Community composition analysis of altered vegetation communities following the release of grazing pressure

Abstract

Determining community composition and recognizing successional gradients of community recovery following release from disturbance is vital in determining proper land management techniques. Successful native plant recovery depends on biotic and abiotic factors and the type and degree of anthropogenic disturbance. Degraded vegetation communities need initial survey efforts to determine the extent of degradation followed by consistent standardized monitoring to determine transition along successional gradients. The aim of this study was to determine community composition and successional gradients following release from livestock grazing. To this end, initial surveys were completed at the Lost Trail National Wildlife Refuge during the summers of 2013 and 2014, with the aim of evaluating the composition of each previously mapped community type and making recommendations for future management practices. Prior to any fieldwork, various vegetation sampling methods were compared including, Daubenmire percent canopy cover (DPCC), point-intercept and modified Whittaker plots. The DPCC method was determined to be the most efficient for current and future sampling efforts, balancing the quality of data and the time needed for collection. Using this method, a minimum of 60 Daubenmire frames were sampled from 16 vegetation communities. The USFWS project objectives were to (1) determine if each of the premapped community types were named correctly, and (2) collect enough vegetation data to determine a 20% change in the five most common species with an accuracy of 80%. Species area curves were plotted, and sample adequacy calculated to determine if each community was adequately sampled. It was found that a minimum of 24 to 180 sample frames are necessary to sufficiently describe all communities. However, this number may increase as the communities transition to native-dominated stands. Litter depth was found to be the only statistically significant abiotic factor related to community composition (P = 0.03): litter depth is highly correlated with non-native species (r = 0.904), and the lack of litter is correlated with the presence of three climax species (r = 0.736). The intermontane grasslands in this refuge were found to be part of the Northern Fescue Grasslands rather than part of the Palouse Prairie.