Damage and recovery assessment of the Philippines' mangroves following Super Typhoon Haiyan
Introduction
Mangroves are highly productive coastal ecosystems found within the intertidal zones of the tropics and subtropics ranging from 35° N to 40° S latitude (Giri et al., 2011b). Mangroves provide numerous ecosystem goods and services that support human livelihoods and well-being, and are critically important to nature and society (Alongi, 2002, Duke et al., 2007). Mangroves have traditionally been used by coastal populations for construction materials, food, fuel, and medicine (Walters, 2005). In addition to providing suitable breeding and feeding grounds for numerous aquatic and avian species, undisturbed mangrove ecosystems provide coastal protection from erosion, tropical cyclones, and tsunamis (Alongi, 2008, Chmura et al., 2003, Lee et al., 2014); are closely coupled to neighboring ecosystems (e.g., sea grasses and coral reefs) (Mumby et al., 2004); and store carbon (McLeod et al., 2011, Siikamäki et al., 2012, Twilley et al., 1992).
Despite the well-understood importance of mangroves, this biome has become among the most threatened in the past half century (Van Lavieren et al., 2012). Globally, pressures from land use competition have resulted in extensive deforestation and degradation. Brackish-water aquaculture, agriculture, salt production, infrastructure development, and forest extraction are among the leading drivers of mangrove loss, worldwide (Food and Agriculture Organization of the United Nations, 20, Primavera, 1995, Primavera, 2005a). Natural disturbances such as high water surge, tropical cyclones, tsunamis, and wave action have also contributed to mangrove loss (Cornforth et al., 2013, Giri et al., 2008, Paling et al., 2008); however, mangroves are generally more resilient to natural perturbations than to human-induced disturbances (Jimenez et al., 1985).
Typhoon Haiyan, known as “Super Typhoon Yolanda” in the Philippines, made landfall in Eastern Samar, Philippines, on November 8, 2013. According to the Saffir-Simpson hurricane wind scale (SSHWS), Haiyan was rated as a category 5 hurricane with maximum sustained winds of over 251 km/h and wind gusts greater than 300 km/h (Fig. 1). The inordinately powerful typhoon damaged 1.1 million housing structures, displaced 4.1 million people, and caused over 6000 deaths (National Disaster Risk Reduction and Management Council, 2013, United States Agency for International Development, 2014). In the aftermath of Typhoon Haiyan, the Philippines' Environment Secretary announced plans for mangrove replanting and rehabilitation throughout the Philippines to provide bio-protection from future natural disasters similar to Haiyan (Department of Environment and Natural Resources, 2013). Effective mangrove restoration requires precise information on the geographic distribution as well as extent and severity of damage. Time-series remotely sensed measurements coupled with in situ observations are needed to monitor mangrove damage and recovery at a large spatial scale. Typically, studies of storm impacts on mangroves have used either remote sensing (Wang and D’Sa, 2009, Wang, 2012) or re-surveys of forest plots (Kauffman and Cole, 2010, Smith et al., 2009); however, neither on their own provide a complete assessment. Therefore, the aim of this study is to use remote sensing, coupled with ground observations, to map and quantify change in mangrove condition resulting from Typhoon Haiyan and monitor the subsequent temporal pattern of recovery. The data and information from this work are useful for developing rehabilitation and conservation strategies and providing baseline information for future monitoring.
Section snippets
Study area
The Republic of the Philippines is an archipelago of 7107 islands located off the southeastern coast of Asia. With an extensive coastline comprising numerous low-wave energy intertidal bay areas and a tropical climate, the Philippines provides ideal environmental conditions for mangrove growth. In 2010, the total mangrove area of the Philippines was approximately 240,000 ha, with the greatest extent located in the provinces of Palawan, Sulu, and Siargao Island, Surigao del Norte (Long et al.,
Results
We found general patterns of mangrove damage with the greatest decreases in NDVI values, indicating increasing severity of mangrove disturbance, occurring in proximity to Typhoon Haiyan's eye transect. According to Chen et al. (Chen et al., 2013), most tropical storms cause the greatest damage severity on the right and front side of the eye track, where wind and wave stress can be up to 25% greater than on the left. Consistent with most tropical storms (Dahal et al., 2014), the greatest extent
Discussion
Tropical storms are a frequently occurring phenomenon in the Philippines and greatly influence mangrove forest dynamics. Similar to most mangroves worldwide, mangroves in the Philippines are mostly located in remote and inaccessible regions, making it difficult, if not impossible, to conduct a comprehensive impact assessment from field surveys alone. Remote sensing offers consistent, timely, and reliable measurements that allow disturbance monitoring across large areas.
The results from this
Author contributions
All listed authors contributed to study design. Authors Long and Giri performed analysis and Long prepared figures and wrote the first draft of the manuscript. Giri, Primavera, and Trivedi revised the draft. Primavera and Filipino colleagues organized the field surveys, with suggestions from Trivedi. All authors read and approved the final version of the manuscript.
Conflicts of Interest
The authors declare no conflicts of interest.
Acknowledgments
Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Work performed under U.S. Geological Survey contract G13PC00028. ZSL gratefully acknowledge the efforts of the field team including representatives from Guiuan Development Foundation (GDFI), Environmental Leadership and Training Initiative (ELTI), Haribon Foundation, Tambuyog Development Center, Conservation International, University of the Philippines Diliman,
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2022, Forest Ecology and ManagementCitation Excerpt :In reality, the calculated project benefits are affected by natural disasters. Natural disturbances such as high water surges, tropical cyclones, tsunamis, and wave action are contributors to mangrove loss, however, mangroves are generally more resilient to natural disasters than to anthropogenic disturbances (Long et al., 2016). Hence, climate-related damages to mangrove ecosystems also threaten human communities that rely on them for subsistence livelihoods (Chow, 2018).
- 1
Contractor to the U.S. Geological Survey (USGS) Earth Resources Observation and Science (EROS) Center.
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Work performed under U.S. Geological Survey contract G13PC00028.