Tree Architecture

Architecture is a term usually applied to our built environment, but it also can apply to natural systems - to trees, for example. Trees are naturally programmed to grow in predictable patterns that are unique to each species.

Buildings are constructed in Greek Revival or Postmodern styles, but nature constructs trees in coffeetree or river birch styles. Many people think of trees in terms of their flower color, foliage and attractiveness, but their most significant characteristic is their natural style or architecture.

Perhaps the most obvious architectural feature of trees is their size. The range of variability is tremendous. In Missouri, tulip poplar in the Bootheel region can reach over 150 feet, while the shrublike wild plum tops out at around 12 feet in a north-central fencerow. In the forest, oaks, hickories, ashes, maples and lindens form a lofty branch canopy over the subservient ironwood, redbud and serviceberry, which compete for limited sunlight in the understory.

Another important aspect of tree architecture is branching habit, or the natural arrangement of trunk, limbs, branches or twigs. Some trees develop a pronounced central stem extending to the top, resulting in an overall conical or pyramid tree shape. This is called "excurrent branching" by botanists.

Species that conform to this branching habit are the familiar needled evergreen pines, spruces, junipers and the deciduous baldcypress. Some trees have strong excurrent branching in their youth, but gradually give way to a more spreading shape in old age. Examples include pin oak, sweetgum, blackgum, lindens, sycamore and tulip poplar.

Trees that grow by dividing their main stems into multiple, equal-sized branches, as opposed to one main stem, are botanically known as "deliquescent." Trees with this growth habit tend to develop a fan or V shaped outline. Examples of this type are the once familiar American elm, hackberry, honeylocust, yellowwood and redbud.

Knowing a tree's growth habit, together with landscape position, can be used for identification. The coarse, light-colored branches of sycamore make it stand out from other trees, especially in winter. The conical shape and stiffly arranged horizontal side branches of pin oak make it easy to spot.

Dense, reddish-twigged trees in low areas are likely willows. Pole straight evergreens with sparse bottom branches on Ozark hilltops are shortleaf pine. Many other trees have signature characteristics which are actually more distinct when viewed from a distance.

A practical application of tree architecture is planning for tree planting and care. Need new street or shade trees? Good candidates would be tall growing species with ascending branches, so that a branch canopy can be developed over time. Examples include ashes, maples, lindens and some oaks.

Want good turfgrass? Then select a large-growing tree that is open enough to allow lots of sunlight through - a honeylocust, for example. If maximum shade is needed, denser trees can be selected - sugar maple, linden or beech.

Knowledge of tree growth habit can also help us decide what trees not to plant. Trees that grow with lots of low branches, such as hawthorns and spruce, or trees with descending lower branches, such as pin oak, will not be good choices where eye-level open space is required for visibility. Excurrent trees (central stem) are especially bad choices for planting under utility wires. Their fate is to be beheaded when lines must be cleared at some time in the future.

Knowledge about tree size and branching habit is the key to pruning that looks right when the job is finished. Ignoring natural branching patterns before removing branches will produce trees that are strange looking misfits. If you are unsure about natural growth patterns, study other trees of the same species.

Try to visualize the growth of trees after branches are removed. If there will be obvious problems, such as not enough room for future growth, consider removing a tree and replacing it with one that can grow to fit into its surroundings. It is easier to work with natural growth patterns rather than work against them.

Some architecture is timeless - the Greek Parthenon for example. But also timeless is nature's tree architecture. Each species has a style that makes it different from all others. We tend to be wowed by eye-catching spring flowers, summer foliage and fall colors, but they could not exist without framework providing distinct size, shape and character. If we pay attention to natural growth habits, we can better understand trees and how to live with them.

Tree Pruning Guidelines, Using Tree Architecture

• In pruning, work with rather than against the tree's natural form.
• Preserve the main framework of a tree if possible by removing smaller rather than larger limbs.
• If it is necessary to remove a major branch or limb, remove it as early as possible in the life of the tree.
• Remove entire limbs or branches at their base to preserve the natural growth habit.
• Remove a few branches at two- to three-year intervals rather than waiting for pruning needs to accumulate. Don't remove more than one third of a tree's live limbs in one year.