Supporting weak structures
Why would a tree need supporting?
When trees are allowed to develop outside of a nursery or without formative pruning, they can develop features that are not biomechanically optimal such as included and non-included V-shaped unions. These unions between branches or stems do not form auxiliary wood fibres at the apex of the union, these auxiliary fibres consist of swirling patterns of interlocking fibres that provide additional tensile strength (Slater and Ennos, 2015). We do this to prevent a branch or tree from failing and causing harm or damage to people or buildings and to prevent the loss of culturally or biologically valuable trees and their habitats (European Arboricultural Standards, 2022). Also, at the same time supporting weak structures and preventing branch or stem failure will also prevent damage to the tree and loss of photosynthetic material from the tree. The loss of foliage bearing branches will result in a reduced capacity to produce energy required for growth and reproduction, whilst requiring more energy for defence and the production of wound wood (Hirons and Thomas, 2017). Exposure of sapwood and central woody tissue at the failure site will provide a vector for decay pathogens to colonise the tree requiring even more energy for defence, whilst potentially leading to decline of the tree (Schwarze et al., 2000).
How do we support trees?
There are several ways in which we can support a tree and stabilise a weak feature, these include:
Dynamic cabling, these are designed to reduce stress peaks on weak features by using rope systems designed to stretch (5-25% elongation) such as the cobra bracing systems, because they are dynamic, they require periodic inspection and may require adjusting. They are most effective when installed in the dynamic zone of a trees crown (where the most movement occurs) which is usually the upper half of the crown (foliage bearing area). There are several configurations depending on the need and formation of the trees crown.
Direct, this is installed between two branches or stems and only provides support in the direction of the rope.
Triangular provides support for the areas secured with the ropes and will reduce swaying in multiple directions. These can be combined to form multiple connections and provide greater support.
Ring or Floating systems only reduce the lateral swaying and is a less common system and can support multiple stems.
Static cabling utilises synthetic ropes or cables (steel wire) that do not stretch (less than 2% elongation) in the same configurations as the dynamic systems. They are installed under load which means having to use a tensioning system to pull the parts of the tree in to allow for instillation and are usually placed in the ‘static’ zone of a tree (lower half of the crown). All items that make up the system should be made of the same material so that the risk of electrolytic corrosion is reduced (European Arboricultural Standards, 2022)
Static bracing systems are made up of steel rods which are installed through weak unions to rigidly stabilise them. Although this method is very strong it does cause damage to the tree vascular system where the hole is drilled and will breach existing barrier zones formed by the tree as a response to dysfunction.
Propping uses ground-based support systems to provide large lateral branches with support from the underside and elevating tension stress on the apex of the branches union. These systems generally consist of a base plate to stop the support from being pushed into the ground, a rod, bar or post and a cup to support the branch. They are custom made for that tree and can vary in their construction material, which must be suitable for the expected load of the branch they will support (European Arboricultural Standards, 2022).
Video 1: Cobra Bracing system (Cobra, 2025)
