title: Increasing biomass in Amazonian forest plots.
abstract: A previous study by Phillips et al. of changes in the biomass of permanent sample plots in Amazonian forests was used to infer the presence of a regional carbon sink. However, these results generated a vigorous debate about sampling and methodological issues. Therefore we present a new analysis of biomass change in old-growth Amazonian forest plots using updated inventory data. We find that across 59 sites, the above-ground dry biomass in trees that are more than 10 cm in diameter (AGB) has increased since plot establishment by 1.22 +/- 0.43 Mg per hectare per year (ha(-1) yr(-1), where 1 ha = 10(4) m2), or 0.98 +/- 0.38 Mg ha(-1) yr(-1) if individual plot values are weighted by the number of hectare years of monitoring. This significant increase is neither confounded by spatial or temporal variation in wood specific gravity, nor dependent on the allometric equation used to estimate AGB. The conclusion is also robust to uncertainty about diameter measurements for problematic trees: for 34 plots in western Amazon forests a significant increase in AGB is found even with a conservative assumption of zero growth for all trees where diameter measurements were made using optical methods and/or growth rates needed to be estimated following fieldwork. Overall, our results suggest a slightly greater rate of net stand-level change than was reported by Phillips et al. Considering the spatial and temporal scale of sampling and associated studies showing increases in forest growth and stem turnover, the results presented here suggest that the total biomass of these plots has on average increased and that there has been a regional-scale carbon sink in old-growth Amazonian forests during the previous two decades.
authors.affiliation: Max-Planck-Institut für Biogeochemie, Postfach 10 01 64, D-07701 Jena, Germany. t.baker@geog.leeds.ac.uk
authors.forename: Timothy R
authors.initials: TR
authors.lastname: Baker
authors.forename: Oliver L
authors.initials: OL
authors.lastname: Phillips
authors.forename: Yadvinder
authors.initials: Y
authors.lastname: Malhi
authors.forename: Samuel
authors.initials: S
authors.lastname: Almeida
authors.forename: Luzmila
authors.initials: L
authors.lastname: Arroyo
authors.forename: Anthony
authors.initials: A
authors.lastname: Di Fiore
authors.forename: Terry
authors.initials: T
authors.lastname: Erwin
authors.forename: Niro
authors.initials: N
authors.lastname: Higuchi
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Killeen
authors.forename: Susan G
authors.initials: SG
authors.lastname: Laurance
authors.forename: William F
authors.initials: WF
authors.lastname: Laurance
authors.forename: Simon L
authors.initials: SL
authors.lastname: Lewis
authors.forename: Abel
authors.initials: A
authors.lastname: Monteagudo
authors.forename: David A
authors.initials: DA
authors.lastname: Neill
authors.forename: Percy Núñez
authors.initials: PN
authors.lastname: Vargas
authors.forename: Nigel C A
authors.initials: NC
authors.lastname: Pitman
authors.forename: J Natalino M
authors.initials: JN
authors.lastname: Silva
authors.forename: Rodolfo Vásquez
authors.initials: RV
authors.lastname: Martínez
mesh_terms: D018533:Biomass; D002244:Carbon / Q000032:analysis; D004784:Environmental Monitoring; D005843:Geography; D008954:Models, Biological; D013020:South America; D013997:Time Factors; D014197:Trees; D014329:Tropical Climate
chemical_list: D002244:Carbon