J Plant Ecol ›› 2020, Vol. 13 ›› Issue (2): 233-240.DOI: 10.1093/jpe/rtaa005

• Research Articles • Previous Articles     Next Articles

Size- and age-dependent increases in tree stem carbon concentration: implications for forest carbon stock estimations

Su-Hui Ma1, *, Anwar Eziz1, Di Tian2, Zheng-Bing Yan1, Qiong Cai1, Min-Wei Jiang1, Cheng-Jun Ji1 and Jing-Yun Fang1   

  1. 1 Institute of Ecology, College of Urban and Environmental Sciences, and Key Laboratory for Earth Surface Processes of the Ministry of Education, Peking University, Beijing 100871, China, 2 College of Life Sciences, Capital Normal University, Beijing 100048, China

    *Corresponding author. E-mail: mash2015@pku.edu.cn
  • Received:2019-10-02 Revised:2020-01-05 Accepted:2020-02-02 Online:2020-02-04 Published:2020-04-01

Abstract:

Aims

Forest biomass carbon (C) stocks are usually estimated by multiplying biomass by a C conversion factor, i.e. C concentration. Thus, tree C concentration is crucial to the assessments of forest C cycles. As stems contribute to the large fraction of tree biomass, the canonical value of 50% or other simplified values of stem C concentration are widely used to represent the values of tree C concentration in the estimations of forest C stocks at different scales. However, C concentration variations between tree organs and within tree size and their impacts on forest C stocks are still unclear.

Methods

We conducted a global analysis of organ C concentration in age-specific trees based on 576 records of tree age, size (diameter at breast height and biomass) and C concentration data to evaluate the relationships between organ C concentrations and the changes of stem C concentration with tree age and size.

Important Findings

Tree C concentration varied significantly with organs. Stem C concentration of trees was significantly correlated with that of other tree organs, except for barks and reproductive organs. The stem C concentration increased significantly with tree size and age, which contributed to the increases in C contents of stems and trees. Using the C concentration in stems to represent the C concentrations of other organs and the whole tree could produce considerable errors in the estimations of forest C stocks (−8.6% to 25.6% and −2.5% to 5.9%, respectively). Our findings suggest that tree C accumulation in forests is related to the size- and age-dependent increases in stem C concentration and using specific C concentration values of tree organs can improve the estimations of forest C stocks.

Key words: tree organs, carbon concentration, forest carbon accounting, tree size, tree age

摘要:

森林生物量碳库通常由生物量乘以碳转化系数(即碳浓度)计算得到。因此,乔木碳浓度对评估森林碳循环至关重要。由于茎的生物量占整株乔木的比例较高,因此在不同尺度的森林碳库评估中,常以茎碳含量为50%或其他经验值代表整株乔木碳浓度。然而,碳浓度在不同器官间和径级间的变异以及其对森林碳库估算的影响仍不清楚。本研究构建了576条特定年龄和个体大小(胸径和生物量)的全球乔木器官碳浓度数据集,分析了全球乔木不同器官之间碳浓度的相关关系和茎碳浓度随着年龄与个体大小的变异规律。结果表明,乔木不同器官间碳浓度存在显著差异。其次,茎碳浓度与其他器官(除皮和繁殖器官)碳浓度显著相关。随着乔木径级和年龄的增大,茎碳浓度升高,导致茎碳含量和乔木碳含量均增大。因此,将茎的碳浓度直接应用于其他器官和整株乔木均会为森林碳库评估引入系统误差(分别为-8.6%–25.6%和-2.5%−5.9%)。本研究结果表明,森林乔木碳累积与茎碳浓度个体大小和年龄依赖的增加有关,使用特定的乔木器官碳浓度值可以提高森林碳库评估。

关键词: 乔木器官, 碳浓度, 森林碳评估, 乔木个体大小, 乔木年龄