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Author: search.filters.author.Farfan-Rios, WilliamSubject: search.filters.subject.Amazon rainforest

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    Wood density variation across an Andes-to-Amazon elevational gradient
    (John Wiley and Sons, 2025)
    Understanding how functional traits are related to species diversity and ecosystem properties is a central goal of ecology. Wood density is a trait that integrates many aspects of plant form and function and is highly variable among species. Previous studies of wood density across elevational gradients have been based on limited sampling and have reported declines with increasing elevation, though even this simple pattern remains unknown, much less its underlying functional and evolutionary relationships. Here, we use one of the longest and most speciose elevational gradients in the world, extending from the Andean tree line to the Amazon basin, to test the extent to which elevation, species composition, phylogenetic affinity and forest structure determine variation in wood density. Using field‐collected wood samples and global databases, we assigned wood density to 1231 species and 31,330 stems across 41 (47.5 ha) mature forest plots arrayed across a 3500‐m vertical gradient. Our results show that mean wood density, either weighted by abundance, basal area or species, was highly variable but tended to decline from low to middle elevations and increase again from mid‐elevations to the tree line. As a result of this non‐linearity, forests at the Andean tree line had higher wood density than their lowland Amazon counterparts. We observed an abrupt transition in wood density at the lower limit of persistent cloud formation (cloud base), where the lowest wood density values were found. The decline of wood density is attributed to a significant shift in life forms, with an abundance of tree ferns at middle elevations and a higher probability of landslides and disturbances favouring a suite of traits associated with low wood density, such as softer wood and higher elasticity. Species turnover explained most of the among‐species variation across the gradient, with elevation having no consistent effect on within‐species variation in wood density. Together, both gradual compositional changes and sharp local changes in the importance of non‐dicot life forms, such as arborescent ferns and palms, define patterns of forest‐level carbon density, with wood density per se controlling ecosystem properties, such as carbon flux, across the Andes‐to‐Amazon elevational gradient.
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    Amazonian and Andean tree communities are not tracking current climate warming
    (National Academy of Sciences, 2025)
    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+ y 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 (TR) across the Amazon-to-Andes gradient were slow relative to regional temperature change. TR were positive and more variable among Andean forest plots compared to Amazonian plots but were highest at midelevations around the cloud base. Across all elevations, TR 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.
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