Time-lapse electrical resistivity tomography observation of subsurface forest ecosystem responses to interacting bark beetle and fire disturbance
Symposium on the Application of Geophysics to Engineering and Environmental Problems 2021
Understanding how disturbance effect forests of the intermountain west is important for ecology, hydrology, and planning human resource usage. In some cases, subsequent disturbances – for example, insect outbreak and fire – may impact the same forest area: the synergistic effects of such a disturbance sequence on carbon and water ecosystem fluxes and interactions with nutrient cycling and vegetation are not fully understood. The location of forest fires is not specifically predictable, and therefore there are relatively few observations of ecohydrological responses during the important first year following fire in areas previously affected by bark beetles. Forest fire is known to effect surface hydrology, such as through the creation of hydrophobic surface layers that influence runoff, however, less is known about the impacts to vadose zone water movement, deep flow, or storage. Furthermore, fire behavior is affected by tree mortality from previous bark beetle outbreaks. This study focuses on a lodgepole pine forest in southern Wyoming where a bark beetle outbreak caused the initial disturbance and was then followed by a 8,500 Ha forest fire disturbance in the summer of 2018, ~10 yr after the peak of the insect outbreak. In order to explore the changes to subsurface hydrology following these subsequent disturbances, we used a time-lapse electrical resistivity tomography transect crossing a gradient from low to high fire severity and spanning four seasons of data acquisition immediately following the fire. Biophysical and soil datasets were also acquired to produce a synoptic view of the surface and subsurface ecohydrological environment. Our results show contrasts across the burned-unburned gradient between vertical velocity of snowmelt water infiltration, heterogeneity of wetting and drying patterns, and total depth of change in storage. These results contribute to improved understanding of water partitioning after and will inform process-based models for prediction ecosystem fluxes in response to interactive disturbances. We anticipate our results to be a starting point for more widespread time-lapse geophysical monitoring of post-disturbance impacts to forest ecohydrology and for exploring controls on the sharpness of disturbance gradients.
Parkesian, A. D.; Bretfeld, M.; Ewers, B. E.; and Frank, J., "Time-lapse electrical resistivity tomography observation of subsurface forest ecosystem responses to interacting bark beetle and fire disturbance" (2021). The Bark Beetles, Fuels, and Fire Bibliography. Paper 488.