*Determining the Effects of Livestock Grazing on Yosemite Toads (Bufo canorus) and Their Habitat

Amy Lind

USDA Forest Service, Sierra Nevada Research Center,
Davis, CA

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ABSTRACT

LIND, AMY1*, ROBERT GRASSO1, SEAN PARKS1, PETER STEIN1, BARBARA ALLEN-DIAZ2, SUSAN McILROY2, KEN TATE3, LESLIE ROCHE3, WILLIAM FROST4, and NEIL McDOUGALD4
1USDA Forest Service, Sierra Nevada Research Center, Davis, CA, alind@fs.fed.us; 2College of Natural Resources, Univ. of California, Berkeley, CA; 3Dept. of Plant Science, Univ. of California, Davis, CA; 4Univ. of California, Cooperative Extension, Division of Agriculture and Natural Resources.

Determining the Effects of Livestock Grazing on Yosemite Toads (Bufo canorus) and Their Habitat.

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. Our goal is to better understand the relationships between livestock grazing and Yosemite toad populations and habitats. The study has two complementary components. Phase I will capitalize on existing data and we will use correlative multivariate analyses to relate toad occupancy at a large number of meadows (n > 50) to a set of environmental variables (both GIS and field-derived) as well as livestock grazing history. Phase II is an experimental study of 20 meadows on the Stanislaus and Sierra National Forests. Four livestock grazing treatments are being implemented in 5 replicate blocks (= grazing allotments): (1) no grazing within the entire meadow, (2) no grazing within breeding areas, (3) grazing to utilization standards throughout the meadow, and (4) historically ungrazed reference meadows. Baseline data were collected in 2005 for 15 meadows; candidate ungrazed meadows were surveyed and final selections will be made in spring 2006. Treatments will be implemented in summer 2006 and meadows will be studied for a minimum of three years. In 2005, we collected data on toad breeding areas, larvae, and metamorphic toads and environmental data at both meadow and local (toad-centric) scales. Environmental data included: meadow topography, plant composition, hydrologic characteristics, water quality, and livestock utilization. We also tested methods for counting tadpoles and marking all life stages of toads. Future analyses will focus on developing toad habitat models and relating toad population status and habitat requirements to livestock utilization levels.

Mountain Yellow-legged Frog Breeding Dynamics in Dusy Basin, Kings Canyon Nat'l Park: ... Snowpack ... Lake Water Level (and) recruitment...

Krishna Feldman

USDA Forest Service, Pacific Southwest Research Station

Berkeley, CA

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ABSTRACT

MATTHEWS, KATHLEEN R.1, KRISHNA V. FELDMAN1*, and IGOR LACAN2
1USDA Forest Service, Pacific Southwest Research Station, Berkeley, CA, kmatthews@fs.fed.us; 2University of California, Berkeley, Department of Environmental Science, Policy and Management, Berkeley, CA

Mountain Yellow-legged Frog (Rana muscosa) Breeding Dynamics in Dusy Basin, Kings Canyon National Park: How do Variable Snowpack and Lake Water Levels Affect Recruitment?

Our 1997-2005 surveys of mountain yellow-legged frogs in Dusy Basin found that most breeding (>70% of egg masses) occurred in shallow (<3m) lakes prone to late summer drying. Up to 4 years of tadpole recruits can be lost when lakes dry due to their extended tadpole phase. In upper Dusy Basin, more than 60% of egg masses were found in one shallow lake (max depth = 1m) that often undergoes a dramatic decrease in volume during years with low snowpack and precipitation. This breeding lake was totally dry by the end of the summer in 4 of 9 years; presumably, all tadpoles died because there was no connectivity to other water bodies. More breeding may now occur in shallow lakes vulnerable to drying because the largest lake in upper Dusy Basin has fish. Few egg masses were found in this larger, deeper lake (max depth = 10 m) either because frogs no longer breed in this lake or egg masses are quickly eaten by fish and not observed in surveys. Other lakes used for breeding are deeper and did not totally disappear in the low snowpack years. In lower Dusy Basin, over 90% of egg masses are found in one (max depth = 1.5 m) of four adjacent lakes; this lake has not dried up in surveys conducted from 1998-2005. To determine if there is a link between water availability and recruitment into adults, we compared the number of metamorphs in breeding lakes prone to drying with those breeding lakes not prone to drying. The lakes that intermittently dry up show low recruitment of metamorphosed frogs. The exclusion of successful frog breeding from the deepest lakes where recruitment may be more successful is another impact of introduced fish on this declining frog population.