Abstract
The Northern Idaho Ground Squirrel (Urocitellus brunneus) is listed as threatened under the Endangered Species Act. It is also an endemic species existing only in the Adams and Valley counties of Idaho. The prevailing hypothesis for the species decline is encroachment of trees into its habitat resulting from fire suppression, referred to as the "fire suppression hypothesis". However, this hypothesis has not been rigorously tested. Using geographic information systems and aerial imaging, changes in abundance of the squirrels' populations were compared to changes in forest canopy coverage over the past 40 years. These comparisons allowed testing of the prevailing hypothesis for the population declines of this rare species by examining the prediction that forest fire suppression has allowed tree growth and encroachment into the squirrel's habitat. The fire suppression hypothesis predicts that the areas with the most pronounced population declines of Northern Idaho Ground Squirrels will have the most pronounced forest encroachment in the areas used by these squirrels. Results show a 50% increase in tree cover over the current and the historical range for the last 40 years. Analysis is still ring on an population scale. The large-scale tree-cover data results suggest that the fire suppression hypothesis is supported, though results are unclear when including comparisons of large-scale population data. Individual population comparison results are not yet complete.