Ecological responses to El Niño–induced surface fires in central Brazilian Amazonia: management implications for flammable tropical forests

Over the past 20 years the combined effects of El Niño–induced droughts and land–use change have dramatically increased the frequency of fire in humid tropical forests. Despite the potential for rapid ecosystem alteration and the current prevalence of wildfire disturbance, the consequences of such fires for tropical forest biodiversity remain poorly understood. We provide a pan–tropical review of the current state of knowledge of these fires, and include data from a study in a seasonally dry terra firme forest of central Brazilian Amazonia. Overall, this study supports predictions that rates of tree mortality and changes in forest structure are strongly linked to burn severity. The potential consequences for biomass loss and carbon emissions are explored. Despite the paucity of data on faunal responses to tropical forest fires, some trends are becoming apparent; for example, large canopy frugivores and understorey insectivorous birds appear to be highly sensitive to changes in forest structure and composition during the first 3 years after fires. Finally, we appraise the management implications of fires and evaluate the viability of techniques and legislation that can be used to reduce forest flammability, prevent anthropogenic ignition sources from coming into contact with flammable forests and aid the post–fire recovery process.

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Inter-comparison and assessment of gridded climate products over tropical forests during the 2015/2016 El Niño

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2017.0406 ◽

2018 ◽

Vol 373 (1760) ◽

pp. 20170406 ◽

Cited By ~ 6

Author(s):

C. Burton ◽

S. Rifai ◽

Y. Malhi

Keyword(s):

Southeast Asia ◽

Tropical Forest ◽

Tropical Forests ◽

Air Temperature ◽

El Niño ◽

El Nino ◽

Congo Basin ◽

Wide Range ◽

Spatio Temporal ◽

The Impact

To understand the impacts of extreme climate events, it is first necessary to understand the spatio-temporal characteristics of the event. Gridded climate products are frequently used to describe climate patterns but have been shown to perform poorly over data-sparse regions such as tropical forests. Often, they are uncritically employed in a wide range of studies linking tropical forest processes to large-scale climate variability. Here, we conduct an inter-comparison and assessment of near-surface air temperature fields supplied by four state-of-the-art reanalysis products, along with precipitation estimates supplied by four merged satellite-gauge rainfall products. Firstly, spatio-temporal patterns of temperature and precipitation anomalies during the 2015–2016 El Niño are shown for each product to characterize the impact of the El Niño on the tropical forest biomes of Equatorial Africa, Southeast Asia and South America. Using meteorological station data, a two-stage assessment is then conducted to determine which products most reliably model tropical climates during the 2015–2016 El Niño, and which perform best over the longer-term satellite observation period (1980–2016). Results suggest that eastern Amazonia, parts of the Congo Basin and mainland Southeast Asia all experienced significant monthly mean temperature anomalies during the El Niño, while northeastern Amazonia, eastern Borneo and southern New Guinea experienced significant precipitation deficits. Our results suggest ERA-Interim and MERRA2 are the most reliable air temperature datasets, while TRMM 3B42 V7 and CHIRPS v2.0 are the best-performing rainfall datasets. This article is part of a discussion meeting issue ‘The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications’.

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Resistance of African tropical forests to an extreme climate anomaly

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2003169118 ◽

2021 ◽

Vol 118 (21) ◽

pp. e2003169118

Author(s):

Amy C. Bennett ◽

Greta C. Dargie ◽

Aida Cuni-Sanchez ◽

John Tshibamba Mukendi ◽

Wannes Hubau ◽

...

