Category: invasive plants

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

Read both: a short call to action (41 pp) based on a long report (952 pp!) Then Act!!!

U.S. Department of Agriculture headquarters; lets lobby these people! photo by Wikimedia

Twenty-three  scientists based around the world published a Letter to the Editor titled “Overwhelming evidence galvanizes a global consensus on the need for action against Invasive Alien Species” It appears in the most recent edition of Biological Invasions (2024) 26:621–626.

The authors’ purpose is to draw attention to the release of a new assessment by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services’ (IPBES).  

The report was issued in September 2023. It is described as the most comprehensive global synthesis of the current knowledge on the bioinvasion process and the impacts of invasive alien species (952 pages!). Its preparation took nearly a decade. Most important, it represents the first consensus among governments and scientists worldwide on the magnitude and extent of the threats that bioinvasions pose to nature, people, and the economy.

The proposed solutions are astoundingly broad and ambitious: transformation of how governments and societies perform. I don’t disagree! However, we need interim steps – “bites of the elephant.”  In my view, the report falls short on providing these.

Our challenge: join others in bringing this analysis to decision-makers’ attention. Can we pull out information that will help persuade U.S. decision-makers – governmental and non-governmental – that the  threat is both urgent and solvable? How do we more effectively advocate for the aggressive, science-based action that we all know is needed?

(I hope that the fact that the report was prepared under the auspices of the Convention on Biodiversity, to which the U.S. is not a party, does not intensify the challenge for us.)

Why we need to restructure the behavior of governments and societies

Bioinvasions are facilitated by policies, decision-making structures, institutions, and technologies that are almost always focused on achieving other goals. Species transport and introduction are driven by policies aimed at promoting economic growth – especially trade. Later stages of invasions, i.e., establishment and some spread, are accelerated by certain uses of land and sea plus climate change. For example, activities that fragment habitats or cause widespread habitat disturbance provide ready places for bioinvasions. Rarely are those who gain by such policies held accountable for the harms they produce via bioinvasions.

To address these unintended consequences, the IPBES report calls for “integrated governance.” Its authors want coordination of all policies and agencies that touch on the indirect drivers, e.g., conservation; trade; economic development; transport; and human, animal, and plant health. Policy instruments need to reinforce – rather than conflict with — strategic invasive species management across sectors and scales. This involves international agreements, national regulations, all governmental sectors, as well as industry, the scientific community, and ordinary people – including local communities and Indigenous Peoples.

The report also calls for establishment of open and inter-operable information systems. This improved access to information is critical for setting priorities; evaluating and improving regulations’ effectiveness; and reducing costs by avoiding duplication of efforts.

Critically important information that is often unspoken:

  • Indirect causes underlying the usual list of human activities that directly promote bioinvasions are the rapid rise of human population and even more rapid rise in consumption and global trade.
  • Biosecurity measures at international borders have not kept pace with the growing volume, diversity, and geographic origins of goods in trade.
  • Continuation of current patterns is expected to result in one-third more invasive species globally by 2050. However, this is an underestimate because today’s harms reflect the consequences of past actions – often from decades ago. Drivers of invasions are expected to grow in both volume and impact.
  • We can prevent and control invasive alien species – but that success depends on the availability of adequate, sustained resources, plus capacity building; scientific cooperation and transfer of technology; appropriate biosecurity legislation and enforcement; and engaging the full range of stakeholders. These require political will.
  • A major impact of bioinvasion is increased biotic homogenization (loss of biological communities’ uniqueness). This concerns us because we are losing the biotic heterogeneity that provides insurance for the maintenance of ecosystem functioning in the face of ongoing global change.
  • The IPBES study asserts that successfully addressing bioinvasions can also strengthen the effectiveness of policies designed to respond to other drivers, especially programs addressing conservation of biological diversity, ensuring food security, sustaining economic growth, and slowing climate change. All these challenges interact. The authors affirm that evidence-based policy planning can reflect the interconnectedness of the drivers so that efforts to solve one problem do not exacerbate the magnitude of others and might even have multiple benefits.

