Why Do Some Trees Lose Their Leaves?

Trees that drop their leaves each autumn are called 'deciduous', from the Latin for 'to fall'.  They drop their leaves because of a weak area (called the abscission layer) at the base of the leaf stalk. When days shorten in autumn the reduction in light triggers the tree to absorb back some of the nutrients in the leaves.  The abscission layer then softens and weakens, causing the leaf to die and drop off.

Dropping leaves gives the tree a rest period (from growing) in the winter, when days are cold.  The large surface area of leaves makes a tree more vulnerable to damage from frost.

Most deciduous trees are native to in the world's temperate climate zones, in middle latitudes regions with relatively mild weather (such as Europe).  There are deciduous trees in the tropics, however, as well as in sheltered places at high latitudes (not far from the North and South pole).

because there is a chemical in the leaf called abscission and it breaks down the cells where the leaf and the and the tree are connected and when the wind blows the leaf is carried away to were ever it falls that is why leaves fall of trees!

Because it is the age of leaves that ran off. I mean leaves have very small life especially in some regions of this world.