Nutrients are drawn from tree leaves to be used next spring, before the leaves are dropped.
Summer is long gone and fall is upon us. The insects are dying off, and a very few flowering plants are making one last effort at reproduction. Trees are also preparing for the cold months ahead.
Daylight becomes so scarce and temperatures so cold that trees native to this type of climate have evolved to enter a heavy dormancy during this period, which, here in northern Indiana, is roughly from November to March. This varies, of course, by species and seasonal factors.
Dormancy is a period of time where metabolic activity in trees is slowed to a crawl to conserve energy. But activity does not stop entirely as aerobic respiration continues, just like a hibernating bear continues breathing and lives off stored energy reserves. However, the process of photosynthesis does cease in broadleaf trees, just as a bear will not eat for several months.
A broadleaf tree is any tree which has broad, flat leaves, as opposed to the needle leaves of coniferous trees. Evergreen, coniferous trees occasionally perform photosynthesis during winter, but it is very rare and never as significant as during the summer months.
All broadleaf trees native to northern Indiana, such as maples and oaks, are deciduous — meaning these trees drop their leaves each fall in anticipation of winter. Trees draw all the nutrients out of leafs before they drop to store in the trunk and root system until next spring. This is partly why leaves turn different colors in the fall. Trees then form an “abscission layer” at the base of the leaf, which physically cuts the leaf off from the rest of the tree.
The leaves are intentionally let go, as holding on to them would prove to be an unnecessary risk. The leaves are no longer needed and the increased surface area would hold snow and ice, adding weight and increasing the chances of breaking a limb.
At the same time during the fall, all trees prepare for next spring by creating new terminal buds at the tip of each small twig. This bud houses and protects the sensitive tissue from which new growth will form the following spring. Buds are unique to each species of tree and are an easy way to identify deciduous trees in the winter.
The flush of new growth which occurs each spring is partly fueled by the nutrients which were pulled from last year’s leaves before dropping, as well as other resources stored during the previous growing season.
So while you’re raking or blowing your leaves, take heart in the fact that your trees are just preparing for their new growth next spring.
KEITH O’HERRIN is the City Forester for the City of LaPorte. He can be found at the Park and Recreation Office at 250 Pine Lake Ave. or reached at 326-9600.
