Southwest Geographic Science Team

:: Wild Sheep Habitat

Climatic Changes and the Effect on Wild Sheep Habitat

Dall's sheep in Denali National Park

Introduction

This study investigates the effects of glacial retreat and loss of historic snowfields on wild sheep habitat in the Alaska Range and Wrangell Mountains of Alaska through analysis of historical (multidecadal) datasets and repeated field observations.  Two study areas are examined, one within Denali National Park and the other in the Wood River area southeast of Fairbanks, Alaska.  We hypothesize that climatic changes are altering the traditional habitat of high-mountain large mammals, particularly Dall’s sheep.  Wild sheep are sensitive to environmental change and may be an effective indicator species of climate change in arctic and high mountain ecosystems.  Our research plans include expanding the geographic scope to include wild sheep habitats in central Asia and possibly far-eastern Russia through collaboration with Dr. Rob Ramey (private consultant) and Dr. Raul Valdez, (Dept. of Fish, Wildlife, and Conservation Ecology, New Mexico State Univ.) 

Methodology

Glaciers near the Wood River study areaA variety of remotely-sensed data, ground-based observations, and existing historic databases are the primary sources from which land-cover information for the study areas is derived.  Landsat satellite imagery is employed to determine glacial retreat and aerial extent over four time periods (1979, 1987, 1994, and 2000).  Change detection datasets and other products will be generated to analyze glacial and phenological change during this multidecadal period.  These products assist in determining variability in land-ice coverage and assessment of its relation to the health and overall condition of the wild sheep habitat.  Historical aerial photography, topographic maps, and historical reports support additional interpretation and provide information on snow and ice distribution prior to availability of satellite data.

MODIS, Landsat, and Quickbird satellite imagery are employed to analyze phenological change at very high (MODIS) and moderate (Landsat) temporal resolutions, along with visual observations (both historic and contemporary) of general habitat health and favored habitat of wild sheep populations.  Analysis of landscape phenology provides information on the integrated response of plant species to climate as reflected in the timing, intensity, and duration of vegetation greenness.  Quickbird imagery is used to capture vegetation pattern and structure, which allows mapping of generalized vegetation types, including woody vs. non-woody vegetation.  GPS points are collected along vegetation transects and within distinct vegetation types to aid in developing vegetation maps of the study areas.  Various phenological, spatial and structural metrics are derived from these data and summarized to define and characterize the observed landscapes.  NDVI products are developed to construct baseline phenology datasets at increasingly higher spatial resolutions of the study areas in Denali National Park and the Wood River area.  The objective is to analyze these data in conjunction with earlier Denali National Park vegetation maps to detect and evaluate vegetation changes in sheep habitat, such as the suspected up-slope encroachment of woody plants in Denali.

Unnamed glacier in the Denali study areaAdditional datasets are being developed to validate apparent phenological changes in Dall’s sheep habitat resulting from glacial, permanent snowfield, and permafrost melting.  These supplemental datasets include GPS points for ground-truth locations mapped using Quickbird and Landsat imagery. Wild sheep feces are being collected and analyzed for nutrient value, digestibility, and vegetation species composition.  In addition, water samples from the base of glaciers, snowfield melt, and permafrost melt are being collected and analyzed for nutrient levels.

By combining the field observations with satellite-based products, the research is aimed at developing a reliable model of habitat change.  Analysis of remotely-sensed data will be coupled with the fecal analysis to assess the nutritional value, digestibility (stress), and species composition of the wild sheep forage and its relation to climatic change.  Subsequent collection of remotely-sensed data will be used to map changes in these landscapes through time.  Such an analysis permits evaluation of changes in the overall quality of wild sheep habitat based on the inferred nutritional value of each landscape type, and provides a means to monitor habitat quality through time.

Once a reliable set of baseline data has been collected and analyzed, models will be developed to predict changes that may occur in the health (nutrient level) of the habitat and forage due to changing climate conditions.

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