• Restoration of Native Plants is Reduced by Rodent-Caused Soil Disturbance and Seed Removal

      Gurney, C. M.; Prugh, L. R.; Brashares, J. S. (Society for Range Management, 2015-07)
      Granivory and soil disturbance are two modes by which burrowing rodents may limit the success of native plant restoration in rangelands. This guild of animals has prolific effects on plant community composition and structure, yet surprisingly little research has quantified the impact of rodents on plant restoration efforts. In this study, we examined the effects of seed removal and soil disturbance by the giant kangaroo rat (Dipodomys ingens) on native plant restoration in a California rangeland. Using experimental exclosures and stratifying restoration plots on and off rodent-disturbed soil, we assessed the individual and combined effects of seed removal and soil disturbance on seedling establishment of four native plant species. Across all species, biotic soil disturbance by kangaroo rats reduced seedling establishment by 19.5% (range = 1-43%), whereas seed removal reduced seedling establishment by only 6.7% (range = 4-12%). Rates of seed removal across species weakly paralleled kangaroo rat dietary preferences. These results indicate the indirect effects of burrowing rodents such as kangaroo rats on native seedling establishment via changes in soil properties may rival or exceed the direct effects of seed removal. © 2015 Society for Range Management. Published by Elsevier Inc. All rights reserved.
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      Society for Range Management, 2015-07
    • Stocking Rates and Vegetation Structure, Heterogeneity, and Community in a Northern Mixed-Grass Prairie

      Lwiwski, T. C.; Koper, N.; Henderson, D. C. (Society for Range Management, 2015-07)
      Currently, livestock management in the North American Great Plains aims for even use of forage, which creates a homogenous landscape. Reintroducing heterogeneity, defined here as the variation in vegetation structure and composition, to native North American rangelands is imperative to maintaining grassland biodiversity, and using a variety of cattle stocking rates on the landscape could accomplish this. We assessed effects of stocking rates on northern mixed-grass prairie vegetation structure, structural heterogeneity, and plant species diversity. The study took place in Grasslands National Park in Saskatchewan, Canada, using nine pastures (∼300 ha) that were grazed at a range of stocking rates from very low to very high for this region. Three of these pastures were ungrazed controls. We used generalized linear mixed models to describe effects of stocking rate on vegetation over 4 years, following the reintroduction of livestock grazing to this landscape after 15 years without grazing. We used a Mantel test to determine whether plant communities changed with varying stocking rates and over time. Effects of grazing on many response variables were cumulative and changed over time. Species richness in uplands increased with stocking rate and time, but richness decreased with stocking rate in lowlands. Heterogeneity generally increased with stocking rate and time in upland but not lowland habitats. While natural annual variability influenced many variables, the cumulative effects of grazing were still apparent. A variety of stocking rates could be used to maximize structural heterogeneity and provide a diversity of habitat structure at the landscape scale. © 2015 Society for Range Management. Published by Elsevier Inc. All rights reserved.