“Well-managed riparian woodlands play an important part in providing habitat essential to the life-cycle of salmon and sea-trout.” States the Prince of Wales in a foreword to the Scottish Native Woods publication, Restoring and Managing Riparian Woodlands, by John Parrot and Neil MacKenzie.
But Dr David Summers, the fisheries manager of the Tay District Salmon Fisheries Board, disagrees with this view. He believes the planting of trees could be a costly mistake. He says, in the Tay Board’s annual report for 2000, “In fact the weight of actual evidence would suggest otherwise, at least if trees are allowed to be prolific.”
In the Scottish Native Woodlands publication, the authors argue that leaf litter from trees growing along the banks of rivers provides food in nutrient-poor upland streams for the larvae of many insects and flies, which are eaten by fish of the salmon family-salmon, sea trout and brown trout.
Dr Summers argues that insects which graze on algae in streams are a more important food source, and that there is a negative impact on algae growth, and the number of such insects in streams shaded by trees.
The two sides also disagree on the food value of land insects such as caterpillars, flies and spiders falling into the water.
Dr Summers believes such insect life does, in fact, benefit the trout, which tends to feed midwater, but that terrestrial flies are of little importance to salmon, a bottom-dwelling species.
And he suggests trees might even reduce the number of insects blown into the water from surrounding land.
The two sides also disagree on the value of debris dams in streams for young salmon and other fish.
The SNW publication says, “woody debris plays a crucial role in rivers, and it’s removal is detrimental to natural stream functioning.”
They argue that such dams help reduce the velocity of running water, maintain water temperature, increase aeration, provide cover for fish and increase the number of territories which fish can occupy.
But Dr Summers believes that while such debris dams can benefit Pacific salmon, the Atlantic salmon, the species found in Britain, are not pool dwellers.
He concludes, “The planting of trees appeals to the popular imagination for its own sake, and is generally assumed to be a good thing. But if the wooding of our streams turns out to be a mistake, it will be costly to rectify.”
