INFLUENCE OF MICRO-HABITAT AND MACRO-HABITAT FACTORS ON COLLEMBOLAN COMMUNITIES IN DOUGLAS-FIR STUMPS DURING FOREST SUCCESSION

We studied the relative importance of micro- and macro-habitat factors on collembolan communities in decaying stumps in three Douglas-fir ec osystems. Each ecosystem contained four seres: regeneration (3-8 years old), immature (25-45 years old), mature (65-85 years old), and old-g rowth stands (over 200 years old). Stumps were classified, depending o n stage of wood decay as: sound, moderate decay, and advanced decay. T he relationship between collembolan communities and habitat factors wa s determined by canonical correspondence analysis (CCA) and detrended correspondence analysis (DCA). Macrohabitat factors (stand age and stu dy site) were the most important ones affecting species distribution. When data were pooled for season and stump decay stages, collembolan c ommunities were characteristically grouped by seres, particularly for the regeneration and old growth. However, only a few species were char acteristic of a particular sere, notably Verragopus alpa, Hymenaphorur a cocklei, and Folsomia stella in old-growth forests, and Anuropharus septentrionalis and Ballistura libra in regeneration seres. In contras t to collembolan species, microhabitat factors in the stump were influ enced more by season than by stand age or site. DCA-ordination indicat ed that within an individual season, microhabitat factors, especially %C, %P and microbial biomass, were important determinants of collembol an distribution. Common and abundant collembolan species tended to be positively correlated with %C, but negatively correlated with %N, %P, numbers of nematodes and microbial biomass. We suggest that collembola n numbers were not directly related to the first four factors and that the negative correlation with microbial biomass was caused by excessi ve grazing on fungi by the Collembola.