A new look at spread rates of exotic diseases in North American Forests

Abstract

Exotic pathogens threaten ecosystems in novel ways, particularly where they are facilitated by stresses such as climate change and forest fragmentation. Although chestnut blight (CB), Dutch elm disease (DED), beech bark disease (BBD), and white pine blister rust (WPBR) are well-studied pathogens, this investigation is the first to provide estimated rates of spread based on an expansive geospatial database and a consistent, rigorous analytical framework. We use quantile regression to analyze 850 records of infection over the last (20th) century. The results show that in the past, forest disease complexes have spread at rates between 7.4 and 31 km year-1, and two-thirds of the estimates were less than 17 km year-1. We estimated the spread of CB at 31 km year-1, DED in eastern North America at 25 km year-1, DED in western North America at 14 km year-1, BBD at 16 km year-1, WPBR in eastern North America at 7.4 km year-1, and WPBR in western North America at 10 km year-1. These results do not predict the rate of spread of future exotic pathogens in North American forests; rather they provide context for predictive models and a heuristic guide until more scientific data are available. © 2010 by the Society of American Foresters.