Mangrove Range Expansion Rapidly Increases Coastal Wetland Carbon Storage

Abstract

The climate change-induced expansion of man- groves into salt marshes could significantly alter the carbon (C) storage capacity of coastal wetlands, which have the highest average C storage per land area among unmanaged terrestrial ecosystems. Mangrove range expansion is occur- ring globally, but little is known about how these rapid climate-driven shifts may alter ecosystem C storage. Here, we quantify current C stocks in ecotonal wetlands across gra- dients of marsh- to mangrove-dominance, and use unique chronological maps of vegetation cover to estimate C stock changesfrom2003to2010ina 567-km 2 wildlife refugeinthe mangrove-salt marsh ecotone. We report that over the 7-yr. period, total wetland C stocks increased 22 % due to man- grove encroachment into salt marshes. Newly established mangrove stands stored twice as much C on a per area basis as salt marsh primarily due to differences in aboveground biomass, and mangrove cover increased by 69 % during this short time interval. Wetland C storage within the wildlife refuge increased at a rate of 2.7 Mg C ha �1 yr. �1 ,m ore than doubling the naturally high coastal wetland C sequestration rates. Mangrove expansion could account for a globally sig- nificant increase of terrestrial C storage, which may exert a considerable negative feedback on warming.