Linking deadwood and soil GHG fluxes in a second growth north temperate deciduous forest (Upper Midwest USA)

Wind disturbance in northern hardwood forests of the US North Central Great Lakes region creates heterogeneously distributed structural attributes such as downed woody debris (DWD) and canopy openings across temporal and spatial scales. The decomposition of DWD contributes to greenhouse gas (GHG) fluxes, provides habitat, and potentially influences soil biogeochemistry. We assessed the effects of DWD addition on soil GHG fluxes in the decade after experimental manipulation of downed woody amounts and canopy openings in a maturing second-growth deciduous forest to (1) determine the spatial relationship between DWD proximity and soil GHG fluxes (CO2, CH4, N2O); (2) evaluate the relationship of decay class, canopy condition and environmental variables to wood decomposition and soil fluxes; and (3) use the fine scale surface patterns to estimate carbon emissions from the ground layer stratum. Our results revealed the shifting influence of individual pieces of DWD on soil microbial activity with advancing wood decay and depending on canopy condition. Modeled daily soil CO2 fluxes increased near moderately and highly decayed DWD in open canopy compared to control soils but decreased near highly decayed wood in closed canopy. Despite high variability and low CH4 (mean: − 0.02 ± 0.01 mg m−2 s−1) and N2O (mean: − 0.0007 ± 0.0008 mg m−2 s−1) soil fluxes, higher uptake in closed canopy paralleled the patterns of CO2 efflux. Our findings indicated that northern hardwood forests have the potential to be important CO2 and trace gas sinks, especially under intact canopy, but that widespread reductions in DWD in secondary forests of the region likely altered potential GHG soil uptake.