Last week a loud cracking noise disturbed the peace and quiet of a hot, still afternoon at St. Catherine's. Within seconds a large oak branch crashed to the ground, narrowly missing the Spirit of Place sculpture that stands at the entrance.
This occurrence had all the hallmarks of Summer Branch Drop (SBD). Once considered a rare event, anecdotal evidence now suggests, it may be more common than was first thought...
Mature or veteran oak trees, along with beech and horse chestnut, are particularly prone to shedding branches during prolonged heat waves or in calm weather, after heavy Summer rainfall.
Why, on windless hot Summer days, do branches showing no apparent defects suddenly and mysteriously crash to the ground? One theory is that when the demands for transpiration (water evaporation from leaves) overwhelms the tree's vascular system... the tree responds by shedding branches. Other theories include tissue shrinkage, internal cracks, difficult to detect rot, and/or ethylene gas being released inside the branch....but there are no definite answers. Consistent warning signs have not yet been established or confirmed.
Above is an image of where the branch split. The wood looks perfectly sound, and even with the most rigorous inspection, it would be nigh on impossible to predict, prior to the branch being aborted, that it would fail.
Liam, Woodland Ranger, is seen here cutting up the branch.
Waste not. Want not. More firewood for the Footprint log burner!
The brash will provide excellent habitat for wildlife. Hopefully it will provide cover for hedgehogs... numbers of which are, sadly, in steep decline
This veteran oak at National Trust owned Jenkins Field is adjacent to the A591 near Ambleside. A very busy road and the pavement is used by many walkers.
In successive years this tree has shed branches in late Summer. The evidence of one branch failure can be seen in the image above. The road was blocked on this occasion until the branch was cut up and removed; the police directed traffic while this was going on! Mercifully no one was underneath the tree when the apparently healthy branches were discarded.
The concern that the tree might abort yet more branches in the future prompted the National Trust, at considerable expense, to reduce the crown of the tree to ensure the safety of walkers and motorists in its vicinity. Close examination showed potential weaknesses in some branches so more pruning was done than was at first envisaged. In the image above a split branch and a cut branch next to it can be seen.
Overall the risks associated with SBD are small and even in hindsight the cause is usually a matter of speculation or an educated guess!
The National Trust carry out regular and thorough tree inspections. Identifiable problems, or quantifiable risks are dealt with as soon as possible.