Squeezed from All Sides: Urbanization, Invasive Species, and Climate Change Threaten Riparian Forest Buffers

Lea Johnson,Scott Drzyzga,Joshua Barth,Claire Jantz,Tara Trammell,Tracie Bishop

doi:10.3390/su12041448

Abstract

Streamside forests of urbanizing coastal regions lie at the nexus of global changes: rising sea levels, increasing storm surge, expanding urban development, and invasive species. To understand how these combined stressors affect forest conditions, we identified forest patches adjacent to urban land, analyzed adjacent land cover, modeled forest inundation, and sampled 100 sites across the Chesapeake Bay and Delaware Bay watersheds. We found that the majority of forest patches are adjacent to urban land and projected flooding will affect 8–19% of regional forested land. We observed non-native invasive plants in 94% of forest plots. Trees were predominantly native, but over half of shrub stems were invasive species and more than 80% of plots contained invasive woody vines. Disturbance of human origin was correlated with abundance of invasive trees. Signs of deer activity were common. Richness and number of growth forms of invasive plants were related to adjacent agricultural land cover. These data reveal that streamside forests are impacted by the interacting stressors of urbanization, climate change, and invasive species spread. Our results emphasize the importance of protection and restoration of forests in urban regions and point to the need for a social-ecological systems approach to improve their condition.

Highlights

Forests in urbanizing coastal zones are undergoing unprecedented change as urbanization accelerates simultaneously with invasive species spread and climate change
To understand the degree to which riparian forests are vulnerable to interactive effects of these combined stressors, we examined riparian forest patches likely to be affected by storm surge and sea level rise along a gradient of city size
The results of this analysis reveal that many forest patches in the study area are vulnerable to combined stressors, and that these vulnerable forests comprise a significant proportion of the forested area in this urbanized region

Summary

Introduction

Forests in urbanizing coastal zones are undergoing unprecedented change as urbanization accelerates simultaneously with invasive species spread and climate change. Coastal ecosystems are vulnerable to global climate change as sea levels rise and storm surge events increase [1,2,3,4]. Streamside forests of urbanizing coastal regions lie at the nexus of these global changes, yet the extent and potential impact of these combined stressors on riparian urban forests and on their ability to provide valuable water filtration and support for biodiversity is currently unknown. These forests are “squeezed” from all sides by adjacent urbanization on land, rising sea levels and storm surge, and from within by non-native invasive plants (Figure 1). Understanding relationships between urban riparian forests and the combined effects of urbanization, climate change, and invasive species requires a social-ecological approach

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Conclusion