Revised German Tree Care Standards Outline Use of New Cabling Systems.
Tree Mechanics Research Guides Change in European Standards.

The ZTV Tree Care Standard (Zusaetzliche Technishe Vertaragsdedingungen und Rechtlinien fuer Baumpflege) was first published 25-years go in Germany, to provide the first definition of general standards for tree care in much of Europe. Through collaboration with practitioners, researchers and arboricultural experts, the standards have undergone five revisions, with the latest in 2006. This evolution in the standards reflect changes in arboriculture that have resulted from ongoing research.
The ZTV guidelines are broad and comprehensive. They include: tree diagnosis methodology, pruning practices, cabling and bracing, root care, alterations of a tree’s environment, to name a few, summerized of course by an outline for implementation,. The latest revisions to the ZTV reflect many of the advancements in cabling systems, such as the use of dynamic cabling and tethering systems. The guidelines also provide useful tables to assist in the proper dimensioning of each type of cabling system. Many US based tree experts have expressed great interest to German tree mechanics experts in this specific aspect of the ZTV. Following is a brief summery of tree cabling concerns as outlined in the ZTV.

The ZTV classifies cabling systems into 3 categories: static, dynamic, and support/tethering.

Static systems were traditionally described as invasive systems that required threaded steel rods to serve as anchors in stems or limbs. Today, static materials, such as steel cables and high strength synthetic ropes, can be connected to non-invasive anchors such as belts and slings. Static systems are used as a reactive measure where loads require constant support. One example from the ZTV is: “.where branch unions are cracked or compromised and have an acute risk of failure” It is noteworthy that, due to their limited reliability, J-lags were not included in the guidelines.

Dynamic systems are described as non-invasive systems, comprised of single or multiple components produced from engineered materials and designed with specific elastic qualities. The ZTV states that the material’s elastic qualities “do not constrain movement but rather slow down oscillations and therefore prevent breakage”.
Depending on the requirements of the installation, different materials can be used,. Higher strength cabling material is less elastic and may require additional shock absorbing components to accommodate the movement required to dampen oscillations.
The ZTV stresses that dynamic cables are not designed to support constant loads, but rather to prevent the peak loading of failure-prone limbs. Dynamic cables are intended to compliment the bending strength of limbs and are therefore to be dimensioned significantly lighter than static cables.

Support/Tethering systems are a new addition to the 2006 revision. These systems are designed to tether a limb to a tree and prevent it from falling to the ground once a failure has occurred. These installations are used under special circumstances, where neither pruning and/or cabling are an option. Tethering systems utilize static cables installed in a near-vertical orientation. The system must be designed with sufficient strength to support the full limb weight.

The ZTV guidelines describe the use of pruning and cabling, or a combination of both, to minimize the need for invasive actions. Research into tree statics has yielded new insights into the cumulative effects of pruning. The safety of a vertical limb can be significantly increased by a slight reduction in height. This results in an obvious reduction of the lever length as well as a reduction in crown surface area. The reduced crown is less exposed to increased wind velocities found higher in the wind profile. Height reduction also changes the natural resonance of a limb and can reduce low frequency oscillations that can introduce excessive bending forces and cause failure. Dynamic cabling combined with light pruning can be utilized to maintain the maximum photosynthetic area in trees that may otherwise require heavy pruning to achieve an acceptable margin of safety. When dealing with old historic trees or species that are poor compartmentalizers, heavy pruning is not often an option.

The ZTV standards reflect the advancements in tree care practices, as defined by ongoing research in Germany. Since their introduction approximately fifteen years ago, synthetic materials used in cabling systems have proven to be an effective alternative to traditional materials. They provide more options for traditional support systems and allow for new strategies for the care and preservation of trees. The 2006 German ZTV standard is an excellent source of arboricultural information and deserves a prominent place in every tree care professionals reference library.

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