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14 Arbor Age / July 2014 www.arborage.com Simply put, the point of tree health care is to promote the health of trees. Easy, right? Except one minor point of contention — what do we mean by "health" and how do we know if we achieved it? These questions appear simple, but start to peel it back and this question becomes more diffi cult. The defi nition or, for that matter, even the existence of health has been a hotly debated topic by doctors, scientists and philosophers for thousands of years. To avoid getting into an existential debate on "The Meaning of Health," for our purposes here we will defi ne health somewhere between "a state of being free from illness or injury" and "a tree's ability to fulfi ll its genetic potential." Now, what data can we collect that would show if our actions as tree health professionals are making a difference? Before we get into that, fi rst let's defi ne another term. When we talk about human fi tness, we often use the terms "health" and "condition" interchangeably, but with trees these are two different things. Good health means the tree has all the air, water, light and nutrients it needs to perform photo- synthesis, grow and reproduce. Good condition means the tree is structurally sound and is a low risk to fail either partially or completely. A tree can be in great health but in poor condi- tion, and, conversely, a tree can be in good physical condition but if, say, the tree was suffering from chlorosis, we would say the tree has a health issue to address. Tree owners tend to col- lapse these two terms together, and can be surprised when an arborist recommends a removal for a tree seen by the profes- sional as in poor condition while the homeowner just sees green leaves and thinks the tree is fi ne. Assessing a tree's condition is most often done subjectively through various condition rating systems. Commonly these systems use a scale with "fl awless specimen" on one end and "dead" on the other. The number of increments on the scale will vary, and can be adjusted depending on the purpose. The International Society of Arboriculture's (ISA) version uses a 1-10 rating that ranks trees Excellent, Very Good, Good, Fair, Poor, Critical, and Dead. The ISA provides defi nitions for each category, making determination fairly simple. Other systems may use fewer categories, such as 1-4 rating, with 4 being "ex- cellent condition" and 1 being "remove." No mater how many condition categories are used, the most important factor for successfully using these systems is consistency, ensuring every evaluator is rating the trees the same. Certain condition criteria are readily apparent when sim- ply looking at a tree. Red fl ags such as splits, leaning, and large dead limbs are obvious, but other factors may not be easily seen. Using simple tools like tapping the trunk with a rubber mallet to detect decay cavities can be useful. If a more empiri- cal method is needed, more advanced tools, such as a Resisto- graph, can give you some real data regarding the thickness of the walls or the extent of a decay column. Other tools, such as a clinometer, can be used to measure not just tree height, but also the angle or severity of tree's lean. There are ways we can attempt to quantify a tree's health as well. Some measurements require specialized equipment or even a laboratory, but others can be simple. Observational rat- ing systems can be useful in quantifying health just as they were when addressing condition. A common leaf color-rating chart, fi rst developed in the 1970s, is a very useful system for visually assessing a leaf 's chlorophyll content. The scale goes PLANT HEALTH CARE PLANT HEALTH CARE B y B r a n d o n G a l l a g h e r W a t s o n All photos provided by Rainbow Treecare Scientifi c Advancements Quantifying Tree Health Observational readings are one way to measure results of trials.