The influence of disturbance and habitat on the presence of non-native plant species along transport corridors Malin J. Hansen a, * , Anthony P. Clevenger b a Department of Biology, University of Regina, 3737 Wascana Parkway, Regina, Sask., Canada S4S 0A2 b Western Transportation Institute, Montana State University, P.O. Box 174250, Bozeman, MT 59717-4250, USA Received 5 January 2005; accepted 24 March 2005 Available online 12 May 2005 Abstract The impact from transportation corridors on surrounding habitat often reaches far beyond the edge of the corridor. The altered disturbance regime in plant communities along corridor edges and vehicle traffic facilitate the spread and establishment of invasive non-native plant species. We compared the frequency of non-native plant species along highways and railways and the ability of these species to invade grasslands and dense forests along these corridors. We measured the frequency of several non-native plant species along transects 0–150 m from the edge of highways and railways in grasslands and forests, as well as at control sites away from corridors. Both transportation corridors had higher frequency of non-native species than respective control sites. Grasslands had higher frequency of non-native species than forested habitats, but the frequency did not differ between the highways and the railways. The frequency of non-native species in grasslands along highways and railways was higher than at grassland control sites up to 150 m from the corridor edge, whereas the frequency in forested habitats along corridors was higher than at forested control sites up to only 10 m from the corridor edge. There was a significant decrease in the frequency of non-native species with increasing distance from both corridors in the forest, while grasslands showed no significant change in non-native species frequency with dis- tance from corridors. This suggests that corridor edges and grassland habitats act as microhabitats for non-native species and are more prone to invasion than forests, especially if disturbed. Our results emphasize the importance of minimizing the disturbance of adjacent plant communities along highways and railways during construction and maintenance, particularly in grassland habitats and in areas sensitive to additional fragmentation and habitat loss. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Transportation corridors; Road ecology; Non-native plant invasions; Habitat effect; Disturbance; Edge effect 1. Introduction Biological invasion by non-native species is a world- wide environmental concern and a focus of current eco- logical research (Alpert et al., 2000). As many landscapes undergo extensive and rapid change because of human activities (Hansson and Angelstam, 1991; Houghton, 1994), plant communities become more sus- ceptible to invasion by non-native plant species and the eradication of non-native plant species in native plant communities can be challenging (Bugg et al., 1997; Benefield et al., 1999; Myers et al., 2001). One of the ma- jor changes associated with landscape modification is the fragmentation of habitat (Bennett, 1999). Frag- mented habitat has more edges than continuous habitat (Tabarelli et al., 1999) and therefore is thought to be more vulnerable to invasion by non-native species (Vito- usek et al., 1997; Lindenmayer and McCarthy, 2001; Watkins et al., 2003) and to loss of native species (Turner, 1996; Tomimatsu and Ohara, 2004; but see Spooner et al., 2004; Spooner, 2005). 0006-3207/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.biocon.2005.03.024 * Corresponding author. Tel.: +1 306 585 4994; fax: +1 306 337 2410. E-mail address: hansen2m@uregina.ca (M.J. Hansen). www.elsevier.com/locate/biocon Biological Conservation 125 (2005) 249–259 BIOLOGICAL CONSERVATION