Approaches for reducing uncertainties in regional forest carbon balance

Accurate estimation of regional terrestrial ecosystem carbon (C) balance is critical in formulating national and global adaptation and mitigation stra tegies in response to global changes. Since the regional C balance cannot b e measured directly, it has been estimated using various models. In such st udies, errors often exceeded the magnitude of the estimated C balance due t o two types of uncertainties: noninclusion of some important factors in the C cycle and the fact that the C balance is a small difference between seve ral large fluxes that can each be determined with only a limited accuracy. In this study, we propose new approaches to reduce these uncertainties and implement them in an Integrated Terrestrial Ecosystem C-budget model (InTEC ). To minimize the first type of uncertainties, InTEC considers all the maj or factors presently known to affect C balance (including climate, atmosphe ric CO2 concentration, N deposition, and disturbances). To reduce the secon d type of uncertainties, InTEC estimates the C balance from historical chan ges in these factors, relative to the preindustrial period. InTEC is built on the basis of widely tested Century C cycling model, Farquhar's leaf phot osynthesis model, and age-NPP relationships, and is constrained by N cyclin g. As a general regional-scale terrestrial ecosystem C budget model, InTEC has so far been applied to Canada's forests [Chen et al., this issue]. The sensitivity analysis showed that these two new approaches reduce the uncert ainty in the C balance of Canada's forests substantially.