Enhanced awareness of height-diameter allometry in response to climate, soil, and competition in secondary forests

The allometry between tree height (H) and diameter (DBH) is a central part of accurate carbon estimation and forest ecological evaluation. However, our awareness of the H-DBH allometry response to stressors is incomplete. For instance, pairwise and higher-order interactions of climate, soil, intraspecific competition, and interspecific competition were ignored, which may have led to important ecological insights not explored in H-DBH allometry. Besides, although secondary forests are cost-friendly mitigation tools requiring rational management, research on H-DBH allometry and management of secondary forests is far from adequate. Therefore, we pioneered the consideration of pairwise and higher-order interactions of competition, climate, and soil to enhance awareness of the relationship between stressors and H-DBH allometry. Moreover, H-DBH simulations under different competitive combinations were provided based on the actual local environmental levels, with the aim of providing targeted recommendations for secondary forests. The results showed that MAT (mean annual temperature), CF (coarse fragments), intraspecific BAL (the basal area of trees larger than the subject tree), and interspecific BAL were dominant stressors. The pairwise, third-, and fourth-order interactions significantly affected and improved the H-DBH model. The interactions affected H more than independent effects at times, and higher-order interactions produced comparable contributions to pairwise interactions. The independent and interactive effects of stressors on H were greatest in medium- and large-sized trees, which suggested sampling medium- and large-sized trees could reduce cost. Furthermore, the influencing directions of stressors on H were inconstant and depended on the gradients of other stressors due to the presence of interactions, which is generally consistent with the pressure gradient hypothesis and ecological laws. The simulation results indicated that the desired H-DBH allometry could be obtained by adjusting BALinter and BALintra according to the actual environmental level and management objectives of each stand. This study highlights the importance of considering interactions in credible H-DBH modeling, stressor impact analysis, and forest management policy development. Given the likelihood of ongoing climate change in the future, this study will assist in promoting sustainable management and informed decision-making in secondary forests.