Biomass Removal in a Black Spruce Ecosystem: Temporal Dynamics of Carbon Loss and Nutrient Fluxes of Coarse Woody Debris.

Coarse woody debris (CWD) in the boreal ecosystem has been hypothesized to play an important role following stand-replacing disturbances such as fire or harvest. After such an event, nutrient-rich leaves, small branches and roots are quickly decomposed (or burned in the case of fire) and CWD, with its slow and steady decomposition, provides essential nutrition to the emerging stand until litterfall and throughfall inputs stabilize again at crown closure (15-20 years). The current study, which is approaching crown closure, was established in 1994 and focuses on carbon loss and nutrient fluxes of coarse woody debris (CWD) across four levels of biomass removal from mature black spruce forested stands. Two soil types (moist, loamy : dry, sandy), with stand replicates, were targeted to test if CWD is a source or sink for nutrients, (especially N and P) and if the decay pattern changed depending on soil type. Preliminary results suggest that N and P concentrations increased over time, and for N, is especially apparent in dry sandy sites. Actual amounts (content) of these nutrients were largely unchanged for the 15 year sampling period, suggesting immobilization (or at least unavailability) of nutrients as carbon is lost from CWD. The biomass removal treatment with the greatest carbon loss and fastest CWD decay rate had the highest initial mass of CWD, indicating possible synergistic decay dynamics.