Browsing by Autor "Christopher E. Doughty"

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Allocation trade‐offs dominate the response of tropical forest growth to seasonal and interannual drought
(Wiley, 2014) Christopher E. Doughty; Yadvinder Malhi; Alejandro Araujo‐Murakami; Daniel B. Metcalfe; Javier E. Silva‐Espejo; Luzmila Arroyo; Juan P. Heredia; Erwin Pardo-Toledo; Luz M. Mendizabal; Victor D. Rojas-Landivar
What determines the seasonal and interannual variation of growth rates in trees in a tropical forest? We explore this question with a novel four-year high-temporal-resolution data set of carbon allocation from two forest plots in the Bolivian Amazon. The forests show strong seasonal variation in tree wood growth rates, which are largely explained by shifts in carbon allocation, and not by shifts in total productivity. At the deeper soil plot, there was a clear seasonal trade-off between wood and canopy NPP, while the shallower soils plot showed a contrasting seasonal trade-off between wood and fine roots. Although a strong 2010 drought reduced photosynthesis, NPP remained constant and increased in the six-month period following the drought, which indicates usage of significant nonstructural carbohydrate stores. Following the drought, carbon allocation increased initially towards the canopy, and then in the following year, allocation increased towards fine-root production. Had we only measured woody growth at these sites and inferred total NPP, we would have misinterpreted both the seasonal and interannual responses. In many tropical forest ecosystems, we propose that changing tree growth rates are more likely to reflect shifts in allocation rather than changes in overall productivity. Only a whole NPP allocation perspective can correctly interpret the relationship between changes in growth and changes in productivity.
Data from: What controls variation in carbon use efficiency among Amazonian tropical forests?
(Chapman University, 2017) Christopher E. Doughty; Gregory R. Goldsmith; Nicolas Raab; Cécile Girardin; Filio Farfan‐Amezquita; Walter Huaraca Huasco; Javier E. Silva‐Espejo; Alejandro Araujo‐Murakami; Antônio C. L. da Costa; Wanderley Rocha
Why do some forests produce biomass more efficiently than others? Variations in Carbon Use Efficiency (CUE: total Net Primary Production (NPP)/ Gross Primary Production (GPP)) may be due to changes in wood residence time (Biomass/NPPwood), temperature, or soil nutrient status. We tested these hypotheses in 14, one ha plots across Amazonian and Andean forests where we measured most key components of net primary production (NPP: wood, fine roots, and leaves) and autotrophic respiration (Ra; wood, rhizosphere, and leaf respiration). We found that lower fertility sites were less efficient at producing biomass and had higher rhizosphere respiration, indicating increased carbon allocation to belowground components. We then compared wood respiration to wood growth and rhizosphere respiration to fine root growth and found that forests with residence times <40 yrs had significantly lower maintenance respiration for both wood and fine roots than forests with residence times >40 yrs. A comparison of rhizosphere respiration to fine root growth showed that rhizosphere growth respiration was significantly greater at low fertility sites. Overall, we found that Amazonian forests produce biomass less efficiently in stands with residence times >40 yrs and in stands with lower fertility, but changes to long-term mean annual temperatures do not impact CUE.
Drought impact on forest carbon dynamics and fluxes in Amazonia
(Nature Portfolio, 2015) Christopher E. Doughty; D. B. Metcalfe; Cécile Girardin; Filio Farfán Amézquita; Darcy Galiano Cabrera; Walter Huaraca Huasco; Javier E. Silva‐Espejo; Alejandro Araujo‐Murakami; Mauricio C. da Costa; Wellington Willian Rocha
ENSO Drives interannual variation of forest woody growth across the tropics
(Royal Society, 2018) Sami W. Rifai; Cécile Girardin; Érika Berenguer; Jhon del Águila Pasquel; Cecilia A. L. Dahlsjö; Christopher E. Doughty; Kathryn J. Jeffery; Sam Moore; Imma Oliveras Menor; Terhi Riutta
Meteorological extreme events such as El Niño events are expected to affect tropical forest net primary production (NPP) and woody growth, but there has been no large-scale empirical validation of this expectation. We collected a large high-temporal resolution dataset (for 1-13 years depending upon location) of more than 172 000 stem growth measurements using dendrometer bands from across 14 regions spanning Amazonia, Africa and Borneo in order to test how much month-to-month variation in stand-level woody growth of adult tree stems (NPPstem) can be explained by seasonal variation and interannual meteorological anomalies. A key finding is that woody growth responds differently to meteorological variation between tropical forests with a dry season (where monthly rainfall is less than 100 mm), and aseasonal wet forests lacking a consistent dry season. In seasonal tropical forests, a high degree of variation in woody growth can be predicted from seasonal variation in temperature, vapour pressure deficit, in addition to anomalies of soil water deficit and shortwave radiation. The variation of aseasonal wet forest woody growth is best predicted by the anomalies of vapour pressure deficit, water deficit and shortwave radiation. In total, we predict the total live woody production of the global tropical forest biome to be 2.16 Pg C yr-1, with an interannual range 1.96-2.26 Pg C yr-1 between 1996-2016, and with the sharpest declines during the strong El Niño events of 1997/8 and 2015/6. There is high geographical variation in hotspots of El Niño-associated impacts, with weak impacts in Africa, and strongly negative impacts in parts of Southeast Asia and extensive regions across central and eastern Amazonia. Overall, there is high correlation (r = -0.75) between the annual anomaly of tropical forest woody growth and the annual mean of the El Niño 3.4 index, driven mainly by strong correlations with anomalies of soil water deficit, vapour pressure deficit and shortwave radiation.This article is part of the discussion meeting issue 'The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications'.
