The effects of seaward distance on above and below ground carbon stocks in estuarine mangrove ecosystems

Georgia De Jong Cleyndert,Robert Marchant,Deo D Shirima,Aida Cuni-Sanchez,Neil Burgess,Kim Calders,Hamidu A Seki,Pantaleo K T Munishi

doi:10.1186/s13021-020-00161-4

Abstract

BackgroundMangrove forests have gained recognition for their potential role in climate change mitigation due to carbon sequestration in live trees, and carbon storage in the sediments trapped by mangrove tree roots and pneumatophores. Africa hosts about 19% of the world’s mangroves, yet relatively few studies have examined the carbon stocks of African mangroves. The available studies report considerable differences among sites and amongst the different pools of carbon stocks. None considered the effects of seaward distance. We present details of AGC and SOC carbon stocks for Lindi in Tanzania, and focus on how these values differ with increasing seaward distance and, how our results compare to those reported elsewhere across Africa.ResultsAGC ranged between 11 and 55 Mg C ha−1, but was not significantly affected by seaward distance. SOC for 0–1 m depth ranged from 154 to 484, with a mean of 302 Mg C ha−1. SOC was significantly negatively correlated with seaward distance. Mangrove type (estuarine/oceanic), soil erosion, soil depth may explain these differences We note important methodological differences in previous studies on carbon stocks in mangroves in Africa.ConclusionThis study indicates that seaward distance has an important effect on SOC stocks in the Lindi region of Tanzania. SOC should be fully incorporated into national climate change mitigation policies. Studies should report seaward distance and to describe the type of mangrove stand to make results easily comparable across sites and to assess the true value of Blue Carbon in Africa. We recommend focusing on trees > 10 cm diameter for AGC, and sampling soils to at least 1 m depth for SOC, which would provide a more complete assessment of the potentially considerable mangrove carbon store.

Highlights

Mangrove forests have gained recognition for their potential role in climate change mitigation due to carbon sequestration in live trees, and carbon storage in the sediments trapped by mangrove tree roots and pneu‐ matophores
As climate change mitigation has come to the fore of international scientific and political discussions [22], there has been an enhanced focus on conserving and restoring degraded ecosystems that are known to function as carbon sinks [10, 22], through mechanisms such as Reducing Emissions from Deforestation and Degradation (REDD+) and other United Nations Framework Convention on Climate Change (UNFCCC) mechanisms increasingly aim to support livelihood developments and mitigate climate change impacts through Green Climate Fund investments [23]
We address four major research questions: do carbon stocks differ with increasing seaward distance? Are there advantages of using 1 ha plots over smaller vegetation plots? What are the effects of using ≥ 5.0 or ≥ 10.0 cm diameter thresholds on above ground carbon (AGC) estimates? And, how do AGC and soil organic carbon (SOC) compare to those reported elsewhere in Africa? We hypothesized that AGC and SOC would increase with increasing seaward distance

Summary

Introduction

Mangrove forests have gained recognition for their potential role in climate change mitigation due to carbon sequestration in live trees, and carbon storage in the sediments trapped by mangrove tree roots and pneu‐ matophores. Africa hosts about 19% of the world’s mangroves, yet relatively few studies have examined the carbon stocks of African mangroves. We present details of AGC and SOC carbon stocks for Lindi in Tanzania, and focus on how these values differ with increasing seaward distance and, how our results compare to those reported elsewhere across Africa. Mangrove type (estuarine/oceanic), soil erosion, soil depth may explain these differences We note important methodological differences in previous studies on carbon stocks in mangroves in Africa. Natural drivers that drive changes in mangrove composition and distribution are important and include hydrological dynamics, the impacts of extreme weather events and sea-level rise which are projected to increase in frequency and magnitude due to global climate change, respectively [6, 21]. The significance of ‘blue’ carbon processes, pools and sinks need to be centrally factored into decision making at all scales—from global policy issues on climate change, through to resource management at sectoral (e.g. fisheries) and national levels, and even as a criterion in the selection of prospective Marine Protected Areas [24]

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