Spatial structure and composition of the soil mesofauna in differently-managed forest stands

Soil mesofauna are known to have important effects on the soil flora,nutrient cycling, and plant growth. However, the factors affecting thedistribution and composition of soil mesofauna are poorly understood. Thisstudy examined the effects of environmental variables on soilmicroarthropod density and richness within an old-growth Douglas fir forest,a regrowth stand, a stand disturbed by wildfire, and a green-tree retentionharvest site. Within stands, arthropod density and richness were found to beaffected by the proximity of mature trees, by vertical position in the soil, bythe depth of the organic horizon, by the presence of ground cover and ofectomycorrhizal fungus, and by soil bulk density. Most of these variablescould be related to food availability. The effect of trees was probably due toeffects of root systems on the soil microflora.
Arthropod density and richness were lower in the burned and loggedsites, and the species compositions of these sites were different both from theundisturbed sites and from each other. The functional groups of arthropodspresent in the burned site indicated that it, like the undisturbed sites, was a
fungus-dominated rather than a bacteria-dominated soil. The functionalgroups present in the green-tree retention harvest site, on the other hand,suggested that the soil in that site was dominated by bacteria. Bacterial soilsare thought to be more typical of grasslands than of coniferous forests; theinfluence that this type of soil community will have on the future vegetationof the harvest site remains to be determined.