An international study has found tropical trees have remained minimally affected by droughts but an increase in climate change events is likely to have long-term effects on stem growth resilience.
Emeritus Professor Patrick Finnegan, from The University of Western Australia's School of Biological Sciences, was a co-author of the study led by Wageningen University & Research and published in Science.
"Carbon dioxide, taken from the atmosphere through photosynthesis, is stored in tree trunks for many decades," Professor Finnegan said.
"This long-term carbon sequestration can help mitigate climate change however, stem growth usually slows down during periods of drought, causing less carbon dioxide to be stored."
The study used tropical tree-ring data collected from more than 20,000 tree-ring series from nearly 500 locations in 36 countries – from wet and warm Amazonian forests to dry forests in southern Africa and cooler Asian mountain forests.
Researchers determined the driest years since 1930 for all locations and then calculated how much narrower the tree rings were during those years compared to normal years. They also measured the width of tree rings in the two years following a drought.
Lead researcher Professor Pieter Zuidema, from Wageningen University & Research, said the findings showed on average across the tropics, trees grew 2.5 per cent less during drought years compared to years with normal or above-average rain.
"The growth dip largely disappeared in the year following the drought, but drought effects are increasing as climate change progresses and has likely already caused more trees to die," Professor Zuidema said
The effects of droughts differed significantly between the research areas, however stem growth slowed down a lot more than the global average (by over 10 per cent) mainly in the hotter and drier locations.
Researchers combined data from long-term forest monitoring studies for each dry year and found drought may cause an 0.1 per cent increase in tree mortality, which resulted in extra carbon dioxide emissions from rotting dead wood.
"This may seem like an insignificant amount, but if you take into account all the world's tropical areas it equates to roughly as much extra carbon dioxide being released into the atmosphere as Germany's annual emissions," Professor Zuidema said.
"It would take decades before that amount will be taken up again through tree growth."
