Abstract
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.
Highlights
Invasive forest insects and diseasesorganisms that damage or kill trees and are not native to the ecosystemare major threats to forests
In order to combine these measures of spread with other point data on infection, I measured the shortest distance in any direction from the start of infection to 10 evenly spaced points along each front of infection, i.e., each isoline for each invasive species
Was undefined so the 90th provided the best estimate of the unconstrained spread rate
Summary
Invasive forest insects and diseasesorganisms that damage or kill trees and are not native to the ecosystemare major threats to forests. Invasive forest insects and diseases have removed dominant tree species, reduced diversity, altered disturbance regimes, and affected ecosystem function in North America. The effect of invasive organisms is exacerbated by climate change [3], more frequent extreme climatic events [4,5], and forest fragmentation [6]. In addition to their ecological costs, exotic forest invaders have a large economic impact on both forest products and ecosystem services [7].
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