link to climate change – Center for Invasive Species Prevention

Scientists: Introduced forest pest reshaping forests, with many bad consequences … will regulators step up?

The number of introduced forest pathogens are increasing – creating a crisis that is recognized by more scientists. These experts say tree diseases are reshaping both native and planted forests around the globe. The diseases are threatening biodiversity, ecosystem services, provision of products, and related human wellbeing. Some suggest that bioinvasions might threaten forests as much as climate change, while also undermining forests’ role in carbon sequestration.

Unfortunately, I see little willingness within the plant health regulatory community to tackle improving programs to slow introductions. Even when the scientists documenting the damage work for the U.S. Department of Agriculture – usually the U.S. Forest Service — USDA policy-makers don’t act on their findings. [I tried to spur a conversation with USDA 2 years ago. So far, no response.]

counties where beech leaf disease has been detected

What the scientists say about these pests’ impacts

Andrew Gougherty (2023) – one of the researchers employed by the USDA Forest Service – says that emerging infectious tree diseases are reshaping forests around the globe. Furthermore, new diseases are likely to continue appearing in the future and threaten native and planted forests worldwide. [Full references are provided at the end of the blog.] Haoran Wu (2023/24) – a Master’s Degree student at Oxford University – agrees that arrival of previously unknown pathogens are likely to alter the structure and composition of forests worldwide. Weed, Ayers, and Hicke (2013) [academics] note that forest pests — native and introduced — are the dominant sources of disturbance to North American forests. They suggest that, globally, bioinvasions might be at least as important as climate change as threats to the sustainability of forest ecosystems. They are concerned that recurrent forest disturbances caused by pests might counteract carbon mitigation strategies.

Scientists have proclaimed these warnings for years. Five years ago, Fei et al. (2019) reported that the 15 most damaging pests introduced to the United States — cumulatively — had already caused tree mortality to exceed background levels by 5.53 teragrams of carbon per year. As these 15 pests spread and invasions intensify, they threaten 41.1% of the total live forest biomass in the 48 coterminous states. Poland et al. (2019) (again – written by USFS employees) document the damage to America’s forest ecosystems caused by the full range of invasive species, terrestrial and aquatic.

Fei et al. and Weed, Ayers, and Hicke (2013) also support the finding that old, large trees are the most important trees with regard to carbon storage. This understanding leads them to conclude that the most damaging non-native pests are the emerald ash borer, Dutch elm disease fungi, beech bark disease, and hemlock woolly adelgid. As I pointed out in earlier blogs, other large trees, e.g., American chestnut and several of the white pines, were virtually eliminated from much of their historical ranges by non-native pathogens decades ago. These same large, old, trees also maintain important aspects of biological diversity.

It is true that not all tree species are killed by any particular pest. Some tree genera or species decrease while others thrive, thus altering the species composition of the affected stands (Weed, Ayers, and Hicke). This mode of protection is being undermined by the proliferation of insects and pathogens that cumulatively attack ever more tree taxa. And while it is true that some of the carbon storage capacity lost to pest attack will be restored by compensatory growth in unaffected trees, this faster growth is delayed by as much as two or more decades after pest invasions begin (Fei et al.).

ash forest after EAB infestation; Photo by Nate Siegert, USFS

Still, despite the rapid rise of destructive tree pests and disease outbreaks, scientists cannot yet resolve critical aspects of pathogens’ ecological impacts or relationship to climate change. Gougherty notes that numerous tree diseases have been linked to climate change or are predicted to be impacted by future changes in the climate. However, various studies’ findings on the effects of changes in moisture and precipitation are contradictory. Wu reports that his study of ash decline in a forest in Oxfordshire found that climate change will have a very small positive impact on disease severity through increased pathogen virulence. Weed, Ayers, and Hicke go farther, making the general statement that despite scientists’ broad knowledge of climate effects on insect and pathogen demography, they still lack the capacity to predict pest outbreaks under climate change. As a result, responses intended to maintain ecosystem productivity under changing climates are plagued by uncertainty.

Clarifying how disease systems are likely to interact with predicted changes in specific characteristics of climate is important — because maintaining carbon storage levels is important. Quirion et al. (2021) estimate that, nation-wide, native and non-native pests have decreased carbon sequestration by live forest trees by at least 12.83 teragrams carbon per year. This equals approximately 9% of the contiguous states’ total annual forest carbon sequestration and is equivalent to the CO₂ emissions from more than 10 million passenger vehicles driven for one year. Continuing introductions of new pests, along with worsening effects of native pests associated with climate change, could cause about 30% less carbon sequestration in living trees. These impacts — combined with more frequent and severe fires and other forest disturbances — are likely to negate any efforts to improve forests’ capacity for storing carbon.

Understanding pathogens’ interaction with their hosts is intrinsically complicated. There are multiple biological and environmental factors. What’s more, each taxon adapts individually to the several environmental factors. Wu says there is no general agreement on the relative importance of the various environmental factors. The fact that most forest diseases are not detected until years after their introduction also complicates efforts to understand factors affecting infection and colonization.

The fungal-caused ash decline in Europe is a particularly alarming example of the possible extent of such delays. According to Wu, when the disease was first detected – in Poland in 1992 – it had already been present perhaps 30 years, since the 1960s. Even then, the causal agent was not isolated until 2006 – or about 40 years after introduction. The disease had already spread through about half the European continent before plant health officials could even name the organism. The pathogen’s arrival in the United Kingdom was not detected until perhaps five years after its introduction – despite the country possessing some of the world’s premier forest pathologists who by then (2012) knew what they to look for.

Clearly, improving scientific understanding of forest pathogens will be difficult. In addition, effective policy depends on understanding the social and economic drivers of trade, development, and political decisions are primary drivers of the movement of pathogens. Wu calls for collaboration of ecologists, geneticists, earth scientists, and social scientists to understand the complexity of the host-pathogen-surrounding system. Bringing about this new way of working and obtaining needed resources will take time – time that forests cannot afford.

However, Earth’s forests are under severe threat now. Preventing their collapse depends on plant health officials integrating recognition of these difficulties into their policy formulation. It is time to be realistic: develop and implement policies that reflect the true level of threat and limits of current science.

Background: Rising Numbers of Introductions

Gougherty’s analysis of rising detections of emerging tree diseases found little evidence of saturation globally – in accord with the findings of Seebens et al. (2017) regarding all taxa. Relying on data for 24 tree genera, nearly all native to the Northern Hemisphere, Gougherty found that the number of new pests attacking these tree genera are doubling on average every 11.2 years. Disease accumulation is increasing rapidly in both regions where hosts are native and where they are introduced, but more rapidly in trees’ native ranges.This finding is consistent with most new diseases arise from introductions of pathogens to naïve hosts.

