HYDROLOGIC AND SOIL CHARACTERISTICS OF UNCOMPAHGRE FRITILLARY BUTTERFLY (CLOSSIANA IMPROBA) HABITAT, SAN JUAN MOUNTAINS, COLORADO

Endangered species management requires a holistic understanding of the biological, environmental, and hydrologic factors that contribute to habitat livability. This study examines changes in soil moisture, rainfall, stream levels, and water source in and around Uncompahgre Fritillary Butterfly (Clossiana improba) colonies in an attempt to understand how alpine soil hydrology impacts habitat livability. The habitat requirements of the federally endangered C. improba are poorly understood. C. improba occupies northeast facing patches of snow willow (Salix nivalis) at elevations around 4,000m in the northern San Juan Mountains, Colorado. However, many patches of S. nivalis meeting all of these criteria are unoccupied for unknown reasons.

Soil moisture data from six different sites in and around C. improba colonies demonstrate that soil moisture is highly heterogeneous, with season long averages ranging from 0.13 +/-0.035 to 0.44 +/- 0.05 m³/m³. Soil moisture generally increased in response to rainfall events of 0.04” or more both instantaneously and over longer periods of time, but the exact response of different sites is variable. Isotopic data collected during the summer of 2017 suggest that the majority of soil water originates from snowmelt, with increasing contributions from rainfall later in the season. Finally, stream discharge near the Uncompahgre Peak butterfly colony fluctuates daily, with minimum stream flow occurring approximately eight-hours after peak temperature and evapotranspiration. Soil moisture, stream flow, and rainfall data were collected during the summer of 2018, an extreme drought year. In total, these data describe a complex and variable hydrologic system. Basal moisture levels originate from snowmelt, but change in response to subsequent rainfall events. An understanding of alpine soil hydrology will be useful for future management in the face of a changing climate. As the climate warms, the San Juan Mountains are expected to see decreased snowfall and earlier snowmelt. These changes will drastically alter the hydrology of alpine areas, possibly with serious consequences for sensitive species like C. improba.