| Summary: | Mountain pine beetle (Dendroctonus ponderosae, MPB) is a forest pest endemic to the Rocky Mountain West. Since the late 1990s, millions of hectares of lodgepole pine forest have experienced extensive tree mortality due to MPB disturbance and this may have significant implications for forested mountain water supplies. MPB disturbance may affect the amount of moisture that enters and leaves the forest hydrologic system, through changes in snowpack accumulation, snowmelt timing, transpiration and subsequently soil water content. The cumulative effect of these changes is that soil moisture is expected to be higher in disturbed forests as the hydrologic system responds to increased inputs and the cessation of canopy transpiration that accompanies tree mortality. This research examined how MPB-disturbance affects the forest water balance in three plots in western Montana using direct observation and modeling methods. Peak SWE, snowmelt and post-snowmelt water balance parameters were measured in three study plots: a non-disturbed lodgepole pine plot, a plot consisting of lodgepole pine trees in the advanced stage of MPB disturbance, and a nearby clear cut. No significant differences in peak SWE and snowmelt timing were measured between the MPB-disturbed and non-disturbed due to the higher stand density and basal area. However, post-snowmelt measurements of soil moisture, rainfall, understory evapotranspiration and canopy transpiration indicated higher net precipitation and understory evapotranspiration in the MPB-disturbed plot. Additionally, soil moisture was higher in the MPB-disturbed plot, which was likely explained by the absence of canopy transpiration fluxes. Additionally, beyond the factors quantified in this initial study, it is likely that topography and variability in stand characteristics played an important role for observed differences in soil water content. This study provides first steps towards assessing the implications of MPB for changes in mountain water supplies in forested catchments. Future work should seek to use additional study plots with more similar stand characteristics and local topography.
|
|---|
