Impacts of the Easter Freeze on Oak Mast Production
The following article written by Dr. Wayne Clatterbuck, Associate Professor, Forest Management and Silviculture, appeared in a newsletter published by the UT Institute of Agriculture Department of Forestry, Wildlife, and Fisheries.
The below-freezing temperatures in early April have impacted the flowering and thus fruit and seed production of many of our hard mast species, but particularly oaks, hickories and walnut. The seeds from these species provide a great amount of food for wildlife during the winter months. The scarcity of seed will also hinder current year regeneration potential of these trees.
The stage of leaf emergence at the time of the freeze made a difference as to which trees were impacted. The combination of the above-average temperatures in March, allowing bud break and flowering to proceed earlier than normal and the severe cold temperatures that followed affected the tissues of leaves and fruiting structures that were just emerging. Those older tissues that already had been growing for a few weeks were not as affected, as well as those trees that tend to leaf out later. Walnut and hickories were not as damaged because they are among the last tree species to leaf out in the spring. However, the oaks were heavily impacted across the state.
Oaks are composed of two families: red oaks and white oaks. It takes those species in the white oak family (white, chestnut, chinkapin, bur, swamp chestnut, post) one growing season to produce acorns from flowering. Most of these trees will have limited acorn production this year because the freeze killed most of the flowers. Alternatively, it takes two growing seasons from pollination for red oak (northern red, southern red, cherrybark, Shumard, willow, water, pin, black, scarlet) to produce acorns. Flowers are pollinated in the first year. However, fertilization and maturation of the acorn does not occur until the second year. Thus, there will be little red oak acorn production in 2008 because of the 2007 freeze. The fate of the red oak acorns pollinated in 2006, that will mature in 2007, is unknown. It takes about 12 months (May and June of the second growing season) for the pollen tube containing the pollen to connect with the ovary for fertilization to take place. We do not know at present the impact of the freeze on the fertilization process of red oaks in 2007. Red oak acorns should be visible and growing by the beginning of July if fertilization was successful.
Even if fertilization took place, the stress incurred by the spring freeze and the additional stress of current moisture deficits will cause many acorns to abort. Most areas of Tennessee are in drought conditions with rainfall being 10 or more inches below normal at present. Insects and birds will also consume many acorns. Considering the flowering of most oaks (red and white) was inhibited by the freeze, the uncertainly of red oak acorns pollinated in 2006, the current drought conditions, and that an increasing proportion of acorns are consumed by insects when acorn production is limited, it is safe to assume that mast (acorn) production will be limited in 2007 and somewhat limited in 2008. Wildlife populations will probably decrease because of the scarcity of hard mast. Many animals will be searching for food outside their usual habitats in urban areas and in urban-rural interface areas.
Hopefully, variation in the degree of leaf and flower emergence across Tennessee before the freeze will allow some hard mast production. However, it is much too early to predict the fall of 2007 or 2008 mast or acorn crop. Indications are that the mast crop will be limited. The best way for a manager to determine the mast crop for a given year is to conduct a mast survey in late summer and early fall after acorn maturation but before acorn drop.
For more information contact Wayne Clatterbuck at 865.974.7990 or wclatterbuck@utk.edu.
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