Skip to main content

Goal: Apply Knowledge Globally Tree diversity regulates nonnative pest invasions in forest ecosystems

Hemlock woolly adelgid
An example of forest pest invasion: nonnative Hemlock wooly adelgid (Adelges tsugae). Hemlock trees grown under sunnier conditions may be more likely to survive infestations. (Courtesy photo by Chris Evans, University of Illinois,


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.


Nonnative pests often cause cascading ecological impacts with multiple detrimental socioeconomic consequences. However, it’s unclear how plant diversity may influence insect and disease invasions. High species diversity in host communities may facilitate pest invasions by providing a wider variety of ecological opportunities. Diversity can also dilute invasion success, because low host dominance may make it more difficult for pests to establish. Most studies have focused on fine-scale, experimental, or individual pests, while broad-scale studies, especially in natural ecosystems, are extremely rare. SRS scientists led a study that combined a dataset of 130,210 forest plots with a county-level pest occurrence dataset. They found that tree-pest diversity relationships are hump-shaped. Their results were published in the Proceedings of the National Academy of Sciences (PNAS). 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.

Principal Investigator
Qinfeng Guo, Research Ecologist
4854 - Eastern Forest Environmental Threat Assessment Center
Strategic Program Area
Invasive Species
Tree diversity regulates forest pest invasion
CompassLive Article
How Tree Diversity Affects Invasive Forest Pests
Research Partner
Andrew M. Liebhold (NRS)
External Partners
Kevin M. Potter (NCSU)
Songlin Fei (Purdue University)
Jun Wen (Duke University)