Modeling mass and nitrogen remaining in litterbags for Canadian forest and climate conditions

Abstract

A new Forest Litter Decomposition Model (FLDM) is presented to simulate mass, N and carbon/nitrogen ratios (C/N) according to the 1992–1998 leaf litterbag data of the Canadian Intersite Decomposition Experiment (CIDET). This experiment involved 10 litter types, with litterbags placed on the ground of 18 upland and 3 wetland sites across Canada. The calibrated model based on first-order reaction kinetics calculates total mass, N concentration and C/N for each litter type and location using: three compartments (fast, slow, and very slow), four parameters for compartment initialization; three for compartment-based decay; three to assess the climate influence on decay; and one each to determine the rate o f N-mineralization and the final C/N ratio. With FLDM, the initial fast fraction is determined from the initial water-extractable and acid-hydrolyzable or acid-unhydrolyzable portions of the litter; the initial ash content determines the ratio between the slow and very slow fractions. Mean July and January air temperatures, and annual precipitation, determine the climate effect on litter decay. Initial N concentration and the upland-wetland difference determine the N-mineralization coefficient. Model performance was fairly consistent by litter type, location, and year; r2 ranged from 0.83 to 0.97, from 0.64 to 0.92 and from 0.54 to 0.93 for mass remaining, N concentration and C/N, respectively. Key words: Forest litterbags, organic matter decomposition, N concentrations, climate, litter type, CIDET