Belgium's trees shed leaves early due to drought, mimicking autumn

Trees across Belgium are exhibiting premature autumn-like leaf drop due to ongoing drought stress, a phenomenon being closely monitored by ecophysiologists like Kathy Steppe from Ghent University.

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Trees may seem static, but internally they are very active and things are being arranged.

Steppe utilizes sensors through the Treewatch.net network and a dedicated experimental forest to listen to the "story" trees tell about the drought. "We see that conifers, like spruce and pine, are having a harder time with the heat than our deciduous trees," Steppe explained. This has led to significant damage in Christmas tree farms. However, the heat is also taking a toll on deciduous species, making them susceptible to drought.

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We see that conifers, like spruce and pine, are having a harder time with the heat than our deciduous trees.

"Trees may seem static, but internally they are very active and things are being arranged," Steppe stated. When drought stress sets in, several internal phenomena occur. The tree trunk shrinks as the tree uses its internal reserves, leading to dehydration. In response, the tree gradually closes its stomata, the small pores on the underside of leaves used for transpiration, as a protective measure.

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When the water potential, a measure of how well a tree can absorb and distribute water, becomes negative, air can enter the tree instead of water.

This process can lead to embolism, a hydraulic failure within the tree. "When the water potential, a measure of how well a tree can absorb and distribute water, becomes negative, air can enter the tree instead of water," Steppe described. "All the vessels through which water normally travels from the roots to the leaves fill with air, naturally preventing water from reaching the leaves." This embolism causes deciduous trees to drop their leaves, resembling autumn but differing significantly from the natural seasonal change. "Actually, it's a protective method by the trees: by dropping its leaves, the tree protects its other structures so that it can continue next year," she added.

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This embolism causes deciduous trees to drop their leaves. Actually, it's a protective method by the trees: by dropping its leaves, the tree protects its other structures so that it can continue next year.