Interactions of temperature and moisture with respiration from coarse woody debris in experimental forest canopy gaps

Coarse woody debris (CWD) and canopy gaps are thought to be important structural components that influence forest ecosystem processes, yet few studies have assessed whether these features interact to influence decay dynamics, and we know of none that does so under controlled experimental canopy gap conditions. By manipulating forest structure to create canopy openings, we tested whether canopy gaps, through their influence on microclimate, affect the respiration rate of CWD in a mature second-growth northern hardwood forest of Wisconsin, USA. We sought to determine the relative contribution of moisture or temperature as predictors of respiration, and to provide estimates of the annual C emission from CWD in these treatments. Differences in the surface temperature of CWD were apparent immediately following gap treatments, with debris in gaps staying significantly warmer than beneath undisturbed canopy. Coarse woody debris moisture content differed more between gaps and undisturbed canopy in the second post-treatment year due to higher insolation and temperature in gaps relative to undisturbed canopy. The gap treatment increased respiration rates and altered the relationship with CWD temperature and moisture in complex ways. The impacts of gap creation on C fluxes from CWD depended on the range of temperature and moisture being examined. The interaction of the temperature and moisture of the debris in combination with the decay class explained 60% of the observed variation in CWD respiration beneath undisturbed canopies. In gaps, only 23% of the variation of flux could be explained by environmental variables. Annual C fluxes were 128.2 g C kg−1 year−1 in canopy openings and 108.5 g C kg−1 year−1 in undisturbed canopy locations.

► CWD in experimental canopy gaps experiences greater surface temperatures and decreased moisture conditions.
► In undisturbed canopy areas, CWD respiration is related to the interaction of moisture, temperature and decay class of CWD.
► The creation of experimental canopy gaps altered the relationship between CWD respiration, temperature and moisture.
► CWD respiration in small experimental canopy gaps exceeds rates under intact canopy by 18%.