Gougherty says his estimates are almost certainly underestimates for a number of reasons. Countries differ in scientific resources and their scientists’ facility with English. Scientists are more likely to notice and report high-impact pathogens and those in high-visibility locations. Where national borders are closer, e.g., in Europe, a minor pest expansion can be reported as “new” in several countries. New pathogens in North America appear to occur more slowly, possibly because the United States and Canada are very large. He suggests that another possible factor is the U.S. (I would add Canada) have adopted pest-prevention regulations that might be more effective than those in place in other regions. (See my blogs and the Fading Forest reports linked to below for my view of these measures’ effectiveness.)

Wu notes that reports of tree pathogens in Europe began rising suddenly after the 1980s. He cites the findings by Santini et al. (2012) that not only were twice as many pathogens detected in the period after 1950 than in the previous 40 years, the region of origin also changed. During the earlier period, two-thirds of the introduced pathogens came from temperate North America. After 1950, about one-third of previously unknown disease agents were from temperate North America. Another one-third was from Asia. By 2012, more than half of plant infectious diseases were caused by introduction of previously unknown pathogens.

What is to be done?

Most emerging disease agents do not have the same dramatic effects as chestnut blight in North America, ash dieback in Europe, or Jarrah dieback in Australia. Nevertheless, as Gougherty notes, their continued emergence in naïve biomes increases the likelihood of especially damaging diseases emerging and changing forest community composition.

Gougherty calls for policies intended to address both the agents being introduced through trade, etc., and those that emerge from shifts in virulence or host range of native pathogens or changing environmental conditions. In his view, stronger phytosanitary programs are not sufficient.

Wu recommends enhanced monitoring of key patterns of biodiversity and ecosystem functioning, He says these studies should focus on the net outcome of complex interactions. Wu also calls for increasing understanding of key “spillover” effects – outcomes that cannot be currently assessed but might impact the predicted outcome. He lists several examples:

the effects of drought–disease interactions on tree health in southern Europe,
interaction between host density and pathogen virulence,
reproductive performance of trees experiencing disease,
effect of secondary infections,
potential for pathogens to gain increased virulence through hybridization.
potential for breeding resistant trees to create a population buffer for saving biological diversity. Wu says his study of ash decline in Oxfordshire demonstrates that maintaining a small proportion of resistant trees could help tree population recovery.

Quirion et al. provide separate recommendations with regard to native and introduced pests. To minimize damage from the former, they call for improved forest management – tailored to the target species and the environmental context. When confronting introduced pests, however, thinning is not effective. Instead, they recommend specific steps to minimize introductions via two principal pathways, wood packaging and imports of living plants. In addition, since even the most stringent prevention and enforcement will not eliminate all risk, Quirion et al. advocate increased funding for and research into improved strategies for inspection, early detection of new outbreaks, and strategic rapid response to newly detected incursions. Finally, to reduce impacts of established pests, they recommend providing increased and more stable funding for classical biocontrol, research into technologies such as sterile-insect release and gene drive, and host resistance breeding.

Remember: reducing forest pest impacts can simultaneously serve several goals—carbon sequestration, biodiversity conservation, and perpetuating the myriad economic and societal benefits of forests. See Poland et al. and the recent IUCN report on threatened tree species.

SOURCES

Barrett, T.M. and G.C. Robertson, Editors. 2021. Disturbance and Sustainability in Forests of the Western United States. USDA Forest Service Pacific Northwest Research Station. General Technical Report PNW-GTR-992. March 2021

Clark, P.W. and A.W. D’Amato. 2021. Long-term development of transition hardwood and Pinus strobus – Quercus mixedwood forests with implications for future adaptation and mitigation potential. Forest Ecology and Management 501 (2021) 119654

Fei, S., R.S. Morin, C.M. Oswalt, and A.M. 2019. Biomass losses resulting from insect and disease invasions in United States forests. Proceedings of the National Academy of Sciences. www.pnas.org/cgi/doi/10.1073/pnas.1820601116

Gougherty AV (2023) Emerging tree diseases are accumulating rapidly in the native and non-native ranges of Holarctic trees. NeoBiota 87: 143–160. https://doi.org/10.3897/neobiota.87.103525

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

Lovett, G.M., M. Weiss, A.M. Liebhold, T.P. Holmes, B. Leung, K.F. Lambert, D.A. Orwig, F.T. Campbell, J. Rosenthal, D.G. MCCullough, R. Wildova, M.P. Ayres, C.D. Canham, D.R. Foster, S.L. Ladeau, and T. Weldy. 2016. Nonnative forest insects and pathogens in the United States: Impacts and policy options. Ecological Applications, 26(5), 2016, pp. 1437-1455

Poland, T.M., Patel-Weynand, T., Finch, D., Miniat, C. F., and Lopez, V. (Eds) (2019), Invasive Species in Forests and Grasslands of the United States: A Comprehensive Science Synthesis for the United States Forest Sector. Springer Verlag.

Quirion, B.R., G.M. Domke, B.F. Walters, G.M. Lovett, J.E. Fargione, L. Greenwood, K. Serbesoff-King, J.M. Randall, and S. Fei. 2021 Insect and Disease Disturbance Correlate With Reduced Carbon Sequestration in Forests of the Contiguous US. Front. For. Glob. Change 4:716582. [Volume 4 | Article 716582] doi: 10.3389/ffgc.2021.716582

Weed, A.S., M.P. Ayers, and J.A. Hicke. 2013. Consequences of climate change for biotic disturbances in North American forests. Ecological Monographs, 83(4), 2013, pp. 441–470

Wu, H. 2023/24. Modelling Tree Mortality Caused by Ash Dieback in a Changing World: A Complexity-based Approach MSc/MPhil Dissertation Submitted August 12, 2024. School of Geography and the Environment, Oxford University.

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/

www.fadingforests.org

Non-Native Moths in England: Ever Upward

*Platyperigea kadenii* — one of the moth species that feeds on native plant species introduced recently to Great Britain. Photo by Tony Morris via Flickr

Will phytosanitary agencies and the international system respond to continuing introductions of non-native species?

A new study confirms that introductions of insects continue apace, links this pattern to the horticultural trade, and examines the role of climate change in facilitating introductions. This study focuses on moths introduced to the United Kingdom (Hordley et al.; full citation at the end of the blog). The study sought to detect any trends in numbers of species establishing and the relative importance of natural dispersal vs. those assisted – intentionally or inadvertently – by human activities.

The authors determined that moths continue to be introduced by both processes; there is no sign of “saturation”. This finding agrees with that of Seebens and 44 others (2017; citation below), which analyzed establishments of all types of non-native species globally. The British scientists found that rapidly increasing global trade is the probable driver of the recent acceleration of human-assisted introductions. They emphasize the horticultural trade’s role specifically. Climate change might play a role in facilitating establishment of species entering the UK via human activities.

Hordley et al. found that long-term changes in climate, not recent rapid anthropogenic warming, was important in facilitating introductions of even those moth species that arrived without human assistance. As they note, temperatures in Great Britain have been rising since the 17^th Century. These changes in temperature have probably made the British climate more suitable for a large number of Lepidoptera. The data show that the rate of natural establishments began rising in the 1930s, 60 years before anthropogenic changes in temperatures became evident. Hordley et al. point out that an earlier study that posited a more significant role for climate change did not distinguish between insect species which have colonized naturally and those benefitting from human assistance.

