Frozen treetops. Photo by Valerie West.
At first it was pretty. Snow in February, excited kids, a good time to stay inside and watch the flakes fall softly to the ground. Then it didn’t stop, and it got colder and colder. Soon you couldn’t get out of the driveway, pipes were freezing or worse — they were breaking. It lasted for a week rather than the day or two that most folks in Louisiana have come to expect from our rare winter snows, and people weren’t the only ones caught off guard. Many tree species were set to start putting out their leaves in anticipation of the upcoming spring weather when this cold blast hit. Like the pipes in our walls, many of those trees suffered some damage to the “pipes” that carry water and nutrients inside the tree.
So, what do I mean when I say the tree’s “pipes” froze? If you could look at the inside of a tree branch you would see the rows of cells that move water and nutrients around the tree. These cells are called the xylem and phloem and are in every twig, branch, stem and root on the tree. Xylem transports water and nutrients from the roots to the top of the tree. Phloem transports the energy created by photosynthesis in the form of sugars and starches from the top of the tree down to the roots. These rows of phloem and xylem cells are just inside the bark layer. If you go to the very end of the smallest twig on the tree, there is a thin layer of bark or epidermis. This layer is so thin that it cannot insulate the “pipes” just beneath it. As you move further down the limb, as the limb gets wider, so does the layer of bark. The thicker the layer of bark, the better insulated the “pipes” are from frost damage. When the tree gets ready to put on leaves in the spring, the activity in the xylem and phloem increase. The more active these cells are, the more water they have inside them. So, just like the pipes in our homes, when the “pipes” in the tree froze, some of them broke because they just didn’t have enough insulation from the cold.
Now, we had several hardwood tree species that were getting ready to put out their spring leaves. These are the trees that were damaged the most. This group includes native trees like black oak and post oak as well as nonnative trees like chinaberry and Chinese tallow. Evergreen trees such as live oaks had some frost damage to leaves but not twig and branch damage. When the weather adjusted back to springtime normal, these damaged trees could be spotted easily in the landscape. They were the ones without any leaves. If you were patient, leaves did eventually appear, but not where you expected them to. Many of these species began to leaf out along the main branches and tree trunks rather than at the ends of their branches. For most trees this will help them to generate enough energy to repair the internal damage, and by the next year they should be almost back to normal.
This is not always the case. Some trees put out leaves and then within a few months the tree suddenly turned brown and died. Damaged trees may have had enough energy to put out new leaves, but if they have an unseen condition, such as root rot, they don’t have enough energy to fight off infection and repair freeze damage. As a result, they die. Landowners should be observing any freeze damaged trees on their property monthly to make sure that they are still fighting back. If your yard tree has lost the battle, contact your area extension agent for a list of licensed arborists to help you safely remove the tree from your property. If dead trees in the landscape are located away from structures and are not a hazard to the homeowner or property, they can be left for wildlife habitat.
If you have any questions about your yard trees after the storm or would like an extension agent to come visit your property, contact your local LSU AgCenter office and an area horticultural agent or forestry agent will be glad to help.
Left, tree is trying to recover from freeze damage. Right, tree is dying from secondary issue after freeze damage. Photos by Valerie West.
Valerie West is a forestry extension agent in the LSU AgCenter Northwest Region.