Earlier this week, I went along to the patrollers team meeting at the Water of Leith Conservation Trust Visitor Centre. The patrollers are people who walk their designated length of the river every week, picking litter, recording wildlife (including non-native invasive species) and looking out for pollution incidents.
This week's meeting focussed on invasive non-native species of plants and animals that affect the river. A speaker from the River Forth Fisheries Trust spoke about identifying and managing the major species of concern.
Giant Hogweed, which was originally introduced as an ornamental is of major concern because each plant can produce many thousands of seeds and they can lie in the soil for 17 years so it can take many years to eradicate. In addition it's sap burns the skin on contact. It can only be controlled by spraying it with glyphosphate that is considered safe for other plants, waterways and bees.
Japanese Knotweed, which was also introduced as an ornamental, shades out all competitors and can grow through concrete, causing chaos on building sites. It is generally controlled by injecting glyphosphate directly into the stems near the base of the plant. This is most effective if carried out at the end of the season, by which time the plants energies are being directed towards the roots and so the poison will be carried directly to the roots and kill the plant most speedily.Japamese Knotweed is edible, it's a bit like rhubarb, apparently, but as in Scotland you can't remove it from site, so unless you want to spend endless days making knotweed crumbles over a camping stove, then it's not a realistic method of control.
I was most interested to find out more about Himalayan Balsam. As we noticed on our last trip to Dumfries and Galloway, areas that are thick in Himalayan Balsam in the summer were a mass of attractive spring flowers earlier in the year and I had been lulled into a false sense of Himalayan Balsam perhaps not being so bad after all, despite its revolting smell. After all the flowers are pretty and the bees like it. However at this meeting we learned that the real problem with Himalayan Balsam is when it grows on riverbanks and crowds out all the summer vegetation. Not only is this bad for the summer plants but it means that in the winter, when Himalayan Balsam dies right back (unlike most other summer flowers which would be persistant) and then the riverbanks are left bare from autumn to late spring and become very prone to erosion. Himalayan Balsam can be uprooted very easily and must then be destroyed, because it re-roots very easily.
Invasive plants need to be controlled starting from the source of a river, as the seeds or, in the case of Japanese knotweed rooting segments of stem, are carried downstream.
The Water of Leith also is home to a number of mink, which originally got into the wild when over enthusiastic animal rights activists released them from fur farms. Mink have been a huge problem on British waterways, they are very aggressive and eat anything. However, as our rivers have got cleaner and otters have returned then they outcompete mink (otters are much bigger than mink and will fight them). Since mink have been exterminated from the Trossachs, the endangered water vole has returned. The River Forth Fisheries Trust and the Water of Leith Conservation Trust are working together to set up some mink rafts along the river. Despite sounding like some sort of luxury boating experience for the mink, these are recording devices - the mink will run onto the rafts and leave their footprints there so we can get some idea of how active they are along the river. We can then assess whether the mink need to be controlled or whether the two or three resident otters are dominant enough to keep the mink under control.
If you see any invasive species in Scotland, you can record them on the RAFTS Invasive Species Recording Site. You can learn more about which species to look out for on the RAFTS Invasive Species Site. (RAFTS is the River and Fisheries Trust of Scotland, which represents all the rivers and fisheries trusts in Scotland).
As ever, red text contains hyperlinks which take you to other websites where you can find out more