Modeling Bark Beetle Pressure for Pine Forests of Mexico

Carlos Fabián Vargas, Yolanda Salinas, Gerardo Zúñiga, Alan A. Ager, and Jane L. Hayes

Instituto Politecnico Nacional Biological Variation and Evolution Laboratory, Mexico City, Mexico (1-3) and USDA Forest Service Pacific Northwest Research Station (4,5)

Bark beetles in the genus Dendroctonus are significant causes of mortality for over half of the more than 40 species of pines (Pinus) that occur in Mexico and there is a growing need for a bark beetle risk predictive capabilities to help forest managers mitigate beetle impacts.  The host relationship between beetles and pines is weak; most of the 12 species of bark beetles attack a number of pine species and considerable overlap of these hosts occurs.  The geographic distribution of bark beetle populations is highly influenced by environmental factors such as temperature and elevation, rather than strictly by the distribution of potential hosts, and thus many beetle species are more prevalent in certain portions of their host range.  Given these considerations, and a data set consisting of point observations of pine - beetle species throughout Mexico, we devised a measure of beetle pressure by considering the cumulative pine - beetle  exposure at each site.  Local density of beetles and geographic range maps for pine species were generated from point maps using kernal density functions.  The beetle pressure index was calculated by summing the beetle density over all pine-beetle combinations present in that pixel.  While other variables like stand density and tree size are most likely important determinants of potential beetle risk, the beetle pressure index provided an informative broad scale indicator of potential for bark beetle impacts on pine forests in Mexico.

corresponding author:

Jane L. Hayes
USDA Forest Service
Pacific Northwest Research Station
1401 Gekeler Lane
La Grande, OR 97850-3368
541-962-6549
jlhayes@fs.fed.us