GROUNDWATER DEPENDENT ECOSYSTEMS AND THEIR RESILIENCY AGAINST LANDSCAPE CHANGE IN THE WYOMING ROCKY MOUNTAIN HEADWATERS

The Snowy Range Mountains, located in Wyoming’s Medicine Bow National Forest (MBNF), are found in the central Rocky Mountain region and are headwater to the North Platte and Laramie Rivers. The Rocky Mountains have experienced many ecohydrological shifts including reduced snowpack, decreased soil moisture, and multiple vegetation disturbances from drought, bark beetle epidemics, and wildfire. Most notably, the MBNF has experienced a multi-decade bark beetle epidemic where dead trees supplied fuel for a 716 km² fire in 2020 that spurred intense tree kill and soil burn. Lodgepole pines, the dominant MBNF species normally follow a recovery trajectory following canopy fire through the spread of serontinous cones, but in many bark beetle kill areas these cones were not viable to produce new seedlings and promote regeneration. However, seedling regeneration has been observed near wetland springs and perched aquifers. Mature trees that were completely untouched by fire in groundwater supported areas are able to send their viable seedlings and promote forest regeneration to transition areas. The stability that groundwater provides to these ecosystems remains unknown at the landscape scale. In this study, multiple lines of evidence are used to evaluate the ecohydrological setting of wetland springs and their role as hydrologic refugia in the MBNF along a 36 km transect from the headwater region where forests are recovering. This transect is a hillslope gradient that ranges from 2,400 to 3,600m amsl where snow varies from 0.8 m at 2,400m to 1.2 m at 3,500m amsl. Stable isotopes, geochemistry, historical well data, and current hydrological monitoring are used to evaluate the conditions for forming groundwater dependent ecosystems that support forest recovery after one or more disturbances. Results yield new insights into groundwater flow systems in mountain watersheds threatened by climate change and the conditions in which these flow systems function to enhance forest recovery after disturbance.