Abstract - Grassland Stability: An Experimental Analysis of Local Resistance and Resilience
Krueger, Kirsten Ann. 1988. Grassland Stability: An Experimental Analysis of Local Resistance and Resilience. PhD Dissertation. Colorado State University. 64 p.
The ecological concept of community equilibrium is undergoing extensive re-examination. Currently, there is no empirically-based, unitary understanding of the concept. In this regard, one goal of the present study was to experimentally-investigate two aspects of equilibrium, resistance and resilience, over short tiem and local spatial scales. For several reasons, grasslands were ideally suited to this study. Another goal of the study was to compare continuouly grazed and long-time (ca. 50 y) ungrazed sites in the study area, Wind Cave National Park. The global hypothesis was that grazed areas were more resistant and resilient to disturbance than ungrazed areas, due to their divergent selective regimes over the past 50 y. Despite 50 y of differential selection pressures on grazed versus ungrazed areas, there were few differences between vegetation characterisics, and responses to experimental treatments, between these areas. The weight of experimental evidence caused rejection of the global hypothesis in almost all cases. For example, 24 of 25 characteristics on grazed, and 21 of 25 characteristics on ungrazed sites variously showed resistance of compositional structure to clipping and burning, resilience of physical structure of the vegetation canopy to burning, and resistance of tillering (a function correlate) to clipping. The present results lend support to an equilibrium interpretation of the dynamics of both grazed and ungrazed vegetation communities under study. Thus, (resistance and resilience) stablility occurs even over short time, and local spatial scales, as opposed to the popular supposition that equilibrial dynamics do not occur at these scales. The results are also examined for their implications for hierarchy theory. Qualitative stability properties of the overall Wind Cave systmen are discussed.