Atmospheric rivers, saturated soil, high winds with gusts over 50 mph, flooding… These are terms we have heard almost daily from our local news. Added to this list is the ominous warning of tree failures. We are well versed in what causes trees to fail, but what I want to share with you, is how trees work to prevent falling over. Because contrary to popular belief, trees don’t want to fall any more than we want them to. So how do trees protect themselves from root failure? 

Trees start with straight roots
There is a difference between a tree that grew naturally and one that grew in a pot at the nursery. Trees in nature generally have no infrastructure to interfere with their growth.  Their roots are driven by the search for water and grow away from the trunk in a relatively straight line. Tree roots can extend way past the dripline of the tree and at least twice the distance the tree is tall (so a 50’ tree could have roots that expand 100’ in every direction!). This provides a broad base of support for the tree. Nursery-grown trees start out in a can and the risk is if they are left in the can for too long, the roots will hit the side and start circling, creating a condition known as ‘girdling roots’. If the circling roots are not cut out at the time of planting, they will continue to grow in a circle and can limit the root base for the tree, predisposing it to failure and/or other problems.  


Trees use their taproot for support when young  

Every tree starts with a tap root (a long root that extends downward) that provides stability while a sapling. You can see this when you pull up an oak seedling. However, most taproots don’t continue to grow ever more deeply. Some trees retain some sort of taproot, where the soil conditions allow growth, but deep soils lack the oxygen and nutrients that roots need to survive. In clay soils (which are predominant in Contra Costa County) the taproot on mature trees will die back the tree will and send its energy into producing horizontal or what is known as lateral roots.  


Trees establish sinker roots 

As a tree grows and adds more wood mass to its trunk and branches, it realizes it needs more support, so the tree sends down “sinker roots” which function just like it sounds.  Instead of growing horizontally away from the trunk, sinker roots grow down at an angle to anchor the tree to the ground. In this picture, the soil has been washed away, and you can see the sinker roots. Sinker roots can be found close to the trunk, usually a distance of 3 times the diameter of the tree. (For example, if the tree is 24″ in diameter (measured 4 feet up from the ground), you would find sinker roots within a zone up to six feet from the trunk). That’s why this area is known as the “structural root zone” because it is paramount to the trees’ stability that any excavation and /or root pruning be avoided. 


Trees use adversity to fortify their root system 

Every breeze, gust of wind, and storm imprints itself on a tree and the tree uses that knowledge to fortify itself against future impacts. Young trees use wind to strengthen their root system, adding bulk to existing roots that are the most buffeted by prevailing winds. Roots put on additional wood in a similar fashion as they do with their branches and trunks adding annual rings. 


Trees use stored energy to keep their roots healthy 

Trees produce food with their leaves through the process of photosynthesis and then allocate these precious resources to growth and maintenance. Trees are always on the lookout for the introduction of decay knowing how damaging it can be to their stability. The removal of too much foliage can shrink the production of food and limit how much a tree can spend on fighting insects and disease as well as decay. Our recent 3-year drought has had a major impact on the health of trees’ roots and is one of the factors we had so many tree failures this winter.  

In conclusion

As you can see trees work very hard to stay upright. The picture of this oak tree is a testament to a tree’s resiliency. Even though the supporting soil has slid away, the tree is doing everything it can to remain rooted in the soil and remain upright. 

If you are unsure about the root health of your tree or want to know how you can help your tree maintain its root health, just call our office and arrange an appointment with one of our certified arborists for a free tree inspection.