Climate change and the Amazon: assessing the impact of climate on tree growth using tree ring widths and isotopes

Lead Research Organisation: University of Leeds
Department Name: Sch of Geography

Abstract

The Amazon rainforest may be very vulnerable to climate change. If the earth warms as predicted, much of the Amazon rainforest could disappear by the end of the century, as tropical trees should be unable to cope with higher temperatures and frequent droughts in the future. Such a 'die-back' of the Amazon rainforest could be disastrous for global warming, as the vast stores of carbon contained in the Amazon would be emitted back into the atmosphere as greenhouse gases. This will speed-up global warming. Such a scenario is predicted by computer models that simulate responses of vegetation to climate. However, it is still very uncertain how sensitive rainforest trees are to changes in climate like increasing atmospheric CO2 concentrations, higher temperatures, and droughts. One way of getting insights into how trees will respond to future climate is by looking at how trees have responded to similar conditions in the past. An effective approach of doing this is by using tree rings, as they provide an historical archive of growth rates over their entire life (i.e., 200 years or more), which can be related to the climate conditions at the time of ring-formation. Therefore, I propose to use tree rings of tropical trees to assess how sensitive trees have been to changes in temperature, drought, solar radiation, and increases in atmospheric CO2-concentrations over the last century. I will measure ring widths and stable isotope concentrations in tree rings to analyse the responses of tree growth to climatic and atmospheric changes. Ring width measurements will give insight in growth responses, and carbon isotopes will help understand the underlying processes behind any growth responses by giving detailed information on photosynthesis and plant water use. For example, by studying long-term trends in growth rates and plant water use, I will be able to test whether increases in CO2 concentrations over the past century have indeed stimulated tropical tree growth, as has often been proposed. By linking year to year variation in growth rates to variation in droughts, temperature and solar radiation, I will determine the main climatic factors controlling tropical tree growth. My study will improve our understanding of sensitivity of tropical trees to predicted changes in climate and increasing atmospheric CO2 and allow a better assessment of the likelihood of the predicted disappearance of the Amazon rainforest over the next century.

Publications

10 25 50
 
Description I discovered that oxygen isotope ratios in tree rings from the Amazon can be used as a proxy (indicator) for the intensity of Amazon precipitation during the wet season. This new technique provides an important means to study the hydrological cycle of the Amazon in the past, which will improve our understanding of recent changes observed in the hydrological cycle. Some important questions that can be addressed using this technique are for example, to which degree recent change in the Amazon hydrology are unprecedented and likely due to global warming, or whether observed recent changes are part of natural cycles of the Amazon climate.
Another key finding of my research is that reconstructions in trends in plant water use efficiency using carbon isotope ratios in tree rings may be severely affected by changes in trees' water use efficiency during height growth. Many studies have attributed observed trends in tree rings to increases in atmospheric CO2 but these results show that failing to correct for developmental changes severely affects such trends. My findings show that trees probably have a rather modest response to increases in atmospheric CO2 leading to more efficient CO2 assimilation or reduced water losses.
Finally, I found why some recent studies on tropical tree growth -using tree rings- lack the expected growth increase. Using model simulations I demonstrated that the studies are biased due to the sampling design and correction for these biases, results actually in growth increases as expected. However, various sampling biases associated with tree ring analysis mean that interpretation of tree ring trends remains difficult.
Exploitation Route Response of tropical trees to atmospheric CO2 are relevant to climate modelling significantly influencing predictions for future CO2 levels.
Understanding to which degree recent events in the Amazon basin are part of a natural cycle or man-made will help preparing policy makers for the future.
Sectors Agriculture, Food and Drink,Environment

 
Description The outcome of my studies provide an approach to obtain more insights in the interactive effects of climate, CO2 and vegetation of the Amazon basin. These results are important to assess the contribution of man-made climate change to recent extremes (droughts and flooding) in the amazon. Climate extremes directly affect the people living in the Amazon, but also economically affect countries in south America as changes in rainfall affect agriculture and hydroelectric power generation. At a global scale it is important to know how the climate and forests in the amazon basin will be evolving under a warming climate as the basin is main driver for global climate, yearly transpiring large amounts of water and fixing large quantities of atmospheric CO2. My studies show that trees may respond to increase in CO2 by increasing the efficiency of water use. This may translate in either a reduction of transpiration rates or more efficient photosynthesis (or both) Yet these aspects of tree physiology are poorly understood and require careful evaluations in order to understand and predict forest responses in a higher CO2 world.
First Year Of Impact 2012
Sector Agriculture, Food and Drink,Environment
Impact Types Societal

 
Description IP_ 1314_0512 Is the hydrological cycle of the Amazon changing? An isotopic tree ring study.
Amount £26,700 (GBP)
Funding ID IP_ 1314_0512 
Organisation Research Councils UK (RCUK) 
Sector Public
Country United Kingdom
Start  
 
Description IP_ 1314_0512 Is the hydrological cycle of the Amazon changing? An isotopic tree ring study.
Amount £26,700 (GBP)
Funding ID IP_ 1314_0512 
Organisation Research Councils UK (RCUK) 
Sector Public
Country United Kingdom
Start  
 