More Key Findings

  • Overall, 9% (3,500) of an estimated 37,000 alien species established in novel environments are invasive (those for which scientists have evidence of negative impacts). Proportions of invasives is high among many taxonomic groups: 22% of all 1,852 alien invertebrates; 14% of all 461 alien vertebrates; 11% of all 141 alien microbes; and 6% of all 1,061 alien plants. (The discussion of probable undercounts relates to aquatic systems and certain geographic regions. However, I believe these data are all undermined by gaps in studies.)
  • Invasive alien species – solely or in combination with other drivers – have contributed to 60% of recorded global extinctions. Invasive species are the only driver in 16% of global animal and plant extinctions. Some invasive species have broader impacts, affecting not just individual species but also communities or whole ecosystems. Sometimes these create complexoutcomes that push the system across a threshold beyond which ecosystem restoration is not possible. (No tree pests are listed among the examples.)

dead whitebark pine in Glacier National Park; photo by National Park Service

  • The benefits that some non-native – even invasive – species provide to some groups of people do not mitigate or undo their negative impacts broadly, including to the global commons. The report authors note that beneficiaries usually differ from those people or sectors that bear the costs. The authors cite many resulting inequities.
  • There are insufficient studies of, or data from, aquatic systems, and from Africa; Latin America and the Caribbean; and parts of Asia.
  • The number of alien species is rising globally at unprecedented and increasing rates. There are insufficient data specifically on invasive species, but they, too, are thought to be rising at similar rates.
  • Horticulure is a major pathway for introducing 46% of invasive alien plant species worldwide.
  • Regarding invasive species’ greater impact on islands,the IPBES report mentions brown tree snakes on Guam and black rats on the Galapagos Islands. It also notes that on more than a quarter of the world’s islands, the number of alien plants exceeds the total number of native ones. See my blogs on non-native plants on Hawai`i and Puerto Rico. In addition, I have posted several blogs regarding disease threats to rare bird species in Hawai`. The IPBES report does not mention these.  

Where the Report Is Weak: Interim Steps

  • The report endorses adoption of regulated species (“black”) lists.
  • The report emphasizes risk analysis of species. Unfortunately IPBES’ analysis was completed before publication of the critique of risk analysis methods by Raffa et al. ( (2023) (see references). However, we must take the latter into consideration when deciding what to advocate as U.S. policy.
  • The report authors call for more countries to adopt national legislation or regulations specifically on preventing and controlling invasive species. (They note that 83% of countries lack such policies). They also list the many international agreements that touch on invasive species-relevant issues. However, Raffa et al. found that the number of such agreements to which a country is a party bears no relationship to the numbers of alien species detected at its border or established on its territory.
  • The challenge to risk assessment posed by multiple sources of uncertainty can be managed by recognizing, quantifying, and documenting the extent of that uncertainty.

Beech leaf disease – one of many non-native pests that were unknown before introduction to a naive ecosystem. Photo by Jennifer Koch, USDA Forest Service

  • I appreciate the report’s emphasis on the importance of public awareness and engagement, but I thought the discussion of effective campaigns lacked original ideas.

The report did not fulfill its own goal of fully exploring unappreciated impacts of policies in its discussion of habitat fragmentation. For example, the report notes that grazing by feral alien ungulates facilitates the spread of invasive alien plant species. However, it does not mention the similar impact by livestock grazing (Molvar, et al. 2024).

SOURCES

Molvar, E.M., R. Rosentreter, D. Mansfield, and G.M. Anderson. 2024. Cheat invasions: History, causes, consequences, and solutions. Hailey, Idaho: Western Watersheds Project, 128 pp.

Raffa, K.F., E.G. Brockerhoff, J-C. GRÉGOIRE, R.C. Hamelin, A.M. Liebhold, A. Santini, R.C. Venette, and M.J. Wingfield. 2023. Approaches to forecasting damage by invasive forest insects and pathogens: a cross-assessment. BioScience 85 Vol. 73 No. 2 (February 2023) https://academic.oup.com/bioscience  

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 Management & Biodiversity

brown creeper; photo by Francesco Veronesi;

In the context of reading about forest succession (see previous blogs) I came upon a new publication by Akresh et al. (full citation at the end of this blog.) The article explores the impact of various silvicultural treatments on bird conservation in eastern North America. They note that forest managers are challenged to balance the opposing habitat needs of organisms that, on one hand, depend on structurally diverse old-growth forests and, on the other hand, those that inhabit more open areas or shrubs.

The authors conducted a meta-analysis of studies that examined birds’ responses to three silvicultural regimes: low-retention stands, shelterwoods, and high-retention stands. These terms were not defined in the article. According to Michigan State University extension, in shelterwood systems, all mature trees are harvested in a two- or three-stage process over several years. The other classes presumably reflect the proportion of trees remaining after the harvest.

