This article first appeared in The Landscaper magazine in November 2019
A recent study published by the International Union for Conservation and Nature (IUCN) has found that more than half of Europe’s endemic trees - those that don’t exist anywhere else on earth - are threatened with extinction.
Popular Tree species in the Sorbus genus, which include the Mountain Ash (Sorbus aucuparia subsp. maderensis) and the Crimean Rowan (Sorbus tauricola) are particularly vulnerable, with 75 percent of Europe’s Sorbus species assessed as threatened.
The horse chestnut (Aesculus hippocastanum) famed for producing conkers, has also been classified as vulnerable following declines caused by the leaf-miner moth (Cameraria ohridella) - an invasive species originating from the mountainous regions of the Balkans.
According to the study, the primary threats to these species are climate change, the loss and destruction of Europe’s wild areas, agriculture and the introduction of alien invasive species.
While most of the above are beyond the direct control of those in the landscaping industry - it does raise the question - should we stop planting non-native species in order to protect those indigenous to the area?
Native species of course tend to harbour far more wildlife than their exotic counterparts. According to the table extracted from various scientific studies by the Offwell Woodland and Wildlife Trust - Indigenous oak species harbour 284 insect species and varieties of Willow support 266.
In stark contrast, the table shows that the highly invasive Rhodedron ponticum, first introduced to Britain in 1763 and now covers roughly 3.3 per cent of Britain’s total woodland - harbours zero insects.
The aforementioned study does recognise that even some native species - Yew for example, due to its toxicity, only supports four species of insect. It should also be noted that plants do of course serve a greater role for species other than providing food. Buddleja davidii for instance, introduced to the UK in the 1800s, although invasive and disliked by many for their association with railway lines, is often cited as being one of the best plants for wildlife in this country.
In fact, according to the RHS just 8 % of the 402 non-native plants established in the wild in Great Britain are stated to have a negative impact. This suggests It is not necessarily an issue of where the plant itself originates from, but the effect it has on the ecosystem as a whole.
Therefore, perhaps we should be less patriotic when it comes to our trees and shrubs and instead, be looking to plant ‘foreign’ species in order to compensate for the native plants prone to disease? The beloved horse chestnut mentioned above, now seen as a staple of the Britain’s parklands, is actually an import itself - arriving from Turkey in the late 16th century.
Furthermore, some researchers are now suggesting that as the summers get hotter and drier, some of the more exotic species may well be better suited to the climate of the future than our native species and that this could actually be a benefit of global warming, possibly producing fruits in the UK that up until now have not been possible - therefore eliminating the need to import these from far flung places.
We do of course need to take responsibility though and ensure we are not introducing more pests and diseases into the UK for the sake of having beautiful gardens and landscapes.
It seems that nowadays, no discussion involving imports would be complete without the mention of the ‘B-word’ and it seems Brexit (if and when it happens) could play its role in preventing pests and diseased plants from entering these shores, as plants could be subject to stricter checks when imported from the bloc.
The RHS has already taken its own measures - in 2018 it banned nine species of plants grown outside of Britain from the Chelsea Flower Show, including lavender and rosemary in an attempt to stop the spread of disease brought in from the continent.
Of course it will be a huge disappointment if we have to say goodbye to any of the beloved species that help to define the British landscape, and we should be doing all we can to prevent this decline, and the decline of the ecosystems they support. We should also take into consideration whether importing particular varieties of shrubs and trees from potentially thousands of miles away, will offer positive differences and benefit a space more than something grown closer to home. We are lucky to have access to such a wonderful array of plants and as long as the environmental impacts are considered, then we can hopefully choose and plant varieties that will support our planet for generations to come.