Vegetation dynamics following grazing cessation on the Channel Islands, California Public Deposited

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  • March 22, 2019
  • Corry, Patricia Mary
    • Affiliation: College of Arts and Sciences, Department of Biology
  • European introduction of grazing livestock converted large areas of perennial-dominated native plant communities to exotic, mostly annual-dominated communities in much of the arid and semiarid western U.S. Grazing-induced type conversions of vegetation are particularly widespread in the Mediterranean-climate ecosystems of California, where exotic annual grasslands have largely replaced native shrublands and grasslands. Land managers are increasingly retiring arid and semiarid lands from grazing in an effort to reverse these changes and promote native vegetation recovery, but such recovery is often slow or nonexistent. Exotic grasslands can exhibit remarkable compositional stability even where native propagules are available. Where spontaneous recovery of native plant communities does occur, it tends to be spatially and temporally variable and seemingly unpredictable. Why some exotic-dominated communities are rapidly recolonized by native species upon release from grazing while others persist indefinitely is poorly understood. Long-term vegetation monitoring at the California Channel Islands provides an opportunity to determine factors associated with spontaneous recovery of native vegetation following the removal of nonnative herbivores. This study used time-series vegetation data and environmental data to identify patterns in post-grazing native vegetation recovery among taxa and environments, assess the utility of certain ecological theories in predicting recovery, and develop hypotheses about factors controlling native vegetation recovery. Site environmental characteristics explained post-grazing succession on the Channel Islands better than did ecological theories invoking biodiversity as a predictor or correlate. Exotic species richness and abundance consistently correlate with fine-grained substrates, and more generally with higher site heat load. Results suggest that competition for soil moisture is an important control on native vegetation recolonization. Response to grazing cessation also differed among taxa. Theoretically invasive traits did not predict differences in response among native woody species, but drought dormancy did, suggesting the importance of drought-coping strategies among taxa. Differential response among exotic species indicates possible post-grazing environmental changes and can inform prioritization of eradication efforts. Application of this type of trend analysis to the development of restoration goals and strategies is discussed.
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  • In Copyright
  • Peet, Robert K.
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  • University of North Carolina at Chapel Hill
  • Open access

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