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Why do some leaves live longer than others?

Tree leaves have highly different lifespans. For instance, monkey puzzle tree leaves can live for over two decades, and Picea growing in the Chinese Gongga Mountains can thrive for thousands of years, growing in harsh environments with leaves that last about 20 years. On the other hand, maple leaves last only a season, and blueberry leaves may survive for just three months. 

According to a recent study published in the journal Science Advances, these major differences are driven by the “economic” choices faced by different trees.

“We already knew that conifers and other evergreen trees make longer-living leaves the closer they are to the poles,” said study lead author Han Wang, an expert in Plant Ecology at the Tsinghua University in Beijing. “Deciduous trees do the opposite. Their longest lasting leaves are found at the tropics.”

“And we knew that long-lived leaves tend to be tougher and thicker, and more expensive to build. Now, we have identified the major environmental factors at play, and summarized them in two equations. These leaf economic traits are fundamental to the carbon cycle and nutrient economy.”

The scientists tested their equations on data about thousands of tree species from hundreds of ecosystems worldwide. “Each species is essentially taking a punt on the best way to maximize carbon absorption,” said study co-author Ian Wright, a plant ecologist at the Macquarie University in Australia.

“Evergreen conifers growing in poor soil in areas with a long cold winter can only thrive if they make long term investments in their leaves. Whereas deciduous trees, like the maple, race to create new leaves and capture carbon in the summer sun before leaf-drop in autumn. The economically rational decision for a maple tree is to invest in fast growing, cheap but flimsy leaves.”

These findings have the potential of turning Ecology into a predictive science that will enable the construction of better, more accurate global and regional climate models, while allowing land managers to better model forests and other types of vegetation in order to predict how climate change will affect a variety of ecosystems, and farmers to better estimate crop yields and the impact of climate change on agriculture.

By Andrei Ionescu, Staff Writer

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