ROOT-ZONE SOIL-TEMPERATURE VARIATION ASSOCIATED WITH MICROSITE CHARACTERISTICS IN HIGH-ELEVATION FOREST OPENINGS IN THE INTERIOR OF BRITISH-COLUMBIA

Low soil temperatures have been suggested as a factor contributing to poor rooting of planted conifer seedlings and hence a cause for failure of some high-elevation reforestation efforts. Few studies have attempted to document soil temperature variation and its causal factors in post-logged, high-elevation openings during the growing season, A field survey of afternoon soil temperature (at a depth of -10 cm from the mineral soil surface) was conducted in six high-elevation clear-cuts located in the Engelmann Spruce-Subalpine Fir (ESSF) biogeoclimatic zone in central British Columbia, Canada, On a clear summer day, a difference of 8 degrees C in afternoon soil temperatures was measured between the warmest microsites (bare mineral soil, 17.6 +/- 2.5 degrees C) and the coolest microsites (covered by forest floor and vegetation, 9.3 +/- 0.7 degrees C), Heavily covered microsites showed little diurnal or spot-to-spot (microsite) variation in soil temperature. Conversely, microsites with little surface cover exhibited the greatest spatial and temporal variability in soil temperature, Variation in afternoon root-zone soil temperature (T) was most strongly associated with the combination of thickness of duff (forest floor) (D), cumulative % vegetation cover (C), and % soil moisture (M), Comprised of these three microsite attributes, a multiple regression model, T = 24.06 - [1.05(ln(C)+ 1.64(ln( D)) + 1.38(ln(M))](R(2) = 0.73) was created which predicts high-elevation afternoon soil temperatures to within +/- 2.0 degrees C. Multiple regression models including relative surface irradiance (as a percentage of above canopy light), cumulative % vegetation height, micro-slope and micro-aspect were less predictive. The relationship between afternoon soil temperature and each microsite attribute generally showed a strongly negative curvilinear pattern, described by double exponential decay functions, Microsites associated with suboptimally low afternoon soil temperatures(< 12 degrees C) during the growing season were widespread (70 to 80% of the sampled areas) in the surveyed high-elevation openings.