SOIL FAUNA COMMUNITIES IN 2 DISTINCT BUT ADJACENT FOREST TYPES ON NORTHERN VANCOUVER-ISLAND, BRITISH-COLUMBIA

The composition of major soil fauna groups throughout the soil profile in adjacent old growth western red cedar (Thuja plicata Donn) - western hemlock (Tsuga heterophylla (Raf.) Sarg.) and mature hemlock - amabilis fir (Abies amabilis (Dougl.) Forbes) forests on northern Vancouver Island was compared as part of an integrated study on the possible causes of poor growth of plantation Sitka spruce (Picea sitchensis (Bong.) Carr.) on cedar-hemlock cutblocks. In addition, we examined seasonal changes in vertical distribution of soil fauna within the forest floor of both forest types. At five times between August 1989 and March 1991, four methods were used to extract soil fauna: hand sorting, high-gradient extraction, modified Baermann funnel, and the Formalin method. Forty-one faunal groups were identified in both forest types. The hemlock - amabilis fir forest maintained a higher abundance and biomass of soil fauna than the cedar-hemlock forest. Nematoda were numerically dominant in both forest types followed by Acari, Collembola, and Copepoda. Diplopoda, Enchytraeidae, Diptera larvae, and Acari dominated soil fauna biomass in both forests. Similarity indices indicated that the forest types have similar group diversity. The majority of Nematoda, Acari, and Collembola were found in the LF and H horizons in both forest types. On average, more than 50% of the Acari and Collembola populations were found in the LF horizon while approximately 30% of the Nematoda were found there.