title: Rate of tree carbon accumulation increases continuously with tree size.
abstract: Forests are major components of the global carbon cycle, providing substantial feedback to atmospheric greenhouse gas concentrations. Our ability to understand and predict changes in the forest carbon cycle--particularly net primary productivity and carbon storage--increasingly relies on models that represent biological processes across several scales of biological organization, from tree leaves to forest stands. Yet, despite advances in our understanding of productivity at the scales of leaves and stands, no consensus exists about the nature of productivity at the scale of the individual tree, in part because we lack a broad empirical assessment of whether rates of absolute tree mass growth (and thus carbon accumulation) decrease, remain constant, or increase as trees increase in size and age. Here we present a global analysis of 403 tropical and temperate tree species, showing that for most species mass growth rate increases continuously with tree size. Thus, large, old trees do not act simply as senescent carbon reservoirs but actively fix large amounts of carbon compared to smaller trees; at the extreme, a single big tree can add the same amount of carbon to the forest within a year as is contained in an entire mid-sized tree. The apparent paradoxes of individual tree growth increasing with tree size despite declining leaf-level and stand-level productivity can be explained, respectively, by increases in a tree's total leaf area that outpace declines in productivity per unit of leaf area and, among other factors, age-related reductions in population density. Our results resolve conflicting assumptions about the nature of tree growth, inform efforts to undertand and model forest carbon dynamics, and have additional implications for theories of resource allocation and plant senescence.
authors.affiliation: US Geological Survey, Western Ecological Research Center, Three Rivers, California 93271, USA.
authors.forename: N L
authors.initials: NL
authors.lastname: Stephenson
authors.affiliation: US Geological Survey, Western Ecological Research Center, Three Rivers, California 93271, USA.
authors.forename: A J
authors.initials: AJ
authors.lastname: Das
authors.affiliation: Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Republic of Panama.
authors.forename: R
authors.initials: R
authors.lastname: Condit
authors.affiliation: School of Biological Sciences, University of Nebraska, Lincoln, Nebraska 68588, USA.
authors.forename: S E
authors.initials: SE
authors.lastname: Russo
authors.affiliation: Department of Forest and Ecosystem Science, University of Melbourne, Victoria 3121, Australia.
authors.forename: P J
authors.initials: PJ
authors.lastname: Baker
authors.affiliation: 1] School of Biological Sciences, University of Nebraska, Lincoln, Nebraska 68588, USA [2] Mathematical Biosciences Institute, Ohio State University, Columbus, Ohio 43210, USA (N.G.B.); German Centre for Integrative Biodiversity Research (iDiv), Halle-Jena-Leipzig, 04103 Leipzig, Germany (N.R.).
authors.forename: N G
authors.initials: NG
authors.lastname: Beckman
authors.affiliation: Department of Plant Sciences, University of Cambridge, Cambridge CB2 3EA, UK.
authors.forename: D A
authors.initials: DA
authors.lastname: Coomes
authors.affiliation: Department of Geography, University College London, London WC1E 6BT, UK.
authors.forename: E R
authors.initials: ER
authors.lastname: Lines
authors.affiliation: School of Botany, University of Melbourne, Victoria 3010, Australia.
authors.forename: W K
authors.initials: WK
authors.lastname: Morris
authors.affiliation: 1] Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Republic of Panama [2] Spezielle Botanik und Funktionelle Biodiversität, Universität Leipzig, 04103 Leipzig, Germany [3] Mathematical Biosciences Institute, Ohio State University, Columbus, Ohio 43210, USA (N.G.B.); German Centre for Integrative Biodiversity Research (iDiv), Halle-Jena-Leipzig, 04103 Leipzig, Germany (N.R.).
authors.forename: N
authors.initials: N
authors.lastname: Rüger
authors.affiliation: Jardín Botánico de Medellín, Calle 73, No. 51D-14, Medellín, Colombia.
authors.forename: E
authors.initials: E
authors.lastname: Alvarez
authors.affiliation: Instituto de Ecología Regional, Universidad Nacional de Tucumán, 4107 Yerba Buena, Tucumán, Argentina.
authors.forename: C
authors.initials: C
authors.lastname: Blundo
authors.affiliation: Research Office, Department of National Parks, Wildlife and Plant Conservation, Bangkok 10900, Thailand.
authors.forename: S
authors.initials: S
authors.lastname: Bunyavejchewin
authors.affiliation: Department of Botany and Plant Physiology, Buea, Southwest Province, Cameroon.
authors.forename: G
authors.initials: G
authors.lastname: Chuyong
authors.affiliation: Smithsonian Institution Global Earth Observatory-Center for Tropical Forest Science, Smithsonian Institution, PO Box 37012, Washington, DC 20013, USA.
authors.forename: S J
authors.initials: SJ
authors.lastname: Davies
authors.affiliation: Universidad Nacional de Colombia, Departamento de Ciencias Forestales, Medellín, Colombia.
