Carabid beetles (Coleoptera: Carabidae) differentially respond to soil management practices in feed and forage systems in transition to organic management

We conducted a 3-yr cropping systems experiment in central Pennsylvania, USA, to determine the effects of initial cover crop species, tillage and resulting environmental variables on the activity-density (A-D), species richness, community composition and guild composition of carabid beetles (Carabidae: Coleoptera) during the transition from conventional to organic production. We compared four systems in a factorial combination of a mixed perennial sod (timothy, Phleum pratense L.) and legumes (red clover, Trifolium pratense L.) or annual cereal grain (cereal rye, Secale cereale L.) followed by a legume (hairy vetch, Vicia villosa Roth) as initial cover crops, and soil management using full tillage (moldboard plow) or reduced tillage (chisel plow) implemented in soybeans followed by maize in the subsequent year. The experiment was established twice, first in autumn 2003 (S1) and again in autumn 2004 (S2) in an adjacent field, in a randomized complete-block design with four replicates in each Start. We collected a total of 2181 adult carabid beetles. Approximately 65% of the carabid beetles collected were from six species. Indicator Species Analysis showed that several carabid species were indicative of treatment, e.g., Poecilus chalcites was a strong indicator for treatments with an initial cereal rye cover crop. Eleven environmental variables explained variation in carabid A-D, richness and the A-D of species categorized by size class and dominant trophic behavior, respectively, but varied in significance and direction among guilds. Soil moisture was a significant effect for total carabid A-D in both S1 and S2. Redundancy analyses revealed some similar and some idiosyncratic responses among informative species for the cover crop×tillage treatments through the 3-yr rotation. The most consistent factors that distinguished species assemblages among years and treatments were the number and intensity of soil disturbances and perennial weed density. The consistent occurrence of soil disturbance indicators in multivariate analyses suggests that future studies that aim to compare the effects of nominal soil management treatments on carabid beetles and other soil-associated arthropods should quantify frequency and intensity of disturbance associated with crop management practices.