Modeling forest leaf-litter decomposition and N mineralization in litterbags, placed across Canada: A 5-model comparison

The performances of five carbon (C) and nitrogen (N) cycling models (FLDM, CENTURY, SOMM, DOCDOM and CANDY) were compared for their ability to quantify mass and N remaining in 10 g leaf-litterbags across the wide range of litter types and sites of the Canadian Intersite Decomposition Experiment (CIDET), over a 6-year period. These models differ in their structure and assumptions, number of compartments, predictor variables and coefficients. Calibrated model outputs displayed similar but not identical trends for mass and N remaining, but differed substantially in mass and N contents per model-defined compartments. The quality of fit between model calculations and data varied as follows: FLDM > CENTURY > DOCMOD > CANDY > SOMM for mass remaining (0.73 < r2 < 0.92), and FLDM > DOCMOD > CENTURY > SOMM > CANDY for the changing N concentrations inside the bags (0.40 < r2 < 0.80). FLDM calculations were the most consistent by CIDET site (21), litter type (10), and years of litterbag retrieval (1993–1998). Best-fitted models were used to project mass remaining and N concentrations inside the bags over the next 50 years, using mean July and January air temperatures, and annual precipitation and initial litter composition as independent predictor variables. Projected model outputs converged for mass remaining, but diverged for the N concentrations, i.e., (1 ± 0.5) g and (2 ± 1)% at year 50, respectively.