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ACORNS: An Oak Trees Nut
By Sara Allison
Cooling temperatures and leaves changing color are certain signs of autumn. At this time of year, it's also easy to notice wild animals gathering food to store for winter. One food, which is a staple of many animals' diets, is the acorn. Animals that depend on this nut for sustenance vary from the small, including jays, woodpeckers and squirrels to larger animals, like deer and bear.
The type of tree that bears the acorn is the oak tree. There are about 400 species of oak trees found in the northern hemisphere, including more than 50 types in the United States. Most oaks must mature about 20 years before they produce acorns.
An acorn contains a seed, inside a cupule, which is protected with a cap. Acorns are tastier and more nutritious than most other seeds, containing protein, fat and minerals. Their size makes them easy for forest animals to gather. Seeds take 6 to 18 months to mature, but also are durable, sometimes surviving on the forest floor for months.
Since there are so many types of oak trees, their acorns vary as well, but all are safe for human consumption. Some, including the red oaks' acorns contain tannins, which are bitter and less desirable to eat. The acorn from these trees takes about 18 months to mature and is shaped a bit long, with a wooly shell interior. One type of red oak found in California is the coast live oak, which bears a reddish brown acorn that grows up to about 3.5 cm long. The acorn from the coast live oak grows quicker than most red oak acorns, maturing about 7 or 8 months after pollination.
White oak trees are found throughout Europe, Asia, North Africa and North America. Several types of white oaks are also found in California. White oaks produce acorns, which are shorter, from about 1.5 - 2.5 cm, and mature in about 6 months. There is no hair within the shell of these acorns and they have a sweet to slightly bitter taste, which is nuttier than most other acorns.
One type of white oak native to Southern California is the Engelmann Oak, also known as the Pasadena Oak. These trees must live within 20 miles of the ocean, but they are rapidly disappearing because they are often cut down to build new homes. The Arroyo Seco Foundation encourages people who own an Engelmann Oak to collect those acorns when they fall to the ground in September and October. The group works for the restoration of the tree, and they plant the acorn seeds to propagate and preserve this Southern California oak.
The canyon live oak (an intermediate oak in section Protobalanus) is an evergreen oak found in California Coast Ranges and sprouts acorns, which can occur in pairs or solitarily. These seeds are contained in light brown ellipse shaped acorns, and grow up to 5 cm long. A thick, shallow cup covered with yellowish hairs protects the seed of these acorns. They mature in one season and fall to the ground in October.
Other types of acorns, not found in North America are the sections Mesobalanus and Cerris. The former species is closely related to white oaks, and its acorns mature in 6 months. These acorns are longer and their shell is hairless. The Cerris trees take longer to produce a mature acorn-18 months-and their taste is more bitter. The inside shell is hairless to slightly hairy.
Depending on the size of an oak tree and the weather it endures, if a deep-rooted oak gets sufficient water, its acorn production can be up to 6000 lbs per acre. Although many of these acorns don't get used many feed animals and keep more oak trees growing, making acorns an important part of a forest's circle of life.