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TREES, PLEASE: Tree Pruning Standards

By Tim Clancy.

The American National Standards Institute (ANSI) is the keeper of standards for all sorts of products and services. These are known as voluntary consensus standards. This means that while no one is compelled to follow them, the standards have been developed by consensus from a committee made up of stakeholders in the various ANSI subject areas.

Back in the days of the wild west for tree care (prior to 1991), the standard for tree care was decentralized and left to various agencies and private contractors.

Each developed their own "standard." This, of course, led to confusion and inconsistent tree care. The need for a scientific standardized approach was recognized and tree care made a sort of leap from the dark ages to modern times and developed a national standard.

There is a national standard for tree care commonly referred to as ANSI A300. The standard consists of ten parts as follows:

1. Pruning

2. Soil Management

3. Supplemental Support Systems

4. Lightning Protection Systems

5. Management

6. Planting and Transplanting

7. Integrated Vegetation Management

8. Root Management Standard

9. Tree Risk Assessment

10. Integrated Pest Management (IPM)

It is a credit to the tree care industry that these standards are reviewed and updated periodically. The pruning standard has been updated several times since its initial publication. Some of this is due to advancement in the understanding of how trees work and to the discovery that there is some ambivalence in the definitions that needs to be cleared up.

The current tree pruning standards (Part 1) were released in April 2017. There were some significant changes since the previous version, including the introduction of the concept of pruning systems. The pruning systems currently recognized in the standards are: a) natural; b) pollarding; c) topiary; d) espalier; and e) pleach. In addition to these pruning systems, four types of pruning cuts are described and defined. These are: a) branch removal cut; b) reduction cut; c) heading cut; and d) shearing cut. Using this information, tree care contractors can then develop tree pruning specifications. These specifications require an objective for pruning be established along with identifying the pruning systems to be used and the types of cuts to be made. For example:

The pruning objective is to control and maintain the size of the subject tree. Reduction cuts will be made on branches 1.5" and larger to maintain the tree's height at x feet. The pruning system to be used is the natural system, the intent being to maintain a form typical of the subject species.

In the past, the standards specified that no more than 25% of live foliage be removed in any one year. This was well-intentioned but led to various interpretations that resulted in what the standards committee considered over pruning and did not take into account situations where removing more than 25% live foliage was necessary to achieve the objectives.

I consider the new standards to be an improvement and encourage anyone involved in tree pruning decisions to require the standards be utilized in all aspects of tree care. Though the standards are voluntary, this is one way to identify qualified companies you're considering to work on your trees.

Photos: Left:: Magnolia with natural form; Right: Over pruned Queen Palm.

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