Seasonal trends of Amazonian rainforest phenology, net primary productivity, and carbon allocation
(Wiley, 2016) Cécile Girardin; Yadvinder Malhi; Christopher E. Doughty; Daniel B. Metcalfe; Patrick Meir; Jhon del Águila Pasquel; Alejandro Araujo‐Murakami; Antônio C. L. da Costa; Javier E. Silva‐Espejo; Filio Farfán Amézquita
Abstract The seasonality of solar irradiance and precipitation may regulate seasonal variations in tropical forests carbon cycling. Controversy remains over their importance as drivers of seasonal dynamics of net primary productivity in tropical forests. We use ground data from nine lowland Amazonian forest plots collected over 3 years to quantify the monthly primary productivity ( NPP ) of leaves, reproductive material, woody material, and fine roots over an annual cycle. We distinguish between forests that do not experience substantial seasonal moisture stress (“humid sites”) and forests that experience a stronger dry season (“dry sites”). We find that forests from both precipitation regimes maximize leaf NPP over the drier season, with a peak in production in August at both humid (mean 0.39 ± 0.03 Mg C ha −1 month −1 in July, n = 4) and dry sites (mean 0.49 ± 0.03 Mg C ha −1 month −1 in September, n = 8). We identify two distinct seasonal carbon allocation patterns (the allocation of NPP to a specific organ such as wood leaves or fine roots divided by total NPP ). The forests monitored in the present study show evidence of either (i) constant allocation to roots and a seasonal trade‐off between leaf and woody material or (ii) constant allocation to wood and a seasonal trade‐off between roots and leaves. Finally, we find strong evidence of synchronized flowering at the end of the dry season in both precipitation regimes. Flower production reaches a maximum of 0.047 ± 0.013 and 0.031 ± 0.004 Mg C ha −1 month −1 in November, in humid and dry sites, respectively. Fruitfall production was staggered throughout the year, probably reflecting the high variation in varying times to development and loss of fruit among species.
Source and sink carbon dynamics and carbon allocation in the Amazon basin
(Wiley, 2015) Christopher E. Doughty; Daniel B. Metcalfe; Cécile Girardin; Filio Farfán Amézquita; Lucile Durand; Walter Huaraca Huasco; Javier E. Silva‐Espejo; Alejandro Araujo‐Murakami; Mauricio C. da Costa; Antônio C. L. da Costa
Abstract Changes to the carbon cycle in tropical forests could affect global climate, but predicting such changes has been previously limited by lack of field‐based data. Here we show seasonal cycles of the complete carbon cycle for 14, 1 ha intensive carbon cycling plots which we separate into three regions: humid lowland, highlands, and dry lowlands. Our data highlight three trends: (1) there is differing seasonality of total net primary productivity (NPP) with the highlands and dry lowlands peaking in the dry season and the humid lowland sites peaking in the wet season, (2) seasonal reductions in wood NPP are not driven by reductions in total NPP but by carbon during the dry season being preferentially allocated toward either roots or canopy NPP, and (3) there is a temporal decoupling between total photosynthesis and total carbon usage (plant carbon expenditure). This decoupling indicates the presence of nonstructural carbohydrates which may allow growth and carbon to be allocated when it is most ecologically beneficial rather than when it is most environmentally available.
