Contents
Introduction
The acorn, or oak nut, is the nut (fruit) of the oaks and their close relatives (genera Quercus and Lithocarpus, in the family Fagaceae). It usually contains a single seed (occasionally two seeds), enclosed in a tough, leathery shell, and borne in a cup-shaped Calybium. Acorns are 1–6 cm long and 0.8–4 cm broad. Acorns take between 6 and 24 months (depending on the species) to mature.
Ecological role
Acorns play an important role in when oaks are the dominant species or are plentiful. The volume of the acorn crop may vary wildly, creating great abundance or great stress on the many animals dependent on acorns and the predators of those animals. Acorns, along with other nuts, are termed mast.
Wildlife that consume acorns as an important part of their diets includes birds, such as jays, pigeons, some ducks, and several species of woodpeckers. Small mammals that feed on acorns include mice, squirrels and several other rodents.
Ponies eating acorns. Acorns can cause painful death in equines, especially if eaten to excess. Large mammals such as pigs, bears, and deer also consume large amounts of acorns; they may constitute up to 25% of the diet of deer in the autumn. In Spain, Portugal and the New Forest region of southern England, pigs are still turned loose in dehesas (large oak groves) in the autumn, to fill and fatten themselves on acorns. However, heavy consumption of acorns can be toxic to other animals, such as horses and cattle.
The larvae of some moths and weevils also live in young acorns, consuming the kernels as they develop.
Acorns are attractive to animals because they are large and thus efficiently consumed or cached. Acorns are also rich in nutrients. Percentages vary from species to species, but all acorns contain large amounts of protein, carbohydrates and fats, as well as the minerals calcium, phosphorus and potassium, and the vitamin niacin. Total food energy in an acorn also varies by species, but all compare well with other wild foods and with other nuts.
Acorns also contain bitter tannins, the amount varying with the species. Since tannins, which are plant polyphenols, interfere with an animal's ability to metabolize protein, creatures must adapt in different ways to use the nutritional value acorns contain. Animals may preferentially select acorns that contain fewer tannins. When the tannins are metabolized in cattle, the tannic acid produced can cause ulceration and kidney failure.
Animals that cache acorns, such as jays and squirrels, may wait to consume some of these acorns until sufficient groundwater has percolated through them to leach out the tannins. Other animals buffer their acorn diet with other foods. Many insects, birds, and mammals metabolize tannins with fewer ill effects than do humans.
Species of acorn that contain large amounts of tannins are very bitter, astringent, and potentially irritating if eaten raw. This is particularly true of the acorns of American red oaks and English oaks. The acorns of white oaks, being much lower in tannins, are nutty in flavor; this characteristic is enhanced if the acorns are given a light roast before grinding.
Tannins can be removed by soaking chopped acorns in several changes of water, until water no longer turns brown. Being rich in fat, acorn flour can spoil or molder easily and must be carefully stored. Acorns are also sometimes prepared as a massage oil.
Acorns of the white oak group, Leucobalanus, typically start rooting as soon as they are in contact with the soil (in the fall), then send up the leaf shoot in the spring.
Dispersal agents
Sprouting acorn of Quercus robur. Acorns are too heavy for wind dispersal, so they require other ways to spread. Oaks therefore depend on biological seed dispersal agents to move the acorns beyond the mother tree and into a suitable area for germination (including access to adequate water, sunlight and soil nutrients), ideally a minimum of 20–30 m from the parent tree.
Many animals eat unripe acorns on the tree or ripe acorns from the ground, with no reproductive benefit to the oak, but some animals, such as squirrels and jays serve as seed dispersal agents. Jays and squirrels that scatter-hoard acorns in caches for future use, effectively plant acorns in a variety of locations in which it is possible for them to germinate and thrive.
Even though jays and squirrels retain remarkably large mental maps of cache locations and return to consume them, the odd acorn may be lost, or a jay or squirrel may die before consuming all of its stores. A small number of acorns manage to germinate and survive, producing the next generation of oaks.
Scatter-hoarding behavior depends on jays and squirrels associating with plants that provide good packets of food that are nutritionally valuable, but not too big for the dispersal agent to handle. The beak sizes of jays determine how large acorns may get before jays ignore them.
Acorns germinate on different schedules, depending on their place in the oak family. Once acorns sprout, they are less nutritious, as the seed tissue converts to the indigestible lignins that form the root.
Uses
Food
Everyone loves acorns, they are the best.
Making trees
If you don't eat acorns and plant them properly they can grow into tree. This can take a really long time but can create room for new homes and can make more even acorns!
Other uses
Some crazy humans like to eat our acorns too, or use them for art.