Equine Grazing in Managed Subalpine Wetlands: Effects on Arthropods and Plant Structure as a Function of Habitat
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Grazing management necessarily emphasizes the most spatially extensive vegetation assemblages, but landscapes are mosaics, often with more mesic vegetation types embedded within a matrix of drier vegetation. Our primary objective was to contrast effects of equine grazing on both subalpine vegetation structure and associated arthropods in a drier reed grass (Calamagrostismuiriana) dominated habitat versus a wetter, more productive sedge habitat (Carex utriculata). A second objective was to compare reed grass and sedge as habitats for fauna, irrespective of grazing. All work was done in Sequoia National Park (CA, USA), where detailed, long-term records of stock management were available. We sampled paired grazed and control wet meadows that contained both habitats. There were moderate negative effects of grazing on vegetation, and effects were greater in sedge than in reed grass. Conversely, negative grazing effects on arthropods, albeit limited, were greater in the drier reed grass, possibly due to microhabitat differences. The differing effects on plants and animals as a function of habitat emphasize the importance of considering both flora and fauna, as well as multiple habitat types, when making management decisions. Sedge supported twice the overall arthropod abundance of reed grass as well as greater diversity; hemipteran and dipteran taxa were particularly abundant in sedge. Given the greater grazing effects on sedge vegetation, greater habitat provision for terrestrial arthropods, and value as aquatic arthropod habitat, the wetter sedge assemblage is worthy of additional consideration by managers when planning for grazing and other aspects of land usage.
KeywordsLand management Pack stock grazing Subalpine wetland Terrestrial arthropod assemblages Vegetation assemblages Disturbance
Rick Dodson and Steve Case were outstanding field assistants, and Marie French was her usual meticulous self while sorting samples. We thank Sequoia National Park for their excellent support, especially from Corie Cann, Erik Frenzel, Erika Jostad, and Charisse Sydoriak, and WMRC faculty and staff, especially Vikki DeVries, Frank Powell, and John Smiley. The paper was improved through review by, or discussion with, Liz Ballenger, Beverly Collins, Dave Graber, Rebecca Efroymson, Peggy Moore, Sarah Sheehan, Matthew Taylor, Harold Werner, and an anonymous reviewer. This project was supported by the National Park Service (J8R07080005), and the current study built upon earlier work funded by the NPS (J8C07100004, J8R07070006, and J8R07030011). Angela Evenden expertly assisted with agreement development via the Californian and Great Basin Cooperative Ecosystems Studies Units.
This study complies with the laws of the USA. We obtained a Scientific Research and Collecting permit from the US National Park Service for work in Sequoia National Park for each year of the study. No protected species were sampled.
Conflict of interest
The authors declare that they have no conflict of interest.
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