Impacts of Climate Change-Caused Soil Freezing on Plants in a Northern Hardwood Forest

As the scientific certainty of projected climate change increases, it is critical that we understand how climate change will interact with other regional human-caused disturbances to ecosystems. For example, the Northern Forest region receives among the highest rates of acid deposition in the United States. Excess deposition of nitrogen can saturate living organisms’ demand for nitrogen in forest ecosystems, causing nitrate leaching, acidification of soils and surface groundwater, plant nutrient imbalances, forest decline, and eutrophication of coastal waters.

One example of climate change that may impact forest nitrogen retention is the documented and forecasted changes in precipitation during winter months. In the northeastern United States, forests have experienced an increase in winter rainfall events and a decrease in the duration and depth of snowpack. A reduction of snowpack in forests can induce soil freezing even when the ambient temperature is higher than average. Soil frost can cause significant increases in fine root mortality and loss of root vitality, increased leaching of nitrogen and other essential nutrients, acidification of soils, and increases in seasonal nitrogen fluxes to streams. The increased damage to fine roots following soil freezing suggests that reductions in plant activity could be influencing nitrogen losses, but the relationship between soil freezing and plant nutrient uptake and productivity has not been measured.

This NSRC research project will quantify plant responses to changes in the soil freezing regime in a northern hardwood forest at the Hubbard Brook Experimental Forest in New Hampshire. Snow removal treatments will be used to induce soil freezing over two consecutive winters beginning December 2007.