The relationship between water availability and forest dynamics in Northern Minnesota

Abstract

Forested ecosystems play a major role in global and local water budgets, returning approximately 40% of total annual precipitation back to the atmosphere in the form of evapotranspiration. In the contiguous U.S., forested watersheds generate about 50% of runoff and management decisions include both afforestation and deforestation to create desired water yields. Since climate change is expected to increase watershed exports (in the form of increased evapotranspiration), understanding the intricate role of forested watersheds in the utilization, storage, and supply of water is necessary. For instance, some northern forest species exploit deeper water, but few studies have focused on niche diversification and differential exploitation of soil water in northern forests, in which root activity, depth, and lateral extent vary among species to partition soil moisture. Given that many northern forest landscapes experience a summer moisture deficit, particularly near the western biome boundary, this niche diversification may be key in sustaining some species and may affect overall forest water use and productivity. This dissertation sought to utilize a unique, 45-year in situ network of soil moisture measurements from the Marcell Experimental Forest (MEF) in northern Minnesota in order to investigate the relationship between plant available water and tree growth in the northern forests.