Sweden trees show early autumn colors due to drought

Trees in parts of Sweden have begun displaying autumn colors as early as mid-August, a phenomenon researchers attribute to drought stress rather than the change in season.

Henrik Sjöman, a researcher at SLU Alnarp and the Gothenburg Botanical Garden, explains that trees undergo this change to manage water loss. When soil is too dry, trees must shed leaves to prevent further dehydration. During this process, the tree reabsorbs nutrient-rich green chlorophyll, allowing other existing pigments to become visible.

Different species react at different rates; for example, birch trees tend to change color much faster than oak trees. While drought is considered a primary cause, forest researcher Ola Langvall of SLU notes that other factors, such as fungal infections or the natural lifespan of leaves following early spring budding, may also contribute to the early color shifts.