The distribution and habitat preferences of introduced species in the Mount Holyoke Range, Hampshire Co., Massachusetts

Introduced species make up about 15% of the flora of the Mount Holyoke Range, Hampshire County, Massachusetts, one of the core natural areas in the state. Geographic Information Systems software was used to compare the distribution of sample locations with introduced invasive species, introduced non-invasive species, or only native species as a function of distance from disturbance corridors that included roads and power-line right-of-ways. Habitat preferences were also analyzed for the two groups of introduced species. Thirty-nine percent of 475 geo-referenced sample locations had introduced species. Of these, twice as many had introduced non-invasive species as had introduced invasive species, with Poa compressa the most common species in the first group and Berberis thunbergii the most common in the second group. A high proportion of sample locations for both groups of introduced species were close to disturbance corridors, with about a third of the sample locations with these groups found within 50 m of disturbance corridors and most of the rest found within 300 m. The distributions of both groups of introduced species differed significantly from the distribution of native species, but not from each other. Disturbed habitats had the highest frequency of both groups of introduced species, but their relative frequency differed in other habitats. Introduced invasive species were common in moister habitats, which may restrict their spread in the range, while introduced non-invasive species tended to occupy drier habitats on upper slopes. These more open habitats may function as a refuge for some species in the introduced non-invasive group. However, high frequencies of both groups in disturbed habitats and the similarity in distribution suggests that human activities associated with disturbance corridors and past land use are of major importance in determining the distribution of both groups of introduced species across the landscape.