authors.forename: A
authors.initials: A
authors.lastname: Duque
authors.affiliation: Wildlife Conservation Society, Kinshasa/Gombe, Democratic Republic of the Congo.
authors.forename: C N
authors.initials: CN
authors.lastname: Ewango
authors.affiliation: Unité Mixte de Recherche-Peuplements Végétaux et Bioagresseurs en Milieu Tropical, Université de la Réunion/CIRAD, 97410 Saint Pierre, France.
authors.forename: O
authors.initials: O
authors.lastname: Flores
authors.affiliation: School of Environmental and Forest Sciences, University of Washington, Seattle, Washington 98195, USA.
authors.forename: J F
authors.initials: JF
authors.lastname: Franklin
authors.affiliation: Instituto de Ecología Regional, Universidad Nacional de Tucumán, 4107 Yerba Buena, Tucumán, Argentina.
authors.forename: H R
authors.initials: HR
authors.lastname: Grau
authors.affiliation: State Key Laboratory of Forest and Soil Ecology, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110164, China.
authors.forename: Z
authors.initials: Z
authors.lastname: Hao
authors.affiliation: Department of Forest Ecosystems and Society, Oregon State University, Corvallis, Oregon 97331, USA.
authors.forename: M E
authors.initials: ME
authors.lastname: Harmon
authors.affiliation: 1] Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Republic of Panama [2] Department of Ecology and Evolutionary Biology, University of California, Los Angeles, California 90095, USA.
authors.forename: S P
authors.initials: SP
authors.lastname: Hubbell
authors.affiliation: Smithsonian Institution Global Earth Observatory-Center for Tropical Forest Science, Smithsonian Institution, PO Box 37012, Washington, DC 20013, USA.
authors.forename: D
authors.initials: D
authors.lastname: Kenfack
authors.affiliation: Department of Life Science, Tunghai University, Taichung City 40704, Taiwan.
authors.forename: Y
authors.initials: Y
authors.lastname: Lin
authors.affiliation: Wildlife Conservation Society, Kinshasa/Gombe, Democratic Republic of the Congo.
authors.forename: J-R
authors.initials: JR
authors.lastname: Makana
authors.affiliation: Instituto de Ecología Regional, Universidad Nacional de Tucumán, 4107 Yerba Buena, Tucumán, Argentina.
authors.forename: A
authors.initials: A
authors.lastname: Malizia
authors.affiliation: Facultad de Ciencias Agrarias, Universidad Nacional de Jujuy, 4600 San Salvador de Jujuy, Argentina.
authors.forename: L R
authors.initials: LR
authors.lastname: Malizia
authors.affiliation: Department of Forest Ecosystems and Society, Oregon State University, Corvallis, Oregon 97331, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: Pabst
authors.affiliation: Faculty of Forestry, Kasetsart University, ChatuChak Bangkok 10900, Thailand.
authors.forename: N
authors.initials: N
authors.lastname: Pongpattananurak
authors.affiliation: Taiwan Forestry Research Institute, Taipei 10066, Taiwan.
authors.forename: S-H
authors.initials: SH
authors.lastname: Su
authors.affiliation: Department of Natural Resources and Environmental Studies, National Dong Hwa University, Hualien 97401, Taiwan.
authors.forename: I-F
authors.initials: IF
authors.lastname: Sun
authors.affiliation: Sarawak Forestry Department, Kuching, Sarawak 93660, Malaysia.
authors.forename: S
authors.initials: S
authors.lastname: Tan
authors.affiliation: Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331, USA.
authors.forename: D
authors.initials: D
authors.lastname: Thomas
authors.affiliation: US Geological Survey, Western Ecological Research Center, Arcata, California 95521, USA.
authors.forename: P J
authors.initials: PJ
authors.lastname: van Mantgem
authors.affiliation: State Key Laboratory of Forest and Soil Ecology, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110164, China.
authors.forename: X
authors.initials: X
authors.lastname: Wang
authors.affiliation: Landcare Research, PO Box 40, Lincoln 7640, New Zealand.
authors.forename: S K
authors.initials: SK
authors.lastname: Wiser
authors.affiliation: Forest Ecology and Restoration Group, Department of Life Sciences, University of Alcalá, Alcalá de Henares, 28805 Madrid, Spain.
authors.forename: M A
authors.initials: MA
authors.lastname: Zavala
mesh_terms: D000375:Aging / Q000378:metabolism; D018533:Biomass; D049628:Body Size; D002244:Carbon / Q000378:metabolism*; D057486:Carbon Cycle; D002980:Climate; D005843:Geography; D008954:Models, Biological; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism; D018401:Sample Size; D013045:Species Specificity; D013997:Time Factors; D014197:Trees / Q000033:anatomy & histology* / Q000145:classification / Q000254:growth & development / Q000378:metabolism*; D014329:Tropical Climate
chemical_list: D002244:Carbon