Woody debris is a recalcitrant carbon pool, storing carbon in complex molecules for extended periods of time. It has been shown that temperature and moisture are major drivers in decomposition from this pool. Additionally, under certain circumstances, both species and size can influence decomposition. It is not known, however, how the woody debris carbon pool in the moist, temperate forests of New England will respond to climate change, specifically soil warming. An increase in decomposition of woody debris could cause a pulse of carbon dioxide to exit the forest thus greatly reducing its storage potential.

We looked at the accumulation of woody debris and its decomposition under a soil warming scenario using the soil warming plots at Harvard Forest in Central Massachusetts. We first measured the amount of woody debris accumulating in the two plots to see if warming was influencing the quantity of debris entering the woody debris pool. We then placed debris of two size classes (2 cm diameter and 4 cm diameter) and four New England tree species (Tsuga canadensis, Quercus rubra, Acer Saccharum and Betula lenta) in the soil warming and control plots and measured the change in decomposition over the first year.

We found that four years into the study, the soil warming treatment did not increase the amount of woody debris accumulating on the forest floor. However it did greatly increase the decomposition of woody debris from this pool. Under ambient conditions, we saw a significant difference in decomposition among some species, but this species difference was completely lost with soil warming. We did not see an influence of size on decomposition between the two treatments. Surprisingly, we found that moisture content did not differ greatly between the two treatments for most species, though warming did show an increasing trend in moisture content for all species and size classes. These results suggest that soil warming may not increase the amount of debris entering the forest, but could result in an increase in decomposition of woody debris across species and size.