Strong Tree Structures

by | May 13, 2021 | Arboriculture, Horticulture, Maintain, Nursery

Industry Insights With Florida Grower John Conroy

John interviews Dr. Ed Gilman: urban tree specialist, prolific author and University of Florida environmental horticulture professor.

He teaches the architecture of tree branch and root structure, and why it is critical for tree success in the landscape.

John: Ed, what are the main reasons planted trees fail or succeed in the landscape.

Ed: There are three main reasons for a tree’s success or failure. First, the pruning at planting; second, grades and standards; and third, the root system and depth. 

John: What issues have you seen when there was no pruning at planting? 

Ed: I’ve traveled to many countries, have pruned trees and learned a lot from arborists worldwide. The indelible common thread that I have observed is that lower trunk and branch architecture is pretty uniform in regard to urban planted trees. Whether it’s Singapore, Hong Kong, Boston or Seattle, hardwoods of different species have similar structures. In those places and more, after the tree gets installed and established, nobody is really in charge of training the tree to develop sustainable architecture. Landscapers and homeowners might prune the low branches away but don’t always think about the branches higher in the canopy. Without structural pruning, defects can develop which shorten tree life. 

John: What’s the best way for landscapers to tell if a tree has a proper branch structure?

Ed: What we look for is a trunk (central leader), that is considerably larger than any of the branches. It’s best to have branches about half the size of the trunk. Here in Florida, the Florida Fancy or Florida #1 specification requires that no branches are greater than two-thirds the diameter of the trunk. If they are larger than the desirable ratio then you simply reduce that branch to slow its growth by cutting back to a lateral live branch. This process is called subordination. You can develop good branch architecture and still achieve the silhouette customers want, a rounded, upright oval or a pyramid shape, depending on the species. The bottom line is, whether it’s a city, a homeowner’s association, a commercial or residential client, they don’t want trees falling in weather, and they don’t want the replacement cost of a tree that fails due to a weak structure. 

John: What are some of the structural defects you’ve seen?

Ed: I have seen trees all over the planet from topicals, elms, maples and oaks where failure occurred on branches present on the trunk at planting. This is halfway up the crown or at the top of the nursery crown. If this were taken care of by specifying a tree that meets Florida Fancy standards, or by structural pruning at planting, we would see fewer of these issues occurring.

In the next insight, Ed will discuss more about root circles and how proper root care and development benefits a tree.

John Conroy

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