Category: invasive species

“Ecological memory” determines a forest’s resilience — implications of bioinvasion to New Zealand’s unique flora

kauri dieback

Scientists in New Zealand are saying explicitly that a forest’s unique mixture of species matters when considering the future. This mixture is the result of the forest’s evolutionary history. Losing members of the biological community reduces the forest’s ability to respond to current and future stresses – its resilience.

New Zealand’s forests are part of the broader legacy of the ancient supercontinent of Gondwanaland – the island nation’s plants have close relatives in South America, the Pacific Ocean islands, and Australia. Still, these forests are unique: 80% of New Zealand’s plant species are endemic. The forests are also species-rich. The warm temperate evergreen rain forests of the North Island are home to at least 66 woody plant species that can reach that reach heights above six meters (Simpkins et al. 2024).

These forests have been severely changed by human activity. In just ~ 750 years people have cut down approximately 80% of the original forest cover! (Simpkins et al. 2024) Of the eight million hectares of surviving native forest, a little over five million hectares is managed for the conservation of biodiversity, heritage, and recreation.  Another 2 million hectares are plantations of non-native species.

sites in New Zealand where pine plantations are “wilding”

All these forests are challenged by introduced mammals – from European deer to Australian possums. Climate change is expected to cause further disturbance, both directly (through e.g., drought, extreme weather) and indirectly (e.g., by facilitating weed invasion and shifting fire regimes) (Simpkins et al. 2024).

Pathogen threats are also common threats to the native trees of the Pacific’s biologically unique island systems. For example, Ceratocystis lukuohia and C. huliohia (rapid ‘ōhi‘a death, or ROD). The latter is killing ‘ōhi‘a (Metrosideros polymorpha) on the Hawaiian Islands. More than 40% of native plant species in Western Australia are susceptible to Phytophthora cinnamomi. Here I focus on two pathogens, kauri dieback and myrtle rust, now ravaging New Zealand’s native flora. No landscape-level treatment is available for either pathogen.

When considering this suite of challenges, Simpkins et al. focus on these two pathogens’ probable impact on forest carbon sequestration. They worry in particular about erosion of the forests’ resilience due to loss of “ecological memory” – the life-history traits of the species (e.g., soil seed banks) and the structures left behind after individual disturbances.

one of the largest remaining kauri trees, “Tane Mahuta”, in Waipoua Kauri Forest; photo by F.T. Campbell

Kauri Dieback

The causal agent of Kauri dieback, Phytophthora agathidicida, is a soil-borne pathogen that spreads slowly in the absence of animal or human vectors. The disease affects a single species, Agathis australis (kauri, Araucariaceae). However, kauri is a long-lived, large tree that is a significant carbon sink. It probably modifies local soil conditions, nutrient and water cycles, and associated vegetation. Also, kauri has immense cultural significance.

Simpkins et al. note that kauri dieback threatens stand-level loss of A. australis – that is, local extinctions. In the absence of disturbance Kauri trees can grow to awe-inspiring size. In the 19th Century, before widespread logging, some were measured at 20 meters or more in circumference. Consequently, kauri dieback might cause a decline in aboveground live carbon storage of up to 55%. This loss would occur over a period of hundreds of years, not immediately.

Huge kauri are not likely to be replaced by other long-lived emergent conifers (based on an analysis of one species, Dacrydium cupressinum). Instead, kauri are probably going to be replaced by late-successional angiosperms. The authors discuss the ecological implications for levels of carbon storage and proportions of trees composed of Myrtaceae – exacerbating damage caused by myrtle rust (see below).

The expectation of Simpkins et al. that kauri will suffer at least local extinctions is based on an assumption that no kauri trees are resistant to the pathogen. Fortunately, this might not be true: different Agathis populations show various levels of tolerance to Agathis dieback. Identification and promotion of some levels of resistance could enable A. australis to retain a diminished presence in the landscape.

However, Lantham, et al. make clear that containing kauri dieback remains “challenging,” despite its discovery nearly 20 years ago (in 2006). Scientists and land managers have little information on the distribution of symptomatic trees, much less of the pathogen itself. This means they don’t know where infection foci are or how fast the disease is spreading.

As is often true, the pathogen is probably present in a stand for years, possibly a decade or more, before symptoms are noticed. This means that the current reliance on public reports of diseased trees, or targetting surveillance on easy-to-access sites (e.g., park entrances and along existing track networks), or at highly impacted areas readily identified through aerial methods, fails to detect early stages of infection. Indeed, it seems probable that P. agathidicida had been present in New Zealand’s ecosystems for decades before its formal identification.

The Waipoua forest is one of the largest areas of forest with old kauri stands in the country. A new analysis of aerial surveys done between 1950 and 2019, shows how the forest is changing. The number of dead trees increased more than four-fold and the number of unhealthy-looking trees increased 16-fold over these 70 years. Kauri dieback is now widespread in this forest, especially in areas near human activities like clearing for pasture or planting commercial pine plantations).

Lantham et al. have developed a model which they believe will help identify areas of higher risk so as to prioritize surveillance and inform responses. These could delimit the disease front and help implement quarantines or other measures aimed at limiting the spread of P. agathidicida to uninfected neighboring sites.

I hope New Zealand devotes sufficient resources to expand surveillance and management to levels commensurate with the threat to this ecologically and culturally important tree species.

Leptospermum scoparia; photo by Brian Gatwicke via Flickr

Myrtle Rust

Myrtle rust is a wind-borne disease that affecting numerous species in the Myrtaceae, including some of the dominant early successional species (e.g., Leptospermum spp.). Simpkins et al. expect that myrtle rust might hasten the decline of two such tree species (L. scoparium and Kunzea ericoides). However, these trees’ small size and rapid replacement by other species during succession minimizes the effect of their demise on carbon storage.

Because I am concerned about the irreplaceable loss to biodiversity, I note that Simpkins et al. also feared immediate threats to some trees in the host Myrtaceae family, specifically highly susceptible species such as Leptospermum bullata.

As I reported in a recent blog, a second group of scientists (McCarthy et al.) explored the threat from myrtle rust more broadly. Austropuccinia psidii has spread through Myrtaceae-dominated forests of the Pacific islands for about 20 years.

Trees in the vulnerable plant family, Myrtaceae, are second in importance (based on density and cover) in New Zealand’s forests. Successional shrub communities dominated by the two species named above, Kunzea ericoides and Leptospermum scoparium, are widespread in the northern and central regions of the North Island and in northeastern and interior parts of the South Island. These regions’ vulnerability is exacerbated by the area’s climate, which is highly suitable for A. psidii infection (Simpkins et al. 2024).

McCarthy et al. concluded that if Leptospermum scoparium and Kunzea ericoides prove to be vulnerable to myrtle rust, their loss would cause considerable change in stand-level functional composition across these large areas. They probably would be replaced by non-native shrubs, which are already common on the islands. Any resulting forest will differ from that formed via Leptospermeae succession.

These authors also worry that the risk to native ecosystems would increase if more virulent strains of the myrtle rust pathogen were introduced or evolved. They note that A. psidii is known to have many strains and that these strains attack different host species.

SOURCES

Latham, M.C., A. Lustig, N.M. Williams, A. McDonald, T. Patuawa, J. Chetham, S. Johnson, A. Carrington, W. Wood, and D.P. Anderson. 2025.  Design of risk-based surveillance to demonstrate absence of Phytophthora agathidicida in New Zealand kauri forests. Biol. Invasions (2025) 27, no. 26

McCarthy, J.K., S.J. Richardson, I. Jo, S.K. Wiser, T.A. Easdale, J.D. Shepherd, P.J. Bellingham. 2024. A Functional Assessment of Community Vulnerability to the Loss of Myrtaceae from Myrtle Rust. Diversity and Distributions, https://doi.org/10.1111/ddi.13928

Simpkins, C.E., P.J. Bellingham, K. Reihana, J.M.R. Brock, G.L.W. Perry. 2024. Evaluating the effects of two newly emerging plant pathogens on North Aotearoa-New Zealand forests using an individual-based model.  Ecological Modelling, www.elsevier.com/locate/ecolmodel

Posted by Faith Campbell

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

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

or

www.fadingforests.org

More pests in Europe & Mideast – hazard to North American trees

giant sequoia; photo by Matthew Dillon via Flickr

The pest alert system “PestLens” has again alerted us to plant pests in Europe or Asia that feed on species closely related to tree species native to North American forests.  Two of the insects named in the alert apparently pose a hazard to icons of the forests of America’s Pacific coast forests, giant sequoia and redwood.

I hope APHIS is using this information to alert port and on-the-ground staff and perhaps initiating more in-depth risk assessments.

