Established invasive plant species monitoring: Haleakalā National Park 2012 summary report

In 2012 and 2013, the Pacific Island Network Inventory and Monitoring program established transects to monitor non-native, invasive plant species at Haleakalā National Park. Belt transects were utilized to monitor non-native species frequency and abundance in two plant communities, wet forest and subalpine shrubland. Repeated monitoring of these plant communities is planned to occur at five year intervals with objectives to detect change in non-native plant composition, distribution frequency, and cover. Because this report represents the first read of transects, an analysis of change over time is not possible. Instead, the objectives of the initial report are to 1) summarize and compare non-native richness at the plant community level, 2) determine the most common (i.e., most frequent) non-native species within each plant community, and 3) document the spatial distribution of non-native species cover across each plant community. The wet forest plant community, encompassing Kīpahulu Valley, ranged from 240-2280 m, while the subalpine shrubland ranged from 1980-3000 m, encompassing the park’s summit, headquarters, and several hiking trails open to the public. These plant communities have a history of feral ungulate disturbance along with recent and ongoing efforts to control non-native plants and animals. The study area included approximately 7,000 ha and a total of 60 non-native species were documented. Eight species of management concern to the park were recorded in the wet forest. Three of these species were the most frequently encountered non-native plants; including the shrub, Clidemia hirta, the herb, Hedychium gardnerianum, and the tree, Psidium cattleianum. Neither C. hirta nor H. gardnerianum were documented along transect surveys conducted 24 years prior. Non-native plant cover within the wet forest generally decreased with increased elevation. Ten species of management concern to the park were recorded in the subalpine shrubland. However, these species occurred at relatively low frequencies along transects. Overall, non-native plant frequency was higher in the subalpine shrubland than in the wet forest. This was largely due to the herb, Hypochaeris radicata, and the grass, Holcus lanatus, the most frequently encountered non-native species in the subalpine shrubland plant community. The results from the established invasive plant species monitoring provide a snap-shot assessment of the non-native plants in these relatively intact plant communities and compliment other plant monitoring protocols conducted by I&M, such as Focal Terrestrial Plant Community Monitoring and Early Detection of Invasive Plant Species. In addition to supplementing less-frequent surveys conducted by the park’s Resource Management division, these data collected by I&M are intended to contribute to the science-based management of Haleakalā National Park and provide consistent vegetation monitoring across the parks within the Pacific Island Network. Importantly, future I&M monitoring efforts will allow for change detection along these permanent transects and increase spatial sampling area with newly established temporary transects.