Akresh et al. focussed on “community conservation scores,” not on protecting individual bird species. They followed the level of conservation concern for the two communities developed by the Partners-in-Flight program

Shrubland Birds

Akresh et al. note that a high proportion of open-canopy, shrubland bird species are declining range-wide; their habitat is already quite limited in eastern North America and continues to decline. Consequently, the Birds-in-Flight program gives them a high priority for conservation measures.

eastern bluebird – prefers open areas; photographer not named; Pickpic

The researchers found that clearcuts (presumably = low retention) and shelterwoods typically had the highest conservation scores because they provide habitat for the declining avian group, shrubland birds. More heavily harvested forests also support non-avian taxa such as pollinators and other arthropods, mammals, snakes, and vascular plants.

Forest Birds

Stands on which 40%–70% of tree were retained also have a high conservation score because they provide habitat for both shrubland and “mature forest” species. Only a few species, e.g., ovenbird and brown creeper, had lower densities in moderately harvested stands than in unharvested forests. The majority of “mature forest” species had relatively higher or equal densities in the sites on which 40%–70% of trees are retained than in unharvested stands. They suggest that several mature-forest bird species prefer the increased understory vegetation density found in these stands.

ovenbird; Wildreturn; Wikimedia Commons

Unharvested and lightly thinned stands, in which 70%–100% of trees remain, had the lowest conservation scores. The first explanation is that these forests don’t support shrubland bird species.

A second reason, Akresh et al. suggest, is that the second-growth forests now widespread in eastern North America are quite young (even if they have not been logged for at least 50 years). They are even-aged and lack the structural diversity of true old-growth forests. The authorsappear to place the greatest importance on the lack of dense understory vegetation, although otherkey elements of mature forests are also missing, e.g., large-diameter trees and snags, continuous canopy, and deep leaf litter. They concede that some bird species depend on forest characteristics that they did not examine. They did not provide examples of these other ecological attributes.

Akresh et al. note that their study concerns only bird species’ use of forests during the breeding season. Some species use other habitat types at other seasons. Furthermore, data were insufficient to analyze some species altogether. A more comprehensive analysis might have raised the conservation score of older forests. I would add that restoration of true old-growth forests depends on allowing some late-seral stands to continue aging.

Finally, fauna other than birds also depend on forest ecosystems and need to be considered when choosing management approaches. The authors mention salamanders and other amphibians, fungi, invertebrates, and lichens – some of which might be of conservation concern themselves.

Gaps in the forest: complicating factors

Akresh et al. mention deer browsing as an influence on understory conditions once, but do not explore this. I am surprised that they don’t expand this statement by a paragraph or two, given the role deer play in suppressing understory vegetation.

Nor do they mention possible impacts of invasions by non-native plants. As my earlier blogs have reported, plant invasions are common in many forested areas in eastern North America. These studies recommend great care in activities that open the forest canopy. Drs. Akresh and King have told me that they believe that forest managers in this region are well aware of invasive plant issues and already incorporate this concern into their management decisions. They referred me to two studies that indicate a very mixed picture of invasive plant impacts on birds (Labbe and King, 2020; Nelson et al, 2017. see full citations below).

multiflora rose – most common invasive plant on forest plots; photo by Famartin

Not Discussed: Insects as food sources

The studies analyzed by Akresh et al. explore levels of nesting success and bird species’ foraging on fruits of non-native shrubs. Others have focused on the reduced numbers of insects feeding on non-native plants; these insects are the principle food for many perching birds’ nestlings. Douglas Tallamy has documented lower numbers of a wide variety of birds which depend on the insect food supply.

SOURCES

Akresh, M.E., D.I. King, S.L. McInvale, J.L. Larkin, A.W. D’Amato. 2023. Effects of forest management on the conservation of bird communities in eastern North America: A meta-analysis. Ecosphere. 2023; 14:e4315. https://onlinelibrary.wiley.com/r/ecs2

Labbe, M.A. and D.I. King. 2020. Songbird Use of Native and Invasive Fruit in the Northeastern USA. Wildlife Society Bulletin. Volume 44, Issue 3. September 2020

Nelson, S.B, J.J. Coon, C.J. Duchardt, J.DL Fischer, A.J. Kranz, C.M. Parker, S.C. Schneider, T.M. Swartz, J.R. Miller. 2017. Patterns and mechanism of invasive plant impacts on North American birds: a systemic review. Biological Invasions. Volume 19, pp. 1547-1563.