The posting on February 27, 2025 reported that cotton jassid, Jacobiasca lybica (Hemiptera: Cicadellidae), affects not just cotton and citrus but also Cupressus sempervirens (Mediterranean cypress) [Cupressaceae]. More than a dozen North American trees species are in this family, including

  • Sequoiadendron giganteum or giant sequoia. Giant sequoia is listed as an endangered species by the IUCN with fewer than 80,000 remaining in its native California.
  • Chamaecyparis thyoides and C. lawsoniana (Port-Orford cedar). Port-Orford cedar has been decimated in its native range by an introduced pathogen, Phytopthora lateralis. A major breeding effort has developed trees that are resistant to the pathogen; they are now available for people to plant.
  • Thuja occidentalis, also known as northern white-cedar, eastern white-cedar, or arborvitae,
  • Taxodium ascendens, also known as pond cypress
  • several Juniperus
  • Hesperocyparis macrocarpa also known as Cupressus macrocarpa, or the Monterey cypress. NatureServe ranks the cypress as GI – critically imperiled.

Cotton jassid been reported from several countries in Europe, Africa, and the Middle East.

China has reported the existence of a previously unknown bark beetle species, Phloeosinus metasequoiae (Coleoptera: Curculionidae). It was found infesting Metasequoia glyptostroboides (dawn redwood) trees in China. Affected trees exhibited reddened leaves and holes and tunnels in branches.

China has also discovered a several new hosts utilized by the fungus Pestalotiopsis lushanensis (Sordariomycetes: Amphisphaeriales). Formerly known to infect tea (Camellia sinensis) and several other plant species, P. lushanensis has now been found shoot causing blight and leaf drop on a conifer, deodar cedar (Cedrus deodara) and leaf spots on an angiosperm with congeners in North America — the rare Chinese species, Magnolia decidua. There are eight species of Magnolia native to North America.

Magnolia grandiflora; photo by DavetheMage via Wikimedia

APHIS’ ability to respond to alerts remains uncertain.

The agency’s probationary employees have been fired – just as at other agencies. APHIS staff were prohibited from participating in last week’s annual USDA Invasive Species Research Forum – the 33rd such meeting. The bird flu emergency is demanding all the attention and funds.

So – how can the rest of us fill in?

At the USDA Research Forum I again presented a poster urging greater attention to tree-killing pathogens. Scientists have made considerable progress in identifying factors that indicate whether a non-native insect might pose a significant threat (see blogs on conifer and deciduous species; more to come!). However, USDA had not funded a similar effort to improve understanding of pathogens. The most promising strategy so far are sentinel plantings. However, these systems have weaknesses; I will blog in the near future about another analysis.

I propose that APHIS start by working with independent scientists to determine the actual, current level of pathogens associated with various types of incoming goods. Contact me directly if you wish to read the text of my poster.

Posted by Faith Campbell

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

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

or

www.fadingforests.org

Coming to an Ecosystem Near You??

Xylotrechus chinensis; EPPO photograph

Europe has been invaded by two insect species that North Americans should be watching out for. First, a Cerambycid, the wasp-mimicking tiger longicorn beetle, Xylotrechus chinensis. And second,the Buprestid cypress jewel beetle, Lamprodila festiva. We should also ensure that none of the other 500+ beetles introduced to Europe poses a threat to our trees. These are summarized in a 2024 paper by Bunescu et al.

Tiger Longicorn Beetle

This beetle is native to eastern Asia. It feeds on and kills mulberry trees (Moraceae: Morus spp.). It might also attack apple and pear trees and grapevines – Asian sources report these as hosts. The status of grapevines has been questioned by a Spanish experiment, in which artificial inoculations failed. I have seen no further information about the vulnerability of apple (Malus spp.) and pear (Pyrus spp.) (Saarto i Monteyu, Costa Ribeu, and Savin 2021)

In Europe, the pest threatens mulberry trees which are commonly planted for shade and ornamentation, especially in southern France, Spain and Greece (Saarto i Monteyu, Costa Ribeu, and Savin 2021). For example, there are more than 20,000 mulberry trees in Athens (EFSA 2021). The trees’ abundance contributes to spread of any associated pests, the level of damage caused by falling branches, and the expense of tree removal. Economic damages are those typically associated with wood-borer invasions of urban areas. That is, the cost of tree removals, loss of shade and amenity values, and increased risk of injury from falling branches.

We Americans should be concerned, too. Wild red mulberry (Morus rubra) occupies much of the eastern United States, from southern New England west to southeastern Minnesota, then south along the eastern edge of the Great Plains to central Texas, and east to southern Florida. It is also found in Bermuda. It grows primarily in flood plains and low moist hillsides. . Presumably it would also be attacked by Xylotrechus chinensis, although I don’t know whether anyone has tested this. As a native tree, red mulberry plays a role in natural ecosystems, including wildlife food supplies. Thus, America would see even more significant losses if Xylotrechus chinensis were to establish.

Morus rubra in Fairfax County, Virginia; photo by Fmartin via Wikipedia

Red mulberry is already declining in parts of its central range, possibly due to a bacterial disease. The effects and extent of this disease have not been investigated thoroughly.

Apples and pears are important crops across North America; the farm-gate value is estimated at $3.2 billon.

Introductions of the beetle to Spain, France, and Greece might have resulted from inadequately-treated wood packaging or other wood products. Detections of the species in wood imports were reported in Germany in 2007 and 2017 (Saarto i Monteyu, Costa Ribeu, and Savin 2021). The U.S. has also intercepted X. chinensis at least once, at the port of Philadelphia, in 2011 (EFSA 2021).

These detections have raised questions to which no-one yet has answers. First, can X. chinensis develop in cut logs? The European Food Safety Agency concluded that it can (EFSA 2021). Second, one detection involved a shipment of wooden items made from birch (Betula spp.) and willow (Salix spp). It is not yet clear whether these taxa are also hosts (EFSA 2021). (The wood species were not specified in the case of the other interceptions.) I have blogged often about how “leaky” the wood packaging pathway has been; to see these blogs, scroll below the “archives” section of the webpage, then click on the category “wood packaging”.

European scientists believe X. chinensis might also be transported in shipments of plants for planting. However, the beetle prefers to oviposit on large trees. This pathway is less viable for the United States since USDA APHIS allows imports of mulberries (Morus) and pears (Pyrus) only from Canada. Apple trees (Malus spp.), however, may be imported from France – which hosts an introduced population of X. chinensis – and other European countries.  

Detection of any invasion by X. chinensis will pose the usual difficulties associated with woodborers. In some European cities, hundreds or even a thousand trees were infested before the outbreak was detected (EFSA 2021).

I am concerned that the Europeans appear to have been slow to respond to the threat from Xylotrechus chinensis. After several outbreaks were discovered in Greece, France, and Spain in 2017 and 2018, the European and Mediterranean Plant Protection Organization (EPPO) added X. chinensis to its Alert List. This action requires member states (which are not limited to European Union members) to report new outbreaks and inform about efforts to either stop or eradicate them (Saarto i Monteyu, Costa Ribeu, and Savin 2021).

Shortly afterwards the European Union Commission requested the European Food Safety Agency (EFSA) to conduct a risk assessment. This analysis was completed in 2021. (It contains lots of photos of the insect and its damage.) The analysis concluded that Xylotrechus chinensis could probably infest most areas in the Union and cause significant damage. The species meets the criteria for designation as a quarantine pest in the Union. However, as of December 2024, this action had not been taken. As a result, control measures for this species are not mandatory.

Introductions continue; an outbreak in Lombardy, Italy, was found in June 2023 (Sarto i Monteys, Savin, Torras i Tutusaus & Bedós i Balsach 2024).  European regulations – following IPPC standards – also are linked to named pests and known outbreak locations. Such restrictions almost guarantee that the pest will continue to spread from not-yet-detected outbreaks. (Decades ago, after the emerald ash borer invasion, Michigan’s State Plant Regulatory Official, Ken Rasher, noted that, to be effective, “slow the spread” efforts must apply to areas beyond the known limits of the pest’s range.) The EFSA risk assessment did suggest delimitation of buffer zones around known European outbreaks. I don’t know whether such zones have been set up.

The risk assessment also recommended [true?] improving detection of this insect by developing male pheromones as lures. These have not been acted on. Guidance on best timing for treatment [trunk injections of systemic insecticides] also appears to have been taken up by Greece but not by Spain (Sarto i Monteys, Savin, Torras i Tutusaus & Bedós i Balsach 2024).

These authors include more information about the Xylotrechus chinensis life cycle and trajectory of the invasion,. They note that climate change appears to be altering the insect’s phenology. Especially, the adult flight period is beginning earlier in the spring.

Lamprodila festiva; Udo Schmidt via flickr

Cypress jewel beetle

This second pest of concern is a buprestid that attacks trees in the Cupressaceae. Infested trees generally die within a few years.

