Insect Outbreaks and Environmental Heterogeneity in Patagonian Nothofagus Forests

PARITSIS, J, J SMITH, TT VEBLEN

Las Vegas, NV, EE.UU.

Congreso; 2009 Annual Meeting of the Association of American Geographers; 2009

Association of American Geographers

Investigating the influences of environmental variables on the spatial occurrence of insect outbreaks is crucial in understanding their dynamics and identifying susceptible areas. In the Patagonian Nothofagus forests severe defoliations caused by Ormiscodes spp. moths have been recorded during the last ca. 30 years but spatially explicit studies are lacking. Using Landsat TM images and ancillary data we analyzed the influences of key environmental variables (vegetation, topography, and precipitation) on the spatial occurrence of a severe and extensive Ormiscodes outbreak that occurred in 1986 in northwestern Patagonia. Our results suggest that all the analyzed variables influenced the spatial distribution of the defoliated areas. Higher elevation forests of Nothofagus pumilio were proportionally more affected by the outbreak than lower elevation forests of Nothofagus species (N. dombeyi and N. antarctica). Additionally, stands located at intermediate elevations and on north-facing slopes (drier and warmer) were also more defoliated than expected. Finally, stands growing on areas with intermediate precipitation, relative to the distribution of N. pumilio along the precipitation gradient, were proportionally more defoliated than drier and moister areas. Ecological interpretations of our results provide insight into the spatial dynamics of insect defoliations in Patagonia.