Effects of snow cover manipulation and climate factors on the development of soil frost in forested boreal peatlands in Minnesota, USA

Abstract

Black spruce (Picea mariana) peatlands play an important ecologic and economic role in the temperate-boreal region of North America, providing a valuable timber resource in addition to performing important ecosystem functions. Climate models project decreases in the amount of snowfall throughout the temperate-boreal region by 2100, as average wintertime temperatures increase. While the effect of a loss of snow cover on soil frost dynamics has been well-studied in mineral soil environments through the use of snow removal techniques, similar analysis on decreased snow cover in peatland soils is less common and related effects unclear. To fill this gap in understanding, we used a paired-plot experimental design to assess the effect of snow removal on soil temperature and frost development at six forested peatland sites in northern Minnesota, USA, during the winters of 2017-2018 and 2018-2019. Treatments were either 1) removal of snow throughout the winter, or 2) ambient snow conditions. During both years of the study, there was a significant effect of snow removal by mid-winter that continued into late winter and spring, where removal of snow correlated with increased soil frost depth and colder soil temperatures, as compared to plots with ambient snow cover. Following the first winter of the study, it was found that soil frost persisted much later in snow removal plots, and snow removal plots had colder soils through much of the summer growing season. In addition, during the frozen season, soil temperatures in the removal plots were highly responsive to air temperature fluctuations to depths of 20 cm or more, resulting in increased variability in temperature, whereas the ambient snow cover soils exhibited little fluctuation and maintained temperatures near 0° C for much of the winter season. These results indicate that predicted changes to the amount and form of wintertime precipitation in the temperate-boreal zone may result in increased development of soil frost in forested peatland systems. However, the increased reactivity of soil temperature to air temperature fluctuations may offset the effect of decreased snow cover if average winter air temperatures are higher, as currently predicted.