Summary

Studies have demonstrated that climate change is likely to impact mountain ecosystems across the globe, most typically through changes in temperature and shifts in water and nutrient availability, which could lead to upward shifts in species ranges over time. It is unclear, however, the extent to which plant species are shifting their ranges upslope in Hawaiʻi, and whether the rate of movement is different between native and non-native plant species. Mauna Loa, a 13,100 ft. (3,992 m) active volcano on Hawaiʻi Island, experienced a mean annual temperature increase of 1.07 degrees C (1.93℉) between 1970 and 2010, with no detected change in annual precipitation across the gradient, and the authors found it an excellent place to test for species range shifts.

The researchers analyzed long-term vegetation monitoring data from 1970 and 2010 from transects on the southeastern slope of Mauna Loa, Hawaiʻi in order to explore potential shifts in the elevation of both native and non-native plants. To do this, the team re-surveyed 46 vegetation plots in 2010 using the same methodology as the original 1970 surveys, which included collecting presence/absence information and the percentage cover in each vegetation layer (i.e., tree, shrub, and herb layers). To compare shifts in native and non-native species they calculated mean elevation, elevation range, and the upper and lower elevation limits of 69 species that occurred in both the 1970 and 2010 data sets.

The authors found that over a 40-year period, the direction and magnitude of shifts and whether they were driven by changes in the lower, mean, or upper limits depended on the individual species. Strawberry guava shifted its mean elevation ~233 ft. (71 m) upslope due to changes in both its upper and lower limits; weeping-grass had a large increase in mean elevation driven by an increase in its upper limit but not lower limit; molasses grass shifted downward in mean elevation by ~244 ft. (74 m), and Asian sword fern increased in mean elevation with a change in its upper, but not lower elevational limits

Take Home Points

• Individual non-native plant species showed wide variability in their elevation shifts with some species raising their upper elevational limit significantly but not their lower limit (e.g., weeping-grass, Microlaena stipoides), and others increasing both their lower and upper limits (e.g., bamboo orchid, Arundina graminifolia). Some non-native species actually shifted downward over the 40-year period (e.g., red-top grass, Melinis repens).
• The mechanisms driving shifting distributions of non-native plants are largely unknown and could be due to a variety of factors, including: 1) non-native species are still spreading to fill their climate niche, 2) increased disturbances/greater spread (e.g., changing fire regime), 3) enhanced anthropogenic dispersal (building of roads and their use), or 4) changes in habitat suitability due to a changing climate.
• The authors found that native species were generally experiencing shrinking ranges, because the lower limits of their range had increased in elevation and the upper range stayed the same. The authors believe that this stationary upper limit is likely due to the trade-wind inversion (TWI) which abruptly limits rainfall at that higher elevation. In contrast, non-native species experienced a rise in lower and higher elevation limits – perhaps because many non-native species had not yet reached the TWI elevation.

Management Considerations

• Consider increased monitoring efforts that may help detect shifts in non-native plant distributions, especially at the lower and upper elevation limits of species.
• Consider assisting native plant species dispersal across their ranges as conditions change, especially if natural dispersal corridors are absent or degraded. Non-native plants may be able to respond more rapidly to changes in environmental conditions, putting native species at a disadvantage.
• Consider increasing protection efforts for native plants or collecting seeds for future propagation and reintroduction efforts at low elevations, as non-native tree cover is increasing more rapidly than native species cover in these areas.

Summary

Merremia peltata (M. peltata) is a woody vine found throughout warm, tropical regions of the Pacific Islands and its native/non-native status across the region is uncertain. In parts of the Pacific, it is considered a troublesome weed that can smother trees and reduce native biodiversity, and the Australia and Hawaiʻi Weed Risk Assessments classify it as “high risk.” In some locations, however, this species can play an important role in rainforest regeneration and it is known to support biodiversity when growing in the forest canopy. How this species distribution will be impacted by climate change is currently unknown.

To determine the current distribution as well as potential future distributions under climate change, Taylor and Kumar used species distribution modeling based on experimental observations of M. peltata growth response to temperature, soil moisture, current distribution, and seasonal phenology. They used occurrence data to assess the fit of the model to current distributions and considered two end-of-century global climate model projections for future distribution (a warmer/much drier projection and a much warmer/less dry projection).

Results

M. peltata is expected to both expand and contract its range in response to modeled climate shifts over time. Generally, range expansion is expected on Fiji, Hawaii, New Caledonia, and Vanuatu, and contractions are expected in Papua New Guinea and the Solomon Islands. Areas currently not suitable are expected to become suitable under a future climate. In addition, substantial range contraction under a future climate is expected in Papua New Guinea. Finally, the projected changes to future ranges were consistent between climate models for Fiji, Hawaiʻi, New Caledonia, and Vanuatu, but differed for the other countries and appeared to be strongly related to rainfall.

