Grass Mortality and Turnover Following Core Rangeland Restoration Practices
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2017 The Society for Range Management. Published by Elsevier Inc. All rights reserved. In rangelands, management interventions have sought to minimize disturbances that decrease survival of perennial grasses to avoid compositional shifts toward less desirable species. However, the effects of rangeland management techniques on perennial grass survival and turnover are not known for individual species because the discipline has largely focused on structural metrics, measuring cover or biomass rather than tracking individual plants. In this study, we quantified perennial grass survival and recruitment in response to core rangeland restoration practices across multiple soil types to determine the potential for different interventions to cause shifts to undesirable grass community assemblages. We mapped individual grass tufts and recorded basal area annually. We used these maps to track survival and recruitment of grasses in response to mechanical brush removal, chemical woody plant control, and low-intensity prescribed burning. Additionally, we performed ordinations of the grass community to explore compositional shifts resulting from management interventions. We found perennial grass mortality to be higher for mechanically treated plots on all soil types than it was in chemically treated plots, burned plots, or untreated controls. Levels of mortality from fire were similar to baseline mortality in control plots for all soil types. However, relative species turnover was variable among soils and treatments. Brush removal only resulted in compositional shifts on sandy soils, where annual grasses and species capable of rapid expansion following disturbance became dominant. Differential responses are related to differences in species turnover, which is a function of individual grass species mortality and recruitment mediated by interactions between management approach and abiotic conditions. Given this response variability, understanding effects of management actions on perennial grass turnover and the potential for those actions to result in a community shift toward less desirable species is necessary for managers to achieve restoration goals on encroached rangelands.
