Micronesian Mangrove Forests Show Some Resilience to Sea-Level Rise

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In a recent report supported by the Pacific Islands CASC, researchers modeled how mangrove forests in the Federated States of Micronesia may respond to sea-level rise in coming decades. They projected that island mangroves will likely be resilient to low and moderate sea-level rise rates, but that extreme changes in water levels could outpace natural climate adaptation mechanisms. 

Mangrove forests, with trees in the background and many aboveground roots in the foreground

Mangrove forest in Micronesia.

(Credit: Karen Thorne, USGS Western Ecological Research Center. Public domain.)

Mangrove forests are critical ecosystems for Micronesian communities, serving as both a source of important resources, such as seafood and timber, and as storm breaks that protect inland communities from storm surge and tsunamis. Healthy mangroves are resilient to some amount of sea-level rise, as waters may be outpaced by soil build up through natural processes of biomass accumulation, like decay of fallen leaves. Yet climate change projections indicate that future sea-level rise rates could overwhelm mangrove’s natural resilience mechanisms, threatening island mangrove forests. 

In a new USGS report, researchers from the Pacific Islands CASC, USGS, USDA Forest Service, Micronesia Conservation Trust, the Conservation Society of Pohnpei, and Pohnpei Forestry teamed up to explore how future sea-level rise may affect Micronesian mangrove forests. The team simulated future mangrove forests under different sea-level rise scenarios, specifically looking at how rising water levels will interact with tree species composition and natural soil accumulation. As a proof of concept, they tested the model on mangrove forests on the island of Pohnpei, which also served as the source of field data used to calibrate the model.  

They found that healthy mangroves on Pohnpei are likely to be resilient to low and moderate rates of sea-level rise, but faster changes in water levels could result in sharp declines in species diversity and eventual loss of many mangrove forests on the island. Mangrove vulnerability varied across the island, with forests on the leeward side showing more susceptibility to sea-level rise. Researchers are working with on island stakeholders in outreach efforts to local community leaders, management groups, and politicians to translate the modeling results.  As they expand this work to other islands, the authors hope their results will help stakeholders in the Federated States of Micronesia identify and preserve mangrove forests resilient to sea-level rise and develop strategies to increase the resilience of mangroves across the islands.  

This work was part of the project The Future Resiliency of Mangrove Forests to Sea-Level Rise in the Western Pacific: Initiating a National Assessment Approach supported by the Pacific Island CASC. Check out the project website here

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