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4 results on '"Galbraith, D.R."'

1. Death from drought in tropical forests is triggered by hydraulics not carbon starvation

Author

Rowland, L., da Costa, A.C.L., Galbraith, D.R., Oliveira, R.S., Binks, O.J., Oliveira, A.A.R., Pullen, A.M., Doughty, C.E., Metcalfe, D.B., Vasconcelos, S.S., Ferreira, L.V., Malhi, Y., Grace, J., Mencuccini, M., and Meir, P.

Subjects
Droughts -- Physiological aspects -- Health aspects -- Environmental aspects -- Brazil, Forests and forestry -- Research -- Brazil, Starvation -- Physiological aspects -- Health aspects -- Analysis, Environmental issues, Science and technology, Zoology and wildlife conservation
Abstract

Drought threatens tropical rainforests over seasonal to decadal timescales (1-4), but the drivers of tree mortality following drought remain poorly understood (5,6). It has been suggested that reduced availability of non-structural carbohydrates (NSC) critically increases mortality risk through insufficient carbon supply to metabolism ('carbon starvation') (7,8). However, little is known about how NSC stores are affected by drought, especially over the long term, and whether they are more important than hydraulic processes in determining drought-induced mortality. Using data from the world's longest-running experimental drought study in tropical rainforest (in the Brazilian Amazon), we test whether carbon starvation or deterioration of the water-conducting pathways from soil to leaf trigger tree mortality. Biomass loss from mortality in the experimentally droughted forest increased substantially after > 10 years of reduced soil moisture availability. The mortality signal was dominated by the death of large trees, which were at a much greater risk of hydraulic deterioration than smaller trees. However, we find no evidence that the droughted trees suffered carbon starvation, as their NSC concentrations were similar to those of non-droughted trees, and growth rates did not decline in either living or dying trees. Our results indicate that hydraulics, rather than carbon starvation, triggers tree death from drought in tropical rainforest., Drought-response observations from both field-scale experiments and natural droughts have demonstrated increased mortality over the short-term (1-3 years), with notably higher vulnerability for some taxa, and for larger trees (6,9,10). [...]

