All organisms found on earth eventually die. Lifecycles can be as short as hours or as long as thousands of years. One of the longest living organisms on this big blue ball is the tree. It can live for decades, centuries and in some cases even millennia. Trees are useful in an uncountable number of ways: they provide beauty, habitats, ground control as well as environmental and emotional benefits to humans. Certainly, man has found an affinity toward trees!
Unfortunately, not all trees live to their full genetic potential. They cannot get up and move when their environment changes for the worse and must survive the many stresses that are brought their way. If these stresses are not addressed it can eventually cause a mortality spiral and death. Some trees are planted with the goal of a shorter life aka for harvesting their wood but generally, our goal is to prolong the life and maximize the benefits we receive from trees. In order to accomplish this we need to come up with a plan of stress reduction. I have listed some of the stresses that trees might face throughout the course of a year:
Fungal or bacterial attack
Root zone soil compaction
Each major incident that occurs during the life of a tree will cause a biological response that consumes some of its stored energy. If a tree suffers multiple events in a relatively short period of time (this could be within several years of each other) it can cause serious decline of the tree. Some events are so stressful that a tree will decline quickly or die (ex: storm damage).
Most Common Stresses
Man Made Stresses
As we attempt to alleviate the stresses a tree may be experiencing we need to ask ourselves which of the stresses are the most serious? In my work as a professional arborist here in southeast Idaho I have noticed that approximately 75% of the trees that die in our area die from two main reasons:
Mechanical injury to tree trunks from mowers and lawn trimmers
Root crown or collar rot from improper tree planting depth
Both of these problems are man-made, needless, and completely correctable!
Root Crown Rot
My main goal while discussing this subject is to provide methods to diagnose and eliminate root crown decline.
The root crown is where the trunk ends and the root system begins. The trunk of the tree is from the top of this root crown and up along the main stem until we reach the scaffold branching. This is a very critical area as it pertains to tree health because this is where the main body of the trees vascular is housed. The vascular system in the trunk provides the highway for the movement of water, nutrients, carbohydrates and sugars throughout the entire tree, so any damage to the tree in this area has more impact than any other.
When a tree is young it soon begins to develop a buildup of wood at its base, this widening of the base is known as the root flare. The tree causes this to happen due to a strengthening reaction from its exposure to wind. Locating and positioning the root crown is a little easier if we know that it is right at the bottom of the flare. When we plant a tree, it is important that the root crown at the base of the root flare be placed slightly above soil level to ensure that the entire trunk of the tree, including the root flare, is above ground (see planting diagram). Finding the root crown before planting may require excavating lightly in a balled and burlapped or potted tree to locate the base of the tree flare and then ensure that it ends up slightly above soil level when planting the tree.
Image from Pacific Northwest Chapter of the ISA
Planting Too Deep
Planting at the right depth is important because no part trunk of the tree is meant to be below soil level, especially in a very wet environment. When a tree is planted too deeply soil or mulch surrounds this area and cause a chronic condition of fungal or bacterial rot to begin and eventually kill the cambium or live meristematic tissue of the tree just below the soil surface. In other words, root crown rot strangles the vascular system tissue that is necessary for the tree to function.
What can I do if my tree is already planted to deep?
Any tree can be inspected for root crown rot by observing if the root flare is visible above the soil level. If little or no root flare is observed, it is likely that the tree has been planted too deeply and needs attention. Carefully excavating all soil or mulch next to the trunk will reveal the location of the root flare. Keep in mind that sometimes root flares can be located as many as 8 to 10 inches below the surface which will pose a serious problem in the future. The trunk below soil level will appear to be soft and brown if root crown rot is present.
The simplest thing to do is to replace the excavated soil with a more coarse material such as 1 ½ “washed rock or gravel. The rock will allow water to drain and so will not retain as much moisture against the trunk. This procedure will be adequate in preventing damaging fungal organisms around the trunk due to the relatively dry climate of southeast. It should not be necessary to apply fungicides or chemicals to prevent problem once the moisture retaining soils have been removed and replaced.
How can I prevent future problems?
Root crown rot can usually be prevented by making sure that plant material is healthy and then planted at the proper depth. A mulched area surrounding the tree is an easy way to ensure that mowers or line trimmers cannot mechanically injure the trunk. Mulch should not be piled up around the trunk so feathering it down as you approach the trunk is a good idea. Finally, plants generally prefer to receive a good deep watering and then have a dry period of time to allow oxygen to reenter the root system. This drying out time is necessary in order to prevent drowning. Daily watering is not needed nor recommended.