Impact of Sea-Level Rise on Coastal Plants and Cultural Sites

Science Center Objects

One of the impacts of global climate change for the Hawaiian Islands is a projected increase in sea level of about one meter by the year 2100. This change will impact both biological and cultural resources located along the coastline. Few intact native coastal and lowland plant communities remain in Hawai‘i. Many of those that remain contain listed endangered species and provide important habitat for other species such as seabirds, shorebirds, and native invertebrates. Where upslope habitats are available, some coastal plant communities may be able to migrate in response to sea level rise. However, in sites that have no upslope opportunities due to habitat modification by human development, the species and communities are vulnerable to loss. Similarly, many native Hawaiian cultural sites are found in coastal areas and are highly vulnerable to sea level rise since they are fixed in place. This project will use projections of sea‐level rise and coastal inundation to assess the vulnerability of native plant communities and associated cultural sites between now and 2100.

Kamehame Beach on Big Island, Hawai‘i
Kamehame Beach, Hawai‘i Island, Hawai‘i. Photo: J. Jacobi

Overview:

Coastal strand vegetation
Coastal strand vegeation in Kamilo, Hawai‘i. Photo: R. Warshauer

One of the impacts of global climate change for the Hawaiian Islands is a projected increase in sea level of about one meter by the year 2100. This change will impact both biological and cultural resources located along the coastline. Few intact native coastal and lowland plant communities remain in Hawai‘i. Many of those that remain contain listed endangered species and provide important habitat for other species such as seabirds, shorebirds, and native invertebrates. Where upslope habitats are available, some coastal plant communities may be able to migrate in response to sea level rise. However, in sites that have no upslope opportunities due to habitat modification by human development, the species and communities are vulnerable to loss. Similarly, many native Hawaiian cultural sites are found in coastal areas and are highly vulnerable to sea level rise since they are fixed in place. This project will use projections of sea‐level rise and coastal inundation to assess the vulnerability of native plant communities and associated cultural sites between now and 2100.

An understanding of how sea level rise may affect remaining native plant communities will be needed to develop and implement adaptation measures. Roads, human communities or geology may act as barriers to natural shoreline retreat, and in those areas, active management or relocation efforts may be necessary. Using a landscape‐based vulnerability analysis framework, we will characterize the relative vulnerability of sites and species to sea level rise, determine the important proximate causes of vulnerability for each, and propose adaptation options.

Project Objectives:

The Pacific Islands Ecosystem Research Center has access to approximately 150 location records of coastal native vegetation from surveys conducted by Center personnel and other sources. Further surveys using the methodology described in Warshauer et al. (2009) will be conducted, as needed, to extend coverage under this project to the  remaining areas of the coastline of the main Hawaiian Islands (excluding Ni‘ihau) that still contain coastal

plant communities. We will delineate and characterize these native shoreline plant communities with regard to species, diversity, disturbance, and other factors. Elevations of these plant communities will be derived from LiDAR‐based DEMS developed by the US Army Corps of Engineers and other sources.

Ilima and Hinahina at Kaena Point on Oahu Island, Hawaii
‘Ilima and Hinahina at Ka‘ena Point on O‘ahu, Hawai‘i. 

Progress:

During 2015 the coastal vegetation along the coastlines of the main Hawaiian Islands were assessed through a combination of image analysis, combined with data from new and previous field surveys. Image analysis has been conducted using the very high-resolution imagery obtained by Pictometry International, which has a spatial resolution of approximately 20 cm. Status of the plant communities is assigned to one of five categories, based on a combination of vegetation structure and species composition. Additionally, data on important cultural resource sites has been compiled from various sources and is being generalized into a non-sensitive format for analysis. As soon as the vegetation status surveys have been completed we will be focusing on sites with high-quality coastal vegetation and intersecting their distribution with projected sea level rise maps obtained from NOAA and the University of Hawaii at Manoa, as well as with current and projected coastal development areas based on Hawaii State and County land use zoning maps.