Functional-trait contrasts between terrestrial and epiphytic ferns in Taiwanese subtropical cloud forests

Aims

Extensive research on the leaf economics spectrum (LES) has improved insights into functional traits and their environmental interactions. Several studies explored trait correlations in angiosperms and ferns, expanding their ecological significance. However, knowledge gaps persist, especially concerning East-Asian ferns and the differences between terrestrial and epiphytic ferns in LES.

Location

East Asia, Northern Taiwan.

Methods

Data were collected along an elevation gradient (870–2130 m a.s.l.) in northern Taiwan, where we measured nine leaf traits for 47 terrestrial and 34 epiphytic ferns across 59 vegetation plots within subtropical forests. We explored trait–trait and trait–environment relationships at the species and community levels for both terrestrial and epiphytic ferns while accounting for phylogenetic constraints.

Results

Epiphytes had lower specific leaf area (SLA) and leaf nitrogen, greater trait variance and trait space than terrestrial species, suggesting they are ecologically distinct. These differences observed at species and community levels appear to emerge because epiphytes undergo stronger water and nutritional stress along the elevation gradient. In addition, three groups were detected within epiphytes reflecting their strategies for water and nutrient stress adaptation. Trait correlations largely resembled angiosperm LES patterns but were less apparent in epiphytes. SLA and leaf dry matter content (LDMC) were consistently correlated to water stress traits, which might contribute to the restricted LES trait range of both life forms in our study. Traits exhibited a strong phylogenetic signal, with marked differences between SLA and LDMC correlations in phylogenetics-corrected vs raw data. Trait–environment relationships were similar for several water stress-related traits across both species groups, but stronger relationships were more evident in terrestrial ferns.

Conclusions

Trait patterns are not entirely equivalent for epiphytic and terrestrial species or communities and should not be extrapolated across life forms. Distantly related species with various evolutionary backgrounds could dismantle LES patterns at the species level. Strong phylogenetic constraints may influence the trait–environment response of epiphytic species.