The authors expect introductions to continue, spurred by ongoing environmental and economic changes. Fortunately, very few of the introduced moths had any direct or indirect negative impacts. (The box-tree moth (Cydalima perspectalis) is the exception. [Box-tree moth is also killing plants in North America.]

boxtree moth; photo by Tony Morris via Flickr

Still, they consider that introductions pose an ongoing potential risk to native biodiversity and related human interests. Therefore, they advocate enhanced biosecurity. Specifically, they urge improved monitoring of natural colonizations and regulation of the horticultural trade.

Hordley et al. estimated the rate of establishment during the period 1900 – 2019 for (i) all moth species; (ii) immigrants (i.e., those introduced without any human assistance); (iii) immigrants which feed on native hosts; (iv) immigrants which feed on non-native hosts; (v) adventives (i.e., species introduced with human assistance); (vi) adventives which feed on native hosts; and (vii) adventives which feed on NIS hosts.

Their analysis used data on 116 moth species that have become established in Great Britain since 1900. Nearly two-thirds of these species – 63% – feed on plant species native to Great Britain; 34% on plant species that have been imported – intentionally or not. Data were lacking on the hosts of 3 species.

Considering the mode of introduction, the authors found that 67% arrived through natural colonization; 33% via human assistance. Sixty-nine percent of the 78 species that were introduced through natural processes (54 species) feed on plant species native to Great Britain; 31% (24 species) feed on non-native plants. Among the 38 species whose introduction was assisted by human activities, one-half (19 species) feed on native plant species; 42% (16 species) feed on introduced hosts.

Regarding trends, they found that when considering all moth species over the full period, 21.5% more species established in each decade than in the previous decade. This average somewhat obscured the startling acceleration of introductions over time: one species was reported as established in the first decade (1900–1909) compared to 18 species in the final decade (2010–2019).

The rate of introduction for all immigrant (naturally introduced) species was 22% increase per decade. Considering immigrant species that feed on native plants, the rate of establishment was nearly the same – 23% increase per decade – when averaged over the 120-year period. However, a more detailed analysis demonstrated that these introductions proceeded at a steady rate until 1935, then accelerated by 11% per decade thereafter. In contrast, immigrants that feed on non-native plants have maintained a steady rate of increasing establishments – 13% per decade since 1900.

Adventive species (those introduced via human assistance) increased by 26% per decade. The data showed no signs of saturation. The rates of introduction were similar for adventives that feed on both native plants (22%) and non-native hosts (26%). Again, additional analysis demonstrated a break in rates for adventives that feed on native hosts. The rate was steady until the 1970s, then significantly increased during the years up to 2010. (The scientists dropped data from the final decade since lags in detection might artificially suppress that number.)

In summary, Hordley et al. found no significant differences in trends between

the number of species that established naturally (20%) vs. adventives (26%).
immigrant or adventive species that feed on native vs. non-native hosts.

The authors discuss the role of climate change facilitating bioinvasion by spurring natural dispersal, changing propagule pressure in source habitats, changing the suitability of receiving habitat, and changing in pathways for natural spread, e.g., altered wind and ocean currents. They recognize that the two modes of colonization – adventives and immigrants – can interact. They stress, however, that the two colonization modes require different interventions.

Although their findings don’t support the premise that a surge of natural colonizers has been prompted by anthropogenic warming, Hordley et al. assert that climate clearly links to increased moth immigration to Britain and increased probability of establishment. They note that even so assisted, colonists still must overcome both the natural barrier of the English Channel and find habitats that are so configured as to facilitate breeding success. They report that source pools do not appear to be depleted — moth species richness of neighboring European countries greatly exceeds that in Great Britain.

I would have liked to learn what factors they think might explain the acceleration in both natural and human-assisted introductions of species that feed on plant species native to Great Britain. In 2023 I noted that scientists have found that numbers of established non-native insect species are driven primarily by diversity of plants – both native and non-indigenous.

Hordley et al. assert that Great Britain has advantages as a study location because as a large island separated from continental Europe by the sea – a natural barrier – colonization events are relatively easy to detect. However the English Channel is only 32 km across at its narrowest point. I wonder, whether this relatively narrow natural barrier might lead to a misleadingly large proportion of introduced species being natural immigrants. I do agree with the authors that moths are an appropriate focal taxon because they are sensitive to climate and can be introduced by international trade. Furthermore, Britain has a long tradition of citizen scientists recording moth sightings, so trends can be assessed over a long period.

Hordley et al. stress that they measured only the temporal rate of new species’ establishments, not colonization pressure or establishment success rate. They had no access to systematic data regarding species that arrived but failed to establish. Therefore, they could not deduce whether the observed increase in establishment rates are due to:

(1) more species arriving—due either to climate-driven changes in dispersal or to accessibility of source pools; or

(2) higher establishment success due to improved habitat and resource availability; or

(3) both.

Hordley et al. noted two limitations to their study. First, they concede that there is unavoidably some subjectivity in classifying each species as colonizing naturally or with human assistance. They tried to minimize this factor by consulting two experts independently and including in the analysis only those species on which there was consensus.

Second, increases in detection effort and effectiveness might explain the recent increases in establishment rates. They agree that more people have become “citizen scientists” since 1970. Also, sampling techniques and resources for species identification have improved considerably. They note, however, that Seebens et al. (2018) tested these factors in their global assessment and found little effect on trends.

Hordley et al. believe that they have addressed a third possible limitation – the lag between introduction and detection – by running their analyses both with and without data from final decade (2010-2019). The results were very similar qualitatively.

SOURCE

Hordley, L.A., E.B. Dennis, R. Fox, M.S. Parsons, T.M. Davis, N.A.D. Bourn. 2024. Increasing rate of moth species establishment over 120 years shows no deceleration. Insect Conserv. Divers. 2024;1–10. DOI: 10.1111/icad.12783

Seebens, H. et al. 2017. No saturation in the accumulation of alien species worldwide. Nature Communications. January 2017. DOI: 10.1038/ncomms14435

Seebens, H. et al. 2018. Global rise in emerging IAS results from increased accessibility of new source pools. Proceedings of the National Academy of Sciences. www.pnas.org/cgi/doi/10.1073/pnas.1719429115

Posted by Faith Campbell

www.fadingforests.org

Forest Regeneration — Need to See Holistic Picture

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.

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

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

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

www.fadingforests.org

Birds v. mosquitoes: hope in Hawai`i

‘i‘iwi (Drepanis coccinea) – formerly very common from low to high elevations; photo by James Petruzzii_U

The endangered honeycreepers (birds) of Hawaiian forests are receiving the attention they deserve – and desperately need. There is good news! Promising and significant efforts are under way, matched to a recent strategic plan. However, it is too early to know their results.

