Identifying a Sessile Oak Tree
It is a huge deciduous tree and can grow up to a height of 40m. Unlike English and pedunculate oak, the acorns are stalkless. The trunk sits more upright and the branches are also straighter with longer leaf stalks than those of the English oak.
As oak’s age they form a wide crown that spreads right around and develops thick branches on the lower parts of the trunk. Since the tree has a light or open canopy, it allows wild flowers such as primroses and bluebells to grow on the woodland floor below. Before they mature the bark is very smooth with a greyish brown colour, once matured it becomes rough with deep fissures.
They have a monoecious reproductive system, meaning both male and female parts are located on the same tree. The green male flowers are catkins, while the female flowers (bracts) are red buds and hang in bunches. Once pollinated by wind, the red female buds turn into a large glistening seed with a wooden shell at the base. A young acorn is green but turns brown before falling.
The reason it is called sessile oak is because the acorns are not produced on stalks like English and pedunculate oak (peduncles), and instead grow on the outer twigs (sessile).
Significance to Wildlife
It does not particularly matter which oak animals and insects inhabit as they all support an abundance of wildlife. More than 280 insects inhabit the tree which also attracts many of their predators such as birds. You will often find lichens, mosses and liverworts growing on the bark of the tree and deadwood cracks provide a perfect habit for roosting bats and nesting birds. Small mammals such as red squirrels, badgers and jays also eat the acorns.
As the fallen leaves decompose during autumn, they develop into a thick mould on the woodland floor and in turn provide a good habitat for beetles and fungi.
How We Use Oak
One the toughest and most hard-wearing timbers known to man, it was used for many years, primarily for ship building until the mid-19 century and still remains a great choice for structural beams. Historically, all the main elements (leaves, acorns and bark) of the tree were thought to cure lots of medical problems such as inflammation, kidney stones and diarrhoea. Today we use it for things like wine barrels, firewood and flooring.
A long time ago, acorns were collected by humans and turned into flour to make bread. It is a technique that died out 10,000 years ago, mainly because of domestic wheat production. Now we just leave the acorns for mammals and birds.
Threats, Pests and Diseases
There are a high number of oak trees in Britain and they are protected from over harvest. However, there are still numerous pests and diseases that are affecting them. The foliage can be severely damaged by the oak Processionary moth which increases the changes of infection from yet more diseases. The moth is also a hazard to human health and can cause problems with breathing as well as itchy skin from the tiny hairs on its body.
Other diseases affecting the tree include chronic oak decline and acute oak decline. These conditions are serious threats to the trees health and can be caused by a number of factors. It was first brought to attention back in the 1920s that a large number of mature oaks were declining. The most affected are today are central and southern parts of England. You can usually spot this by a thin canopy and broken branches as well bleeding cankers on the trunk.