Cover of “The CODIT Principle: Tree Biology and Arboriculture, Second Edition.” Photo courtesy of the International Society of Arboriculture (ISA).

In the August 2017 issue of TCI Magazine, I reviewed Dirk Dujesiefken and Walter Liese’s “The CODIT Principle: Implications for Best Practices,” after the original German edition was translated into English. A greatly expanded second edition, titled “The CODIT Principle: Tree Biology and Arboriculture, Second Edition,” has now been translated, and for good reason. Few things benefit arborists worldwide more than a basic understanding of tree biology, the CODIT principle and how trees respond to wounding – and the many implications for tree care.

More than 40 years of combined research by these two authors complement and expand upon Dr. Alex Shigo’s early work, including expanded concepts and the now-popular Hamburg Tree Pruning Method. (If you haven’t heard of the Hamburg Method, you really must check it out!) They say a picture is worth a thousand words, and the book’s many full-color pictures and drawings clearly convey its concepts.

In Chapter 2, which focuses on tree biology, trees are described as some of the largest and longest-lived organisms on earth. A short section on tree survival strategies is discussed, including how their many adaptations to environmental conditions and extremes give them that remarkable survival ability.

Of course, the ability to compartmentalize is a big part of that. In the previous edition, trees were described as either effective compartmentalizers or weak compartmentalizers. In this edition, the authors went a step further by including a two-page table of effective and weak compartmentalizers by tree genus/species.

Specific attention has been given to the tree’s response to various kinds of wounding. Pruning, topping, injection and bore holes, nails, screws, sun necrosis, lightning strikes and cracks are included.

The latest information on wound treatments and their effectiveness is well covered. Treating fresh collision or mechanical wounds with an opaque film is described step by step – something we as arborists should be doing more of. Wound treatments, including tar products, disinfectants, wood preservatives and polyurethane foam, are all reviewed as well.

The goal of biology-based tree care is, of course, using the tools and knowledge we have gained to best serve the tree. Is there an optimal time to prune? How do we factor seasonality, insect and disease prevention, pruning objective, dose and species response?

Greater knowledge leads to better decisions. Shigo taught us that in nature there are no absolutes, and that there is often no single correct way of doing things. We must draw upon our knowledge to make those sometimes-difficult decisions. The second edition includes 58 additional pages that apply tree-biology principles to everyday practice.

The last chapter, titled “Implementation in Arboricultural Practice,” includes sections from the European Tree Pruning Standard. Because of the recent international exchange of knowledge, the practices they describe are very similar to ours in the United States. Formative pruning of young trees and maintenance pruning are covered in depth, as are crown lifting, deadwood removal, basal sprout removal, reduction pruning and restoration pruning. If you contract tree work, this chapter provides valuable information for writing those bid specs concisely and fairly for all bidders involved.

This is a valuable, highly recommended reference publication and a great addition to the serious arborist’s personal library. It’s been added to mine.

Steven F. Pregler is an ISA Certified Arborist and retired city forester with more than 35 years of experience working for the city of Dubuque, Iowa. “The CODIT Principle: Tree Biology and Arboriculture, Second Edition” by Dirk Dujesiefken and Walter Liese is published by the International Society of Arboriculture (ISA).