Description The Amazon hydrological cycle: past, present and future
Amount £664,000 (GBP)
Funding ID NE/K01353X/1 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 01/2014 
 
Title Height-diameter input data and R-code to fit and assess height-diameter models, from 'Field methods for sampling tree height for tropical forest biomass estimation' in Methods in Ecology and Evolution 
Description 1. Quantifying the relationship between tree diameter and height is a key component of efforts to estimate biomass and carbon stocks in tropical forests. Although substantial site-to-site variation in height-diameter allometries has been documented, the time consuming nature of measuring all tree heights in an inventory plot means that most studies do not include height, or else use generic pan-tropical or regional allometric equations to estimate height. 2. Using a pan-tropical dataset of 73 plots where at least 150 trees had in-field ground-based height measurements, we examined how the number of trees sampled affects the performance of locally-derived height-diameter allometries, and evaluated the performance of different methods for sampling trees for height measurement. 3. Using cross-validation, we found that allometries constructed with just 20 locally measured values could often predict tree height with lower error than regional or climate-based allometries (mean reduction in prediction error = 0.46 m). The predictive performance of locally-derived allometries improved with sample size, but with diminishing returns in performance gains when more than 40 trees were sampled. Estimates of stand-level biomass produced using local allometries to estimate tree height show no over- or under-estimation bias when compared with estimates using measured heights. We evaluated five strategies to sample trees for height measurement, and found that sampling strategies that included measuring the heights of the ten largest diameter trees in a plot outperformed (in terms of resulting in local height-diameter models with low height prediction error) entirely random or diameter size-class stratified approaches. 4. Our results indicate that even remarkably limited sampling of heights can be used to refine height-diameter allometries. We recommend aiming for a conservative threshold of sampling 50 trees per location for height measurement, and including the ten trees with the largest diameter in this sample. 
Type Of Material Database/Collection of data 
Year Produced 2018 
Provided To Others? Yes  
 
Description Collaboration with GFZ Potsdam 
Organisation Helmholtz Association of German Research Centres
Department German Research Centre for Geosciences
Country Germany 
Sector Private 
PI Contribution Delivering samples for analysis, doing analysis in Potsdam, and scientific discussions
Collaborator Contribution Sample analysis, training of graduate and postgraduate students.
Impact publications and data.
Start Year 2007
 
Description Collaboration with INPA, Brazil, Manaus 
Organisation National Institute of Amazonian Research
Country Brazil 
Sector Public 
PI Contribution JOint fieldwork and research program on floodplain trees in the Amazon, application for grants and phd studentships, and paper writing and publishing.
Collaborator Contribution facilitation research program in Brazil.
Impact - publications - research material
Start Year 2011
 
Description Collaboration with University of Leicester 
Organisation University of Leicester
Country United Kingdom 
Sector Academic/University 
PI Contribution Delivering samples for isotope analysis, and scientific interpretation of results
Collaborator Contribution Isotope analysis for research.
Impact Insights into carbon isotope discrimination of tropical trees. Yet to be fully published.
Start Year 2010
 
Description Keynote talk during TRACE meeting (Tree-rings in Archaeology, Climatology and Ecology, 2019) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact I gave keynote talk to large audience at the TRACE 2019 meeting, on Tree-rings in Archaeology, Climatology and Ecology.
Title of talk : Tree ring in the tropics
Year(s) Of Engagement Activity 2019
URL http://pastglobalchanges.org/calendar/2019/127-pages/1906-trace19
 
Description Media interest Oxygen isotope study 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact There was large media interest from the publication of my tree ring isotope study in PNAS which resulted in media contacting me for more information

International media reporting on isotope study, including BBC, BBC mundo (in spanish), NERC planet earth, science daily, epoch time, red orbit and various more.
Year(s) Of Engagement Activity 2012
URL http://www.bbc.co.uk/news/science-environment-19788671
 
Description Oral presentation in Ecuador 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Schools
Results and Impact Oral presentations in Ecuador at the universities in Quito and Puyo, on tree ring studies in the Amazon

Students were enthused by the talk and two student research placement followed.
Year(s) Of Engagement Activity 2013
 
Description Oral presentation in Suriname 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Oral presentation on work on tree ring in the Amazon during field visit to Suriname

Interest from a wide local audience in Suriname.
Year(s) Of Engagement Activity 2013
 
Description Organisation of tree ring workshop, Pantanal 2013 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact This 4 day workshop was very well perceived by the participating students and led to increased knowledge and interest in tree rings in the tropics.


the impact is increased research efforts on this subject throughout south america and established collaboration which resulted in a joint phd with Brazil
Year(s) Of Engagement Activity 2012
 
Description Presentation at KNAW Colloqium. Amsterdam, the Netherlands, 16-18 september 2012 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact I was invited to present two of my studies on oxygen and carbon isotopes in tropical tree rings during the Academy Colloquium in Amsterdam (16-18 september 2012) titled, "Stomatal conductance through time: towards accurate estimates of physiological CO2 -forcing of the climate".
My results contributed to peers thinking on this topic.

The talks and participation in this symposium led to very relevant contacts with peers.
Year(s) Of Engagement Activity 2012