It might come as a surprise to some, but trees in the southwestern desert are not going to live forever. Sure, there are some desert ironwoods, Olneya tesota, along washes which have enjoyed the past few hundred years, but as for our urban based tree palette, premature decline and senescence is a constant concern. Thus, the overall management objective should be to provide benefits that outweigh costs – a basic definition of sustainability.
I was recently asked what I considered the single most important activity that a municipality on a tight, and often decreasing, budget can do to help maintain a viable urban forest. Initial thoughts covered the big picture concepts of protection ordinances, planning for adequate soil volume and rooting space, appropriate species selection and placement.
Then I considered the importance of selecting quality nursery stock, proper planting technique, irrigation delivery, and arranging for after planting care. But all too often some of these are beyond the control of a humble urban forester.
One thing the resource manager can do is work with field staff, or a contractor, to provide “training” for the tree during its early years. Given the importance of all best management practices working together, structural pruning during the first five years of a tree’s growth might actually be the key to managing a sustainable urban forest on a limited budget.
We are all generally aware of the benefits of structural pruning for young, intermediate, and even mature trees, to help develop, enhance and maintain structurally stable trees. Careful pruning and guidance during establishment can serve to provide the greatest overall benefits for the lowest input and costs. This important tool can help to limit potential risks, promote health, and possibly reduce maintenance costs over the life of the tree.
The majority of our commonly planted southwestern trees tend to exhibit a decurrent growth form. These open grown park and street landscape trees tend to lose the central leader early with long, lower hanging branches developing to support the crown and offer protection of the trunk.
Often, our young trees are not managed during the first few years, encouraging growth to provide the desired shade while developing a poor growth form requiring increased maintenance. This deferred maintenance is not saving budget dollars, rather creating unnecessary expenditures; turning our assets into liabilities.
Problems of visibility obstruction and pedestrian/vehicular access can lead to harsh maintenance activities, large wounds, and tree loss in later years. Early structure pruning can help to limit codominant stems and the occurrence of included bark, provide good branch spacing and help reduce the need for large branch removal in the future.
We have all observed trees on a newly planted project having been over-elevated and “thinned” (lion-tailed) to provide clearance and visibility. These substandard practices promote poor structural development, as many of the remaining lower branches will eventually still have to be removed.
Subordinating these lower branches can often address the immediate objective and help to promote upright growth, increase trunk diameter and create favorable branch and trunk taper. Working to manage the branch aspect ratio on young trees leads to smaller wounds once these branches are removed.
There is often a reluctance to reduce and/or remove branches on young trees, and explaining this importance to stake holders (project managers/decision makers/citizens) can be a challenging exercise. A thoughtful review of the urban forest management objectives including safety and the reduction of potential risk, enhancing environmental benefits, and creating social amenities for the community all on a limited budget can support the importance of the technique. While many people can agree on the first three goals, having a maintenance or pruning budget go farther often attracts the most attention.
Like many arborists, I find it quite satisfying to observe a healthy tree maturing over the years. Let’s work to reverse the trend toward managing disposable landscapes by making healthy and cost effective choices for trees from the beginning.
The urban forest is an open laboratory providing an opportunity to observe, learn, and educate. Although other objectives of care are required in our daily work, helping a tree to develop a structurally sound form is a best practice to provide sustainable growth and benefits from our urban forest.
Richard Adkins is The Gilbert Arborist, a certified arborist and member of the American Society of Consulting Arborists. He has produced a pruning video at https://www.youtube.com/watch?v=n7IJjjkSTCk. For more information, contact Adkins at 480.244n3356 or email firstname.lastname@example.org.