LETTERTesting metabolic ecology theory for allometricscaling of tree size, growth and mortality in tropicalforestsHelene C. Muller-Landau,1*Richard S. Condit,2JeromeChave,3Sean C. Thomas,4Stephanie A. Bohlman,5SarayudhBunyavejchewin,6Stuart Davies,2Robin Foster,7SavitriGunatilleke,8Nimal Gunatilleke,8Kyle E. Harms,2,9Terese Hart,10Stephen P. Hubbell,2,11AkiraItoh,12Abd Rahman Kassim,13James V. LaFrankie,14, Hua SengLee,15Elizabeth Losos,16Jean-Remy Makana,17TatsuhiroOhkubo,18Raman Sukumar,19I-Fang Sun,20Nur SupardiM. N.,21Sylvester Tan,22JillThompson,23Renato Valencia,24Gorky Villa Mun˜oz,24ChristopherWills,25Takuo Yamakura,26George Chuyong,27HandanakereShivaramaiah Dattaraja,19Shameema Esufali,8PamelaHall,2,28Consuelo Hernandez,24David Kenfack,29SomboonKiratiprayoon,30Hebbalalu S.Suresh,19Duncan Thomas,31Martha Isabel Vallejo32and PeterAshton33AbstractThe theory of metabolic ecology predicts specific relationships among tree stemdiameter, biomass, height, growth and mortality. As demographic rates are important toestimates of carbon fluxes in forests, this theory might offer important insights into theglobal carbon budget, and deserves careful assessment. We assembled data from 10 old-growth tropical forests encompassing censuses of 367 ha and > 1.7 million trees to testthe theory’s predictions. We also developed a set of alternative predictions that retainedsome assumptions of metabolic ecology while also considering how availability of a keylimiting resource, light, changes with tree size. Our results show that there are nouniversal scaling relationships of growth or mortality with size among trees in tropicalforests. Observed patterns were consistent with our alternative model in the one sitewhere we had the data necessary to evaluate it, and were inconsistent with thepredictions of metabolic ecology in all forests.KeywordsAsymmetric competition, demographic rates, forest dynamics, light availability,metabolic theory of ecology, resource competition theory, tree allometry.Ecology Letters (2006) 9: 575–5881Department of Ecology, Evolution and Behavior, University ofMinnesota, 1987 Upper Buford Circle, St Paul, MN 55108, USA2Smithsonian Tropical Research Institute, Unit 0948, APO-AA,34002-0948, USA3Laboratoire Evolution et Diversite´Biologique UMR 5174,CNRS/UPS, baˆtiment IVR3, Universite´Paul Sabatier, 118 routede Narbonne, 31062 Toulouse, France4Faculty of Forestry, University of Toronto, 33 Willcocks St,Toronto, ON, Canada5Department of Ecology and Evolutionary Biology, PrincetonUniversity, Princeton, NJ, USA6Research Office, National Parks Wildlife and PlantConservation Department, 61 Paholyothin Road, Chatuchak,Bangkok 10900, Thailand7The Field Museum, 1400 S. Lake Shore Drive, Chicago, IL60605-2496, USA8Department of Botany, Faculty of Science, University ofPeradeniya, Peradeniya 20400, Sri Lanka9Department of Biological Sciences, Louisiana State University,202 Life Sciences Building, Baton Rouge, LA 70803-1715, USA10Wildlife Conservation Society, International Programs, 185thSt. and Southern Blvd, Bronx, NY 10460, USAEcology Letters, (2006) 9: 575–588 doi: 10.1111/j.1461-0248.2006.00904.x 2006 Blackwell Publishing Ltd/CNRS. No claim to original US government worksINTRODUCTIONTree growth and mortality rates vary widel y among tropicalforests worldwide (Baker et al. 2003; Phillips et al. 2004), yetrelationships of tree growth and mortality rates to treediameter show fundamental similarities that suggest generalunderlying principles (Coomes et al. 2003). Recently, thetheory of metabolic ecology has generated specific predic-tions about the functional form of these relationships(Enquist et al. 1999; Brown et al. 2004). Such a generaltheory could potentially advance fundamental understandingof forest stru cture and dynamics, and also provide a basisfor predicting future changes in associated carbon pools andfluxes (Phillips et al. 1998; Clark et al. 2001).The metabolic theory of ecology strives to apply basicprinciples of physics, chemistry and biology to explain thephysiology and performance of individual organisms andthereby the structure of popul ations, communities andecosystems (West et al. 1997; Brown et al. 2004). West et al.(1997) pioneered these efforts with predictions for the scalingof metabolic rates (in plants, gross photosynthetic rates) withbody mass based on the scaling of resource uptake andredistribution within optimized networks (e.g. arteries andxylem). West et al. (1999) derived additional prediction s forthe scaling of height, biomass, diameter and leaf area in plants.In combination with assumptions relating growth andmortality to metabolic rate, Enquist et al. (1999) and Brownet al. (2004) extend these to make further predictions for th escaling of plant growth and mortality respectively.There is considerable debate about the validity andconsistency of the underlying assumptions of metabolicecology (e.g. Dodds et al. 2001; Kozlowski & Konarzewski2004; Meinzer et al. 2005). For trees in particular, we suggestthat the scaling of metabolic rates with size will depend notonly on the potential for resource uptak e and redistributionthat is central to metabolic ecology theory, but also onavailability of these resources. Small plants in the shadedunderstory of forests are much farther from their maximumpotential metabolic rates than the canopy trees that overtopthem. Light is a limiting resource for plant growth in tropicalforests (Chazdon & Pearcy 1986; King 1994; Graham et al.2003), and competition for light is strongly size asymmetric(Weiner 1990). In addition, site-specific mortality factorsmight affect some size classes more than others and thuschange the scaling of mortality with size. For example,hurricanes induce more mortality among large trees (Zimm-erman et al. 1994), while fires and large mammals causemore mortality among small trees (Ickes et al. 2005;11Department of Plant Biology, University of Georgia, Athens,GA 30604, USA12Laboratory of Plant Ecology, Graduate School of Science,Osaka City University, Osaka 558-8585, Japan13Forest Management and Ecology Program, Forestry andConservation Division, Forest Research Institute Malaysia,52109 Kepong, Selangor, Malaysia14Center for Tropical Forest Science-Arnold Arboretum AsiaProgram, Nanyang Technological University, 1 Nanyang Walk,Singapore 637617, Singapore15Sarawak Forest Department, Jalan Stadium, Petra Jaya,Kuching, Sarawak 93660, Malaysia16Organization for Tropical Studies, Duke