Bluff prairies of southeastern Minnesota: Competition as a driving force of community structure and composition.

摘要

The bluff prairie ecosystem of southeastern Minnesota provides an unusual opportunity to evaluate various effects of global change including increases in nitrogen, changes in precipitation, and increases in tree canopy cover. Specifically the shallow soil, low nitrogen and water availability of the steep karst landscape allows the examination of dominant species competition in unproductive habitats and the effect of eastern red cedar (Juniperous virginiana) invasion into the bluff prairie system.; The first study was designed to determine how eastern red cedar invasion affects the bluff prairie system. This study examined changes in species structure and composition and how these changes affect light availability, nutrient cycling and other soil properties. The objective was to assess the effects of eastern red cedar presence on plant composition, light environment, and soil properties of the dry, nitrogen poor steep bluff prairie system. The results of this study indicate that species composition alters soil and canopy factors such as light penetration and nutrient dynamics, which result in feedbacks that further alter community composition.; The invasion of eastern red cedar into the bluff prairie system may be one of the most visually obvious effects of global change, it is not the only aspect of interest to ecologists attempting to understand the dynamics of unproductive systems and how these dynamics might respond to other global changes such as increases in nitrogen and changes in precipitation.; Therefore, the second and third portions of the study are designed to determine how similar dominant species compete for limiting resources in unproductive environments. The objective was to assess the competitive relationship of two C4 grass species (Sorghastrum nutans and Schizachyrium scoparium) as adult bunches and at the germination/establishment stage. This study suggests the competitive relationship between Sorghastrum nutans and Schizachyrium scoparium differs according to life stage (adult bunches vs. growth and establishment stage). This study also indicates that existing nutrient limitations are affected by slope resulting in intricate competitive interactions that influence community composition.