Evolutionary history of host trees amplifies the dilution effect of biodiversity on forest pests

Abstract

Biodiversity appears to strongly suppress pathogens and pests in many plant and animal systems. However, this “dilution effect” is not consistently detected, and when present can vary strikingly in magnitude. Here, we use forest inventory data from over 25,000 plots (>1.1 million sampled trees) to quantify the strength of the dilution effect on dozens of forest pests and clarify why some pests are particularly sensitive to biodiversity. Using Bayesian hierarchical models, we show that pest prevalence is frequently lower in highly diverse forests, but there is considerable variability in the magnitude of this dilution effect among pests. The strength of dilution was not closely associated with host specialization or pest nativity. Instead, pest prevalence was lower in forests where co-occurring tree species were more distantly related to a pest’s preferred hosts. Our analyses indicate that host evolutionary history and forest composition are key to understanding how species diversity may dilute the impacts of tree pests, with important implications for predicting how future biodiversity change may affect the spread and distribution of damaging forest pests.

The more, the healthier: Tree diversity reduces forest pests and pathogens

“…In this issue, Gougherty and Davies [ 3 ] present a third, and compelling, approach to assessing the frequency of dilution effects. Using data from forest surveys conducted by the United States Department of Agriculture (USDA) Forest Service, Gougherty and Davies compiled a record of the prevalence of damage inflicted by 60 forest pests and pathogens in more than 25,000 forest plots across the US.…”

“…As Gougherty and Davies [ 3 ] point out, we should expect greater pest problems in forests with low diversity, whether that low diversity results from natural or human causes. Their findings suggest several avenues for future research.…”

“…In an ironic twist, the new work of Gougherty and Davies [ 3 ] relies on the USDA’s Forest Inventory and Analysis (FIA) database. The FIA was funded through the McSweeney-McNary act of 1928, which directed the USDA to inventory the nation’s forests to facilitate extraction of forest resources, especially timber.…”