City Trees is a premier publication focused on urban + community forestry. In each issue, you’ll learn how to best manage the trees in your community and more!
Issue link: http://read.dmtmag.com/i/232632
CT: How did you happen to choose this subject for a book? A few years ago a California arborist called me to advise him about a problem he was having, and told me that he and another consultant had evaluated a tree's condition but had widely differing opinions. He concluded: "I ended up wondering if we even looked at the same tree." Not long afterward, I attended a lecture by a university tree pathologist. He was reporting on the effect of a treatment, and ended with the following: "When I returned to the tree two years later, you know, it looked pretty good." I realized that these two very different events pointed to the same problem: in urban forestry we do not have a shared professional way to speak about tree health that rests on a sound scientific base. CT: What's wrong with a simple scale like "good, fair, poor, critical"? Nothing. I use it a lot when all I want is not to waste any time—for instance on younger trees with goodquality crowns or older trees that are nearly dead. But as soon as I start looking at trees in between those two extremes, it quickly gets tricky. Everyday health terms lack clear definition, are poorly separated from each other (when does "fair" become "poor," exactly?) and often rely on a gut feeling that is hard to explain and justify. For those reasons, I only use a simple scale at the end of a professional examination of tree condition, never in place of it. ly restricts their usefulness for most of us. On the one hand, the relatively objective system developed by the USDA Forest Service for rural forestry inventory and analysis (FIA) demands a high resource level in terms of time and personnel that few urban forest professionals can afford. On the other hand, the well-known condition rating of the Council on Tree and Landscape Appraisal serves the goal of tree valuation, combines health and stability, and relies on strongly subjective criteria. The variant of the USDA FS system used in i-Tree Eco might seem both practical and precise at first glance, because it uses 5% categories of dieback to report on tree condition. But serious reservations exist: 1) some species and size-classes display health problems with traits other than dieback, e.g., many conifers and young deciduous trees; 2) dieback only shows up relatively late in a downward health spiral, so it provides no information about less critical states of health; 3) dieback does not commonly show up in nature on a continuous and high-resolution scale, since we typically see either a lot or a little; and 4) dieback does not permit evaluating health important to other questions of urban forestry such as young tree establishment. Equally important is the fact that such a simple scale does not actually aim to measure anything definite. The method in my book derives in part from earlier USDA Forest Service research, and my intent is similar to that predecessor's: make a rough estimate of a tree's photosynthetic capacity, the ultimate source of its health. CT: Can't we just use other methods that already exist? The difficulty of trying to do that is that the methods that exist were not developed for the routine work of urban forestry, a fact that severewww.urban-forestry.com Careful examination of this red oak (Quercus rubra) reveals a very low vitality, indicated here by the large amount of small twig death throughout the crown. Note that its normal crown shape has also been altered by the loss of most of the larger lateral branches. 15