Print PageOver the last 100 years, a steady stream of non-native forest insect and pathogen species, many of which have caused catastrophic changes to forest and urban ecosystems, has inundated North America. Based upon historical data, it has been possible to quantify patterns of invasion spread for these species and draw inferences about the process that are most important in determining the magnitude and direction of invasion spread.
Results/Conclusions
Analysis of historical spread by 78 different species of non-native forest insects and diseases indicates an average rate of invasion spread of 5.2 km / yr. Surprisingly, rates of spread did not differ significantly among four ‘guilds’ of pest species: foliage-feeders, wood/phloem-borers, sap-feeders and pathogens, despite basic biological differences in life histories (including dispersal) among these groups. These results highlight the importance of long-range dispersal mediated by humans in the spread of forest pests.
Geospatial data on the distribution of host trees for these forest pest species indicates that most non-native forest pests in N. America have not yet invaded their entire potential range. Consequently, we can expect that the aggregate impacts of these species will continue to increase, even if new international quarantines were to be put in effect that diminished the establishment of new species.
The spread of most forest pest species is dominated by ranges ‘jumping ahead’ in discrete colonies as a result of long-distance dispersal. Because populations are small when such colonies are founded, Allee dynamics are critical to understanding spread. Such behavior, including the dominance of Allee effects, offers opportunities for containment of invasion spread via searching for and destroying new colonies ahead of the principal invasion front.