Keyword(s):

Tropical Forests ◽

El Niño ◽

Tree Mortality ◽

El Nino ◽

Southern Oscillation ◽

Carbon Sink ◽

El Niño Event ◽

Dry Conditions ◽

Carbon Losses

The responses of tropical forests to environmental change are critical uncertainties in predicting the future impacts of climate change. The positive phase of the 2015–2016 El Niño Southern Oscillation resulted in unprecedented heat and low precipitation in the tropics with substantial impacts on the global carbon cycle. The role of African tropical forests is uncertain as their responses to short-term drought and temperature anomalies have yet to be determined using on-the-ground measurements. African tropical forests may be particularly sensitive because they exist in relatively dry conditions compared with Amazonian or Asian forests, or they may be more resistant because of an abundance of drought-adapted species. Here, we report responses of structurally intact old-growth lowland tropical forests inventoried within the African Tropical Rainforest Observatory Network (AfriTRON). We use 100 long-term inventory plots from six countries each measured at least twice prior to and once following the 2015–2016 El Niño event. These plots experienced the highest temperatures and driest conditions on record. The record temperature did not significantly reduce carbon gains from tree growth or significantly increase carbon losses from tree mortality, but the record drought did significantly decrease net carbon uptake. Overall, the long-term biomass increase of these forests was reduced due to the El Niño event, but these plots remained a live biomass carbon sink (0.51 ± 0.40 Mg C ha−1 y−1) despite extreme environmental conditions. Our analyses, while limited to African tropical forests, suggest they may be more resistant to climatic extremes than Amazonian and Asian forests.

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Short-term effects of drought on tropical forest do not fully predict impacts of repeated or long-term drought: gas exchange versus growth

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2017.0311 ◽

2018 ◽

Vol 373 (1760) ◽

pp. 20170311 ◽

Cited By ~ 12

Author(s):

Patrick Meir ◽

Maurizio Mencuccini ◽

Oliver Binks ◽

Antonio Lola da Costa ◽

Leandro Ferreira ◽

...

Keyword(s):

Tropical Forest ◽

El Niño ◽

Tree Mortality ◽

El Nino ◽

Short Term ◽

Sapwood Area ◽

Plant Hydraulics ◽

Trade Offs ◽

The Impact

Are short-term responses by tropical rainforest to drought (e.g. during El Niño) sufficient to predict changes over the long-term, or from repeated drought? Using the world's only long-term (16-year) drought experiment in tropical forest we examine predictability from short-term measurements (1–2 years). Transpiration was maximized in droughted forest: it consumed all available throughfall throughout the 16 years of study. Leaf photosynthetic capacity was maintained, but only when averaged across tree size groups. Annual transpiration in droughted forest was less than in control, with initial reductions (at high biomass) imposed by foliar stomatal control. Tree mortality increased after year three, leading to an overall biomass loss of 40%; over the long-term, the main constraint on transpiration was thus imposed by the associated reduction in sapwood area. Altered tree mortality risk may prove predictable from soil and plant hydraulics, but additional monitoring is needed to test whether future biomass will stabilize or collapse. Allocation of assimilate differed over time: stem growth and reproductive output declined in the short-term, but following mortality-related changes in resource availability, both showed long-term resilience, with partial or full recovery. Understanding and simulation of these phenomena and related trade-offs in allocation will advance more effectively through greater use of optimization and probabilistic modelling approaches. This article is part of a discussion meeting issue ‘The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications’.

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ENSO Drives interannual variation of forest woody growth across the tropics

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2017.0410 ◽

2018 ◽

Vol 373 (1760) ◽

pp. 20170410 ◽

Cited By ~ 13

Author(s):

Sami W. Rifai ◽

Cécile A. J. Girardin ◽

Erika Berenguer ◽

Jhon del Aguila-Pasquel ◽

Cecilia A. L. Dahlsjö ◽

...

Keyword(s):

Tropical Forest ◽

Water Deficit ◽

Tropical Forests ◽

El Niño ◽

Vapour Pressure ◽

El Nino ◽

Vapour Pressure Deficit ◽

Shortwave Radiation ◽

Soil Water Deficit ◽

Woody Growth

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 (NPP stem ) 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’.

