The speed of invasion: rates of spread for thirteen exotic forest insects and diseases.
Invasive, exotic insects and diseases have a devastating effect on North American forests. The rate of spread, or range expansion, is one of the main determinants of an invasive organism's impact, and can play a major role in structuring management response options. To better understand how exotic organisms have spread through our forests, this study employs a consistent, rigorous analytical framework to analyze a comprehensive geospatial database for the spread of seven exotic insects and six diseases. This study includes new data for six insects and two diseases in combination with five invasive species previously analyzed using the same technique. The quantile regression analysis of over 3000 records of infestation over the preceding century show that the rate of spread of invasive forest insects and diseases ranges from 4.2 km.year-1 to 57.0 km.year-1. The slowest disease spread was white pine blister rust (Cronartium ribicola) at 7.4 km.year-1 while the most rapid disease spread was chestnut blight (Cryphonectria parasitica) at 31.3 km.year-1. The slowest insect spread was balsam woolly adelgid (Adelges piceae) (4.2 km.year-1) while the fastest was emerald ash borer (Agrilus planipennis) at 57.0 km.year-1. Species that can fly long distances or are vectored by flying insects have spread faster than those that are passively dispersed. This analysis highlights the difficulty of estimating spread rates from studies of individual dispersal or flight distances, but the estimated spread rates in this study are generally in line with previous estimates.