An Invasive Species Assessment System for the North Carolina Horticultural Industry

Abstract

ABSTRACT

TRUEBLOOD, CLARA ENGLERT. An Invasive Species Assessment System for the North Carolina Horticultural Industry. (Under the direction Dr. Joseph C. Neal and Dr. Thomas G. Ranney).

While a small proportion of nonindigenous species successfully naturalize and even fewer become invasive, those that do may alter ecosystem processes and negatively impact native community composition. Many potentially invasive species were introduced and sold for horticultural purposes. The North Carolina Nursery and Landscape Association (NCNLA) has supported the development of an invasive assessment protocol designed to systematically assess the potential invasiveness of ornamental plants suspected to affect natural areas in the state. The North Carolina protocol incorporates and builds upon elements of existing assessment models to evaluate the potential invasiveness of plant species in accordance with regional environmental conditions. The ranking and scoring systems and qualitative and quantitative measurements of existing regional and national assessment models were compared to develop the framework for an assessment tool unique to North Carolina. The North Carolina assessment criteria are based on a framework of weighted sets of indices that evaluate and rate ecological impacts, potential for expanded distribution, management difficulty, and the economic value and benefits of non-native ornamental species. According to the combined weighted results, the model generates a recommendation for evaluated species ranging from 'unlikely to be invasive' to ‘invasive and not recommended for use.' The North Carolina invasive protocol is non-predictive and intended for species that are available in the horticultural trade. The assessment model incorporates a unique cost/benefit analysis and weighs economic benefits against the ecological risk of selling potentially invasive ornamental plants. An online survey of NCNLA members was designed to assess the market value of potentially invasive plant species produced in the North Carolina nursery industry. We found that potentially invasive ornamental plant species have substantial value to the nursery industry in North Carolina. Total statewide wholesale value attributed to the 18 potentially invasive surveyed plants was estimated at roughly $206 million, or approximately 23.1% of state-wide industry sales. The assessment protocol was used to evaluate the invasiveness of 25 nonnative taxa. Three species, Celastrus orbiculatus (Oriental bittersweet), Lonicera japonica (Japanese honeysuckle), and Vitex rotundifolia (Beach Vitex) were categorized as highly invasive with severe environmental impacts, great potential for natural dispersion, and high management difficulty. Nine species were categorized as Moderately Weedy. All of the Moderately Weedy species are sold in the North Carolina nursery industry and either identified by land managers in North Carolina as potentially invasive plants or categorized as invasive species in other state assessments. Thirteen species were classified as Noninvasive with limited ecological impact, distribution and invasive potential, and management difficulty. The majority of the Noninvasive species are nonnative plants with very high economic value in the North Carolina nursery industry that have not been shown to invade natural areas. By modifying the criteria utilized in existing assessments and tailoring the model for the North Carolina horticultural trade, we have created an assessment system unique to the nursery industry that may be completed using resources available in North Carolina. The assessment results are intended to allow the NCNLA to advise their members regarding plants that are purported to be invasive.