Jays, squirrelling acorns away for winter, are one of the main ways oak trees spread, explains Pip Webster
In a bumper year, an oak tree can produce 50,000 acorns, which is good news for the jay
Mighty oaks from little acorns grow” (14th Century proverb), though it does take a while. Oak is one of the hardest and most durable timbers on the planet, its high tannin content rendering it resistant to insect and fungal attack, but it takes up to 150 years before the tree is big enough to harvest.
Famously used to build British naval ships, the oak has long been prized as a symbol of strength and survival: sacred to many, gods, kings and emperors were crowned in oak leaves. ‘Gospel oaks’ marked parish boundaries and were the site of annual religious ceremonies even in Christian times.
Two species of oak are native to Britain: Pedunculate oak, also known as English oak or Common oak, grows throughout Britain, particularly in lowland woods, along hedgerows and as a field tree. The naturally shorter-stemmed and bushier configuration was ideal for the ribs and knees of ships. The Sessile oak is typically found in upland woodlands of the north and west, thriving in wet and rocky locations, and is used for fuel, charcoal and tanning. Both species can grow in lowland woods and they hybridise, so it isn’t always easy to identify the species you are moored under.
The Pedunculate bears acorns upon stems (peduncles), with leaves that have little or no petiole; on the Sessile, the acorns are hard up against the twig (Latin sessilis means stalkless) with leaves on short petioles.
The word ‘acorn’ comes from the Old English aecern, meaning berry or fruit, and it became applied to the most important forest produce. Our ancestors may have subsisted on acorns before they started to work the land and, from the Middle Ages until the 18th Century, people drove their pigs into the oak woods on common land to feed on the abundant crop (pannage). Acorns grow from the inconspicuous windpollinated oak catkins, though rarely in significant numbers until the tree is at least 40 years old.
In a bumper year each tree can produce 50,000 acorns. They start to form in early summer, ripen from green to an autumnal brown, and then fall with or without their ‘cupule’ to form a dense carpet in October or November. Much of this rich food source will not get the chance to germinate, being eaten by squirrels, mice, deer, badgers and numerous birds – but an oak tree may live for 800 years, and it only needs one acorn to replace it.
Acorns are too heavy to be dispersed by the wind, but squirrels and jays in particular store them away for the winter, often burying them some distance from the wood. Autumn is the best season to see the busy jay, the most colourful of our corvids (crow family). A shy pinkish-brown bird, its black and white flight feathers, with beautiful blue and black wing coverts, black tail and white rump show up well as it flies away. Look for it when you hear the loud ‘kschaach’ alarm call, a rasping shriek, often repeated twice, when the bird is disturbed. Highly intelligent birds, jays are adept at mimicry, copying calls of predators, including the domestic cat, and the alarm notes of smaller birds like the blackbird.
Jays set up private larders of several thousand acorns over a period of about two months. They carry three or four acorns at once in their specially large oesophagus, sometimes for several miles, to separate hiding places. The acorns are normally cached in natural crevices or holes, often in damp ground, the burial site being disguised with dead leaves, sticks, pebbles and earth. They seem able to remember where most of them are, but some get left and are able to germinate into oak seedlings. This is probably the most important method whereby oaks spread uphill.