Andean forests are a global biodiversity hotspot harboring many species living within narrow climate ranges. These ecosystems also harbor high functional diversity of plants, but it is still unclear how species and their functional attributes will respond to the ongoing climate change along environmental gradients and through time. In this study, we aim to investigate whether Andean forests are changing their functional composition over time along the elevational gradient by assessing temporal changes in species composition and abundance and representativeness of their functional traits. If climate change is leaving a fingerprint in functional composition, traits associated with temperature would be the ones that should show the most detectable changes with increases in temperature. For example, warmer temperatures exacerbate the reduction of both leaf area (LA) and specific leaf area (SLA), leading plant communities towards more conservative strategies over time. We used temporal forest dynamic of nine 1-ha permanent plots along 2.800 m in elevation in the north of Colombian Andean forest, and in situ functional characterizations of seven morphological traits of 1,104. Using the Trait Driver Theory, we tested whether directional shifts exist in the functional composition of Andean forests in response to climate change and species dynamics. We quantify the shift in functional composition by calculating the central moments of trait distribution and their rate of change. We assessed the response of species and functional composition to changes in climate and demography by assessing the covariation between changes in traits distribution moments and changes in climatic variables, mortality, and recruitment. Our results show a directional change in the functional composition. The trends move toward more conservative strategies over time along elevation. Changes in most traits were explained by historical increases in minimum temperature and individual mortality. Changes in climatic conditions and the demographic response of species are leading to an increase in the dominance of more stress and heat-tolerant species within Andean communities. These changes are reflected in temporal decreases in traits such as specific leaf area along elevation and demonstrate the adaptation capacity of Andean species to new environments.
Andean forests, Climate change, Elevational gradient, Functional turnover, Forest plots,