Insect Infestations Linked to Shifts in Microclimate

Abstract

Changes in vegetation due to drought‐influenced herbivory may influence microclimate in ecosystems. In combination with studies of insect resistant and susceptible trees, we used long‐term herbivore removal experiments with two herbivores of piñon (Pinus edulis Endelm.) to test the general hypothesis that herbivore alteration of plant architecture affects soil microclimate, a major driver of ecosystem‐level processes. The piñon needle scale (Matsucoccus acalyptus, Herbert) attacks needles of juvenile trees causing them to develop an open crown. In contrast, the stem‐boring moth (Dioryctria albovittella Hulst.) kills the terminal shoots of mature trees, causing the crown to develop a dense form. Our studies focused on how the microclimate effects of these architectural changes are likely to accumulate over time. Three patterns emerged: (i) scale herbivory reduced leaf area index (LAI) of susceptible trees by 39%, whereas moths had no effect on LAI; (ii) scale herbivory increased soil moisture and temperature beneath susceptible trees by 35 and 26%, respectively, whereas moths had no effect; and (iii) scale and moth herbivory decreased crown interception of precipitation by 51 and 29%, respectively. From these results, we conclude: (1) the magnitude of scale effects on soil moisture and temperature is large, similar to global change scenarios, and sufficient to drive changes in ecosystem processes. (2) The larger sizes of moth‐susceptible trees apparently buffered them from most microclimate effects of herbivory, despite marked changes in crown architecture. (3) The phenotypic expression of susceptibility or resistance to scale insects extends beyond plant‐herbivore interactions to the physical environment.