UCLA

The islands of Hawaii consist of an isolated region that may be severely impacted by climate change. Currently, 134 endemic Hawaiian plants are considered extinct and 33% of the native flora are listed as threatened or endangered under the U.S. Endangered Species Act. Many of these species reside in protected areas, yet there have been no comprehensive studies assessing the impacts of climate change on this critical region. Our study examines the future climate vulnerability of native vegetation types in protected areas by utilizing a bioclimatic variables dataset containing baseline and end-of-century (NCAR RCP 8.5) climate projections for the Hawaiian Islands. We assessed seven native vegetation types (Native Dry Forest, Native Dry Shrub, Native Mesic Forest, Native Mesic Grassland, Native Mesic Shrub, Native Wet Forest, and Native Wet Shrub) using a Forest-Based Classification and Regression approach to determine how distribution ranges of these vegetation types will be impacted by climate change by the end of the century. Our study determined there are statistically significant differences for all pairwise comparisons of the selected native vegetation types in relation to baseline annual precipitation means and annual temperature means, apart from temperature overlap between Native Mesic Grassland and Native Dry Forest classifications. We utilized a multi-category classification approach as well as an individualized single category classification approach to determine potential future vegetation distributions under the NCAR RCP 8.5 climate scenario for the year 2100. Overall, the multi-category classification model had a higher classification accuracy compared to the individualized approach, however the multi-category classification approach results in an exclusionary determination of vegetation type for each pixel, whereas the individualized approach allows for overlap and may be useful for highlighting regions that can sustain two or more vegetation types in the future. Agreement between both methods found that across the entire archipelago, Native Dry Shrub is anticipated to experience the greatest contraction in range followed by Native Wet Forest, while Native Mesic Forest is anticipated to experience the greatest expansion in range, followed by Native Mesic Shrub. Understanding the relationship between future climate and vegetation vulnerability can prove to be vital for land management and conservation efforts as we plan to allocate resources towards areas that aremost severely affected by climate change.