Cross‐scale effects of multi‐strata plant diversity on ecosystem multifunctionality in temperate forests

Abstract Unravelling the complex interplay between biodiversity and ecosystem multifunctionality (EMF) in naturally assembled communities is crucial. However, studies on the effects of biodiversity and species composition across different forest strata on EMF at varying spatial scales are still limited in temperate forests. Based on a large set of field observations, we explored the relationships between the diversity of trees and understory herbs and EMF across multiple spatial scales. Within the Hill–Chao numbers framework, we measured diversity in different forest strata and decomposed regional community EMF into α‐ and β‐components. Linear mixed‐effects models and structural equation modelling were applied to investigate the relationships between tree and herb α‐diversity and α‐EMF (the capacity of a specific community to deliver multiple ecosystem services and benefits), as well as between tree and herb β‐diversity and β‐EMF (the spatial dissimilarity of multiple ecosystem functions among local communities). We found that α‐EMF positively responded to tree α‐diversity, though less so by herb α‐diversity. Within regional communities, both tree and herb β‐diversity had positive effects on β‐EMF, with comparable relative importance. Synthesis . Our results show that tree and understory herb diversity (an often overlooked component of forest communities) are both essential for sustaining ecosystem multifunctionality (EMF) across multiple spatial scales in naturally assembled temperate forests of northeastern China. By integrating multi‐strata plant diversity across different spatial scales, our study provides new insights into the patterns and mechanisms underlying the biodiversity–EMF relationship in these forest ecosystems.