In The Loanan valley at Stronechrubie
The River Loanan is one of two main feeders of Loch Assynt, entering the loch at its south-eastern corner, as does the other one, the River Traligill. Originating in Loch Awe, its course winds northwards for some 6km. Its western tributaries drain quartzite slopes below Canisp, Meallan Liath Mhor and Beinn Gharbh. The eastern ones are shorter, apart from the Allt nan Uamh, but they all originate in or traverse limestone, including the impressive crags at Sron Chrubaidh.
The northern part of the valley (photo 1) contains what has been described as ‘a well-defined push moraine complex’ (Lawson, 1995), thick layers of silts, sands and gravels, which emerge as mounds in places, but are covered elsewhere by deep peat.
A query about the ecological interest of the Loanan valley prompted us to start re-surveying it by 1km square, and we made a start on the afternoon of 13th June 2024, in NC2419, south of the lodge at Stronechrubie (map, photo 2). We followed the southernmost of several small burns running off the limestone scarp to the east, which are culverted under the road. They then cross the valley to join the river.
Burn course
The upper parts of the burn follow grassy courses cut through the peat (photo 3), with a mixture of marsh and waterside species, such as cuckooflower Cardamine pratensis, marsh hawk’s-beard Crepis paludosa, northern marsh-orchid Dactylorhiza purpurella, ragged-robin Lychnis flos-cuculi and valerian Valeriana officinalis. The presence as well of fairy flax Linum catharticum is an indication of base-rich water. We also came across signs of occupation by water voles, holes about the size of a tennis ball surrounded by cropped ‘lawns’ (photo 4).
Further down, the burn widens, running over a gravelly bottom (photo 5), with aquatics such as marsh marigold Caltha palustris (photo 6), and the stony cases of caddisfly larvae Agapetus sp. anchored on larger stones (photo 7). In places the burn has been actively eroding the adjacent peat, revealing the buried remains of ancient Scots pines (photos 8-9). They flourished here for a few hundred years, in a warm interlude about 4500 years B.P., before being overwhelmed by renewed growth of peat when the climate deteriorated. Not long afterwards, Gwen had a fleeting glimpse of a male argent and sable moth, the larvae of which feed on bog myrtle in the adjacent wet heathland.
River Loanan
Shortly after finding the bog pines, we reached the junction of the burn with the river (photo 10). Here the influence of the limestone sources of its eastern tributaries became very apparent, with a fringe of quaking grass Briza media along the water’s edge (photos 11-12).
Downstream, the course of the river is quite rocky in places (photo 13). The outcrops are pipe rock, a form of quartzite that is markedly mineral-deficient. However, rich vegetation on grassy shelves beside the river continued to show the influence of its base-rich waters, with calcicoles such as the tall downy oat-grass Helictotrichon pubescens, as well as long-stalked yellow-sedge Carex lepidocarpa, northern bedstraw Galium boreale, alpine bistort Persicaria vivipara and yellow saxifrage Saxifraga aizoides.
We also noted a few trees, hanging out over the river, where they were protected from browsing (photo 14). They were mostly grey willow Salix cinerea or downy birch Betula pubescens, although we did find one well-browsed alder Alnus glutinosa (photo 15).
Island and gravel bars
About 300m below the confluence of the burn and river, the Loanan splits around a large gravelly island (photo 16). This is covered with an impenetrable thicket of gorse Ulex europaeus, sheltering a few scattered rowans Sorbus aucuparia and, on our visit, a singing willow warbler. We kept to the eastern bank (photo 17), where the peat was again being actively eroded, revealing layers of what we took to be downy birch stems and roots (photo 18), probably dating back, like the bog pines, to the brief warmer period some 4500 years BP.
We had a good look at the vegetation on one of the gravel bars (photo 19), predictably finding the leaves of colt’s-foot Tussilago farfara (photo 20). Although this plant occurs widely elsewhere on disturbed ground in urban and industrial settings, this is its ‘natural’ habitat. There was also a full suite of lime-loving species, adding hair sedge Carex capillaris and flea sedge C. pulicaris to those already mentioned.
In conclusion
Shortly afterwards we left the river course, made our way to the road, and walked back along the verge to where we started (with care, since cars speed along this stretch). This yielded a further ten fairly predictable species, including the roadside halophyte northern saltmarsh-grass Puccinellia distans borealis, which is actively spreading along roadsides in the north, and may well be ‘new’ to this 10km square.
In some three hours we logged 130 species. More importantly, we had begun to appreciate how much base-rich water off the limestone contributes to the diversity of the vegetation along narrow burn and river corridors. This is in stark contrast to the typically species-poor communities in the wet heathland on adjacent deep peat, which has been further impoverished in places by historic peat cutting (photo 21).
Incidental observations of animal life included sand martins overhead (they nest nearer the mouth of the river), a toad, a frog, and a very distinctive small lacewing (photo 22). Stephen Moran identified this later as Micromus variegatus. The only other local record of which was made by him on a Field Club meeting at Inchnadamph (NC2521) on 17th August 2008, a nice coincidence.
Ian M. Evans and Gwen Richards
Reference. Lawson, T.J. (ed., 1995). The Quaternary of Assynt and Coigach. Field Guide. Cambridge, Quaternary Research Association.
Photos by the authors