Non-Native Invasive Plants: Distribution and Impact at Papahana Kuaola

Abstract

Invasive plants have detrimental effects globally, including the state of Hawaiʻi, where they endanger native species and cultural practices. Invasive species can outcompete native plants for habitat and resources. Papahana Kuaola, a non-profit organization in Heʻeia on Oʻahu, has observed a high number of invasive plants on their property. This high density of invasive plants has inhibited their ability to perform restoration work. The goal of this study was to develop new information on the distribution and impact of invasive species present in active restoration areas at Papahana Kuaola by identifying invasive plants and creating a catalog based on their risk of invasiveness. This information can be used by Papahana Kuaola to inform ongoing efforts to eradicate invasive species on actively managed sites. I conducted biological field surveys to identify invasive plants on active restoration areas of the property. After the current invasive species were identified, identified species were then ranked by their perceived risk (high, medium, or low) according to the Hawaiʻi Pacific Weed Risk Assessment (HPWRA) based on 49 criteria. Plants not already scored by the HPWRA were independently scored using the same 49 criteria to give an estimated risk score. GPS coordinates were then used to develop maps of each species and risk group in ArcMap. Overall, 61 unique invasive species were identified at Papahana Kuaola: 49 high risk species, 7 medium risk species, and 5 low risk species. We focused on incipient populations, those invasives that have potentially severe negative impacts but limited populations. There are 18 incipient species on site that have 5 or less cluster counts, indicating low current populations. These species have been divided into 5 prioritization levels. The first grouping of incipient species include Schoenoplectus californicus, Adiantum raddianum, Dysphania ambrosioides, and Plantago major. By focusing eradication on these species, Papahana Kuaola will be able to minimize their spread and impact. The development of an invasive species catalog, along with appropriate management recommendations will inform restoration of native species at Papahana Kuaola, as well as other locations in Hawaiʻi.