Spatial Patterns of Stem Tissue Carbon Content in Fagaceae Species from Typical Forests in China

Fagaceae plants are dominant species in subtropical and temperate forests in China. Studying the geographical pattern of their carbon contents can provide key parameter support for high-precision forest carbon accounting. To investigate the spatial variation and influencing factors of carbon content in bark, sapwood, and heartwood, stem samples from 168 individual trees belonging to 41 species of 5 genera in the Fagaceae family were collected from different regions of China. Carbon was determined with the dry combustion method using an elemental analyzer. The variation in carbon content was partitioned, carbon content among tissues were compared, spatial patterns with latitude and longitude and relative importance of interpreting variables were quantified. The carbon content of stem tissues ranged from 411 to 563 mg·g−1. Variation was primarily driven by geographical location (34%–53%), followed by residuals (26%–40%). The inter-species difference also made significant contributions, ranging from 23% (bark) and 21% (sapwood) to 18% (heartwood). Generally, the carbon content among the three tissues followed the order: bark (494 ± 26 mg g−1) (±SD) < sapwood (503 ± 21 mg g−1) < heartwood (509 ± 23 mg g−1). There was an obvious geographical variation pattern in stem carbon content. The carbon content of different tissues gradually decreased with northward latitude and westward longitude. Aridity index (with a relative importance of 22%), longitude (38%), and solar radiation (27%) were the most important driving factors of bark, sapwood, and heartwood C, while the influence of temperature and precipitation was weak. The results highlight the importance of geographical and environmental gradients over taxonomic differences and provide critical parameters for improving forest carbon storage estimates in China.