The Mighty Oak
The oak tree is a common sight across the UK landscape, and with over 500 species worldwide you don’t have to look too closely to see just how special they are.
Our two main species here in the UK are the English Oak (Quercus robur) and the Sessile Oak (Quercus petraea).
As well as being an impressive sight, the Oak is home to a whopping 2,300 of wildlife species, providing vital habitat and food. According to the Woodland Trust there is no other tree here in the UK that supports such a diverse and abundant variety of wildlife.
Research published by the UK Centre of Ecology and Hydrology showed that 2,300 species are dependant on oak for survival, and incredibly 229 of those species are only found on oak, and not on any other species of tree. Proving just how special oak trees are!
Oak trees are long lived with many species living up to 1000 years, and knowing what we do about how valuable they are to wildlife, each oak has the potential for up to 1000 years of supporting wildlife.
Another great reason to get out and plant more trees!
Life cycle -
Oak trees have both male and female flowers on the same trees and rely on wind pollination. The male flowers grow in long dangly clusters and are blown around easily in the wind to spread the pollen. The female flowers are the tiny red bud like flowers that are slightly hidden between the leaves. The flowers appear around April to May depending on the weather and soils conditions.
Though each tree has male and female flowers on the tree, some species are reliant on the pollen from e different tree for successful pollination. It is the pollinated flower that develops into the acorn that forms in a woody cup structure, once the acorn is ready it is realised from the cup.
The oak’s ‘seed’ is of course the acorn, an easily recognisable structure that helps us to identify the tree.
When the acorn falls to the ground germination typically takes 3 - 8 weeks depending on the species and conditions. The soil moisture is an influencing factor as it needs to be moist but not water-logged. Temperature is another important influencing factor determine the rate of germination, while some species need a great degree of light and warmth and other species thrive in the shady, cooler areas.
Once germinated, the first delicate shoots will become visible as the sapling starts to develop its first leaves - these first delicate leaves are called cotyledons. They are capable of low amounts of photosynthesis as well as being a nutrient store for the rapidly growing sapling.
The young tree is still classed as a sapling until approximately three years old. The vital stage of sapling growth is still heavily influenced by the health and moisture count of the soil as well as weather conditions. Older trees are influenced by this too, but as they get bigger and stronger they are able to ‘weather the storm’ a little more and adapt to conditions, where as saplings aren’t as robust yet.
From this stage onwards the oak makes rapid growth and develops stronger and denser leaf cover. The increased leaf cover with stronger mature leaves helps to increase the rate of photosynthesis so increases the energy available to the tree.
An oak tree is considered mature between 30 - 40 years old, and when it is able to produce acorns itself.
Leaves -
Most oaks are deciduous - with a few exceptions that are evergreen so retain their leaf cover all year - but here in the UK our native species are deciduous.
The leaves have a distinctive lobed shape, each species has a slight variation of leaf shape but the over all look of the leaf is fairly similar. The younger leaves are a bright vibrant green, as they contain less chlorophyll, and as they mature they darken in colour as their chlorophyll levels increase and the leaf becomes tougher and more fibrous.
In Autumn time the chlorophyll in the leaves starts to denature which causes the leaves to change colour with vibrant yellows, oranges and reds before falling to the ground.
Shape -
The oak is easy to identify due to its characteristic shape, growing with a wide rounded crown and thick wide spreading lower branches. The trunk of the oak becomes wider and more gnarled looking with age.
Bark -
The bark is rough in texture with deep fissures that run in a vertical pattern. The fissures get deeper as the tree matures and ages. On a younger tree the bark is a silvery brown, becoming darker brown with age.
There are many distinguishing features to identify the oak, with its characteristic leaves, acorns and impressive stature - so look out for oak trees on your next adventure, and remember what an incredible habitat and food that they provide for our precious wildlife.
