Soil respiration (Rs) has been estimated to account for carbon (C) emission of >100 Pg yr⁻¹ globally, and specifically in forests, may represent the main determinant of the ecosystem C-balance. In many forested areas, the forest canopy may not reflect minor topography of the forest floor. We assumed that minor topography, especially within an overall plane area, correlates with significant differences in soil moisture and thereby effects Rs.

We studied Rs within an oak forest in the Oak Opening Region (NW Ohio) using a LI-6400 with the standard soil chamber over the 6-yr period 2004−2009. Eight Rs plots, each including six individual sample collars, were spread randomly over a forest area of ca. 100 ha using the USDA Forest Service Forest Inventory and Analysis (FIA) plot design.

Results/Conclusions

Soil temperature (Ts) and soil volumetric water content (VWC) exerted the first- and second important control on Rs, respectively. Similarly plausible, VWC at the plot scale was subject to minor topography in the area (< 5 m elevation difference), with different VWC regimes exerting significant influence on Rs. Based on results from general linear mixing model, both VWC and seasonal amount of precipitation had a significant influence on Rs at elevated sites, whereas the model did not suggest similar influence at the depression sites. Rs at elevated and lower sites emitted 13.3 t and 15.7 t C ha yr, respectively, based on the six-yr average of biweekly-interpolated measurement data. Estimates indicated that lower elevated sites with increased VWC can significantly change the total Rs with a contribution of less than 10% of the forest area. The results suggest that even minor topography can range high in the hierarchy of factors regulating Rs in temperate forests.