By Mike Allen
Written for the Winnipeg Free Press ‘Tree Care’ Column October 5th, 2008
There is hardly a week that goes by that I do not receive a request for information or to visit and inspect large trees. Typically people are concerned about the safety of these trees, or perhaps they feel the tree is getting too old and has approached the end of its life. Perhaps there is a feature in these trees that has triggered a specific concern: weeping bark, cracks, creaking of the branches, overhanging branches, or a hole in the trunk. The list of concerns can go on. In some people’s minds a tree that is 70 feet or more in height is simply too dangerous because it is too tall. Here is a common question I get:
Q: There is a grouping of three large elms trees easily 80 feet high about 60 feet from our house. We live by the Red River and these trees must have been here for a very long time. We like the trees but we want to know how can we drastically prune back these giants because we are concerned that they will topple over and collapse into our house?
A: The word ‘drastically’ comes up in these enquiries many times. There seems to be a sense of desperation an owner has about these trees. There is a process of careful observation that I follow when I point out the features of larger and older trees to their owners. I am very mindful that I do not down play a tree which is obviously not safe. Here is what I look for:
- Does the crown (the upper structure of leaves and branches) look full and green? A weak looking crown maybe the result of damaged roots.
- Is the crown balanced? That is, is there a lop-sided appearance to the tree that seems to have its crown growth more on one side than centered on the trunk? This may simply corrected by pruning to create a balanced crown.
- Has there been a severe branch cut that has left a decayed portion of the branch stub very visible? That will likely be a sign of some wood decay in that location.
- Is the tree a survivor? This is an extremely important point. Older and larger trees that are healthy do have a strategy of reinforcing weak areas within the tree. A healthy tree will reinforce weak areas through adding on columns of strengthening wood tissue to support and compensate for weakness. Often the bark has a lighter grey tone where the tree produces these reinforcements.
- Is there a noticeable flaring out of the trunk or trunks from the ground? As trees age they will thicken their bases to provide additional support for their increasing height. Arborists refer to this feature as the ‘butt flare’. A sign of a weak growing tree may be the absence of the butt flare.
- Are there cavities in the trunk? These are likely the dens of small mammals or nesting areas for birds. A cavity is not necessarily a concern. Trees usually reinforce the wood and thicken the bark around any hole in the trunk or large branch.
- Are there any stains weeping from the bark of deciduous trees either in the trunk or from large branches? Large poplars can show dark stains where internal fluids have oozed out of a crack or small hole in the bark. Poplars are relatively short lived trees compared to elms, oaks, ashes and basswoods. Poplars may become infected with a fungal disease that opens up the bark by killing living cells that lie just under the bark in a region referred to as the cambium. These openings are referred to as cankers.
- Are there many dead branches and weeping cankers in older coniferous evergreen trees such as spruce and pine? Lower dead branches are common in these trees as they age. They should be pruned off at the trunk. Upper dead branches interspersed with living branches may be a serious concern as this may be an indication of extensive wood rot in the upper part of the tree. Internal extensive wood rot can lead to trunk failure and breakage in these coniferous trees.
Many old trees in Winnipeg especially those near rivers will live to a great age beyond 200 years. Poor pruning techniques such as ‘topping’ will definitely shorten the life spans of mature trees. Man’s manipulation of trees to ‘make them safe’ by drastically cutting them back does exactly the opposite. Drastic cuts that remove a large portion of the trunk and branches will in fact make a tree less safe. In most instances the trees were much better off before such measures were taken. A thorough examination of larger, older trees by a specialist can result in peace of mind. They may be specialized needs that have to be addressed in the tree, but they can be dealt with through proper arboricultural methods rather than ‘gut reaction’.
I will be giving an illustrated seminar on the care of these older trees along with another arborist, Gerry Engel of Tree Life, on October 15th at 7 pm in Room 2M 70 at the University of Winnipeg. We will put their heritage and environmental value in an entertaining and informative perspective. Call me at 831-6503 for more information.