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

Eastern National Parks: Forest Regeneration Failing in 69%

Gettysburg battlefield; now under attack by emerald ash borer (see below)

Kathryn Miller and colleagues (full citation at end of blog) have published a study that examined the status and trends of forest regeneration in 39 National parks from Virginia to Maine. Four-fifths of the forest plots in the study are classified as mature or late successional – so at first glance the forests look healthy. However, the researchers made an alarming finding: in 27 of 39 parks, forest regeneration is failing – either imminently or probably. Acadia National Park is an exception; it is the only park in the study experiencing healthy regeneration. They warn that without intense, sustained – and expensive! – intervention, these forests are likely to be converted to other types of ecosystems. [I  blogged recently about findings regarding regeneration in eastern forests: here  and  here  and here and here.

The forests’ understories have too few seedlings and – especially – saplings to maintain themselves. Worse, in many cases the seedlings and saplings are not the same species as the mature trees that form the canopy. The saplings are shorter species that never reach the canopy. That is, species like pawpaw (Asimina triloba), American holly (Ilex opaca), American hornbeam (Carpinus caroliniana), and eastern redbud (Cercis canadensis) are regenerating, rather than the oaks (Quercus spp.), hickories (Carya spp.), maples (Acer spp.), and pines (Pinus spp.) that constitute the canopies of mature forests in these parks.

Miller and colleagues call these “regeneration mismatches.” In about half of the parks, these native canopy tree species make up less than half of current saplings and seedlings. This situation suggests the forests’ species composition will shift substantially, thereby undermining resilience in the face of other challenges, such as invasive plants and pests and climate change.

In many of these National parks, Miller and colleagues found abundant ash regeneration. For example, ash (Fraxinus spp.) constitute more than half of all seedlings in four parks (Johnstown Flood and Friendship Hill in Pennsylvania; Catoctin Mountain in Maryland; Manassas Battlefield in Virginia).  Miller and colleagues consigned ash species to the “subcanopy class” because the emerald ash borer (EAB) has caused such high mortality of mature trees. They think regard it unlikely that current and future seedlings will ever reach full size. The devastating impact is most starkly illustrated in Gettysburg National Battlefield Park. Consistent deer management since 1996 has been rewarded: the Park ranks at the top for regeneration among the 39 parks. However, more than half of the seedlings and a quarter of the saplings are ashes. EAB has shifted the Park’s otherwise secure regeneration status into probable failure.

When regeneration fails:  too many deer

Throughout the study region, the overwhelming reason regeneration fails is browsing by overabundant deer. The level of deer browse is considered “acceptable” in only four parks. Deer suppress the number of seedlings and saplings. They also skew species composition of native subcanopy species toward those less palatable. Miller and colleagues found that canopy tree density and cover and past human land use had minimal impacts on seedling and sapling numbers or species composition.

Overabundant deer also promote invasion and spread of non-native plants, which are the second most important factor impeding regeneration. Together, invasive plants and non-native earthworms are ecosystem engineers that negatively impact soil and cause cascades of biotic and abiotic impacts throughout forest ecosystems.

Many of the parks experiencing the most severe impacts of chronic deer browse also have the highest invasions by non-native plants. A natural process of regeneration occurs when the death or collapse of mature trees create gaps in the forest canopy. Where deer and invasive shrubs overlap, this process is often hijacked. Instead of nearby native tree species accelerating their growth toward the canopy, thickets of invasive shrubs crowd the space.

For this reason, Miller and colleagues recommend that park management prioritize treating invasive plants in canopy gaps of disturbed stands to avoid forest loss. They recommend deliberate creation of canopy gaps to promote resilience only for parks, or stands within parks, that have low deer and invasive plant abundance or the capacity to intensively manage invasive plants in gaps.

In most parks, non-native tree species are rare, less than 2% of total regeneration. In seven parks, though, non-native trees exceed ten percent of seedlings and/or saplings. In three parks, saplings of non-native trees are increasing. These are primarily tree-of-heaven (Ailanthus altissima) and Norway maple (Acer platanoides). In Saratoga National Historical Park, seedlings of common buckthorn (Rhamnus cathartica) are increasing.

