Blue tit, photo courtesy of Tim Blackburn
Wood pigeon, photo courtesy of Tim Blackburn
European jay, photo courtesy of Tim Blackburn
Michael Thain, Author of the Penguin
Dictionary of Biology
The native oak is for many a symbol of strength, survival and endurance and the national tree both of England and Germany. In England it was the timber used to build medieval cathedrals, the roof of Westminster Hall, ships of the Elizabethan era and Nelson’s fleet. The tree is the symbol of the National Trust, and its leaves, that of the Woodland Trust.
There are two English species: the European oak (Quercus robur), the pedunculate or ‘English’ oak; and Quercus petraea, the sessile oak, whose acorns, unlike those of the pedunculate oak, do not grow on stalks). Both survived the last European glaciation in the south of France and the north of Spain, where DNA analysis reveals that most of the British oak population originated. But it is thought the land bridge with Europe only gave them about 800 years to reach Britain. Since oaks are climax vegetation they would only have grown where soil had already been developed by earlier succession and it is likely that then as now the European jay (Garrulus glandarius) played a part in their colonization and expansion. Compared with ash (Fraxinus excelsior) and sycamore (Acer pseudoplatanus), oaks are slow growing and require nurturing if in competition with such species.
Oak fruits, acorn nuts, are not produced until the tree is at least 40 years old and peak acorn fecundity usually occurs around 80 – 120 years. Wildlife that consume acorns as an important part of their diets include 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. They can cause painful death if eaten in excess by horses but may make up 25% of the autumn diet of deer, which like pigs can presumably detoxify their tannins.
A survey recently discovered that England has more ancient oaks than the rest of the Europe combined, 1,200 previously unknown but still surviving medieval and Tudor oaks being found – making 3,400 in total. About 85% are between 400-600 years old while 12% date back 600-800 years and 3.4% (117 trees) between 800-1,000 years.
In addition to producing acorn mast, oaks harbour more insect species (284) and lichen species (324) than any other native tree – only willows, birches and hawthorn coming anywhere close. It is clear why ash (41 insects) and sycamore (15 insects) attract so few passerine birds by comparison, especially in the nesting season when caterpillars abound. As shelter and nesting sites for birds and mammals, mature oaks are unsurpassed, especially when boughs fall and leave holes (e.g., for tawny owls and stock doves).