Soil and litter organisms in Pacific northwest forests under different management practices

Abstract

Soil and litter organisms are important indicators of stress and disturbance to forest ecosystems. In this study, soil and litter organisms were monitored for their response to different forest management practices. Litter and soil cores (0–10, 10–20 cm) were collected at approximately 8 week intervals over a 19 month period from a low elevation 110–140-year-old Douglas-fir forest and adjacent 8-year-old clearcut and from a high elevation 200–250-year-old Douglas-fir forest and adjacent 5-year-old clearcut. The low elevation clearcut had been broadcast burned and replanted with Douglas-fir trees and a grass–legume mixture whereas the high elevation clearcut was not burned, large woody debris was left, and it was replanted with Douglas-fir, Noble-fir, Grand-fir, and western white pine. The litter and soil cores were analyzed for types of microarthropods and numbers of nematodes, fungi, culturable, aerobic bacteria, spore-forming bacteria, and chitin-degrading bacteria. Microbial community metabolic profiles, using the Biolog™ method, were also generated for the 0–10 cm soil samples. Populations of Pseudomonas spp. were analyzed in the litter and soil samples using 16S rDNA fingerprints. Plant surveys were conducted to identify potential relationships of soil organisms to plant community composition. At both elevational field sites, there were significantly ( P<0.05) higher levels of nematodes and microarthropods in litter and soil in forest plots than in clearcut plots. Bacterial and fungal populations were also significantly higher in litter in forest plots than in clearcut plots at the high elevation site. In the litter and soil at the low elevation site and the soil at the high elevation site, however, microbial levels were higher in clearcut plots than in forest plots. The Pseudomonas spp. populations and the microbial community metabolic profiles in the 0–10 cm soil differed significantly between the forest and clearcut plots at the low elevation site but not at the high elevation site. At both elevational field sites, the plant cover (%) and plant density were significantly higher in clearcut plots than in forest plots. These observed differences in the population size and composition of organisms between mature forests and both low management and high management clearcuts demonstrated the impacts forest management practices may have on the soil ecosystem.