Preliminary Comparative Effects of Close-to-Nature and Structure-Based Forest Management on Carbon Sequestration in Plantations of the Loess Plateau, China.

plantations on the Loess Plateau face challenges such as poor quality and high mortality rates due to high initial value density and improper thinning practices. To prevent further deterioration of these forests, it is essential to identify suitable forest management methods as soon as possible. Within plantations under different management methods (structure-based forest management [SBFM], close-to-nature forest management [CNFM], and unmanaged), after 5 years of investigation, we analyzed the changes in forest structural complexity and growth partitioning using size inequality (Gini), size-growth relationship (SGR), and growth dominance coefficient (GDC). A linear mixed-effects model was applied to evaluate the impact of these practices on forest stands. We also compared the trends of the average annual breast height area increment (BAI) and projected the net-zero timeline after thinning. The results showed that: (1) thinning management temporarily reduced the Gini due to the removal of a certain number of trees. However, the Gini rebounded significantly, and the forest structure became increasingly complex again, and the rebound of SBFM stands was greater than that of CNFM; (2) in the unmanaged stands, larger trees contribute more to stand growth. In the managed stands, the changes in GDC and SGR reflected an increasing contribution of smaller trees to overall growth; and (3) thinning management increased BAI, and this effect became more pronounced over time. Notably, carbon neutrality was projected to be achieved 7.8 years in CNFM stands, which was earlier than the 8.7 years in SBFM stands. These research results will provide a theoretical basis for managing and determining the trees to be harvested for high-density, low-quality plantations of the Loess Plateau.