Modeling Climate-Driven Changes to Dominant Vegetation in the Hawaiian Islands
Hawaiʻi is home to a rich diversity of native plants, about 90 percent of which are found nowhere else in the world. However, changing climate conditions may reduce the amount of suitable habitat for native plants and contribute to the spread of invasive plant species. The goal of this project was to better understand how Hawaiian native and invasive plants will respond to climate change. Scientists focused on 10 important native and five important invasive plant species, using over 35 years of data from thousands of locations in Hawai‘i to assess the plants’ preferred climate conditions and model their likely best future habitat based on climate change projections. The resulting maps and findings provide an initial set of decision support tools to help resource managers identify key locations for conserving native plants (and the birds and insects that rely on them) and for anticipating and controlling the spread of invasive plant species.
There is a broad consensus within the scientific community that global climate is undergoing a comparatively rapid change. Since many plants and animals depend on specific types of climate, it is imperative to understand:
- The details of species’ climatic preferences
- How climates may change in the future
- How species may respond to these changes
Species distribution modeling (SDM) is an increasingly important tool to address conservation biology and global change issues. As Fortini and colleagues described in their largest vulnerability assessment in the US, SDMs provide critical information on biological refuges and potential future shifts in species ranges. In addition, climate changes could alter not only range, but abundance and capacity to persist. Whereas explicit spatial habitat models typically project occurrence, here we generate species models of abundance projected in response to environmental predictors.
This project gathered together over 35 years of data from thousands of locations in Hawai‘i where vegetation was surveyed recording the details of all plant species found at each site. This permitted us to relate characteristics of the vegetation to specific aspects of the climate (in terms of rainfall and temperature, for example) that can be derived from detailed climate maps. We excluded highly invaded plots for the native species models, whereas agricultural and urban areas were included in the modeling to show pre-development scenarios. We focused on ten important native and five important invasive plant species (mostly trees) in order to understand the characteristics of each species’ preferred climatic habitat.
Species were selected based on their ecological “importance” in communities, as well as on how much field data was available to analyze for this study. Colleagues at the University of Hawai‘i at Mānoa, USGS, NOAA, and other agencies were simultaneously researching how climate is changing and producing maps of projected future climate. Using these climate projections, and the relationships we have drawn about each species’ preferences, we produced estimates of where species’ best habitat may be in the future.
For native species, this is important because these areas may be key locations to focus conservation efforts, especially since many unique animals depend on native vegetation. For invasive species, these projections provide managers a powerful tool with which to target areas for control before invasive species are able to move into new habitats (and potentially disrupt natural ecosystem processes).
To that end, we also examined characteristics of species growth rates and how their fruits/seeds are dispersed in order to understand how quickly they may be able to respond to changing climates and potentially move into newly emerging habitat. Together, the present and future habitat maps and the ecological characteristics of our focal species provide an initial set of supporting tools for managers and decision makers.