Effects of removing exotic invasive species from the ecotones of two granite rock outcrops in the southeastern Piedmont of the United States

Melissa Caspary,James Affolter

doi:10.3391/mbi.2013.4.3.06

Abstract

Piedmont granite rock outcrops in the southeastern United States support a plant community rich in endemic and rare plant species. The ecotones of the granite outcrop and Piedmont oak hickory forest communities are under increasing pressure from exotic invasion and the potential impacts of this invasion on the native plants in these communities are unclear. We conducted an experimental removal of invasive plant species at the ecotone of two granite rock outcrops and monitored species richness and plant occurrence along random belt transects in invaded, uninvaded, and removal plots for three years. These transects captured a representative sample of the plant community from the rock edge 20 m into the forest interior. Hemispherical photographs and soil samples were used to monitor changes in light availability and soil nutrients. Vegetation classes demonstrated spatial distribution patterns related to proximity to rock edge and depth of soil, but removal of invasive species had no apparent effect on percent cover or native plant richness. Sodium, calcium, and magnesium were all found to be significant predictors of invasive species occurrence and sodium and calcium were correlated with soil depth. This research effort suggests that the occurrence of invasive species are not significantly impacting overall species richness in the ecotone of outcrop plant communities, however changes to the species richness of this plant community in response to invasive species removal may take longer to detect.

Highlights

The identification and management of high-value areas (HVAs) require trade-offs between competing economic, environmental, social and cultural needs
This paper describes the initial risk reassessment process to evaluate whether Undaria, an Unwanted Organism, posed a risk to the values in a set of six HVAs identified by Biosecurity New Zealand ( Ministry of Primary Industries)
This paper focuses on New Zealand, as a model system, the threat Undaria poses to HVAs in other countries is apparent and as such the risk method presented is applicable to both Undaria introductions in other countries and introductions of other species

Summary

Introduction

The identification and management of high-value areas (HVAs) require trade-offs between competing economic, environmental, social and cultural needs. Introduced species are ranked as one of the top five-threats to biodiversity (Lubchenco et al 1991; Mooney and Hobbs 2000) and when coupled with the synergistic effects of climate change (McLachlan et al 2007; Hellmann et al 2008; Rahel and Olden 2008; Rahel et al 2008) it is likely that the threat from introduced species will increase, not diminish This may be true for HVAs that were initially considered “safe” from particular introduced species threats due to environmental and biogeographic constraints including higher diversity related to biotic resistance and isolation from primary invasion points. Our increased understanding of invasion ecology, coupled with the rapidly changing environment, suggests that a re-assessment of the risks posed by introduced species to these areas, and a re-evaluation of the management actions and options to protect such areas from introduced species, is needed (Hewitt and Huxel 2002; Byers 2005; Wyatt et al 2005; Klinger et al 2006; Lewis et al 2004)

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Conclusion