Abstract
Invasive exotic plants pose a serious threat to the ecological integrity of forests in the eastern United States. Presence and expansion of these plants are closely associated with human-caused disturbances. Land preservation to exclude human-caused disturbances could protect against invasions, yet natural disturbances persist. We ask if windthrow forest disturbances in preserved National Park lands facilitate exotic species invasions. We hypothesized that exotic plant expansion is positively correlated with forest canopy disturbance from windthrow and proximity of disturbed area to forest edge. Pre and post-disturbance data from National Park Service long-term vegetation monitoring were used to analyze exotic plant richness and abundance in four National Park Service units affected by 2012 severe storms. No significant difference in exotic plant richness or cover occurred between disturbed (n = 18) and undisturbed plots (n = 262) over three years following disturbance. Exotic plant cover prior to disturbance was positively correlated with the amount of nearby linear edge habitat, but there were no significant correlations between edge and change in exotic plant cover following disturbance. Lack of increase in exotic plants after windthrow disturbance suggests that land preservation provides short-term resistance to invasion.
Highlights
Land preservation, a key strategy of conservation biology, is the effort to protect habitat from human-caused impacts such as fragmentation, development, species loss, and the encroachment of invasive exotic plants [1,2]
DEWA, located along the Delaware River, has had longer and more intensive agricultural use than the other National Park Service (NPS) units, as well as having a much greater human population density both historically and currently. These factors have led to a higher proportion of exotic plants in DEWA compared to the NPS units in West Virginia [33]
Disturbed plots had significantly more coarse woody debris (CWD) than the remaining park plots prior to the disturbance event (Figure S1, Table S1). This higher pre-disturbance CWD volume in GARI disturbed plots is likely due to the older forests found within that park unit [33]
Summary
A key strategy of conservation biology, is the effort to protect habitat from human-caused impacts such as fragmentation, development, species loss, and the encroachment of invasive exotic plants [1,2]. The establishment and range expansion of exotic plants are closely associated with human disturbances such as logging, mining, road construction, agriculture, horticulture, and development [3,4,5]. This link between exotic plants and anthropogenic disturbance is the result of both direct and indirect effects. Invasive exotic plants tend to be pioneer species with high reproductive rates and effective propagule dispersal mechanisms [8], traits amenable to colonizing newly disturbed areas [9]. Roads and private lands can be pervasive, creating a patchwork of edge habitat
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