Root-feeding insect densities and their effects on fine root dynamics in oak-dominated forests of the southern Appalachians

The turnover of fine root biomass is a substantial carbon flux in terrestrial ecosystems. Because insect herbivores consume fine root tissue, they can have major impacts on nutrient dynamics, energy stored as biomass, and plant allocations of C and N toward root system repair and defense. Furthermore, root system responses can vary across species and successional stages. In this study, set in two oak-dominated Appalachian forests, we are assessing the influences of natural root-feeding insect assemblages on fine root dynamics in both recently harvested and mature stands. Ingrowth cores were installed in a randomized split-plot block design to quantify fine root biomass production with and without an insect removal treatment (randomly assigned to ingrowth cores). Alterations in the allocation of C and N are being tested by analyzing C:N ratios of fine root tissue and surrounding soil, and cores will be collected to assess root productivity. Here we report analysis of insect larvae collected during core installation. Root-feeding insects of Elateridae (wireworms) and Scarabidae (white grubs) were sufficiently abundant to alter fine root biomass production. Mean wireworm density was estimated as 75,170 larvae per hectare (C.V. = 72.9); white grubs numbered 35,374 larvae per hectare (C.V.=154.4). Herbivore density and species composition varied with space and time (e.g. differences in wireworm density: by site, p=0.0002; by time, p=0.2563). These data suggest that herbivore community structure and potential impacts of herbivores on root productivity are variable both within and across plant successional stages.