Читать книгу Natural History in the Highlands and Islands - F. Darling Fraser - Страница 16

This is the most westerly portion of Scotland, the seventh degree of West Longitude passing down through the middle of this long range of islands which effectually shields the northern half of the West Highland coast. If we study a population map we see that the greater part of the people on the Long Island, as the whole group is called, are fairly densely packed on to the western fringe. Some more dense places are also found on the extreme east of Lewis, as on the Eye Peninsula or Point as it is always called in Lewis. By merely looking at a map one might ask why the people are so densely grouped on the west side where harbours are fewer and where the force of the Atlantic Ocean is unbroken. The very fact of human density of population is surprising to anybody accustomed to the alarming rate of depopulation on the mainland shore of the West Highlands. The Hebridean has a love of home which is unconquerable. There he has remained through thick and thin, sticking to his fringe which is between the mighty ocean and the deadening peat bog of the interior.

The half-million and more acres of the Outer Isles mean nothing in relation to the human population which lives there because to a large extent the interior is just as uninhabitable as the ocean. The people being confined to the coastal fringe live what might be called an open urban existence without town planning.

The overpowering reason for the human species being confined to this fringe is that here the awful blanket of peat ends and the ocean has thrown up an immense weight of shell sand. As the dunes have stabilized through the millennia and the stiff marram grass has given way to kinder herbage, a light lime-rich soil has formed. There are miles and miles of the white sand on the Atlantic shore, and above it the undulating machair (Plate XIXb) of sweet grass on which are reared great numbers of Highland and cross cattle. Flocks of barnacle geese come to the machair in winter and add to the humus content of the sandy soil. The prevailing south-westerlies continue to blow winter and summer, year after year, century after century. The tangle from the shallows of the ocean, the various Laminarias of the marine botanist, is torn from its bed and washed up on the beaches. Man comes down with his ponies and carts and creels and takes up some of it to spread on ploughed portions of the machair. All these things are helping to make soil, and the sand itself in these gales, especially if the winds are dry, is being blown up towards the blanket of peat which overlies the archaean gneiss of the Hebrides. The sand sweetens the peat, causes its barren organic matter to be unlocked and become fruitful of herbage for man’s beasts. Their dung still further ameliorates the peat. Such is the constant process, in which the storm is a necessary and beneficent factor in allowing and maintaining fertility. But once the coastal strip is crossed the peat reigns supreme. Its blanket must have increased about ten feet since early man came to the Outer Isles, for only the tops of the fine Megalithic stones at Callernish, Lewis, were showing when Sir James Mathieson of the Lews undertook their excavation. The landscape in the bog is shortly described—a low undulating plateau of peat, bare grey rock of gnarled shape, and thousands of small and large lochans of brown acid water. If we wander through these areas of peat we shall come upon drier knolls where the rock comes to the surface or is not far beneath, and here we shall find turf and greenness for a space. The shielings of Lewis have been and still are here. They are the summer dwellings of a pastoral people taking advantage, for their cattle and sheep, of the short spell when the peat grows its thin crop of sedge and drawmoss. The people lived on the little knolls as on islands, bringing their cattle up to them twice a day for the milking; throwing out their household waste—little that it was—and adding their own quota of dung and urine. The shieling life is mostly gone but the green knollies in the sea of rock and peat remain.

We may digress at this point to consider the nature of peat, this substance which covers a million and a half acres of the Highlands and Islands and the existence of which is a most important factor in the natural history of the area and of the scenery. A study of the peat is interesting not only for what it grows and harbours now, but for the history to be deduced from a deep profile of it. Peat forms under the influence of certain definite conditions and their consequences: the first requirements are high precipitation and a general coldness of atmosphere in the growing season sufficient to inhibit bacterial activity in the waterlogged soil, but not cold enough to prevent growth of certain plants. A vegetational complex of sour bog plants, such as sphagnum moss (Plate 22b), sedges of various kinds and cross-leaved heather, soon occupies the ground to the exclusion of all those plants which need a well aerated soil and a supply of basic compounds. The rain impoverishes the original soil by washing out plant foods and then, by creating waterlogged and therefore anaerobic conditions, prevents the action of normal soil bacteria in breaking down the dead vegetation into humus. Such necessary decomposition does not keep pace with vegetative production by the plants, so that a gradually thickening layer of peat forms. The peat, thus composed of organic matter without lime, is highly acid in character, which is a still further check to bacterial action. Even the run-off water from the poor rocks such as gneiss and Torridonian is charged with unneutralized carbonic acid. With compaction and age, the peat becomes colloidal in texture, a fact of much influence in the behaviour of peat in holding water or being dried. The normal water content of peat as it lies in the bog is as high as 93.5 per cent.

