In Context #14 (Fall, 2005, pp. 18-22); copyright 2005 by The Nature Institute
The Forming Tree
The trees you see below are in their winter habit. Without leaves, the form of the crown displays itself through the intricate branching pattern of the limbs. Each of these trees has a history behind it and the crown form reveals some of that history. But the history is no straightforward matter. It has different facets and in each particular tree is unique.
First, each tree belongs to a species. As a red oak or a white ash, a tree is part of a specific hereditary current that connects it with all other members of the species. Although a species has considerable plasticity and shows an often surprising variety of forms, it is nonetheless usually possible, with a bit of practice, to identify a tree species in the winter through its bark, branching pattern, buds, and so on.
The particular shape of the crown and the size of the trunk relative to the crown in an individual tree express a different facet of the tree's history. A tree's crown develops over time and no broad-leafed tree maintains the same shape when it grows from a sapling to a twenty-or hundred-year-old tree (see Figure 1). While growing, the shape transforms. All the trees you see in the Figure 2 had, as young trees, branches growing out of the trunk near to the ground. But all of these branches have since died off. As the trunk grew in diameter, the bark grew around the scar where the branch had separated from the trunk. The branchless lower stretches of the old trunk therefore no longer reveal outwardly the tree's growth history. The tracks are present, however, as knots