Earthworms, arthropods and plant litter decomposition in aspen (Populus tremuloides) and lodgepole pine(Pinus contorta) forests in Colorado, USA
We compared the abundance and community composition of earthworms, soil macroarthropods, and litter microarthropods to test faunal effects on plant litter decomposition rates in two forests in the subalpine in Colorado, USA. Litterbags containing recently senesced litter of Populus tremuloides (aspen) and Pinus contorta (lodgepole pine) were placed in aspen and pine forests to monitor their decay rates and quantify litter microarthropod abundance. Earthworms and macroarthropods were collected by hand from the soil. Three species of earthworms were found in the aspen forest: Octolasion cyaneum, an anecic worm; Dendrobaena octaedra, an epigeic worm and Aporrectodea trapezoides, an endogeic worm.We found a higher density and fresh biomass of earthworms in the aspen (40 worms m–2 and 4.4 g m–2) than in the pine forest (0.8 worms m–2 and 0.6 g m–2). The lodgepole pine contained only earthworm species, D. octaedra. Macroarthropod density did not differ between the forests. Total density of microarthropods in the aspen and lodgepole pine forests was 6.40 and 5.24 individuals g–1 of dry litter, respectively and did not significantly differ between forests. The percent of mass remaining was different between litter species (r2 = 0.73, P < 0.01). Aspen litter decayed significantly faster than pine regardless of location. The percent of mass remaining of aspen and lodgepole pine were significantly correlatedwith the density of earthworms in both forests (P < 0.01). In the pine forests, the percent mass remaining of aspen and lodgepole pine litter was also significantly correlated with the density of mites (Acarina) (P = 0.03), prostigmatid mites (P = 0.02) and the total abundance of litter fauna (P = 0.02). Our results suggest that introduced earthworms play an important role on litter decomposition in the aspen forest, and that litter decomposition in these subalpine sites might be influenceddifferentially by various groups of soil and litter fauna.