Topographic Distribution of Soil Temperatures on a Mountainous Landscape of Northern Colorado.

Soil temperatures were measured using remote data loggers on four sites within Rocky Mountain National Park, Colorado. The sites are on representative steep slopes and are located to provide comparisons of differing elevations and opposing slope aspects. Elevations range from 2655 to 3230 meters, and plant communities range from ponderosa pine savanna to subalpine fir forest. Mean soil temperatures for annual, summer, and winter periods were determined and related to elevation, aspect, and plant communities. With increasing elevation, mean annual soil temperatures decreased from 7.6° to 1.8° C, and mean summer temperatures decreased from 14.4° to 3.7°. Mean winter soil temperatures had a surprisingly narrow range between sites, from -0.4° to 1.0°, with no clear elevational pattern.  The sites in subalpine fir forest were clearly in the cryic regime; the site in the Douglas-fir forest was in the frigid regime. The south-facing ponderosa pine savanna site at the lowest elevation was inconclusive but tending toward a mesic regime. The high elevation site with a north aspect had a very small difference between mean summer and mean winter temperatures (3.4°), and was solidly in the isofrigid temperature class.  The isofrigid class has not been recognized to date in soil surveys in this region, but this data suggest it may be extensive on cool aspects in the subalpine zone. The data indicates that aspect has a pronounced effect on soil temperatures. On warm aspects the mesic regime may extend to higher elevations than previously believed. These patterns can be extrapolated to similar areas in the southern Rocky Mountains and will contribute to more accurate prediction of temperature regimes in future soil survey work.