The Spring Freeze: Observations
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June 6, 2007
"This White Oak still had lingering brown leaves - evidence of the freeze. "
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"Latest Observations... two months after the freeze."
In the article below, Richard Evans, Director, UT Forest Resources Research and Education Center, describes the effects on Plants, Wildlife, and Insects.
Plants
It appears that most of the spring freeze damage has run its course, and those woody trees and shrubs that were injured have compensated by putting on new growth below the point of most "girdling" freeze damage. Any above-ground damage should be apparent - dead tips and split bark being the most common.
It is a natural tendency to cut-out the dead tips, but there a few guiding principles that you should follow and conditions to look for, before you decide where to make the pruning cut. First principle, if the tips of the branches are dead, cut-out the dead portion to a point where there is a living branch. (You may want to reference "Tree Pruning".) However, the second principle is a little more complicated. If there is associated freeze injury, such as split bark below the obvious dead tips and some secondary live branches above the split(s), then other considerations come into play. This condition is most apparent on the Arboretum's azaleas, spicebush, crept myrtle, and some newly planted (young and tender) trees.
 
Some woody plants can overcome bark splitting, depending on severity of the split (the split's width in proportion to the diameter of the branch) and thrift of the plant. A good reference on bark splitting is UT Extension's "Bark Splitting on Trees". Referencing the Arboretum's spicebush (Lindera bensoin), the bark splits seem to be healing nicely (growing closed from the side's inward), so we have opted to make the pruning cut above the most severe bark-split, preserving some of the new growth of branches above this point and retaining some of the structural integrity of the plant. Also, we recognize that taking this tact may mean coming back later to remove more of the branches, if we misjudged the significance of the injury and the bark split continues to degrade. An alternative approach is to continue the wait-and-see process until the consequence of new growth and bark-split damage become more apparent. If the secondary branches grow strongly, and the bark splits heals-over, or nearly closes, make the pruning cuts at the junction of the first strong branch below the worst of the bark splits.
Damage to our woody plants is only one of several near-term and far reaching impacts of the late Spring Freeze of 2007. At the UT Forest Resources Center & Arboretum many of the research projects are tied to ecological conditions associated with populations of insects, mammals, amphibians, and birds. As observations are being made and data collected, there seem to be some interesting associations that are probably entangled in the ecological web of soil, weather, plants, and animals.
Wildlife
The most obvious effect of the spring freeze is in the amount of hard and soft mast (fruits, seeds, and nuts) available for our feathered and furry friends. As a result of the freeze, the flowers of some of our most important mast-bearing trees and shrubs were frozen - walnuts, hickories, white and red oaks, mulberries, hackberries, and many others. At this point there seems to be a real deficit in forest foods for wildlife, and how this condition will ultimately affect some wildlife species that rely heavily on mast is yet to be determined. Interestingly, some of the soft mast plants, blackberry and elderberry being the most notable, seem to have not only avoided freeze damage, but are actually setting fruit in profusion. Dr. Wayne Clatterbuck, Associate Professor, Forest Management and Silviculture, describes the impacts on oak mast production in an article Impacts of the Easter Freeze on Oak Mast Production in our "Tree Facts".
Browse - stems, buds, and leafs of woody stems - is another important food component in the diet of some wildlife species, most notably, deer. During the period after "the freeze" the canopy trees in our forest were "leafless" for several weeks, allowing higher than usual amounts of sunlight to reach the forest floor. This condition enhanced vegetative growth of many plants that are normally deprived of sunlight during this part of the growing season. The resulting condition appears to stimulate vegetative growth in plants in the sub-canopy and on the forest floor, and thus seems to have increased available browse for browsing wildlife species.
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Left: Yellow Poplar with sparse re-leafing at six weeks allowing understory growth. Top: Yellow Poplar after two months.
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Another curious event that seems to be associated with the freeze was the disruption of the mating season for some wildlife. Dr. Todd Freeburg, Assistant Professor, UT Psychology Department, presently conducts a study of vocal communication among chickadees at the this Center. He observed the cessation of chickadees mating after the freeze, and then a new mating cycle began approximately two weeks afterwards. A similar behavior was also observed in the Center's wild turkey population. How this phenomenon may affect brood counts in these and other bird species has not been determined.
Associate Professor and Wildlife Extension Specialist with the UT Forestry, Wildlife, and Fisheries Department, Dr. Craig Harper, reports that although the spring freeze may have killed the flowers on some important early blooming mast-producing trees and shrubs, there are some other less affected mast-bearing plants - blackcherry, mulberry, persimmon, and blackgum - that may offer some food to sustain wildlife populations through this period of shortage. Wildlife species are adapted in dealing with natural cycles of food shortages, weather, drought, and general hard times that frequently occur.
Insects
Insect's ability to survive freezing temperatures seems to be all about microclimate and microhabitats, or so says Dr. Bill Klingeman, Associate Professor and Entomologist, with the UT Plant Science Department. Unlike plants, insects have the ability to move and search for warmer habitat. An aphid, for example, may simply leave its exposed location branch tip and drop to the ground to escape a frozen death. Microclimates exist in small niches in the environment - under leaves on the ground or under the loose bark of a tree - that capture and hold heat during periods of rapidly falling temperatures. This temperature difference may be as much as 10 to 30 degrees higher than air temperature. Any insect that did not seek cover during this spring's freezing temperatures may have, you might say, "got caught out on a limb" and froze to death. Insects that naturally occupied microhabitats that offered protection - ground and wood-borrowing insects - would have been less susceptible to the dip in temperatures. However, did observation prove this theory correct?
This year we were fortunate to be hosting a research project of Dr. Karen Vail, Associate Professor, UT Entomology and Plant Pathology Department, who was investigating carpenter bees preference for different types of wood and wood coatings. This coincidence caused us to pay close attention to the populations of carpenter bees that have a "taste" for the wood fascia boards on the Arboretum's office building and program shelter. Before the freeze, carpenter bees were numerous; however, after the freeze there were none to be found. One would expect these insects, who typically occupy burrowed cavities/tunnels in wood, to be insulated from the freezing temperatures. Yet, they did not escape the freeze and were found dead and lying-about on the ground in near vicinity of their work area. This observation left us puzzled, and it spelled the demise of Dr. Vail's research efforts for this season. As a post-script, about week threes after the freeze, a few carpenter bees were seen "back on the job", but the numbers were a mere fraction of the pre-freeze population.
Another insect of interest, which we humans had just as soon seen killed by the freeze, are ticks. Our measure of the tick population is by the amount of complaints we receive from our field staff, research staff, and students. Before the freeze, everyone was complaining about what a bad tick year this seemed to be... and afterwards, hardly a complaint - that is, until recently. Apparently, the tick population was reduced but, like the carpenter bees, they seem to have re-bounded. Complaints are now back to a near normal level. (Hint: do you know how to remove those tiny ticks that you can feel, but barely see... DuckŪ Tape!)
As a final thought, several wildlife species depend on insects as a staple in their diet. It may be fortunate for these birds and mammals that some insects are clever enough to get out of the cold! Craig Harper reports that his field checks of insect populations (grasshoppers, leaf hoppers, and caterpillars) that are important to sustaining wildlife populations, are abundant and well within a range of normal expectations.
Return to "The Spring Freeze: Impact of the Drought"
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