Why Do Some Deciduous Trees Keep Their Leaves In Winter?
This time of year, in late winter, the sky is often gray, and the skyline is a stark outline of bare trees – except for a few odd ones that manage every year to keep their leaves long after raking and bagging season is over. Have you ever wondered why oak trees, American beeches, and a handful of other trees hold on to their leaves?
Itâ€™s called marcescence, from the Latin marcescent-, meaning to wither or shrivel, which is appropriate given that the leaves are dead, they are just not gone. Other deciduous trees when temperatures dive and sunlight grows scarce, reabsorb their chlorophyll as a part of their self-preservation process. This causes them to turn color dramatically. The cells that exist between the twig and the leaf stem then release enzymes and form an abscission layer causing the leaf to â€œunglueâ€ itself and fall off.
Sometimes when trees are â€œsurprisedâ€ by early frosts or unseasonably cold weather, there will be leaf die off, but these leaves will not fall. They remain on the tree until they are forced off by pressure from wind or snow – or until the lengthening days and warmer temperatures of spring communicate to the tree that it is time for a new growth cycle. Then expanding buds will pry off the old leaves and new ones will appear.
Scientists speculate on why some trees exhibit marcescence. One theory is that the presence of dead leaves deters herbivores like deer from feasting too much on marcescent trees. The leaves and twigs of marcescent trees are both less nutritious and less tasty – and therefore safer from predation.
Another type of speculation is related to the survival of the tree itself. Marcescent trees are often smaller trees, which in nature would be part of a forestâ€™s undercanopy. These trees would have access to less light and be less sensitive to environmental changes in the fall, but as the leaves on the larger trees surrounding them fall, they might get a final boost of light, aiding in their growth. Or perhaps the leaves hang on because itâ€™s a way for these trees to ensure a second round of mulch – and therefore a renewed supply of nutrients and protective layering. Itâ€™s difficult to say exactly why this phenomenon occurs, but it does, and marcescent trees benefit from it.
For homeowners with marcescent trees, it may be a bit of a hassle to rake another round of leaves come spring, so when youâ€™re doing it think of how these trees have adapted and changed in order to survive the same long winter we all must. If that doesnâ€™t help, remind yourself that many animals shelter from the wind and cold behind these leaves, and perhaps that will.
If you need advice on how to best care for any of your trees, do not hesitate to contact an expert at Chop. That is the area of our expertise.