Why do deciduous lose their leaves?

Answer 1

Plants which loose their leaves in the fall/ autumn are called deciduous.

Leaf fall is triggered by a number of factors:

• Decrease in average daylight hours

• Decrease in average temperature

• and in some instances decrease in the level of available moisture.

At this point enzymes are released into the plant and stop the production of chlorophyll (the green photosynthetic pigment in leaves and stems). Some species of plants absorb what nutrients are left in the leaves back into the trunk or stem of the plant, in most cases other pigments such Beta-Carotene and Xanthophyll are left behind in the leaves (enhancing the colour effect)

An abscission layer forms between the petiole and the stem, this is basically a layer of callus cells so that the leaf does not leave an open wound when if falls, the abscission layer also facilitates the breaking away of the leaf from the stem.

Leaves fall when the abscission layer breaks - disturbed by the wind or under their own weight.

There are a number of reasons why deciduous plants drop their leaves:

• Fall is normally the onset of cold winters, in most cases if the foliage remained behind on the tree it would simply be damaged by snow, frost or wind. Ice crystals can begin to form in the cells at a temperature of about 4 degrees C, these grow and puncture/ rupture the cells killing them; this is the reason for the cold related phenomon known as "black frost"

• Some winter climates have snow, this means that there is in actual fact very little usable water available to the plant (ground water is frozen and snow does not melt readily and provide sufficient water for the plant to survive).

• Trees with large surface areas in storm frequented areas are regularly damaged by high winds, shedding leaves increase the aerodynamics of the plant and is a survival mechanism.

• The leaves which are shed collect around the base of the plants and are normally covered by snow, this assists in creating a bit of a buffer zone and possibly preventing root damage (like a blanket).

• After winter the fallen leaves decompose and release what nutrients and minerals they have stored inside them back into the soil - which the plant then reabsorbs.

Answer 2

Winter is approaching.