Mixed evergreen and deciduous forests boost local climate resilience, nutrient dynamics, and photosynthetic performance assessed by remote sensing

Abstract

Mixed forests, consisting of tree species from diverse ecological niches, often show increased productivity. Photosynthesis, a crucial process for tree biomass accumulation, can be influenced by species mixing, although direct evidence linking species mixing to enhanced photosynthetic efficiency is limited. One benefit of species mixing is the improvement of local climatic conditions and nutrient supply, but it remains uncertain whether these factors directly enhance photosynthesis. This study uses datasets of solar-induced chlorophyll fluorescence from the Orbiting Carbon Observatory-2 (OCOSIF) and the Global OCO-2 products (GOSIF) as proxies for photosynthetic activity. It investigates the effects of species mixing on stand-level photosynthetic activity in evergreen-deciduous forests on the Loess Plateau. The study also assesses the roles of local climatic variability and nutrient availability. The datasets cover plots with spatial resolutions of 0.02° by 0.01° for OCOSIF and 0.05° by 0.05° for GOSIF, with sample counts of 416 and 369, respectively, spanning from 2014 to 2022. Through generalized additive mixed models and structural equation models, the research reveals that the mixing effects of evergreen and deciduous trees on solar-induced fluorescence follow a multimodal pattern corresponding to the proportion of evergreen trees. Peak effects are influenced by factors such as canopy moisture variability and soil nutrient dynamics, with canopy moisture variability having the most significant impact. In conclusion, the mixing of evergreen and deciduous trees on the Loess Plateau enhances stand-level photosynthetic performance, mainly driven by stability in water supply and nutrient availability.