The effect of snow depth on overwinter survival in Lobelia inflata

The snowpack in high altitude and latitude regions provides thermal insulation during the cold season. Recent climate change has resulted in a decrease in both the duration and the reliability of this snowpack and may thus affect overwinter survival of biota. Here we use a manipulation approach to ask how snow depth affects ground surface temperatures and how this in turn affects survival of the overwintering rosette stage in the monocarpic plant Lobelia inflata. A shallow but consistent insulation layer (R-value of 3) was sufficient to reduce temperature fluctuations and the accumulation of sub-zero degree-days substantially. For all treatments > R3 these measures were negligible. Survival results are consistent with a crucial role of thermal insulation to successful overwintering of Lobelia inflata rosettes: without a consistent snowpack survival was low (11%); with an insulation effect of R3 or greater survival increased dramatically (81%). The winter prior to the manipulation study was characterized by an anomalous absence of snow at the onset of cold temperatures. This resulted in substantially greater accumulation of sub-zero degree-days at the soil surface and almost 100% rosette mortality in the field. This study shows that inconsistent and reduced snowpack - a prediction of climate change - will have critical effects on plant survival because of increased temperature fluctuations and extreme temperatures experienced at the soil surface.