Spatial Patterns of Soil Surface C Flux in Experimental Canopy Gaps Jason D. Schatz,* Jodi A. Forrester, and David J. Mladenoff Department of Forest and Wildlife Ecology, University of Wisconsin, 1630 Linden Drive, Madison, Wisconsin 53706, USA ABSTRACT To explore within-gap spatial patterns of soil sur- face CO 2 flux, we measured instantaneous soil surface CO 2 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 CO 2 flux was higher in the northern 1/3 and northern edge of gaps compared to the central and southern por- tions. 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 ) com- pared 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. Key words: Canopy gap; C flux; Gap microcli- mate; Respiration; Soil temperature; Soil flux; Northern hardwood forest. INTRODUCTION In northern hardwood forests, disturbance regimes tend to be dominated by relatively small scale dis- turbances leaving a patchwork of canopy gaps formed by the death of single trees or small groups of trees (Frelich and Lorimer 1991; Dahir and Lorimer 1996). At any given time, small gaps at various stages of succession cover a significant portion of the landscape, with typical estimates of 10 % or more in various eastern North American forests (Runkle 1982; Kneeshaw and Bergeron 1998; Keller and Hicks 1999). Soil surface CO 2 flux (R S ) constitutes the second largest carbon flux in forest ecosystems (Raich and Schlesinger 1992; Gower and others 1996) and is sensitive to many biotic and abiotic factors affected by canopy gaps, including soil temperature (T S ), soil moisture, and vegetation dynamics. Not sur- prisingly, gap formation has been found to affect R S , although the magnitude and direction of that effect is not always consistent. Some studies have reported higher R S within gaps compared to adja- cent contiguous forest (for example, Scharenbroch and Bockheim 2008), some lower (for example, Brumme 1995), some found no significant differ- ences (for example, Stoffel and others 2010), and others reported that relative R S between canopy openings and contiguous forest changed with time since harvest (for example, Schilling and others 1999; Peng and Thomas 2006). Given the con- spicuousness of small canopy gaps in northern Received 7 October 2011; accepted 24 February 2012; published online 20 March 2012 Electronic supplementary material: The online version of this article (doi:10.1007/s10021-012-9535-1) contains supplementary material, which is available to authorized users. Author Contributions: Jason D. Schatz: Performed research; analyzed data; wrote paper. Jodi Forrester: Conceived and designed study; per- formed research; edited and contributed to paper text and analysis. David Mladenoff: Conceived and designed study (PI); edited paper. *Corresponding author; e-mail: jschatz2@wisc.edu Ecosystems (2012) 15: 616–623 DOI: 10.1007/s10021-012-9535-1 Ó 2012 Springer Science+Business Media, LLC 616