The ongoing drought is weakening trees and could cause branches to fall, Brussels Environment said on Thursday, warning the public to be “very careful in parks, under trees, but also in forests and along the sides of streets, especially in parking areas.” The drought, particularly in Brussels, increases the risk of branches falling despite being healthy, something seen regularly in recent days in city as well as in the forest. Plane trees have also been losing their bark.
When exposed to the summer sun, adult trees in the region lose 1,000 to 3,000 litres of moisture per day. This causes raw sap to move up to the leaves and cool them so that they do not burn, which is what happens when the tree can no longer hydrate itself for a prolonged period.
When the sun is intense, branches sometimes fall, irrespective of their size or the tree’s state of health, due to the formation of tiny gas bubbles when the tree’s transpiration rate is high. “If the bubbles become larger and fill the canals taking water to the leaves, the circulation of the sap can be interrupted,” the Brussels environment and energy administration explained. This embolism can cause the branch to break, it added.
According to the administration, the phenomenon is hard to foresee, and research is being conducted to understand how the tree protects itself against it. “In the meantime, teams from the Green Spaces Division, with the help of the phytosanitary cell, are carrying out a daily monitoring of our green spaces, which represent a total of 40,000 trees in more than 80 sites,” Brussels Environment stressed.
It said it was doing everything possible to ensure the safety of passers-by.