The bark of the paper birch is white, whereas the bark of the aspen is an off-white color with a greenish tinge. Then we ventured into Gallistel Woods. This forest is an example of a southern mesic forest. We continued our tour with a discussion about why deciduous trees drop their leaves. These trees drop their leaves because it is too costly for them to hold on to them during the winter.
Winter is a season of drought because all the available water is tied up in ice or snow.
As a result, trees can't get enough water to support having leaves. In addition, trees lose water from their leaves due to evaporation. In winter, a drought period, trees do not want to lose any of their water, so they get rid of their main evaporative surfaces. Trees lose their leaves in the fall because an abscission layer forms between the leaf stem and the branch. Once this layer forms, the leaf is cut off from the tree's energy supply.