Snow Removal and Ambient Air Temperature Effects on Forest Soil Temperatures in Northern Vermont

but snow cover will decrease. In this paper, we examine potential effects of a reduction in snow cover on northWe measured deciduous forest soil temperatures under control (unmanipulated) and snow-free (where snow is manually removed) eastern forests by examining soil temperatures under conditions for four winters (at three soil depths) to determine effects control and snow-free (where snow is manually reof a snow cover reduction such as may occur as a result of climate moved) conditions for four consecutive years between change on Vermont forest soils. The four winters we studied were 1 December and 30 April. characterized as: ‘cold and snowy’, ‘warm with low snow’, ‘cold with In cold temperate mixed deciduous-evergreen forests, low snow’, and ‘cool with low snow’. Snow-free soils were colder than where there is a persistent insulating snow layer through controls at 5and 15-cm depth for all years, and at all depths in the much of the winter, a slight rise in average ambient two cold winters. Soil thermal variability generally decreased with both increased snow cover and soil depth. The effect of snow cover temperature can change thermal dynamics in the biologon soil freeze-thaw events was highly dependent on both the depth ically active top 30 cm of soil in different ways. The of snow and the soil temperature. Snow kept the soil warm and effects of warmer air on soil temperature depend on reduced soil temperature variability, but often this caused soil to the extent that the insulating snow layer is reduced (Yin remain near 0 C, resulting in more freeze–thaw events under snow and Arp 1993; DeGaetano et al., 1996). If the elevated at one or more soil depths. During the ‘cold snowy’ winter, soils under ambient temperatures are coupled with an increase in snow had daily averages consistently 0 C, whereas snow-free soil precipitation this will further alter the effects of climate temperatures commonly dropped below 3 C. During the ‘warm’ warming on the soil (Pikul et al., 1989; Lehrsch et al., year, temperatures of soil under snow were often lower than those of snow-free soils. The warmer winter resulted in less snow cover to 1991). insulate soil from freezing in the biologically active top 30 cm. The Although the average soil temperature may change possible consequences of increased soil freezing include more root very little as a consequence of higher ambient temperamortality and nutrient loss, which would potentially alter ecosystem ture and a reduced snow cover, the variation in daily dynamics, decrease productivity of some tree species, and increase soil temperature may be greater. This may increase the sugar maple (Acer saccharum Marshall) mortality in northern hardnumber of freeze–thaw cycles, affecting root mortality, wood forests. soil aggregate stability, and nutrient loss (Auclair et al., 1996; Edwards 1991; Lehrsch et al.1991; Ron Vaz et al., 1994; Stottlemeyer and Toczydlowski 1991). AdditionO and future climate changes have the ally, an increase in root-zone soil freezing and thawing potential to substantially alter the structure and events causing increased root desiccation has been imfunction of northeastern forests. The Intergovernmental plicated in dieback events in northern hardwood forests Panel on Climate Change (IPCC) estimates that global (Auclair et al., 1996). average surface temperatures have increased by 0.6 Whatever the direct effect of climate change on soil ( 0.2 C) over the past century (Houghton et al., 2001; temperature, the long-term indirect effects of increased IPCC, 2001). The amount and form of precipitation has soil freezing because of reduced snow on northern forest also changed over the past century. The IPCC estimates ecosystem health is potentially profound (Auclair et al., that there has been a 0.5 to 1% per decade increase 1996; Groffman et al., 2001a; Robitaille et al., 1995; in northern hemisphere precipitation at mid to high Bertrand et al., 1994). Several studies in the northeastlatitudes over the past century; and that globally there ern mixed-deciduous forests have linked prolonged mild has been a 10% reduction in the extent of snow cover over the past 40 yr (Houghton et al., 2001; IPCC, 2001). soil freezing (caused by winter snow drought) to inCurrent climate change models predict that these trends creases in soil nitrate, (Groffman et al., 2001b), to inwill continue this century (Houghton et al., 2001; IPCC, creases in soil N, P, and C losses (Fitzhugh et al., 2001), 2001). These models predict a 1.4 to 5.8 C rise in average and to increased root mortality (Groffman et al. 1999; global temperatures by 2100, with mid to high latitude, Tierney et al., 2001). northern hemisphere land masses experiencing above Together, these studies suggest that a reduction or average increases in temperature, especially during the removal of a snow layer resulting in a loss of thermal winter (Houghton et al., 2001; IPCC, 2001). Winter prebuffering can cause an early disruption of the winter cipitation at these same latitudes is projected to increase, soil nutrient storage. This can lead to ecosystem leaching losses during winter when plant and microbial demand K.L.M. Decker, D. Wang, C. Waite, and T. Scherbatskoy, School of is likely to be low. Soil freezing can also reduce quality Natural Resources, George D. Aiken Center, Univ. of Vermont, Burlington, VT 05401. K.L.M. Decker currently at: Ecosystem Science and quantity of sap of sugar maples (Robitaille et al., and Technology Branch; NASA-Ames Research Center; M/S 242-4; 1995). Thus information about the freezing behavior of Moffett Field, CA 94035. Received 27 Sept. 2001. *Corresponding soil under different winter conditions can be useful to author ([email protected]). forest managers interested in both maple syrup production and ecosystem health. Published in Soil Sci. Soc. Am. J. 67:1234–1243 (2003).  Soil Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: IPCC, Intergovernmental Panel on Climate Change.