Alien Plant Invasion in Mixed-grass Prairie: Effects
of Vegetation Type and Anthropogenic Disturbance
Management Implications
Planting alien species, for whatever reason, within or near the boundaries of a natural area is risky. Bromus inermis is clearly a threat to native vegetation in the vicinity of the roads where it was planted. The extent to which it might spread over time is yet unknown. Weedy contaminants of seed may also be dispersed into native vegetation. The additional cost of obtaining native seed is likely small compared to the cost of eradicating an unwanted alien invader.
Vegetation type matters. Some are more at risk to invasion by alien species than others, and thus will require more intensive management if alien species are to be excluded. As in other studies (DeFerrari and Naiman 1994, Planty-Tabacchi et al. 1996, Stromberg et al. 1997, Stohlgren et al. 1998), riparian areas seem especially at risk. Disturbance, as we defined it in this study, was rarely associated with the most abundant alien species (e.g., E. esula, M. officinalis, and P. pratensis), which suggests that simply limiting construction of roads, trails, and other facilities will not protect vulnerable areas from invasion.
Differences in the frequencies of alien species between the two park units at TRNP suggest that prediction will always be uncertain. A monitoring plan that emphasizes the most vulnerable vegetation types and includes searches for all known potential invaders is critical for early detection as well as to determine which species are, in fact, increasing in number and range. Such strategic planning is an important first step in prioritizing use of limited resources for alien plant control.
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