What happens to the leaves in autumn: the intelligent strategy of trees
The change in leaf color during autumn is not an accident but a perfectly programmed process by plants. When you walk through the Marimurtra Botanical Garden these days, you can witness this fascinating natural phenomenon.
But why does it happen exactly?
The key trigger is light. As the days get shorter, the plant detects that the hours of sunlight are no longer sufficient to maintain photosynthesis —the process that turns light into energy— efficiently. It’s time to stop the machinery of the leaf and prepare for winter.
Priority: recycle
The first thing the tree does is not to change color, but to “move out”. Before shedding its leaves, the plant begins an active process to recover the most valuable nutrients they contain, especially nitrogen and other essential elements. These compounds are transported to the branches and roots, where they are stored as reserves. This is the crucial investment that allows deciduous plants to have the energy they need to sprout vigorously in spring.
The great “unmasking”
Only after this recycling process begins does the visual change start. Chlorophyll, the pigment that gives the green color and is vital for photosynthesis, is a molecule that degrades quickly without light. Since the tree no longer needs to photosynthesize, it stops producing it. When the dominant green disappears, something fascinating happens: other pigments that were always present in the leaf but hidden by chlorophyll are revealed. Carotenoids emerge, responsible for the spectacular yellow and orange tones we see in many trees in the Garden. In other species, cold and light stimulate the production of anthocyanins, which create the intense reds and purples.
Therefore, autumn doesn’t “paint” the leaves but rather “unpaints” the green, revealing the colors that were hidden underneath.
What happens if there’s drought?
This orderly color transition, however, requires time and optimal conditions. Yet drought —a frequent reality in our Mediterranean climate— changes everything.
If the tree has suffered stress due to lack of water, it cannot afford this slow recycling process. It switches to emergency mode and must “cut off” the connection with the leaf quickly to prevent further water loss. In this case, the leaf dries suddenly, with all its nutrients and pigments still inside, going directly from green to brown. It’s an abrupt senescence, a necrosis, that deprives us of the chromatic variety.
So, when you walk through Marimurtra and enjoy an explosion of yellows and reds, you’re not just seeing a beautiful landscape; you’re witnessing the evidence of a successfully executed natural cycle: an orderly, efficient, and ingenious retreat.
