Compositional response of Amazon forests to climate change

Abstract

Most of the planet's diversity is concentrated in the tropics, which includes many regions undergoing rapid climate change. Yet, while climate‐induced biodiversity changes are widely documented elsewhere, few studies have addressed this issue for lowland tropical ecosystems. Here we investigate whether the floristic and functional composition of intact lowland Amazonian forests have been changing by evaluating records from 106 long‐term inventory plots spanning 30 years. We analyse three traits that have been hypothesized to respond to different environmental drivers (increase in moisture stress and atmospheric CO 2 concentrations): maximum tree size, biogeographic water‐deficit affiliation and wood density. Tree communities have become increasingly dominated by large‐statured taxa, but to date there has been no detectable change in mean wood density or water deficit affiliation at the community level, despite most forest plots having experienced an intensification of the dry season. However, among newly recruited trees, dry‐affiliated genera have become more abundant, while the mortality of wet‐affiliated genera has increased in those plots where the dry season has intensified most. Thus, a slow shift to a more dry‐affiliated Amazonia is underway, with changes in compositional dynamics (recruits and mortality) consistent with climate‐change drivers, but yet to significantly impact whole‐community composition. The Amazon observational record suggests that the increase in atmospheric CO 2 is driving a shift within tree communities to large‐statured species and that climate changes to date will impact forest composition, but long generation times of tropical trees mean that biodiversity change is lagging behind climate change.

Wood allocation trade‐offs between fiber wall, fiber lumen, and axial parenchyma drive drought resistance in neotropical trees

“…However, while this evolutionary strategy might have been beneficial under past climatic conditions, it can become unsuited in a warmer and dryer climate. Enhanced drought‐induced mortality of high wood density embolism sensitive tree taxa might be driving observed compositional changes in neotropical forests (Esquivel‐Muelbert et al, ). Furthermore, increased drought‐induced mortality might underlie the observed trend of increased tree mortality observed in the Amazon Basin (McDowell et al, ) and the associated decline of the Amazon carbon sink strength (Brienen et al, ).…”

“…Drought resistance is defined here as the ability to survive and reproduce in an environment that experiences recurrent seasonal drought. We use the species specific water deficit affiliation (WDA) (Esquivel‐Muelbert et al, , ) and drought‐induced mortality to quantify drought resistance. The WDA is the maximum climatological water deficit (mm) of an area in which a species has its center of gravity in terms of distribution.…”

“…The species‐specific water deficit affiliation (WDA) values were retrieved from the datasets of Esquivel‐Muelbert, Galbraith, et al (); Esquivel‐Muelbert et al (). The WDA is the average cumulative water deficit (CWD) value of the area in which the specific species has its center of gravity in terms of distribution (see Esquivel‐Muelbert, Galbraith, et al, for a description of the methods).…”

Disturbances amplify tree community responses to climate change in the temperate–boreal ecotone

“…Similar evidence is also beginning to emerge for latitudinal shifts (Boisvert‐Marsh, Périé, & Blois, ; Fisichelli, Frelich, & Reich, ; Sittaro et al, ). However, because of the focus on shifts at range limits (e.g., leading and rear edges of species ranges), there has been little empirical work on the effect of climate change on tree community composition and abundance distributions within the core of the species range itself (e.g., Esquivel‐Muelbert et al, ; Searle & Chen, ).…”

Vegetation response to climatic changes in western Amazonia over the last 7,600 years

“…An alternative possibility is that the ecological resilience of everwet forests is lower than that of seasonal forests because they do not routinely suffer drought stress. In the absence of this physiological stress, trees do not evolve adaptations such as microphyly, deep root systems or being facultatively deciduous and are, therefore, more vulnerable to atypical drought (Aleixo et al, ; Brando et al, ; da Costa et al, ; Esquivel‐Muelbert et al, ; Levine et al, ). Some support for this hypothesis is evident in the mortality of canopy trees in western Amazonia following the strong droughts of 2005, 2010 and 2015 (Alencar, Brando, Asner, & Putz, ; Asner & Alencar, ).…”