Litter decomposition in western red cedar and western hemlock forests on northern Vancouver Island, British Columbia

Abstract

Litter decomposition and changes in N and organic chemicals were studied for 2 years in two forest types: old-growth western red cedar (Thuja plicata Donn) and western hemlock (Tsuga heterophylla (Raf.) Sarge) and 85-year-old stands of western hemlock and amabilis fir (Abies amabilis (Dougl.) Forbes) that developed after a major windstorm. We tested the hypothesis that lower rates of mass loss and different patterns of nutrient release in decomposing litter could explain lower nutrient availability in the cedar–hemlock type. Decomposition rate of a standard litter substrate, lodgepole pine needles, was almost identical in the two forest types indicating that each type had similar microenvironmental conditions for decomposers. Salal leaves had a lower lignin to N ratio and decomposed and released N more rapidly than the conifer litters. Among the conifers, cedar had poorer litter quality (higher lignin to N ratio), decomposed more slowly, and released considerably less N during the study. Cedar litter contributes to lower N availability in cedar–hemlock forests, but other factors, such as lower external N cycling and complexing of N with secondary carbon compounds during later stages of decomposition, are also likely to have a major influence on N availability. Keywords: Thuja plicata, Tsuga heterophylla, decomposition, litter quality, N cycling.