The linkages between photosynthesis, productivity, growth and biomass in lowland Amazonian forests
(Wiley, 2015) Yadvinder Malhi; Christopher E. Doughty; Gregory R. Goldsmith; Daniel B. Metcalfe; Cécile Girardin; Toby R. Marthews; Jhon del Águila Pasquel; Luiz E. O. C. Aragão; Alejandro Araujo‐Murakami; Paulo Brando
Understanding the relationship between photosynthesis, net primary productivity and growth in forest ecosystems is key to understanding how these ecosystems will respond to global anthropogenic change, yet the linkages among these components are rarely explored in detail. We provide the first comprehensive description of the productivity, respiration and carbon allocation of contrasting lowland Amazonian forests spanning gradients in seasonal water deficit and soil fertility. Using the largest data set assembled to date, ten sites in three countries all studied with a standardized methodology, we find that (i) gross primary productivity (GPP) has a simple relationship with seasonal water deficit, but that (ii) site-to-site variations in GPP have little power in explaining site-to-site spatial variations in net primary productivity (NPP) or growth because of concomitant changes in carbon use efficiency (CUE), and conversely, the woody growth rate of a tropical forest is a very poor proxy for its productivity. Moreover, (iii) spatial patterns of biomass are much more driven by patterns of residence times (i.e. tree mortality rates) than by spatial variation in productivity or tree growth. Current theory and models of tropical forest carbon cycling under projected scenarios of global atmospheric change can benefit from advancing beyond a focus on GPP. By improving our understanding of poorly understood processes such as CUE, NPP allocation and biomass turnover times, we can provide more complete and mechanistic approaches to linking climate and tropical forest carbon cycling.
The productivity, allocation and cycling of carbon in forests at the dry margin of the Amazon forest in Bolivia
(Taylor & Francis, 2013) Alejandro Araujo‐Murakami; Christopher E. Doughty; Daniel B. Metcalfe; Javier E. Silva‐Espejo; Luzmila Arroyo; Juan P. Heredia; Marcio Flores; Rebeca Sibler; Luz M. Mendizabal; Erwin Pardo-Toledo
Background: The dry transitional forests of the southern Amazonia have received little attention from a carbon cycling and ecosystem function perspective, yet they represent ecosystems that may be impacted by global climate change in the future. Aims: To compare the full carbon cycle for two 1-ha forest plots that straddle the ecotone between humid forest and dry forest in Amazonia, ca. 100 km from Santa Cruz, Bolivia. Methods: 2.5 years of measurements of the components of net primary production (NPP) and autotrophic respiration were collected. Results: Total NPP was 15.5 +/- 0.89 Mg C ha(-1) year(-1) at the humid site and 11.27 +/- 0.68 Mg C ha(-1) year(-1) at the dry site; a total Gross Primary Production (GPP) of 34.14 +/- 2.92 Mg C ha(-1) year(-1) and 26.88 +/- 2.70 Mg C ha(-1) year(-1) at the two sites. Carbon use efficiency for both sites was higher than reported for other Amazonian forests (0.45 +/- 0.05 and 0.42 +/- 0.05). Conclusions: Drier soil conditions selected for the dry deciduous tree species which had higher leaf photosynthesis and total GPP. NPP allocation patterns were similar at the two sites, suggesting that in terms of carbon allocation, the dry forests of the southern Amazonia behave as a scaled-down version of wetter humid forests.
What controls variation in carbon use efficiency among Amazonian tropical forests?
(Wiley, 2017) Christopher E. Doughty; Gregory R. Goldsmith; Nicolas Raab; Cécile Girardin; Filio Farfan‐Amezquita; Walter Huaraca Huasco; Javier E. Silva‐Espejo; Alejandro Araujo‐Murakami; Antônio C. L. da Costa; Wanderley Rocha
Abstract Why do some forests produce biomass more efficiently than others? Variations in Carbon Use Efficiency ( CUE : total Net Primary Production ( NPP )/ Gross Primary Production ( GPP )) may be due to changes in wood residence time (Biomass/ NPP wood ), temperature, or soil nutrient status. We tested these hypotheses in 14, one ha plots across Amazonian and Andean forests where we measured most key components of net primary production ( NPP : wood, fine roots, and leaves) and autotrophic respiration (R a ; wood, rhizosphere, and leaf respiration). We found that lower fertility sites were less efficient at producing biomass and had higher rhizosphere respiration, indicating increased carbon allocation to belowground components. We then compared wood respiration to wood growth and rhizosphere respiration to fine root growth and found that forests with residence times <40 yrs had significantly lower maintenance respiration for both wood and fine roots than forests with residence times >40 yrs. A comparison of rhizosphere respiration to fine root growth showed that rhizosphere growth respiration was significantly greater at low fertility sites. Overall, we found that Amazonian forests produce biomass less efficiently in stands with residence times >40 yrs and in stands with lower fertility, but changes to long‐term mean annual temperatures do not impact CUE .