NITROGEN MINERALIZATION AND DECOMPOSITION IN FOREST FLOORS IN ADJACENT PLANTATIONS OF WESTERN RED CEDAR, WESTERN HEMLOCK, AND DOUGLAS-FIR

To determine if western red cedar (Thuja plicata Donn) litter contribu tes to low N availability in cedar-hemlock forests, we measured concen trations of N and rates of net N mineralization in forest floors from single-species plantations of cedar, western hemlock (Tsuga heterophyl la (Raf.) Sarg.), and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franc o) on the same site in coastal British Columbia. Concentrations of tot al and extractable N and rates of net N mineralization during laborato ry incubations were lowest in the cedar forest floor and highest in Do uglas-fir. Less C was mineralized in the cedar forest floor during inc ubation, and the amount of N mineralized per unit C was least in cedar . Rates of mass loss of foliar litter of the three species were simila r during the first 50 weeks of a 70-week laboratory incubation, but ce dar lost mass more quickly during the final 20 weeks. Rates of net N m ineralization in the forest floors were significantly correlated with the initial percent N, C/N, % Klason lignin, and lignin/N of foliar li tter. Foliar litter of cedar had lower concentrations of N and greater proportions of alkyl C (based on C-13 NMR spectroscopy) than Douglas- fir litter. These characteristics of cedar litter may contribute to lo w N availability in cedar-hemlock forest floors. Concentrations of alk yl C (waxes and cutin) may be better than lignin for predicting rates of mass loss and N mineralization from litter.