Overgrazing
Overgrazing by large herbivores such as red deer and sheep has been the primary cause of the lack of tree regeneration in the Caledonian Forest in the past 150-200 years. As a result, by the late 20th century, most of the remnants of the forest consisted only of old trees, because all the seedlings were eaten before they could grow to more than a few centimetres in height.
With the red deer population in the Highlands having increased from 150,000 to over 350,000 since 1965, and in the absence of any natural predators to control those numbers, the only tree seedlings to grow successfully have been those inside fenced areas or in remote locations inaccessible to the deer.
Red deer are a forest dwelling species, and are an important component of the Caledonian Forest, but at present their numbers are totally out of balance with the small fragments of our native forests which remain. Although all trees are browsed by deer, broadleaved trees are more palatable than Scots pine, and have probably been selectively overgrazed for centuries, so that they are disproportionately under-represented in many of the forest remnants today. Rowan (Sorbus aucuparia) and aspen (Populus tremula) are perhaps the most-preferred of all trees by the deer, so there is virtually no chance of these species regenerating in unprotected areas under present conditions.
This is graphically shown by these photographs, which illustrate the effects of deer browsing on the same rowan seedlings on the West Affric Estate in Glen Affric over a period of many years.
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To see how tree seedlings can grow over a similar period of time when not suppressed by grazing pressure, see the Practical Results Of Our Work section.
Alan Watson Featherstone
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