Leaflet, Winter 2015 - Why Did My Tree Fail?
Monday, March 23, 2015
by: Peter Green, Plant Health Care Manager, Four Seasons Tree Care

Section: Trends and Tips

Leaflet, Winter 2015 – Why Did My Tree Fail?

Welcome to the fourth issue of “The Leaflet,” yet again researched for you by Peter Green, Four Seasons Tree Care's scruffy Tree Health Manager. Our goal is for each Leaflet to be concise, yet highly informative, as we explore the various tree issues you may encounter here in San Diego. This will be a brief look at some of the reasons trees fail.

The Tree: Your large tree that fell over or split in two.
The Problem: Too large, heavy, old, and poorly structured.
The Treatment: Choose the correct tree for the site and improve structure through appropriate pruning.

This time of the year, we frequently send out work-order crews to pick up failed trees. Some of these trees fail at ground level because of root decay, and some fail because of poor root development. These are problems that we might not have noticed prior to failure as the defect is hidden underground.  

Then there are the failures that happen above ground – large limbs that split off the tree. These are usually structural problems, where the branch attachment point is not strong enough to hold the large branch that grows heavier each year. Weight reduction pruning can decrease the chances of this happening. Or, more simply and cost effectively, have the trees structure pruned at the time of planting. 

Most structural flaws were on the tree at installation. These structural flaws usually stay with the tree until it fails many years later. A well trained arborist could fix a lot of future problems with some early pruning. Unfortunately, we are often told that an untrained landscaper will be “caring” for the tree until it is over 15 feet tall. Early poor trimming leads to over-raising, multiple leaders, and poor aspect ratios between trunks and branches. When branches are the same size as the trunk they have a high likelihood of failure. When a tree is mature, large pruning cuts leave wounds that are excellent access points for decay organisms. When trees are small, we can make small corrective cuts that tend to heal well and don’t lead to massive amounts of decay. 

What I am proposing is structural pruning to promote strong central leaders and reduce the chance of future failures. This work needs to be performed in the first year after planting. Have an objective when you have any of your trees pruned: promote good structure, do not cause harm, and question the function of arbitrary tree pruning!

Thanks for reading!  
~ Peter Green, Plant Health Care Manager, Four Seasons Tree Care