My training for the Great North Run takes me along the banks of the River Wear and, since writing about Himlayan balsam recently (see “An Indian summer on our riverbanks …”) I have had plenty of opportunities to both observe and ponder the biology of this plant. I remembered, just after posting my piece on Himalayan balsam, that some former colleagues at Durham University had done some research on this species just after I had left. Another colleague had commented wryly that they had managed to prove that Himalayan balsam lives by river banks though, on reading their work, it is clear that this was a rather unfair judgement. It is also wrong, as I noticed this morning as I pushed through stands of Himalayan balsam that were encroaching on the path I was running along, some distance from the river. I have run along this path for several years but this year is the first when I have noticed Himalayan balsam in such abundance.
Coiled seed pods of Himalayan balsam, photographed on the Durham river banks, July 2014.
If you look closely at the seed pods you can see that they are tightly coiled, like springs. And, when you brush against a mature seed pod, these springs are capable of catapulting the seeds for several metres. This characteristic, in fact, is the reason why the Latin name of the genus is “Impatiens” (“impatient”). Each plant can produce many seeds, so all it takes is for a few of these to land in suitable conditions and the stand of Himalayan balsam will, by the next year, have extended itself by a few metres. The predilection for river banks is partly because these are associated with fertile, moist, often shaded, soils where the seeds are able to thrive, but also because the natural flooding of the river can transport the seeds rapidly between locations. However, my former colleagues at Durham also noted that Himalayan balsam was also strongly associated with roadsides and, indeed, Frank Smythe, in Valley of Flowers, does not record Himalayan balsam in its natural habitat as being so strongly associated with rivers.
Knowing where Himalayan balsam grows was, however, only the start, as they were able to use their knowledge of the plant’s distribution to build a mathematical model that described how Himalayan balsam spreads and then to manipulate the model to simulate various options for controlling the spread. They concluded that, once established, Himalayan balsam would be very difficult to eradicate, regardless of strategy. That’s no big surprise, given what we know about the biology of the plant and also from knowledge of efforts to control other invasive weeds. But that, too, got me thinking …
We are, now, less than 10 months away from a general election. Expect many fine words about the environment to be spoken between now and then. But, as is often the way, it will be the economy, health and education which will dominate the campaigns. Politicians will look for environmental policies that will either give a quick and demonstrable benefit or Grand Gestures with maturation times that extend well beyond the term of the next parliament. Control of invasive weeds fails on both counts. The paper on control strategies concludes: “If eradication is a serious goal of control programmes then they must be co-ordinated at a regional or national scale, involve greater investment and extend over a longer duration”. In other words, they will need a bigger slice of the budget that the environment is likely to be allocated. Moreover, how can regional or national co-ordination be achieved in governments committed to reducing the size of the public sector? No, I’m afraid that control of Himalayan balsam is very unlikely to feature on any politician’s to-do list in the immediate future.
Collingham, Y.C., Wadsworth, R.A., Huntley, B. & Hulme, P.E. (2000). Predicting the spatial distribution of non-indigenous riparian weeds: issues of spatial scale and extent. Journal of Applied Ecology 37 (Suppl. 1) 13-27.
Wadsworth, R.A., Collingham, Y.C., Willis, S.G., Huntley, B. & Hulme, P.E. (2000). Simulating the spread and management of alien riparian weeds: are they out of control? Journal of Applied Ecology 37 (Suppl. 1) 28-38.