Inherent water-use efficiency (IWUE) is a vital parameter connecting the carbon and water cycles. However, the factors influencing the IWUE in different forest ecosystems are still a subject of debate. In this work, FLUXNET platform measurements of 67 forest sites were used to detect trends of the IWUE of four forest ecosystems, namely deciduous broadleaf forests (DBF), evergreen broadleaf forests (EBF), needle-leaf forests (ENF), and mixed forests (MF). The IWUE differed significantly among different forest ecosystems and positively correlated with temperature and solar radiation. The IWUE of EBF was the highest at 32.02 g·C·Kg·H₂O⁻¹. The values of DBF and MF were similar and higher than that of ENF. With increasing latitude, the IWUE increased first and then decreased, with a maximum of 35° N. The IWUE of EBF was negatively correlated with precipitation and leaf area index. Temperature and solar radiation were the main factors controlling the IWUE of forest ecosystems, whereas precipitation was the major factor controlling the inter-annual variation in the ΔIWUE of forest ecosystems. Our results provide a scientific basis for the study of forest carbon sinks, forest eco-hydrological processes, and forest ecosystem responses to global climatic changes.

Studying the factors influencing ecosystem regulation services in southwestern Zhejiang is of great significance for formulating reasonable pricing strategies for forest ecosystem regulation services and optimizing ecological security. This study constructed a theoretical framework for analyzing forest ecosystem regulation services and assessed the spatiotemporal evolution and influencing factors of forest ecosystem regulation services using InVEST model calculations and spatial autocorrelation analysis. The results showed that all ecosystem services of forests in the study improved from 2000 to 2019, with the exception of soil conservation. The water conservation function increased significantly from 2000 to 2019, with an overall increase of 3.53%. The biodiversity conservation function in 2019 also increased significantly, with an average increase of 2.16% compared with 2000. The synergies mainly occurred between water source regulation and soil conservation, soil conservation and biodiversity, and forest recreation and carbon storage. Forest Reserve was precipitation, canopy closure, elevation, and soil texture, and their driving forces differed at different time scales. The trade-offs mainly occurred between soil conservation and forest recreation, forest recreation and biodiversity, and carbon storage and biodiversity. The research results provide a reference for achieving ecological protection and high-quality development in the southwestern region of Zhejiang.