Management Considerations

• Consider strengthening quarantine regulations and enforcement as well as surveillance around ports and airports in order to prevent the introduction of species like Merremia peltata, especially in areas where climatic suitability is expected to expand the species range in the future.
• Where M. peltata is non-native, consider potential future climate change distributions when prioritizing areas for intervention, such as eradication or containment.
• Where M. peltata is native, consider potential future climate change distributions to inform conservation strategies; modeling may identify areas of potential range contraction or refuges where protection could be prioritized.
• Consider monitoring for impacts to agriculture, native plant communities, or culturally important plant species; factors such as disturbance (clearing, typhoons) or growth form (ground or tree vine) may influence its impact on the community.

Take Home Points

• Species distribution modelling of current and potential future ranges can play an important role in invasive plant management as ranges and habitat suitability shift with changing climatic conditions.
• Increased access to species occurrence records, as well as climate-informed distribution modelling is needed to support informed decision-making.
• Integrated assessments that investigate large-scale changes to ecosystems due to multiple interacting factors are needed. How species shift in the future will depend not just on the direct effects of climate change, but also on changes in land use and disturbance, new invasive species arrivals, nutrient pollution, and species interactions.

Through a cooperative agreement with the University of Hawai’i Office of the Vice President for Research and Innovation (OVPRI), the U.S. Army Garrison is responsible for ensuring compliance with the Federal Endangered Species Act on more than 50,000 acres of U.S. Army training ground on the island of Oʻahu. The ANPRO manages 90 of the 474 federally listed endangered species in Hawaiʻi, including plants, birds, land snails, and insects. These ecologically and culturally valuable species are often located in remote, mountainous terrain that can only be accessed by highly trained biologists and technicians using 4WD vehicles and helicopters. To attain the program’s goal of balancing the requirements of the Army’s training mission with its natural resource responsibilities, the ANRPO maintains nurseries and a seed bank for rare endemic species, and engages in monitoring and surveying activities, biocontrol research and deployment, eradication of invasive plant and animal species, building fencing to keep out feral pigs and goats, and hosts public volunteer workdays to foster community engagement in conservation.

The Pacific RISA team was most excited to see the highly endangered Hawaiian land snails, known as kāhuli, which through habitat loss, climate change, predator introduction, and over-collection have been disappearing at an alarming rate. There are estimated to have once been up to 750 species across the Hawaiian Islands, but 90% of them are now thought to be extinct. Our hike would take us through forests of native species (many of which are being managed by ANRPO), up to two protected snail enclosures, one managed by the Army, and the other by the State’s Division of Forestry and Wildlife (DOFAW) and Snail Extinction Prevention Program (SEPP).

We met ANRPO Conservation Manager Jane Beachy and Rare Plant Program Coordinator Tim Chambers at the ANRPO baseyard where we were briefed, equipped with weeding tools, and fitted with spiked shoes for the steep and often muddy trail. After a 45 minute drive to the trailhead in the Wai‘anae Mountains, we hiked to Kahanahāiki, where we immediately noticed biocontrol on the very pervasive and invasive strawberry guava (Psidium cattleianum), and passed a number of rodent traps and fencing designed to keep out feral goats and pigs. Tim stopped along the way to point out the extensive work ANRPO has done to reintroduce native species, including grasses, ferns, and more well-known species like koa and ʻōhiʻa. ANRPO must not only contend with extreme conditions, predators. and invasives, but also the effects of climate change, which climate models predict will result in higher temperatures and drier conditions in the Wai‘anae Mountains.

We reached the Army snail enclosure, designed to keep out a multitude of predators, and got to work weeding out invasive species throughout the enclosure. The Army snail enclosure was recently invaded by yellow crazy ants (Anoplolepis gracilipes), so the remaining snails have been removed to SEPP’s captive rearing facility.

Our next stop was the State snail enclosure, where we immediately spotted the native tree snail Achatinella mustelina, endemic to the Wai‘anae Mountains and listed as critically endangered by the IUCN Red List Ranking. The snails seem to be thriving there – we found many of them living on the underside of the leaves of the pāpala kēpau (Rockia sandwicensis) and olopua (Notolaea sandwicensis) trees.