Beech regeneration in Prince William Forest Park

Role of other pests

Miller and colleagues express fear that beech bark disease and beech leaf disease might have effects similar to those of EAB, leading to a greater “regeneration debt” in parks where American beech (Fagus grandifolia) is the dominant regeneration component. They cite specifically Prince William Forest Park in northern Virginia, [25 mi2] Rock Creek Park in the District of Columbia, [2.7mi2] and Saratoga National Historical Park. [5.3 mi2] The authors also suggest that thickets of beech root sprouts formed in response to BBD can suppress regeneration of other native canopy species and so might need to be managed.

Miller and colleagues mention hemlock woolly adelgid (HWA), but provide very little information. They report that Saint-Gaudens National Historical Park in New Hampshire (the home and studio of sculptor Augustus Saint-Gaudens) is at particular risk because of growth of both beech and eastern hemlock (Tsuga canadensis). I know that Delaware Water Gap National Recreation Area [109m2] has experienced major losses of mature hemlocks. [Shenandoah National Park has also, but it was not included in the study.]

Hemlock Ravine, Delaware Water Gap National Recreation Area; photo by Nicholas T via Flickr

Miller and colleagues report that Acadia National Park is seeing recovery of red spruce (Picea rubens) from a major fire in 1947 and possibly also from acid rain. They do not mention the longer-term threat from the brown spruce longhorned beetle. Their focus is on forest dynamics largely unaffected by deer.

In the same way, the authors make no mention of the absence of dogwood trees, presumably because they had been eliminated by dogwood anthracnose decades ago. Nor do they mention vascular streak dieback of redbud; the causal agent still uncertain. [See Annie Self’s presentation to National Plant Board, August 2023.]

dead ash tree in Shenandoah National Park

One omission is large enough that it might affect the study’s findings. At mi2 Shenandoah is the largest National Park in the region. It was not included in the study because the Park’s forest monitoring process is not compatible with those in other NPS units. All the other parks – including Acadia (562 mi) – are much smaller, protecting historic sites like Civil War battlefields.

RECOMMENDATIONS

Miller and colleagues recommend that deer management be initiated in parks classified as at imminent or probable regeneration failure, if such programs are not already under way. They warn that effective deer management requires sustained commitment. Studies of deer exclosures show that full forest recovery from chronic deer overabundance can take as long as 40–70 years.

The authors also recommend actions to open the subcanopy to facilitate growth of saplings belonging to desired species. They caution that deer predation must be controlled. Furthermore, either invasive plant cover must be low, or management must ensure that that the park has sufficient resources to sustain an invasive plant control program – especially if invasive plants are combined with abundant deer.

Parks experiencing compositional mismatches and that are dominated by oak–hickory forest types might also benefit from prescribed burning. Again, deer browse pressure must be minimized. In addition, regeneration of oaks and hickories must already be present.

In park forests dominated by species vulnerable to lethal pests, e.g., beech-, ash-, or hemlock-dominated forest stands, Miller and colleagues recommend considering planting alternative native canopy species and protecting those plantings from deer. Park managers should also consider thinning beech thickets formed after beech bark disease kills canopy trees.

Media coverage

The Washington, D.C., public radio station, WAMU, reported on this research   on the air (broadcast December 20) and on its website. It is written by Jacob Fenston, with great photographs by Tyrone Turner. The story emphasized the link between deer and invasive plants – since regeneration in eastern deciduous forest happens by saplings taking advantage of gaps formed when mature trees die. The story quotes DC-area people on their efforts to contain vines. The Natural Resource Manager at Catoctin Mountain Park [8 mi2] describes that park’s longstanding deer control program. The story also mentions impacts of EAB and threat of BLD.

News – Funding for these parks to counter the threats!

Lead author Kathryn Miller has informed me that the Bipartisan Infrastructure Law and Inflation Reduction Act has provided the 39 parks involved in this study over $10 million to improve forest resilience largely through reduction of invasive plants and overabundant deer.

Of course, invasive species threats to National parks are not limited to the Northeast – nor are they new. I have raised this problem from the beginning. To see these blogs, on the “nivemnic” website, scroll down below the archives to the “categories”, then click on “national parks”.

SOURCE

Miller, K.M., S.J. Perles, J.P. Schmit, E.R. Matthews, 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

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

U.S. Department of the Interior’s Guidance on Nature-Based Solutions

whitebark pine in Glacier National Park killed by white pine blister rust; National Park Service photo

As I noted in the accompanying blog, the U.S. Department of Interior has also weighed in on how to mitigate climate change as part of the Nation’s response to COP24 of the UN Framework Convention on Climate Change.

