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.
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| 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.
