Functional diversity and trait variation along an elevational gradient in a temperate mixed forest, northeast China

Functional diversity, a core component of biodiversity, reflects the variation in organismal traits that underlie ecosystem processes. Despite its importance, how functional diversity and trait variation across interspecific and intraspecific levels respond to elevational gradients remains poorly understood in temperate forest ecosystems. This study investigates the functional diversity and trait variation of woody plants along an elevational gradient (700–1250 m) in a temperate mixed forest, Northeast China, by measuring 14 key functional traits across 57 woody species (including a total of 476 individuals) in 45 plots and quantifying five functional diversity indices. Results showed that functional richness (FRic), functional evenness (FEve), and functional dispersion (FDis) decreased significantly with elevation, while functional divergence (FDiv) and Rao’s quadratic entropy (RaoQ) increased. Redundancy analysis identified elevation and slope collectively explaining 70.5 % of the variation in community functional structure. Principal component analysis revealed that trait variation was structured along two independent axes: PC1 (52.3 %) represented a topographic stress gradient, while PC2 (23.2 %) reflected soil nutrient availability. Community-weighted mean traits revealed strong coordination among structural traits and trade-offs within the leaf economics spectrum. Variance partitioning demonstrated that interspecific variation dominated morphological traits (51–76 % of variance), whereas intraspecific variation explained most of the variation in physiological traits (46–66 %). This study provides a descriptive foundation for understanding how forest communities are structured across elevations and highlights the need to incorporate both inter-and intraspecific trait data in functional ecology studies. • FRic, FEve, FDis fell; FDiv, RaoQ rose with elevation. • Elevation and slope are the key topographic drivers. • Traits show coordination vs. trade-offs; inter- vs. intra-specific variation differs.