Allt Beithe Garbh is a 23 acre exclosure that we established for forest restoration in 1995. It was the second of ten fenced areas that we erected between 1994 and 2000 in partnership with the National Trust for Scotland (NTS) on their West Affric estate. The growth of trees since then demonstrates very effectively how a forest will naturally re-establish in the absence of over-grazing by red deer and sheep.
The exclosure protects a section of the Allt Beithe Garbh watercourse, which flows southwards from the hills on the north side of the glen, about one kilometre west of the Alltbeithe Youth Hostel. Like many Gaelic place names, it is quite descriptive, as indicated by the English translation, ‘rough burn or stream of the birch’ and presumably was derived from the steep, rock-strewn nature of the watercourse, where birches grew.
The site was selected for protection because it was one of the few locations on West Affric (along with the Allt Coire Ghaidheil watercourse, on the eastern boundary of the estate) where scattered patches of remnant trees still survived when the land was purchased by NTS in 1993. Those trees consisted of small groups of downy birch, rowan and eared willow that were clinging on in steep locations along the Allt Beithe Garbh, where they were out of reach of grazing by red deer.
Along with the Allt Coire Ghaidheil exclosure, it was one of two sites fenced to facilitate natural regeneration from the seed source provided by the remnant trees there. The other areas fenced on West Affric all had planting done in them, because of the lack of old trees there that could provide seeds for a new generation to grow from. All ten exclosures were planned and implemented by Adam Powell, who worked for Trees for Life for 19 years, and was our Field Officer for most of that time.
In the years since the fence was erected, natural regeneration of some trees has occurred at Allt Beithe Garbh, but it has not been quite so prolific or successful as at Allt Coire Ghaidheil. This is largely due to the fact that fewer trees existed at Allt Beithe Garbh when the area was protected. In fact, subsequent surveys that were carried out to satisfy the conditions of the Woodland Grant Scheme funding that paid for the fence showed that there were enough young trees growing there to meet the grant requirements, but 80% of them were rowans. Normally the main tree in a naturally-regenerating young woodland area like this would be downy birch, but because there were only a few old birches there, the regeneration has been restricted by that. In contrast, the seeds of rowans are transported by birds which have eaten rowan berries, and are deposited in their droppings, enabling the tree to colonise sites such as this, which can be far from a parent tree.
Tree regeneration has been variable across the area enclosed by the fence, with some parts containing dense stands of young trees, and other areas having none at all. When the trees reach maturity, this will give a varied appearance to the forest, and as such, is entirely natural. However, by contrast, a young woodland like this that consists of 80% rowans is obviously not natural, and in response to this imbalance, NTS has organised the supplementary planting of some downy birches there in recent years.
In addition to the regeneration of trees, the Allt Beithe Garbh exclosure offers a very good, visible example of the process of succession becoming re-established in the absence of overgrazing by red deer. The fence line provides a clear demonstration of this, with the vegetation outside being restricted to grasses (which are adapted to cope with grazing), whereas inside, the grass is being replaced by heather as the natural succession process, from grassland to dry heath, takes effect. Pioneer trees – the birches, rowans and eared willows that are there – then grow through the heather, and will, if given a chance over time, be replaced by slower-growing later successional tree species, such as oak, hazel etc. and indeed Scots pine too.
Like the other exclosures on West Affric, Allt Beithe Garbh graphically illustrates that the forest will recover in remote, largely tree-less landscapes like this, if it is given the opportunity to do so by reducing or removing the excessive grazing pressure. As with the other fenced areas on West Affric, this one is a key component in the series of ‘stepping stones’ of new woodland we’re helping to establish that will provide a Forest Habitat Network from the native pinewoods at the eastern end of Glen Affric through to the West Coast.
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