Interior’s Nature-Based Solutions “Roadmap” (citation at the end of the blog) is 480 pages long! It includes lots of pictures and extensive lists of examples of various types of projects. The document reviews “nature-based” restoration techniques, the benefits they provide in various realms (ecosystem, economy, social values); and the challenges or barriers likely to be encountered. These analyses cover six types of ecosystems – coastal (further divided into five subgroups), forests, grasslands (two types), inland wetland habitats, riverine habitats (three subgroups), and built environments. The obvious emphasis on aquatic and semi-aquatic habitats reflects the Department’s responsibilities. The threat from invasive species is recognized in each case. Plus there are separate chapters discussing management/removal of invasive pests and pathogens, plants, and vertebrates in all types of ecosystems.

The document’s purpose is to provide Interior’s staff – and others who are interested – with reliable information on determining the conditions and goals under which “nature-based” strategies perform best, the benefits they are likely to provide, instructive examples, and additional resources. Much of the information is intended to help staff persuade skeptics that a “nature-based” approach can solve a climate-related problem, such as sea level rise, as well as, or better than, “grey” infrastructure. This includes discussion of: construction and maintenance costs, efficacy in solving a specific problem, and managing conflicts over land use. Also, it considers benefits to other realms, for example, protecting biodiversity and providing opportunities for recreation and mental and physical well-being.

I will focus on aspects dealing with forests. These occur in several chapters. Each chapter has a brief description of the climate and other services provided by that ecosystem type, followed by sections on ways forward (“Technical Approach”), factors affecting site suitability, tools and training resources, likely benefits and outcomes (economic and ecological), barriers and solutions, and examples of projects.

The forest chapter (Chapter 10) discusses forest conservation and restoration with an emphasis on improving forest health, including fuels management, reforestation, and addressing threats from native and non-native pests. One proposed solution is thinning. This measure is said to enhance tree health and promote invasive plants. The “Roadmap” does not recognize that experts consider thinning is helpful in managing native pests such as mountain pine beetle but not non-native pests.

I was startled to find another suggestion – to plant native tree species that are resistant to non-native pests to restore stands. The “Roadmap” refers readers to the National Park Service Resilient Forests Initiative for Region 1 [which reaches from Virginia to Maine]. The Initiative encourages collaboration among parks with similar issues; provides park-specific resource briefs for 39 parks in the Region; and offers management strategies for a host of problems. These include invasive species control, prescribed fire, deer management, silvicultural treatments, tree planting, and fencing. My confusion is that – as far as I know – there are no sources of trees resistant to the non-native pests plaguing forests of the Northeast, e.g., beech, butternut, chestnut, hemlocks, ash, and oaks.

test planting of pathogen-resistant whitebark pine seedlings in Glacier National Park; photo by Richard Sniezko

In the “Tools” section Chapter 10 lists forest restoration guides published by the U.S. Forest Service (USFS) and the International Union of Forest Research Organizations. The “Examples” section includes a few thinning projects.

Chapter 16 advises on enhancing urban forests, which provide many benefits. The chapter stresses the importance of ensuring that projects’ budgets can support protecting trees from such risks as flooding, fire, pests, disease, “invasive species” (presumably other than insects or pathogens), and climate change. The authors note that urban trees are often more susceptible to pests because of their proximity to human activities that facilitate pests’ spread. However, there is no mention that such pests spread to nearby natural forests. They warn against planting a single tree species. An issue noted but not discussed in detail is the use of non-native species in urban forests, some of which have already become invasive.

Three chapters discuss invasive species per se — insects and pathogens (Chap. 26), plants (Chap 27), and vertebrates (Chap. 28) Each chapter summaries invasion stages and stresses the importance of preventing new introductions, detecting them early, and responding rapidly. Most of the text deals with managing established populations – with the emphasis on applying integrated pest management (IPM).  Each raises caveats about biological control agents possibly attacking non-target organisms. Again, the authors emphasize the necessity of ensuring availability of adequate resources to carry out the program.