Nearly two and a half years ago, I blogged about efforts by a multi-agency consortium (“Birds, Not Mosquitoes” ). It was working to suppress populations of non-native mosquitoes, which vector two lethal diseases: avian malaria (Plasmodium relictum) and avian pox virus (Avipoxvirus). A single bite from an infected mosquito is enough to weaken and kill birds of some species, e.g., the ‘i‘iwi.

The threats from these diseases – and their spread to higher elevations as mosquitoes respond to climate change – pile on top of – other forms of habitat loss and inroads by other invasive species. All of the 17 species of honeycreeper that have persisted until now are listed as endangered or threatened under the federal Endangered Species Act. Four are in danger of extinction within as little as 1 – 2 years. These are ‘Akeke`e (Loxops caeruleirostris), ‘Akikiki (Oreomsytis bairdi)), Kiwikiu (Maui parrotbill, (Pseudonestor xanthophrys), and `Akohekohe (Palmeria dolei).

All these bird species are endemic to the Hawaiian archipelago — found nowhere else on Earth. They are already remnants. Nearly 80 bird species have gone extinct since people first colonized the Hawaiian Islands 1,500 years ago. Eight of these extinctions were recognized in October 2021. Extinction of the final cohort would compromise the integrity of unique ecosystems as well as the Islands’ natural and cultural heritage.

I rejoice to report that the federal government has responded to the crisis. In late 2022 several Interior Department agencies adopted a multiagency Strategy for Preventing the Extinction of Hawaiian Forest Birds. The strategy specifies responsibilities for the key components of the program. These include: a) planning and implementing landscape-level mosquito control using Incompatible Insect Technique (IIT); b) translocating birds to higher elevation sites on other Hawaiian islands; c) establishing captive populations of at-risk birds; and d) developing next-generation tools that increase the scope or efficacy of these actions. All these activities are being developed and conducted through intensive consultation with Native Hawaiians.

On August 8, 2023, the Secretary of Interior announced the allocation of $15,511,066 for conservation and recovery efforts for Hawaiian forest birds. About $14 million of the total was from the Bipartisan Infrastructure Law (Public Law 117-58). The funds are being channelled primarily through the U.S. Fish and Wildlife Service (FWS) ($7.5 million) and the National Park Service (NPS) ($6 million). Other sources of funding are the “State of the Birds” Program (FWS – $963,786); the national-level competitive Natural Resource grants program (NPS – $450,000); and the Biological Threats Program of the U.S. Geological Survey (USGS – $100,000).

What Is Under Way

I do worry continuing these efforts will be harder once their funding is subject to annual appropriations. However, they are a good start!

Steps have been taken on each of the four key component of the Strategy for Preventing the Extinction of Hawaiian Forest Birds:

a) Planning and implementing landscape-level mosquito control using Incompatible Insect Technique (IIT – see below) to reduce the mosquito vector of avian malaria.

The Consortium has obtained all necessary state permits, regulatory approval of the approach by the U.S. Environmental Protection Agency, and done required consultations under the Endangered Species Act.
The Department of the Interior has funded a public-private partnership between the National parks and The Nature Conservancy (TNC) to develop, test, and carry out the first deployments of IIT. These occurred in May 2023 at high-elevation sites on the island of Maui. The next releases are planned for Kaua`i.
Consortium participants are carrying out the consultations and scientific preparations need to support the next deployment on the Big Island.

b) Translocating birds to higher elevation sites on the one island where they exist – Hawai`i.

Initial planning has begun to guide translocation of the endangered Kiwikiu (Maui parrotbill) and Akohekohe to higher-elevation, mosquito-free, habitats on the Big Island.

c) Establishing captive populations of the most at-risk species

To facilitate captive breeding of the four most endangered species, the two existing aviaries in Hawai`i need to be expanded. Space must be provided for at least 80 more birds. A contract has been signed for construction of this new aviary space.

d) Developing next-generation tools that increase the scope or efficacy of these actions.

Lab capacity has been expanded to monitor the effectiveness of IIT, as well as for developing next-generation mosquito control tools.

those who decide funding work here … & they work for us!!!!

The Incompatible Insect Technique (IIT) explained

The incompatible insect technique has been used successfully elsewhere to combat mosquitoes that transmit human diseases. Many insect taxa – including mosquitoes – harbor a naturally-occurring bacteria (Wolbachia). This bacterium has more than one strain or type. When a male mosquito with one type of Wolbachia mates with a female mosquito bearing a different, incompatible type, resulting eggs do not hatch. The IIT project releases male mosquitoes that have an incompatible strain of the bacterium than do local females. (Male mosquitoes do not bite animals seeking a blood meal, so releasing them does not increase the threat to either birds or people.) Implementation requires repeat treatment of sites at a cost of more than $1 million per site per year. It is hoped that this cost will fall with more experience.

Funding for the Strategy’s Four Components

As I noted above, much of the funding for these efforts has come from the Bipartisan Infrastructure Law (Public Law 117-58). Grants under this one-time statute are intended to cover project costs for perhaps five years. Other sources of funds are Congressional appropriations to Interior Department agencies under programs which presumably will continue to be funded in future years. These include the “State of the Birds” program; Endangered Species Act (ESA) implementation, especially its §6 Cooperative Endangered Species Conservation Fund; and State Wildlife Grants administered by the U.S. Fish and wildlife Service. However, funding under these programs is never guaranteed and competition is fierce. I hope participants – and the rest of us! – can be effective in lobbying for future funds required to save Hawaii’s birds from extinction.

a) Deploying IIT

Over Fiscal Years 2017 – 2021 (ending September 2021), Interior Department agencies supported the IIT program by:

Providing $948,000 to the State of Hawai`i from “State of the Birds”, State Wildlife Grants, and Endangered Species Act (ESA) §6;
The U.S. Fish and Wildlife Service provided $545,000 plus staff time’
National Park Service provided $1.2 million for IIT preparations at Haleakala National Park and surrounding state and Nature Conservancy lands
U.S. Geological Survey provided about $7.05 million in research on Hawaiian forest birds, invasive mosquitoes, and avian malaria.

The State of Hawai’i allocated $503,000 and employee staff time.

In addition,

the National Fish and Wildlife Fund provided a total of $627,000 in grants to TNC and American Bird Conservancy for Wolbachia IIT.
TNC committed to supporting some of the initial costs to deploy Wolbachia IIT for the first site in Hawai`i through a contractor (see below)
American Bird Conservancy provided funding for coordination and public outreach.

In FY2022 (which ended in September 2022),

NPS provided $6 million for on-the-ground work on Maui, also development and initial production of Wolbachia IIT.
Interior Department Office of Native Hawaiian Relations provided in-kind services to engage with Native communities’ members

b) Moving endangered birds to mosquito-free areas at high elevations on the Big Island

This is planned to begin by 2030. Interior committed unspecified funds to planning and consultation with Native Hawaiians.

c) Rearing captive birds

FWS supports operation of the two existing aviaries through two funding channels: $700,000 annually provided directly to the aviaries, plus another $500,000 per year through ESA §6through the State of Hawai`i. The San Diego Zoo – which operates the aviaries — provides $600,000 – $800,000 per year in the form of in-kind services, staffing, veterinarians, and administrative support. Interior’s Office of Native Hawaiian Relations provided in-kind services to support to engagement with Native Hawaiian community members

d) Regarding exploration of “next-generation” mosquito control tools

The FWS provided $60,000 to a scientific laboratory to study precision-guided Sterile Insect Technique (pgSIT) tools to protect bird species threatened by avian malaria.

