Relationship between the geographical environment and the forest carbon sink capacity in China based on an individual-tree growth-rate model

Abstract

Forests play an important role in the global carbon cycle, and the growth of forest trees is essential to forest carbon sinks. It is necessary to explore the diameter at breast height (DBH) growth of trees and to quantify the effects of different factors on their growth to predict forest development. This study constructed an individual-tree annual growth-rate model of 41 dominant tree species in China to explore the effects of genetic characteristics and the environment on tree growth and the relationship between forest carbon sink capacity and the geographical environment. The model was estimated and evaluated based on 492,555 samples of 7801 permanent plots (covering 31 provinces in mainland China) and then decomposed into a general annual growth-rate component and an environmental modifier component. The results showed that tree species and size were the dominant factors that affected the growth rate, showing an inverse J-curve trend, and temperature was the most important of all environmental factors. In addition, there was a significant correlation between the potential aboveground carbon sink (PACS) and the geographic growth pattern index (GPI) (Spearman’s = 0.445, p-value < 0.001) and a significant correlation between the geographic growth structure index PACS and the geographic growth structure index (GSI) (Spearman’s = 0.014, p-value < 0.001). Areas with high GPI and GSI may have better environmental conditions for tree growth, leading to higher PACS. In China, the GPI was higher in the southeastern regions than in the northwestern regions and was also higher in the more humid regions than in the dry regions, resulting in a higher PACS. In conclusion, in forest resource management and future afforestation planning, we should first consider the suitability of the geographical environment, and then take the topographical structure into consideration to determine the proportion of suitable tree species and forest structure.