Data from: Carbon content of tree tissues: a synthesis

Assessing the potential for forest carbon (C) capture and storage requires accurate assessments of C in live tree tissues. In the vast majority of local, regional, and global assessments, C content has been assumed to be 50% of tree biomass; however, recent studies indicate that this assumption is not accurate, with substantial variation in C content among tree species as well as among tissue types. Here we conduct a comprehensive literature review to present a global synthesis of C content in tissues of live trees. We found a total of 253 species-specific stem wood C content records owing to 31 studies, and an additional 34 records of species with C content values of other tissues in addition to stem wood. Stem wood C content varied significantly as a function of biome (tropical, subtropical/ Mediterranean, temperate/ boreal) and species type (conifer, angiosperm). Conifer species exhibited greater wood C content than angiosperm species (50.8 ± 0.7% (95% C.I.) vs. 47.7 ± 0.3%, respectively), a trend that was consistent among all biomes. Although studies have documented differences in C content among plant tissues, interspecific differences in stem wood appear to be of greater importance overall: among species, stem wood C content explained 37, 76, 48, 81, and 63% respectively of the variation in bark, branch, twig, coarse root, and fine root C content values, respectively. In each case, these intraspecific patterns approximated 1:1 linear relationships. Most published stem wood C content values (and all values for other tree tissues) are based on dried wood samples, and so neglect volatile C constituents that constitute on average 1.3 – 2.5% of total C in live wood. Capturing this volatile C fraction is an important methodological consideration for future studies. Our review, and associated data compilation, provides empirically supported wood C fractions that can be easily incorporated into forest C accounting, and may correct systematic errors of ~1.6 – 5.8% in forest C assessments.评估森林碳（Carbon, C）捕获与封存潜力，需要精准测定活立木组织中的碳含量。在绝大多数本地、区域及全球尺度的碳评估中，碳含量均被假定为树木生物量的50%；但近期研究表明这一假定并不准确，不同树种以及不同组织类型间的碳含量存在显著差异。本研究开展全面文献综述，对活立木组织的碳含量进行全球综合分析。基于31项研究，共获得253条针对特定树种的茎干木材碳含量记录，另有34条记录涵盖了除茎干木材外其他组织的碳含量数据。茎干木材碳含量随生物群系（热带、亚热带/地中海型、温带/寒温带）以及物种类型（裸子植物、被子植物）的不同而存在显著差异。裸子植物的木材碳含量高于被子植物，分别为50.8±0.7%（95%置信区间）与47.7±0.3%，这一趋势在所有生物群系中均保持一致。尽管已有研究证实植物不同组织间的碳含量存在差异，但总体而言，茎干木材的种间差异更为重要：在物种层面，茎干木材碳含量分别解释了树皮、枝条、细枝、粗根以及细根碳含量变异的37%、76%、48%、81%与63%。所有组织类型的种内碳含量关系均近似于1:1的线性关系。绝大多数已发表的茎干木材碳含量数据（以及所有其他树木组织的碳含量数据）均基于干燥木材样品，因此忽略了活木中平均占总碳含量1.3%~2.5%的挥发性碳组分。对该挥发性碳组分的测定，是未来研究中需重点关注的方法学要点。本综述及配套的数据汇编工作，提供了经实证支撑的木材碳占比参数，可便捷应用于森林碳核算工作，同时可修正森林碳评估中约1.6%~5.8%的系统性误差。