Peat varies in consistency from being highly fibrous to the state of a black amorphous substance, depending on age and the type of vegetation. The Highland crofter is well aware of these details and his methods of winning peat for fuel vary from place to place. Cottonsedge peat is tough and fibrous and can be “footed” (i.e. set up on end to dry in pyramids of four bricks) and handled later with very little loss. Lower, older, amorphous peat is very brittle and cannot be set up.

The ages of the peat deposits have been tentatively fixed as beginning about 7000 B.C. at the close of the Boreal period. The warmish dry climate which grew forests of pine, birch and hazel now became warmish and wet, bringing about destruction of the scrub hazel vegetation by moss. The Atlantic period closed between 5000 and 4000 B.C. and a cooler and somewhat drier sub-Boreal period set in with a rapid development of peat. This continued until near our era which may be termed cold and wet and sub-Atlantic. The peat to-day is still making in some places as on the main bog of Lewis, and receding in others, as in parts east of the Cairngorms where the stumps of forest trees are coming forth as the peat crumbles away. Continual burning on western hills is probably having more influence than we know in checking or denuding the peat which is the only cover the rocks have, but in Lewis there is very little burning, the slopes are gentle and the succession of blanket bog is not being much disturbed, except by cutting for fuel.

The colours of the Atlantic coast are vivid blues and greens and the bright cream of sands. Inland, sombre colours are paramount and the lochans do not reflect the colour of the sky from their dark depths as does the sea above its floor of white sand. But the Hebrides are not all a dark plateau. The southern end of Lewis (Plate VII) and most of Harris are hilly. The Forest of Harris gives us rough going as anywhere in the Highlands and the Clisham rises to a fine peak of 2,622 feet. The red deer which live in these fastnesses are small, but have very well-shaped heads. The pine marten was also to be found there until recently. Its very wildness is the best protection this piece of country has. The lower deer forests of Park and Morsgail are fairly heavily poached of their deer, in an island of such heavy human population.

The Hebridean burns a lot of peat. His peat stacks are far larger than those of the mainland. By cutting peats he is doing two jobs—providing the wherewithal for comfort at the fire, and removing some of the great pervading blanket. He does not come upon bed rock at the foot of the peat banks but on to a layer of boulder clay which, when mixed with the top thin layer of sedge and peat, will shortly turn into fairly good soil providing much better grazing than anything from the top of the peat. The boulder clay came there by glacial action before the peat was laid down. Our Lewisman makes new ground this way and there is no doubt that if the modern mechanical tools such as the scraper and bulldozer were brought into operation on what is commonly called the skinned land, the agricultural scientist could make much good land in Lewis without attempting to conquer the upper layer of the peat.

As might be expected, the bird life of the interior of the Outer Hebrides is poor in variety and scanty, the nesting grey lag geese and red-necked phalarope (Plate XXXIIa) being probably the most interesting members. The geese feed on the crofting ground and on the machair but return into the maze of the interior to nest. The coasts are rich in sea birds, ducks and waders.

The Outer Hebrides are often described as being treeless, but the term is relative. The people who write about them are usually those who have a considerable experience of trees and tend to take them for granted. The Outer Hebrides are neither treeless, nor need they continue to be so desperately short of trees as they are. The grounds of Stornoway Castle on the east side of Lewis are famous. There are hundreds of acres of trees here, mostly conifers, but with a fair sprinkling of hardwoods and deciduous trees. These are Lady Mathieson’s legacy to the Hebrides. Indeed, it needed courage to start tree-planting from scratch. She planted another piece with larch and other conifers half-way across Lewis, near Achmore, and these made good trees, but were blown down by a terrific gale on March 16, 1921. There are 90-year-old Corsican pines of hers at the head of Little Loch Roag, growing quite straight to 35 feet high. There is another plantation of deciduous and coniferous trees at Grimersta on the Atlantic coast of Lewis. Another plantation of conifers sheltering a house, Scalisgro, on the east side of Little Loch Roag, is less than twenty-five years old, and twelve years ago several acres of conifers were planted in Glen Valtos in the Uig district of Lewis. Sycamores are the great standby of a tree lover on an ocean coast. Several good ones are to be seen at Tarbert, Harris. And at Borve on the west side of Harris there are several acres of stunted mountain pines. More trees are to be found about Ben More Lodge in South Uist, and there are a few more in the north glen of Barra. Heslop Harrison has recently drawn attention to the birch wood, complete with bluebells and wood sorrel, on the slopes of the Allt Vollagair, South Uist. As has been mentioned already, many of the islands in the Lewis lochs are covered with dwarf rowans. That the Outer Hebrides were once a wooded area may be deduced on archaeological grounds as well as on the living relics. Baden-Powell and Elton (1936–37) excavated an Iron-Age midden at Galson on the north-west coast of Lewis. They found bones of wild cat and blackbird among the refuse, both creatures of woodland and savannah. The age of the midden was reckoned at 1,500 years or thereabouts.

