Jays, squir­relling acorns away for win­ter, are one of the main ways oak trees spread, ex­plains Pip Web­ster

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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.

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