the Pacific and Caribbean. USFS International Institute of Tropical Forestr. January 2022. General Technical Report IITF-54 https://doi.org/10.2737/IITF-GTR-54

Moyano, J., R.D. Dimarco, J. Paritsis, T. Peterson, D.A. Peltzer, K.M. Crawford, M.A. McCary,| K.T. Davis, A. Pauchard, and M.A. Nuñez. 2024. Unintended consequences of planting native and NIS trees in treeless ecosystems to mitigate climate change. Journal of Ecology. 2024;00:1-12

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm

or

www.fadingforests.org

California bill – model for other states?

invasion of wild/black mustard Brassica nigra; photo by carlbegge via Flickr

A California state legislator has proposed a bill to expand state efforts to counter invasive species. Should we support it – and others like it in other states?

The bill is Assembly Bill 2827 introduced by Assembly Member (and former Majority Leader) Eloise Reyes of the 50th Assembly District. She represents urban parts of southwestern San Bernardino County, including the cities of Rialto, Colton, and Fontana.

According to media reports, Reyes was prompted to act by the current outbreak of exotic fruit flies, which as of some months ago resulted in detections in 15 California counties.

The bill is much broader than agricultural pests, however. It would find and declare that it is a primary goal of the state to prevent the introduction, and suppress the spread, of invasive species within its borders.  I applaud the language of the “findings” section:

(a) Invasive species have the potential to cause extensive damage to California’s natural and working landscapes, native species, agriculture, the public, and economy.

(b) Invasive species can threaten native flora and fauna, disrupt ecosystems, damage critical infrastructure, and result in further loss of biodiversity.

Paragraph (c) cites rising threats associated with increased movement of goods, international travel, and climate change — all said to create conditions that may enhance the survival, reproduction, and spread of these invasive species, posing additional threats to the state.

(d) It is in the best interest of the state to adopt a proactive and coordinated approach to prevent the introduction and spread of invasive species.

California sycamore attacked by invasive shot hole borer; photo by Beatriz Nobua-Behrmann

The bill calls for

  • The state agencies, in collaboration with relevant stakeholders, to develop and implement pertinent strategies to protect the state’s agriculture, environment, and natural resources.
  • The state to invest in research, outreach, and education programs to raise awareness and promote responsible practices among residents, industries, and visitors.
  • State agencies to coordinate efforts with federal, local, and tribal authorities.

However, the bill falls short when it comes to action. Having declared that countering bioinvasion is “a primary goal of the state”, and mandated the above efforts, the bill says only that the California Department of Food and Agriculture (which has responsibility for plant pests) is to allocate funds, if available, to implement and enforce this article. Under this provision, significant action is likely to depend on holding agencies accountable and providing increased funding.

removing coast live oak killed by goldspotted oak borer; photo by F.T. Campbell

Would this proposed legislation make a practical difference? I have often complained that CDFA has not taken action to protect the state’s wonderful flora. For example, CDFA does not regulate firewood to prevent movement of pests within the State. It has not regulated numerous invasive plants or several wood-boring insects. These include the goldspotted oak borer; the polyphagous and Kuroshio shothole borers; and the  Mediterranean oak borer.

On the other hand, CDFA is quick to act against pests that might enter the state from elsewhere in the country, e.g., spongy moth (European or Asian), emerald ash borer and spotted lanternfly.

I hope Californians and the several non-governmental organizations focused on invasive species will lobby the legislature to adopt Assembly Bill 2827. I hope further that they will try to identify and secure a source of funds to support the mandated action by CDFA and other agencies responsible for managing the fauna, flora, and other taxa to which invasive species belong.

I applaud Ms. Reyes’ initiative. I hope legislators in other states will consider proposing similar bills.

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm

or

www.fadingforests.org

Europe outlaws “ecocide”

American bullfrog (Lithobates catesbeianus); photo by Will Brown via Wikimedia; one of invasive animals deliberately introduced to Europe in the past

In February 2024 the European Parliament approved legislation outlawing “ecocide” and providing sanctions for environmental crimes. Member states now have two years to enshrine its provisions in national law.

