Will Hawaiʻi Volcanoes' Protected Plant Areas Still Fit Their Plants in 2090?

Habitat types in the modeling, clockwise from top left: (A) lowland dry habitat where native vegetation is projected to contract; (B) mesic habitat where species richness may decrease by half; (C) wet habitat with plants that may contract to outside the park; (D) wet habitat expected to transition to mesic habitat; (E) dry habitat expected to become mesic and more favorable. Hawaii Volcanoes National Park/Mark Wasser.

More than 1,000 native plant species grow in the state of Hawaiʻi, most of them found nowhere else on Earth, and nearly one-third are listed as endangered or threatened by the U.S. Fish and Wildlife Service. At Hawaiʻi Volcanoes National Park, managers protect them most intensively in Special Ecological Areas (SEAs), focal sites managed to keep native plant communities and endangered species going. A team of eight researchers asked whether those areas will still suit those plants once the climate changes.

The question

Rainfall and temperature patterns in the islands are shifting and are expected to keep changing. Under future conditions the SEAs, which are roughly configured to protect representative plant communities and important species by controlling the most invasive plant and animal species, may no longer suit the native species that live in them. Managers also wanted to know whether expanding invasive plants could threaten places where natives now predominate, and what new communities might appear in and next to the SEAs.

How the team modeled it

The researchers used bioclimatic envelope models, which link climate conditions to where a species has been recorded in order to estimate the habitat that can support viable populations. Global climate models are too coarse for the islands' small-scale terrain, so the team used climate projections that a University of Hawaiʻi research center had downscaled to a much finer resolution. They modeled the ranges of 29 native and 10 invasive plants of management interest at four points in time: 2000, 2040, 2070 and 2090. For 2090 the scenario assumed moderate warming of 2.5°C (4.5°F) and more variable rainfall across most of Hawaiʻi. Because climate models are uncertain, they ran 400 possible changes and counted a place as within a species' range only if at least 80% of them made it suitable. They grouped the park's 147 SEA management blocks into 37 SEAs.

What they found for native plants

• About two-thirds of the modeled native species (18 of 29) were projected to lose range, and about one-third (11 of 29) to gain it. The biggest losses were for species with narrow climate needs, such as ʻōhelo kau lāʻau, ʻōlapa and uluhe, projected to lose 97%, 87% and 87% of their range, while lama was projected to gain 75%.
• Range losses were expected mostly in coastal and lower-elevation areas, and gains mainly in high montane and subalpine habitats, for the few species that colonize young lava flows.
• Across the park's 37 SEAs, native ranges were projected to shrink on balance. In 15 SEAs they may shrink substantially, including the SEAs around the lower Mauna Loa Strip and around Kīlauea Crater, which get intense visitation and matter to cultural practitioners. Most SEAs, especially those below 1,200 m, were projected to lose most of the native species modeled.
• Today the park's richest areas for native species line up well with the SEAs, but by 2090 most of the richest spots were projected to lie outside the SEAs. Relatively rich remnants, with 19 or more overlapping native species, were projected on the eastern edge of the Mauna Loa Southwest Rift tract, the eastern part of the Olaa tract and areas south and east of the East Rift tract.

What they found for invasive plants

Nine of the 10 invasive plants were projected to lose range in the park, with lantana the exception. That could reduce the need for control measures for those species and help some natives by easing competition. The authors urge caution: the models rely on reported distributions in Hawaiʻi and may not capture the species' full physiological limits, many invasive species have yet to reach equilibrium there so the projections are likely conservative, and other invasive plants that were not modeled will keep occupying these habitats.

What it could mean for management

The authors say managers can reasonably consider enlarging existing SEAs or creating new ones where future hotspots are likely, and improving habitat connectivity so species can shift and spread, while noting that how climate and plants will actually respond remains to be validated. The park works with state, federal and private landowners as a member of the Three Mountain Alliance to protect more than a million acres (400,000 ha) of watershed on Hawaiʻi Island, and the projections could help set priorities there. Weather stations in the areas expected to change most, and vegetation monitoring, would show how fast conditions and plants are changing.

Fencing and ungulate control, invasive species control and outplanting will stay critical. But if climate change is very rapid, the projected habitat changes might grossly underestimate real changes in distribution when natives cannot adapt quickly or compete with invasives. Assisted colonization, moving plants outside their documented ranges in anticipation of better future conditions, may be an option for species with long generation times, low reproduction, poor dispersal or a position near their physiological limits, such as lama, olopua and alaheʻe.

Sources

• Richard J. Camp (U.S. Geological Survey), Rhonda Loh (National Park Service), S. Paul Berkowitz and Kevin W. Brinck (Hawaiʻi Cooperative Studies Unit, University of Hawaiʻi at Hilo), James D. Jacobi (U.S. Geological Survey), Jonathan Price (University of Hawaiʻi at Hilo), Sierra McDaniel (National Park Service) and Lucas B. Fortini (U.S. Geological Survey), Potential impacts of projected climate change on vegetation management in Hawaiʻi Volcanoes National Park, Park Science 34(1), 2018, pp. 22-31, National Park Service; rewritten in hubnx's own words.