Radiative Forcings from Albedo and Carbon Dynamics after Disturbance in Massachusetts Forests

Abstract:

Recent efforts have sought to compare and contrast the radiative forcings excited by forest disturbances due to both biogeochemical and biogeophysical mechanisms (Bonan et al., 2008) using either in situ measurements (e.g. Randerson et al., 2005; Randerson et al., 2006) or modeling (e.g. Brovkin et al., 2004). Study of boreal forest disturbances led to the important finding that the albedo increase from snow exposure after a canopy destroying fire offsets the warming from carbon emissions (Randerson et al. 2005). Similar study is lacking for temperate forests, leading to uncertainty about the net effect of albedo and carbon forcings following their disturbance. This work quantifies the gross and net radiative forcings from albedo and carbon mechanisms at two clear cut sites in Harvard Forest, Massachusetts, one a Norway spruce plantation clear cut in 2008 and the other a red pine plantation cleared in 1990. Carbon fluxes are estimated from detailed biomass inventories at both sites, as well as additional measurement with eddy covariance at the 2008 clearing. Associated radiative forcing is estimated with conventional methods estimating the perturbation to CO2 in the atmosphere and its lifetime considering ocean uptake (pulse response) and vegetation regrowth. Albedo change is assessed with Landsat derived albedo for both sites, as well as in situ measurements at the 2008 clearing. Associated radiative forcing is estimated with the model-derived radiative kernels provided by Shell et al (2008). From these extensive records we offer an in depth characterization of albedo and carbon forcings immediately following disturbance through to canopy closure and stem exclusion stages of forest growth in a mid-latitude temperate forest region.