Coarse woody debris accelerates the decomposition of deadwood inputs across temperate forest

Wood decomposition is regulated by multiple controls, including climate
and wood traits, that vary at local to regional scales. Yet decomposition
rates differ dramatically when these controls do not. Fungal community
dynamics are often invoked to explain these differences, suggesting that
knowledge of ecosystem properties that influence fungal communities will
improve understanding and projection of wood decomposition. We hypothesize
that deadwood inputs decompose faster in forests with higher stocks of
downed coarse woody material (CWM) because CWM is a resource from which
lignocellulolytic fungi rapidly colonize new inputs. To test this
hypothesis, we measure decomposition of 1,116 pieces of fine woody
material (FWM) of five species, incubated for 13 to 49 months at five
locations spanning 10°-latitude in eastern U.S. forest. We place FWM
pieces near and far from CWM across observational transects and
experimental common gardens. Soil temperature positively affects
location-level mean decomposition rates, but these among-location
differences are smaller than within-location variation in decomposition.
Some of this variability is caused by CWM, where FWM pieces next to CWM
decompose more rapidly. These effects are greater with time of incubation
and lower initial wood density of FWM. The effect size of CWM is of the
same relative magnitude as for the known controls of temperature, deadwood
density and diameter. Abundance data for CWM is available for many forests
and hence may be an ecosystem variable amenable for inclusion in
decomposition models. Our findings suggest that conservation efforts to
rebuild depleted CWM stocks in temperate forests may accelerate
decomposition of fresh deadwood inputs.