Spatial Patterns of Soil Surface C Flux in Experimental Canopy Gaps

To explore within-gap spatial patterns of soil surface CO₂ flux, we measured instantaneous soil surface CO₂ flux, soil surface temperature, and soil moisture in north–south transects across canopy gaps and in adjacent contiguous forest from April to November 2010 in a second-growth northern hardwood forest in Wisconsin, USA. Throughout the growing season, soil surface CO₂ flux was higher in the northern 1/3 and northern edge of gaps compared to the central and southern portions. These patterns were driven primarily by within-gap variation in soil temperature, which was itself driven by within-gap patterns of insolation. Most locations in the northern 1/3 and northern edge of gaps had significantly higher modeled total growing season C flux (mean 725 g C m⁻²) compared to the contiguous forest (mean 706 g C m⁻²), whereas C flux in the central and southern portions of gaps (mean 555 g C m⁻²) was significantly lower than both the contiguous forest and the northern portions of gaps.