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Managing Veteran Trees

Arborist Danny Lippi attaches the terminal end of a tree lightning protection system in a veteran live oak.

Dr. Kim Coder of the Warnell School of Forestry at the University of Georgia has published many articles on his research of veteran tree management and has many beneficial insights on the topic. Dr. Coder states, “Emphasis should be placed on minimizing the number of branch orders, shortening branch length, and reducing branch weight. Reductions should be timed so that a number of years occur between treatments.” Coder continues, “Old trees are burdened by their mass, reach, and size. Reduction of tree reach, extent, and mass above ground can reduce risk of structural failure and improve transport (of nutrition and energy) and path problems (vascular tissue constriction).”

What this means is that trees do not plan to age or grow. And because trees are mechanical structures as well and living organisms, they will eventually become too large (massive and over-extended) to self support. This is the point of life where trees will begin to break apart and shorten those vascular pathways and over-extended and heavy limbs in a process called “retrenchment”. Pruning older trees should seek to prevent those chaotic and large failures. Reasons to prune older trees are “over-extended lateral limbs, bark inclusions, decay and degradation from wood-decay fungi or pests, clearance, and others.

Kim Coder, Managing Aging Trees, Arborist News, International Society of Arboriculture, Champaign, Illinois, 2005.
Notice there is some dieback in the upper branches. Overall the crown is small when compared to the size of the trunk. Photo provided by Philip van Wassenaer, Urban Forest Innovations, Inc., Mississauga, Ontario
A large cavity does not necessarily mean the tree is at high risk of failure. The amount of solid wood around the cavity, the location of the cavity and the size of the crown should be considered when evaluating risk. Photo provided by Philip van Wassenaer, Urban Forest Innovations, Inc., Mississauga, Ontario

First, it is important to understand what a veteran tree is. A veteran tree is one that is clearly “over the hill.” It is on the downward slope of maturity. It probably has significant amounts of decay, structural defects and its health is declining. This is the stage when many people and unfortunately many tree services call for a “mercy removal” of the tree.

Veteran trees differ from younger trees physiologically. In veteran trees the ratio of photosynthetic area (leaf surface) to biomass decreases so energy produced in the leaves is used for maintenance of existing tissues and productionof defensive chemicals. Lower energy reserves mean less energy is available for growth. On the other hand young trees have a high ratio of photosynthetic area to biomass. Young trees generate surplus carbohydrates which are used for rapid growth.

So why keep these declining relics? These ancient veterans are a link to our past and often have been around during significant historical events. In our urban society most veteran trees are no longer retained and managed. A few old trees attract tourist because of their existence during historical events, but most old trees are neglected. Many more have already been lost, cut down for development, agriculture, for safety reasons or just because they are old and defective. A mercy killing is often prescribed.

England and many parts of Europe are on the forefront of maintaining veteran trees long after many cultures would have brought out the chain saw for a final basal cut. One outstanding link to Managing Veteran Trees is Veteran Trees: A Guide to Good Management.

Management of a veteran tree often involves pruning. But we must remember the real reason for pruning should be to prolong the life of the veteran tree. Pruning should be done only on a limited basis for safety. The temptation to work excessively on veteran tree in order to demonstrate that one is managing it should be avoided. Pruning live branches removes stored food reserves and carbohydrate-producing leaves. So limit pruning of veteran trees to dead branches and a small amount of branch end weight reduction whenever possible.

If you must prune live branches, observe the following: If it appears the tree is relatively strong and healthy, it may likely respond to pruning. If the tree has many dead branches and stubs and few epicormic sprouts, then it will probably not respond to pruning. Consequently, pruning such a veteran tree should be avoided. Of course remove dead branches that are a safety hazard.