Why Do Trees Lose Leaves in Winter?
Some trees with broad-bladed leaves lose their leaves in the winter because the tree has a rest period during the cold weather, and the leaves are not needed for the production of food. These trees are called deciduous trees-from the Latin decidere which means to fall. They drop their leaves in temperate or cold climates, but remain evergreen in the tropics.
Common deciduous trees in the Northern Hemisphere include several species of ash, aspen, beech, birch, cherry, elm, hickory, hornbeam, maple, oak, poplar and willow. In tropical and subtropical regions, deciduous trees include several species of acacia, baobab, roble, ceiba, chaca and guanacaste.
Shedding leaves helps trees to conserve water and energy. As unfavorable weather approaches, hormones in the trees trigger the process of abscission whereby the leaves are actively cut-off of the tree by specialized cells. The word abscission shares the same Latin root word as that in scissors, scindere, which means “to cut.”
At the start of the abscission process, trees reabsorb valuable nutrients from their leaves and store them for later use in their roots. Chlorophyll, the pigment that gives leaves their green color, is one of the first molecules to be broken down for its nutrients.
This is one of the reasons why trees turn red, orange, and gold colors during the fall. At the end of the abscission process, when the leaves have been shed, a protective layer of cells grows over the exposed area.
The shedding of leaves may also help trees to pollinate come springtime. Without leaves to get in the way, wind-blown pollen can travel longer distances and reach more trees.