Tree diversity regulates nonnative pest invasions in forest ecosystems

The relationship between tree diversity and forest pest invasions is crucial to invasion ecology and for devising management approaches that can mitigate the enormous damages caused by nonnative pests. Using data from across the conterminous United States, Forest Service scientists showed that tree species diversity may facilitate or hinder pest invasions, and that the strength of the relationship varies with overall tree diversity. Until now, how these relationships play out in natural forest landscapes has been poorly understood.  

Hemlock woolly adelgid on leavesNonnative pests often cause cascading ecological impacts with multiple detrimental socioeconomic consequences. However, how plant diversity may influence insect and disease invasions remains unclear. High species diversity in host communities may facilitate pest invasions by providing a wider variety of ecological opportunities, but it can also dilute invasion success because low host dominance may make it more difficult for pests to establish. Most studies have focused on small-scale, experimental, or individual pest/disease species, while large-scale studies, especially in natural ecosystems, are extremely rare. A study based on a unique large dataset encompassing 130,210 forest plots with a county-level pest occurrence dataset across the United States led by Forest Service scientists and published in the Proceedings of the National Academy of Sciences (PNAS) indicates that tree-pest diversity relationships are hump-shaped. Pest diversity increases with tree diversity at low tree diversity levels (due to facilitation or amplification) and is reduced at higher tree diversity (due to dilution). Thus, tree diversity could regulate forest pest invasion through both facilitation and dilution that operate simultaneously, but their relative strengths vary with overall diversity. These findings show that the role of native species diversity in regulating nonnative pest invasions is more complex than previously understood. 

 

Pictured: An example of forest pest invasion: nonnative Hemlock woolly adelgid (Adelges tsugae). Hemlock trees grown under sunnier conditions may be more likely to survive infestations. Photo by Chris Evans, courtesy of the University of Illinois and Bugwood.org.


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Research Partners: Andrew M. Liebhold, USFS-Northern Research Station and Czech University of Life Sciences Prague; Kevin M. Potter, North Carolina State University and USFS-Southern Research Station. 

External Partners/Collaborators: Songlin Fei, Purdue University; Jun Wen, Duke University.

Contact: Qinfeng Guo, Research Ecologist, Eastern Forest Environmental Threat Assessment Center, qinfeng.guo@usda.gov.


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