Scotland's forests of American trees

In April of this year I had the pleasure of backpacking along a 80-mile trail in Scotland, the Rob Roy Way. Situated in the Highlands near Glasgow, the trail begins near Loch Lomond and winds its way to the town of Pitlochry on the edge of the famous Cairngorms National Park in central Scotland. My partner and two other long-time friends and hiking buddies spread the 80 miles over 8 days. 

Three highlights of the trip:  the lovely Highland scenery; the weather was delightful for hiking - cool-ish and dry; and there were no major injuries along the trail.

Carpet of American Sitka spruce trees overlooking a small highland lake

Tree harvest activity is visible for miles

Focusing in on the scenery, it struck me how much of the landscape along the trail was occupied by cultivated plantations of pine trees. Before the trip, my naive idea of the Highlands was of windswept moors, heather, and stones. But, the reality of what I saw in this corner of Scotland was much more managed, with lots of tree farms and sheep folds.

Also, being the horticultural novice that I am, I was surprised to learn the vast majority of the trees growing on the plantations are introduce from North America (Sitka spruce, Douglas fir) or from Europe (Norway spruce). The native Scots pine trees are relatively uncommon as a commercial variety.

Signs of successive tree harvests

Sitka spruce forest along a Highland trail

Economic benefit for Scotland

Although managed forests make up only 1% of Scotland's GDP, the plantations are critical to the economies of many rural highland communities. Scotland's forests produce 90% of the UK's homegrown timber supply. Despite the massive timber plantations of Scotland, the UK is still a net importer of wood products.

Environmental impact

Ecologically, large tracks of non-native American trees are uninhabitable by some wildlife species which have co-evolved with native tree species. Large monocultures of pines cause acidification of local streams from their decaying needles, which damages local fish stocks such as wild salmon. Large monocultures also encourage the spread of invasive pests, such as emerald ash borer and Dutch elm disease, which can quickly wipe out entire plantations.

Regimented rows of Sitka spruce trees

Sitka spruce

• Sitka spruce (Picea sitchensis) is the dominant species in Scotland's forest industry.
• Native the northwest coast of the North American continent, the spruce grows well in the cool wet climate of Scotland.
• One of the largest of all tree species on Earth, Sitka spruce in its native range of North America can grow to over 300 feet in height and 6 centuries in age. But in Scotland the trees are harvested at 35 to 50 years, less than 100 feet in height.
• The spruce's commercial value lies in its fast growth compared to native pines, adaptation to the cool wet climate, disease resistance, and high-quality wood.

Distinctive blue-green color of Sitka spruce branches

Scots pine alternative to non-native trees

• Recently introduced into law, the Forestry and Land Management (Scotland) Act of 2018 explicitly requires "the conservation and enhancement of the environment by means of sustainable forest management" as a core directive.
• Among the provisions, it encourages crop diversity with and emphasis on native tree species such as Scots pine (Pinus sylvestris).
• Scots pine is Scotland's only native commercial conifer, it anchors both the native restoration targets and the timber production targets.
• Although laudable, compared to Sitka spruce and Douglas fir, Scots pine grows more slowly and has somewhat poorer wood quality for commercial uses. Doing the right thing for the environment has an obvious cost to the economy.

Lonely Scots pine tree

Scots pine tree, lone sentinel in an open field of the Scottish Highlands