Data from: Trait patterns of epiphytes compared to other plant life forms along a tropical elevation gradient

Compared to other plant life forms, epiphytes remain understudied. Understanding the responses of epiphytes to changing environmental conditions is necessary to predict changes in ecosystem functioning especially in subtropical and tropical regions. We investigated the functional traits of epiphytes along a large elevation gradient on Mount Kilimanjaro, Tanzania. We measured traits of co-occurring trees and terrestrial non-tree life forms, and compared changes in community-weighted means of traits (CWM) and trait spread, the range of observed trait values. We chose traits linked to growth and persistence: leaf area, specific leaf area, leaf dry matter content, stem specific density, plant height, leaf carbon, leaf nitrogen, and leaf phosphorus. For most traits, differences in community-weighted means between life forms exceeded differences within life forms along the elevation gradient. Many CWM showed linear changes with elevation, but no response and unimodal patterns were also frequent. This was best explained by temperature, or a combination of temperature with precipitation or humidity, indicating effects of these factors on the distribution of epiphytic and non-epiphytic species. Trait spread did not change with elevation in nearly half of the traits, but hump-shaped patterns were also common, probably a result of weaker environmental filtering in the gradient center. The magnitude of trait spread, i.e. the variability between species of the same life form within communities, was highest for terrestrial non-trees. Excluding ferns from the analyses lead to marked differences in trait patterns for epiphytes, as ferns made up 59 % of the epiphytic species, while playing a minor role in the other groups. The observed differences can be explained by a dichotomy in epiphytic life strategies, with tough-leaved xero-tolerant species on one side and succulent soft-leaved species on the other. However, the influence of phylogeny was lower than expected from the taxonomic composition of the three life form groups. Our results emphasize that environmental constraints act upon functional traits of epiphytes, trees and terrestrial non-trees. The differences in trait expressions, arguably adaptations of the different life forms, need to be taken into account in conservation contexts as well as when modeling the effects of global change on ecosystems. species traitsThe functional traits of the species used in this study. Traits covered: Leaf area, Specific leaf area, Leaf dry matter content, Canopy height, Stem specific density, Leaf C, Leaf N, Leaf P. Units are given in the second sheet of the table. For methods, please refer to the original publication. This is the original version as used in the publication. The latest version is always in the TRY database (try-db.org).CWM and trait spreadCommunity-weighted means, trait spread, and fraction of total cover represented by the sampled species for trees, epiphytes, and terrestrial non-trees including and excluding ferns and fern allies. Units are given in the second sheet of the table.plot elevationElevation of the plots used in this study. Units are given in the second sheet of the table. For precipitation, mean temperature, and mean humidity, please refer to Mwangomo, E., Otte, I., Detsch, F., Nauss, T., Hemp, A. & Appelhans, T. (2014) Monthly and annual climate data averaged from 2011 to 2013 for 79 research plots on the southern slopes of Mt. Kilimanjaro - V 1.0. pp. DOI: 10.5281/zenodo.11695.