In its native Mediterranean range, the beetle feeds on native Juniperus, Cupressus and Tetraclinis. In invaded urban landscapes of Europe it attacks primarily introduced Cupressaceae , particularly Thuja, Chamaecyparis, Platycladus, Callitris, and some hybrids (Cupressocyparis). It has also been recorded as damaging Sequoia sempervirens (Brunescu, et al., 2024). (Genera in bold are native to North America.)

Thuja occidentalis; photo by H. Zell via Wikimedia

White cedar, Thuja occidentalis is the focus of Brunescu, et al.’s article. It is native to eastern Canada and much of the north-central and northeastern United States. The European and Mediterranean Plant Protection Organization (EPPO) has identified eight species in the Lamprodila genus as important pests, (Brunescu et al. 2024) so the danger might be more widespread. The invasion of Europe is probably the result of adult flight or other short-range transport. The article does not suggest pathways that the species might exploit to cross oceans.

SOURCES

Bunescu, H., T. Florian, D. Dragan, A. Mara, I-B. Hulujan, X-D. Rau. 2024  The Cypress Jewel Beetle Lamprodila Festiva Linné, 1767 (Coleoptera: Buprestidae), an Invasive Major Pest of Thuja Occidentalis Linné in Romania Hop and Medicinal Plants, 2024 XXXII, No. 1-2, 2024.

Saarto i Monteyu V., A. Costa Ribeu. I. Savin. 2021a. The invasive longhorn beetle Xylotrechus chinensis, pest of mulberries, in Euro: Study on its local spread & efficacy of abamectin control Plos One January 29, 2021. https://doi.org/10.1371/journal.pone.0245527

Sarto i Monteys, V., I. Savin, G. Torras i Tutusaus & M. Bedós i Balsach. 2024b. New evidence on the spread in Catalonia of the invasive longhorn beetle, Xylotrechus chinensis, & the efficacy of abamectin control. Scientific Reports | (2024) 14:26754 | https://doi.org/10.1038/s41598-024-78265-x  www.nature.com/scientificreports/

Posted by Faith Campbell

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

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

or

www.fadingforests.org

How beech leaf disease spreads in the forest

BLD symptoms; photo by Matt Borden, Bartlett Tree Experts

As beech leaf disease (BLD) is detected in an ever-expanding number of counties from Michigan to Maine south to Virginia, scientists are trying to clarify how the causal nematode — Litylenchus crenatae ssp. mccannii (Lcm) – spreads. One focus is on local spread from tree to tree. Mankanwal Goraya and colleagues set up an experiment in Stone Valley Forest, a recreation and research site managed by Penn State in Huntington County, Pennsylvania. BLD is present – although I have not been able to determine for how many years. [The full citation to Goraya et al. is provided at the end of this blog.]

Goraya et al. (2024) set up four stands, each bearing three funnels, at varying distances from naturally BLD-infected American beech (Fagus grandifolia) trees. Two stands were at 3.51 m from symptomatic trees of starkly different sizes: one of the trees had a dbh of 50 cm, the other of only 5.6 cm. A third close-up stand was set up at 2.20 m from another large tree, having a dbh of 46 cm. The fourth stand was set up at a significantly longer distance, 11.74 m from a symptomatic beech tree; this tree was also small, with a dbh of 5 cm. This arrangement allowed the scientists to detect influences of both distance from the source of infection and relative canopy size of the source tree. They consider dbh to be an adequate substitute for canopy size. There was apparently no other effort to determine or vary the height of “source” trees, although I think that might influence speed of the wind flowing through the canopy.

Goraya et al. also tested whether it is possible to detect the presence of Lcm in association with other invertebrates that live in beech forests. To do this, they counted numbers of nematodes in frass from six species of caterpillars that had been feeding on leaves of infected trees, and in two spider webs spun in the branches of symptomatic trees. They also determined whether these nematodes were alive (active) or inactive – presumably dead.

The study makes clear that Lcm’s life cycle and impact are not as surprising as initially thought. Several species in the family Anguinidae – to which Lcm belongs – are considered significant pests. These nematodes can parasitize aerial parts of the plants (leaves, stems, inflorescences and seeds), causing swellings and galls. Furthermore, they are migratory; they can move across the surface of host tissues using water films. Once they have penetrated the host tissues, they can induce host cell hyperplasia and hypertrophy, resulting in leaf or bulb deformities, shorter internodes, and neoplastic tissues. Furthermore, heavy rainfall and wind are known to play significant roles in the dissemination of plant-infecting nematodes. In their desiccated state on infected seeds, some species of this family can survive passage through animals’ gastrointestinal digestive tract (e.g., domestic livestock, insects, & birds).

A crucial factor is that Lcm can reach densities of thousands of nematodes per leaf by late summer or early fall, increasing the likelihood of their exposure to facilitating environmental conditions at the time they migrate from leaves to buds. And once established within the bud tissues, the nematodes feed on bud scales and newly forming leaves to develop & increase their pop #s. They also use the bud as protection from adverse environmental conditions.

Goraya and colleagues collected samples every other day from September 9 to November 23, 2023 – the period when Lcm migrate from highly infected leaves to newly forming buds. [I note that it in the mid-Atlantic – where Lcm is spreading – we had an extensive drought in autumn 2024 – more than 30 days without any rain from early October into November. I hope scientists are monitoring BLD spread sufficient closely to see whether this drought affected dispersal.]

Nematodes dispersal linked to weather

Goraya and colleagues collected 324 samples from the funnels. Eighty-two percent (n =266) of the samples had nematodes; up to 92% were identified as Lcm. Non-Lcm nematodes were distributed across different genera, mostly classified as free-living nematodes. While several hundred nematodes were found in the funnels on most days, numbers peaked noticeably on some days in September and October.   A startling 2,452 nematodes were recovered from a single funnel in October. Depending on the sample, up to 67% of Lcm recovered from the funnels were active.

Analysis of the environmental (weather) variables found that increases in wind speed, humidity, and precipitation (rainfall) coincided with higher numbers of Lcm being recovered from the funnels.  However, the effect of wind speed becomes less positive as precipitation increases or vice versa. Goraya et al. suggest a pronounced negative interaction between wind and rain. At low precipitation levels, increased wind speed might facilitate Lcm dispersal. As rainfall increases, higher wind speeds might carry the Lcm nematodes farther away. Support is seen in the fact that fewer nematodes were found in the funnels closer to the BLD-infected trees during these periods. Really heavy rain might push a significant preponderance of nematodes to the ground. The scientists point to a very complex interplay between weather patterns and Lcm population dynamics and dispersal.

BLD symptoms on beech tree in Fairfax County, Virginia – a dozen miles from known infestation; photo by F.T. Campbell

The model did not show any significant influence of maximum temperature on nematode numbers in autumn. Goraya et al. do not speculate on whether temperatures might play a role during summer, as distinct from cooler autumn periods.

Goraya et al.’s findings differ from those of previous studies. Earlier documentation of wind dispersal of nematodes concerned primarily free-living species. It was unexpected to find consistently much higher numbers of Lcm – especially because Lcm is a plant-parasitic nematode. Another surprise is the high proportion of nematodes that are active.

Goraya et al. conclude that because Lcm is actively migrating in large numbers during autumn months, it is primed to take advantage of favorable weather. This nematode will likely survive and thrive in the environmental conditions of beech forests in northeastern North America.

Considering the effect of distance, some findings fit expectations: significantly more Lcm were recovered from funnels placed near symptomatic “source” trees than from those farther away. However, this was not a simple relationship. For example, in two cases the scenarios seemed nearly alike: both “source” trees were large (dbh 46 or 50 cm) and symptoms were “medium-high” (more than half of leaves presenting dark-green interveinal bands). Distance of funnels from the “source” tree differed minimally: 2.2 m versus 3.51 m. Still, the number of nematodes retrieved from the two sets of funnels differed significantly: one set of funnels recovered the highest number of Lcm nematodes obtained during the entire experiment – 2,452; the second contained only up to 600 nematodes. The authors do not offer an explanation.

I am not surprised by the apparently strong correlation between numbers and proximity to the disease source (a symptomatic tree). Nor am I surprised that Lcm nematodes were also found in funnels 11 meters away. I do wonder, however, why they are certain that no source was closer. Detecting early stage infections is notoriously difficult.

beech with large canopy; photo by F.T. Campbell

Goraya et al. also evaluated the effect of size of the source tree. They used dbh a substitute for larger canopies. Trees with larger canopies can host more nematodes, so are likely to contribute more to dispersal events. Two sets of funnels were equidistant from separate “source” trees – 3.51 m. One tree was small – 5.6 cm dbh, 11% as large as the other tree (50 cm). They collected many fewer Lcm nematodes from the smaller tree – the maximum was only 132 compared to 600 (a decrease of 78%).

