11 Jul When you look up, it’s time to think down.
What happens in the canopy of the tree is usually related to what is happening to the roots underneath the soil. Now that we are moving into July and the heat of the summer in Minnesota, root issues with trees will be start to be identifiable by examining the canopy of trees.
When leaves turn fall colors in July it is not a sign of an early winter. It is a sign that something is restricting the trees ability to photosynthesize. Oranges, reds and yellows appear in leaves when the green of chlorophyll is gone. With less chlorophyll, photosynthesis is reduced and therefore the trees are not able to create the necessary metabolites they need to grow and survive.
Other signs of photosynthetic stress are illustrated by trees have smaller leaves or needles than are typical. Additional symptoms are loss of leaves from the inner portions of the canopy and chlorosis; the leaves being a lighter green-yellow than normal.
(Figure 1) This Autumn blaze maple has been in a state of decline for several years.
All of these symptoms are observed on trees during severe multi-year droughts. So a connection of these symptoms with root water availability is accurate. But, unlike trees surviving drought conditions, when it appears on otherwise “healthy” trees just increasing water availability is not going to help the trees recover. This is the same scenario with nutrient availability. Although the symptoms are similar, fertilization, just like watering, is not likely to help. There is frequently another condition, or conditions that are exacerbating the problem.
Conditions that create the symptoms
Damage to the root systems of trees is commonly attributable to making changes in landscapes. Putting in a new driveway, expanding the deck or creating a boulder terrace design for the backyard can all impact existing tree roots.
The majority of “feeder” roots, those used for water and nutrient uptake, are in the top 12” of soil. In clay soils, common in the Twin Cities, these roots are primarily in the upper 6” of soil. Any building activity that either cuts into those roots, compacts the soil around those roots or adds more soil to cover those roots will damage those roots. The extent of damage can be mitigated by planning ahead of time to protect the roots. The larger the root protection zone around the tree, the better.
After the fact, soils impacted by construction activities can be remediated using soil amendments to create a better environment in which replacement roots can grow. But, the loss in roots due to the construction will take years to recover to get back to what they were before.
Roots and trunks are not compatible. If a root grows into trunk tissue the two tissues will not graft. They will grow into each other and cause compression in both sets of tissues. This compression can lead to tissue death and can cause a restriction in nutrient and water uptake. While this is incompatibility is not a common occurrence in natural settings, it can be a problem with nursery grown trees that are transplanted into landscapes.
When trees are grown in pots or other artificial products, the roots will grow out as they do in nature, but will be forced to circle once they hit the edge of the container. While not an issue in the nursery, or for that matter for the first years of the trees in the landscape, it will become an issue if those roots remain. As the trunk of the tree and the roots expand and grow, there will inevitably be a conflict when they come into contact. When they do come into contact the compression will begin, until the roots will girdle the trunk tissues of the tree restricting the transport of water, nutrients and photosynthate.
This systemic decline of the tree due to “stem girdling roots” is usually discovered when the trees have been planted in the landscape for around 10 years. That’s how long it takes for the trunk to grow out to the circling roots. It is often misdiagnosed as a water/drought condition or a problem with the nutritional content of the soils. When decline is first noticed the problem can be diagnosed by simply using a shovel to dig around the base of the trunk until you find the “trunk flare” and “root collar” of the tree.
(Figure 2) Note the flare of the trunk as it enters the soil. Trees should always have a flare exposed above ground. If it isn’t obvious then it is necessary to dig down to determine how deep the tree was planted and to examine the roots.
A healthy root and trunk interface has roots radiating out from the trunk. An unhealthy root and trunk interface has roots curving around the trunk.
(Figure 3) This is the same Autumn blaze maple as in Figure 1. Notice the arrows showing the concentric rings of girdling roots after a diagnostic excavation. More girdling roots may be hiding under the top roots.
For stem girdling roots on established trees, an excavation of the soil around the trunk of the tree is needed to ascertain the extent of the problem. When it is determined that a tree can be saved, then the circling roots can be surgically removed and treated to prevent them from growing again. At that time a soil amendment is applied to the exposed soil to encourage the growth of adjacent non-circling roots. By the time significant decline is identified, the root problems can be too significant to be remedied.
Figure 4. If girdling is too severe, then it may not be possible to surgically remove the impacting roots.
So the next time you look up and notice early fall color or canopy issues with trees on your property, think down. Remember the old adage, “As go the roots so does the tree”.
Dr. John E. Lloyd, Ph.D. is President of Plant Health Doctors, LLC in the Twin Cities. He provides his blog to Ostvig Tree Care as a service to educate clients and practitioners in the maintenance of healthy trees and landscapes. He can be contacted through Ostvig Tree Care at info@OstvigTree.com.