Within the last month, back to back Hurricanes Florence and Michael have created stress on communities throughout our state and across the Southeast. While the loss of life and livelihoods are always of primary concern, many people have also had to deal with downed or broken trees and the resulting cleanup. However, less noticeable to the broken stems and branches is the effect that storm winds may have by stripping trees of foliage and causing root damage.
Following Hurricane Florence, some trees (and other plants) are exhibiting a strange response. Although we expect hardwoods to be dropping their leaves this time of year, many damaged trees are instead growing new leaves. In addition, some spring flowering trees are flowering now… in the fall. Several different species are exhibiting this growth including Bradford pear, black walnut, flowering dogwood, and the black gums. Particularly noticeable, in the areas that received the strongest winds is the occurrence of new growth on the north or northeast side of the tree with old foliage on the opposite side.
What is causing this response? As we approach autumn, most trees have fully formed leaf and flower buds that have already been set in anticipation of next growing season. The normal yearly processes include periods of shortened daylight and cooler temperatures. The physiology of plants is adapted to these annual cycles, causing plant growth and flowering to occur when we expect.
However, a less understood mechanism under which plants may grow leaves or flowers is stress. Often, we think of stress on plants as being caused by drought, a late frost, or some similar type of situation. However, in the case of our recent hurricanes, trees were stripped of their leaves after the buds were prepared for the next year but before the leaves had shut down their normal processes. This stimulates bud break and the initiation of foliage and flowering, events we typically expect in the springtime. The refoliation response is meant to keep up the mechanisms involved in moving substances to the roots in preparation for winter while flowering may result in seed to continue the species even if the parent tree dies.
Is there anything that can be done? Many of the processes associated with the tree responses mentioned are poorly understood and raise several questions. Will the tree have time to set buds again before winter? Is the tree going to flower in the spring as normal? Are root reserves being used to grow additional foliage thereby weakening the tree? All of these are valid questions, and all of these will have some bearing on next year’s growth. As an example, tree growth rings have been used to pattern hurricane occurrence in the Southeastern United States. These growth rings show variation related to the severity of hurricanes. But, these trees were still alive many years following the storms in question.
The best course of action is to monitor your trees. Most likely, the tree will survive although it may exhibit different growth patterns next spring as compared to most years. These changes could include later formation of leaves and less flowering than normal. In more severe cases involving extensive foliage loss and/or root damage; the tree could succumb to insect and disease organisms that often strike weakened trees.
At the end of the day, don’t stress yourself! The best course of action is to make sure your tree has the resources it needs including adequate water and nutrients. Continue monitoring your tree throughout the coming winter and next growing season and seek help from the N.C. Forest Service and other tree care professionals should you notice problems.
Doyle, Thomas W. and Lance E. Gorham. (1994). Detecting Hurricane History and Effect From Tree Rings. US Dept. of Interior: National Biological Survey, Research information Bulletin 48.
Duryea, Mary L. and Eliana Kampf. (2017). Wind and Trees: Lessons Learned from Hurricanes. University of Florida IFAS Extension, FOR 118.
Takeno, Kiyotoshi. (2016). Stress Induced Flowering: The Third Category of Flowering Response. Journal of Experimental Botany, Vol. 67 (No. 17). Pp. 4925-4934.
Wargo, Philip M. (1991). Remarks on the Physiological Effects of Defoliation on Sugar Maple and Some Impacts on Syrup Production. U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station. Gen. Tech. Rep. NE-147, Pp. 241-250.