Maternal Dall’s Sheep Habitat in Chugach State Park: Application of Landsat, MODIS and ASTER Satellite Imagery to Detect Vegetation Community Transition via Time Series Analysis

Nursing Dalls Sheep ewes and their lambs are nutritionally dependent on the flora occurring in protective "escape terrain”. This habitat is defined as steep terrain with rocky outcroppings interspersed with talus and narrow swaths of dwarf shrub tundra. One hypothesis states that changes in this specific and localized habitat via climate mediated, low-shrub expansion may be reducing the nutritive value of this "escape terrain". A possible mechanism contends that that less nutritious low shrubs (> 0.5m Alnus spp., Salix spp.) may be supplanting the highly nutritious dwarf shrub tundra formerly present within “escape terrain”. If such a transition in vegetation were occurring, maternal ewes may have less access to nutritious forage leading to a reduction in fecundity resulting in the observed and documented population declines.
Using a 30 year time series (1986 - 2016) of satellite observations compiled from Landsat, MODIS and ASTER platforms, the objective of my study is to detect and quantify changes in Dall’s sheep lambing habitat within Chugach State Park. Using spectral classification techniques, the research will 1) assess the quantity of previously un-vegetated bare ground that has been converted into vegetated ground; 2) monitor the change within vegetated areas by assessing “greenness” covariate values as reported by NDVI and Tasseled Cap indices; and 3) conduct field vegetation surveys to ground-truth satellite observations; 4) and to measure the composition and age structure of vegetation communities located in sheep lambing habitat near “escape terrain”. Detection of habitat change via these methods in combination with applied statistical modeling techniques will provide insight into how climate-mediated vegetation succession could impact Dall’s sheep habitat and thus future populations.