It's autumn in Paris this August. In the streets of the capital, the trees have already shed their leaves, which now cover the Parisian sidewalks, signalling a premature change of season. It's all the more disconcerting for strollers who would have expected a completely different, greener landscape in the middle of summer.
The reason for this curious phenomenon? Successive heat waves. These have activated various defense mechanisms in the trees. On the one hand, the lack of water prevents the sap from circulating in the tree's vessels, and thus from reaching the leaves, which then die. On the other hand, drought slows down respiration. Since this means rejecting water vapour through the leaves, they dry out when the heat peaks, and fall in turn. This is how the streets of Paris become adorned with dead leaves.
This phenomenon can also have a more lasting impact on the health of trees: since leaves enable photosynthesis, their early fall makes them more vulnerable for the coming winter period, and some may not survive it.
