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16 Arbor Age / July 2014 www.arborage.com the average leaf area per unit of ground surface area, and can be measured by taking a statistically signifi cant number of leaves from four sides of the tree. Area is then either mea- sured manually, by using an electronic area meter, or by using specialized scanning software. The leaf area is then divided by the area under the tree, measured from drip line to drip line, to give you the LAI. This index can be useful for measuring health, as trees that are performing well tend to have normal sized leaves for that species while trees that are struggling tend to produce smaller leaves. Using LAI, researchers can evaluate the responses to different treatments, but, as most trees only produce one set of leaves per year, this can be a diffi cult metric for more immediate responses. Measuring how the health of a tree is varying day to day can be more challenging, but, with the right equipment, can yield valuable data. Just as your doctor measures your vital signs — blood pressure, pulse rate, breathing — plants have metabolic processes that can be measured too. Chlorophyll fl orescence is one of the more common measurements taken to assess overall tree vigor. One of the most pronounced physi- ological responses to stress is a reduction in net photosynthesis; and using a chlorophyll fl orescence meter can be a quick way to determine the photosynthetic potential of a leaf. Chloro- phyll can also be measured in the fi eld using a handheld SPAD meter that quickly reads the chlorophyll content of leaves. Arborists of the future will, of course, simply scan the tree with their ArborTron 3000 Healthometer and get instant info on the current health and remedies for every malady conceiv- able. But until then, we will continue to measure health in all these different ways. There are many other ways not mentioned here that scientists can use to attempt and quantify health; but no matter how or what data is collected, turning that data into actions that help improve the life and vitality of trees is the ultimate goal. Tree health care is still an emerging science and new analysis tools are being created, tested and adopted all the time. Keeping up with the current ways we can quantify tree health can help make you a better tree health professional — at least until the ArborTron 3000 comes out. Brandon Gallagher Watson is creative director at Rainbow Treecare Scientifi c Advancements, and is an ISA Certifi ed Arborist (#MN- 4086A). PLANT HEALTH CARE PLANT HEALTH CARE Ash leaf samples. Canopy density can evalute health. Setting up hemispherical imaging tool. Software is used to analyize hemisphere photo data.