The hike back took us along a ridgeline where we had sweeping views of the North and West shores of O‘ahu. It also took us past a very successful plot of reintroduced hāhā (Cyanea grimesiana subsp. obatae), federally listed as endangered and found only in the Wai‘anaes. The hāhā was in bloom and its floral display seemed to surprise even our guides – their enthusiasm was contagious, and we all clambered down a steep hillside to get a closer look. ANRPO collaborates with DOFAW’s Native Ecosystem Protection and Management (NEPM) program to manage this unusual lobelia.

We would like to thank Jane and Tim for sharing their time and mo‘olelo (stories) about the good, the bad, and the ugly of what it takes to restore an ecosystem, and for the incredible job they are doing of managing natural resources in the Wai‘anaes under so much uncertainty.

Army Natural Resources Program Oʻahu
https://oanrp.com/about/

Hawaii Snail Extinction Prevention Program
https://dlnr.hawaii.gov/ecosystems/sepp/

How to Help Native Snails
https://dlnr.hawaii.gov/ecosystems/sepp/howtohelp/

ANRPO and UH
https://research.hawaii.edu/noelo/anpro-and-uh/

Oʻahu Invasive Species Committee (OISC)
https://www.oahuisc.org/

Division of Forestry and Wildlife: Native Ecosystems Protection and Management, Rare Plant Program
https://dlnr.hawaii.gov/ecosystems/rare-plants/

Adapted from the East-West Center Press Release 

Among the findings of the Fifth US National Climate Assessment, released by the White House, are that climate change in Hawaiʻi and the Pacific Islands worsens inequities and threatens unique island ecosystems, along with cultural resources, human health, livelihoods, the built environment, and access to clean water and healthy food. The assessment concludes that adaptation strategies incorporating local and Indigenous knowledge can improve the resilience of Pacific Island communities, and that efforts to reduce greenhouse gas emissions and limit climate change impacts are now underway in every US region, including the Pacific Islands.

The report’s chapter on Hawaiʻi and US-Affiliated Pacific Islands was written by 16 authors, including Pacific RISA’s Abby Frazier, Victoria Keener, Zena Grecni, Kirsten Oleson, and Chris Shuler. The chapter has 41 technical contributors and is backed by nearly 500 citations from published literature.

“Climate change continues to threaten things we care about,” said Frazier, now an assistant professor at Clark University and the Hawai‘i-Pacific chapter’s lead author. “As the devastating hurricane-fueled wildfires on Maui and Typhoon Mawar in Guam made clear, when communities are already hurting from stressors like COVID-19, extreme weather can multiply harms. The sooner we scale up global action to curb threats from climate change, the better. Fortunately, cutting emissions or preparing for new extremes also creates immediate local benefits—improved health, a stronger economy, and more resilient communities.”

The chapter’s key takeaways for the region include:

• Climate change impairs access to healthy food and water. Increasing temperatures, altered rainfall, flooding, pollution, and fisheries decline will further affect food and water availability.
• Climate change undermines human health. Climate shocks and stressors compromise healthcare and worsen long-standing social and economic inequities that contribute to illness, but community strengths and adaptation measures can boost resilience.
• Rising sea levels harm infrastructure and islands’ economies. Sea level rise intensifies loss of territory and disrupts livelihoods, but governments and communities are innovating through renewable energy, green infrastructure, and sustainable economic growth.
• Responses help to safeguard tropical ecosystems and biodiversity. Increased fire risk, severe droughts, and ocean changes have broad negative impacts on native plants and wildlife, and ocean ecosystems. Effective adaptation strategies include ecosystem protection and restoration, invasive species measures, and fire prevention.
• Indigenous Peoples and their knowledge systems are central to the resilience of island communities amidst the changing climate.

New since the Fourth National Climate Assessment, published in 2018, is the chapter’s inclusion of a key message on human health and its emphasis on food security, integration of Indigenous knowledge, and recognition of data inequities for the Pacific Islands and US Caribbean.

About the Fifth National Climate Assessment

Mandated in the Global Change Research Act of 1990, the National Climate Assessment provides authoritative scientific information about climate change risks, impacts, and responses in the US. The assessment reflects the scientific consensus and is widely used for decision-making but does not include policy recommendations nor advocate for any specific policy.

The Fifth National Climate Assessment includes 32 chapters on physical science, national-level sectors (such as water, energy, agriculture, ecosystems, transportation, health, infrastructure, etc.), regional impacts in the US, and responses. The assessment was written by a diverse team of more than 500 authors and more than 250 technical contributors from every state. The report has undergone multiple rounds of review, including three opportunities for public comment, extensive agency review, and an external review by the National Academies of Sciences, Engineering, and Medicine. The Hawai‘i and US-Affiliated Pacific Islands chapter has 16 authors and 41 technical contributors and is backed by nearly 500 citations from published literature.