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The Evolution of The Vegetation of Northern Scotland
As the ice melted from the last ice age it revealed the bare mud underneath. Mostly a wet sticky sodden clay or perhaps sandy or gravelly in places. Not much nutrient humus to be found in such material, and the constant freezing and then washing with meltwater made it a most unattractive soil. The first plant inhabitants would be typical Tundra occupants. The start is made with lichens such as the 'reindeer moss', and mosses like the woolly hair-moss. The saxifrages are notable among the higher plants and the Mountain Avens (Dryas octopetala). As these plants die and form humus then the grasses and sedges start to appear along with low shrubs of willow and juniper. We still have the tea-leaved willow as a remnant of this type of coloniser.
By 6500 B.C. the weather was getting warmer and drier so that trees would not get their roots waterlogged in winter and the wind was not so fierce as to damage them in spring. A forest began to form. First birch and hazel, alder and rowan then later pines, oaks and ash in some places. The remains of this forest are to be seen in the peat deposits all over the north, and since the sea level was lower than it is now some of the forest remains are in the present sea bed.
By 5500 B.C. the weather had become warm and more moist. The rain poured down in torrentss and the land surface became waterlogged. The trees died. The dead leaves and their plant remains fell into the wet and just stayed there because the bacteria which break down the debris cannot work in still water. The remains formed layers of peat which grew thicker as the land became covered in sphagnum moss and cotton sedges. It was into such a place that the first settlers came to live. They could travel over the moor more readily than through the forest and they could live on the drier sand-dune areas where drainage was good.
Around 3000 B.C. the weather began to get dry and quite cool. The land began to take on a cover of shrubs and grasses and Mesolithic and Bronze Age men lived in a country which was heavily wooded in the straths and lightly wooded in the open country. The woods were horrifying places - dark, impenetrable and filled with boars, wolves and other undesirable creatures.
Once again the rains came at about 500 B.C. and for a time it must have been very wet for all the trees were swamped. in peat which grew very fast into layers up to 30 feet thick which covered most of the land mass. This is the peat cover which is to be seen today for much of the land has never recovered from its effects.
The time of the Broch builders was as the land was recovering from the deluge and some well drained areas became free of the peat. Slowly the straths were lightly wooded again and the soil became sweet enough for the early farmers to practice their arts.
From this time on the surface vegetation has been strongly influenced by man's activities. The keeping of goats and later of sheep prevented the regeneration of the birch wood which might have formed. Increasingly large areas of land were cleared for arable farming and boggy areas were drained for grazing. The burning of the peat moors ensures that the hill land will make no further progress towards its natural state.