A practical approach for assessing the sensitivity of the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS3)

We present a case study approach to assessing the sensitivity of the dead organic matter sub-module of the operational-scale version of the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS3) to variation in model parameters controlling inputs to and throughput in this module. Parameters examined included those controlling biomass growth and turnover, dead organic matter decay and model initialization. Our approach is based on the use of sensitivity and uncertainty analysis software packages that are freely available on the Internet and accessible to model users. We simulated four different landscapes, three with different species but the same rotation length and one using the same species with two different rotation lengths, to evaluate interactions between modelled scenarios and assumptions about parameter variability. We assessed the impacts of parameter variation on stocks and fluxes. The model was sensitive to variation in parameters controlling the foliage and fine root pathways, but the sensitivity differed depending on whether a softwood or hardwood landscape was being simulated. Our findings indicate that inferences drawn from sensitivity and uncertainty analysis of forest carbon models are specific to the landscapes and time horizons being modelled.