STUMPS AS A HABITAT FOR COLLEMBOLA DURING SUCCESSION FROM CLEAR-CUTS TO OLD-GROWTH DOUGLAS-FIR FORESTS

We studied the natural succession of the collembolan fauna during the decomposition of stumps in successional Douglas-fir ecosystems at thre e sites on southern Vancouver Island, British Columbia, Canada. Each s ite was represented by four seres, comprising regeneration (3-8 years old), immature (25-45 years old), mature (65-85 years old), and old gr owth stands (> 200 years old). A total of 216 samples collected during autumn. winter and spring yielded 15601 individuals, comprising 72 sp ecies, 40 genera and 12 families. Most of the species encountered (63. 8%) were common to all sites. Densities on a volume basis equaled thos e in soil. Well-decayed stumps contained about 850000 individuals m-3. This species-rich and numerically abundant collembolan fauna was esse ntially a subset of the soil fauna. The composition of the collembolan community was more sensitive to the successional status of the forest than to season of sampling or to decay status of the wood. Stumps pro vided a suitable habitat for most soil Collembola and emphasizes the i mportance of this woody debris in forest ecosystems. Favourable moistu re conditions make this habitat an important refugium for these arthro pods during early stages of forest succession. By virtue of the large population in stumps, Collembola likely contribute greatly to the deco mposition of this woody material.