Ecohydrology of an outbreak: mountain pine beetle impacts trees in drier landscape positions first

Vegetation pattern and landscape structure intersect to exert strong control over ecohydrological dynamics at the watershed scale. The hydrologic implications of vegetation disturbance (e.g. fire, disease) depend on the spatial pattern and form of environmental change. Here, we investigate this intersection at Tenderfoot Creek Experimental Forest (TCEF), Montana, with a focus on the mountain pine beetle (Dendroctonus ponderosae) epidemic currently affecting the Rocky Mountains. We calibrated QuickBird remote sensing imagery with a leaf-level spectral library of local vegetation. We used this spectral library to determine diagnostic vegetation indices for differentiating stages of beetle infestation within the 37 km TCEF watershed. These indices formed the basis of a three-component mixing model to establish the extent and magnitude of beetle infestation across the TCEF watershed. We compared disturbance patterns with spatially distributed topography and vegetation variables derived from a light detection and ranging-based digital elevation model of TCEF. We determined that certain landscape characteristics (low vegetation density, south-facing slopes, steep slopes, locations with small contributing areas and locations with lower values of the topographic wetness index) were significantly more likely to exhibit the effects of beetle infestation. Our efforts to monitor vegetation mortality across space and time provide a context for assessing landscape susceptibility to initial mountain pine beetle infestation and how outbreak (i.e. landscape scale infestation) patterns may affect watershed ecohydrology via altered water and biogeochemical cycles. Copyright © 2012 John Wiley & Sons, Ltd.