Mechanisms of mixed forests enhancing community productivity and their effects on climate response

Although the relationship between biodiversity and ecosystem functioning (BEF) has been extensively studied, the mechanisms by which species mixing ratios in mixed forests regulate community productivity and tree responses to climatic stress through interspecific interactions remain poorly understood. In this study, we systematically investigated how different species mixing ratios influence ecosystem functioning in temperate Pine–Oak mixed forests.

First, using dendrochronological methods, we assessed tree climate sensitivity as well as resistance (Rt), recovery (Rc), and resilience (Rs) under both short-term and long-term drought conditions. We found that species mixing does not universally reduce climate sensitivity or enhance drought resistance; rather, only moderate mixing ratios optimize drought resistance and recovery, especially for oak. In contrast, pine shows reduced drought resistance when the proportion of oak is high, suggesting that the biodiversity effect may be asymmetric among different species.

In addition, from the perspective of spatial and phenological niche differentiation in resource use, we revealed the mechanisms by which mixing ratios regulate community productivity across multiple temporal scales (yearly, monthly, and daily). Tree-ring width served as a proxy for productivity, providing five-year average annual values, while microcore techniques captured monthly and daily dynamics of growth. Monthly changes in leaf area index (LAI) and community-weighted mean photosynthetic capacity (CMW-Pn) were monitored, and stable isotope tracers, hydraulic traits, and soil nutrients were used to evaluate water and nutrient niches. Our results demonstrate that complementary use of light resources among different tree species is the primary mechanism driving increased productivity in mixed forests, exerting a much stronger influence than water or nutrient factors. Specifically, the key determinant of productivity lies in community-level light interception capacity rather than photosynthetic capacity alone. In addition, phenological niche differentiation plays a crucial role in enhancing productivity. Through daily-scale growth monitoring, we quantified this mechanism for the first time: asynchronous growth phenology among species substantially reduced interspecific competition and strengthened temporal resource complementarity, ultimately increasing overall community productivity by approximately 15%.
These findings provide new mechanistic insights into enhancing and sustaining productivity in mixed forests under climate change.