Groundwater Supported Vegetation Refugia as a Mechanism of Forest Recovery in a Rocky Mountain Watershed Impacted by Disturbances
Authors
Ye Zhang1* (yzhang9@uwyo.edu), Danielle Berardi1, Xiaonan Tai2, Andrew Parsekian1, Brent Ewers1
Institutions
1University of Wyoming, Laramie, WY; 2New Jersey Institute of Technology, Newark, NJ
Abstract
Groundwater can form consistently wetter land surface areas to support greater ecosystem productivity across scales and climate zones. The research team examined the conditions under which groundwater facilitates forest recovery after disturbance(s) in the Medicine Bow National Forest (MBNF) where logging, bark beetle, and wildfire disturbances occurred in recent decades. For a 40×25 km2 area spanning subalpine to montane forests, field surveys revealed that groundwater-supported forest refugia (GSFR) occur along the entire elevation gradient in the form of forested/shrub wetlands, springs, and perched aquifers (Zhang et al. 2023). These features have sheltered trees against one or more disturbances although seed-bearing trees can facilitate forest recovery only if water table is of suitable depth, is persistent, and in the case of wildfire, soil and seeds remained viable after the fire. GSFR can change over time, driven by feedback between disturbance, vegetation response, and hydrology: at a forested and shrub wetland, a 2020 wildfire that burned surrounding uplands may have resulted in a raised local water table that stressed formerly healthy trees in the wetland, casting doubts about its future refugium status. These field observations are being tested at site and landscape scales using a coupled ecohydrological model calibrated against historical and new measurements (i.e., colocated climate, vegetation, soil moisture, and groundwater data). Simulation results suggest (1) for a subalpine wetland and upland site, understory growth must be represented to accurately model post-beetle-kill recovery; (2) at the landscape scale, high average soil moisture surrounding GSFRs maintained evapotranspiration and gross primary productivity during a drought year while the latter half of the growing season saw greater growth; and (3) at both scales, water and light were the limiting factors affecting the growth and survival of tree seedlings. The team will implement a new competition scheme into the model, enabling the seedlings to compete for water and light with coexisting shrubs, grasses, and forbs.
References
Zhang, Y., 2023. “Forest Recovery After Disturbances Facilitated by Groundwater: A Study at the Medicine Bow Mountains in Southeastern Wyoming,” Colloquium, Department of Geosciences, University of Montana.