Tree-Ring Research in the Amazon

The articles in Geophysical Research Letters (Granato-Souza et al 2020) and Environmental Research Letters (Stahle et al 2020), and the six-minute video (“Amazon Climate and Tree Growth Connections across the Americas”), describe the decadal variability of tree-ring reconstructed rainfall in the Amazon and the correlation of climate and tree growth extremes across the Americas.

Key points:

1.  The frequency of drought and flood extremes have increased during the last 40-years in the Amazon watershed.  These changes constitute a major challenge to society because the cause of these recent extremes is not clear.  They might be due to deforestation, anthropogenic climate change, or natural climate variability. 

2.  Few instrumental measurements of rainfall in the Amazon Basin are longer than 70 years and that is too short to clearly define decadal to centennial scale climate variability. 

3.  Tree-ring chronologies from old Cedrela odorata trees are well correlated with wet season rainfall totals over the eastern Amazon and indicate strong 30- to 40-year fluctuations in reconstructed rainfall over the past 250-years, prior to widespread deforestation or strong human influence on global climate change.   

4.  Tree growth extremes in the Amazon River basin are also correlated with tree growth anomalies of opposite sign over large parts of North and South America during the past 250-years.  

5.  These Pan American tree growth patterns reflect similar interactions of precipitation between the tropics and extra-tropics that are driven primarily by the El Nino/Southern Oscillation.   

6.  Understanding the causes of these extremes and the decadal fluctuations in tree-ring reconstructed rainfall will be important to the sustainability of the Amazonian biome.   

click here to view Stahle et al. (2020) research article in Environmental Research Letters

click here to view Granato-Souza et al. (2020) research article in Geophysical Research Letters

Quotes:

“The new Cedrela chronologies from the Amazon, when compared with the hundreds of tree ring chronologies in temperate North and South America, document this Pan American resonance of climate and ecosystem extremes in the centuries before widespread deforestation or human caused climate change” 

“The long climate history written in the growth rings of old Cedrela trees in Amazonia will surely be important to the sustainability of the biome.” 

– David Stahle, Distinguished Professor, Department of Geosciences, University of Arkansas, Fayetteville