The recent strong winds we have been experiencing have lead to some significant tree failures.
In summer trees carry much more weight on their branches owing to leaf cover and water transportation. The leaf cover also adds massively to the wind loading on the tree. As a result, strong winds in the summer months can lead to limb failure or total failure from the roots. Total failure is called windthrow.
Weaknesses in branch attachments caused by damage, disease or poor structure will often be the point of failure. Sometimes small branches will fall from a tree and this may just be the trees mechanism for reducing the sail area of the tree. I.e. it sacrifices some to save the whole.
The photographs shows where an historic cut site has allowed a fungus to degrade the wood at an already weak branch union. The base of the branch rotted over time and the resultant branch failure took out the power lines to the village. The whole tree has been compromised by the extent of the decay and will have to be removed. However, two new trees are to be planted nearby in the autumn as replacements.