Carbon Stocks across a Fifty Year Chronosequence of Rubber Plantations in Tropical China

Chenggang Liu,Xiaotao Lü,Jiaping Pang,Martin Jepsen,Jianwei Tang

doi:10.3390/f8060209

Abstract

Transition from forest to rubber (Hevea brasiliensis Muell. Arg.) plantation has occurred in tropical China for decades. Rubber has been planted on 1 million ha to provide raw materials to the rubber industry. The role of various-aged rubber plantations in carbon (C) sequestration remains unclear. The biomass C accumulation including latex C and C distribution in soil of five different-aged stands (7, 13, 19, 25 and 47 years old) were examined. The total biomass C stock (TBC) and total net primary productivity (NPPtotal), whether with or without latex C, had a close quadratic relationship with stand age. Regardless of stand age, around 68% of the C was stored in aboveground biomass, and NPPlatex contributed to approximately 18% of C sequestration. Soil organic carbon stock in the 100-cm depth remained relatively stable, but it lost about 16.8 Mg ha−1 with stand age. The total ecosystem C stock (TEC) across stands averaged 159.6, 174.4, 229.6, 238.1 and 291.9 Mg ha−1, respectively, of which more than 45% was stored in the soil. However, biomass would become the major C sink rather than soil over a maximal rubber life expectancy. Regression analysis showed that TEC for rubber plantation at 22 years is comparable to a baseline of 230.4 Mg ha−1 for tropical forest in China, and would reach the maximum value at around 54 years. Therefore, rubber plantation can be considered as alternative land use without affecting net forest ecosystem C storage. In addition to the potential C gains, a full set of ecosystem and economic properties have to be quantified in order to assess the trade-offs associated with forest-to-rubber transition.

Highlights

Increasing atmospheric carbon dioxide (CO2 ) concentrations and global climate change are of growing concern to humankind
We found that the C stock of litter in each stand was greater than that of foliage, suggesting that litter should be considered an essential component in total biomass C stock (TBC) assessment
Regardless of stand age, around 68% of the C was stored in aboveground biomass, and NPPlatex contributed to approximately 18% of C sequestration

Summary

Introduction

Increasing atmospheric carbon dioxide (CO2 ) concentrations and global climate change are of growing concern to humankind. The world’s forests are a critical component of the terrestrial ecosystem and play a significant role in regulating the global carbon (C) cycle by serving as C sinks, thereby potentially mitigating future impacts of climate change [1]. Tropical forests represent about half of the global forest area and are believed to be the largest C reservoir of terrestrial biota [2]. They hold approximately 470 Pg C in live biomass, debris, and soil organic matter, which is approximately 55% of Forests 2017, 8, 209; doi:10.3390/f8060209 www.mdpi.com/journal/forests. Large areas of naturally-regenerated tropical forests have been lost due to land use changes, which resulted in the emission of around 1.4 Pg C year−1 to the atmosphere during 1990–2010 (~15% of global anthropogenic CO2 emissions for that time period) [4].

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