Edge effects : native and non-native plant distribution along single use and multi-use trails in the Santa Monica Mountains National Recreation Area, California

Abstract

Recreational impacts (such as hiking, biking, and horseback riding) on surrounding biotic communities are dictated by trail usage, where trails are the major transportation system and facility most commonly found in protected areas. The distribution of trails can contribute to the introduction of non-native species and a reduction in leaf litter through repeated trampling. As such, these impacts associated with trails are a major concern for park managers. The following questions were addressed within the Santa Monica Mountains National Recreation Area (a federally managed protected area in southern California): (1) Will trailside (edge) vegetation have more exotic species (species richness and abundance) compared interior vegetation along single-use (hiker-only) trails and multi-use trails? (2) Will chaparral or coastal sage scrub communities (CSS) for each trail type exhibit differential plant community diversity and composition due to their differences in litter cover? Trailside vegetation significantly differed in native/exotic species richness and composition from interior vegetation demonstrating an edge effect on both types of trails and in both plant communities. Not only was there a significant increase in trailside exotic species richness and composition in comparison to interior vegetation, multi-use trails exhibited a significantly higher proportion of exotic species richness and composition along the trailside in comparison to the trailside along single-use trails. Additionally, coastal sage scrub plant communities exhibited significantly lower mean percent litter cover, as well as significantly higher exotic species richness and composition along the trailside as compared to the trailside in chaparral communities. Implications from this study argue for the wisdom of concentrating use and impact on a small portion of a recreation area due to rapid impact and slow recovery of certain vegetation types (i.e., CSS). Therefore results from this study would suggest concentrating multi-use trails on chaparral habitats rather than CSS habitats.