Summer Branch Drop

This pecan couldn't hold the weight of this third of its trunk anymore. It did have a narrow branch union and a bark inclusion (bad structure).
This pecan couldn’t hold the weight of this third of its trunk anymore. It did have a narrow branch union and a bark inclusion (bad structure).

It has been hot and dry recently with no major storms to speak of, so why have we been so busy cleaning up “storm damage”? That question has been asked since at least the 1880’s, and unfortunately no definitive answer has been found. On calm hot summer days large branches will fall out of trees for no apparent reason, a phenomenon known as summer branch drop or sudden limb drop. Many of these branches appear to be healthy with no signs of decay, insects, or poor structure. They drop without warning, and unlike with snow, ice, or wind there seems to be no predictors.

Summer Branch Drop

Summer branch drop can affect a large number of tree types including but not limited to Maple, Elm, Ash, Oak, Pecan, and Walnut all of which we have seen recently. Mature trees are usually affected most by summer branch drop, and may drop branches as large as a meter in diameter.

What we know

  • Leaves and fruit add weight in summer increasing strain on the branches

    Summer Branch Drop
    From this angle you can see how large the limb was. Removing load from the top with reduction cuts could have possibly prevented this break however there would have still been structural issues with the trunk. (included Bark and narrow branch union)
  • Hollow, decayed, and poor structure increase the possibility of breakage
  • Very long branches (protruding from the canopy) have higher risk of breaking

Breakage is likely to increase when any and all of these factors are added, but these do not account for all cases of summer branch drop.

What may contribute

  • Under calm conditions transpiration may be reduced due to high humidity in the canopy, there by increasing the water load (weight) of branches
  • Reduced transpiration and increased temperatures may result in stress induced ethylene production which erodes the cell wall cementation
  • One of more of these reasons in combination with the previous list is mostly likely the cause

The main reason limbs healthy in appearance break is unfortunately speculative due to lack of research. A certified Arborist can identify some or many risks but unfortunately we may not be able to address them all.

What can you do

  • Call Wellnitz Tree Care
    • We can tell you where potential defects may be and help mitigate risks
    • We can also prune long limbs to reduce load forces minimizing the risk of breakage
  • If you think your tree might be at risk
    • Avoid parking under it
    • Don’t place picnic tables or other structures under it
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