The Amazon rainforest may be able to survive long-term drought caused by climate change but could experience “profound changes” including the death of large trees and a diminished ability to absorb carbon, researchers have warned.
A study by the University of Edinburgh and the Universidade Federal do Para in Brazil suggests adjusting to a drier, warmer climate will have major consequences for the tropical rainforest which spans more than two million square miles.
Findings from the study – which was the longest-running on the impact of drought on tropical rainforest – suggest the Amazon could experience “excess tree deaths” and “vast” carbon release, also reducing its immediate capacity to act as a carbon sink for human activity.
Parts of the Amazon are expected to become drier and warmer, but the long-term effects are poorly understood and previous research suggested climate change and deforestation could lead to a sparser forest or savanna.
An area of rainforest in north-eastern Amazonian Brazil, roughly the size of Trafalgar Square, was subjected to drought conditions for 22 years in an experiment, with more than a third loss of biomass recorded.
The experiment began in 2002 with thousands of transparent panels installed above the ground to redirect roughly half of the rainfall to a system of gutters, taking it away from the trees in the one-hectare region.
Analysis by the researchers showed most of the largest trees in the study area died during the first 15 years, and the forest stabilised.
For seven years after the large initial biomass losses, the availability of water increased for the surviving trees, research showed, and tests on these trees found they were no more drought-stressed than neighbouring trees not subjected to drought.
Overall, the area lost more than a third of biomass – tree trunks, branches, stems and roots where carbon is stored in vegetation.
Excess tree deaths during the first 15 years of the study caused carbon loss, but surviving trees in the area are now making slight carbon gains, according to a report published in the journal Nature Ecology and Evolution.
The study region has less woody biomass than typical Amazon rainforests but more than many dry forests and savannas – suggesting the rainforest has some long-term resilience to drier conditions but at a high cost, scientists said.
The biomass the Amazon could lose and the time required to stabilise may be underestimated, as the study only assessed the effects of soil drought, while further research is needed to assess changes to moisture in the air, temperature and storms or fires, according to researchers.
The study was led by professors Patrick Meir of the University of Edinburgh and Antonio Carlos Lola Da Costa of the Universidade Federal do Para and the Museu Paraense Emilio Goeldi, Brazil.
It also involved researchers from the universities of Exeter and Cardiff, and Creaf in Spain, and was supported by the Natural Environment Research Council, the Royal Society and the UK Met Office Newton Fund.
Dr Pablo Sanchez Martinez, of the University of Edinburgh’s School of GeoSciences, said: “Our findings suggest that while some rainforests may be able to survive prolonged droughts brought on by climate change, their capacity to act as both a vital carbon store and carbon sink could be greatly diminished.”
Prof Meir added: “Ecological responses to climate can have very large impacts on our environment, locally and globally.
“We cannot understand and predict them without long-term collaborative research of this sort.”
