U. of Michigan notes study that shows old-growth trees more drought-tolerant than younger ones

A new study published in the journal Nature Climate Change has revealed that old-growth trees are more drought-tolerant than younger trees and can withstand future climate extremes more efficiently, the University of Michigan said in a news release. 

The study, which analyzed more than 20,000 trees on five continents, was conducted by a team of researchers from the University of Michigan, Indiana University, the University of Hong Kong, the University of Iowa, Guangzhou University, Shenyang Agricultural University, and Université de Picardie Jules Verne. 

The lead author of the study, Tsun Fung (Tom) Au, a postdoctoral fellow at the Institute for Global Change Biology, emphasized the findings underscore the importance of preserving the world's remaining old-growth forests. These forests are biodiversity strongholds that store large amounts of planet-warming carbon, he said.

“The number of old-growth forests on the planet is declining, while drought is predicted to be more frequent and more intense in the future,” Au said. “Given their high resistance to drought and their exceptional carbon storage capacity, conservation of older trees in the upper canopy should be the top priority from a climate mitigation perspective.” 

The researchers also found that younger trees in the upper canopy showed greater resilience if they managed to survive drought, defined as the ability to return to pre-drought growth rates. Younger trees, however, are more sensitive to drought and could have a severe impact on forests in the short term. 

The study's authors emphasized that the implications of their findings will require further study since reforestation has been identified as a potential nature-based solution to help mitigate climate change. 

The Sharm el-Sheikh Implementation Plan, published during the 2022 United Nations Climate Change Conference in Egypt (COP27), reaffirmed the importance of maintaining intact forest cover and associated carbon storage as a social and environmental safeguard.

The researchers used long-term tree-ring data from the International Tree-Ring Data Bank to analyze the growth response of 21,964 trees from 119 drought-sensitive species during and after droughts of the past century. They focused on trees in the uppermost canopy and separated them into three age groups, young, intermediate and old. 

The researchers examined how age influenced drought response for different species of hardwoods and conifers. In conclusion, managing forests for their ability to store carbon and be resilient to drought could be an important tool in responding to climate change, said senior author Justin Maxwell of Indiana University. 

The findings of the study, which represent the net effects of thousands of trees in diverse forests across five continents, are unusual in their focus on trees in the upper forest canopy and could have huge impacts on regional carbon storage and the global carbon budget.