How do trees stay warm in winter?

Why do the leaves on beech trees stay on in the winter?

• Answer:

  Deciduous trees generally lose their 'dead leaves' yearly, thru a process called leaf abscission. Ofcourse there are always exception and there are some species of plants that dont abscess their leaves, like many in the plant family Fagaceae which contains the genera of oaks, chestnuts and beech. While its not exactly clear why it happens, I do have some interesting tidbits... Its been asked alot in botany depts why this happens to this family specifically. Recently, there has been lots of work done showing the actual genes and cellular mechanisms of abscission. And simply put, it seems that Fagaceae doesnt turn those genes on very well but the leaf is definitely unhooked from the rest of the plant... in essence dead weight, just not fallen off. I could imagine some evolutionary benefits of leaves falling in the spring as opposed to fall. Specifically not letting leaf disease overwinter in the warm soil but the harsh windblown branch. Also spring time leaf mulching. Dr Evert of UWMadison who is a well known plant anatomist prof did some of the initial work to confirm that infact the leaf of the non abscessed Fagaceae was dead weight to the plant. I believe even to this day, he doesn't have a solid reason on the 'why' but you can research his work if you want the original research papers. The leaves of a mature beech tree will fall during the Autumn and early Winter. The leaves of a well maintained beech hedge will stay on all Winter. This is either due to the close grouping of the cut hedge or the fact that young, protected shoots can hold on to their dead leaves.