Non-Defensive Conservation Arboriculture

Care of a veteran tree requires a different approach than would a young, maturing tree. As trees decline, they can be maintained with an appropriate degree of risk management, and contribute to our environment in ways that young trees simply cannot. When a tree has grown to the maximum size its landscape allows it may begin to shrink its canopy inward. Scaffold limbs and branches may shear off in winds. Large dead structures remain, and wildlife moves in to hollows. Over long periods of time, epicormic sprouts originating low on the trunk may grow into trees in their own right, rooting right through basal decay and finding their way to the soil below, much like a nurse log found in a rain forest. Thus trees in some cases have the ability to live perpetually.

Conservation arboriculture seeks to mimic this natural process. Retrenchment pruning is a multi-stage process implemented over several years if not decades, wherein parts of the tree are reduced systematically in an attempt to encourage inner canopy generation of new stems and leaves. Dead woody structures that are stabile are left in the tree rather than automatically being removed. Where cuts are made with chainsaws and handsaws, the cut end is scarred up, imitating a natural break, and exposing more of the wood to fungi already present in the tree. This allows for a greater variety and quantity of habitat to be present within the tree system. Better yet is for branches to be mechanically broken.

A large cottonwood, Populus trichocarpa, was recently retrenched in the City of Kent, WA, USA. This tree is growing next to an arterial road, a walking trail, a water ditch, and residential townhomes. Thus, management of risk was called for. Three arborists from Tree Resource, as well as arborists from the City of Kent, spent a day instituting stage one of the retrenchment process. The tree, which may already be into its second century, will be monitored and further reduced as necessary over the next fifteen to twenty years.

People are beginning to understand more and more, the value of conserving our veteran and ancient trees. They are a living history of our region.

Trees make us happier, inspire us with awe, and instill in us a respect for all life.