The species is under attack by rapid ohia death [https://www.dontmovefirewood.org/pest_pathogen/ceratocystis-wilt-ohi-html/]
I welcome new attention to the threats posed to tree species around world.
Last week, at the conclusion of Conference of the Parties (COP) to the Convention on Biodiversity (CBD), the International Union for the Conservation of nature (IUCN) released its most recent iteration of the Red List of Threatened Species. The headline was that 38% of the world’s trees are at risk of extinction.
This is the finding of a decade-long Global Tree Assessment. The assessment was led by Botanic Gardens Conservation International and IUCN’s Species Survival Commission Global Tree Specialist Group. Partners in the effort included Conservation International, NatureServe, Missouri Botanical Garden and Royal Botanic Gardens, Kew. The project was funded primarily by Fondation Franklinia. The foundation was formed in 2005 expressly to conserve threatened tree species! I regret that I had not heard about it before.
At least 16,425 of the 47,282 tree species assessed are at risk of extinction. Trees now account for over one quarter of species on the IUCN Red List, and the number of threatened trees is more than double the number of all threatened birds, mammals, reptiles and amphibians combined. Tree species are at risk of extinction in 192 countries around the world.
No surprise: the highest proportion of threatened trees is found on islands. Island trees are at particularly high risk due to deforestation for urban development, conversion to agriculture, invasive species, pests and diseases. Climate change is increasingly threatening trees, especially in the tropics, through sea-level rise and stronger, more frequent storms.
The COP was held in Cali, Columbia. This is fitting because South America is home to the greatest diversity of trees in the world. Twenty-five percent – 3,356 out of 13,668 assessed species are at risk of extinction. Forest clearance for crop farming and livestock ranching are the largest threats on the continent. Dr Eimear Nic Lughadha, Senior Research Leader in Conservation Assessment and Analysis at the Royal Botanic Gardens, Kew, said this percentage is sure to increase as many additional tree species are described for science.
IUCN spokespeople emphasized that the loss of trees is a major threat to thousands of other plants, fungi and animals. Cleo Cunningham, Head of Climate and Forests at Birdlife International pointed out that over two-thirds of globally threatened bird species are dependent on forests. Speakers also noted that people depend on trees; over 5,000 of the tree species on the Red List are used in construction, and over 2,000 species provide medicines, food and fuels.
Sam Ross, Sustainable Business Project Analyst at ZSL, noted that “Despite growing pressure to halt worldwide deforestation by 2030, … most of the world’s 100 most significant tropical timber and pulp companies have made limited progress in disclosing their zero deforestation and traceability commitments. We must all do more to safeguard these vital forest ecosystems, especially consumer goods manufacturers, financial institutions funding forestry, and agriculture companies.”
IUCN and the Red List Partners are launching a global social media campaign to raise awareness and funds to accelerate species assessments and reassessments. The campaign will culminate at the IUCN World Conservation Congress in Abu Dhabi, in October 2025.
Impacts from Pathogens Continue to Increase
Meanwhile, in North America and elsewhere, infections by tree-killing pathogens are spreading and intensifying.
Phytophthora ramorum (sudden oak death)
In California, P. ramorum the statewide rate of tree infection in 2024 doubled from 2023. Expansions were most obvious in Mendocino and Del Norte counties. Worse, California has now detected a third strain of P. ramorum in its forests. The NA2 strain was first detected in Del Norte County in 2020. Now it has been found in five sites closer to the “core” of the infestation closer to San Francisco Bay. Dr. Matteo Garbelotto believes the strain – formerly known only in nurseries – had been present for some years. It appears to be more aggressive than the strain long present in forests – NA1 – and might be favored by warmer temperatures. [The EU1 strain was detected in Del Norte County in 2021.]
Oregon has been wrestling with the EU1 strain since 2015; the NA2 strain since 2021. Beginning in late 2022, authorities have discovered multiple disease outbreaks between the Rogue River and Port Orford (farther north than the area previously known to be infected). Many of these new outbreaks are the EU1 lineage. The state is struggling to carry out eradication treatments using funds from state legislative appropriations, support from USDA Forest Service and USDI Bureau of Land Management, USDA Agriculture Research Service, and direct Congressional appropriations. The last resulted from assertive lobbying!
The Government Accountability Office is studying interactions between climate change and agricultural pests; sudden oak death is one of four focal pests. The report is expected to be released in 2025.
[Most of this information is from the California Oak Mortality Task Force (COMTF) webinar on 29 October, 2024. Recording available here.]
Cronartium ribicola White Pine Blister Rust
Limber pine (Pinus flexilis) is heavily infected by blister rust in Alberta; in its U.S. range
the disease is increasing. Scientists had been cheered by the presence of major gene resistance (MGR) in limber pine to the rust. However, a strain of blister rust in Alberta has been determined to be virulent despite this gene (Liu et al. 2024). Scientists might have to launch a breeding program to try to enhance quantitative disease resistance (QDR) in the species. Unfortunately, the frequency and level of partial resistance in limber pine has been very low in trees tested so far. Scientists now must test more limber pines to see whether some have higher levels of QDR.
Southwestern white pine (Pinus strobiformis) presents the same problem; the MGR gene might even be the same gene. Some some populations of SWWP have higher partial or quantitative disease resistance.
BLD continues to be detected in new sites. According to Matthew Borden of Bartlett Tree Research Laboratories, since 2021, BLD has been detected in five counties in Virginia:
- Prince William County — Prince William Forest Park;
- Fairfax County: southern Fairfax County on the border with Prince William County (Fountainhead Park, Hemlock Overlook Park, and Meadowood Special Recreation Area), somewhat farther north (Burke Lake Park), and northern edge (Great Falls);
- Loudoun County;
- Stafford County – just outside the city of Fredricksburg and along the Spotsylvania river
- New Kent County in Wahrani Natural Preserve
Several of these outbreaks – e.g., southern Fairfax County, Stafford County, and Loudoun County – are 20 miles or more away from other known outbreaks. Virginia Department of Agriculture staff are monitoring the disease. All these sites are near water – although the Potomac River in Loudoun County is above the fall line so narrower than at the other sites.
SOURCE
Liu, J-J., R.A. Sniezko, S. Houston, G. Alger, J. Krakowski, A.W. Schoettle, R. Sissons, A. Zamany, H. Williams, B. Rancourt, A. Kegley. 2024. A New Threat to Limber Pine (Pinus flexilis) Restoration in Alberta and Beyond: First Documentation of a Cronartium ribicola race (vcr4) Virulent to Cr4-Controlled Major Gene Resistance. Phytopathology. Published Online:25 Sep 2024 https://doi.org/10.1094/PHYTO-04-24-0129-R
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/
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