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TRAINING TRAINING & EDUCA& EDUCATION Risk Assessment T Tree Dynamics and Why do trees move the way they do, and what does that mean for me and you? By Michael "House" Tain he subjects of tree dynamics and risk assessment are vitally important for every tree care professional. Industry profession- als do not have to look very hard to find a multitude of classes, audio-visual options,and books explaining the ins and outs of tree risk assessment; nor do they have to look far to see the results of risks underestimated, tree dynamics misunderstood, or hazards even unrecognized as the bodies and injuries pile up month- ly throughout the nation. In their simplest forms, tree dynamics is the way a tree moves and responds to forces both natural and artificial,and risk assessment is evaluating a given tree for the hazard it presents to civilians and tree care professionals.At times, both of these topics have been misunderstood or misinterpreted.In the case of risk assessment,the focus was often on civilians rather than the workers involved.Certainly the risk presented by a tree to the public needs to continue to be part and parcel of a risk assessment,but it is equally important that the folks who work upon it, and the forces they create, be considered as well. Although there is no substitute for hands-on field education, the basic principles and knowledge introduced here will help tree crews better understand not only what to look for,but why it is so important. Tree dynamics As mentioned,tree dynamics is the way the tree moves and responds to those forces that affect it.This may be due to natural forces such as being exposed to prevailing winds and developing stronger wood on one side of the trunk or the other in response, supporting/stabilizing roots, or even a particular canopy shape.An observant tree care worker will notice that a healthy tree uses its entire structure to absorb and dissipate the force of the wind,with all of its parts moving regardless whether they 14 Arbor Age / July/August 2012 are directly affected by the force.This same process holds true when arti- ficial forces are at work on the tree,a large branch removal will be reflected by movement throughout the canopy.Conversely,an absence of move- ment in a branch or a particular part of the canopy can be evidence of a disconnect from the tree's natural energy absorption system,such as decay, a hollow,or even a crack.The individual tree's system or dynamic should be taken into account prior to starting work,as it will provide excellent indicators on possible problem areas, and even dictate how the work should be carried out. An example of a structural failure in the scaffold section during an ice storm. Photo by Michael "House" Tain www.arborage.com