The Sitka spruce, although not native to Scotland, grows exceptionally well in Scotland's nutrient-poor soils and damp climate. Following the loss of forests during World War I, large Sitka spruce plantations were planted across Scotland.   

Forest management practices can lead to detrimental impacts on water courses with the most significant issue being diffuse pollution.

Historically, commercial forest blocks were planted up to the edge of the watercourse. This led to the loss of bankside vegetation due to the dense canopy blocking out sunlight which plants need to grow, and subsequent bank erosion due to a lack of understorey and the shallow root system of Sitka spruce. 

Timber is typically harvested and extracted from the forest using heavy machinery. Continually tracking heavy machinery back and forth across the site during heavy rainfall can lead to diffuse pollution, where preventative measures are not taken.  

The Sitka spruce is still the most popular commercial tree species (typically comprising 50-60% of a plantation) although it is no longer planted up to the water’s edge. Other commercial species grown include European larch, Norway spruce, Douglas fir and Scots pine. Furthermore, all new woodland creation schemes comprise a proportion of native broadleaves, some of which are planted in a mosaic along the riparian corridors.  The root systems of native broadleaves help to strengthen the riverbank, the patchy canopy provides dappled shading for the watercourse thus keeping temperatures down, whilst the introduction of leaves and woody material to the water, supports the life cycles of invertebrates and fish.

Careful planning and management of harvesting operations can ensure that diffuse pollution is prevented - for example by considering the gradient and time of year when planning harvesting operations across the site; disconnecting drains from water courses; marking out exclusion zones; using silt traps; and avoiding tracking heavy machinery through watercourses.

Best practice advice here: Forestry & Water Scotland - Know the Rules - 2nd Edition.

Forestry is widespread in the catchment and mapping of current and future plantations is in progress. An audit of the economic contribution forestry makes to the economy in the catchment will be available in 2026.