Funding for the portions of these programs dependent upon annual appropriations is uncertain. Current signs are promising: House and Senate bills to fund for the current year (Fiscal Year 2024) – which began in October 2023! – both support at least some aspects of the program. According to American Bird Conservancy, the Senate appropriations bill has allocated $2.5 million to parts of the program. According to the Committee report, the House appropriations bill allots $4.7 million to the State of the Birds program to respond to urgent needs of critically endangered birds. The report goes on to direct the FWS to “incorporate adaptation actions into new and revised recovery plans and recovery implementation strategies, such as with the mosquito vector of avian pox & malaria in the revised Hawaiian Forest Birds recovery plan. …” Per the report, the Appropriations Committee “continues to encourage the [NPS] to respond to the urgent landscape-scale needs of critically endangered forest birds with habitats in national parks.” The report then specifies species threatened by non-native mosquitoes carrying avian malaria and other pathogens. Finally, the report allocates $500,000 to the U.S. Geological Survey for research on the Hawaiian forest birds.

Meanwhile, the American Bird Conservancy is preparing to advocate for $20 million for FY25 through “State of the Birds” Activities and associated NPS and USGS programs. The details of this amount have not yet been laid out.

CISP will support this request and urges you to do so also. We will suggests ways to help when we know more.

Posted by Faith Campbell

www.fadingforests.org

IUCN Leaders: “We Cannot Solve One Problem by Creating Others”

ash trees killed along Mattawoman Creek in Maryland; photo by Leslie A. Brice

Two important players published documents pressing for “nature-based” solutions to climate change in response to the December 2023 24^th Convention of the Parties to the UN Framework Convention on Climate Change.

First, chairs of seven IUCN expert Commissions released a joint statement calling for addressing both climate change and biodiversity loss simultaneously. The elected Commission Chairs represent over 15,000 scientists, scholars, policy makers, economists, lawyers, and other experts who work on issues related to this mission (including me, as well as current and former CISP board members!).

Second, the U.S. Department of the Interior issued detailed guidelines on how to do this.

In this blog, I review the IUCN pronouncement. I will discuss the DOI’s guidelines in a separate blog.

I welcome this statement because I have seen examples of climate “solutions” that worsen the biodiversity crisis. For example, Lugo et al. (2022; full citation at end of this blog) claim to assess the abundance, geographic distribution, contribution to forest structure (including carbon), & temporal trends of non-native tree species. However, they focus almost exclusively on levels of carbon storage. They do not discuss other impacts of non-native tree invasions.

More informative is the 2019 study by Fei et al. ; full citation at end of the blog) that estimated that 41% of total live (woody) biomass in forests of the “lower 48” states was at risk from the most damaging of introduced pests. I pointed out link to blog 159 that elms and beech began dying decades before the underlying (Forest Inventory and Analysis; FIA) data began to be collected. Consequently, the reported mortality rates underestimate the actual loss in biomass associated with these pests. In that blog, I noted that USFS scientists are shifting to new models that will result in a slight bump in overall biomass for the U.S. largely because of increased recognition of the biomass in crowns and limbs. That methodology has now been published.

the “survivor elm” at Longwood Botanical Garden; photo by F.T. Campbell

I also summarized findings by Badgley et al. (2022) that the California cap-and-trade program does not adequately incorporate sequestration losses tied to mortality of tanoak (Notholithocarpus densiflorus) caused by sudden oak death. I noted that California — and North America as a whole – are home to other tree-killing pathogens and insects.

As the IUCN statement clearly demonstrates, climate change and biodiversity loss are inseparable, interdependent, and mutually reinforcing. However, countries’ and businesses’ approaches now fall short of what scientific evidence indicates is needed. We must have bold, transformative, and holistic efforts by scientists – and everyone else.

The IUCN’s full statement has 10 points, which the organization’s blog compresses to four:

1. Integrate Climate and Biodiversity Efforts

The climate and biodiversity challenges require coherent, consistent, and integrated actions that simultaneously limit global warming to a maximum of 1.5^oC, conserve and sustainably use biodiversity, and restore degraded ecosystems. Only by considering climate and biodiversity as parts of the same complex, systemic challenge can decision-makers develop effective solutions that maximize benefits while minimizing risks.

“green” infrastructure in urban spaces; Washington, D.C.

2. Enhance Ecosystem Integrity

We humans must maintain, enhance, and restore ecosystem integrity in order to halt biodiversity decline and species extinctions and to maintain the ecosystem services that underpin human well-being. Appropriate actions to conserve and restore terrestrial and marine ecosystems also support climate change mitigation, adaptation, and limits on temperature increases. This is true, however, only as long as chosen actions complement—and are not in lieu of—ambitious reductions of greenhouse gas emissions from fossil fuels, industrial processes, and land-use change.

The full IUCN statement also notes that the effects of “nature-based solutions” must be verified through a robust accounting system. IUCN has released separately a Global Standard for Nature-based Solutions which provides eight specific criteria.

3. Equitably transforming the way we live

Addressing the biodiversity and climate crises will require systemic changes in the way we live. These demand rapid and far-reaching actions across all sectors of a type, scale, and speed never before attempted. IUCN notes, several times, that these transformations must be realized in ways that are equitable and consider impacts on the most vulnerable populations, e.g., indigenous peoples, women, and youth.

IUCN calls for a rapid phase out of fossil fuels, paired with an accelerated and equitable deployment of sustainable clean or renewable energy generation and distribution. In the full statement, IUCN urges countries to avoid relying on unproven — and untested — geoengineering technologies.

4. Prop the Window Open

The window of opportunity to address climate change and biodiversity loss is closing rapidly. Protecting 30% of the Earth’s terrestrial and marine areas by 2030 — a goal adopted by the parties to the Global Biodiversity Convention in late 2022 — will require significant expansion of protected areas in only seven years. I note that while the U.S. is not a party to the biodiversity convention, the Biden Administration has accepted this goal. The IUCN states that achieving this goal depends on greater collaboration across the international agreements on biodiversity, climate change, desertification, and the United Nations’ Sustainable Development Goals. The full statement notes that the United Nations Environment Program (UNEP) calls for tripling expects that funding for nature-based solutions.

old-growth forest in the Pacific Northwest; photo by Richard Orr, via Wikimedia

The IUCN commission chairs warn that delegates at COP28 – and presumably others focused on the climate crisis — must be alert to possible conflicts between biodiversity conservation and climate change mitigation. They cite particularly actions aimed at transitioning energy supplies to “green” sources. This risk arises during choices of sites for solar facilities, wind farms, hydropower dams, and the locations and methods for deep-sea mining for minerals. The IUCN Standard provides guidance for navigating these conflicts.