Still, small trees can apparently support spread of the nematode to a reasonable distance. The fourth set of funnels was set up more than three times farther away (11.74 m) from an infected tree of a similar size (dbh = 5 cm) but recovered almost the same number of Lcm nematodes (0 – 119).

I find it alarming that both small trees in this part of the experiment had low BLD symptoms – only a few leaves were banded. Yet they apparently are the source of Lcm spread. The alternative, as I noted above, is that other “source” trees were in the vicinity but were not detected, possibly because they did not yet display symptoms?

Goraya et al. conclude that “source” tree size directly impacts the number of recovered nematodes. In addition, wind plays a pivotal role in their local distribution. This suggests a complex dispersal pattern in which proximity to the source leads to higher numbers of nematodes but longer-distance spread is possible.

Tussock moth; photo by Jon Yuschock via Bugwood

 Nematodes’ association with other organisms

Goraya et al. (2024) collected one each of six caterpillar species from BLD-symptomatic trees. The frass of one – the tussock moth caterpillar (Halysidota tessellaris) — contained 12 nematode specimens — 10 of them Lcm. Two of the Lcm were alive and active. Their presence indicates that Lcm can survive passage through the caterpillar’s gastrointestinal tract. The authors conclude that caterpillars feeding on symptomatic leaves might contribute to local dispersal of Lcm.

Hundreds of Lcm were recovered from the two spider webs collected from the branches of a BLD-infected beech tree. From one web, 255 nematodes were captured; 58 were active. In the second web there were only 34 Lcm, but one-third — 10 – were active.

Goraya et al. (2024) hypothesized that any biotic form having the ability to move from a BLD-infected tree would be able to transport Lcm to other non-infected trees. Beyond caterpillars, they speculate that birds consuming these caterpillars might also disperse Lcm. Doug Tallamy has documented that many birds feed on caterpillars, link although he is focused on those that consume caterpillars in the spring, not the autumn. They note that others are studying that the bird species that feed on beech buds (e.g., finches) might transport nematodes. They note the need for additional research to clarify whether the nematode can survive birds’ digestive system.

Re: detection of live Lcm in spider webs, Goraya et al. suggest two possible interpretations: 1) this finding demonstrates that nematodes might fall from leaves, potentially spreading the infection to other trees beneath the canopy. (Supporting this idea is the fact that sub-canopy trees are often heavily infected with BLD and are frequently the first to exhibit BLD symptoms.) 2) Nematodes in spider webs are very likely to be transported by other “incidental organisms” (e.g., insects, birds, mammals) that feed on invertebrates trapped in webs — thereby potentially increasing the number and impact of nonspecific nematode vectors.

In conclusion, Goraya et al. found that many factors, e.g., distance & size of infected beech trees, wind speed, & humidity, contribute significantly to Lcm dispersal. The multitude of organisms interacting beneath the canopy also play a role.

They suggest that several major questions still need to be explored. These include how Lcm navigate environmental factors in their spread; and whether Lcm can survive – perhaps in a anhydrobioses state –transport over long distances, whether by abiotic or biotic vectors.

I remind my readers of the importance of beech in the hardwood forests in northeastern North America. Many wild animals, including squirrels, wild turkeys, white-tailed deer, and bears depend on beechnuts for fats and proteins. Moreover, some insects birds rely on beech tree canopies for shelter & nesting.

Other Hosts

Beech leaf disease attacks not just American beech (Fagus grandifolia). In North America, it has also attacked planted European beech(F. sylvatica), Chinese beech (F. engleriana), and Oriental beech (F. orientalis). Thus if it spreads it could have severe impacts across forests of much of the Northern Hemisphere.

range of European beech; from Royal Botanic Gardens, Kew

I appreciate that this project was funded by the USDA Forest Service International Program. I will pursue information concerning efforts by USFS Research and Development and the Forest Health Protection program.

SOURCE

Goraya, M., C. Kantor, P. Vieira, D. Martin, M. Kantor. 2024 Deciphering the vectors: Unveiling the local dispersal of Litylenchus crenatae ssp mccanni in the American beech (Fagus grandifolia) forest ecosystem  PLOS ONE |https://doi.org/10.1371/journal.pone.0311830 November 8, 2024 1 / 16

Posted by Faith Campbell

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

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

or

www.fadingforests.org

Impacts of introduced rust on unique flora — New Zealand’s expectations

predicted community vulnerability from A. psidii mediated mortality of Kunzea ericoides & Leptospermum scoparium; from McCarthy et al.

Scientists in New Zealand have recently completed a study of the probable impact of myrtle rust – caused by Austropuccinia psidii – on plants in the plant family Myrtaceae. McCarthy et al. say their results should guide management actions to protect not only the unique flora of those islands but also on Australia and Hawai`i – other places where key dominant tree species are susceptible to myrtle rust. The disease attacks young tissue; susceptible Myrtaceae become unable to recruit new individuals or to recover from disturbance. Severe cases can result in tree death & localized extinctions

[I note that myrtle rust is not the only threat to the native trees of these biologically unique island systems. New Zealand’s largest tree, kauri (Agathis australis), is threatened by kauri dieback (caused by Phytophthora agathidicida). On Hawai`i, while the most widespread tree, ‘ōhi‘a (Metrosideros polymorpha) is somewhat vulnerable to the strain of rust introduced to the Islands, the greater threat is from a different group of fungi, Ceratocystis lukuohia and C. huliohia, collectively known as rapid ‘ōhi‘a death. On Australia, hundreds of endemic species on the western side of the continent are being killed by Phytophthora dieback, caused by Phytophthora cinnamomi. [I note the proliferation of tree-kiling pathogens; I will blog more about this in the near future.]

Myrtle rust arrived in New Zealand in 2017, probably blown on the wind from Australia (where it was detected in 2010). In New Zealand, myrtle rust infects at least 12 of 18 native tree, shrub, and vine species in the Myrtaceae plant family. Several of these species are important in the structure and succession of native ecosystems. They also have enormous cultural significance.

McCarthy et al. note that species differ in their contribution to forest structure and function. They sought to determine where loss of vulnerable species might have the greatest impact on community functionality. They also explored whether compensatory infilling by co-occurring, non-vulnerable species in the Myrtaceae would reduce the community’s vulnerability. Even when co-occurring Myrtaceae are relatively immune to the pathogen, only some of them – the fast-growing species – are likely to fill the gaps. They might lack the functional attributes of the decimated species.

To identify areas at greatest risk, McCarthy et al. took advantage of a nationwide vegetation plot dataset that covers all the country’s native forests and shrublands. The plot data enabled McCarthy et al. to determine which plant species not vulnerable to the rust are present and so are likely to replace the rust host species as they are killed.

Leptospermum scoparium; photo by Alyenaa Buckles via Flickr

McCarthy et al. concluded that forests and shrublands containing Kunzea ericoides and Leptospermum scoparium are highly vulnerable to their loss. Ecosystems with these species are found predominantly in central and southeastern North Island, northeastern South Island, and Stewart Island. While compensatory infilling by other species in the Myrtaceae would moderate the impact of the loss of vulnerable species, if these co-occurring species were unable to respond for various reasons, such as also being infected by the rust pathogen, community vulnerability almost always increased. In these cases the infilling species would probably have different functional attributes. In many areas the species most likely to replace the rust-killed native species would be non-native shrubs. Consequently, early successional woody plant communities, where K. ericoides and L. scoparium dominate, are at most risk.

Because the risk of A. psidii infection is lower in cooler montane and southern coastal areas, parts of inland Fiordland, the northwestern South Island and the west coast of the North Island might be less vulnerable.

Austropuccinia psidii has been spreading in Myrtaceae-dominated forests of the Southern Hemisphere since the beginning of the 21st Century. It was detected in Hawai`i in 2005; in Australia in 2010; in New Caledonia in 2013, and finally in New Zealand in 2017. Within 12 months of its first detection in the northern part of the North Island it had spread to the northern regions of the South Island.

Specific types of Threat

Succession

The ecosystem process most at risk to loss of Myrtaceae species to A. psidii is succession. About 10% of once-forested areas of New Zealand are in successional shrublands, mostly dominated by Kunzea ericoides and Leptospermum scoparium. Both species are wind dispersed, grow quickly, are resistant to browsing by introduced deer, and are favored by disturbance, especially fire. Both are tolerant of exposure and have a wide edaphic range (including geothermal soils). Still, K. ericoides prefers drier, warmer sites while L. scoparium tolerates saturated soils, frost hollows and subalpine settings.

