For more than 30 years, Arbor Age magazine has been covering new and innovative products, services, technology and research vital to tree care companies, municipal arborists and utility right-of-way maintenance companies
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www.arborage.com Arbor Age / July 2014 15 from 1-10, but uses the number 7 as "normal" for that species. For example, say we are doing research on optimal rates for injectable nutrient supplements used to correct an issue such as chlorosis. We would take baseline data on the color of each tree, assigning a number based on how yellow or how green the tree is. Treatments of various rates would be applied to the trees, and follow-up observation ratings would be made. Comparing to the baseline data, we can determine which rates improved the trees to their "normal" color, which were not strong enough, and which rates caused the tree to be abnormally green. This exact trial could utilize more empirical data by taking leaf samples into a lab and determining the precise quantity of chlorophyll molecules by chemical analysis. Lab work can also yield data regarding nutrient content, secondary metabolites, or even the presence of toxins. Root samples can be analyzed for stored starch content. All of this data can be used as a proxy measurement for a tree's health. While collecting samples and having them analyzed may yield more accurate results, it also adds to the labor, time, and cost of the trial. Researchers are constantly evaluating which data collection methods give the most accurate and pertinent information while balancing that with the time and budget allotted for the trial. Evaluating the fullness, or density, of a tree's canopy is an- other common way researchers and arborists evaluate tree health. Measurements such as percent fi ne twig dieback can give an indication of how stressed a tree's canopy is. Subjec- tive ratings, such as percent-canopy, are frequently used in tree health care. For example, it is commonly said that an infested ash tree can be saved from emerald ash borer if the tree has less than 30 percent canopy decline. There have been visual guides developed to help establish guideline for what 10-, 20- or 30-percent decline looks like that can help create some consistency to this subjective method. If a more objective measurement is needed, canopy den- sity can be assessed through more empirical methods. Im- aging tools such as hemispheric photos taken from below the tree can give data on the fullness of a canopy. Leaf area index (LAI) is a canopy density metric that is frequently used in forestry as a way to predict forest productivity, but it can be used in arboriculture as well. LAI is quantifi ed as Ash trees planted near parking lots. A resistograph can provide data on a tree's structure. New tech improves data collection methods.