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Monday with Mike: Invasive Trees

Monday with Mike: Invasive Trees

Unwelcome Residents

Two trees and one shrub are causes of concern on the Common, as they can become ‘invasive ‘if allowed to get out of control.

Robinia (Robinia pseudoacia ) also known as Locust tree or false acacia is native to the Appalachian mountains (USA)  but has run wild across southern Canada to California.  Fast growing, it is often planted as a garden tree, particularly the more golden leaved ‘Frisia’ clone from Holland.  It can be ornamental, with its yellow flowers like acacia and good autumn foliage colours. Rumour has it that robinia was introduced to England by a farmer in Barnes as a commercial venture looking to grow a local wood that could be used instead of hickory for tool handles. As the story goes the venture was a failure, but the trees soon spread – they seed easily , but it is their spread by suckering which makes them a real nuisance and very hard to get rid of once established.  They have limited use as a host for invertebrates, being of too recent arrival, and they are regarded as ‘invasive’.  On the Common there are several stands in sensitive areas which we are looking to bring under control.  Cut logs are re-used as posts (when straight enough, since it is a harder timber than oak) or to line pathways etc.

Tree of Heaven (Ailanthus altissima) is a member of the mainly tropical Quassia family.  Originally from China, it grows very tall (and rapidly)  and spreads mainly by suckering, with roots often reaching out 30 m or more. It is not said to spread by seed in this country, but that is hard to believe, since isolated trees are found in  places where they are unlikely to have been planted – while they do seem to spread well along the railway lines.  It was introduced in 1751 and planted in several squares and parks in London, as well as gardens in the South-East but has become invasive.  There are examples on Barnes Common near the Putney boundary  as well as near the Station, while there are also several growing around an old stump on the railway side near Vine Road Rec. (and by the disused signal box).  Our management plan includes removing them from the Common, but due to the suckering we are having to evaluate the best means of achieving this without encouraging the suckering (simply felling the parent tree means its roots will start supplying the suckers – and we all know the cautionary tale of Hydra)  or causing damage to adjoining trees.

Laurel is also invasive – whilst it is a shrub rather than tree, it shades out all vegetation beneath it, and spreads rapidly – it is a garden escape and does nothing for biodiversity.  It has probably arrived on the Common thanks to garden waste being dumped over the years.

Final note… this is my sign off from these reports on the trees and shrubs of Barnes Common.  It has been a pleasure to think about them all during Lockdown, to follow them through Spring into high Summer, and now to look forward to a period of rest! May I thank Sharon Morgan for all her work on these weekly articles – checking facts, adding insights, and making sure my jottings make sense. Do look out for her September series relating to all things food growing!

We hope that it has inspired you to look with fresh eyes, do your own research – and to think about what you see from your car or train window, or when staying somewhere else.

Please do enjoy your summer, and hopefully we will all be able to return to a more sane world before too long.

Mike Hildesley 11th August 2020.

Banner image: Rampant Robinia and Tree of Heaven hedge at Vine Road Growing Beds. Image: Sharon Morgan