Cattle Grazing and Conservation of a Meadow-Dependent Amphibian Species in the Sierra Nevada

Abstract

World-wide population declines have sharpened concern for amphibian conservation on working landscapes. Across the Sierra Nevada's national forest lands, where almost half of native amphibian species are considered at risk, permitted livestock grazing is a notably controversial agricultural activity. Cattle (Bos taurus) grazing is thought to degrade the quality, and thus reduce occupancy, of meadow breeding habitat for amphibian species of concern such as the endemic Yosemite toad (Anaxyrus [ = Bufo] canorus). However, there is currently little quantitative information correlating cattle grazing intensity, meadow breeding habitat quality, and toad use of meadow habitat. We surveyed biotic and abiotic factors influencing cattle utilization and toad occupancy across 24 Sierra Nevada meadows to establish these correlations and inform conservation planning efforts. We utilized both traditional regression models and Bayesian structural equation modeling to investigate potential drivers of meadow habitat use by cattle and Yosemite toads. Cattle use was negatively related to meadow wetness, while toad occupancy was positively related. In mid and late season (mid July–mid September) grazing periods, cattle selected for higher forage quality diets associated with vegetation in relatively drier meadows, whereas toads were more prevalent in wetter meadows. Because cattle and toads largely occupied divergent zones along the moisture gradient, the potential for indirect or direct negative effects is likely minimized via a partitioning of the meadow habitat. During the early season, when habitat use overlap was highest, overall low grazing levels resulted in no detectable impacts on toad occupancy. Bayesian structural equation analyses supported the hypothesis that meadow hydrology influenced toad meadow occupancy, while cattle grazing intensity did not. These findings suggest cattle production and amphibian conservation can be compatible goals within this working landscape.

Montane meadow hydropedology, plant community, and herbivore dynamics

“…Vegetation is characterized by a dense cover of largely perennial graminoid and herbaceous species. For the enrolled meadows, meadow-scale peak herbaceous biomass production ranged from 1000 to 3300 kg/ha (based on monitoring data from -2008Roche et al 2012). …”

“…Meadows were grazed by cattle under normal U.S. Forest Service allotment management, and were subject to annual grazing standards for (1) herbaceous vegetation use (remove no more than 35% of current year's forage production); (2) riparian woody plant use (remove no more than 20% of current year's leader growth); (3) streambank disturbance by livestock (no more than 10% of streambank physically damaged by hoof impact); and (4) streambank vegetation height (maintain a mini-mum of four inches) (Clary and Webster 1990, Hall and Bryant 1995, Clary and Leininger 2000, Freitas et al 2014. For the enrolled meadows, average meadow-scale herbaceous forage use by cattle over three grazing seasons ranged from 0 to 50% (based on monitoring data from -2008Roche et al 2012). …”

“…A meadow patch hydrologic rating scale was previously developed and calibrated at 31 sites within 10 study meadows equipped with ground water wells and monitored intensively throughout three years, 2006through 2008(see McIlroy and Allen-Diaz 2012, and Roche et al 2012 for data and analyses). All 115 sample sites in this study were categorized along this relative wetness scale with scores ranging from 0 to 6, as integers (Roche et al 2012).…”

“…All 115 sample sites in this study were categorized along this relative wetness scale with scores ranging from 0 to 6, as integers (Roche et al 2012). Sites were rated based on extent and timing of surface flooding and saturation, dominant plant functional groups (e.g., wetland obligates), and hydric soil indicators (mineral vs. organic layers, depth of peat accumulation in organic soils, and abundance of redox concentrations and depletions in mineral soils).…”

“…These diverse meadow systems provide flood water retention and sediment stabilization, maintain summer stream base flows, and support unique habitat and forage resources for pollinators, wildlife, and domestic grazing animals (Hatfield and LeBuhn 2007, Roche et al 2012, Acreman and Holden 2013. Meadows are important regional carbon and nitrogen sinks (Norton et al 2011), and support species-rich plant communities distinct from the surrounding forest matrix (Allen-Diaz 1991, Kuhn et al 2011).…”