Plant invasion at landscape and local scales along roadways in the mountainous region of the Greater Yellowstone Ecosystem

Abstract

Roadways are increasingly recognized as common points of entry for non-native species into natural habitats in mountainous areas. Studies were conducted within the Greater Yellowstone Ecosystem from 2003 to 2007 to evaluate (1) landscape scale patterns of non-native plant richness along roadways, and (2) local scale factors influencing native and non-native plant richness and cover, and surrogate non-native plant (SNP) emergence in an invaded habitat. At the landscape scale, non-native plant richness decreased with increased elevation and increased distance from the road, and was positively correlated to the proportion of plots with signs of disturbance. Non-native plant richness also varied by habitat type: sagebrush steppe had the highest and alpine the lowest. At the local scale, in sagebrush steppe, SNP emergence was negatively associated with increased distance from the road, and percent cover of litter was positively associated with SNP emergence. The proportion of non-native plant cover and richness decreased, while the proportion of native cover and native species richness increased with distance from road. Our study suggests that landscape scale variables such as elevation and habitat type influence non-native plant success, and that while local conditions adjacent to the road may be favorable for non-native plants, factors which vary at the local scale can also effect non-native plant establishment away from the roadside. This highlights the need for studies to evaluate multiple scales when assessing patterns and processes driving non-native plant invasions, and suggests that sagebrush steppe may be resistant to invasion as long as it remains undisturbed.