Kunzea ericoides; photo by Tony Foster via Flickr

Loss of these two species would result in a considerable change in stand-level functional composition across a wide variety of locations. Their extensive ranges mean that it would be difficult for other species – even if functionally equivalent – to expand sufficiently quickly. Second, non-native species are common in these communities. All of these invaders – Ulex europaeus, Cytisus scoparius and species of Acacia, Hakea and Erica – promote fire. Some are nitrogen fixers. While they can facilitate succession, the resulting native forest will differ from that formed via Leptospermeae succession. Furthermore, compensatory infilling by the invasive species might also reduce carbon sequestration. Successional forests dominated by K. ericoides are significant carbon sinks owing to the tree’s size (up to 25 m under favorable conditions), high wood density, and long lifespan (up to ~150 years). In contrast, shrublands dominated by at least one of the non-native species, U. europaeus, are significant carbon sources.

Northern and central regions of the North Island and the northeastern and interior parts of the South Island are most vulnerable to the loss of these species since these successional shrub communities are widespread and the area’s climate is highly suitable for A. psidii infection. The southern regions of the South Island, including Stewart Island, are somewhat protected by the cooler climate.

Fortunately, neither Kunzea ericoides nor Leptospermum scoparium has yet been infected in nature. Laboratory trials indicate that some families of K. ericoides are resistant. Vulnerability also varies among types of tissue – i.e., leaf, stem, seed capsule.  

Metrosideros umbellata; photo by Stan Shebs via Wikimedia

Forest biomass

Although from the overall community perspective loss of species in the Metrosidereae would have a lower impact than loss of those in the Leptospermeae, there would be significant changes associated with loss of Metrosideros umbellata. This species can grow quite large (dbh often > 2 m; heights up to 20 m). That size and its exceptionally dense wood means that M. umbellata stores high amounts of carbon. Also, its slow decomposition provides habitat for decomposers. Lessening the potential impact of loss of this species are two facts: its litter nutrient concentrations and decomposition rates do not differ from dominant co-occurring trees; and, most important, it grows primarily in the south, where weather conditions are less suitable for A. psidii infection. One note of caution: if A. psidii proves able to spread into these regions, not only M. umbellata but also susceptible co-occurring Myrtaceae species are likely to be damaged by the pathogen.

Highly specific habitats

McCarthy et al. note that their study might underestimate the impact of loss of species with unique traits that occupy specialized habitats. They focus on the climber Metrosideros excelsa. This is an important successional species that helps restore ecosystems following fire, landslides, or volcanic eruptions. The species’ tough and nutrient poor leaves promote later successional species by forming a humus layer and altering the microenvironment beneath the plant. Its litter has high concentrations of phenolics and decomposes more slowly than any co-occurring tree species.  [They say its role is analogous to that of M. polymorpha in primary successions on lava flows in Hawai`i.] M. excelsa dominates succession on many small offshore volcanic islands, rocky coastal headlands and cliffs.

Another example is Lophomyrtus bullata, a small tree that is patchily distributed primarily in forest margins and streamside vegetation. This is the native species most affected by A. psidii; the pathogen is likely to cause its localized extinction. McCarthy et al. call for assessment of ex situ conservation strategies for this species.

Each of these species is represented in only seven of the plots used in the analysis, so community vulnerability to their loss might be underestimated.

Another habitat specialist, Syzygium maire, is found mostly in lowland forests, usually on saturated soils. It currently occupies only a fraction of its natural range due to deforestation and land drainage. Evaluating the impact of loss of S. maire is complicated by its poor representation in the database (only six plots), and the fact that many of the co-occurring species are also Myrtaceae.

Lack of data similarly prevents detailed assessment of the impacts from possible loss of other species, including M. parkinsonii, M. perforata and L. obcordata. McCarthy et al. say only that their disappearance will “take the community even further from its original state”.

McCarthy et al. warn that the risk could increase if more virulent strains of A. psidii were introduced or evolved through sexual recombination of the current pandemic strain. Other scientists have discovered strong evidence that the many strains of A. psidii attack different host species (see Costa da Silva et al. 2014).

New Zealand bell bird (Anthornis melanura); photo from https://animalia.bio/new-zealand-bellbird

McCarthy et al. note that other factors are also important in determining the impact of loss of a plant species. Especially significant is the host plant species’ association with other species. They say these relationships are poorly understood. One example is that only four Myrtaceae species produce fleshy fruits. Loss or decline of these four species might severely affect populations of native birds, many of which are endemic. Many invertebrates – also highly endemic — are dependent on nectar from other plants in the family.

In their conclusion, McCarthy et al. note that A. psidii has been introduced relatively recently so there is still time to reduce the disease’s potential consequences. They suggest such management interventions as identifying and planting resistant genotypes and applying chemical controls to protect important individual specimens. They hope their work will guide prioritization of both species and spatial locations. They believe such efforts have substantial potential to reduce myrtle rust’s overall functional impact to New Zealand’s unique ecosystems.

SOURCES

Costa da Silva, A; P.M. Teixeira de Andrade, A. Couto Alfenas, R. Neves Graca, P. Cannon, R. Hauff, D. Cristiano Ferreira, and S. Mori. 2014. Virulence and Impact of Brazilian Strains of Puccinia psidii on Hawaiian Ohia (Metrosideros polymorpha). Pacific Science 68(1):47-56.  doi: https://dx.doi.org/10.2984/68.1.4

McCarthy, J.K., S.J. Richardson, I. Jo, S.K. Wiser, T.A. Easdale, J.D. Shepherd, P.J. Bellingham. 2024. A Functional Assessment of Community Vulnerability to the Loss of Myrtaceae From Myrtle Rust. Diversity & Distributions, 2024; https://doi.org/10.1111/ddi.13928

Posted by Faith Campbell

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

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

or

www.fadingforests.org

Phytophthora here, Phytopthora there … level of threat is unclear

Mt. Triglav – highest peak in the Slovenian (Julian) Alps; photo by Gunter Nuyts via Pexel

Scientists have discovered sizable diversity of pathogenic Phytophthora species in Europe, specifically in the Alps of northeastern Italy and western Slovenija.  They have also named a new species, and noted the need to change the definition of species previously named. See Bregant et al. – full citation at the end of this blog – open access!

Two of its findings are especially important for the US

First, the authors document the vulnerability of alpine areas to 18 Phythophthora species. Most of the plant hosts they studied have congenerics in mountainous areas of North America: Acer, Alnus, Betula, Fagus, Fragaria, Fraxinus, Ilex, Juniperus, Larix, Lonicera, Lycopodium, Pinus, Populus, Quercus, Rhododendron, Rubus, Salix, Sorbus, Taxus, and Vaccinium.

Second, the paper discusses how junipers are at particular risk. I remind you that P. austrocedrii has recently been detected in nurseries in Ohio and Oregon. This is another non-native Phythophthora that attacks junipers. I hope authorities are actively seeking to determine whether P. austrocedrii is present in nurseries or natural systems in other parts of the country.

The genus Phytophthora includes many serious plant pathogens, from the one that caused the disastrous potato blight of Ireland (Phytophthora infestans) to globally important forest-destroying invasive species, e.g., P. cinnamomi and “sudden oak death” P. ramorum.

Bregant et al. surveyed 33 small tree, shrub, and herbaceous plant species in 54 sites on the Italian island of Sardinia and the Alps of both northeastern Italy and western Slovenija. Altitudes varied from the valley bottom (700 m) to above tree line (2100 m). Sites included typical forests, riparian ecosystems, and heathlands.

The 360 isolates taken from 397 samples belonged to 17 known Phytophthora species. Some species are widespread and well-known, e.g., P. pseudosyringae. Three isolates belonged to a putative new species described by Bregant et al. – Phytophthora pseudogregata sp. nov. This total of 18 taxa was unexpectedly high. Many of the species are able to cause aerial infections via production of caducous sporangia. These can infect various organs of the plant host: fruits, leaves, shoots, twigs and branches; and cause necrosis and rots. They detected 56 new host–pathogen associations. All are listed, by type of host, in Tables 4 – 6 of the paper.

The surprising diversity and detection of taxa previously described in Australia (see below) illustrate   scientists’ still poor understanding of this genus. They also confirm fears that the global phytosanitary system is unable control intercontinental movement of Phytophthora.

The authors express concern because Alpine and subalpine regions are important hotspots for floral biodiversity. The great variation in altitude, aspect, moisture regimes, etc. – including extreme conditions – results in many different habitats on small spatial scales, with large numbers of both plant species and endemics in very confined spaces. The pathogens they discovered are spreading and compromising the biodiversity of these ecologically fragile habitats.

