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

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 (NPP total), 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 NPP latex 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.

Stand age‐related effects on soil respiration in rubber plantations (Hevea brasiliensis) in southwest China

“…In this study, the litter production increased from the 12‐ to the 32‐year plantation and decreased from the 32‐year to the 49‐year plantation (Table ). Thus, we can speculate that mature rubber plantations may have greater NPP than young and old‐growth rubber plantations, which was also reported by a recent study in rubber plantations of different stand age in Xishuangbanna (Liu et al, ). Furthermore, the relatively higher tree density may also lead to greater photosynthate transported to root systems in mature plantations (Table ), and hence show higher root activities and root respiration, giving rise to the R A variation among different stands.…”

“…This means that most of the rubber plantations will become old-growth stands that need to be felled and replanted in the coming two decades. Although the total ecosystem C storage will increase with increasing stand age (Liu et al, 2017), our results showed that increasing R S with increasing stand age will partly offset the increased soil C storage, keeping it relatively stable in the long term. Therefore, the effect of stand age on rubber plantation C exchange and soil C dynamics should be evaluated in future studies estimating regional/global-scale rubber plantation C storage.…”

“…This result was consistent with those of Ma et al () and Zhao et al () in coniferous and deciduous plantations in north China, and with those of Clark et al () in slash pine plantations in north Florida, USA. Although previous studies showed that soil C sequestration increased with increasing rubber plantation stand age in Xishuangbanna (Liu et al, ), the higher Q 10 of R S along with rubber tree growth could partly offset the C storage increment under the future global warming scenario. To better understand the effect of age on the soil C dynamics and the changes in the feedback of C exchange to increasing temperature in plantations, future studies should pay more attention to the variation in the response of R S to increasing temperature in rubber plantations of different stand age.…”

“…Lang, Cadisch, Xu, and Blagodatsky () found that R S decreases after the conversion of tropical rainforest to rubber plantation, and Song et al () found that the C sink strength was significantly higher in an established rubber plantation than in a primary tropical rainforest. Within rubber plantations of different stand ages, Liu et al () found that the total ecosystem C stock increased with increasing stand age. To clearly demonstrate the changes in C dynamics resulting from rubber plantation growth, the responses of R S components to variations in stand age‐related factors and the relative responses of the R S components to increasing temperature in rubber plantations of different stand ages are needed.…”

“…These include: soil temperature and soil water availability (Zhou, Guo, & Meng, 2013;Zhou, Xu, Kang, & Sun, 2015;Zimmermann, Davies, Peña de Zimmermann, & Bird, 2015), vegetation type (Bahn et al, 2010;Raich, Tufekcioglu, Rustad, Huntingdon, & Boone, 2000), substrate availability (Zheng et al, 2009), nutrient input (Raich & Schlesinger, 1992;Schaefer, Feng, & Zou, 2009), soil texture (Dilustro, Collins, Duncan, & Crawford, 2005) and topography (Kang et al, 2010). Moreover, forest metabolism changes as stand age increases, which influences forest net primary production (Gower, Mcmurtrie, & Murty, 1996;Yan, Wang, Zhou, & Zhang, 2006), soil C stocks (Liu, Pang, Jepsen, Lü, & Tang, 2017), plant root activity (Wang et al, 2017) and soil microbial activities (Bauhus, Pare, & Cote, 1998;Lucas-Borja, Hedo, Cerdá, Candel-Pérez, & Viñegla, 2016). All of these may have a great impact on forest R S .…”