The Affric Highlands rewilding team are working hard to restore river woodlands. As climate change increasingly impacts the landscape, these will connect fragments of existing native woodland, reducing flood risk, boosting fish populations, and enhancing biodiversity.
Shadier, cooler rivers
“Water temperature is already rising in Scotland,” says Paul Greaves, the Riparian Officer attached to the Affric Highlands rewilding team. “Restoring woodland and increasing the amount of shade along rivers will help to minimise temperature increases in the future.”
Juvenile Atlantic salmon begin to struggle when water temperatures rise above 20°C. At 23°C juvenile salmon experience thermal stress and exhibit behavioural changes, ceasing to feed and abandoning territories. For a species already facing a multitude of threats, getting into hot water is the last thing it needs. A study conducted in the summer of 2018, found that around 70% of Scotland’s rivers exceeded the 23°C threshold at least once. When this year’s data is all in, it seems likely that the hot summer of 2022 will have set new unwanted records. In the River Spey, water temperatures are calculated to have risen 2-3°C in the last 100 years and current trends suggest that summers like 2018 could occur every other year by 2050.
Flood risk is another growing concern as Scotland’s rivers are subjected to heavier downpours in our changing climate, causing rivers to rise rapidly. Deforestation has compounded this problem, as trees both intercept water before it enters rivers and naturally facilitate water infiltration into the ground, acting to regulate the extremes of flood and drought associated with treeless catchments. Without tree cover, water sluices off the hills straight into swamped river systems. Fierce flows can scour riverbeds clean of the life they hold, washing away spawning beds and flushing juvenile salmon out of rivers altogether, leaving young fish stranded as floodwaters recede.
Given these wider challenges, a key aim of the Affric Highlands river rewilding plan is to restore trees to bare banks, allowing natural processes to come to the fore, reducing flood risk, improving water quality and sheltering more life. In Glen Affric, mixed woodland already lines parts of the lochs and the lower reaches of the River Affric, including bays skirted by deep rows of birch, rowan and aspen. Steep-sided burns have sheltered some of these trees from the grazing pressure on the surrounding moorland, creating a valuable seed source of locally adapted trees.
Where possible, natural regeneration of these surviving fragments will be promoted within fenced exclosures, protecting seedlings from grazing animals, but where sections of river extend too far from existing seed sources planting is being planned, utilising saplings grown from locally sourced seeds. For some years now, Glen Affric has seen significant planting effort along its loch shores and burns, feathering the water’s edge with a fresh green canopy and providing sources of shelter and food for wildlife.
Towards wilder rivers
Increasing the size and connectivity of Affric Highlands’ riparian habitats will increase the landscape’s resilience to disturbance in this era of climate breakdown, stabilising riverbanks, slowing the flow following heavy rainfall, providing cool shade in summer and offering vital shelter. Wet woodlands create a wide variety of habitats, with rotting wood full of grub-filled cavities and potential nesting holes. Trees also lock up carbon, add nutrients to the river via falling leaves, and create dappled shade from the summer sun, while the woods themselves create a cooler microclimate. Below the water’s surface, woody debris that falls into the river shelters young fish and diversifies stream flows, creating and protecting vital spawning beds.
Want to know more?
- More about the Affric Highlands rewilding landscape
- Visit the Affric Highlands
- Rewilding actions in Affric Highlands are financially supported by FedEx
- Trees for Life