Forest Attributes and Soil Moisture Availability Drive Ecosystem Multifunctionality of Forests in Eastern Tibetan Plateau, China.

Forests deliver multiple essential ecosystem functions, and most natural forests occur in highly heterogeneous environments and span different developmental stages. Despite this complexity, the relative influences of biotic and environmental drivers on ecosystem multifunctionality (EMF) remain insufficiently understood across temporal and spatial scales. Here, we surveyed forests along elevational (1800-3500 m) and successional (early to late) gradients on the eastern Tibetan Plateau, quantify how climate, soil properties, and forest attributes (diversity, stand structure, and functional traits) regulate EMF. EMF was constructed from eight indicators representing nutrient cycling, plant productivity, and water conservation. Further, we assessed variation in biodiversity effects, including selection and complementarity effects. We found that soil moisture, functional diversity, and the coefficient of variation in stand diameter exert significant positive effects on EMF, whereas species richness-the most commonly used diversity metric-shows no significant effect. Mean annual temperature and soil bulk density, by contrast, have significant negative effects. The strengths of both selection and complementarity effects vary along elevational and successional gradients, with complementarity effects becoming markedly stronger at higher elevations. Overall, our findings reveal the mechanisms through which climate, soil properties, and forest attributes jointly regulate EMF, underscoring the pivotal roles of plant functional diversity and structural heterogeneity in sustaining the multifunctionality of subalpine forests. Results provide a robust empirical foundation for improving natural forest EMF and restoration management.