Published
2015

2. Amazon tree dominance across forest strata

Author

Draper, F.C., Costa, F.R.C., Arellano, G., Phillips, O.L., Duque, A., Macía, M.J., ter Steege, H., Asner, G.P., Berenguer, E., Schietti, J., Socolar, J.B., de Souza, F.C., Dexter, K.G., Jørgensen, P.M., Tello, J.S., Magnusson, W.E., Baker, T.R., Castilho, C.V., Monteagudo-Mendoza, A., Fine, P.V.A., Ruokolainen, K., Coronado, E.N.H., Aymard, G., Dávila, N., Sáenz, M.S., Paredes, M.A.R., Engel, J., Fortunel, C., Paine, C.E.T., Goret, J.-Y., Dourdain, A., Petronelli, P., Allie, E., Andino, J.E.G., Brienen, R.J.W., Pérez, L.C., Manzatto, Â.G., Zambrana, N.Y.P., Molino, J.-F., Sabatier, D., Chave, J., Fauset, S., Villacorta, R.G., Réjou-Méchain, M., Berry, P.E., Melgaço, K., Feldpausch, T.R., Sandoval, E.V., Martinez, R.V., Mesones, I., Junqueira, A.B., Roucoux, K.H., de Toledo, J.J., Andrade, A.C., Camargo, J.L., del Aguila Pasquel, J., Santana, F.D., Laurance, W.F., Laurance, S.G., Lovejoy, T.E., Comiskey, J.A., Galbraith, D.R., Kalamandeen, M., Aguilar, G.E.N., Arenas, J.V., Guerra, C.A.A., Flores, M., Llampazo, G.F., Montenegro, L.A.T., Gomez, R.Z., Pansonato, M.P., Moscoso, V.C., Vleminckx, J., Barrantes, O.J.V., Duivenvoorden, J.F., de Sousa, S.A., Arroyo, L., Perdiz, R.O., Cravo, J.S., Marimon, B.S., Junior, B.H.M., Carvalho, F.A., Damasco, G., Disney, M., Vital, M.S., Diaz, P.R.S., Vicentini, A., Nascimento, H., Higuchi, N., Van Andel, T., Malhi, Y., Ribeiro, S.C., Terborgh, J.W., Thomas, R.S., Dallmeier, F., Prieto, A., Hilário, R.R., Salomão, R.P., Silva, R.C., Casas, L.F., Vieira, I.C.G., Araujo-Murakami, A., Arevalo, F.R., Ramírez-Angulo, H., Torre, E.V., Peñuela, M.C., Killeen, T.J., Pardo, G., Jimenez-Rojas, E., Castro, W., Cabrera, D.G., Pipoly, J., de Sousa, T.R., Silvera, M., Vos, V., Neill, D., Vargas, P.N., Vela, D.M., Aragão, L.E.O.C., Umetsu, R.K., Sierra, R., Wang, O., Young, K.R., Prestes, N.C.C.S., Massi, K.G., Huaymacari, J.R., Gutierrez, G.A.P., Aldana, A.M., Alexiades, M.N., Baccaro, F., Céron, C., Muelbert, A.E., Rios, J.M.G., Lima, A.S., Lloyd, J.L., Pitman, N.C.A., Gamarra, L.V., Oroche, C.J.C., Fuentes, A.F., Palacios, W., Patiño, S., Torres-Lezama, A., Baraloto, C., Draper, F.C., Costa, F.R.C., Arellano, G., Phillips, O.L., Duque, A., Macía, M.J., ter Steege, H., Asner, G.P., Berenguer, E., Schietti, J., Socolar, J.B., de Souza, F.C., Dexter, K.G., Jørgensen, P.M., Tello, J.S., Magnusson, W.E., Baker, T.R., Castilho, C.V., Monteagudo-Mendoza, A., Fine, P.V.A., Ruokolainen, K., Coronado, E.N.H., Aymard, G., Dávila, N., Sáenz, M.S., Paredes, M.A.R., Engel, J., Fortunel, C., Paine, C.E.T., Goret, J.-Y., Dourdain, A., Petronelli, P., Allie, E., Andino, J.E.G., Brienen, R.J.W., Pérez, L.C., Manzatto, Â.G., Zambrana, N.Y.P., Molino, J.-F., Sabatier, D., Chave, J., Fauset, S., Villacorta, R.G., Réjou-Méchain, M., Berry, P.E., Melgaço, K., Feldpausch, T.R., Sandoval, E.V., Martinez, R.V., Mesones, I., Junqueira, A.B., Roucoux, K.H., de Toledo, J.J., Andrade, A.C., Camargo, J.L., del Aguila Pasquel, J., Santana, F.D., Laurance, W.F., Laurance, S.G., Lovejoy, T.E., Comiskey, J.A., Galbraith, D.R., Kalamandeen, M., Aguilar, G.E.N., Arenas, J.V., Guerra, C.A.A., Flores, M., Llampazo, G.F., Montenegro, L.A.T., Gomez, R.Z., Pansonato, M.P., Moscoso, V.C., Vleminckx, J., Barrantes, O.J.V., Duivenvoorden, J.F., de Sousa, S.A., Arroyo, L., Perdiz, R.O., Cravo, J.S., Marimon, B.S., Junior, B.H.M., Carvalho, F.A., Damasco, G., Disney, M., Vital, M.S., Diaz, P.R.S., Vicentini, A., Nascimento, H., Higuchi, N., Van Andel, T., Malhi, Y., Ribeiro, S.C., Terborgh, J.W., Thomas, R.S., Dallmeier, F., Prieto, A., Hilário, R.R., Salomão, R.P., Silva, R.C., Casas, L.F., Vieira, I.C.G., Araujo-Murakami, A., Arevalo, F.R., Ramírez-Angulo, H., Torre, E.V., Peñuela, M.C., Killeen, T.J., Pardo, G., Jimenez-Rojas, E., Castro, W., Cabrera, D.G., Pipoly, J., de Sousa, T.R., Silvera, M., Vos, V., Neill, D., Vargas, P.N., Vela, D.M., Aragão, L.E.O.C., Umetsu, R.K., Sierra, R., Wang, O., Young, K.R., Prestes, N.C.C.S., Massi, K.G., Huaymacari, J.R., Gutierrez, G.A.P., Aldana, A.M., Alexiades, M.N., Baccaro, F., Céron, C., Muelbert, A.E., Rios, J.M.G., Lima, A.S., Lloyd, J.L., Pitman, N.C.A., Gamarra, L.V., Oroche, C.J.C., Fuentes, A.F., Palacios, W., Patiño, S., Torres-Lezama, A., and Baraloto, C.

Abstract

The forests of Amazonia are among the most biodiverse plant communities on Earth. Given the immediate threats posed by climate and land-use change, an improved understanding of how this extraordinary biodiversity is spatially organized is urgently required to develop effective conservation strategies. Most Amazonian tree species are extremely rare but a few are common across the region. Indeed, just 227 ‘hyperdominant’ species account for >50% of all individuals >10 cm diameter at 1.3 m in height. Yet, the degree to which the phenomenon of hyperdominance is sensitive to tree size, the extent to which the composition of dominant species changes with size class and how evolutionary history constrains tree hyperdominance, all remain unknown. Here, we use a large floristic dataset to show that, while hyperdominance is a universal phenomenon across forest strata, different species dominate the forest understory, midstory and canopy. We further find that, although species belonging to a range of phylogenetically dispersed lineages have become hyperdominant in small size classes, hyperdominants in large size classes are restricted to a few lineages. Our results demonstrate that it is essential to consider all forest strata to understand regional patterns of dominance and composition in Amazonia. More generally, through the lens of 654 hyperdominant species, we outline a tractable pathway for understanding the functioning of half of Amazonian forests across vertical strata and geographical locations.