The authors say their study emphasizes the need to assess the full diversity of Phytophthora species and the factors driving the emergence and local spread of these invasive pathogens. They specify studying the Phytophthora communities on fallen leaves to evaluate host specificity, geographic distribution and survival strategies of the main Phytophthora species detected in this study. They report that scientists are currently mapping the distribution of the new species, P. pseudogregata, in the Alpine habitats and trying to establish its natural host range.

another view of the Julian Alps; photo via Rawpixl

Bregant et al. point out that increased scientific interest over the last 30 years has led to discovery of several previously unknown Phytophthora species and pathogen-host associations. They note that all but two of the taxa in one taxonomic grouping, Sub-clade 6b, have been described in the last 12 years. The majority of taxa have been described from forest ecosystems. This trend is depicted in Figure 8 of the article. This figure also displays which species were isolated from nurseries, agricultural systems, and forest ecosystems.

Results by Plant Type – Disease incidence was highest in shrub vegetation, alpine heathlands and along the mountain riparian systems. The most impacted ecosystems were heathlands dominated by common juniper & blueberry, and riparian systems dominated by alders. In these ecosystems, the Phytophthora-caused outbreaks had reached epidemic levels trend with a high mortality rate. On shrubs and heath formations, disease was initially observed in small areas and progressively spread in a concentric manner affecting more plant species.

Hosts and Diseases – Table 3 in the article lists the 33 host plant species, briefly describes the symptoms, and in some cases provides incidence and mortality rates. Those hosts described as suffering “sudden death” included Alnus viridis, Calluna vulgaris, Genista corsica, Juniperus communis, Lycopodium clavatum, Pinus mugo,Rhododendron ferrugineum, Salix alpine, Vaccinium myrtillus and Vaccinium vitis-idaea

Role of P. pseudosyringae – The most common and widespread species detected was P. pseudosyringae. It constituted more than half of the isolates (201 of the 360). Also, it infected the highest number of hosts (25 out of 33, including all three plant types). It was isolated at 36 of the 54 sites distributed throughout all geographic regions. Seventeen of the host–pathogen associations were new to science. (See Tables 4-6, in the paper.)

Vaccinium myrtillis – a vulnerable host; photo by Tatyana Prozovora via Wikimedia

P. pseudosyringae dominated disease agents in the shrub community, especially among high-altitude shrubs and heaths, e.g., blueberry, dwarf pine, juniper, rhododendron, and alpine willows. Bregant et al. note that these shrubs are extremely low-growing (an adaptation to high elevation conditions). This form might favor attack by Phytophthora sporangia and zoospores present in fallen leaves. Vaccinium myrtillus suffers particularly severe disease – as previously reported in Ireland. In their laboratory studies, Bregant et al. found P. pseudosyringae to be highly aggresse on common juniper (Juniperus communis), producing wood necrosis and shoot blight only four weeks after inoculation.

The importance of P. pseudosyringae in mountainous regions has been found in previous studies in Asia, Europe, and North and South America. However, the authors call for further study of certain aspects of the species. These regard infectivity and survival of the species’ sporangia in infected tissues fallen to the ground; and the ability of oospores to persist for years in environments subject to extreme low temperatures. The former could increase the risk of outbreaks and promote faster disease progression.

The authors suggest P. pseudosyringae’s survival stems from its production of very large and thick-walled chlamydospores. This reported feature is in contradiction with the original species description, which prompts Bregant et al. to call for a correction.

Other Species, Old and New – P. cactorum was the only Phytophthora species other than P. pseudosyringae detected on all three types of hosts (small trees, shrubs, and herbaceous plants). Phytophthora plurivora was the second-most isolated species. It was detected on 12 hosts in 24 sites.

The new putative species — Phytophthora pseudogregata sp. nov. – was detected on Alnus viridis, Juniperus communis, and Rhododendron ferrugineum. As noted above, scientists are now testing whether other plant species are also hosts. It was detected at two sites in Italy — Borso del Grappa and San Nicolò di Comelico; and one site in Slovenija.

Juniperus communis; photo by Joan Simon via Flickr

Diseases of Juniper – Koch’s postulates have been fulfilled, demonstrating that eight Phytophthora species – the new P. pseudogregata sp. nov. as well as P. acerina, P. bilorang, P. gonapodyides, P. plurivora, P. pseudocryptogea, P. pseudosyringae, P. rosacearum – are pathogenic on common juniper (Juniperus communis). The lesions caused by P. pseudosyringae were significantly larger than those caused by other species. Lesions caused by P. pseudosyringae, P. plurivora and acerina progressively girdled the twigs causing shoot blight, browned foliage & wilting symptoms.

Most Threatening Phytophthora clades – The most-frequently isolated Phytophthora species belong mainly to clades 1 and 3 – including P. pseudosyringae. Bregant et al. say these species have several advantages for surviving in mountainous ecosystems: they produce caducous sporangia useful for aerial infections and they tolerate relatively low temperatures. Twoother species in clade 3 were isolated only from the mountains of Sardinia. One, P. psychrophila, was isolated from bleeding cankers on an oak species, Quercus pubescens. Its geographic distribution and impact are still unknown. A second species, P. ilicis, is a well-known pathogen on various hollies in Europe and North America.

Four species belonging to subclade 1a were isolated in the Alps of northeastern Italy and Slovenija. P. cactorum is a widespread polyphagous pathogen found from tropical to temperate climates. It has been responsible for severe diseases on agricultural crops and forest trees. Its occurrence in cold areas has recently been reported in Europe and Australia. The recently described P. alpina has the highest ability to survive in extremely cold conditions. It was detected on four hosts – Alnus viridis, Lonicera alpigena, Vaccinium myrtillus, and V. vitis-idaea.

Some species, e.g., P. hedraiandra and P. idaei, were reported for the first time in natural ecosystems in Europe. They have previously been linked to root and foliar disease in agricultural and ornamental nurseries.

The second-most common species in the Bregant et al. study, P. plurivora, was isolated from 54 symptomatic samples from 12 plant species; eight of the hosts are new. It is common in forest ecosystems of Central Europe – which is now considered to be its region of origin. Little is known about the closely related P. acerina. To date, the latter has been detected widely in agricultural systems, nurseries, forests, and ornamental trees in northern Italy and Sardinia. It is much more rarely found elsewhere. Both P. acerina and P. plurivora are already known to be primary pathogens involved in decline of common and grey alder in Italy.

Five of the Phytophthora species in this study, including the new species P. pseudogregata, are in Clade 6. These include pathogens very common in European forests, e.g., P. bilorbang and P. gonapodyides. Others have more limited or still unknown distributions, e.g., P. amnicola and P. rosacearum. These five species’ ability to cause aerial infections on mountain vegetation might warrant re-evaluation of the reputation of species in this clade being saprophytes or only occasional weak opportunistic pathogens.

P. pseudogregata – in sub-clade 6a – was originally described in 2011 in wet native forests in Australia and on dying alpine heathland vegetation in Tasmania. It has recently been reported in the Czech Republic and Finland. The related P. gibbosa is known to occur only in Australia, where it is associated with dying native vegetation on seasonally wet sites.

Two species of clade 8 — P. kelmanii & P. syringae — have a very limited distribution. A third – P. pseudocryptogea — is widespread in Italian ecosystems from Mediterranean areas to the tree line in the Dolomites. One species from clade 7 (P. cambivora) isolated, mainly from stem bleeding cankers of small trees and shrubs. It has two mating types; bothoccurr in the Alps of northeastern Italy and neighboring Slovenija — on Alnus incana, Laburnum alpinum and Sorbus aucuparia.

SOURCE

Bregant, C., G. Rossetto, L. Meli, N. Sasso, L. Montecchio, A. Brglez, B. Piškur, N. Ogris, L. Maddau, B.T. Linaldeddu. 2024. Diversity of Phytophthora Species Involved in New Diseases of Mountain Vegetation in Europe with the Description of Phytophthora pseudogregata sp. nov. Forests 2023, 14, 1515. https://doi.org/10.3390/f14081515 https://www.mdpi.com/journal/forests

Posted by Faith Campbell

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

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

or

www.fadingforests.org

Too Many Deer; Too Few Forest Seedlings & Wildflowers

white flowered trillium (Trillium grandiflorum); via PICRYL One of the “charismatic wildflowers” mentioned by Blossey and colleagues

Bernd Blossey, Darragh Hare, and Don Waller have published a plea that America’s federal government take the lead in formulating a new national program on managing deer. Otherwise, they fear that deer populations will not be reduced to ecologically sustainable levels. I find their argument convincing and well-sourced. I agree that Americans need to figure out how to address this threat. (The full citation is at the end of this blog).

First, Blossey and colleagues describe the damage caused by overabundant deer:

  • severe declines in populations of many native forest herbs and shrubs, probably including disappearing wildflowers;
  • their replacement by non-native species that are less palatable;
  • poor regeneration of many canopy hardwood species;
  • decreased forest resilience, lowering  forests’ ability to adapt to stressors, especially climate change;
  • decreased ability of forests to deliver benefits that are of increasing value to many people;
  • increased prevalence of wildlife and human diseases associated with the spread and size of  growing tick populations; and
  • people – and deer — killed vehicle accidents on roads.

