Dean Brigham Young University Provo, Utah, United States
Invasive species threaten the survival of native island ecosystems. On the island of Molokai, Hawaii, the invasive tree Prosopis juliforia, has overtaken all costal dune areas resulting in the loss of native vegetation’s habitat. Chenopodium oahuense and Sesbania tomentosa, two endemic plants have experienced significant habitat loss as a result of invasion and are both endangered. With the loss of native low-lying ground cover the area has likewise experienced a loss of seabird-nesting habitat. The introduction of invasive mammals has reduced all seabird populations to Molokai’s tall coastal sea cliffs and offshore islands. The rapid decline of Molokai’s dune system has prompted multiple restoration efforts across Molokai’s Northwest coast, particularly within the Mokio Preserve. The goals of our study were to evaluate the effectiveness of restoration projects in restoring native plant and animal habitat across the Mokio Preserve, a restoration area consisting of a large portion of Molokai’s Northwestern coastal dunes, where populations C. oahuense, S. tomentosa, and reintroduced seabirds (Ardenna pacifica) can be found. Our approach to addressing our goals was to create a land-cover map via the collection and processing of UAV (unmanned aerial vehicle) obtained imagery into a species-level classified orthophotomosaic, with which we compared species richness and abundance across time-segmented restoration areas. We were able to use point data representing endangered populations, seabird nesting sites, and other species identification to determine the approximate abundance of species throughout restored and unrestored areas. Here we show species richness to be highest in areas where Kiawe removal occurred earlier. The more recent removal areas exhibited lower species richness when compared to earlier removal areas, yet remained significantly higher when compared to areas where there was no removal. We conclude that Kiawe removal and other restoration methods utilized in the Mokio Preserve are effective in restoring species richness. Likewise, longer time intervals from initial removal events are related to higher levels of species richness. In conclusion, this study suggests invasive species removal and predator restrictive measures in similar highly invaded environments can be effective in restoring native ecosystems. Our results also support the further use of UAVs and classification software as effective tools in ecosystem restoration.