Published
2021

3. Linking hydraulic traits to tropical forest function in a size-structured and trait-driven model (TFS v.1-Hydro)

Author

Christoffersen, B.O. Gloor, M. Fauset, S. Fyllas, N.M. Galbraith, D.R. Baker, T.R. Kruijt, B. Rowland, L. Fisher, R.A. Binks, O.J. Sevanto, S. Xu, C. Jansen, S. Choat, B. Mencuccini, M. McDowell, N.G. Meir, P.

Abstract

Forest ecosystem models based on heuristic water stress functions poorly predict tropical forest response to drought partly because they do not capture the diversity of hydraulic traits (including variation in tree size) observed in tropical forests. We developed a continuous porous media approach to modeling plant hydraulics in which all parameters of the constitutive equations are biologically interpretable and measurable plant hydraulic traits (e.g., turgor loss point πtlp, bulk elastic modulus ϵ, hydraulic capacitance Cft, xylem hydraulic conductivity ks,max, water potential at 50% loss of conductivity for both xylem (P50,x) and stomata (P50,gs), and the leafg: sapwood area ratio Al: As). We embedded this plant hydraulics model within a trait forest simulator (TFS) that models light environments of individual trees and their upper boundary conditions (transpiration), as well as providing a means for parameterizing variation in hydraulic traits among individuals. We synthesized literature and existing databases to parameterize all hydraulic traits as a function of stem and leaf traits, including wood density (WD), leaf mass per area (LMA), and photosynthetic capacity (Amax), and evaluated the coupled model (called TFS v.1-Hydro) predictions, against observed diurnal and seasonal variability in stem and leaf water potential as well as stand-scaled sap flux. Our hydraulic trait synthesis revealed coordination among leaf and xylem hydraulic traits and statistically significant relationships of most hydraulic traits with more easily measured plant traits. Using the most informative empirical trait-trait relationships derived from this synthesis, TFS v.1-Hydro successfully captured individual variation in leaf and stem water potential due to increasing tree size and light environment, with model representation of hydraulic architecture and plant traits exerting primary and secondary controls, respectively, on the fidelity of model predictions. The plant hydraulics model made substantial improvements to simulations of total ecosystem transpiration. Remaining uncertainties and limitations of the trait paradigm for plant hydraulics modeling are highlighted. © Author(s) 2016.

Published
2016

4. Analysing Amazonian forest productivity using a new individual and trait-based model (TFS v.1)

Author

Fyllas, N.M. Gloor, E. Mercado, L.M. Sitch, S. Quesada, C.A. Domingues, T.F. Galbraith, D.R. Torre-Lezama, A. Vilanova, E. Ramírez-Angulo, H. Higuchi, N. Neill, D.A. Silveira, M. Ferreira, L. Aymard C., G.A. Malhi, Y. Phillips, O.L. Lloyd, J.

Abstract

Repeated long-term censuses have revealed large-scale spatial patterns in Amazon basin forest structure and dynamism, with some forests in the west of the basin having up to a twice as high rate of aboveground biomass production and tree recruitment as forests in the east. Possible causes for this variation could be the climatic and edaphic gradients across the basin and/or the spatial distribution of tree species composition. To help understand causes of this variation a new individual-based model of tropical forest growth, designed to take full advantage of the forest census data available from the Amazonian Forest Inventory Network (RAINFOR), has been developed. The model allows for within-stand variations in tree size distribution and key functional traits and between-stand differences in climate and soil physical and chemical properties. It runs at the stand level with four functional traits - leaf dry mass per area (Ma), leaf nitrogen (NL) and phosphorus (PL) content and wood density (DW) varying from tree to tree - in a way that replicates the observed continua found within each stand. We first applied the model to validate canopy-level water fluxes at three eddy covariance flux measurement sites. For all three sites the canopy-level water fluxes were adequately simulated. We then applied the model at seven plots, where intensive measurements of carbon allocation are available. Tree-by-tree multi-annual growth rates generally agreed well with observations for small trees, but with deviations identified for larger trees. At the stand level, simulations at 40 plots were used to explore the influence of climate and soil nutrient availability on the gross (ΠG) and net (ΠN) primary production rates as well as the carbon use efficiency (CU). Simulated ΠG, ΠN and CU were not associated with temperature. On the other hand, all three measures of stand level productivity were positively related to both mean annual precipitation and soil nutrient status. Sensitivity studies showed a clear importance of an accurate parameterisation of within- and between-stand trait variability on the fidelity of model predictions. For example, when functional tree diversity was not included in the model (i.e. with just a single plant functional type with mean basin-wide trait values) the predictive ability of the model was reduced. This was also the case when basin-wide (as opposed to site-specific) trait distributions were applied within each stand. We conclude that models of tropical forest carbon, energy and water cycling should strive to accurately represent observed variations in functionally important traits across the range of relevant scales. © Author(s) 2014.

Published
2014

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