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Tree Cracks


       Continued contemplation by the Tree Care Arborist at Olson Tree Care of tree biology and the forces they come in contact with takes us back to years spent in the Ozark mountains. We are nature lovers at our core, finding solace in the trees. 

       During those years spent loving the forest, we developed an instinctual knowledge of trees propensity for failure. Fast forward through several decades spent providing Tree Service in Urban Forests and the truth is still the same. 

       What has changed?

       The answer in short is us. 

       In civilized society we expect order, reliability etc. We expect our toilets to flush with the pull of a handle. In comparison we have come to expect trees to comply with our functional understanding of how things should work (no Tree Cracks allowed!). 

       Trees do not operate under the same criteria. They are flowing, competing trial and error living organisms that survive to the end by any means necessary. At times failure is a part of the solution. While shoot/branch competition and success is driven by production, the tree has little else to do but succumb to a dominant branch that is successfully converting energy. In this drive for success branch crotch form is not part of the equation.

       In short, Olson Tree Care has found that some Arborist in Des Moines and Societal expectations are the problem, not the tree or the tree cracks.

Shear cracks are in line with the grain of the wood

Shear Crack

Crack between 2 halves leading to failure

Included Bark Crack

Included Bark Cracks


       Left unchecked an included bark crack can destroy a tree. 

      What are the odds? 

       Low, but that depends on force applied. With increasing inclement weather more force can be expected.

       What are the industry norms?

       - Bolt, cable etc. (does any of these reduce force applied?)

       These options I have found to be widely practiced for included bark cracks and not very successful. Location of installation, tensile strength of materials used, force applied and reaction wood of tree are all fluctuating factors reducing predictability.

       Strategy for success?

       - Reduction pruning of weakest section or both if co dominant stems. This action reduces force applied and is more predictable and effective. Wind speed increases exponentially based on height from surface. Increased height equals increased speed. (Not to mention reduced lever arm)

       Drawbacks to strategy?

       - A tree with low vitality or reduced foliage increases the risk of decline and reduction of reaction wood in the area of the included bark crack.

Shear Crack vs. Ribbed Crack

       A ribbed crack is a shear crack properly dealt with by a tree, leading us to wonder... when is removal needed if the tree often can correct?

       Olson Tree Care recently came across a sugar maple (Acer saccharum), with shear cracks and spent a week pondering our recommendation. While Tree Risk Assessment focuses on target, damage and risk of failure, it leaves out one important area.... a trees ability to correct. Only 1 note on most forms is “vigor” and it does not factor in to the risk rating.

       Terms like “extreme”, “likely” and “failure” are hard hitting, leading to cabling or removal.

       The only 2 factors that seem important are “Target” and “Trees ability to correct”. I.E. ability for biological growth dedicated to correcting the deficiencies - structural wood. With high value targets such as kids etc, then those hard hitting terms are properly placed and sometimes allowing a tree time to correct may not be prudent. With low value targets those words are not of value and the focus of Tree Risk Assessment should be placed on a “TREE’S ABILITY TO CORRECT”.

        In the words of one ISA instructor.. “if there is no target, there is no risk” Without a high value target the focus of Tree Risk Assessment should be on the health of tree

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