According to a recent analysis of over 20,000 trees across five continents, older trees in the forest canopy are more tolerant of drought than younger ones and could be more resilient to future climate extremes.
According to Au, the study's lead author, the world's old-growth forests are disappearing.
Canopy Capabilities
From a climate mitigation perspective, preserving older trees in the upper canopy should be the top priority due to their exceptional capacity for carbon storage and high resistance to drought.
The researchers also discovered that younger trees in the upper canopy demonstrated greater resilience, which is defined as the capacity to resume pre-drought growth rates if they can survive drought.
While selective logging, deforestation, and other threats have caused old-growth forests to disappear globally. Following reforestation, either through natural succession or tree planting, forests have become more and more predominated by younger trees.
Younger trees are anticipated to become more crucial to ecosystem health and carbon sequestration as forest demographics change over time.
Tolerant vs. Resilient
They discovered that while younger upper canopy trees are more drought resilient, older upper canopy trees are more drought tolerant.
These results suggest that drought's impact on forests in the short term may be severe due to the high number of younger trees and their increased susceptibility to drought, which has significant implications for future carbon storage in forests.
But over time, those younger trees have a better capacity to bounce back from drought, which might be advantageous for the carbon stock.
Implications of Climate Change
Au and colleagues state that given that the Intergovernmental Panel on Climate Change has identified reforestation as a potential nature-based strategy to assist in climate change mitigation, those implications will need further research.
The importance of maintaining an intact forest cover and the carbon storage it provides as a social and environmental safeguard was also reaffirmed in the Sharm el-Sheikh Implementation Plan, which was released during the COP27 United Nations Climate Change Conference in Egypt in 2022.
Justin Maxwell from Indiana University said that these discoveries have implications for forest management practices. In the past, people have managed forests to encourage tree species that produce the highest-quality wood.
The results imply that managing forests for their capacity to store carbon and be drought-resistant could be a key tactic in combating climate change and that taking into account the age of the forest is a crucial factor in how the forest will react to drought.
Read also: Spread of Drought-Resistant Trees on Grasslands a Big Problem, Here's Why
Uppermost Canopy, Drought Responses
To study the growth response of exactly 21,964 trees from 119 drought-sensitive species during and after droughts in the previous century, the researchers applied long-term tree-ring data from the International Tree-Ring Data Bank, Science Daily reports.
They concentrated on the tallest canopy of trees.
Conifers in the study had smaller age-related drought-response differences than hardwoods, which the researchers attribute to the fact that needle-bearing trees typically live in more arid climates.
Instead of concentrating on a single forest type, the new study is a synthesis that represents the overall effects of thousands of trees in diverse forests across five continents.
According to the authors, another distinctive feature of the new study is its emphasis on trees in the upper forest canopy, which lessens the confounding effects of tree height and size, PhysOrg reports.
The study led by Au, where Maxwell is a senior author, was published in the journal Nature Climate Change.
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