Assessing the Impacts of Climate Change-Induced Soil Frost on Plant Nutrient Uptake and Productivity in a Northern Hardwood Forest
Projected changes to winter temperature and precipitation regimes suggest forests of the northeastern United States will experience a decreased snowpack and increased depth and duration of soil frost in winter. Previous studies show that increased soil frost leads to greater fine root mortality and decreased fine root vitality in northern hardwood stands, with increased leaching of nitrogen from soil. Reduced plant nutrient uptake following soil freezing could be a mechanism for increased forest nitrogen losses.
NSRC researchers examined impacts of reduced winter snowpack and increased soil frost on tree nutrient uptake and productivity in four paired plots within sugar maple-American beech stands at the Hubbard Brook Experimental Forest in New Hampshire. Each pair consisted of a snow-removal treatment plot and an undisturbed reference plot. The winter of 2007/2008 and the following growing season served as the pre-treatment baseline year. Snow was then removed for the first six weeks of winter in treatment plots during 2008/2009 and 2009/2010. Even after snow removal ended and a snow pack accumulated on the plots, soil frost persisted for the duration of the winter.
During the growing season, researchers measured root nutrient uptake and tree productivity. Results showed that increased soil frost reduced uptake of ammonium, a form of nitrogen, by fine roots of mature sugar maple during the early growing season, a critical period for nutrient cycling in Northern Forest ecosystems. This suggests that a decreased winter snowpack and increased soil frost may lead to intensified spring nitrogen losses in Northern Forest ecosystems.