They decompose
They fall off.
Autumn, or Fall. That's pretty much why they call it Fall. the leaves FALL off trees.
Evergreen trees lose only a few old leaves at a time.
In the fall. Trees pull back some moisture from leaves before they dessicate, turn brown, and fall off.
Gravity, wind, birds, squirrels
Deciduous.
because its cold and they freese and fall off
All trees are perennial. Deciduous trees drop their leaves in the Autumn. Evergreens do not drop them at any specific time of year.
Maple leaves turn a beautiful red color and do fall off the tree.
I believe all maples lose their leaves in the fall but certain oak trees keep their leaves all year. The "live oak" is named such because it keeps its leaves through the winter.
Usually in late October, or very early November.
The easy answer to that is evergreen leaves! It's not that simple though, for instance some trees manage to keep their dead leaves over winter and some deciduous trees keep their leaves over winter.