Why do leaves of the trees fall?

Question

Why do leaves of the trees fall?

Answer 1

The other answers are either proximate explanations (of the "leaves fall because plants shed them" variety) or mere speculation. The ultimate reason that certain plants shed their leaves in fall has to do with reduced photosynthetic function in autumn and winter due to the shorter days, and the possible damage inflicted on plants if they attempt to retain their leaves. For the latter, I quote:

"Winter is a certainty that all vegetation in the temperate zones must face each year. Perennial plants, including trees, must have some sort of protection to survive freezing temperatures and other harsh wintertime influences. Stems, twigs, and buds are equipped to survive extreme cold so that they can reawaken when spring heralds the start of another growing season. Tender leaf tissues, however, would freeze in winter, so plants must either toughen up and protect their leaves or dispose of them.

The evergreens-pines, spruces, cedars, firs, and so on-are able to survive winter because they have toughened up. Their needle-like or scale-like foliage is covered with a heavy wax coating and the fluid inside their cells contains substances that resist freezing. Thus the foliage of evergreens can safely withstand all but the severest winter conditions, such as those in the Arctic. Evergreen needles survive for some years but eventually fall because of old age.

The leaves of broadleaved plants, on the other hand, are tender and vulnerable to damage. These leaves are typically broad and thin and are not protected by any thick coverings. The fluid in cells of these leaves is usually a thin, watery sap that freezes readily. This means that the cells could not survive winter where temperatures fall below freezing. Tissues unable to overwinter must be sealed off and shed to ensure the plant's continued survival. Thus leaf fall precedes each winter in the temperate zones."

From: http://www.na.fs.fed.us/Spfo/pubs/misc/l...

Answer 2

the leaves die off and dry out and then fall.

Answer 3

As the tree gets older, more leaves clump together on a few branches. It becomes rather heavy, and as the joints weaken, the weight becomes too much. Therefore, the leaves are shed. Also, as the leaves die, there is not much flow of water from the branches to the leaves, so the joints get rather dry. Therefore, they weaken and the leaves drop.

Answer 4

usually the leaves got seeds on them so when the leafs fall the seeds go into the ground and grow up to be more trees.

Answer 5

1. anything going up has to come down oneday

2. due to gravity

3. they are too old to hold on to a tree for long

4. this is biology