Role of tree size in moist tropical forest carbon cycling and water deficit responses.

Drought disproportionately affects larger trees in tropical forests, but implications for forest composition and carbon (C) cycling in relation to dry season intensity remain poorly understood. In order to characterize how C cycling is shaped by tree size and drought adaptations and how these patterns relate to spatial and temporal variation in water deficit, we analyze data from three forest dynamics plots spanning a moisture gradient in Panama that have experienced El Niño droughts. At all sites, aboveground C cycle contributions peaked below 50-cm stem diameter, with stems ≥ 50 cm accounting for on average 59% of live aboveground biomass, 45% of woody productivity and 49% of woody mortality. The dominance of drought-avoidance strategies increased interactively with stem diameter and dry season intensity. Although size-related C cycle contributions did not vary systematically across the moisture gradient under nondrought conditions, woody mortality of larger trees was disproportionately elevated under El Niño drought stress. Thus, large (> 50 cm) stems, which strongly mediate but do not necessarily dominate C cycling, have drought adaptations that compensate for their more challenging hydraulic environment, particularly in drier climates. However, these adaptations do not fully buffer the effects of severe drought, and increased large tree mortality dominates ecosystem-level drought responses.

[1]  J. Sperry,et al.  Trends in wood density and structure are linked to prevention of xylem implosion by negative pressure , 2001, Oecologia.

[2]  J. Sperry,et al.  Does leaf shedding protect stems from cavitation during seasonal droughts? A test of the hydraulic fuse hypothesis. , 2016, The New phytologist.

[3]  David Galbraith,et al.  Linking hydraulic traits to tropical forest function in a size-structured and trait-driven model (TFS v.1-Hydro) , 2016 .

[4]  S. Stark,et al.  Forest structure along a 600 km transect of natural disturbances and seasonality gradients in central‐southern Amazonia , 2016 .

[5]  R. Corlett.  The Impacts of Droughts in Tropical Forests. , 2016, Trends in plant science.

[6]  K. Anderson‐Teixeira,et al.  Carbon dynamics of mature and regrowth tropical forests derived from a pantropical database (TropForC‐db) , 2016, Global change biology.

[7]  Y. Malhi,et al.  Death from drought in tropical forests is triggered by hydraulics not carbon starvation , 2015, Nature.

[8]  N. McDowell,et al.  Larger trees suffer most during drought in forests worldwide , 2015, Nature Plants.

[9]  H. Beeckman,et al.  Seeing Central African forests through their largest trees , 2015, Scientific Reports.

[10]  F. Biondi,et al.  Pervasive drought legacies in forest ecosystems and their implications for carbon cycle models , 2015, Science.

[11]  N. McDowell,et al.  Darcy's law predicts widespread forest mortality under climate warming , 2015 .

[12]  Kalle Ruokolainen,et al.  Hyperdominance in Amazonian forest carbon cycling , 2015, Nature Communications.

[13]  Norman A. Bourg,et al.  CTFS‐ForestGEO: a worldwide network monitoring forests in an era of global change , 2015, Global change biology.

[14]  Deborah Lawrence,et al.  Effects of tropical deforestation on climate and agriculture , 2015 .

[15]  B. Nelson,et al.  Improved allometric models to estimate the aboveground biomass of tropical trees , 2014, Global change biology.

[16]  S. Hubbell,et al.  Improving estimates of biomass change in buttressed trees using tree taper models , 2014 .

[17]  Oliver L. Phillips,et al.  Amazon palm biomass and allometry , 2013 .

[18]  Yadvinder Malhi,et al.  Confronting model predictions of carbon fluxes with measurements of Amazon forests subjected to experimental drought. , 2013, The New phytologist.

[19]  Stephen Sitch,et al.  Simulated resilience of tropical rainforests to CO2-induced climate change , 2013 .

[20]  Bettina M. J. Engelbrecht,et al.  Species distributions in response to individual soil nutrients and seasonal drought across a community of tropical trees , 2013, Proceedings of the National Academy of Sciences.

[21]  F. Bongers,et al.  Effects of disturbance intensity on species and functional diversity in a tropical forest , 2012 .

[22]  Andrew J. Larson,et al.  Ecological Importance of Large-Diameter Trees in a Temperate Mixed-Conifer Forest , 2012, PloS one.

[23]  M. G. Ryan,et al.  Relationships Between Tree Height and Carbon Isotope Discrimination , 2011 .

[24]  Nathan J B Kraft,et al.  Functional traits and the growth-mortality trade-off in tropical trees. , 2010, Ecology.

[25]  F. Woodward,et al.  Terrestrial Gross Carbon Dioxide Uptake: Global Distribution and Covariation with Climate , 2010, Science.

[26]  O. Phillips,et al.  Effect of 7 yr of experimental drought on vegetation dynamics and biomass storage of an eastern Amazonian rainforest. , 2010, The New phytologist.

[27]  H. Muller‐Landau,et al.  Rethinking the value of high wood density , 2010 .

