UK tree identification: five common urban trees
Britain is home to around a hundred common tree species, with some of the most popular thriving in urban areas. London alone contains over eight million trees, thereby earning its classification as an urban forest. That's almost one tree per person.
Read on to learn about the UK's most popular street trees and their distinctive features, as well as the benefits that urban trees provide us.
What are the most common urban trees in Britain?
Museum botanist Dr Fred Rumsey, a specialist in British plants, says, 'The commonness of particular street trees can alter over time due to changes in planting fashions, as well as their ability to survive in a given climate or against particular pests.
'For example, twenty years ago, it would have been incredibly rare to see an olive tree anywhere in Britain, but now it would not be so unusual to see one in someone's garden. Before long they may be more widely planted on streets.'
Below is a list of five of the most common trees found in UK urban areas. They also happen to be deciduous, so our parks and streets look very different in winter.
Plane tree (Platanus x hispanica)
Botanists believe that the plane tree was born from the American sycamore and the Oriental plane during the mid-seventeenth century. Also known as the London plane due to its commonness in the capital city, it was widely planted as a street tree during the eighteenth and nineteenth centuries, inspired by the Parisian trend of lining streets with leafy trees.
The plane tree is a resilient giant, growing up to 35 metres tall.
The mottled olive, brown and grey bark breaks away in large flakes to reveal new cream-coloured bark underneath. This process cleanses the tree of pollution that has been stored in the outer bark.
The plane tree is monoecious, which means that both the male and female ball-shaped flowers grow on the same tree. After pollination, female flowers develop into spiky fruits with dense clusters of seeds which are dispersed by wind during winter and spring. This fluff can cause respiratory problems in people.
The sturdy plane tree is suitable for city life for many reasons. It requires little root space and can survive in most soils and a wide range of temperatures. Although it has a large canopy, it is suitable for pollarding (a style of pruning where the upper branches are cut back dramatically), so its growth can be kept compact.
However, the size of the tree can be a problem on busy roads. The need to prune and manage the roots which sometimes crack through the pavement makes smaller trees a more favourable option.
'We will see a lot more exotic trees being planted in towns and cities due to climate change,' adds Fred. 'Whether the plane tree continues to be amongst the most common urban trees in Britain remains to be seen.'
Sycamore (Acer pseudoplatanus)
The sycamore tree is thought to have been introduced to the UK during the sixteenth century. The leaves form an attractive, broad, rounded crown, making it a popular choice in parks and gardens. It can also be found along roadsides.
Sycamore trees can grow up to 35 metres and live up to 400 years.
Small green flowers hang in spikes during spring. After pollination, they develop into brown seeds with wings, which spiral to the ground like helicopter blades.
Sycamore trees are a great source of food for a number of animals. Aphids and caterpillars feed on the leaves, the flowers provide pollen and nectar to bees and other insects, and the seeds are eaten by birds and small mammals.
English oak (Quercus robur)
English oaks are the most common out of the five oak species in Britain. Only two are native species, although two or more are widely naturalised and many species occur in specialised collections.
The native tree grows quickly during the first hundred years and slows thereafter, reaching 40 metres in height.
Oak trees can live over a thousand years. They redirect their energy from their canopy into extending their lifespan and, as a result, shorten with age.
English oaks form a broad and spreading crown with sturdy branches beneath as they mature. The open canopy enables light to penetrate, allowing flowers such as primroses to grow below.
Oak trees are home to a rich biodiversity: they host and feed over 280 species of insects and birds. In urban areas, these include the caterpillar of the purple hairstreak butterfly (which feed on the leaves), marsh tits (which use the holes and crevices in the bark for nests) and bats (which may roost in old woodpecker holes).
In autumn, a layer of decaying leaves forms beneath the tree. This supports invertebrates, including the stag beetle, and many fungi.
Oak trees produce fruits commonly known as acorns. One tree can produce about 25 million acorns in its lifetime. However, it takes 40 years before an oak tree produces its first acorns and about 120 years before peak productivity.
Acorns are born on long stalks, a key characteristic that occurs only in this species and helps with identification. Each acorn contains only one seed.
Silver birch (Betula pendula)
The silver birch grows fast in its youth, reaches 25 metres on average and can live up to 200 years.
