Xylem hydraulic safety and construction costs determine tropical tree growth

B. Eller, C., de V. Barros, F., R.L. Bittencourt, P., Rowland, L., Mencuccini, M., S. Oliveira, R. (2018) Xylem hydraulic safety and construction costs determine tropical tree growth. Plant Cell and Environment. 41: 548-562.
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Doi: 10.1111/pce.13106

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Estimating Carbon Avoided from the Implementation of Reduced-Impact Logging in Sabah, Malaysia

Galante M.V., Pinard M.A., Mencuccini M. (2018) Estimating Carbon Avoided from the Implementation of Reduced-Impact Logging in Sabah, Malaysia. International Forestry Review. 20: 58-78.
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Doi: 10.1505/146554818822824192

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The objective of this study was to investigate the design and application of a carbon baseline for commercial timber harvest activities involving conventional timber harvest activities (CNV), relative to reduced-impact logging (RIL) in Sabah, Malaysia. As only RIL is eligible to be practiced in production forests, a baseline of CNV was estimated from the literature. The principle of net present value was applied to the post-harvest accumulation of carbon stocks after RIL to model a conservative 'crediting' baseline. Two areas representing opposite ends of a range of anthropogenic disturbance were sampled, with an old growth lower montane forest, and a lowland severely logged-over dipterocarp forest investigated before-, and two- and three-years after harvest, respectively. Areas impacted by CNV were estimated to contain 12-39% of pre-harvest carbon stock, relative to 57-63% under RIL and estimated to accumulate carbon in the range of 0.68-1.25 tC ha-1 yr1, averaging 14-55 years for recovery; in-line with body of knowledge. While the main limitation was our inability measure CNV directly, a balance of understanding is required for the development of a 'best estimate' using the literature. © 2018 Commonwealth Forestry Association. All rights reserved.

Llegeix més

Tree size and climatic water deficit control root to shoot ratio in individual trees globally

Ledo, A., Paul, K.I., Burslem, D.F.R.P., Ewel, J.J., Barton, C., Battaglia, M., Brooksbank, K., Carter, J., Eid, T.H., England, J.R., Fitzgerald, A., Jonson, J., Mencuccini, M., Montagu, K.D., Montero, G., Mugasha, W.A., Pinkard, E., Roxburgh, S., Ryan, C.M., Ruiz-Peinado, R., Sochacki, S., Specht, A., Wildy, D., Wirth, C., Zerihun, A., Chave, J. (2018) Tree size and climatic water deficit control root to shoot ratio in individual trees globally. New Phytologist. 217: 8-11.
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Doi: 10.1111/nph.14863

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Preliminary growth functions for Eucalyptus gunnii in the UK

Leslie, A.D., Mencuccini, M., Perks, M.P. (2018) Preliminary growth functions for Eucalyptus gunnii in the UK. Biomass and Bioenergy. 108: 464-469.
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Doi: 10.1016/j.biombioe.2017.10.037

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Drivers and mechanisms of tree mortality in moist tropical forests

Mcdowell N., Allen C.D., Anderson-Teixeira K., Brando P., Brienen R., Chambers J., Christoffersen B., Davies S., Doughty C., Duque A., Espirito-Santo F., Fisher R., Fontes C.G., Galbraith D., Goodsman D., Grossiord C., Hartmann H., Holm J., Johnson D.J., Kassim A.R., Keller M., Koven C., Kueppers L., Kumagai T., Malhi Y., Mcmahon S.M., Mencuccini M., Meir P., Moorcroft P., Muller-Landau H.C., Phillips O.L., Powell T., Sierra C.A., Sperry J., Warren J., Xu C., Xu X. (2018) Drivers and mechanisms of tree mortality in moist tropical forests. New Phytologist. : 0-0.
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Doi: 10.1111/nph.15027

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Tree mortality rates appear to be increasing in moist tropical forests (MTFs) with significant carbon cycle consequences. Here, we review the state of knowledge regarding MTF tree mortality, create a conceptual framework with testable hypotheses regarding the drivers, mechanisms and interactions that may underlie increasing MTF mortality rates, and identify the next steps for improved understanding and reduced prediction. Increasing mortality rates are associated with rising temperature and vapor pressure deficit, liana abundance, drought, wind events, fire and, possibly, CO2 fertilization-induced increases in stand thinning or acceleration of trees reaching larger, more vulnerable heights. The majority of these mortality drivers may kill trees in part through carbon starvation and hydraulic failure. The relative importance of each driver is unknown. High species diversity may buffer MTFs against large-scale mortality events, but recent and expected trends in mortality drivers give reason for concern regarding increasing mortality within MTFs. Models of tropical tree mortality are advancing the representation of hydraulics, carbon and demography, but require more empirical knowledge regarding the most common drivers and their subsequent mechanisms. We outline critical datasets and model developments required to test hypotheses regarding the underlying causes of increasing MTF mortality rates, and improve prediction of future mortality under climate change. © 2018 New Phytologist Trust.

