Ecosystem carbon stocks of mangroves across broad environmental gradients in West-Central Africa: Global and regional comparisons

Globally, it is recognized that blue carbon ecosystems, especially mangroves, often sequester large quantities of carbon and are of interest for inclusion in climate change mitigation strategies. While 19% of the world’s mangroves are in Africa, they are among the least investigated of all blue carbon ecosystems. We quantified total ecosystem carbon stocks in 33 different mangrove stands along the Atlantic coast of West-Central Africa from Senegal to Southern Gabon spanning large gradients of latitude, soil properties, porewater salinity, and precipitation. Mangrove structure ranged from low and dense stands that were 35,000 trees ha-1 to tall and open stands >40m in height and -1. Tremendous variation in ecosystem carbon (C) stocks was measured ranging from 154 to 1,484 Mg C ha-1. The mean total ecosystem carbon stock for all mangroves of West-Central Africa was 799 Mg C ha-1. Soils comprised an average of 86% of the total carbon stock. The greatest carbon stocks were found in the tall mangroves of Liberia and Gabon North with a mean >1,000 Mg C ha-1. The lowest carbon stocks were found in the low mangroves of the semiarid region of Senegal (463 Mg C ha-1) and in mangroves on coarse-textured soils in Gabon South (541 Mg C ha-1). At the scale of the entirety of West-Central Africa, total ecosystem carbon stocks were poorly correlated to aboveground ecosystem carbon pools, precipitation, latitude and soil salinity (r2 = ≤0.07 for all parameters). Based upon a sample of 158 sites from Africa, Asia and Latin America that were sampled in a similar manner to this study, the global mean of carbon stocks for mangroves is 885 Mg C ha-1. The ecosystem carbon stocks of mangroves for West-Central Africa are slightly lower than those of Latin America (940 Mg C ha-1) and Asia (1049 Mg C ha-1) but substantially higher than the default Intergovernmental Panel on Climate Change (IPCC) values for mangroves (511 Mg C ha-1). This study provides an improved estimation of default estimates (Tier 1 values) of mangroves for Asia, Latin America, and West Central Africa.

全球范围内，蓝碳生态系统（blue carbon ecosystems），尤其是红树林（mangroves），通常能够固存大量碳，因此被纳入气候变化减缓战略的考量范畴。尽管全球19%的红树林分布于非洲，但该区域的红树林却是所有蓝碳生态系统中研究程度最低的类群之一。本研究对西非-中非大西洋沿岸（从塞内加尔至加蓬南部）的33处不同红树林林分开展了生态系统总碳储量量化工作，采样范围覆盖了纬度、土壤性质、孔隙水盐度及降水的显著梯度变化。红树林林分结构跨度极大：从每公顷35000株的低矮密植林分，到高度超40米的开阔林分。研究测得的生态系统碳（C）储量存在极大差异，范围为154至1484兆克碳每公顷（Mg C ha⁻¹）。西非-中非区域所有红树林的平均生态系统总碳储量为799兆克碳每公顷。土壤碳库平均占总碳储量的86%。碳储量最高的区域为利比里亚及加蓬北部的高大红树林林分，其平均碳储量超过1000兆克碳每公顷。碳储量最低的区域则为塞内加尔半干旱区域的低矮红树林（463兆克碳每公顷），以及加蓬南部粗质地土壤上的红树林（541兆克碳每公顷）。在整个西非-中非区域尺度下，生态系统总碳储量与地上碳库、降水量、纬度及土壤盐度均相关性极弱（所有参数的决定系数r²≤0.07）。基于本研究采用相似采样方法获取的非洲、亚洲及拉丁美洲共158个样点数据，全球红树林碳储量的平均水平为885兆克碳每公顷。西非-中非区域红树林的生态系统碳储量略低于拉丁美洲（940兆克碳每公顷）与亚洲（1049兆克碳每公顷），但远高于政府间气候变化专门委员会（Intergovernmental Panel on Climate Change, IPCC）给出的红树林默认碳储量值（511兆克碳每公顷）。本研究为亚洲、拉丁美洲及西非-中非区域的红树林默认碳储量估值（一级默认值，Tier 1 values）提供了更精准的估算结果。