The widespread impacts of white-tailed deer (Odocoileus virginianus) in forests of the East are well-documented (see my previous blogs for a few examples; scroll below the “Archives” to find “Categories”). Blossey and colleagues note examples of similar impacts in the West, attributed to elk (Cervus elaphus) and black-tailed and mule deer (Odocoileus hemionus).

The authors review the decimation of deer populations in earlier centuries and the efforts of state wildlife agencies to rebuild their populations during the 20th Century. The problem, in their view, is that federal and — especially — state wildlife agencies have retained their traditional focus on managing wildlife for recreational hunters. However, recreational hunters make up a small and shrinking proportion of all Americans. Many more people now engage in “non-consumptive” enjoyment of wildlife.

lack of regeneration in Rock Creek Park, Washington D.C.; photo by Sam Sheline, NatureServe, via Flickr

State agencies’ narrow focus might partly arise from fragmented authorities. Agencies other than wildlife departments are responsible for addressing some repercussions of overabundant deer. These include threats to human health, loss of agricultural crops.

For several reasons, Blossey and colleagues call for federal leadership.  They think that only a national strategy can address, in a holistic way, the interrelated deer, human health, forest, and biodiversity crises. The strategy’s goal should be to protect species that are in decline because of over-browsing by deer and to avoid further declines in environmental and human health.

The authors reason that states are tied to traditional constituencies. Also, they have difficulty acting across jurisdictional boundaries. Second, few state wildlife agencies have authority to protect plant and invertebrate species. Yet these are the taxa most directly affected by overabundant deer. Blossey and colleagues point out that, of the ~1,300 species listed under the federal Endangered Species Act, 942 are plants and 287 are invertebrates.

They point out that deer also suffer the effects of overpopulation. Chronic wasting disease is spreading. It causes a slow, agonizing death of affected animals. Another 2.1 million deer are killed each year in vehicle crashes. [According to the World Animal Foundation, the current number of deer killed in traffic crashes is 1.8 million — 300,000 fewer.) Again, these deaths are often gruesome. Finally, the principal population “control” now is death by starvation in winter. This, too, is cruel. 

Blossey and colleagues say that return of large predators, even where feasible, will not result in sufficient reduction in deer populations. Nor will encouragement of greater hunting pressure on does.

They note that the federal government owns nearly 30% of the United States’ terrestrial surface area. Management is divided among many agencies – National Park Service, Fish and Wildlife Service, Bureau of Land Management, USDA Forest Service, Department of Defense, and many smaller agencies.  Management approaches vary. However, it would be possible to bring them into agreement – although, in some cases, this would require new legislation.

Another issue requires resolution:  federal agencies’ authority to manage wildlife on federal land.. The states have repeatedly claimed constitutional and legal authority to manage (vertebrate) wildlife on the federal lands within their borders. This assertion was countered years ago by Nie et al. (2017):

‘Federal land management agencies have an obligation, not just the discretion, to manage and conserve fish and wildlife on federal lands. … [M]ost states have not addressed the conservation obligations inherent in trust management; rather, states wish to use the notion of sovereign ownership as … a source of unilateral power but not of public responsibility. Furthermore, the states’ trust responsibilities for wildlife are subordinate to the federal government’s statutory and trust obligations over federal lands and their integral resources.’

Blossey and colleagues assert that managing wildlife (typically defined as mammals, birds, and fish) is much broader than establishing hunting seasons or methods. Furthermore, the concept of “public trust resources” means resources should be managed for all citizens, not just the fewer than 10% of US residents who hunt. A growing proportion of society expects this management to support healthy and diverse environments.

The authors stress that reducing deer overpopulations is necessary to meet numerous policy goals. These include fulfilling obligations under international treaties related to climate change, invasive species, and threatened species; restoring and conserving the nation’s forests to provide habitat; and adopting “nature-based” climate adaptations, such as carbon sequestration. They express the hope that recent presidential mandates to better quantify and value natural assets will increase awareness of the harm caused by deer overpopulation. Their proposed national strategy would develop goals and metrics to match specific environmental and human health outcomes.

Of course, management of deer must extend beyond federal property lines. This will require cooperation among states, Tribes, and private landowners.

The paper proposes the North American Waterfowl Management Plan as a model. Under this scheme the US Fish and Wildlife Service works with states, tribal governments, Mexico, and Canada to ensure accurate information on waterfowl populations a to calculate harvest levels. States implement their assigned quotas through their own regulations. Waterfowl hunters purchase Duck Stamps to fund the monitoring efforts. This program has worked well for most species covered by the program. Waterfowl are one of the few bird groups that have not declined dramatically.

Reducing deer populations will probably require lethal control. Studies indicate that at least 60% of does must be removed from a population to reduce herd sizes over time. Other means have been attempted at regional or larger landscape levels, such as sterilization, fertility control. These methods have failed even when paired with recreational hunting. Lethal approaches will probably distress many people. However, Blossey, Hare, and Waller believe the program would be supported if it is understood to be undertaken with the goal of improving the health of both humans and also the environment.

In the end, Blossey, Hare, and Waller say they are not willing to leave the killing to cars, disease, and starvation. They emphasize our moral responsibility to protect humans and the many other species that rely on diverse ecosystems. Our policies and choices created the problem, so we must try to correct it.

SOURCES

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

Nie, M., C. Barns, J. Haber, J. Joly, K. Pitt and S. Zellmer. 2017. Fish and Wildlife Management on Federal Lands: Debunking State Supremacy. Environmental Law, Vol. 47, no. 4 (2017).

Posted by Faith Campbell

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

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

or

www.fadingforests.org

Proposed new surveillance approach: focus on the receiving ecosystem

Whitebark pine – a foundational & keystone species in high elevation mountains of the West; photo by Walter Siegmund

A British scientist has proposed a new way to conduct early pest detection surveillance that she thinks will better serve resource managers: prioritize ecosystems which would suffer the greatest alteration if a non-native plant pest decimated one or more plant species. She says scientists should focus on foundational species and maintaining habitat resilience.

Dr. Ruth J. Mitchell leads the Biodiversity and Ecosystems Group within the Ecological Sciences Department at the James Hutton Institute in Aberdeen, Scotland. The Institute works on issues relevant to sustainable management of natural resources. I provide a full citation of her article at the end of the blog.

Dr. Mitchell’s focus is on protecting biological diversity. She worries that introduced plant pests can drive large-scale declines in native plant species. She mentions several examples, including chestnut blight and ash decline. Those declines, in turn, can cause a range of cascading effects on associated species that use the host plant for feeding, breeding and shelter, and on ecosystem functioning. To be prepared to counter this level of risk, managers of natural habitats need to know which habitats and plants are at greatest risk in order to prioritize surveillance of the most likely human actions and sites; and allocate resources to address the most damaging invasions.

Her proposal: prioritize host plant species or habitats which ecological theory indicates an invasion would have the greatest ecological impact. In other words, focus on “foundational species” — plant species that drive key ecosystem functions; or low (plant) diversity habitats — based on the assumption that diverse communities are more stable and resilient than less diverse communities.

Mitchell notes that ecological theory posits that if a foundation species is lost or declines, its disappearance will have a greater effect on the ecosystem than if non-foundation species are impacted. She believes that although there is no list of foundation species, scientific staff can develop appropriate lists for their site. For her study, she made the simplistic assumption that those species that occur at high abundance are most likely to be foundation species. Regarding the second, habitat-resilience criterion, Mitchell assumed that a pest which eliminates a plant species in a low-diversity habitat is likely to have a greater ecological impact on that habitat’s functioning than would extinction of a species in a high-diversity habitat, which is likely to have redundancies.

Mitchell asserts that these approaches to surveillance take account of an invasion’s impacts on broader associated species and ecosystem functions – on biodiversity broadly. These suggested methods have other advantages, too. They avoid the bias in existing lists of pests, which consist predominantly plants of commercial importance; and they don’t need to be updated frequently.

Mitchell identifies four ways to prioritize surveillance efforts based on the potential host rather than the potential pest. The surveillance monitoring might target:

(1) Plant genera known to host the pests (including pathogens) most likely to establish (Host-pest);

(2) Habitats harboring hosts for the greatest number of pests most likely to establish (Habitat-pest);

(3) Plants classed as foundation species (Foundation-species);

(4) Habitats with low plant species diversity and hence low resilience (Habitat-resilience).

Mitchell analyzed the damage that 91 pest species might cause to plant species which occur at 25% or higher cover in 12 broad habitat types in the United Kingdom. As a case study, she also looked at 22 vegetation communities within one of those habitat types (heathland). (See the article for a discussion of how she derived her list of 91 pests, their hosts, and the entity responsible for designating the habitat types.)

