Recently, The Tweed Foundation has been undertaking the digitisation of photographic slides taken at various habitat restoration sites, where it has carried out work over the last twenty years, as a record of changes to the areas. Over the last 15-20 years, The Tweed Foundation has spent over £2m, with the help of European grant-aid, enhancing the Tweed headwaters, to improve habitat for juvenile fish with fencing and planting regimes, and the removal and easing of instream obstacles to fish passage. Having these photographs as digital images, and as an archive of work undertaken, now allows sequences to be put together in documents, and two examples from a bankside fencing site on a burn near Ashkirk are shown here:
This sequence not only shows the great increase in bankside vegetation with the removal of grazing pressure but also how an actively eroding bankside scar can heal when vegetation is allowed to take hold on it. Scars like these erode because they are made unstable by the washing away of the material at their base by flowing water, but if this “toe” area is stabilised, the face of the scar stabilises and vegetation can start to grow over it, further stabilising it. Both these processes need the removal of grazing pressure in order to get started.
The early images in both these sequences show what would be generally regarded as typical, “natural”, upland Borders streams. However, the changes that happened when grazing pressure was removed shows that actually they were very far from being “natural” and their appearance was the product of all-year-round grazing rather than their natural state, which would be more like the images later in the sequences.
From the point of view of the fish in the burn, the increase in the bankside vegetation gives them more cover from predators and will increase the amount of leaf litter entering the water to feed the aquatic invertebrates on which the fish feed. More terrestrial invertebrates will also live alongside the stream and be food for fish. Temperatures will also be reduced by the shading effects of this vegetation, a factor that could become of great importance in future years.