Patterns of exotic plants in relation to anthropogenic edges within urban forest remnants

Abstract

Question

How is the abundance of exotic plants within urban forest remnants influenced by distance to the edges of forest boundaries and recreational trails?

Location

Halifax, Nova Scotia, Canada.

Methods

Gradients in the cover of exotic plants, as well as the richness of exotic and native vascular species, were examined as a function of distance from anthropogenic forest boundaries and recreational trails. Plants were sampled in 2 m × 10 m and 10 m × 10 m plots distributed among 11 urban forest remnants. Randomization tests were used to quantify the distance of edge influence from both forest boundaries and trails, and to determine if there was an interaction between them.

Results

The cover and richness of exotic plants and richness of native species decreased with increasing distance from forest boundaries and trails. Edge influences extended to distances of ca. 50 and 3 m for forest boundaries and trails, respectively, and were stronger for measures of understorey than of overstorey vegetation. Vegetation was simultaneously influenced by both edge types such that exotic cover and richness were higher when in close proximity to two edges than when subject to either edge alone (i.e. a positive interaction).

Conclusions

It is important to consider the influence of edges in the design and management of forest remnants to improve the ability to conserve native biodiversity within cities. Results from this study may be used to guide the design of such systems, particularly by suggesting appropriately sized patches and trail densities.

The study complements a gap in the knowledge concerning patterns of exotic plants in urban forest fragments of North America. Edge influence on vegetation in urban parks extended to 50 m from forest boundaries and to 3 m from interior trails. Exotic plants were more abundant in proximity to multiple edges providing evidence of edge interaction.