Chapter 26 addresses Invasive and Nuisance Insects and Pathogens. Examples listed include Asian longhorned beetle, emerald ash borer, hemlock woolly adelgid, spongy moth, Dutch elm disease, sudden oak death, laurel wilt, white pine blister rust, chestnut blight and butternut canker. (All these invaders are profiled under the “invasive species” tab here). The examples also include several native pests, e.g., mountain pine beetle, southern pine beetle, and several pathogens, including Swiss needlecast. I am confused by a statement that priorities for management should be based on pests’ traits; my understanding of the science is that other factors are more important in determining a pest’s impact. See, for example, Lovett et al. 2006.This chapter reiterates the impractical advice to plant trees resistant to the damaging pest. I also wonder at the following statement:

“The process of detection and prevention will need to continue over time to prevent reintroductions or reinvasions of nuisance or invasive pests and pathogens. In some cases, long-term management will be required to contain and prevent spread.” [p. 425] I believe long-term management will required in all cases!

The tools listed in the chapter include various DOI websites re: training and funding; the USDA website listing states’ plant diagnostic laboratories; a USDA IPM “road map”; The Nature Conservancy’s guidebook for assessing and managing invasive species in protected areas; the DOI Strategic Plan; and the University of Georgia’s Center for Invasive Species and Ecosystem Health.

Chapter 27 discusses invasive and nuisance plants. It starts by noting that an estimated 5,000 non-native plant species are stablished in the US. While not all are invasive, there is still potential for these plants to spread and cause harm. The authors state that controlling such plants reduces fire risk and lowers demand for water in arid areas.

The authors say early management is crucial to eradicate or control invasive plant species. Because plant invasions cross property lines, agencies must form partnerships with other agencies and private landowners. Because invasive and nuisance plant species are so widespread, managers must set priorities. The “Roadmap” suggests focusing on sites at the highest risk, e.g., heavily trafficked areas. Continued effort will be necessary to prevent reinvasions or reintroductions. However, long-term management and containment can be incredibly costly and labor-intensive.

lesser celandine invade bottomlands of Delaware Water Gap National Recreation Area

The “Roadmap” complains that many invasive and nuisance plant species are still offered for sale; in fact, that this is the primary pathway by which invasive plants enter the US, (While which we have known this for decades, it is encouraging to see a U.S. government report say:  “Advocating for federal regulation and cohesive local policies for preventing invasive [plant] sales is essential to avoid disjointed state rulings.” – even if it does not specify which agencies should take the lead.  

In the “Tools” section the chapter lists two USFS guides on managing invasive plants; two California Invasive Plant Council guides; the Interior Department’s 2021 Invasive Species Strategic Plan; EDDMapS (a University of Georgia site on which members of the public can report invasive species); and the TNC guidebook for Assessing and Managing Invasive Species in Protected Areas.

Chapter 28 addresses invasive & nuisance vertebrates (called “wildlife”). It notes that invasive animals are present in more than half of all US National parks. It briefly mentions the Lacey Act as providing legal power to curb the introduction and spread of these animals. It does not discuss strengths and weaknesses of this statute, both of which are substantial. This chapter repeats the odd wording from the pest and pathogen chapter – that in some cases long-term management will be required to contain and prevent spread of invasive species. I find it doubtful that short-term actions will be effective in virtually all cases.

Tools listed include Interior guides on IPM, funding sources, and protecting aquatic systems along with the Department of Interior’s 2021 Invasive Species Strategic Plan. Other tools include the USDA guide on IPM, EDDMapS, and the TNC guidebook.

Forests were also mentioned in the discussion of assisted migration of coastal wetlands to avoid drowning by rising seas (Chapter 1). The text notes that forests upland from coastal wetlands might be killed – either as a result of waterlogging as sea levels rise or as deliberate action to make room for the new marsh. Mortality in either case will reduce carbon sequestration. The authors also note the probability that invasive plants – shrubs in the woods, Phragmites on the edge of the wetland — will be present and have to be controlled.

SOURCES

Lovett, G.M, C.D. Canham, M.A. Arthur, K.C. Weathers, R.D. Fitzhugh. 2006. Foret Ecosystem Responses to Exotic Pests and pathogens in Eastern North America. BioScience Vol 56 No. 5 May 2006.

Warnell, K., S. Mason, A. Siegle, M. Merritt, & L. Olander. 2023. Department of the Interior Nature-Based Solutions Roadmap. NI R 23-06. Durham, NC: Nicholas Institute for Energy, Environment & Sustainability, Duke University. https://nicholasinstitute.duke.edu/publications/department-interior-nature-based-solutions-roadmap.

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