%0 Journal Article
%T Spatial Dispersal of Douglas-Fir Beetle Populations in Colorado and Wyoming
%A John R. Withrow
%A John E. Lundquist
%A Jos¨¦ F. Negr¨®n
%J ISRN Forestry
%D 2013
%R 10.1155/2013/542380
%X Bark beetles (Coleoptera: Curculionidae: Scolytinae) are mortality agents to multiple tree species throughout North America. Understanding spatiotemporal dynamics of these insects can assist management, prediction of outbreaks, and development of ¡°real time¡± assessments of forest susceptibility incorporating insect population data. Here, dispersal of Douglas-fir beetle (Dendroctonus pseudotsugae Hopk.) is estimated over four regions within Colorado and Wyoming from 1994 to 2010. Infestations mapped from aerial insect surveys are utilized as a proxy variable for Douglas-fir beetle (DFB) activity and analyzed via a novel GIS technique that co-locates infestations from adjacent years quantifying distances between them. Dispersal distances of DFB infestations were modeled with a cumulative Gaussian function and expressed as a standard dispersal distance (SDD), the distance at which 68% of infestations dispersed in a given flight season. Average values of SDD ranged from under 1£¿kilometer for the region of northwestern Colorado to over 2.5£¿kilometers for infestations in Wyoming. A statistically significant relationship was detected between SDD and infestation area in the parent year, suggesting that host depletion and density-dependent factors may influence dispersal. Findings can potentially provide insight for managers¡ªnamely, likelihood of DFB infestation increase for locations within two to five kilometers of an existing infestation. 1. Introduction The Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins, (DFB hereafter) is a major mortality agent of Douglas-fir, Pseudotsuga menziesii (Mirbel) Franco, across the Western United States [1, 2]. As a native insect and a natural disturbance agent, it is always present as an endemic influence, playing an important ecological role by killing diseased or otherwise stressed trees. DFB exhibits one generation per year and attacks new hosts every year during its dispersal flight from early spring and through the summer depending on geographic location. The insect overwinters primarily in the adult stage and as larvae inside the host tree [2]. Population levels increase periodically, resulting in widespread tree mortality [3] which can impact management resource objectives and ecosystem services. These eruptive populations usually develop after other disturbances such as fire [4], windstorms [5], or defoliation [6] events which provide an abundance of stressed trees that the insect can exploit. Once stressed trees are no longer a suitable resource, populations can disperse into surrounding stands, where the insect
%U http://www.hindawi.com/journals/isrn.forestry/2013/542380/