Take a close look
TAKE A CLOSE LOOK…….
1 For around forty years, I was connected with, and working at, the Aigas Field Centre in Strath Glass, Inverness-shire. I always felt that my most important work there was being closely involved with the training of the seasonal Rangers; I was there, in effect, to introduce them in some depth to the landscapes of the Northern Highlands and Islands in which they would be working. And at some stage, particularly latterly, I would ask them to interpret the photograph above. (Try that, if you want to……).
2 This image is, in this context, important in two ways. Although such generalisations must be made with great care, this is indeed probably one of the most natural landscapes in Europe; being on a remote headland on the North Coast it is extremely exposed, scoured by salt-laden winds. Look at the stunted bracken in the foreground; in sheltered glens not that far away it reaches six feet in height. Despite the favourable geology of the foreground, planting trees here would be a huge waste of stock and time……………and would destroy the natural landscape that is there.
3 The other important message from the photograph is that in the far North and West, subtle visible differences in the landscape may have considerable and important implications; anyone, or any body, who has ambitions for part of this landscape needs to be truly aware of those implications.
4 The fundamental component of the landscape is, of course, the geology, (which is crucial in the above photograph). Underneath it all lies the very ancient Lewisian Gneiss, around 3,000,000 years in age. It is extremely hard and resistant to erosion, but, in places, criss-crossed by igneous dykes, which can give rise to a richer soil chemistry. This, combined with the concomitant complex relief, can make the Lewisian landscape more diverse and rich than might be expected; linear woods often follow the line of the complex dykes.
5 Above it lies the massive thickness of the hard Torridonian Sandstone: although there are a few thin, calcareous bands on the hills, “ Torridonian rocks are generally uniformly acidic and….support vegetation that is floristically poor “. (1). Strictly speaking, these rocks can be described as ‘permeable’ but they lie so often in deep, largely horizontal strata, that any soil above them is often waterlogged.
6 The summits of many of the sandstone mountains are covered with the pale Cambrian Quartzite, but there are also often extensive dip-slopes. They produce “ some of the most acidic and base-poor, rock-origin habitats in Britain” (2). Being almost pure quartzite and effectively impermeable, angled slabs of this rock are often devoid of any vegetation.
7 To the east of the Lewisian-Torridonian-Cambrian foreland, lies the complex zone of the Moine Thrust, which requires more detailed consideration than can be given here (1). Along that line, there appear ‘islands’ of limestone; porous and producing real green grass, as near Durness, Elphin, and on Sleat of Skye.
8 In the illustration above the bulk of the picture is on Limestone, covered in heather and bracken, dry underfoot, while the background is sodden, with coarse grasses, being on Quartzite. Geology really makes a difference………
9 What little soil erodes from these rocks evolves under the influence of the climate, and it often seems to me that you have to live in the far North and West to realise how truly oceanic it is. This means that we have lots of rain, with low summer temperatures and evaporation rates; all that rain hangs around in, and alters, the soil. Everyone thinks they know this, but it takes statements like the following for the reality to sink in:
“ The extreme wetness of the climate ensures that waterlogging occurs almost irrespective of the underlying geology”: (3) this is certainly true; in Assynt, peat has formed on some of the porous limestone. And: “ The occurrence in Britain of a naturally treeless tundra type of ecosystem far to the south of its main circumpolar distribution and at very low altitudes is also a feature of great ecological and bioclimatic interest”. (3). Although this refers specifically to what we now know as the Flow Country, to the east of the Moine thrust, the climatic differences east and west cannot be significant; the patterned bog and very deep peats of the Flows would appear west of the Moine Thrust, were the landforms not much more complex. (And, in fact, there are, for instance, small areas of patterned bog in Assynt).
10 “Climate” is not just about rainfall, days of rain, and low temperatures, it is also, and significantly, about wind. The North and West is very windy. “ Wind is certainly a major limiting factor so far as tree growth is concerned, and the prevalence of southwesterlies is borne out by the restriction of trees, in some areas, to north- and east-facing slopes “(1); this is even true at sea-level. A very good example of this is the marked difference between the northeast- and southwest- facing shores of Loch a’ Chairn Bhain in Assynt (a sea-loch).
11 The factor of exposure is often underestimated, but seaside plantings soon show its effects. Prevailing winds blow light seeds (birch, for instance) downwind; this effect has well been seen along the Assynt coast from Drumbeg to Kylesku. Part of the problem is the salt-laden nature of the prevailing southwesterlies: the seaward side of coastal bushes and trees is often blasted brown as the first, soft, green leaves emerge in the Spring. My mother lived some five miles from the sea, with ground of some 300 metres in height between her and the shore; on occasion she had to wash the salt from her windows. The effects of exposure may be seen all over Assynt and Coigach, for instance, in the plantings which have been done over the last thirty or more years; even ridges of around 150 metres in height count as ‘exposed, high ground’ this far north.
12 The combination of factors discussed above means that tree-planting in the Northwest of Scotland is more difficult than it is often thought; climate, exposure and altitude have been shown over decades to impose real limits on what is possible. And areas where the bedrock is Torridonian Sandstone or Cambrian Quartzite are particularly inhospitable. Of course, trees sometimes do grow on the Torridonian, but generally only where the drainage is good; the pinewood on Ben Shieldaig is on a steep, sunny and relatively sheltered slope, for instance.
13 Finally, of course, much of this geology is normally covered by deep peat, or peaty soil: NEITHER SHOULD EVER BE PLANTED, in order to avoid releasing carbon dioxide and methane to the atmosphere. And, in any case, such ground often fails to grow trees of any size; again, anyone wishing to plant trees in the North and West should examine carefully what has happened to those that were planted in such places - there are plenty failed schemes to inspect, or a number which have involved repeated attempts and a serious loss of tree-stock……which nowadays should be regarded as valuable, regardless of its market price.
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See ‘Flora of Assynt’ by P.A. and I.M. Evans, G.P. Rothero; perhaps the most detailed, authoritative and important account of any Highland area.
As above, quoting Chris Ferreira.
See ‘Birds, Bogs and Forestry’, Nature Conservancy Council, 1987. This, which is not nearly often enough read, was actually a revolutionary document at the time. Its relevance extends well beyond the Flow Country itself.