title: Pervasive alteration of tree communities in undisturbed Amazonian forests.
abstract: Amazonian rainforests are some of the most species-rich tree communities on earth. Here we show that, over the past two decades, forests in a central Amazonian landscape have experienced highly nonrandom changes in dynamics and composition. Our analyses are based on a network of 18 permanent plots unaffected by any detectable disturbance. Within these plots, rates of tree mortality, recruitment and growth have increased over time. Of 115 relatively abundant tree genera, 27 changed significantly in population density or basal area--a value nearly 14 times greater than that expected by chance. An independent, eight-year study in nearby forests corroborates these shifts in composition. Contrary to recent predictions, we observed no increase in pioneer trees. However, genera of faster-growing trees, including many canopy and emergent species, are increasing in dominance or density, whereas genera of slower-growing trees, including many subcanopy species, are declining. Rising atmospheric CO2 concentrations may explain these changes, although the effects of this and other large-scale environmental alterations remain uncertain. These compositional changes could have important impacts on the carbon storage, dynamics and biota of Amazonian forests.
authors.affiliation: Smithsonian Tropical Research Institute, Apartado 2072, Balboa, Republic of Panamá. laurancew@tivoli.si.edu
authors.forename: William F
authors.initials: WF
authors.lastname: Laurance
authors.forename: Alexandre A
authors.initials: AA
authors.lastname: Oliveira
authors.forename: Susan G
authors.initials: SG
authors.lastname: Laurance
authors.forename: Richard
authors.initials: R
authors.lastname: Condit
authors.forename: Henrique E M
authors.initials: HE
authors.lastname: Nascimento
authors.forename: Ana C
authors.initials: AC
authors.lastname: Sanchez-Thorin
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Lovejoy
authors.forename: Ana
authors.initials: A
authors.lastname: Andrade
authors.forename: Sammya
authors.initials: S
authors.lastname: D'Angelo
authors.forename: José E
authors.initials: JE
authors.lastname: Ribeiro
authors.forename: Christopher W
authors.initials: CW
authors.lastname: Dick
mesh_terms: D001272:Atmosphere / Q000737:chemistry; D001938:Brazil; D002245:Carbon Dioxide / Q000378:metabolism; D004463:Ecology; D017753:Ecosystem; D011157:Population Dynamics; D013045:Species Specificity; D014197:Trees / Q000502:physiology*
chemical_list: D002245:Carbon Dioxide