Snow depth manipulation and its influence on soil frost and water dynamicsin a northern hardwood forest

Climate change will likely result in warmer winter temperatures leading to less snowfall in temperate forests. These changes may lead to increases in soil freezing because of lack of an insulating snow cover and changes in so il water dynamics during the important snowmelt period. In this study, we m anipulated snow depth by removing snow for two winters, simulating the late development of the snowpack as may occur with global warming, to explore t he relationships between snow depth, soil freezing, soil moisture, and infi ltration. We established four sites, each with two paired plots, at the Hub bard Brook Experimental Forest (HBEF) in New Hampshire, U.S.A. and instrume nted all eight plots with soil and snow thermistors, frost tubes, soil mois ture probes, and soil lysimeters. For two winters, we removed snow from the designated treatment plots until February. Snow in the reference plots was undisturbed. The treatment winters (1997/1998 and 1998/1999) were relative ly mild, with temperatures above the seasonal norm and snow depths below av erage. Results show the treated plots accumulated significantly less snow a nd had more extensive soil frost than reference plots. Snow depth was a str ong regulator of soil temperature and frost depth at all sites. Soil moistu re measured by time domain reflectometry probes and leaching volumes collec ted in lysimeters were lower in the treatment plots in March and April comp ared to the rest of the year. The ratio of leachate volumes collected in th e treatment plots to that in the reference plots decreased as the snow abla tion seasons progressed. Our data show that even mild winters with low snow fall, simulated by snow removal, will result in increased soil freezing in the forests at the HBEF. Our results suggest that a climate shift toward le ss snowfall or a shorter duration of snow on the ground will produce increa ses in soil freezing in northern hardwood forests. Increases in soil freezi ng will have implications for changes in soil biogeochemical processes.