NuttyArb- Tree Failure

Tree Failure.

It is rare that a tree fails and it could be for a number of reasons.

Trees rarely fail on calm days (excluding summer branch drop)- mostly during strong winds- especially if the gusts come from unusual directions. All of the trees in this gallery failed during 70 - 80 mile an hour gales.

Very strong winds are rare in England. A tree is an efficient, self optimised structure. This means that a tree is not over-engineered, in the sense that buildings and structures are. No energy is wasted by strengthening in case of adverse conditions, it will simply grow to normal conditions or those that it finds itself in.

For instance, a tree growing in a forest will grow with the protection of surrounding trees. If those surrounding a trees are felled, then that tree will be exposed to very different conditions that its form is not designed for. Another example is a tree growing on a cliff will form its structure facing strong winds as the norm.

The storms of 1987 devasted many woodlands and parks of Southern England. The trees that failed were, generally, not the old decayed trees, but younger, vigorous trees. A number of factors combined to cause the mass failures of the trees. Autumn was late that year so many trees were still in full leaf. The strong winds brought a lot of rain. This meant that the ground was saturated, dramatically reducing the friction of the soil. Therefore, the trees had a high sail factor, with strong winds and little grip for the roots to anchor the trees.

There is around three deaths per year directly caused by trees failing. This works out to be approximately 1:20000000 chance. H&S risks deems 1:1000000 to be low risk. When conducting tree inspections, it is important to assess a tree accurately and in relation to its local conditions. It is not possible to inspect a tree in relation to adverse condtions such as gale force winds.

Tree Failure.

Tree Failure Gallery