It owes its name to the peeling white bark on its trunk. Young birch trees have smooth bark which peels off in horizontal strips as they get older, resulting in deep ridges.
This native tree is tolerant of a wide range of temperatures. It is wind- and frost-resistant.
The widespread roots allow the tree to survive mineral-poor soils by absorbing nutrients from afar. That and its tolerance to pollution make the silver birch a common sight in urban landscapes such as industrial areas and roadsides, as well as parks and gardens.
The silver birch bears both male and female flowers - called catkins - during spring, on different stems. The male catkins are long, yellow and hanging, while the females are short, bright green and erect.
Silver birches provide food and habitat to more than 300 insect species. The nutrient-filled leaves are a great source of food for aphids, which are consumed by ladybirds and other species further up the food chain. Woodpeckers and other hole-nesting birds often nest in the trunk, while the seeds are eaten by birds such as siskins and greenfinches.
Horse chestnut tree (Aesculus hippocastanum)
The horse chestnut tree is known for its glossy red-brown conkers. It can reach up to 40 metres and live for 300 years.
The species arrived in the British Isles from Turkey in the late sixteenth century and is now widespread in lowland areas across Britain and other parts of Europe.
It is also a popular street tree and a common sight in parks, large gardens and village greens.
In spring, horse chestnut trees produce tall, upright spikes of white flowers with pink or yellow blotches at the base of the petals.
The flowers provide a rich source of nectar and pollen to insects, particularly bees. The leaves are consumed by various caterpillars, which in turn are eaten by birds such as blue tits.
Once pollinated, each flower produces about four or five fruits. These spiky green capsules contain usually one conker (but sometimes two or three) which falls in autumn and is eaten by squirrels and any deer in the neighbourhood.
Why are trees important in towns and cities?
Towns and cities produce a lot of pollution that contaminates the air, water and soil. Trees help to reduce some of the pollution, making the environment a much healthier place for us to live.
Trees keep the air clean by absorbing odour and harmful pollutants such as carbon monoxide, ammonia and sulphur dioxide through their leaves, barks and roots.
Fallen leaves, flowers, fruits or other tree parts form mulches. These provide a natural filter for polluted rainwater, supplying clean water to other plants in the vicinity as well as our rivers and oceans.
Urban landscapes generate a lot of heat from dark concrete, as well as from high energy consumption, which creates waste heat. Trees help to keep the environment cool by offering shade to people and buildings and transpiring water into the air.
The tree canopy also helps to absorb noise and protect homes from heavy wind.
Trees support biodiversity by housing a wide range of animals and providing them with food. They help to make towns and cities an attractive place to live and boost mental health.
'We are a nation of gardeners and we are lucky our urban areas allow us the chance to grow a dazzling range of different trees,' says Fred.
'These provide benefits in so many ways: physically, by supplying shade, reducing noise, filtering air and water, and lessening erosion; mentally, by creating calm, generating a sense of wonder or just by being beautiful; and from a biodiversity perspective, by offering homes to countless animals, fungi and plants.'
What threats do urban trees face?
One of the biggest dangers to trees is disease.
For example, the horse chestnut tree is susceptible to a fungal disease known as bleeding canker.
Symptoms include a rusty-red or black liquid seeping out of the bark, cracking or rotting, premature leaf drop and, eventually, possible death.
Another fungal disease, ash dieback, is having a devastating impact on ash trees across Europe. Its arrival in the UK was confirmed in 2012.
'Diseases can completely change our landscape,' says Fred. 'I watched the majestic elms of my youth dying. They can now only be seen in places like Brighton, where they have been carefully protected.
'It can be difficult to monitor diseases in trees as they often spread rapidly, including in cities. The best thing would be tighter control over imported and exported natural material, and better quarantine.'
Communities can also make a big difference to their neighbourhood's urban forest. This includes preventing damage to trees, reporting trees affected by diseases or pests to the Forestry Commission and planting trees in their gardens and local area.
'Although urban homes tend to have smaller gardens, people can still plant and maintain small trees there which will offer a haven for wildlife,' says Fred.
'With careful consideration of the planting location, trees can also help regulate the temperature of houses and gardens.'
Creative commons image credits
Sycamore tree © Roger Griffith via Wikimedia Commons