Hawaiian Endemic Plants Are Vulnerable to Climate Shifts, New Study Suggests
Over 2,000 different plant species are found in Hawai‘i, however, only half are native to the islands. The other half were introduced by people. Some of these introduced, non-native plant species are not disruptive to the natural ecosystem, while others have become invasive and displace native species by taking over their habitat. Of the approximately 1,000 native plant species, nearly all are endemic to Hawai‘i, meaning they are found nowhere else in the world. Because Hawai‘i’s native plant life is highly endemic, it is more vulnerable to habitat loss that can result from changes in climate and encroachment of non-native or invasive species. Already, one-third of native Hawaiian plants are listed as endangered or threatened by the U.S. Fish and Wildlife Service.
Temperature and rainfall patterns in the Hawaiian Islands are shifting and are expected to continue to change, leading managers at Hawai‘i Volcanoes National Park to ask how these changes may impact plant distributions. Two new reports, co-authored by scientists supported by the Pacific Islands CASC (formerly the Pacific Islands CSC), describe research seeking to answer that question. How plants will respond to changes in temperature and precipitation is a major concern for resource managers, because the park’s Special Ecological Areas (SEAs) may no longer provide suitable habitat for rare and endangered plants under future climate conditions. SEAs are intensively managed research units within Hawai‘i Volcanoes National Park. They were implemented in 1985 as an approach for managing rare and endangered plants by controlling non-native and invasive plant species and animals.
To project how plant species will respond to changing conditions, researchers combined climate data with information on plant distributions for 29 native and 10 invasive plants. The plants chosen for analysis were identified by park resource managers as influential to the management of ecologically sensitive areas, such as Hawai‘i Volcanoes National Park SEAs.
Results show that plant species’ range depends on a number of factors, including temperature, precipitation, soil, and the locations where they were historically found. Projections show that if temperatures increase and precipitation becomes more variable in the future, as some models forecast, by the end of the century, 60% of the native plant species examined in the study could experience a range contraction, while 30% could experience an increase in range size.
Another major finding is that hotspots containing habitats with particularly high numbers of native species may shift to new locations that are outside current SEA boundaries. This is because by the end of the century, many of the existing SEAs might no longer have suitable habitat for most native species of concern. This finding can help managers make decisions about the delineation of boundaries of current and future SEAs.
Along with helping park managers assess the configuration of SEAs, these results can also inform the park’s managers in their efforts to monitor vegetation and work with adjoining landowners to prioritize conservation work on the whole island. The Hawai‘i Volcanoes National Park is a member of the Three Mountain Alliance (TMA), which collaborates with state, federal, and private landowners to protect more than a million acres of watershed. Protection of native species diversity and invasive species management are among the TMA activities that would be directly informed by this study’s results.
This research can also be used by cultural resource managers throughout Hawai‘i. Many native plants discussed in this paper have deep significance to indigenous culture. For example, the Koa (Acacia koa) has been used to craft canoes, dyes and medicines. Hawaiians currently collect traditionally important plants from areas that are within or near Hawai‘i Volcanoes National Park. Science from this study can inform, for example, Hawaiian cultural practitioners by helping them understand where collection sites may need to be relocated to track the shift in plant-species ranges that are due to climate change.
This publication is a product of the Pacific Islands CASC-funded project “Assessing the Potential Effects of Climate Change on Vegetation in Hawai‘i Volcanoes National Park”. Learn more about the projecthere.
Photos (Left to Right): 1. Removal of invasive ginger makes way for Vaccinium berries, important food source for an endemic goose on Hawai‘i (NPS). 2. The ʻōhiʻa lehua (Metrosideros polymorphaI) is a native plant, adapted to growing in Hawai‘i's variable environment (Alan Cressler).
Figure (click to enlarge): Native species richness (of the 29 species) using cool to warm colors to represent overlapping distributions of few to many species, respectively. The top panel shows that the present (year 2000) distribution of hotspots in the national park aligns well with the distribution of SEAs. As shown in the lower panel, projected species richness at the end of the century (year 2090) predominately contracts from the national park, resulting in few species hotspots within SEA boundaries. (Camp et al., 2018)