SOURCES

Fei, S., R.S. Morin, C.M. Oswalt, and A.M. Liebhold. 2019. Biomass losses resulting from insect and disease invasions in US forests. Proceedings of the National Academy of Sciences Vol. 116 No. 35. August 2019

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 United States in Comparison with Tropical Islands in the Pacific & Caribbean. USDA USFS General Technical Report IITF-54.

Posted by Faith Campbell

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

www.fadingforests.org

The White Mountain forest in New Hampshire: 80 years of change, with more ahead

I have been disappointed that a research symposium focused on the northern hardwood forest workshop gave little attention to non-native pests (see citation at end of this blog). A new study based in the Bartlett Experimental Forest in the White Mountains of New Hampshire is more balanced. Ducey et al. (full citation at the end of this blog) analyzed changes in the forest’s species composition and tree size over the past 80 years.

They found that trees of nearly all species are growing into larger sizes as the forest continues to age since the last widespread clearing at the end of the 19^th Century. The same aging is causing a rapid decline in two shade-intolerant species – paper birch (Betula papyrifera) and aspen (Populus tremuloides and P. grandidentata) – which had grown quickly once the cleared areas were abandoned. The mid-shade -tolerant species yellow birch (Betula alleghaniensis) also is declining. Together, the birch and aspen species have declined from a quarter to a third of basal area in 1931 to 10 – 12% in 2015.

Some developments are unexpected. Red maple (Acer rubrum) increased in abundance until the early 1990s, but that growth then levelled off. Sugar maple (Acer saccharum) has declined in abundance except where the forest is managed to retain it.

There is little evidence of tree species migrating upward on slopes in response to changes in the local climate. Major weather events – a hurricane in 1938 and an ice storm in 1998 — caused significant tree mortality across Bartlett Experimental Forest, but not a dramatic change in forest composition.

Eastern hemlock (Tsuga canadensis) is replacing the disappearing birch and aspen on low elevation sites. Hemlock has increased its proportion of basal area from 8 – 10% to a quarter or more. Despite aggressive management aimed at reducing the tree’s presence, American beech (Fagus grandifolia) is on track to dominate large areas of the Bartlett Experimental Forest. Given the tree-killing pests already present in the region, large increases in eastern hemlock, American beech, and red spruce (Picea rubens) are worrying.

Eastern hemlock creates important wildlife habitat for deer and more than 100 other vertebrate species in New England. However, hemlock woolly adelgid (HWA) has been present in New Hampshire since 2000. It is now within 15-20 km of Bartlett Experimental Forest. There is some hope that the region’s cold temperatures might limit HWA’s spread and impacts, but Ducey et al. expect major change when the adelgid arrives.

Ducey et al. cite a separate study demonstrating that mortality caused by beech bark disease (BBD) can be sufficient to upset carbon storage in old-growth forests. On the Bartlett Forest, nearly 90% of beech trees had become diseased by 1950.

Ducey et al. express concern about the possible impact of beech leaf disease (BLD), as well.

BLD has not yet been detected in the White Mountains or New Hampshire, but is in so New England and coastal Maine. Much remains unknown about the disease, including how it spreads and its long-term impacts.

Ducey et al. do not raise pest concerns about red spruce or balsam fir (Abies balsamea), which co-dominate the Bartlett Forest at higher elevations (above 500 m). This silence is disturbing since red spruce can be killed by the brown spruce longhorned beetle, a European woodborer established in Nova Scotia and threatening to spread south. Balsam firs suffer some mortality from feeding by the balsam woolly adelgid, a Eurasian sap-sucker which has been in New England for more than a century.

White ash (Fraxinus americana) is present as a minor component of the Bartlett Forest. Because it is considered to be a valuable timber species, management has resulted in a modest increase in abundance of ash. Ducey et al. expect dramatic reduction — or even elimination of the species — when the emerald ash borer (EAB) arrives. EAB has been detected within ~ 15 km from Bartlett Experimental Forest.

Ducey et al. conclude that silvicultural management applied at the scope and intensity of that in the Bartlett Experimental Forest has moderated some changes. That is, it is maintaining sugar maple and suppressing the increase of beech. Its effect is secondary, however to overall forest development as the forest ages.

SOURCES

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

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

Posted by Faith Campbell

www.fadingforests.org

USFS Lays Out Incomplete Picture of the Future

tanoak trees in southern Oregon killed by sudden oak death; photo by Oregon Department of Forestry; this pathogen is not mentioned by USFS RPA report

In August the USDA Forest Service published the agency’s 2020 assessment of the future of America’s forests under the auspices of the Resources Planning Act. [See United States Department of Agriculture Forest Service Future of America’s Forests and Rangelands, full citation at the end of the blog.] To my amazement, this report is the first in the series (which are published every ten years) to address disturbance agents, specifically invasive species. In 2023! Worse, I think its coverage of the threat does not reflect the true state of affairs – as documented by Forest Service scientists among others.

This is most unfortunate because policy-makers presumably rely on this report when considering which threats to focus on.

Here I discuss some of the USFS RPA report and what other authors say about the same topics.

The RPA Report’s Principle Foci: Extent of the Forest and Carbon Sequestration

The USFS RPA report informs us that America’s forested area will probably decrease 1- 2% over the next 50 years (from 635.3 million acres to between 619 and 627 million acres), due largely to conversion to other uses. This decline in extent, plus trees’ aging and increases in disturbance will result in a slow-down in carbon sequestration by forests. In fact, if demand for wood products is high, or land conversion to other uses proceeds apace, U.S. forest ecosystems are projected to become a net source of atmospheric CO₂by 2070.

Eastern forests sequester the majority of U.S. forest carbon stocks. These forests are expected to continue aging – thereby increasing their carbon storage. Yet we know that these forests have suffered the greatest impact from non-native pests.

I don’t understand why the USFS RPA report does not explicitly address the implications of non-native pests. In 2019, Songlin Fei and three USFS research scientists did address this topic. Fei et al. estimated that tree mortality due to the 15 most damaging introduced pest species have resulted in releases of an additional 5.53 terragrams of carbon per year. Fei and colleagues conceded this is probably an underestimate. They say that annual levels of biomass loss are virtually certain to increase because current pests are still spreading to new host ranges (as demonstrated by detection of the emerald ash borer in Oregon). Also, infestations in already-invaded ranges will intensify, and additional pests will be introduced (for example, beech leaf disease).

I see this importance of eastern forests in sequestering carbon as one more reason to expand efforts to protect them from new pest introductions, and the spread of those already in the country, etc.

A second issue is the role of non-native tree species in supporting the structure and ecological functions of forests. Ariel Lugo and colleagues report that 18.8 million acres (7.6 million ha, or 2.8% of the forest area in the continental U.S.) is occupied by non-native tree species. (I know of no overall estimate for all invasive plants.) They found that non-native tree species constitute 12–23% (!) of the basal area of those forest stands in which they occur.

