Estimation of root biomass and dynamics for the carbon budget model of the Canadian forest sector

Root biomass is expected to contribute significantly to total ecosystem carbon (C) pools and their dynamics. A method for estimating belowground biomass pools and their dynamics was developed for application in the carbon budget model of the Canadian forest sector (CBM-CFS2). Root biomass data for temperate and boreal softwood and hardwood species were compiled from the literature. Total root biomass for softwood and hardwood species was estimated using regression models that incorporate total aboveground biomass as the independent variable. Fine root biomass was estimated as a proportion of total root biomass using a single regression model for softwood and hardwood species combined. A regression model to estimate annual fine root production was derived for softwood and hardwood species. In the CBM-CFS2, net increments of total biomass were estimated using empirical growth functions to predict aboveground biomass. The regression models developed in this study were then used to predict the corresponding root biomass. Total root production was calculated as the sum of net increments, i.e., the change in root biomass per hectare plus annual turnover. The application of this approach to estimate root biomass pools and their dynamics in the CBM-CFS2 is demonstrated. As with all regression models that are developed from regional databases, this approach should not be used to predict root biomass and dynamics of an individual forest ecosystem, because the influence of species, site, and stand characteristics may lead to significant deviations from the regional averages.