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Effects of El Niño drought on tree mortality and growth across forest types at different elevations in Borneo

Forest Ecology and Management ◽

10.1016/j.foreco.2021.119096 ◽

2021 ◽

Vol 490 ◽

pp. 119096

Author(s):

Kazuki Miyamoto ◽

Shin-ichiro Aiba ◽

Ryota Aoyagi ◽

Reuben Nilus

Keyword(s):

El Niño ◽

Tree Mortality ◽

El Nino ◽

Forest Types

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Global warming in Amazonia: impacts and Mitigation

Acta Amazonica ◽

10.1590/s0044-59672009000400030 ◽

2009 ◽

Vol 39 (4) ◽

pp. 1003-1011 ◽

Cited By ~ 11

Author(s):

Philip Martin Fearnside

Keyword(s):

Climate Change ◽

Global Warming ◽

Forest Fires ◽

El Niño ◽

El Nino ◽

Cost Effective ◽

Climatic Conditions ◽

Carbon Accounting ◽

Amazon Forest ◽

Temperature Oscillations

Global warming has potentially catastrophic impacts in Amazonia, while at the same time maintenance of the Amazon forest offers one of the most valuable and cost-effective options for mitigating climate change. We know that the El Niño phenomenon, caused by temperature oscillations of surface water in the Pacific, has serious impacts in Amazonia, causing droughts and forest fires (as in 1997-1998). Temperature oscillations in the Atlantic also provoke severe droughts (as in 2005). We also know that Amazonian trees die both from fires and from water stress under hot, dry conditions. In addition, water recycled through the forest provides rainfall that maintains climatic conditions appropriate for tropical forest, especially in the dry season. What we need to know quickly, through intensified research, includes progress in representing El Niño and the Atlantic oscillations in climatic models, representation of biotic feedbacks in models used for decision-making about global warming, and narrowing the range of estimating climate sensitivity to reduce uncertainty about the probability of very severe impacts. Items that need to be negotiated include the definition of "dangerous" climate change, with the corresponding maximum levels of greenhouse gases in the atmosphere. Mitigation of global warming must include maintaining the Amazon forest, which has benefits for combating global warming from two separate roles: cutting the flow the emissions of carbon each year from the rapid pace of deforestation, and avoiding emission of the stock of carbon in the remaining forest that can be released by various ways, including climate change itself. Barriers to rewarding forest maintenance include the need for financial rewards for both of these roles. Other needs are for continued reduction of uncertainty regarding emissions and deforestation processes, as well as agreement on the basis of carbon accounting. As one of the countries most subject to impacts of climate change, Brazil must assume the leadership in fighting global warming.

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Modelling tropical forest responses to drought and El Niño with a stomatal optimization model based on xylem hydraulics

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2017.0315 ◽

2018 ◽

Vol 373 (1760) ◽

pp. 20170315 ◽

Cited By ~ 34

Author(s):

Cleiton B. Eller ◽

Lucy Rowland ◽

Rafael S. Oliveira ◽

Paulo R. L. Bittencourt ◽

Fernanda V. Barros ◽

...

Keyword(s):

Tropical Forest ◽

El Niño ◽

Optimization Model ◽

El Nino ◽

Soil Drought ◽

Forest Sites ◽

Dynamic Global Vegetation Models ◽

Vegetation Models ◽

Global Vegetation

The current generation of dynamic global vegetation models (DGVMs) lacks a mechanistic representation of vegetation responses to soil drought, impairing their ability to accurately predict Earth system responses to future climate scenarios and climatic anomalies, such as El Niño events. We propose a simple numerical approach to model plant responses to drought coupling stomatal optimality theory and plant hydraulics that can be used in dynamic global vegetation models (DGVMs). The model is validated against stand-scale forest transpiration ( E ) observations from a long-term soil drought experiment and used to predict the response of three Amazonian forest sites to climatic anomalies during the twentieth century. We show that our stomatal optimization model produces realistic stomatal responses to environmental conditions and can accurately simulate how tropical forest E responds to seasonal, and even long-term soil drought. Our model predicts a stronger cumulative effect of climatic anomalies in Amazon forest sites exposed to soil drought during El Niño years than can be captured by alternative empirical drought representation schemes. The contrasting responses between our model and empirical drought factors highlight the utility of hydraulically-based stomatal optimization models to represent vegetation responses to drought and climatic anomalies in DGVMs. This article is part of a discussion meeting issue ‘The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications’.

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