One of the potential impacts of predicted rises in global temperatures, at least in high latitude areas, is alteration of snowpack levels. In particular, warming could reduce the amount of snow cover, and thus actually result in colder soil temperatures due to the loss of thermal insulation provided by snow, with concomitant effects on microbes and/or plant roots. In order to simulate the effects of global warming on forests associated with reduced snow coverage, we removed newly fallen snow within 48 hours of each event within 1.5 X 1.5m “warmed” plots, and allowed natural snowpack to develop in “ambient” control plots in an oak-pine forest in southern Maine USA. We continuously monitored soil temperature and moisture at a depth of 10cm throughout winter and the following spring. As indicators of forest response, we measured both soil respiration and pine seedling photosynthesis for several days immediately following snowmelt in the spring, and then weekly for 2 months
Results/Conclusions
Over a 4 month period from the first winter snowfall until snowmelt in the spring, periodic removal of snow from warmed plots reduced soil temperatures by as much as 3 degrees C as compared to the ambient plots, but had little or no effect on soil moisture. The decrease in temperature persisted for several weeks following snowmelt, and averaged 0.5 C within the first 7 days. Soil respiration rates measured immediately after snowmelt were 27% lower in warmed plots as compared to ambient plots, and remained consistently lower until soil temperatures returned to that observed in the ambient plots. Snow removal had no effect on seedling photosynthesis. Thus in our study, altered snowpack impacted carbon flux from soil, but appeared to be solely the result of short term temperature effects on microbial and/or root respiration rates, as opposed to longer-term impacts (e.g., due to change in microbial communities or root mortality associated with freezing damage) that likely would have been evidenced in more persistent differences in soil respiration rates.