Abscission

This is why every deciduous tree sheds their leaves in autumn.They spend all winter producing buds,All spring sprouting them and then all summer using them.Their leaves are very valuable to the tree,But they are very fragile organs.In winter the leaves face two serious problems,When it freezes this can cause damage to the leaf and the fact that its very dry in winter is their other concern(as its normally dryer in winter than summer).If the leaf was to die and just fall off the tree,The tree would loose all of the valuable nutrients contained within the leaf.So through the process of abscission they seperate the dead leaf from the stem by forming cells at the base of the leaf.Then all of the nutrients are reabsorbed down the tree.Then its down to the wind and rain to take the leaf off the tree.Then through the process of decomposition it is then reutilised back through the roots,In years to come will eventually form a new leaf on the tree.