Carbon dynamics of a ponderosa pine plantation following a thinning treatment in the northern Sierra Nevada

We investigated the impacts of a thinning prescription commonly used to reduce fuel loads in mature ponderosa pine forests of the northern Sierra Nevada Mountains on the distribution of carbon among functionally distinct pools, and on the component fluxes of net ecosystem production (NEP). The biomass of wood, foliage, and roots was highest in the unthinned control stands, lowest in stands measured 3 years after thinning, and intermediate in the stands measured 16 years following the same prescription. While total wood net primary production (NPP) followed the same pattern as biomass across treatments, an apparent doubling of shrub foliage NPP in the 3 years following overstory thinning reduced the impacts of thinning on total foliage NPP. Similarly, reductions in coarse root NPP associated with tree removal were largely offset by increases in fine root production. Compensatory NPP by shrubs and fine roots increased the light use efficiency of thinned stands 60% over that of unthinned plots. Both soil respiration and the decomposition of aboveground dead wood appeared conserved across all treatments. Results suggest that when modeling the influence fuel reduction treatments on regional carbon dynamics, it may be necessary to consider the compensatory responses of understory vegetation as such shifts in growth form can effect meaningful changes in the capture and allocation of carbon in the ecosystem.