UC Davis Department of Plant Sciences

Cattle Grazing, Mountain Meadows, and Sensitive Species

Keywords – amphibian, Yosemite toad, forage quality, Bayesian structural equation modeling, multiple-use, US Forest Service, water quality

Participants Leslie Roche, D.J. Eastburn, Andrew Latimer, Barbara Allen-Diaz, Bill Frost

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Sierran foothill ranching operations depend on government-owned rangeland during dry summer months when annual grasslands enter the inadequate dry forage period.

On public lands, mountain meadows are part of a working landscape, which is managed to balance a multitude of economic, social, and ecological goals. Meadows provide multiple ecosystem services, including maintaining landscape hydrologic functioning, serving as regional C sinks, and supporting distinct plant communities important to both wildlife habitat and domestic cattle grazing. Cattle grazing on public lands is a particularly controversial activity, especially in high elevation ecosystems. Public lands grazing permits generally support low-intensity cattle operations on privately owned lands in the Sierran foothills. These ranching operations depend on government-owned rangeland during dry summer months when annual grasslands enter the inadequate dry forage period. Due to their intrinsic residential value, Sierran foothill ranches are highly susceptible to urban development. For these reasons, some suggest broad-scale reductions in public grazing permits would greatly impact the viability of foothill ranches, forcing owners to sell lands to developers, which would have negative regional socio-economic and ecological implications. However, opponents of public lands grazing maintain that cattle grazing in high elevation ecosystems has intolerable negative impacts on native wildlife species and their habitats.

Due to growing public concern surrounding cattle-wildlife interactions, and impacts of cattle grazing in general, some Sierra Nevada grazing permits have been terminated, and seasonal restrictions have been applied to many remaining active permits. Recently, the issue of potential cattle grazing impacts on an endemic species, Yosemite toad, has become a key example in which there have been disconnects between science and management. Since 2001, there have been considerable management changes based on a suspected linkage between toad population declines and cattle grazing; however, there has been a lack of quantitative evidence supporting this issue. This research was part of a larger collaborative effort, the Yosemite Toad Adaptive Management (YTAM) Project, between the USDA Forest Service-Pacific Southwest Region, UC Berkeley, and UC Davis. The YTAM team was formed to address these gaps in scientific knowledge. The overall project included multiple experimental approaches to investigate the potential impacts of cattle grazing on a sensitive amphibian species, Yosemite toad (Bufo canorus Camp), and its meadow habitat.

You can reach the full report here (view report here >>).     

Our research team addressed two specific studies within the overall project. In the first study, we investigated the potential to alleviate possible negative grazing impacts on hydrologic, water quality, and cover habitat conditions via cattle exclusion treatments. Our objectives were to: 1) determine associations between breeding pool habitat conditions and use of potential breeding pools by toads, and 2) determine how habitat conditions respond to cattle exclusion treatments on the Sierra National Forest, California. We randomly selected two toad occupied and two unoccupied breeding pools in each of 9 meadows for this study (n=36 breeding pools). After baseline data collection in 2006, three meadow fencing treatments were implemented over the course of 3 years. Treatments were fencing to exclude cattle from the entire meadow; fencing to exclude cattle from potential toad breeding and rearing areas, with grazing allowed in the remaining unfenced portion of the meadow; and cattle grazing allowed across the entire meadow. We monitored hydrologic, water quality, and cover habitat factors as well as toad occupancy during the breeding seasons of 2006 through 2008. Concentrations of water quality constituents were uniformly low all years, regardless of treatment. Occupied pools were shallower, warmer, and more nitrogen enriched than unoccupied breeding pools (Fig. 1). We found no evidence of improved toad breeding pool habitat conditions following fencing compared to standard US Forest Service grazing management. See YTAM report for details (view report here >>).

   
  Figure 1. Mean values for habitat metrics which were significantly different (P < 0.05) among Yosemite toad breeding pools occupied 0 of 4 years, 1 to 3 of 4 years, and 4 of 4 years during the period 2005 through 2008. Bars are 1 S.E. of mean.    

 

In the second study, we explored a broader systems approach to the cattle-amphibian interaction question utilizing a Bayesian structural equation modeling approach. We conducted a three year, cross-sectional observational survey of cattle grazing intensity and Yosemite toad occupancy of meadows across the extensive grazing landscape. We surveyed biotic and abiotic factors influencing cattle utilization and toad occupancy across 24 meadows to investigate potential associations between grazing and amphibian occurrence and inform conservation planning efforts. Table 1 summarizes the general site characteristics of meadows enrolled in this study.

 

Table 1. Population of inference for cross-sectional observational study


Toad occupancy, cattle utilization, plant community, and hydrologic data were collected within each meadow. Cattle use was negatively related to meadow wetness, while toad occupancy was positively related to meadow wetness. In mid and late season (mid July through mid September) grazing periods, cattle selected for higher forage quality diets associated with drier meadows (see Figs 2 and 3).

Figure 2. Toad occupancy and annual cattle utilization along a hydrologic gradient of meadows during 2006 to 2008. Toad occupancy rate is calculated as proportion of surveys (three total; 2002/2003, 2007, and 2008) each meadow was occupied. + For fractional logistic regression of toad occupancy rates (panel a), R2 value is from linear regression of predicted values vs. observed values.

 
     

 


  Figure 3. Mid season (August) cattle use and forage quality along a hydrologic gradient of meadows.
     


Bayesian structural equation model analyses supported the hypothesis that meadow wetness had a greater magnitude of influence on toad meadow occupancy than cattle grazing intensity (Fig. 4).

 

Figure 4. Results of Bayesian structural equation modeling for early, mid, and late season cattle use and forage data.  All models suggest toad presence responds to variation in meadow wetness, rather than cattle utilization levels. + = fixed values, ** = 95 % Bayesian credible interval, * = 90 % Bayesian credible interval, NS = Not significant.

 

Overall, this approach allowed us to capitalize upon the variability in the system and investigate a continuum of grazing, which has greater applicability to these extensive grazing systems than more traditional grazed versus ungrazed treatment approaches.

Collectively, these studies illustrate the importance of wet meadow habitat to the conservation of Yosemite toad populations. Factors likely to affect habitat availability include climate change (e.g., increased frequency and severity of drought events and/or flood events), forest successional dynamics, improper grazing management, and hydrologic meadow restoration (Fig 5).



 
 

Figure 5. Conceptual model of landscape-level factors potentially influencing Yosemite toad habitat.

 


 

 

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