Norway maple (*Acer platanoides*); one of the most widespread invasive species in the East. Photo by Hermann Falkner via Flickr

Lugo and colleagues confine their analysis of ecosystem impacts to carbon sequestration. They found that the contribution of non-native trees to carbon storage is not significant at the national level. In the forests of the continental states (lower 48 states), these trees provide 10% of the total carbon storage in the forest plots where they occur. (While Lugo and colleagues state that the proportion of live tree biomass made up of non-native tree species varies greatly among ecological subregions, they do not provide examples of areas on the continent where their biomass – and contribution to carbon storage — is greater than this average.) In contrast, on Hawai`i, non-native tree species provide an estimated 29% of live tree carbon storage. On Puerto Rico, they provide an even higher proportion: 36%.

Brazilian pepper (Schinus terebinthifolius) – widespread invasive in Hawai`i and Florida; early stage invasive in Puerto Rico. Photo by Javier Alexandro via Flickr

In the future, non-native trees will play an even bigger role. Since tree invasions on the continent are expanding at ~500,000 acres (202,343 ha) per year, it is not surprising that non-native species’ saplings provide 19% of the total carbon storage for that size of trees in the lower 48 states (Lugo et al.).

Forming a More Complete Picture: Biodiversity, Disturbance, and Combining Data.

The USFS RPA report has a chapter on biodiversity. However, the chapter does not discuss historic or future diversity of tree species within biomes, nor the genetic diversity within tree species.

Treatment of Invasive Species

The USFS 2020 RPA report is the first to include a chapter on disturbance, including invasive species. I applaud its inclusion while wondering why they have included it only now? Why is the coverage so minimal? I think these lapses undercut the report’s purpose. The RPA is supposed to inform decision-makers and stakeholders about the status, trends, and projected future of renewable natural resources and related economic sectors for which USFS has management responsibilities. These include: forests, forest products, rangelands, water, biological diversity, and outdoor recreation. The report also has not met its claim to “capitalize on” areas where the USFS has research capacity. One excuse might be that several important publications have appeared after the cut-off date for the assessment (2020). Still, the report’s authors cite some of the evaluations that were in preparation as of 2020, e.g., Poland et al.

I suggest also that it would be helpful to integrate data from other agencies, especially the invasive species database compiled by the U.S. Geological Survey, into the RPA. For example, the USGS lists just over 4,000 non-native plant species in the continental U.S. (defined as the lower 48 plus Alaska). On Hawai`i, the USGS lists 530 non-native plant species as widespread. Caveat: many of the species included in these lists probably coexist with the native plants and make up minor components of the plant community.

Specifically: Invading Plants

The USFS RPA report gives much more attention to invasive plants than non-native insects and pathogens. The report relies on the findings of Oswalt et al., who based their data on forested plots sampled by the Forest Inventory and Analysis (FIA) program. (The RPA also reports on invasive plants detected on rangelands, primarily grasslands.) Oswalt et al. found that 39% of FIA plots nationwide contained at least one plant species that the FIA protocol considers to be invasive and monitors. The highest intensity of plant invasions is in Hawai`i – 70% of the plots are invaded. The second-greatest intensity is in the eastern forests: 46%. However, the map showing which plots were inventoried for invasive plants makes clear how incomplete these data are – a situation I had not realized previously.

I appreciate that the USFS RPA report mentions that propagule pressure is an important factor in plant invasions. This aspect has often been left out in past analyses. I also appreciate the statement that international trade in plants for ornamental horticulture will probably lead to additional introductions in the future. Third, I concur with the report’s conclusions that once forest land is invaded, it is unlikely to become un-invaded. Invasive plant management in forests often results in one non-native species being replaced by another. In sum, the report envisions a future in which plant invasion rates are likely to increase on forest land.

If you wish to learn more about invasive plant presence and impacts, see the discussion of invasive plants in Poland et al., my blogs based on the work by Doug Tallamy, and several other of my blogs compiled under the category “invasive plants” on this website.

I believe all sources expect that the area invaded by non-native plant species, and the intensity of existing invasions, will increase in the future.

The USFS RPA links these invasions to expansion of the “wildland-urban interface” (“WUI”). These areas increased rapidly before 2010. At that time, they occupied 14% of forest land. The report published in 2023 did not assess their future expansion over the period 2020 to 2070. However, it did project increased fragmentation in many regions, especially in the RPA Western and Southeastern regions. Since “fragmentation” is very similar to wildland-urban interfaces, the report seems implicitly to project more widespread plant invasions in the future.

plant invasions facilitated by fragmentation; northern Virginia; photo by F.T. Campbell

Specifically: Insects and Pathogens

The USFS RPA report on insects and pathogens is brief and contains puzzling errors and gaps. It says that the tree canopy area affected by both native and non-native mortality-causing agents has been consistently large over the three most recent five-year FIA assessment periods. It notes that individual insects or diseases have extirpated entire tree species or genera and fundamentally altered forests across broad regions. Examples cited are chestnut blight and emerald ash borer.

The USFS RPA report warns that pest-related mortality might be underreported in the South, masked by more intense management cycles and higher rates of tree growth and decay. On the other hand, the report asserts that pest-related mortality is probably overrepresented in the Northern Region in the 2002 – 2006 period because surveyors drew polygons to encompass large areas affected by EAB and balsam woolly adelgid (Adelges piceae) infestations. The latter puzzles me; I think it is probably an error, and should have referred to hemlock woolly adegid, A. tsugae. Documented mortality has generally been much more widespread from insects than diseases, e.g., bark beetles, including several native ones, across all regions and over time, especially in the West – where the most significant morality agents are several native beetles. The USFS RPA report mentions that the Northern Region has been particularly affected by non-native pests, including EAB, HWA, BWA, beech bark disease, and oak wilt. It mentions that Hawai`i has also suffered substantial impacts from rapid ʻōhiʻa death.

Defoliating insects have affected relatively consistent area over time. This area usually equaled or exceeded the area affected by the mortality agents. Principal non-native defoliators in the Northern Region have been the spongy moth (Lymantria dispar); larch casebearer (Coleophora laricella); and winter moth (Operophtera brumata). In the South they list the spongy moth.

More disturbing to me is the USFS RPA report’s conclusion that the future impact of forest insects is highly uncertain. The authorsblame the complexity of interactions among changing climate, those changes’ effects on insect and tree species’ distributions, and overall forest health. Also, they name uncertainty about which new non-native species will be introduced to the United States. I appreciate the report’s avoidance of blanket statements regarding the effects of climate change. However, other studies – e.g., Poland et al. – have incorporated these complexities while still offering conclusions about a number of currently established non-native pests. Finally, I am particularly dismayed that the USFS RPA does not provide analysis of any forest pathogens beyond the single mention of a few.

