Global Partial Beta-Diversity Coupling Among Forest Plant Growth-Form Groups

Abstract

Aim

Understanding how plant communities are structured across space is a central challenge in ecology and biogeography. However, plant communities are often treated as single aggregated units, potentially overlooking differences in spatial turnover among species groups defined by their characteristic growth form, such as trees, shrubs, and herbs. Here, we test whether trees, shrubs, and herbs exhibit congruent spatial patterns of composition turnover by quantifying taxonomic and functional beta-diversity coupling among these growth-form groups at the global scale.

Location

Global.

Time Period

Contemporary.

Taxa Studied

Vascular plants.

Methods

Using 15,263 forest vegetation plots from sPlotOpen, grouped into 288 regional clusters, we quantified taxonomic and functional dissimilarities among plots separately for trees, shrubs, and herbs. Functional dissimilarity was based on community-weighted means of five plant traits. We quantified coupling among growth-form groups using Mantel correlations and related it to macroclimate and within-cluster climatic heterogeneity using spatially cross-validated XGBoost models.

Results

Beta-diversity coupling was predominantly positive across all growth-form comparisons, indicating partial congruence in spatial turnover among growth-form groups. Functional coupling was not stronger than taxonomic coupling, suggesting that coordinated species turnover does not necessarily translate into convergence in ecological strategies. Climatic predictors explained 11%–30% of the among-cluster variation in coupling and showed non-linear associations with temperature, precipitation, and aridity.

Conclusions

Our global analysis shows predominantly positive but only partial congruence in taxonomic and functional compositional turnover among trees, shrubs, and herbs. Coupling varied among growth-form combinations and regions and was only modestly explained by macroclimate, suggesting that it emerges from processes operating across multiple spatial scales. These findings demonstrate the limits of treating forest plant communities as aggregated units or using one growth-form group as a general surrogate for biodiversity change in another.