Effects of throughfall reduction and snow removal on soil physical and biogeochemical properties in aspen forests of northern Minnesota, USA

Abstract

Climate change is projected to alter precipitation patterns across northern latitudes, with decreased snow accumulation and summer rainfall predicted. These changes may alter soil physical and biogeochemical properties, which would have implications for the operability and productivity of forest soils. Reductions in summer and winter precipitation were simulated using a paired-plot design with throughfall reduction and snow removal across four drainage classes at each of three locations in northern Minnesota, USA. Soil temperature and water content were measured every fifteen minutes to a depth of 60 cm, and soil frost depth (winter) and soil strength (summer) were monitored for two years. Soil respiration and extractable nitrogen were measured during two growing seasons, and a laboratory incubation was performed to test the response of carbon and nitrogen fluxes under controlled conditions. Soil temperature and water content increased from well-drained to poorly-drained soils during the winter and growing season, respectively. Snow removal caused large declines in soil temperature and significantly deeper penetration of frost that varied by drainage class, and there were strong relationships between frost depth and freezing degree days. Throughfall reduction had no effect on soil strength, soil respiration, or extractable nitrogen concentrations. Drainage class was a significant, although limited, indicator of soil strength, soil respiration, and extractable nitrogen concentrations. The laboratory incubation confirmed the lack of treatment effect on soil carbon and nitrogen fluxes, and instead showed that drainage class and soil moisture controlled these fluxes. These findings show that the dominant response of forest soils to reduced seasonal precipitation will occur during the winter with decreased soil temperatures and increased frost depth across drainage classes, which has implications for seasonal timber harvesting in northern latitudes under a changing climate.