Assessing the relative importance of disturbance, herbivory, diversity, and propagule pressure in exotic plant invasion

Abstract

The current rate of invasive species introductions is unprecedented, and the dramatic impacts of exotic invasive plants on community and ecosystem properties have been well documented. Despite the pressing management implications, the mechanisms that control exotic plant invasion remain poorly understood. Several factors, such as disturbance, propagule pressure, species diversity, and herbivory, are widely believed to play a critical role in exotic plant invasions. However, few studies have examined the relative importance of these factors, and little is known about how propagule pressure interacts with various mechanisms of ecological resistance to determine invasion success.We quantified the relative importance of canopy disturbance, propagule pressure, species diversity, and herbivory in determining exotic plant invasion in 10 eastern hemlock forests in Pennsylvania and New Jersey (USA). Use of a maximum-likelihood estimation framework and information theoretics allowed us to quantify the strength of evidence for alternative models of the influence of these factors on changes in exotic plant abundance. In addition, we developed models to determine the importance of interactions between ecosystem properties and propagule pressure. These analyses were conducted for three abundant, aggressive exotic species that represent a range of life histories: Alliaria petiolata, Berberis thunbergii, and Microstegium vimineum.Of the four hypothesized determinants of exotic plant invasion considered in this study, canopy disturbance and propagule pressure appear to be the most important predictors of A. petiolata, B. thunbergii, and M. vimineum invasion. Herbivory was also found to be important in contributing to the invasion of some species. In addition, we found compelling evidence of an important interaction between propagule pressure and canopy disturbance. This is the first study to demonstrate the dominant role of the interaction between canopy disturbance and propagule pressure in determining forest invasibility relative to other potential controlling factors. The importance of the disturbance-propagule supply interaction, and its nonlinear functional form, has profound implications for the management of exotic plant species populations. Improving our ability to predict exotic plant invasions will require enhanced understanding of the interaction between propagule pressure and ecological resistance mechanisms.

Fire promotes downy brome (Bromus tectorum L.) seed dispersal

“…5) (Prevéy et al 2010). Several recent studies have documented that disturbance and propagule pressure interact non-linearly to determine the likelihood of species invasions (Clark and Johnston 2009;Eschtruth and Battles 2009;Thomsen et al 2006). Here, the greater than five-fold increase in average diaspore dispersal distance after fire shows that increased dispersal of propagules within disturbances is one mechanism that may explain these nonlinear effects.…”

“…Recent research has shown that such changes may affect how seeds are captured as they move across the landscape (Chambers 2000;Johnston 2011). If a disturbance alters the landscape in a way that facilitates dispersal, then the propagule supply of invasive plants could increase within the disturbed area, exacerbating the effect of the disturbance on promoting invasion (DiVittorio et al 2007;Eschtruth and Battles 2009;Thomsen et al 2006).…”

Manipulating the intrinsic parameters of propagule pressure: implications for bio‐invasion

“…Rates of evolution (Kokko and López-Sepulcre 2007), metapopulation dynamics (Figueira and Crowder 2006), plant-herbivore and predator-prey interactions (Eschtruth and Battles 2009) and population survival and fitness can all be altered with variable colonisation (Burgess and Marshall 2011). An understanding of colonisation processes is particularly important for predicting the establishment of non-indigenous species.…”

Predicting Microstegium vimineum invasion in natural plant communities of the southern Blue Ridge Mountains, USA

“…A common research finding is that invasive plant species abundance increases with human-related disturbance and movement of propagules along roads, trails and water ways (Hodkinson and Thompson 1997;Pollnac et al 2012;Von der Lippe and Kowarik 2007). Establishment rates are lower in intact natural areas (Lonsdale 1999) where disturbance and invasive propagule pressure are generally low (Eschtruth and Battles 2009b), but shade-tolerant invasives can threaten protected natural areas and have detrimental long-term impacts on intact forests (Martin et al 2009). Understanding the spatial patterns of such invasions is critical for anticipating future changes in forest understory composition.…”