The spread of woody exotics into the forests of a northeastern landscape, 1938-1999

This study documents changes in the distribution of non-native woody species from 1938 to 1999 within 30 forests of a 54 km(2) landscape in Monroe County, New York. Within these forests, the mean number of exotic species increased nearly three-fold from 1938 to 1999, and two species not naturalized within the landscape in 1938, Lonicera morrowii and Rosa multiflora, had become widespread by 1999. In 1999, the most abundant exotic was Lonicera morrowii, which had greater cover within forests on wetter portions of the landscape where much of the surrounding agricultural land had been abandoned. Though exotics accounted for < 10% of relative cover within the shrub layer and < 1% of the tree layer, their cover was higher in portions of some forests, especially near edges. In 1999, six species had covers > 25% within patches > 100 m(2): Acer platanoides, Crataegus monogyna, Ligustrum vulgare, Lonicera morrowii, Robinia pseudoacacia and Rosa multiflora. These species in particular may represent on-going invasions that could alter this landscape's forested habitats.