Question

why do some trees lose their leaves in autumn

Answer 1

Leaves must fall. Evergreens can hang on to their leaves through winter, because their foliage is coated in a wax that helps protect against cold, and their cells bear anti-freeze chemicals that ward off winter's worst woes. Not so for broadleaf, or deciduous, trees.

Answer 2

in order to prevent the loss of water as the yranspiration takes place through the trees