The sessile oak flowers between April and May, and produces acorns which ripen from September to October (6). Both male and female flowers occur on the same tree, and the flowers are pollinated by the wind (5). The seedlings of the sessile oak are more tolerant of shade than those of the pedunculate oak (Q. robur), which enables the sessile oak to regenerate in woodlands (7). This deciduous tree is long-lived, often living to around 500 years old and potentially even reaching 1,000 years of age (5).
As well as being long-lived, the sessile oak also grows quite slowly, with individuals not producing their first good crop of acorns until they are around 40 to 50 years old. Acorn production varies between years, but in a good year this species may produce up to 50,000 acorns. Despite this, very few of the acorns successfully go on to grow into mature trees (5). Oaks have an intriguing method of boosting their chances of reproduction and beating the acorns’ many predators. This is done by a relatively low production of acorns for three to four years on average, before the production of a huge crop. This is called a ‘mast year’, and with so many acorns on the ground it is likely that more will survive predation (8).
Acorns were once widely used to feed pigs, and were also ground down to make a substitute for coffee and even types of bread, biscuits and a meal that was added to stews and soup (2) (8). A good crop of acorns was used to predict a good harvest, and a heavy fall of acorns was thought to signal an impending harsh winter (2). However, sessile oaks do not yield as many acorns as pedunculate oaks, and their timber has been less highly valued. Coppicing of these oaks was common in the north and west of the United Kingdom (3), and involved cutting the tree at the base and then leaving it to regrow. This practice produces many thin poles of wood, which would then be harvested every 10 to 14 years (8). The wood was burned in the iron-smelting industry and the bark was used in the leather tanning industry as a source of tannin (3).
Like other oak trees, sessile oaks support a staggering variety of wildlife, and are habitats in their own right (5) (9). During the life of the tree and even after its death, an oak can play host to many hundreds of different species, and is therefore often referred to as a ‘cornerstone species’ (8). The open canopy of the sessile oak also lets light through to the ground, which favours the growth of a diverse ground flora (9).