Wraps Vs Bolts; Pros and Cons
Some adventure park builders claim very vocally that wraps are more ‘ECO’ or ‘green’ and they dont ‘hurt’ trees, these claims generally have their roots in eco marketing and are not showing a full picture. Unfortunately these claims are easy to assimilate because nobody in out to intentionally harm trees, and on first glance it seems true.
To really begin to understand this issue we must consider the effect over time. Trees live long and do things slowly, it is a mistake to compare a drill hole in a tree to a puncture wound in your body.
To be clear , there is no real right answer. Adventure Developments can use both methods, but if your ropes course is a permanent installation (to be in situ for more than 3 months), you prefer minimal ongoing maintenance and quality control costs, and value the health of your trees we generally recommend bolts.
Some pros / cons
1. Quick (drilling a large tree at height can take some time, and effort)
2. Cheap (no specialist tools are required)
3. Adjustability (if you want to change the height of an attachment it can be done simply)
4. Inspections (you can see the wrap all around the girth of the tree, if its corroded its visible, a bolt may be rusty inside a tree)
5. If you plan to harvest your trees for high quality timber, using wraps will minimise markings and stains in the grain.
1. The surest way to kill a tree is to ringbark it. Tiny seedlings can punch through concrete slabs no problem, but if you wrap a piece of flimsy fencing wire around a tree and forget about it, thats a death sentence.
2. Wraps need to be maintained and adjusted. This is more true if you have faster growing trees. (Commonly wraps in eucalyptus will need to be adjusted at least 1 or 2 times per year with a torq wrench)
3. Because the wraps need to be adjusted often, installers commonly use wire rope grips to terminate the wire rope. (This is a perfectly acceptable method but torq on every nut on every termination will need to be checked according to the grip manufacturers recommendations and your susceptibility to unauthorised access and vandalism, as the tightness of a nut cant be checked visually like a swage or ferrule)
4. Tree protectors (These are blocks of wood used to minimise rubbing on the stem), can help by lifting the wire off the stem. These themselves can be moisture / fungus traps in humid climates. choose tree protectors which cover less of the total circumference of a trees girth.
5. Often misunderstood: The strength of a wrap relies critically on the relationship between the girth of the tree and the v formed by the 2 legs of wire rope where the wire grips cinch the wire. Our inspectors commonly see these installed poorly.
1. Modern arboricultural theory including Dr Alex Shigos CODIT (Compartmentalisation Of Decay In Trees) theory, would favour bolts for medium and long term installations in healthy trees every time, because there is less actual damage to the whole circumference of the tree and critically its cambium layer. The tree can actually defend against a bolt, and the wound is quickly sealed (when we put a bolt through a tree, there will be little chance of pulling out a day or two later).
2. Neat and uncluttered.
3. Requires less quality control processes for builders in the field. The minimum breaking strength of bolts is known and often marked on the bolt, all the builder has to do is select the correct sized nut and washer and torq up the nut. The installer of a wrap will need to select the correct components, then on completion accurately measure and record the diameter of the tree and the angle of the v formed in the legs of the wire rope, apply a formula to ensure that the wrap has been created properly. Improper installation of wraps results in greater forces on the legs of wire rope.
1. More expensive than a couple of meters of wire, especially when installation time is considered.
2. Requires specialist tools
3. The shaft of the bolt is hidden within the tree, so is not inspect able.
4. Drills can introduce pathogens directly into trees, and need to be kept clean. (This is especially true in tropical humid environments)