[28]  S. Andelman,et al.  Drought-mortality relationships for tropical forests. , 2010, The New phytologist.

[29]  W. Landman.  Climate change 2007: the physical science basis , 2010 .

[30]  G. Goldstein,et al.  Size-dependent mortality in a Neotropical savanna tree: the role of height-related adjustments in hydraulic architecture and carbon allocation. , 2009, Plant, cell & environment.

[31]  Geoffrey B. West,et al.  A general quantitative theory of forest structure and dynamics , 2009, Proceedings of the National Academy of Sciences.

[32]  James H Brown,et al.  Extensions and evaluations of a general quantitative theory of forest structure and dynamics , 2009, Proceedings of the National Academy of Sciences.

[33]  L. Poorter,et al.  Seedling root morphology and biomass allocation of 62 tropical tree species in relation to drought‐ and shade‐tolerance , 2009 .

[34]  I. C. Prentice,et al.  Evaluation of the terrestrial carbon cycle, future plant geography and climate‐carbon cycle feedbacks using five Dynamic Global Vegetation Models (DGVMs) , 2008 .

[35]  S. Itch,et al.  Evaluation of the terrestrial carbon cycle, future plant geography and climate-carbon cycle feedbacks using five Dynamic Global Vegetation Models (DGVMs) , 2008 .

[36]  D. Nepstad,et al.  Mortality of large trees and lianas following experimental drought in an Amazon forest. , 2007, Ecology.

[37]  Brian J Enquist,et al.  Ecological and evolutionary determinants of a key plant functional trait: wood density and its community-wide variation across latitude and elevation. , 2007, American journal of botany.

[38]  David Kenfack,et al.  Comparing tropical forest tree size distributions with the predictions of metabolic ecology and equilibrium models. , 2006, Ecology letters.

[39]  Stephanie A. Bohlman,et al.  Testing metabolic ecology theory for allometric scaling of tree size, growth and mortality in tropical forests. , 2006, Ecology letters.

[40]  M. G. Ryan,et al.  The hydraulic limitation hypothesis revisited. , 2006, Plant, cell & environment.

[41]  J. Chambers,et al.  Tree allometry and improved estimation of carbon stocks and balance in tropical forests , 2005, Oecologia.

[42]  P. K. Snyder,et al.  Evaluating the influence of different vegetation biomes on the global climate , 2004 .

[43]  Stephen P. Hubbell,et al.  Tropical forest dynamics across a rainfall gradient and the impact of an El Niño dry season , 2004, Journal of Tropical Ecology.

[44]  David A. Coomes,et al.  Disturbances prevent stem size‐density distributions in natural forests from following scaling relationships , 2003 .

[45]  Kaoru Kitajima,et al.  Cloud cover limits net CO2 uptake and growth of a rainforest tree during tropical rainy seasons , 2003, Proceedings of the National Academy of Sciences of the United States of America.

[46]  Stephen P. Hubbell,et al.  Habitat associations of trees and shrubs in a 50‐ha neotropical forest plot , 2001 .

[47]  Stephanie A. Bohlman,et al.  Quantifying the deciduousness of tropical forest canopies under varying climates , 2000 .

[48]  S. Hubbell,et al.  Dynamics of the forest communities at Pasoh and Barro Colorado: comparing two 50-ha plots. , 1999, Philosophical transactions of the Royal Society of London. Series B, Biological sciences.

[49]  Stephen J. Wright,et al.  Light-Gap disturbances, recruitment limitation, and tree diversity in a neotropical forest , 1999, Science.

[50]  Richard Condit,et al.  Tropical Forest Census Plots: Methods and Results from Barro Colorado Island, Panama and a Comparison with Other Plots , 1998 .

[51]  R. Condit.  Ecological Implications of Changes in Drought Patterns: Shifts in Forest Composition in Panama , 1998 .

[52]  Valentín.  Chapter 4. , 1998, Annals of the ICRP.

[53]  D. Burslem,et al.  The interpretation and misinterpretation of mortality rate measures , 1995 .

[54]  S. Hubbell,et al.  Mortality Rates of 205 Neotropical Tree and Shrub Species and the Impact of a Severe Drought , 1995 .

[55]  S. Wright.  Seasonal Drought and the Phenology of Understory Shrubs in a Tropical Moist Forest , 1991 .

[56]  Osvaldo M. R. Cabral,et al.  Stomatal and boundary-layer conductances in an Amazonian terra firme rain forest. , 1990 .

[57]  S. Hubbell,et al.  Methodology for the fifty hectare research plot at Pasoh Forest Reserve. , 1990 .

[58]  E. Leigh,et al.  The Impact of the “El Niño” Drought of 1982-83 on a Panamanian Semideciduous Forest , 1990 .

[59]  R. Dickinson.  Effects of tropical deforestation on climate. , 1980 .

[60]  H. G. Baker,et al.  Comparative Phenological Studies of Trees in Tropical Wet and Dry Forests in the Lowlands of Costa Rica , 1974 .