Why do the leaves on some deciduous trees stay on the branches all winter, instead of falling off?

Question

I notice that the leaves are still attached to some oak trees and beeches, even after four months of cold weather, while the other trees' leaves fell off long ago.

Answer 1

beeches and oaks both experience that phenomenon quite regularly, so do some maples, the fibers connecting the leaves to the branches are stronger, they are still dead, but just not deposited. If you take a close look at dead oak leaves versus a locust leaf it has more fiber and is stronger over all

Answer 2

Trees that lose their leaves are trying to conserve energy. Their leaves detatched so that they don't have to provide the leaves nutrients that they can store to survive through winter. If a winter isn't all that harsh and sometimes just randomly leaves will stay on because there is not the same need to save energy.