Llegeix més

Gap-filling a spatially explicit plant trait database: Comparing imputation methods and different levels of environmental information

Poyatos R., Sus O., Badiella L., Mencuccini M., Martínez-Vilalta J. (2018) Gap-filling a spatially explicit plant trait database: Comparing imputation methods and different levels of environmental information. Biogeosciences. 15: 2601-2617.
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Doi: 10.5194/bg-15-2601-2018

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The ubiquity of missing data in plant trait databases may hinder trait-based analyses of ecological patterns and processes. Spatially explicit datasets with information on intraspecific trait variability are rare but offer great promise in improving our understanding of functional biogeography. At the same time, they offer specific challenges in terms of data imputation. Here we compare statistical imputation approaches, using varying levels of environmental information, for five plant traits (leaf biomass to sapwood area ratio, leaf nitrogen content, maximum tree height, leaf mass per area and wood density) in a spatially explicit plant trait dataset of temperate and Mediterranean tree species (Ecological and Forest Inventory of Catalonia, IEFC, dataset for Catalonia, north-east Iberian Peninsula, 31 900 km2). We simulated gaps at different missingness levels (10-80 %) in a complete trait matrix, and we used overall trait means, species means, k nearest neighbours (kNN), ordinary and regression kriging, and multivariate imputation using chained equations (MICE) to impute missing trait values. We assessed these methods in terms of their accuracy and of their ability to preserve trait distributions, multi-trait correlation structure and bivariate trait relationships. The relatively good performance of mean and species mean imputations in terms of accuracy masked a poor representation of trait distributions and multivariate trait structure. Species identity improved MICE imputations for all traits, whereas forest structure and topography improved imputations for some traits. No method performed best consistently for the five studied traits, but, considering all traits and performance metrics, MICE informed by relevant ecological variables gave the best results. However, at higher missingness (> 30 %), species mean imputations and regression kriging tended to outperform MICE for some traits. MICE informed by relevant ecological variables allowed us to fill the gaps in the IEFC incomplete dataset (5495 plots) and quantify imputation uncertainty. Resulting spatial patterns of the studied traits in Catalan forests were broadly similar when using species means, regression kriging or the best-performing MICE application, but some important discrepancies were observed at the local level. Our results highlight the need to assess imputation quality beyond just imputation accuracy and show that including environmental information in statistical imputation approaches yields more plausible imputations in spatially explicit plant trait datasets. © 2018 Author(s).

Llegeix més

Shock and stabilisation following long-term drought in tropical forest from 15 years of litterfall dynamics

Rowland L., da Costa A.C.L., Oliveira A.A.R., Almeida S.S., Ferreira L.V., Malhi Y., Metcalfe D.B., Mencuccini M., Grace J., Meir P. (2018) Shock and stabilisation following long-term drought in tropical forest from 15 years of litterfall dynamics. Journal of Ecology. : 0-0.
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Doi: 10.1111/1365-2745.12931

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Litterfall dynamics in tropical forests are a good indicator of overall tropical forest function, indicative of carbon invested in both photosynthesising tissues and reproductive organs such as flowers and fruits. These dynamics are sensitive to changes in climate, such as drought, but little is known about the long-term responses of tropical forest litterfall dynamics to extended drought stress. We present a 15-year dataset of litterfall (leaf, flower and fruit, and twigs) from the world's only long-running drought experiment in tropical forest. This dataset comprises one of the longest published litterfall time series in natural forest, which allows the long-term effects of drought on forest reproduction and canopy investment to be explored. Over the first 4 years of the experiment, the experimental soil moisture deficit created only a small decline in total litterfall and leaf fall (12% and 13%, respectively), but a very strong initial decline in reproductive litterfall (flowers and fruits) of 54%. This loss of flowering and fruiting was accompanied by a de-coupling of all litterfall patterns from seasonal climate variables. However, following >10 years of the experimental drought, flower and fruiting re-stabilised at levels greater than in the control plot, despite high tree mortality in the drought plot. Litterfall relationships with atmospheric drivers were re-established alongside a strong new apparent trade-off between litterfall and tree growth. Synthesis. We demonstrate that this tropical forest went through an initial shock response during the first 4 years of intense drought, where reproductive effort was arrested and seasonal litterfall patterns were lost. However, following >10 years of experimental drought, this system appears to be re-stabilising at a new functional state where reproduction is substantially elevated on a per tree basis; and there is a new strong trade-off between investment in canopy production and wood production. © 2018 The Authors.

