/ Soil respiration measurements conducted in the laboratory have been shown to be related to temperature and moisture, with maximum rates at soil temperatures between 25 and 40°C and soil moisture between Ϫ0.01 and Ϫ0.10 MPa. A preliminary study using forest soils from eastern Ken-tucky supported the previous research with soil respiration rates greater at 25°C than at 15°C, with differences in soil respiration rates related to sample site terrain characteristics. To further understand the factors that influence laboratory or potential respiration rates, we conducted a stratified sampling of soils from Robinson Experimental Forest in eastern Kentucky. Sampling was stratified by slope aspect, slope curvature, and landscape position. Potential soil respiration rates varied by slope aspect with NE aspects having greater rates than SW aspects. Rates did not vary by landscape position but did vary by slope curvature on SW aspects with concave curvatures having greater respiration rates than convex curvatures. Predictive soil respiration models based on both terrain attributes and soil chemical properties were created for both slope aspects. The relationships revealed that at this scale soil chemical properties play a more significant role in predicting soil respiration rates than terrain attributes. Models for the NE aspect were stronger than those for the SW aspect. The NE model created from a combination of terrain attributes and chemical properties included extractable Mg, extractable Zn, specific catchment area, and slope aspect (R 2 adj ϭ 0.620). The SW model created from a combination of terrain attributes and soil chemical properties included extractable P, extractable Zn, and tangential curvature (R 2 adj ϭ 0.413).

/ Data on carbon fluxes such as soil respiration are needed to develop strategies for increased carbon sequestration and reduced levels of atmospheric trace gases. Soil respiration is driven by proximal factors (e.g., soil temperature and soil moisture), which affect soil respiration by regulating microbial and root activity, and distal factors (e.g., topography), which affect soil respiration by influencing proximal factors. The objectives of this study were: (1) to relate measured carbon dioxide flux from forest soils to proximal and distal factors; and (2) to develop predictive soil-landscape models of soil respiration across a forested watershed. Carbon dioxide flux from the soil surface was measured monthly for 12 months at sampling points selected using a random stratified approach, with strata established based on slope aspect (NE and SW), slope shape (concave and convex), and slope position (upper, middle, and lower backslope). We generated empirical models using robust linear regression techniques to examine relationships between soil respiration and both proximal (soil physical and chemical properties) and distal factors (terrain attributes calculated from a 30-m digital elevation model). In situ soil respiration rates were greater on the NE-facing slopes than the SW-facing slopes. The models that we developed and validated explain up to 66% of variability in measured soil respiration, although seasonal model relationships varied. Soil temperature was the most consistent proximal factor for predicting soil respiration rates, while slope aspect was the most consistent distal factor among the models.