Leaf-litter arthropods can exert substantial direct and indirect effects on rates of litter decomposition, and hence are important to ecological processes on the forest floor. The activity and abundance of many litter arthropods are strongly affected by changes in moisture. Models predict increased rainfall and increased severity of drought as two outcomes of climate change. We constructed rainout shelters to cover eight 14-m2 fenced plots randomly assigned to either high- or low-rainfall treatments, which were achieved by irrigating at rates that corresponded to high and low periods of rainfall during the past century. Rainfall manipulations were conducted from June through November 2002. Arthropods were sampled by sifting the leaf litter in October 2002. Samples revealed that total arthropod densities were ca. 2x higher in the high-rainfall plots (F1,4=8.05, p=0.047) due to an approximate doubling of spider densities (F1,4=42.7, p=0.003). Collembola, mites, millipedes, centipedes, ants, and insects other than ants did not differ between treatments (all p > 0.21). Thus, effects of differences in rainfall emerged after 4 months of manipulations but only in one of the major arthropod groups. Litter extraction samples, which more accurately measure densities of mites and Collembola, are presently being sorted, and may reveal more complex responses to the rainfall treatment.
Keywords: altered rainfall, leaf-litter arthropods
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