Exotic plant invasions can have important ecological and economic impacts on forest ecosystems. In northern New England, forests are currently being invaded by a number of potentially harmful exotic species, which threaten the health and productivity of these forests. In this study, we examined exotic plant invasions at four sites in northern New England: Petersham, Massachusetts and Norwich, St. Johnsbury, and East Charleston, Vermont. At each site, we analyzed exotic plant richness and abundance in relation to landscape fragmentation, land-use history, logging history, and distance to the nearest roads and forest edges. 

Results/Conclusions

In Petersham, >90% of the exotic plants occurred on former pasture (as opposed to woodlots that were never cleared for agriculture), and >80% occurred on pastures abandoned after 1870. At the three sites in Vermont, exotic plants were equally diverse and abundant at all distances from roads or trails. However, in East Charleston, exotic plants were most diverse and abundant on former cropland, intermediate in diversity and abundance on former pastures, and least diverse and abundant in areas that had always been forested. In addition, the diversity and abundance of exotic plants increased dramatically in areas that were logged recently but not in areas that were not logged. Thus, unlike more remote and less fragmented landscapes, exotic plants may invade forested areas in New England, because much of the land was previously cleared for agriculture and supports more species-depleted forests and enriched soils than areas where little or no land was cleared for agriculture. Furthermore, repeated logging allows exotic plants to invade otherwise relatively uninvaded forests. Because these invasions have the potential to greatly impact forest communities and the natural resources that they provide, it is necessary that we understand the causes and consequences of exotic plant invasions in order to guide managers and conservationists in protecting and enhancing the health and productivity of these forests.