Established invasive plant species monitoring: Hawai‘i Volcanoes National Park

Simon, Melissa; Gross, Jacob; Ainsworth, Alison

In 2010 and 2011, the Pacific Island Network Inventory and Monitoring program monitored established invasive plant species at Hawaiʻi Volcanoes National Park. Belt transects were utilized to monitor non-native species frequency and abundance in two different plant communities, the wet forest and the 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, frequency, and cover. Because this report represents the first year of monitoring, change analysis is not possible. Instead, the objectives of the initial report are to 1) compare non-native richness between plant communities and sampling sites, 2) determine the most common (i.e., most frequent) non-native species within particular areas of the park, and 3) compare frequency and cover of non-native species and life forms at various scales across the park. Locations sampled within the wet forest plant community included Nāhuku/East Rift, ʻŌlaʻa, and Kahuku, while sampling within the subalpine shrubland occurred across all vegetated areas above 2000 m encompassing areas across Kahuku and above Mauna Loa strip road. The study area encompassed approximately 18,000 ha and a total of 108 non-native species were documented within these communities. Abundant non-native species in the Nāhuku/East Rift sampling frame included a fern, Nephrolepis brownii, a grass, Paspalum conjugatum, and the tree Morella faya. Non-native species that dominated ʻŌlaʻa were the shrub, Rubus ellipticus var. orborcordatus, grass Setaria palmifolia, and Psidium cattleianum trees. These wet forests have a history of feral ungulate disturbance, portions have recently burned and been affected by lava flows, and some non-native plant species management has occurred all influencing non-native plant species cover. In the Kahuku wet forest, much of the lower elevation site was recently a cattle pasture and unsurprisingly non-native plants in this community were dominated by introduced pasture grasses including Cenchrus clandestinus and Axonopus fissifolius. The wet forest in the upper elevation of Kahuku contained relatively few non-native plants with two grasses, Anthoxanthum odoratum and Ehrharta stipoides, occurring most frequently in the area. In the subalpine shrubland plant community, non-native plant cover was typically lower than the wet forest; however, the northwest portion of Kahuku did support a relatively large number of non-native species with high frequencies of occurrence. The herb, Hypochoeris radicata, was the most frequently encountered non-native species in the subalpine shrubland plant community. Though the harsh habitat of the subalpine shrubland has experienced little human manipulation, the plant community is still exposed to feral ungulates that can have a negative impact on native plants. 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 adaptive management of Hawai‘i Volcanoes 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. Greater sampling area is critical for assessing efficacy of sampling design and detecting patchy non-natives within these relatively heterogeneous landscapes.

Established invasive plant species monitoring: Hawai‘i Volcanoes National Park

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