Regional, Historical, and Environmental Variation in A. petiolata occurrence in Western Massachusetts

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Kristina Stinson
Dunbar Carpenter

Alliaria petiolata (garlic mustard) is an herbaceous biennial herb that has been present in the New England landscape for over a century. We investigated the ecological and historical factors affecting A. petiolata's invasion pattern across the New England landscape, including forest community structure, geophysical attributes, and habitat fragmentation. One-hundred-and-seventy-five 25× 100 m roadside, forested plots across two ecoregions were visited in the summers of 2006 and 2007. A. petiolata presence and cover, dominant canopy species, slope, and soil moisture were recorded. Additional data on vicinity to water, and road and edge density was obtained for each plot using GIS datalayers from MassGIS. Chi-squared tests showed that A. petiolata does poorly in Quercus¬-dominated forests both in terms of presence (p<.001) and performance measured by cover (p<.001). Acer saachrum and Fraxinus Americana dominated forest, on the other hand, have high degrees of A. petiolata presence (p<.001 in both cases). The prevalence of Quercus in one of the ecoregions, and A. sacharum and F. Americana in the other may help explain the interregional differences in A. petiolata presence. A. petiolata also has a propensity to invade mesic to hydric soils and forests downhill from roads, (p = .04 for soil-moisture, and p=.08 for slope). Habitat fragmentation, as measured in this study, appeared to have little affect on A. petiolata presence or performance. From this it can be concluded that A. petiolata is not likely to be limited by a lack of available forest edge habitat, but that other ecological factors, particularly soil moisture and forest community composition, do appear to affect the distribution of this invasive plant.