Sharp temperature drop can impact trees

This is the second year in a row where portions of Kansas suffered a quick drop in temperature after a warm fall.  This happened late in October.  Unfortunately, some trees may not have been hardened off before this happened.

Trees not hardened off are those most likely to be affected by this sharp drop in temperature.  The first sign that a tree has been affected is marcescence which simply means the leaves don’t drop right away.  Leaves don’t drop right away because they didn’t have enough time to develop an abscission layer at the base of each leaf that allowed it to fall. Though marcescence itself does not harm the tree, it is a clue that further damage may have occurred.  Trees that exhibit marcescence may be perfectly fine, but it will take time to tell. 

It is possible that trees that show evidence of marcescence, may also have suffered damage to the living tissue under the bark. The sharp drop in temperature can damage at least a portion the phloem and the cambium. The phloem carries food made in the leaves to all parts of the plants including the roots. The cambium produces new phloem.  If the phloem and cambium are killed, the cambium cannot produce new, living phloem, and, therefore, the roots don’t receive the food needed to survive and eventually starve to death.

Trees so affected will not die immediately since a healthy root system has stored energy reserves that it can use to keep the tree alive. When those reserves are depleted, the tree will die very quickly.  Usually this occurs during the summer following the year the damage occurred.

Does this damage affect water flow in the tree?  Actually, it does not.  Xylem is the structure in the tree that carries water from the soil throughout the plant.  The reason the tree can still distribute water to the top portion of the tree is due to how a tree grows and, specifically, how xylem works.  Even in perfectly healthy trees, most of the xylem is dead. Portions of this dead xylem forms hollow tubes that carry the vast majority of water and nutrients throughout the plant. Though there are living xylem cells, the contents of those cells make them inefficient in moving water. Therefore, the functional portion of the xylem wasn’t hurt by the freeze because it was already dead. Since this xylem system still works and provides water for the tree, the tree can live for quite a period of time until the roots starve.

Remember, trees with marcescence may be fine.  Even if there was also damage to tree tissues, it all depends on how much of the living tissue under the bark was killed. If only a small portion is killed then the tree will recover. If the entire circumference is killed, the tree will die and there isn’t anything that can be done. Any portion of the trunk where the bark comes off and the underlying layer is brown, is dead.

What to do

Since we don’t know the extent of the damage, if any, we need to insure there is no further stress.  Primarily, that means to water the tree as needed.  This fall continues to be very dry for much of the state.  Keep the soil moist but not waterlogged until freezing temperatures are here to stay.