Synopsis:
This study examined the effect of road improvement and environmental variables on exotic and native plant diversity in roadside verges and adjacent semi-arid grassland, shrubland, and woodland communities of southern Utah. Researchers measured the cover of exotic and native species in roadside verges and both the richness and cover of exotic and native species in adjacent interior communities (50 meters beyond the edge of the road) along 42 roads stratified by level of road improvement (paved, improved surface, graded, and four-wheel drive track). Exotic species richness and cover were more than 50% greater, and the richness of native species 30% lower, at patch interiors adjacent to paved roads than those adjacent to four-wheel drive tracks. The results indicate that the width of roadside verges is strongly positively correlated with exotic species richness and cover. Road improvements influenced both exotic and native species richness in interior communities 50 m beyond the edge of the road, suggests that road improvement affects the distribution of both exotic and native species in lands beyond the influence of roadside disturbance. However, at larger spatial scales, relationships between native and exotic species richness may correspond more with environmental variation.
Conclusions:
Width of roadside verges is strongly positively correlated with exotic species richness and cover. Roads influenced both exotic and native species richness in interior communities 50 m beyond the edge of the road, suggests that roads affect the distribution of both exotic and native species in lands beyond the influence of roadside disturbance.
Thresholds/Learnings:
Sites isolated (>1000m) from roads tended to contain fewer exotic species than sites near (<50m) roads.
