Effects of topography upon mountain pine beetle (Dendroctonus ponderosae) transport and dispersion as indicated by mesoscale meteorological models

The MPB (mountain pine beetle, Dendroctonus ponderosae) is a natural part of the forested ecosystem at endemic population levels. However, due to recent weather conditions and an abundance of mature LPP (lodgepole pine, Pinus contorta), population levels have reached epidemic proportions in several regions of British Columbia. The current outbreak stretches approximately 4.2 million hectares, the largest in the history of the province. Resource managers have recognized the importance of documenting the advance of the MPB through aerial photography (to assess the spatial extent of the previous year’s population) and ground data collection (to determine the spatial extent of newly infested stands). Production of a predictive model of MPB dispersion has the potential to direct ground surveys of MPB infestation and therefore reduce costs. Employing atmospheric models to determine the extent of MPB dispersal, especially over the longer ranges (i.e. between stands) should provide a regional visualization of spatial infestation extent that could become a useful tool for resource managers. As a preliminary step in the production of the full MPB dispersal model, this research seeks to validate the models used and explore fundamental relationships between MPB dispersal and local topography. This research consists of two main parts: validation of the models used in the study with a SO2 case study and determination of fundamental relationships between topography and MPB dispersal. While the accuracy of the two models has been shown in other meteorological studies, they are tested locally (in the Prince George region) by using a case study of sulfur dioxide dispersion for which there are known sources and an existing monitoring network. In terms of the basic modeling process, both portions follow the same general procedures. RAMS is run to produce the 3-dimensional meteorological fields necessary to run HYPACT in dispersing the particles (MPB). The differences between the realistic SO2 case study simulation and the topographical MPB dispersal studies are that the topography of the domain is artificial and initialization is relatively simple in order to fully visualize the effect of topography on local wind circulations. Once RAMS begins running, the topography creates complexity in the wind field due to thermal influences. As a control, a completely flat landscape has first been simulated within RAMS. Two other landscapes consist of a sinusoidal mountain-valley system running in either a north-south or an east-west direction. This tests the effect of each of 4 different aspects (north-, south-, east- and west-facing slopes) with various slopes at different points on the curve at potentially limiting MPB transport and dispersal over the landscape. HYPACT emits an assumed number of beetles at specified sites within the domain. Several sites are tested in each domain to determine the effect of release site on resultant concentration. Using wind fields produced by RAMS, concentration plots are produced. The plots for each landscape are statistically compared, point by point, to the control to determine if an effect is present and if one is found, which topographical conditions offer the greatest forcing on dispersion of MPB.