Why do tree branches fall?

Or in arborist - "why do tree limbs fail?" There are many reasons why we see broken, hanging branches - widowmakers - failed limbs, trees dropping LIVE limbs, losing limbs, or dead branches falling out of trees.

1. They over-extend the canopy. An ideal canopy spread provides ample protection for its limbs, but sometimes due to the growth circumstances and phototropism, certain branches will grow past the majority of the others, making it susceptible to failure. This is when we perform "end weight reduction" - by scrambling out to the tips of a limb and taking material off using proper pruning cuts, we reduce stress on the branch from things as simple as leaf and seed loads - to added weight from snow, ice, rain - weather in general.

2. Decay. "Inclusions" encourage decay, we can provide reductions and supplemental support to help keep included bark together (see previous TERMS blog for more on what this is!) - and reduce deadwood to keep Habitat - if possible - or entirely, to remove risk.

3. Species! Some species are just not meant to live here, and can become brittle and hazardous in the wrong climate. That doesn't mean the tree has to be removed! But pruning and management can help keep it around safely. For example, Mimosa trees are gorgeous, but in this climate (PNW) grow very fast - and that growth rate combined with their water content and structure add up to frequent branch failures.

4. An unfortunate possibility is - tree decline. A dying tree will often start to lose limbs, as decay sets in, or as branches become dead and brittle. This is also often species dependant. For instance, Birch are very soft trees that retain a lot of water, so they decay quickly and we often see dead or dying Birch trees dropping a lot of limbs. Look for centralized or top-down die-back.

5. Disease. Unfortunately, Emerald Ash Borer is ravaging untreated Ash trees, Dutch Elm Disease is doing to Elm - as well as a host of other diseases and fungal infections that are possible in our area. Many of these are treatable - and could save important trees. If you have a tree with a known disease, it's always best to treat it before signs of infection show up.

Regardless of why you're seeing die-back or limbs falling, it's not a bad idea to call an arborist! Falling branches are usually a sign of something, and there's usually something that can be done!