The broadleaf trees are now standing bare without their leaves and they look fairly lifeless, but appearances can be surprisingly deceptive. The aspen has striking white bark but that of the younger trees tends to have a greenish tinge thanks to chloroplasts buried in the inner layer. When sunlight penetrates the thin outer bark it can be enough for photosynthesis, aided by tiny pores in the bark that let carbon dioxide and oxygen gases pass in and out. And so, even in winter, the tree can supplement its food reserves.
Sunlight can also penetrate the thin outer bark of beech or silver birch, or the bark of tender saplings of other trees where there is enough chlorophyll for photosynthesis. Trees such as silver birch have bark that also peels away and may let in more light, but even in the thicker bark of other trees light can still penetrate through cracks, whether the bark is craggy or smooth. And the leaf buds and twigs of many trees can also make food by photosynthesis, even if only for a week or two before the buds open, a welcome boost just as spring gets going.