Llegeix més

Drought stress and tree size determine stem CO2 efflux in a tropical forest

Rowland L., da Costa A.C.L., Oliveira A.A.R., Oliveira R.S., Bittencourt P.L., Costa P.B., Giles A.L., Sosa A.I., Coughlin I., Godlee J.L., Vasconcelos S.S., Junior J.A.S., Ferreira L.V., Mencuccini M., Meir P. (2018) Drought stress and tree size determine stem CO2 efflux in a tropical forest. New Phytologist. 218: 1393-1405.
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Doi: 10.1111/nph.15024

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CO2 efflux from stems (CO2_stem) accounts for a substantial fraction of tropical forest gross primary productivity, but the climate sensitivity of this flux remains poorly understood. We present a study of tropical forest CO2_stem from 215 trees across wet and dry seasons, at the world's longest running tropical forest drought experiment site. We show a 27% increase in wet season CO2_stem in the droughted forest relative to a control forest. This was driven by increasing CO2_stem in trees 10–40 cm diameter. Furthermore, we show that drought increases the proportion of maintenance to growth respiration in trees > 20 cm diameter, including large increases in maintenance respiration in the largest droughted trees, > 40 cm diameter. However, we found no clear taxonomic influence on CO2_stem and were unable to accurately predict how drought sensitivity altered ecosystem scale CO2_stem, due to substantial uncertainty introduced by contrasting methods previously employed to scale CO2_stem fluxes. Our findings indicate that under future scenarios of elevated drought, increases in CO2_stem may augment carbon losses, weakening or potentially reversing the tropical forest carbon sink. However, due to substantial uncertainties in scaling CO2_stem fluxes, stand-scale future estimates of changes in stem CO2 emissions remain highly uncertain. © 2018 The Authors New Phytologist © 2018 New Phytologist Trust

Llegeix més

Changes in tree resistance, recovery and resilience across three successive extreme droughts in the northeast Iberian Peninsula

Serra-Maluquer X., Mencuccini M., Martínez-Vilalta J. (2018) Changes in tree resistance, recovery and resilience across three successive extreme droughts in the northeast Iberian Peninsula. Oecologia. : 1-12.
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Doi: 10.1007/s00442-018-4118-2

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Understanding which variables affect forest resilience to extreme drought is key to predict future dynamics under ongoing climate change. In this study, we analyzed how tree resistance, recovery and resilience to drought have changed along three consecutive droughts and how they were affected by species, tree size, plot basal area (as a proxy for competition) and climate. We focused on the three most abundant pine species in the northeast Iberian Peninsula: Pinus halepensis, P. nigra and P. sylvestris during the three most extreme droughts recorded in the period 1951–2010 (occurred in 1986, 1994, and 2005–2006). We cored trees from permanent sample plots and used dendrochronological techniques to estimate resistance (ability to maintain growth level during drought), recovery (growth increase after drought) and resilience (capacity to recover pre-drought growth levels) in terms of tree stem basal area increment. Mixed-effects models were used to determine which tree- and plot-level variables were the main determinants of resistance, recovery and resilience, and to test for differences among the studied droughts. Larger trees were significantly less resistant and resilient. Plot basal area effects were only observed for resilience, with a negative impact only during the last drought. Resistance, recovery and resilience differed across the studied drought events, so that the studied populations became less resistant, less resilient and recovered worse during the last two droughts. This pattern suggests an increased vulnerability to drought after successive drought episodes. © 2018 Springer-Verlag GmbH Germany, part of Springer Nature

Llegeix més

A multi-species synthesis of physiological mechanisms in drought-induced tree mortality

Adams, H.D., Zeppel, M.J.B., Anderegg, W.R.L., Hartmann, H., Landhäusser, S.M., Tissue, D.T., Huxman, T.E., Hudson, P.J., Franz, T.E., Allen, C.D., Anderegg, L.D.L., Barron-Gafford, G.A., Beerling, D.J., Breshears, D.D., Brodribb, T.J., Bugmann, H., Cobb, R.C., Collins, A.D., Dickman, L.T., Duan, H., Ewers, B.E., Galiano, L., Galvez, D.A., Garcia-Forner, N., Gaylord, M.L., Germino, M.J., Gessler, A., Hacke, U.G., Hakamada, R., Hector, A., Jenkins, M.W., Kane, J.M., Kolb, T.E., Law, D.J., Lewis, J.D., Limousin, J.-M., Love, D.M., Macalady, A.K., Martínez-Vilalta, J., Mencuccini, M., Mitchell, P.J., Muss, J.D., O'Brien, M.J., O'Grady, A.P., Pangle, R.E., Pinkard, E.A., Piper, F.I., Plaut, J.A., Pockman, W.T., Quirk, J., Reinhardt, K., Ripullone, F., Ryan, M.G., Sala, A., Sevanto, S., Sperry, J.S., Vargas, R., Vennetier, M., Way, D.A., Xu, C., Yepez, E.A., McDowell, N.G. (2017) A multi-species synthesis of physiological mechanisms in drought-induced tree mortality. Nature Ecology and Evolution. 1: 1285-1291.
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Doi: 10.1038/s41559-017-0248-x

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