What is most heartening in the woodland situation in the Outer Isles is that the crofters themselves are taking an interest in trees for shelter, and in many a garden you will see a host of willow cuttings bravely shooting forth in summer and making some certain headway against the gales and spray from the Atlantic. Rhododendrons are growing quite well in many places and are at least providing the first cover for something else to grow within their shelter.

The sands and the machairs of the Hebrides are often referred to in this book: in the Sound of Harris there are several islands which seem little else but shell sand, such as Ensay and Berneray; and there is Vallay of North Uist. But I would not wish to neglect the cliffs which are also important in the natural history of the Outer Isles. The great ocean pounds against them and must be gradually wearing them away, but the rock is the old gneiss and holds remarkably well. Sir Archibald Geikie in his Scenery of Scotland calls to mind the measurement of the pounding effect of waves which was made at the Atlantic rock of Skerryvore before the lighthouse was begun in 1845. The summer average weight of pounding was 611 lbs. per square foot; in the winter months it was 2,086 lbs. per square foot, and in the very heavy south-westerly gale of March 29, 1845, a pressure of 6,083 lbs. per square foot was registered. Even when it is water alone that strikes the rock, the wearing effect is far from negligible, but when other loose rock is moved by the water and pounded against the cliff, even our short lifetimes may be able to notice the denuding effect of wave action. I remember an incident on North Rona which certainly opened my eyes to what a big sea could do. It was in December, 1938, in a period of south-westerly gales which would veer to west and north-west and begin again from south-west before the wind had fallen. They were worst in the nights and I would go out in the mornings to see the magnificence of sea against the low cliffs of the northern peninsula. These cliffs were perhaps forty feet high, but sheer, and going into deep water. The top was irregular with occasional ten-foot gullies a few yards wide in which were some very big boulders eight to ten feet thick, and a lot more of a size just too heavy for a man to lift. When there one morning, a sudden shower caused me to take shelter under one of the big pieces of rock. Peppered scars were visible all over the big boulder above and on the smaller ones lying on the smooth floor of the gully. It was evident that the sea had come green into here and rolled the smaller boulders up and down. But observation was not critical enough to question how these smaller boulders could pepper the big one several feet above. When sheltering there again after another tremendous night, it was obvious that the big boulder was not in the same place as it was the day before. Those pepperings had been caused by its own rollings to and fro in the gully under the impulse of the sea which had filled the gully thirty to forty feet above its normal level. That boulder, probably, had done much to wear the gully itself in the course of thousands of years.

Some of the cliffs of the Hebridean coasts are impressive and become the crowded haunts of ledge-breeding sea birds. The precipice of Aonaig in Mingulay is 793 feet. The stacks of Arnamull and Lianamull in Mingulay are also very fine. Harvie-Brown thought Lianamull the closest-packed guillemot station he had ever seen. Barra Head or Bernera, the most southerly island of the Hebrides, has some fine cliffs and in front of the lighthouse on the southern face is a gully which takes a terrific updraught of spray in southerly gales and makes the dwelling of the lighthouse suffer a heavy rain of salt water, a rain of sudden torrential showers of a moment’s duration.

The influence of the sea in times of storm has already been mentioned as a land-making one on the western side of the Hebrides where it throws up sand for biological agencies to work upon. The islands in the Sound of Harris probably change shape through the years, sand being laid down in one place and taken away in another. Pabbay, for example, was the granary of Harris but the sand has encroached over the south-east end and has gone at the west. West again of Vallay, a sandy island of North Uist, the remains of a forest of trees may be discerned at low spring tides. This submerged forest is probably the result of Holocene sinkings, but nevertheless the shell-sand beaches have certainly advanced within historical times. The minister in Harris who was responsible for the account of that parish in the Old Statistical Account of 1794 remarks that certain lands had been lost to the plough within living memory, and that when a sand hill became breached by some agency and was eventually worn away, good loam was sometimes found beneath and even the ruins of houses and churches. Whatever we may have lost in the Holocene sinkings, it may be remarked that the last three thousand years have seen more rising than sinking along Highland coasts.

The tides in the Sound of Harris have an interesting rhythm of their own, accurately noted by the minister in the Old Statistical Account. The following quotation is from the Admiralty Chart of the Sound of Harris: “It may be generally stated that in Summer, in neap tides, the stream comes from the Atlantic during the whole of the day, and from the Minch during the whole of the night. In Winter this precept is nearly reversed. In Spring tides both of summer and winter the stream sets in from the Atlantic during the greater part of the time the water is rising, but never for more than 5¹/₄ hours, and it flows back into the Atlantic during most of the fall of the tide. Where the water is confined by rocks and islands…the velocity is nearly 5 knots…during springs, and not much less during neaps, whilst in other places it does not exceed a rate of 2 to 2¹/₂ knots.”

