Manipulating earthworm abundance using electroshocking in deciduous forests

Abstract

Summary Earthworms influence the biotic and abiotic characteristics of soils, including the diversity and abundance of bacteria and fungi, some of which form essential mycorrhizal connections with plants. The indirect effects that earthworms have on plants through their impacts on mycorrhiza are poorly understood. To investigate the effect of earthworms on mycorrhizae-tree seedling interactions, we manipulated earthworm densities in 1 m2 enclosures located at 12 study sites within four different-aged forest stands at the Smithsonian Environmental Research Center (SERC) in Maryland, USA. The treatment plots were created by trenching around the perimeter and lining the trenches with fiberglass mesh before backfilling. Two types of untrenched plots served as control and leaf litter treatment plots. Enclosures were electroshocked between four and nine times over a two-year period to remove earthworms and to compare densities among treatment and untrenched plots. Earthworms were weighed and identified to determine whether removal by electroshocking varied depending on body size or ecological grouping. Earthworm abundances were 30-50% lower in reduced-density enclosures than in high density enclosures; however, the efficiency of the exclusion treatments varied by earthworm size and ecological group. Manipulating earthworm populations in temperate forests to assess their influence on ecological functions is feasible using electroshocking, but careful planning is essential given the amount of effort required to set-up and maintain the desired experimental conditions.Keywords: earthworm manipulation, electroshocking, deciduous forests