Multilevel trait responses of liana Hedera helix L. to environmental gradients in urban forest ecosystems.

Urban forest ecosystems face increasing abiotic stress due to climate change and anthropogenic pressure, requiring robust indicators of plant adaptation. Hedera helix L., a widespread liana with shoot dimorphism, plays a key role in temperate urban woodlands but remains understudied in terms of multilevel responses to environmental gradients. We assessed vegetative and generative shoots with healthy or damaged leaves across heterogeneous urban forest sites to identify functional responses to volumetric water content (VWC), temperature (t), electrical conductivity (ES), and daily light integral (DLI). VWC and DLI emerged as the key drivers of trait variability. The multilevel adaptive trait responses demonstrated the ecological flexibility of a dominant urban liana. We developed a novel Integrative Ecological Index (IEI) based on normalized trait sub-indices, which captures multilevel plant responses to environmental stress and enables quantitative assessment of urban habitat conditions. IEI was highest in healthy vegetative shoots and lowest in damaged generative shoots. Our findings demonstrate the ecological plasticity of H. helix and its potential as a sensitive bioindicator. This interdisciplinary study provides a scalable trait-based tool to evaluate adaptive capacity and microhabitat conditions in heterogeneous urban environments.