Alien Flora in Grasslands Adjacent to Road and Trail Corridors in Glacier National Park, Montana (U.S.A.)

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Abstract
Alien plant species have rapidly invaded and successfully displaced native species in many grasslands of western North America. Thus, the status of alien species in the nature reserve grasslands of this region warrants special attention. This study describes alien flora in nine fescue grassland study sites adjacent to three types of transportation corridors—primary roads, secondary roads, and backcountry trails—in Glacier National Park, Montana (U.S.A.). Parallel transects, placed at varying distances from the adjacent road or trail, were used to determine alien species richness and frequency at individual study sites. Fifteen alien species were recorded, two Eurasian grasses, Phleum pratense and Poa pratensis, being particularly common in most of the study sites. In sites adjacent to primary and secondary roads, alien species richness declined out to the most distant transect, suggesting that alien species are successfully invading grasslands from the roadside area. In study sites adjacent to backcountry trails, absence of a comparable decline and unexpectedly high levels of alien species richness 100 m from the trailside suggest that alien species have been introduced in off‐trail areas. The results of this study imply that in spite of low levels of livestock grazing and other anthropogenic disturbances, fescue grasslands in nature reserves of this region are vulnerable to invasion by alien flora. Given the prominent role that roadsides play in the establishment and dispersal of alien flora, road construction should be viewed from a biological, rather than an engineering, perspective. Nature reserve man agers should establish effective roadside vegetation management programs that include monitoring, quickly treating keystone alien species upon their initial occurrence in nature reserves, and creating buffer zones on roadside leading to nature reserves.