Changes in Carbon Pool and Stand Structure of a Native Subtropical Mangrove Forest after Inter-Planting with Exotic Species Sonneratia apetala

Weizhi Lu,Luzhen Chen,Guanghui Lin,Canmou Wang,Guangxuan Lin,Xiaona Du,Yan Ma,Wenqing Wang,Shengchang Yang,John F Valentine

doi:10.1371/journal.pone.0091238

Abstract

In this study, we compared stand structure, biomass and soil carbon pools, and litterfall production between a mixed mangrove forest consisting of Aegiceras corniculatum inter-planted with the exotic Sonneratia apetala and a native monospecific forest dominated by A. corniculatum in the intertidal area of Zhanjiang, Guangdong Province, southeast China. The goal of this study was to test the hypothesis that inter-planting fast growing exotic mangrove S. apetala into subtropical native mangrove forests will significantly increase C sequestration. Although the tree heights and basal diameters of S. apetala were significantly higher than those of A. corniculatum, the density of the 12-year-old S. apetala trees in the mixed forest was much smaller than that of A. corniculatum in the monospecific forest. In contrast to several previous studies on S. apetala forests planted directly on mangrove-free mudflats, the mixed mangrove forest showed no significant difference in either standing biomass or soil carbon pools from the native monospecific mangrove forest (p = 0.294 and 0.073, respectively) twelve years after inter-planting with S. apetala. Moreover, carbon cycling was likely speeded up after inter-planting S. apetala due to higher litterfall input and lower C/N ratio. Thus, inter-planting fast-growing S. apetala into native mangrove forest is not an effective way to increase carbon sequestration in this subtropical mangrove forest. Given that exotic plant species may exert negative impact on native mangrove species and related epifauna, this fast-growing mangrove species is not suitable for mangrove plantation projects aiming mainly at enhancing carbon sequestration.

Highlights

Mangrove wetlands have great ecological and economic value, including high primary productivity, effective carbon (C) storage, high epifaunal diversity and great benefits for aquaculture [1,2,3,4,5]
As international climate agreements emphasize Reduced Emissions from Deforestation and Degradation (REDD+) as a key option for mitigating climate change [10], attention has been drawn to C sequestration potentials of mangrove forests, salt marshes and seagrass beds, as well as measures to enhance these C sinks [10,11,12]
The 12-year-old S. apetala comprised the majority of the biomass in the mixed forest (Table 2)

Summary

Introduction

Mangrove wetlands have great ecological and economic value, including high primary productivity, effective carbon (C) storage, high epifaunal diversity and great benefits for aquaculture [1,2,3,4,5]. There is increasing concern about the continued loss and degradation of mangroves, as 35% to 86% of the global mangrove area has been lost during the last several decades [6,7,8,9]. Afforestation and reforestation can be effective methods for increasing forest ecosystem C sequestration [13,14]. Large-scale efforts have been made to restore degraded mangroves and create new mangrove forests around the world [15,16]. In the tropical and subtropical areas of mainland China, plantation is a common method for restoring mangrove forests [17]. It was estimated that the total area of S. apetala plantations in China reached 3800 ha, which accounts for more than 50% of total replanted mangrove area [17]. There were still debates on whether S. apetala in China is an invasive species or a great restoration species [18]

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Conclusion