Observed and anticipated impacts of drought on forest insects and diseases in the United States
Kolb, T. E., Fettig, C. J., Ayres, M. P., Bentz, B. J., Hicke, J. A., Mathiasen, R., ... & Weed, A. S. (2016). Observed and anticipated impacts of drought on forest insects and diseases in the United States. Forest Ecology and Management, 380, 321-334. PDF.
Summary
Droughts are expected to increase in frequency and severity under climate change, and the interaction between droughts and forest pests has been an important research topic. However, the influences of droughts on pest/pathogen induced tree mortality vary widely, making it difficult to understand these interactions. Kolb and colleagues review and synthesize existing research on pest and pathogen interactions with drought to provide a comprehensive look at what to expect in U.S. forests under increasing drought frequency and intensity. They summarize drought interactions with bark beetles (e.g. mountain pine beetle), sapfeeders (e.g. hemlock wolly adelgid), defoliators (e.g. gypsy moth), and fungal/oomycete pathogens (e.g. root rots), and determine if there are any trends in their responses to drought. They found that bark beetles tend to respond negatively to intermediate levels of drought, but cause increased tree mortality during intense droughts. At intermediate drought intensities, some sapfeeders may have increased impacts on trees. Defoliator impacts are inconsistent, though it is unlikely that they will be greatly impacted by drought in eastern U.S. forests. Finally, primary pathogens, such as rusts, Phytophthora, and Dothistroma, will likely be negatively impacted by drought, while secondary pathogens, such as Armillaria, cankers, and root rots, may become more successful.
Take home points
Interactions between pests, pathogens, and drought are complicated, and their impacts on forest health vary even within larger pest and pathogen groups.
While there is evidence that pests will be more successful in drought conditions in the western U.S., in eastern U.S. forests, increasing temperatures and pest interactions will be more important to consider than drought when assessing the potential impacts of climate change.
Management implications
In forests that may experience increasing drought frequency and severity, consider prioritizing the restoration and planting of tree species that are drought tolerant.
In some forests, thinning trees to reduce competition for water may help increase drought tolerance.
Keywords
Climate Extremes; Impact Study; Review; Invasive Invertebrate; Terrestrial Habitat