In praise of Japanese knotweed …


Autumn colours on Pelaw Wood, photographed from Durham Racecourse, October 2015.

There, I’ve said it.   Now to redeem my professional reputation …

It has been a particularly fine autumn, with a long period of warm, dry, calm weather allowing leaves to stay on trees and giving us plenty of opportunities to stroll through Durham and enjoy their colours.   Some of the most vivid yellow-orange colours were right down beside the river, large heart-shaped leaves growing from a tangle of erect stems readily recognisable as Japanese knotweed, Fallopia japonica. There is not normally much good to say about Japanese knotweed, introduced to Britain in about 1850 via Kew Gardens, and now crowding out native species but the colours this autumn were so spectacular that I thought it deserved at least a brief mention here.   We can, perhaps, see the plant from the perspective of the Victorian horticulturists who thought that it would be an attractive addition to the garden flora.


Japanese knotweed on Durham riverbanks, November 2015.

It is all a matter of perspective: autumnal landscapes around Durham are enhanced by introduced maples and sycamores and, indeed, beech trees (not native to the north of England). Even larch, an introduced deciduous conifer, adds to the overall aesthetic, so long as it is planted in small, unregimented patches. But these are not vigorous hard-to-eradicate colonisers like Japanese knotweed or Himalayan balsam (see “The future is pink …”), so we do not damn them with the epiphet “weed”. “Weed” is not a botanical term; it is an anthropocentric word, a declaration of war, if you like, against a plant that intrudes into spaces where we do not think it belongs.   Just for a few weeks each Autumn, however, perhaps we should declare a truce?

The future is pink …

It occurred to me, as I walked along a local river bank with a friend a couple of weeks ago, that anyone under the age of about 30 probably has little idea why ecologists make such a fuss about Himalayan balsam (see The Politics of Pests).   I was explaining how different this place was now compared to when I first visited but for her, the pink flowers of Himalayan balsam were something that she always associated with river banks. Himalayan balsam was as much a feature of the British countryside for her as rabbits – introduced here by the Romans.

I also wrote recently about the barriers that public perceptions create (see “To Constable country, via a blog on fracking …”).   Environmental improvements are expensive and we need to justify expenditure yet, with the passing of time, Himalayan balsam and other invasive plants will become part of people’s experience of rivers, not as intrusive aliens. Their impact on the native vegetation will be something that only a few specialists appreciate.   There is, in fact, a big literature on how public perceptions are important in environmental management, but this has an inherent limitation as even our earliest memories do not extend far enough into the past to give reliable insights into the natural state of lakes and rivers.   In theory, of course, applying the scientific method allows a more objective, less biased evaluation of what we mean by a “natural” ecosystem.   But we ignore public perception at our peril: the case for environmental restoration beyond a state that lay people regard as desirable will need to be made very clearly in order to justify the costs.   An absence of Himalayan balsam is not, itself, a benefit that a lay person will automatically appreciate.


Himalayan balsam growing beside Smallhope Burn, a tributary of the River Browney, near Lanchester, County Durham.

I end this short thread of posts about Himalayan balsam on a pessimistic note.   The river banks we were walking around were part of a country park managed by the local council.   Their budgets have been cut so much that the prospect of manual control of Himalayan balsam is out of the question. Indeed, there is so much Himalayan balsam that any effort to remove it from a single location would have to be an ongoing campaign as it would constantly re-invade from outside.   It may be possible for Wildlife Trusts to marshal volunteers to keep Himalayan balsam at bay on nature reserves, but the co-ordinated regional and national control programmes that I mentioned in The Politics of Pests belong to the world of fantasy, not reality. I have seen the future … and it is pink.


Valinia, S., Hansen, H.-P., Futter, M.N., Bishop, K., Srisskandarajah, N. & Fölster, J. (2012). Problems with the reconciliation of good ecological status and public participation in the Water Framework Directive. Science of the Total Environment 433: 482-490.


A colleague read my blog and passed on a recent press release from CABI announcing the start of a trial release of a rust fungus to control Himalayan balsam.   Laboratory-based trials have established that the fungus damages the Himalayan balsam plants whilst not infecting native species. The field trials are taking place in Berkshire, Middlesex and Cornwall and it will be interesting to see how these perform.   If it is as successful – and cost-effective – as the project team hopes, then maybe the future will not be so pink after all …