The new rules update the list of environmental crimes adopted in 2008 and enhance the sanctions. The goal is to ensure more effective enforcement. Listed among the offenses are:

  • the import and use of mercury and fluorinated greenhouse gases,
  • the import of invasive species,
  • the illegal depletion of water resources, and
  • pollution caused by ships.

This action followed an in-depth analysis of the failures of the previous EU environmental directive, first adopted in 2008 (Directive 2008/99/EC). The review found that:

  • The Directive had little effect on the ground.
  • Over the 10 years since its adoption few environmental crime cases were successfully investigated and sentenced.
  • Sanction levels were too low to dissuade violations.
  • There had been little systematic cross-border cooperation.

EU Member states were not enforcing the Directive’s provisions. They had provided insufficient resources to the task. They had not developed the needed specialized knowledge and public awareness. They were not sharing information or coordinating either among individual governments’ several agencies or with neighboring countries.

The review found that poor data hampered attempts by both the EU body and national policy-makers to evaluate the Directive’s efficacy.

The new Directive attempts to address these weaknesses. To me, the most important change is that complying with a permit no longer frees a company or its leadership from criminal liability. These individuals now have a “duty of care”. According to Antonius Manders, Dutch MEP from the Group of the European People’s Party (Christian Democrats), if new information shows that actions conducted under the permit are “causing irreversible damage to health and nature – you will have to stop.” This action reverses the previous EU environmental crime directive – and most member state laws. Until now, environmental crime could be punished only if it is unlawful; as long as an enterprise was complying with a permit, its actions would not be considered unlawful. Michael Faure, a professor of comparative and international environmental law at Maastricht University, calls this change revolutionary.

Lorton Prison; via Flickr

Another step was to make corporate leadership personally liable to penalties, including imprisonment. If a company’s actions cause substantial environmental harm, the CEOs and board members can face prison sentences of up to eight years. If the environmental harm results in the death of any person, the penalty can be increased to ten years.  

Financial penalties were also raised. Each Member state sets the fines within certain parameters. Fines may be based on either a proportion of annual worldwide turnover (3 to 5%) or set at a fixed fine (up to 40 million euros). Companies might also be obliged to reinstate the damaged environment or compensate for the damage caused. Companies might also lose their licenses or access to public funding, or even be forced to close.

Proponents of making ecocide the fifth international crime at the International Criminal Court argue that the updated directive effectively criminalizes “ecocide” — defined as “unlawful or wanton acts committed with knowledge that there is a substantial likelihood of severe and either widespread or long-term damage to the environment being caused by those acts.”

Individual member states also decide whether the directive will apply to offences committed outside EU borders by EU companies.

Some members of the European Parliament advocate for an even stronger stance: creation of a public prosecutor at the European Union level. They hope that the Council of Europe will incorporate this idea during its ongoing revision of the Convention on the Protection of the Environment through Criminal Law. To me, this seems unlikely since the current text of the Convention, adopted by the Council in 1998, has never been ratified so it has not come into force.

The Council of Europe covers a wider geographic area than the European Union – 46 member states compared to 27. Members of the Council of Europe which are not in the EU include the United Kingdom, Norway, Switzerland, Bosnia-Hercegovina, Serbia, Kosovo, Albania; several mini-states, e.g., Monaco and San Remo; and countries in arguably neighboring regions, e.g., Armenia, Azerbaijan, Georgia, and Turkey.

While I rejoice that invasive species are included in the new Directive, I confess that I am uncertain about the extent to which this inclusion will advance efforts to prevent spread. The species under consideration would apparently have to be identified by some European body as “invasive” and its importation restricted. As we know, many of the most damaging species are not recognized as invasive before their introduction to a naïve environment. On the other side, the requirement that companies recognize new information and halt damaging actions – even when complying with a permit! – provides for needed flexibility.

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm

or

www.fadingforests.org