Research Topics Ecosystem Processes
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Tropical Ecosystems |
Sierra Nevada Ecosystems
Sierra Nevada Ecosystems
About this Research:
Determining the Effects of Livestock Grazing on Yosemite
Toads (Bufo canorus) and their Habitat: An Adaptive Management Study.
Research Project Summary
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
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.
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:
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
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
Methods and Design
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
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.
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
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
2) University of California, Berkeley
3) University of Calfiornia, Davis
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.