Pacific Southwest Research Station

Pacific Southwest Research Station
800 Buchanan Street
West Annex Building
Albany, CA 94710-0011

(510) 559-6300

Research Topics Ecosystem Processes

Title

Determining the Effects of Livestock Grazing on Yosemite Toads (Bufo canorus) and their Habitat: An Adaptive Management Study.

Study Plan
Research Project Summary

The Research

This study is a collaborative effort between the USDA Forest Service, Region 5 (California) and Pacific Southwest Research Station, Sierra Nevada Research Center; and the Universities of California, Davis and Berkeley. The primary goal of the study is to better understand the relationships between livestock grazing and Yosemite toad populations and habitats.

The Yosemite toad (Bufo canorus) is endemic to the Sierra Nevada mountain range from Alpine County south to Fresno Co at elevations from between 1950 and 3450 m (6400 to 11,300 ft). Yosemite toads are typically associated with high montane and subalpine wet meadows and shallow lake shores surrounded by forests of lodgepole pine or whitebark pines. Yosemite toads are believed to have declined or disappeared from at least 50% of known localities during the later part of the 20th century. Long-term monitoring data at Tioga Pass indicates large declines in local populations since the early 1980's although the cause for this decline is unclear. Yosemite toads are a Species of Special Concern in California, a Forest Service Region 5 sensitive species, and a candidate species for federal listing under the Endangered Species Act.

Because of their association with shallow water areas in montane meadows, suspected factors in the decline of Yosemite toads include: livestock grazing, airborne chemical toxins, disease, and climatic shifts and variability (especially temperature and precipitation). Preliminary evidence suggests that livestock use of wet meadow habitats may affect Yosemite toads through: (1) changes to meadow stream hydrology and bank stability (increased down-cutting and head-cutting), (2) changes to water quality, and (3) changes in micro-topography of egg deposition and larval rearing areas. The extent of these potential effects and their relationship to toad population survival and persistence has not been quantified. The results of this study will provide guidance to land managers who are faced with decisions regarding human and livestock use of montane meadows and to better understand the role that livestock grazing may be playing in the decline of the Yosemite toad.

Objectives

The overall objective of this study is to understand the effects of varying levels of livestock grazing on Yosemite toad populations and habitats. USDA Forest Service Region 5 staff formulated two key questions to guide this research:
Does livestock grazing under Forest/Sierra Nevada Forest Plan Amendment Riparian Standards and Guidelines (2004) as represented by the following four treatments have a measurable effect on Yosemite toad populations?
* Grazing in accordance with current utilization and streambank disturbance standards
across the entire meadow.
* Exclusion of livestock in wet areas within a meadow.
* No Grazing within the meadow.
* Ungrazed meadows (not grazed within recent history).

What are the effects of livestock grazing intensity on the key habitat components that affect survival and recruitment of Yosemite toad populations?

Methods and Design

The project is based upon two complementary study designs (described here as Phases I and II) both focused on achieving the established study objectives. The experimental unit for each phase is an individual meadow. Phase I is an observational, cross-sectional survey of a large set of meadows (n>50) which will be sub-sampled from the population of interest (i.e. gradients of toad occupancy and livestock grazing levels throughout the geographic range of the Yosemite toad). Cattle grazing management is not manipulated on-the-ground; rather we are taking opportunistic advantage of the diversity of grazing management which exists across in the Sierra Nevada historically and more recently. This design is based upon the quantification (directly measure) and/or classification (assign to a category such as "low" or "high") of toad population, habitat, vegetation, and cattle grazing variables. Multivariate analysis of these variables in conjunction with covariates (e.g., elevation, meadow size) is then used to identify and quantify associations between toad population, habitat, and specific grazing management factors dependent upon site specific conditions.

Phase II is the experimental component of the study in which cattle grazing is the treatment. Four levels of cattle grazing are being examined. Cattle grazing treatment levels are: 1) compliance with annual grazing standards and guidelines as defined in the most recent Sierra Nevada Forest Plan Amendment (2004); 2) exclusion of cattle from wet areas of the meadow; 3) exclusion of cattle from the entire meadow; and 4) ungrazed by cattle for >15 years (referent condition). Baseline data is being collected in year 1 (2005), and grazing treatments will be implemented and maintained during years 2 through 5 of this study. We are using a randomized complete block design based upon collection of data before and after implementation of grazing treatments across 15 meadows (5 pseudo-replicates of 3 grazing treatment levels), with the inclusion of 5 referent condition meadows to serve as a baseline across the study period (20 meadows total). All study meadows have extant populations of Yosemite toads. This phase of the study will generate data on a large number of dependent or response variables, requiring multiple analyses (development of statistical models for each response variable). Dependent variables available for analysis will be metrics of toad population (e.g., # of toads by life stage, ratios of life stage abundances, density of breeding areas per meadow), habitat (e.g., water temperature, aquatic plant cover), and vegetation (e.g., species cover, diversity, structure). Independent variables will be grazing treatment, which has 4 levels, and year, of which there will be five. Covariate data from each meadow will be available for a suite of static and dynamic factors (e.g., lotic v. lentic, elevation, past grazing pressure, annual pack-stock use, annual snowfall).

Application of Research Results

Results of the study will be presented to Forest Service Regional office and National Forest staff. Once particular phases of the study are complete, we will provide an analysis of effects of grazing treatments and standards and guidelines on Yosemite toad populations and habitat and recommendations for future livestock grazing management.

Location

The extensive scale, correlative component of the study (Phase I) will utilize existing data and strategically collected new data from sites throughout the range of the toad that represent a both a gradient of recent and historic livestock grazing levels and a gradient of Yosemite toad occupancy levels.
The experimental component of the study (Phase II) will take place on at least 15 meadows in active livestock grazing allotments and 5 adjacent ungrazed meadows on the Sierra and Stanislaus National Forests.

Lead Scientists/Collaborators

1.)Lind, A. 1.) Stine, P. 1) Grasso, R. 1) Parks, S. 2)Allen-Diaz, B. 2) McIlroy 3)Tate, K. 3) Frost, B. 3) McDougald, N. 3) Roche, L. 4)Brown, C.

1)USDA Forest Service
Pacific Southwest Research Station
Sierra Nevada Research Center
ph: 510-530-1700

2) University of California, Berkeley
Berkeley, CA

3) University of Calfiornia, Davis
Davis, CA

4) Stanislaus National Forest

Publications and Products

The study plan for this project is currently complete.

* We have created a draft envirogram for the Yosemite toad which depicts the documented and suspected ecological relationships of the species. We are using the envirogram as a tool for developing working research hypotheses and for tracking new information that results from this study and via literature review.