Trees can suffer from many different types of injury in flooding situations. In rapid stream flows, trees may be washed out. Soil may be washed away from the root system.
When soil is washed away from the Root Plate or Zone of Rapid Taper, the tree becomes susceptible to failure in winds. The Root Plate is the primary large roots coming out from the trunk and is the primary support of the tree in winds up to 40 mph. The approximate spread (radius) of the root plate is 3-6 times the trunk diameter at DSH (4.5 feet). In our compacted soils, 6 times is probably the better estimate.
|Tree Failure caused by failure of the root plate.|
When soil is washed away from the transport and absorbing roots, this will reduce water and nutrient uptake and wind stability with winds above 40 mph. However, the influence on a tree’s health and vigor depends on how much of the transport and absorbing roots were actually affected. Some minor loss will not be a problem for healthy trees. Refer to CMG GardenNotes #103, Diagnosing Root and Soil Disorders on Landscape Trees for a discussion on the minimum size of the Tree Protection Zone.
Another major type of damage in flooding is mechanical damage to the bark from debris in the water. When bark is removed down to the wood, it stops the flow of photosynthetic to the roots being feed on that side of the tree and the roots starve over time. As a rule of thumb, if bark is removed less than one-fourth of the way around a trunk, the damage is considered minor. If the bark is removed more than half of the way around the tree’s trunk, the tree is considered to be lost (having no value). This does not mean that the tree will immediately die, just that the future growth potential of the tree is bleak.
When water stands over the root system of trees, roots will suffocate over time. Some species (such as Prunus and Malus) and trees under severe stress are extremely intolerant of standing water. Most species will tolerate standing water for a few days (the likely situation here in Colorado). Some species are rather tolerant of standing water for weeks.