There are a lot of non-native trees in the UK. It might surprise you to know that a lot of parks and green spaces will have more non-native species than native. But how do we define what is native or non-native?
Based on historical records - around 8000 years ago (6,100BC) Britain and Europe were connected by a land bridge called Doggerland. Britain was essentially an ice sheet with very minimal plant life. As the ice age came to an end the sea levels increased which flooded the Doggerland land bridge and formed the Britain that we know today. Any plant species that colonised the land back then are what we class as a native species. Based on this understanding - there are around 40+ truly native trees.
Now that we have a better understanding of what all of this means why are there more non-native trees than native? Two main influences are the Romans and the Victorians. When the Romans invaded Britain and began to setup shop they brought over a lot of their plants. This includes grape vines, Black mulberry and Sweet chestnut to name a few. During the Victorian period even more plants were introduced into Britain such as the Monkey puzzle tree, Giant redwood and Rhododendrons. At the time there was a huge demand for rare and exotic trees for private collections.
It's worth noting that quite a few non native trees are now naturalised in Britain and most people will treat these as native. Sycamore and Horse chestnut are great examples of this. The important thing is that we need to be mindful of our native trees and ensure that we are planting them in higher numbers than non-native. This is easier said than done as each council has it's own way of doing things which can lead to problems further down the line.