The east side of the Outer Isles is entirely different from the populous and spacious west side. Admittedly, north of Stornoway there are the sandy lands of Gress, Coll, Back and Tolsta, and the Eye Peninsula, supporting many crofts, but south of there the land is peat-laden and comes to abrupt cliffs at the sea’s edge. The bird life is nothing like so interesting as on the western side and on such cliffs as exist there. Long arms of the sea, such as Loch Seaforth and Loch Erisort, Loch Maddy and Loch Eport, run far into the interior; indeed, the last two named almost reach the west coast in Uist. To me this east coast of the Hebrides is uninviting and curiously dead. It is my experience that many of the islands off the West Coast of Scotland are much more interesting on their western sides than on their eastern shores. Raasay is an exception.

The east side of Harris from East Loch Tarbert to Rodel is well worth a visit to see what man can do in the shape of difficult cultivation. Take for example the township of Manish where the ground rises at a steep slope from the sea. It is in reality a rough face of rock devoid of soil but holding the peat here and there. The lobster fishers of Manish have actually built the soil of their crofts by creating lazy-beds or feannagan with seaweed and peat. By building up these little patches varying from the size of a small dining-table to an irregular strip of several yards long, the inhabitants have overcome the difficulty of drainage. The women carry seaweed up to the lazy-beds each year, all in creels, for the ground could not be reached by ponies. And all cultivation is of necessity done with the spade. Two crops only are grown, potatoes and oats, and the oats are Avena strigosa, which more than one naturalist has thought to be extinct as a cropping oat and only occurring here and there as a weed. The industry of the people of East Harris and their steadfast persistence with a thousand-year-old style of husbandry are remarkable. The potato is the only new thing, being brought to the Outer Isles in 1752. There are many more primitive townships in the Outer Hebrides working lazy-beds, but none in more disadvantageous position than Manish and its neighbours.

The Outer Isles also have their Atlantic outliers, each little group having its own strong individuality. There is St. Kilda (Plate VIIIa) on the west of the Uists, seventy-four miles out from Lochmaddy via the Sound of Harris; this group of magnificent gabbro architecture has already been mentioned, with the fact that it is the largest gannetry in the British Isles and in the world. It is also the place from which the still growing fulmar population of the British Isles may originally have spread. The islands and their peculiar sub-specific fauna will be described in a later chapter. The Monach Isles are only eight miles west of North Uist, and are likely to follow so many small island groups in becoming uninhabited by man. They are islands of sand caught and built up on reefs of Lewisian gneiss. Another reef to the south of them, Haskeir, has not collected the sand. It is much smaller and uninhabitable but has long been a haunt of the Atlantic seal and was one of the last strongholds before the revival of the species in the present century. The Flannan Isles are twenty-two miles west of Loch Roag, Lewis. They are of gneiss and bounded everywhere by cliffs. The seals feed near them, but of necessity do not breed there because they cannot haul out. The relatively flat tops of the islands are covered with very fine grass which feeds a few sheep. The difficulties of gathering and getting the sheep to and from the boats are likely to be the cause of even this usage being discontinued. The lighthouse is the only inhabited place in the Flannans and to get ashore there can be a ticklish job.

Then to the north and north-east of the Butt of Lewis are Sula Sgeir (Plate XXIIIa) and North Rona (Plate XXIVb), forty and forty-five miles away respectively. There are no beaches on these islands. Their natural history will be described in greater detail in Chapter 10. Suffice it to say here that Sula Sgeir is a gannetry, and like North Rona, St. Kilda and the Flannans, is a station for Leach’s fork-tailed petrel. It is doubtful whether we should be justified in calling Leach’s petrel one of the rarest British birds, but its breeding places are so few and so remote that it is unknown to all but half a dozen naturalists.

We have come to the end of our arm-chair tour of Highland country, from the frontier zone of Perthshire and Angus to that other frontier, the oceanic zone of the Atlantic. I have given but a glimpse of what is without doubt one of the finest scenic and faunistic areas in the world. Whether it survives as such depends very much on the good will and active, participant care of British people. Any area of natural history which is adjacent to a highly populous industrial region is in peril from that very proximity, but there is always the point of view that men’s minds become awakened to natural beauty and the right of wild life to existence for its own sake, and then the proximity may be to the advantage of wild life and the wild places, in the same way that no country sparrows or moorhens are as tame and safe as those of St. James’s Park.