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Human Impacts on the Caledonian Forest 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.

Heavily-overgrazed rowan seedlings on the West Affric Estate, October 1992.

The same rowan seedlings in May 1996.

The same rowan seedlings in May 1999.

By May 2004, almost 12 years after the first photograph was taken, the seedlings have made no net growth, because of the pressure from the deer.

Still chewed down

July 2008, and the rowans are still being kept in check at the same height by the grazing pressure. The growth of these young trees has now been completely crippled for at least 16 years.

June 2012, almost 20 years after the first photo was taken, and the rowans are still completely suppressed by the grazing from deer.

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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Trees for Life is an award winning conservation charity working to restore the Caledonian Forest
and all its species to a large contiguous area in the Highlands of Scotland.

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