This study uses a soil warming experimental facility in an oak-dominated forest to examine for the first time how insect outbreaks affect nutrient cycling and availability to trees under both current temperatures and warmer soils expected in the future. In the southeastern United States caterpillar outbreaks have inflicted high rates of damage to oak trees, including up to 100% defoliation of individual trees. Species involved in this outbreak, black-dotted brown (Cissusa spadix) and common oak moth (Phoberia atomaris), were never known to outbreak before (Cissusa) or only rarely (Phoberia). However, in May 2010 Cissusa broke out for the first time ever recorded in the southeastern U.S., and in May 2011 both caterpillars exhibited outbreak numbers and caused extensive defoliation. In April 2012 these caterpillars broke out again but a month earlier than previous years, likely due to the mild winter of 2011-2012. Such large numbers of leaf-eating insects in a few weeks produce large quantities of excrement (frass) and other soil nutrient additions that may impact nutrient biogeochemical dynamics over an entire year or more. This study will be the first to address how insect outbreaks and warmer soils affect the availability to trees of important nutrients.
Insect outbreaks have been occurring more frequently and are projected to increase in frequency as climate warms. Understanding how forest ecosystems respond to outbreaks of foliage-eating insects concerns forest managers, timber harvesters, hikers, campers, and local and regional property owners. This work will have relevance for understanding soil nutrient availability to trees under current and future warmer conditions and, therefore, for future ecosystem services important to society. These services include, but are not limited to, provisioning of timber, forest carbon sequestration, wildlife habitat, and watershed integrity. During several weeks of outbreak each year, falling frass abundant enough to sound like drizzle and nightly climbing of thousands of caterpillars (per tree) up tree trunks garners much public interest and generates extensive media coverage, providing an excellent opportunity for discourse with the public.
