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| Texas Red Oak displaying fall color. |
Texas is famous for its oak trees, with over 50 different species found in the Lone Star State. Each of these oak species produce acorns, also called oaknuts or mast, which is a collective term for fruits or nuts. The word acorn is related to Gothic term akran which has been interpreted to mean ‘the fruit of the unenclosed land.’ When oaks are dominant in the landscape, as they are here in central Texas, they play an important role in the ecology of the forest.
Acorns usually contain one seed enclosed in a tough, leathery shell, and have a cup-shaped cap or cupule. Depending on the oak species, acorns can take from 5 to 24 months to mature. As a general rule, acorns mature in late summer, turning green to brown, and start falling from oak trees in September and October. Acorns produced by trees in the red oak family (such as Texas Red Oak, Quercus buckleyi) take two years to mature, while acorns produced by trees in the white oak family (such as Bur Oak, Quercus macrocarpa) only take one year.
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| Texas Red Oak Acorns |
Some years, known as mast years, trees produce copious amounts of acorns with smaller crops in the years between. Scientists have proposed a range of explanations for the mystery of what might trigger a mast year, but they do know that it is not resource-driven as annual rainfall and temperature fluctuations are generally much smaller in magnitude than the variation in the crop sizes of acorns. Some scientists hypothesize that masting trees are trying to maximize pollination efficiency. If these trees flower and release pollen at the same time in order to increase their chances of reproduction, since large amounts of pollen correlate with larger amounts of germination, they ultimately produce more acorns. Large, occasional outputs of seeds like acorns appears to be more favorable than frequent, smaller outputs.
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| Bur Oak acorns are our largest acorns. |
Boom and bust years of acorn production actually benefit oak trees from an evolutionary perspective, because acorns are an important, highly nutritious food source for many animals including squirrels, mice, turkeys, blue jays, pigeons, ducks, deer, and bears. In a mast year, these animals can’t consume all of the acorns produced, so some are left to germinate and grow into future oak trees. In leaner years, animal populations are kept in check so there are fewer animals to eat the acorns in the mast years. Over time, a higher proportion of acorns survive to become oak trees.
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| Copious amounts of acorns are produced in a mast year. |
Too heavy for wind dispersal, acorns need other ways to spread beyond the mother tree into a suitable area for germination. Jays, squirrels, and some woodpeckers serve as the main dispersal agents, as they gather and hoard acorns in caches. While they are remarkable in creating mental maps of their cache locations, these animals rarely eat every single acorn, so a small number manage to germinate and produce the next generation of oaks.
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| The Blue Jay is one of many species that cache acorns. |
As autumn arrives and acorns mature and fall from our oak trees, think of the potential in the abundance of acorns produced. As Henry David Thoreau once wrote, “Every oak tree started out as a couple of nuts who stood their ground.”
