Between categories and continua: growth-form organization in global leaf economics spectrum space

Stephen Antheny Mekwan 

The leaf economics spectrum (LES) describes a globally coordinated trade-off between acquisitive and conservative plant resource-use strategies, yet how major plant growth forms are organized within multidimensional LES space and the extent to which these patterns reflect evolutionary history remain incompletely resolved. Using species-level trait data from the TRY Plant Trait Database, we examined ecological and phylogenetic organization across 3,206 vascular plant species representing trees, shrubs, herbs, graminoids, and climbers based on four core functional traits: specific leaf area, leaf nitrogen content, leaf dry matter content, and vegetative height. Principal component analysis identified a dominant acquisitive–conservative LES axis explaining 50.3% of total trait variation, while a secondary height-associated axis explained an additional 25.2%, indicating substantial multidimensional structure within global plant strategy space.

Growth forms occupied significantly differentiated but strongly overlapping regions of multidimensional trait space. Herbs and graminoids were generally associated with more acquisitive strategies, whereas trees and shrubs occupied comparatively conservative regions. Growth-form differentiation remained significant across multivariate and phylogenetically informed analyses and persisted after vegetative height was excluded from the analysis, indicating that observed patterns were not driven solely by differences in plant stature. Phylogenetic analyses revealed strong evolutionary structure in LES positioning while also indicating substantial ecological redistribution across evolutionary lineages. Together, these findings suggest that global plant ecological organization is continuous, multidimensional, and evolutionarily structured, with major growth forms representing overlapping regions of trait space rather than discrete functional categories.