If you are trying to learn how to identify trees in winter, one good place to start is to look for trees which still have their dried leaves attached. In Ontario and most of the northeast USA these will be either beech trees or oaks. The phenomenon of retaining dead leaves in winter is called marcescence.

If the leaves are fairly dark brown and curled  up into untidy clumps, you are probably looking at an oak tree:

Small oak trees in winter

Red oak leaf

On an oak tree, each leaf will be divided up into lobes. If the leaves have pointed edges (like the picture above) then the oak is from the red oak family, if  the edges are curved, it is a type of white oak.

If the leaves are shaped like arrowhead, long and thin and are pale and trnslucent, you are looking at a beech tree. The pale smooth grey bark will confirm this:

Light shines through the leaves of a beech tree

Beech leaves

No-one knows why some trees retain their dead leaves throughout winter. Originally, all trees were evergreen, and able to get energy from sunlight all year round. Deciduous trees gain some advantages from losing their leaves. They lose less water in winter and they are less likely to accumulate enough snow load to cause damage to the branches. So why would any tree keep its dead leaves, which no longer function but could increase the risk of the tree to be damaged by strong winds or heavy snowfalls?

The best theory is that the trees are saving their leaves so that they will fall off in the spring, when the tree needs a layer of mulch to retain water and when the dead leaves can break down and release nutrients which are needed for new growth. This is supported by the observation that leaves are retained mainly by small young trees, and on the lower branches of larger trees. Also, beech and oak tend to grow on dry infertile soil, where the extra water and nutrition would be of greater benefit.

Another theory is that the dead leaves make the tree less easy for deer an other browsing animals to eat. A third idea is that the leaves encourage snow accumulation around the base of the tree, saving the buds from frost damage and storing extra water for spring growth.

Whatever the evolutionary reason behind markescence, it gives us an easy way to identify the beech and oak trees in a forest in winter.