MASS AND NUTRIENT CONTENT OF WOODY DEBRIS AND FOREST FLOOR IN WESTERNRED CEDAR AND WESTERN HEMLOCK FORESTS ON NORTHERN VANCOUVER-ISLAND

Biomass and C, N, P, and K contents of woody debris and the forest flo or were surveyed in adjacent stands of old-growth western red cedar (T huja plicata Donn) - western hemlock (Tsuga heterophylla (Raf.) Sarg.) (CH type), and 85-year-old, windstorm-derived, second-growth western hemlock - amabilis fir (Abies amabilis (Dougl.) Forbes) (HA type) at t hree sites on northern Vancouver Island. Carbon concentrations were re latively constant across all detrital categories (mean = 556.8 mg/g); concentrations of N and P generally increased, and K generally decreas ed, with increasing degree of decomposition. The mean mass of woody de bris was 363 Mg/ha in the CH and 226 Mg/ha in the HA type. The mean fo rest floor mass was 280 Mg/ha in the CH and 211 Mg/ha in the HA stands . Approximately 60% of the forest floor mass in each forest type was d ecaying wood. Dead woody material above and within the forest floor re presented a significant store of biomass and nutrients in both forest types, containing 82% of the aboveground detrital biomass, 51-59% of t he N, and 58-61% of the detrital P. Forest floors in the CH and HA typ es contained similar total quantities of N, suggesting that the lower N availability in CH forests is not caused by greater immobilization i n detritus. The large accumulation of forest floor and woody debris in this region is attributed to slow decomposition in the cool, wet clim ate, high rates of detrital input following windstorms, and the large size and decay resistance of western red cedar boles.