Amazonian and Andean tree communities are not tracking current climate warming

William Farfan-Rios , Kenneth J. Feeley, Jonathan A. Myers, Sebastian Tello, Jhonatan Sallo-Bravo, Yadvinder Malhi, Oliver L. Phillips, Tim Baker, Alex Nina-Quispe, Karina Garcia-Cabrera, Sasan Saatchi, John Terborgh, Nigel Pitman, Abel Monteagudo Mendoza, Rodolfo Vasquez, Norma Salinas-Revilla, Leslie Cayola, Alfredo F. Fuentes, Isabel Loza, Percy Nuñez Vargas, Miles R Silman

Climate change is shifting species distributions, leading to changes in community composition and novel species assemblages worldwide. However, the responses of tropical forests to climate change across large-scale environmental gradients remain largely unexplored. Using long-term data over 66,000 trees of more than 2,500 species occurring over 3,500 m elevation along the hyperdiverse Amazon-to-Andes elevational gradients in Peru and Bolivia, we assessed community-level shifts in species composition over a 40+ year time span. We tested the thermophilization hypothesis, which predicts an increase in the relative abundances of species from warmer climates through time. Additionally, we examined the relative contributions of tree mortality, recruitment, and growth to the observed compositional changes. Mean thermophilization rates across the Amazon-to-Andes gradient were slow relative to regional temperature change. Thermophilization rates were positive and more variable among Andean forest plots compared to Amazonian plots but were highest at mid-elevations around the cloud base. Across all elevations, thermophilization rates were driven primarily by tree mortality and decreased growth of highland (cool adapted) species rather than an influx of lowland species with higher thermal optima. Given the high variability of community-level responses to warming along the elevational gradients, the high tree mortality, and the slower-than-warming rates of compositional change, we conclude that most tropical tree species, and especially lowland Amazonian tree species, will not be able to escape current or future climate change through upward range shifts, causing fundamental changes to composition and function in Earth’s highest diversity forests.