We have gone from record drought to record amounts of snow and rain throughout California. While the winter storms have wreaked havoc on our infra-structure (Oroville dam spillway, flooding in San Jose, etc, they have been a blessing for drought starved trees throughout the west. Years of inadequate rainfall reduced soil moisture leading to an incredible dieback of trees numbering over tens of millions within the state.
The urban environment creates stresses not normally encountered in the wild. In cities and suburbs, trees contend with confined planter area, compacted soils, improper or inadequate irrigation, poor maintenance practices, improper pruning, shading by homes or buildings. Stresses created by the urban environment reduce tree life expectancy, sometimes by as much as 50%.
During the drought, I have seen an increase in tree failure, whether a limb drop or whole tree failure. In most instances, crown, limbs, branch and twig dieback were the obvious symptoms of the drought. Many times, clients mistakenly thought the dieback was caused by disease or insect, however root dieback from minimal soil moisture was the cause of crown dieback.
Now, with the heavy rainfall and wind, tree failure due to saturated soils are on the increase. Trees remain upright due to their root system. Structural and buttress roots grow outward from the trunk at the (root crown), out to the edge of the crown (known as the dripline). At the dripline, the structural roots are 1-2″ in diameter. They continue to grow outward, branching into the small, fine feeder roots that absorb moisture and nutrients. Depending on local conditions, tree roots may extend 1.5 times the tree crown diameter. Based on San Diego soil conditions, most roots grow within the upper three feet, typically 80% of the roots are within the top 18-24″ of the soil.
Roots in dry soil are held in place by friction. However, when rain saturates the ground, it acts as a lubricant, lessening the soil friction holding roots in place. When wind combines with excess weight from rain or snow, the energy is transmitted down the trunk to the roots. Soil root friction reduced by saturation causes roots to loose anchorage, resulting in a failure. When roots fail to support the tree, it is assessed as a root failure. When the entire root ball rotates up from the soil, it is a soil failure.
Homeowners with large trees in close proximity to their property should examine their trees for any change in condition as a warning sign of a potential problem. Changes to be aware of include:
- Is the tree leaning?
- Are there soil cracks at the base of the tree?
- Is the soil lifting, tilting or rippling at the tree base?
- Are there dead limbs or branches in the crown?
- Is there a progression of twig, branch and limb dieback?
- Did the tree drop it’s leaves abnormally early?
- Did the tree not leaf out as in the past?
- Any obvious open cavities, cracks or splits?
- Any animals or insects nesting within a hollow, cavity or crack?
- Any fluids, abnormal sap flow or other discharges from the tree?
- Has irrigation been reduced or eliminated to the tree?
- Has there been construction activity near the tree?
- Have the roots been disturbed by any nearby utility or sidewalk work?
- Is the tree sitting in water, is there proper drainage?
- Has there been a change in grade near the tree?
If you can say yes to any of the above, your tree may have acquired defects that increase the risk of failure. The increased risk of failure may result in property damage or personal injury to your family, friends, or any pedestrian near the tree. A tree with a history of previous failures possesses an increased risk of failing. Trees may not present any obvious signs or symptoms of a defect. Unseen decay may exist within a limb or trunk, or as a root rot.
Whether commercial or residential property, if you are concerned about the health and safety of your trees, you should contact an arborist certified by the International Society of Arboriculture, (ISA). Once certified, the ISA allows arborists to enroll in specialized training to earn the credential of a Tree Risk Assessor Qualified. While anyone may attempt to assess the health and structural integrity of a tree, certified arborists who are qualified in tree risk assessment represent the industry standard and best management practice for tree risk assessment.
Tree risk assessment is the current best management practice to determine tree risk of failure associated with defects. The assessment utilizes a level two basic visual assessment and a two page ISA format for the assessment protocol. The assessor may determine more advanced assessment techniques are required, however usually a basic visual assessment will suffice.
If you have noticed a change in the health or condition of your tree, take proactive measures before a catastrophic accident, call a certified arborist knowledgeable in tree risk assessment.
Click here to read an article published in the LA Times Risk Assessment article.