Fortini, L.B., Jacobi, J.D. (2018). Identifying Opportunities for Long-Lasting Habitat Conservation and Restoration in Hawaii’s Shifting Climate, Regional Environmental Change, 18, 2391-2402. https://doi.org/10.1007/s10113-018-1342-6

Summary

Knowing how major vegetation types (biomes) might shift in a landscape as the climate changes is important for conservation planning.  Investments in restoration or species recovery might best focus on areas that are less likely to change to a different biome, while sites likely to change character to a different biome might present opportunities for translocation.  To investigate the stability of Hawaiʻi’s biomes to projected changes in climate, Fortini & Jacobi first modeled the potential current distribution of four main native biomes (dry shrubland, dry forest, mesic forest & wet forest) across the Hawaiian Islands, and then projected future biome distributions using precipitation and temperature from three end of century climate scenarios downscaled to Hawaiʻi that correspond to average temperature increases of 1.7 degrees Celsius (1.8 degrees Fahrenheit), 2.5 °C (4.5 °F), and 3.3 °C (5.9 °F). Despite large differences in future climate projections, the authors found that 35% of the areas considered are projected to maintain their currently most compatible native biome.  However, some biomes with little expected change in overall extent are projected to experience large shifts in location.

Results

The area suitable to native mesic forest is projected to decrease substantially, while the area suitable to native dry shrubland is projected to expand.  Area suitable to native wet forests increase in a wet climate change scenario and decrease in the drier scenarios. The total area suitable for dry forest remains relatively stable, but shifts across the landscape due to changes from dry forests to dry shrubland that are offset by changes from mesic forest to dry forest. Under all the climate change scenarios considered, a large portion of areas that are currently most suitable to dry shrubland and wet forest are expected to remain suitable to those same biomes. The patterns generally held across all islands, however dry shrubland increases are larger for Oʻahu and Kauaʻi, mesic forest loss is smaller for Hawaiʻi Island, and areas suitable to dry forest on Maui are projected to decrease.

Management Implications

• High-confidence, native-dominated “stasis” areas were mostly wet forest.  These areas offer options for long-term conservation as they are expected to have the greatest resilience across a range of potential future climates.
• Managers of mesic forest and dry forest face the loss or shift of large areas of these forest types and may need to consider a portfolio of tools to conserve the high levels of biodiversity found within.
• A decrease in biome suitability at a location implies increased risk of mortality of native component species and opportunities for establishment of invasive species.
• A portion of the landscape (primarily coastal areas and lower elevation wet forests) is projected to be only marginally suitable for any native biome by the end of the century. These areas may be especially susceptible to biological invasions.

Take Home Points

• Despite a high level of uncertainty, climate change is expected to force large shifts in the major biomes in Hawaiʻi by the end of the century, and proactive approaches will be needed to conserve biodiversity, ecosystem services, and livelihoods associated with affected biomes.
• While this approach reveals potential large-scale shifts in biomes, factors such as substrate age, fog interception, and non-climactic factors may be important for determining vegetation patterns at finer spatial scales. Therefore, there are likely other climate change refugia or areas for “stasis” for species not identified by this study that will be important to find and protect.