Tree rigging is the art of dismantling parts of or whole trees using ropes, blocks and pulleys. It can range from large pieces of timber to awkwardly shaped branches and tight drop zones where damage has to either be kept to a minimum or eliminated entirely. Tree rigging is possibly one of the most complex of all tree working situations and can involve a vast range of knowledge on subjects such as physics, wood properties, equipment ratings, rope strengths and good working communications between a wide range of staff members.
Basic tree rigging
Tree Rigging can be as basic as throwing a rope through a branch union and attaching it to the branch to be removed. Ground persons then hold onto the tail of the rope and the tree climber/arborist cuts the branch off and it is lowered down to the ground by the grounds person. This tree rigging technique is as old as arboriculture itself and relies on a fit and strong grounds person (to hold the weight of the branch), and the climber being able to judge the weight of the wood in relation to the strength of the rope. This technique however also adds in variables that are hard to account for – how much force the grounds person is applying and how much friction is being applied to the branch union by the lowering rope.
High end tree rigging
The opposite end of modern tree rigging is the use of HMPE (high modulus poly ethylene) ropes with no stretch, almost frictionless pulleys installed in the tree, lowering bollards with capstan winches to apply up to 44:1 tension and dynanometres hooked up to laptop computers than can work out the forces and angles involved to enable clinical removal of branches or tree parts over ground or property that cannot be damaged.
Tree rigging techniques
The skill for the modern tree worker is to select a tree rigging technique that sits on a sliding scale between either one of the above techniques – there are many ways to crack an egg, as the saying goes. The tree worker must be aware of the huge forces that can be generated in tree rigging by removing and dropping wood via ropes and that all this force must go somewhere, it never just disappears. It can change into either heat or sound. Lowering too quickly and branch sections that are too heavy can cause ropes to melt and lose strength, or in the worse case the tree can fail, causing a snapping, breaking sound. Due to the dizzying array of modern techniques available to the modern tree worker, these failures can be almost be eliminated but require the correct training and application for safe tree rigging removals. Removal techniques now span from the straight dropping of branches on rope to remote speedlines that can span huge distances and allow the ground workers to limit ground work with heavy wood/branches.
It must always be remembered though that every tree rigging situation can be made as a complex or as simple as the team are happy with, and that that can bring along more potential risks to all involved. Modern tree rigging primarily uses the tree itself and the ropes as huge shock absorbers that dissipate the forces generated. When trees have structural issues this has to be accounted for and sometimes tree rigging will have to give way to a crane, hi-ab or helicopter. But with forethought, correct application of gear and techniques and teamwork, tree rigging has almost endless opportunities for safe and efficient lowering of branches and timber from trees.
The Myth of the Rigging Ropes (Andreas Ross)
Friction Devices for Arboricultural Rigging (Andreas Ross)
Rigging with the Port-a-Wrap (Andreas Ross)
Rigging with the Good Rigging Control System (Andreas Ross)