Towards a Trait-Climate Coupled Biome Framework

Biomes are fundamental units of global vegetation, representing physiognomically distinct plant formations that reflect collective adaptations to environmntal conditions. They provide a crucial framework for biodiversity monitoring and for identifying regions that are most vulnerable to biodiversity loss from land use change and climate shifts. As climate continues to change, the adaptative boundaries of vegetation types are being reshaped, leading to large-scale biome transitions. By defiinition, biomes are inherently shaped by both cliamte and functional traits, since traits directly reflect adaptation strategies. Dominant species within each biome often show convergent trait expressions or physiological structures. However, previous biome classifications have several limitations: 1) simple climate-based schemes that assign biomes without considering plant traits; 2) physiognomic criteria that indirectly reflect cliamte yet lacks explicit trait-climate links; or 3) trait-based classifications without integration of climate drivers. To overcome these limitations, we propose a novel framework that explicitly integrates climate variables and plant functional traits to define state-of-art biome classifications at the globe. Our framework incorporates dominant and co-occurring plant functional types and their corresponding key functional traits, linking them to climatic boundaries related to temperature, humidity and seasonality. The traits considered include leaf characteristics, stem structure, photosynthetic pathways and canopy variables. Using this framework, we identified approximately 20 biome types worldwide, spanning five thermal bands, from tropical to tundra, and four distinct humidity states, from humid rainforests to desert and semi-deserts. Leveraging species distribution models that link species occurrence to both functional traits and climate, we mapped the spatial distribution of these biomes across continents. For the first time, this framework provides a biome definition that unifies distinct vegetation forms, functional traits and their climatic context. It establishes a benchmark for understanding global biome dynamics and constructs a foundation for future studies on vegetation shifts and ecosystem functioning under ongoing climate change.