For both hosts and habitats, Mitchell compared results of two approaches: (a) assessment based on lists of known known pests; and (b) assessment based on potential ecological impact. Surveillance based on known risks i.e. lists of plant pests(i.e., the Hosts-pest and Habitat-pest methods) assumes that scientists have a complete list of pests, their risk of establishment, and their impacts. We know that is not the case. As an illustration, Mitchell’s review of the literature identified 142 insects or pathogens  hosted by plant genera present on British moorlands that are not listed as pests by the appropriate British authority, the UK Plant Health Risk Register (PHRR).

To conduct a “Foundation-species” surveillance program, one must first identify foundational plant species. Mitchell defined those as species that constitute more than 75% cover in any plant community. (While this is admittedly an oversimplification, Mitchell says that the loss or severe decline of such abundant species will have a major impact on community composition.) One then prioritizes surveillance of these species – regardless of whether they are at risk from a known pest. This method emphasizes attention to potential impact to the habitat or plant community. Furthermore, this approach accommodates detection of the ‘known unknown’ pests.

To conduct a “Habitat-resilience” surveillance program, one must first identify the number of species in each habitat or vegetation community that occur at more than 25% cover. One then prioritizes surveillance of those habitats with the lowest average species diversity.

Differences in results

When basing the analysis on lists of known pests threatening all 12 habitat types, two genera stood out as at particular risk: Prunus and Solanum. Each consists of hosts supporting more than 20 of the 91 pests. Another 17 genera comprised hosts of six or more pests. Many of these genera include species that are important in ornamental horticulture or production forestry. Mitchell considers this a flaw. She points out that different genera ranked highest under this system when the focus narrowed to heathland communities. In heathlands, the genera comprising hosts of the most pests were Calluna, Erica, Festuca and Vaccinium.

American elm – a deserving priority for pest surveillance! Photo by F.T. Campbell

I note that from my perspective – concern about pests that kill native trees – several of the 17 genera included in the “known pests” analysis do raise alarm: Acer, Salix, Ulmus, Fraxinus, Pinus, Quercus, Betula, Viburnum, and Juniperus.

Mitchell then tested the results of focusing on habitat types where the highest number of pests were likely to become established. This method gave highest priority to woodlands – because plants in this habitat type can host 87 of the 91 pests. The second priority should be open habitats (defined as disturbed habitats, arable weed communities, weedy pastures, paths, verges, wasteland and urban habitats). Plants in the “open habitat” type can host 54 pests. (While Mitchell did not specify whether she excluded non-native plant species from her calculations, she does write generally about impacts on native flora – so I believe she did.)

Looking specifically at the 22 heathland vegetation communities, Mitchell identified four communities as able to host the greatest number of pests so deserving surveillance priority.

When she focused on “foundation species”, Mitchell found a range of plant species that occur at 75% or greater cover in each habitat. Again, the highest number (71 species) occur in woodlands; the lowest (11 species) grow in Calcicolous grasslands. In the 22 heathland plant communities, the number of plant species meeting this criterion numbered fewer than five in each. Two communities have no “foundation” species for surveillance since no vascular plant species that occur at 75% cover. In both the habitat and community cases, the surveillance priority of managers of each habitat type would concentrate on the species that fit this criterion for the appropriate biome.

Finally, Mitchell identified those habitats or communities with the lowest species richness / fewest species as being at greatest risk of unravelling if they lose one or more species to an introduced pest. The data indicated these to be the Salt Marsh and Swamps and tall-herb fens systems. At the other end of the spectrum, Mesotrophic grasslands and Woodlands have the lowest priority for surveillance because they are species-rich. Of course, communities within a habitat type vary greatly in their species richness and associated resilience. For example, the one heathland community which has only two species occurring at 25% or greater cover has a higher priority than the communities with more such species.

heath – Erica carnea ; photo by H. Zell

Mitchell asserts that prioritizing plant species or habitats for surveillance based on potential ecological impact rather than risk (known pests) provides a less biased process and allows for the detection of the known unknowns pests. The resulting set of priority surveillance targets differs significantly from the set developed by reliance on pest lists. For example, looking at heathland communities, the Host-pest and Foundation-species methodologies share only three of 24 host genera. The differences arise from the PHRR’s bias oflisting predominantly species relevant to agriculture, horticulture, or forestry. None of these genera is listed under the Foundation-species methodology.

Since trade in plants for planting is the main pathway of introduction of non-native pests, Mitchell concedes that plant species in natural habitats that are closely related to species of commercial importance might be more threatened than other species. However, such an approach takes no account of the potential for a pest to jump hosts.

Prioritization based on potential ecological impact rather than known risk has many advantages. The Foundation-species method prioritizes those plant species whose decline would have the greatest impact on wider biological diversity, ecosystem function and service delivery. That is, it incorporates consideration of the wider risks to the whole ecosystem rather than just the risk to a specific plant species. The Habitat-resilience method similarly takes account of the wider ecosystem level impacts, targeting those habitats or communities that might recover less quickly

On a practical level, these approach do not require surveyors (who might be citizen scientists or land manager) to identify specific pests. Instead, the surveyors report signs of unhealthy-looking plants to the relevant authorities, who then identify the cause.

These methods address a universal problem for plant health: the many pests that are previously unknown before their emergence in new regions and on naïve hosts. Mitchell briefly mentions scientists’ continue struggle to identify traits that can forecast potential pest impacts. [See my blogs re: studies by Mech, Schulz, Raffa]

redbay tree killed by laurel wilt disease – a pathogen unknown until it was introduced to southeastern U.S. Photo by F.T. Campbell

Mitchell suggests several ways to adapt these approaches to other countries or improve their targetting. First, scientists can link various pest/host databases (e.g., EPPO or CABI databases) to landcover or biome data and national or regional vegetation classification systems to make the system appropriate for their country or region. Incorporating attention to dirty equipment and movement of soil &/or plants is fitting at sites undergoing habitat restoration.

It is possible to refine the “foundation species” approach by applying a trait-based approach. She names two examples.

Finally, the Habitat-resilience method could be enhanced by integrating metrics of plant phylogenetic and functional diversity to the idea functional redundancy.

Mitchell stresses the need to unite efforts by many agencies and stakeholders within each country, as well as across political boundaries. She asserts that such collaborative efforts are more efficient / less costly, so lessening the restrictions imposed by resource limits. She also advocates reliance on citizen science and “passive surveillance” or chance observations by professionals agents, land-users and owners. These steps can facilitate large-scale surveillance that would otherwise be financially infeasible.

Mitchell highlights the difficulties imposed by the division of responsibilities. Usually the National Plant Protection Organization (NPPO) is responsible for early detection surveillance. The agency’s goal is to detect pests sufficiently early to facilitate eradication – or at least effective control. Its program  is linked to regulatory requirements under the international plant health system. link to blogs & FF reports While the NPPO’s responsibilities include both cultivated and uncultivated (wild) plants, in many countries the NPPO prioritizes plants with commercial value. (This is certainly true in the United States – see my previous blogs & the Fading Forest reports – links provided below; and apparently the United Kingdom [Dr. Mitchell’s article] and Australia.) Protecting plant health in habitats is usually the task of conservation organizations. Mitchell calls for unifying these programs. CISP is advocating draft legislation that aims to fix this gap in the U.S.  link to Welsh bill

What do you think? Is this approach as promising as Dr. Mitchell believes? Is it feasible?

I certainly concur that pest-based surveillance ignores the various categories of “unknown” pests and focus on commercially important species to the detriment of ecologically important ones. However, can such a system provide “early detection” of introduced pests? We have learned that insects and pathogens causing noticeable damage in natural environments have probably been present in a country or region for years – or decades. Perhaps these ecosystem-based criteria should be applied as guidance for selecting species to be monitored in “sentinel plant” programs. The plantings would be established in situations likely to receive pests early in their invasion process, e.g., warehouse districts (for pests in wood packaging) and ornamental nurseries that import growing stock.

Mitchell says the same issues pertain with regard to wildlife disease. See her article for sources.

SOURCE

Mitchell, R.J. 2024. A host-based approach for the prioritization of surveillance of plant pests and pathogens in wild flora and natural habitats in the UK. Biol Invasions (2024) 26:1125–1137 https://doi.org/10.1007/s10530-023-03233-x

Posted by Faith Campbell

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

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

or

www.fadingforests.org

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

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

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

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

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

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

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

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

Why we need to restructure the behavior of governments and societies

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

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

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

Critically important information that is often unspoken:

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

More Key Findings

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

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

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

Where the Report Is Weak: Interim Steps

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

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

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

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

SOURCES

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

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

Posted by Faith Campbell

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

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

or

www.fadingforests.org

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 24th 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 1.5oC, 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

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

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

or

www.fadingforests.org