Regular readers of our blog will know that tackling invasive non-native species (INNS) is an ongoing challenge along the Water of Leith. These species — whether plants or animals — are one of the key drivers of nature loss in the UK. They can harm wildlife and habitats, damage the economy, and, in some cases, even affect our health.
As part of the river management plan, our goal is to remove INNS across the catchment wherever possible. Our main focus is on the “big three” invasive plants:
• Giant Hogweed
• Himalayan Balsam
• Japanese Knotweed
We also act on other invasive species when we find them, including:
• Rhododendron ponticum
• American Skunk Cabbage
• Salmonberry
Our approach has been from the top down, working source to sea. After almost ten years of treating Giant Hogweed on the main Water of Leith channel, our work had reached a scale where we could begin identifying key hotspots. In 2022, we started working up the Murrayburn tributary in search of seed sources — and boy did we find them. So we needed to make some new friends and obtain permission to begin removal. So with permission from local farmers, Heriot-Watt University, Riccarton Shooting Club, Riccarton Garden Centre and Scottish water for allowing access, we have been exploring their land and treating the plants we find.
As mentioned in our spring update, this year we have been trialling Giant Hogweed digging with trained volunteers, focusing on early removal before plants become too large to manage without chemical spraying.
The trial has focused on:
• digging out Giant Hogweed seedlings as they emerge from March onwards when they are too small for chemical spraying.
• removing the full root wherever possible;
• reducing reliance on chemical treatment where practical.
Although digging is more labour-intensive than spraying, we have seen good results where the root has been fully removed. However, where we have not dug deep enough, some plants have regrown. This has reinforced how important careful, thorough root removal is to the success of the approach. It is also way more fun to dig than to spray – as volunteers can really get stuck into destroying this insidious plant
Giant Hogweed Plants Dug
| Water of Leith Visitor Centre Slateford to Balerno. *Has been regularly treated since 2017 so few remain | 77 |
| Slateford to Leith *Treatment started in 2020 | 1602 |
| Murrayburn Tributary – Longstone to Curriehill *Treatment started in 2022 | 4775 |
Total Giant hogweed plants dug – 6454
This heat map showing the density of plants dug – clearly highlighting the clusters on the Murrayburn
The figures and heat map clearly show that a whole-catchment approach is the only way to truly get on top of invasive species. Treating individual sites is important, but long-term progress depends on identifying and tackling sources upstream, including areas beyond the Murrayburn.
Thus, as staff time has allowed, we have continued moving upstream from Balerno, wading through the Larchgrove Estate towards Glenbrook. Along the way, we have found Himalayan Balsam, Japanese Knotweed and some curious new friends keeping an eye on our wading work.
Johnny’s new pals! ….The fight against invasive species continues