I am confused as to why the USFS RPA report makes no mention of Project CAPTURE (Conservation Assessment and Prioritization of Forest Trees Under Risk of Extirpation). This is a multi-partner effort to prioritize U.S. tree species for conservation actions based on invasive pests’ threats and the trees’ ability to adapt to them. Several USFS units participated, including the Southern Research Station, the Eastern Forest Environmental Threat Assessment Center, and the Forest Health Protection program. The findings were published in 2019. See here. Lead scientist Kevin Potter was one of the authors of the RPA’s chapter on disturbance.

redbay (*Persea borbonia*) trees in Georgia killed by laurel wilt; photo by Scott Cameron. Redbay is ranked by Project CAPTURE as 5th most severely at risk due to a non-native pest

“Project CAPTURE” provided useful summaries of non-native pests’ impacts, including the facts that

54% of the tree species on the continent are infested by one or more non-native insect or pathogen;
nearly 70% of the host/agent combinations involve angiosperm (broadleaf) species, 30% gymnosperms (e.g., conifers). When considering only non-native pests, pests attacking angiosperms had greater average severity.
Disease impacts are more severe, on average, than insect pests. Wood-borers are more damaging than other types of insect pests.
Non-native agents have, on average, considerably more severe impacts than native pests.

Project CAPTURE also ranked priority tree species based on the threat from non-native pests (Potter et al., 2019). Tree families at the highest risk to non-native pests are: a) Fagaceae (oaks, tanoaks, chestnuts, beech), b) Sapindaceae (soapberry family; includes maples, Aesculus (buckeye, horsechestnut); c) in some cases, Pinaceae (pines); d) Salicaceae (willows, poplars, aspens); e) Ulmaceae (elms) and f) Oleaceae (includes Fraxinus). I believe this information should have been included in the Resources Planning Act report in order to insure that decision-makers consider these threats in guiding USFS programs.

I also wish the USFS RPA had at least prominently referred readers to Poland et al. Among that study’s key points are:

Invasive (non-native) insects and diseases can reduce productivity of desired species, interactions at other trophic levels, and watershed hydrology. They also impose enormously high management costs.
Some non-native pests potentially threaten the survival of entire tree genera, not just individual species, e.g., emerald ash borer and Dutch elm disease. I add white pine blister rust and laurel wilt.
Emerald ash borer and hemlock woolly adelgid are listed as among the most significant threats to forests in the Eastern US.
White pine blister rust and hemlock woolly adelgid are described as so profoundly affecting ecosystem structure and function as to cause an irreversible change of ecological state.
Restoration of severely impacted forests requires first, controlling the non-native pest, then identifying and enriching – through selection and breeding – levels of genetic resistance in native populations of the impacted host tree. Programs of varying length and success target five-needle pines killed by Cronartium ribicola; Port-Orford cedar killed by the oomycete Phytophthora lateralis; chestnut blight; Dutch elm disease; butternut canker (causal agent Ophiognomonia clavigignenti juglandacearum), emerald ash borer; and hemlock woolly adelgid.
Climate change will almost certainly lead to changes in the distribution of invasive species, as their populations respond to increased variability and longer-term changes in temperature, moisture, and biotic interactions. Predicting how particular species will respond is difficult but essential to developing effective prevention, control, and restoration strategies.

Poland et al. summarizes major bioinvaders in several regions. Each region except Hawai`i (!!) includes tree-killing insects or pathogens.

It is easier to understand the RPA report’s not mentioning priority-setting efforts by two other entities, the Morton Arboretum and International Union for the Conservation of Nature (IUCN). These studies were published in 2021 and their lead entities were not the Forest Service – although the USFS helped to fund the U.S. portion of the studies.

The Morton Arboretum led in the analysis of U.S. tree species. It published studies evaluating the status of tree species belonging to nine genera, considering all threats. The Morton study ranked as of conservation concern one third of native pine species; 31% of native oak species; significant proportion of species in the Lauraceae. The report on American beech — the only North American species in the genus Fagus – made no mention of beech leaf disease – despite it being a major concern in Ohio – only two states away from the location of the Morton Arboretum near Chicago.

valley oak (*Quercus lobata*) in Alameda Co, California; photo by Belinda Lo via Flickr

Most of the species listed by the Morton Arboretum are of conservation concern because of their small populations and restricted ranges. The report’s coverage of native pests is inconsistent, spotty, and sometimes focuses on odd examples.

Tree Species’ Regeneration

Too late for consideration by the authors of the USFS RPA report come new studies by Potter and Riitters that evaluate species at risk due to poor regeneration. This effort evaluated 280 forest tree species native to the continental United States – two-thirds of the species evaluated in the Kevin Potter’s earlier analysis of pest impacts.

The results of Potter and Riitters 2023 only partially matched those of the IUCN/Morton studies. The Morton study did not mention three genera with the highest proportions of poorly reproducing species according to Potter and Riitters: Platanus, Nyssa, and Juniperus. Potter, Morton, and the IUCN largely agree on the proportion of Pinus species at risk. Potter et al. 2023 found about 11% of oak species to be reproducing poorly, while Morton designated a third of 91 oak species to be of conservation concern.

I believe Potter and Riitters and the Morton study agree that the Southeast and California are geographic hot spots of tree species at risk.

Potter and Riiters found that several species with wide distributions might be at risk because they are reproducing at inadequate rates. Three of these exhibit poor reproduction across their full range: Populus deltoids (eastern cottonwood), Platanus occidentalis (American sycamore), and ponderosa pine(Pinus ponderosa). Four more species are reported to exhibit poor reproduction rates in all seed zones in which they grow (the difference from the former group is not explained). These are two Juniperus, Pinus pungens, and Quercus lobata. As I point out in my earlier blog, valley oak is also under attack by the Mediterranean oak borer.

SOURCES

Lugo, A.E., J.E. Smith, K.M. Potter, H. Marcano Vega, and C.M. Kurtz. 2022. The Contribution of Nonnative Tree Species to the Structure and Composition of Forests in the Conterminous United States in Comparison with Tropical Islands in the Pacific and Caribbean. USDA USFS General Technical Report IITF-54

Poland, T.M., T. Patel-Weynand, D.M. Finch, C.F. Miniat, D.C. Hayes, V.M. Lopez, eds. 2021. Invasive Species in Forests and Rangelands of the United States: A Comprehensive Science Synthesis for the United States Forest Sector. Springer Verlag. Available gratis at https://link.springer.com/book/10.1007/978-3-030-45367-1

Potter, K.M., M.E. Escanferla, R.M. Jetton, G. Man, and B.S. Crane. 2019. Prioritizing the conservation needs of United States tree species: Evaluating vulnerability to forest insect and disease threats. Global Ecology and Conservation.

Potter, K.M. and Riitters, K. 2023. A National Multi-Scale Assessment of Regeneration Deficit as an Indicator of Potential Risk of Forest Genetic Variation Loss. Forests 2022, 13, 19. https://doi.org/10.3390/f13010019

United States Department of Agriculture Forest Service. 2023. Future of America’s Forests and Rangelands: The Forest Service 2020 Resource Planning Act Assessment. GTR-WO-102 July 2023

Posted by Faith Campbell