Summer Branch Drop

Several of our mature and healthy oak trees have lost branches this summer, not as a result of August’s storms but during calm, still, summer weather. Our Tree and Woodland Officer, Rich Murphy, came to see what was going on.

He told us that occasionally, apparently healthy and stable trees can lose quite large branches during the summer for no obvious reason. This is known as Summer Branch Drop Syndrome and while it appears to be associated with certain weather patterns, nobody really knows what causes it.

Some of our mature and apparently healthy oaks without their heavy summer foliage.

Summer Branch Drop is thought to be associated with calm, warm weather conditions following a heavy rain shower, a fair description of most of this summer’s weather. Just the added weight of the rainwater on the foliage of a tree in full leaf might be enough to trigger the sudden failure of a branch, especially if there is hidden fungal damage to the heartwood. Or, after summer rain, the high level of air humidity can slow up the rate at which a tree transpires from its leaves, and water pressure can build up inside the sapwood of trunk and branches until it, too, can trigger failure, sometimes quite explosively.

This year’s exceptional crop of acorns….

Rich Murphy also suggested that the enormous weight of this year’s bumper acorn crop might just have been the final straw, tipping oak trees with heavy, wet foliage or increased internal water pressure into the sudden loss of a branch.

As our climate changes and the weather becomes more extreme and less predictable, the park’s biodiversity may respond in ways that are unexpected and not always beneficial to us, the park-goers. Take care; stay safe.


2 thoughts on “Summer Branch Drop

    1. We call that tree the Lone Oak and it is fenced because the heartwood is rotting out. Tree Office Rich Murphy spent some time climbing around in its branches and came to the conclusion that it is no longer safe. It had become a favoured picnic spot for families with children so it was decided that a fence was the only option. I am afraid I don’t know if its condition will make it any more susceptible to Summer Branch Drop Syndrome.

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