Measuring mangrove carbon loss and gain in deltas

David Lagomasino,Seungkuk Lee,Carl Trettin,Emanuelle Feliciano,Aurélie Shapiro,Mwita M Mangora,Temilola Fatoyinbo

doi:10.1088/1748-9326/aaf0de

Abstract

Demand for mangrove forest resources has led to a steady decline in mangrove area over the past century. Land conversions in the form of agriculture, aquaculture and urbanization account for much of the deforestation of mangrove wetlands. However, natural processes at the transition zone between land and ocean can also rapidly change mangrove spread. In this study, we applied a robust field-based carbon inventory and new structural and temporal remote sensing techniques to quantify the magnitude and change of mangrove carbon stocks in major deltas across Africa and Asia. From 2000–2016, approximately 1.6% (12 270 ha) of the total mangrove area within these deltas disappeared, primarily through erosion and conversion to agriculture. However, the rapid expansion of mangroves in some regions during this same period resulted in new forests that were taller and more carbon-dense than the deforested areas. Because of the rapid vertical growth rates and horizontal expansion, new mangrove forests were able to offset the total carbon losses of 5 332 843 Mg C by 44%. Each hectare of new mangrove forest accounted for ∼84% to ∼160% of the aboveground carbon for each hectare of mangrove forest lost, regardless of the net change in mangrove area. Our study highlights the significance of the natural dynamics of erosion and sedimentation on carbon loss and sequestration potential for mangroves over time. Areas of naturally regenerating mangroves will have a much larger carbon sequestration potential if the rate of mangrove deforestation of taller forests is curbed.

Highlights

Forest growth and reforestation rates are crucial information for sustainable forest management practices and informed decision-making for restoration projects (Diaz-Balteiro and Romero 2008)
Landsat 8 Operational Land Imager (OLI) bands were used as inputs for the classification, as well as the normalized band ratios of Normalized Difference Vegetation Index (NDVI), normalized water index, normalized burn ratio, and others outlined in Green et al (1997)
Between 2000–2016 there was a total loss of 12 270 ha of mangrove forests among the four sites, representing 1.6% of the total mangrove area determined in 2000 by Giri et al (2011)

Summary

Introduction

Forest growth and reforestation rates are crucial information for sustainable forest management practices and informed decision-making for restoration projects (Diaz-Balteiro and Romero 2008). Mangrove deforestation has recently been estimated at between 0.16%–0.39% per year at regional and global scales. The underlying datasets used capture neither the dynamic changes caused by natural processes and human disturbances, nor the local scale variability in canopy structure and vegetation biomass (Richards and Friess 2015, Hamilton and Casey 2016, Hamilton and Friess 2018) for accurate accounting of carbon and payments for ecosystem services (PES). The dynamics of mangrove gains and losses have been captured using globally available radar imagery (Thomas et al 2017), but this still does not provide the fine-scale spatial and structural details needed for the valuing of different mangrove forest types for local management and restoration efforts (Ewel et al 1998)

Methods

Results

Discussion

Conclusion