Substrate control of litter decomposition in four Rocky Mountain coniferous forests

The influence of chemical and physical quality of litter on its rate of decomposition was examined by measuring mass loss from 19 diverse litter types, including leaves, needles, forbs, wood, and roots in the Kananaskis Valley of Alberta, Canada. Litter samples drawn from three adjacent forests of lodgepole pine, white spruce, and Engelmann spruce – subalpine fir, and from a small clearcut area, were allowed to decompose for 3 years at their sites of origin. The best predictors of mass loss were the initial concentrations of lignin and labile material in the litter. Adding N or P contents as a second term, rather than as a lignin to nutrient ratio, significantly improved mass loss predictions. There were abrupt limits for the influence of lignin (above 28%) and N (below C:N of 30:1); similar limits were observed for all predictors except labile content. None of these chemical parameters, nor a physical measure, particle diameter, were useful in predicting rates of decomposition of high-lignin, woody substrates. The relative importance of the various litter quality parameters in determining rates of mass loss in the clear-cut area was very similar to that in the forests, despite considerably more rapid decomposition in the clearcut. Key words: decomposition, lignin, litter, nutrients, Rocky Mountains, wood.