This section is from the book "British Wild Flowers - In Their Natural Haunts Vol2-4", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
The exposed nature of the uplands would at first sight appear to be a factor in the dispersal of hillside plants. As a matter of fact, upon the uplands there are extensive associations of a single species, such as Ling, Whortleberry. These as a rule occupy the higher zones, where the less dominant types are as a whole absent.
There are, however, wide associations, as in wet and dry meadows of Sedges, Rushes, Grasses, etc., at lower altitudes. Some of these may grow in such association, as Matweed, etc, as to exclude other types of plants with a different growth-habit. But even here, usually lower down there is a noticeable intermingling of other species. Amongst those with seeds dispersed by the wind are Weld, Rock Rose, Hare's Foot Trefoil, Sainfoin, Dropwort, Salad Burnet, Oak-leaved Mountain Avens, Ploughman's Spikenard, Cotton Thistle, Sheep's Sorrel, Musk Orchid, Fragrant Orchid, Sheep's Fescue, and some of these are dispersed in part by their own mechanism to a shorter distance.
Some are dispersed by animal agency, as Dropwort, Field Scabious. The Hairy Violet is assisted by ants in the dispersal of its seeds. In Touch-me-not and Rest Harrow special Contractile tissue enables the seeds to he jerked when ripe from the pod, as also in Kidney Vetch. Silky Mountain Vetch, and Box.
Hills, as has been explained, are largely the result, apart from denuding agencies and river development, of uplifts or rearrangements of the crust, thus causing a diversity of rocks to be exposed at the surface. Many types of rock may thus outcrop within a short distance, and the plants of a single hill or mountain may thus be of very diverse types. As explained also elsewhere, the older sandy or siliceous types are mainly developed in the west and north, though modern arenaceous rocks occur in the east and south also. Central England, as a whole devoid of hills, is largely made up of clays, loams, marls, and eastward there are calcareous rocks and chalk, with peaty conditions in the lowlands.
The Pennine Axis, and other regions in the west, and Lake district are made up of limestone.
The plants that are described are found upon all these types of soil. Weld, Rock Rose, Hairy Violet, Kidney Vetch, Sainfoin, Drop-wort, Salad Burnet, Wild Thyme, Clary, Box, Musk Orchid are found largely on limestone or chalk, though sandy soil also suits some of these. A sandy soil suits Marsh Mallow, Rest Harrow, Hare's Foot Trefoil, Field Scabious, Cotton Thistle, Sheep's Sorrel, Sheep's Fescue. But Hairy Violet may be found on a sandy or a humus soil. Humus also suits the Gentians and Fragrant Orchid. Touch-me-not requires peat like the last to some extent. Silky Mountain Vetch requires a rocky stony soil.
The reason for the separation of hills, etc., from other types of habitat being mainly one of altitude, the method of survey in this case must be, in order to obtain satisfactory results, carried out by surveying zones of altitude. That is to say, a region from 1-100 ft., and so on upward, should be marked off by aid of an aneroid, or orographic maps, or contours on an ordnance map. The altitudes of plants found between such zones will then be obtained, and it will be possible to determine by such data the exact range upward or downward of each species.
The mode of survey of each piece of ground as an area should be done in the case of the types so far described on those lines, whilst bog and heath or moor may be surveyed, as also any aquatic vegetation, on the lines of the method of survey described elsewhere. There may be pasture (usually predominant), or cornfield, or wood, or roadside and hedges, which should be studied as already suggested.
Other special points to be noticed, and of which data should be kept, are the effect of the wind force, the temperature, and the length of sunlight, rainfall, etc. The aspect and slope, the latter given in angles, and the character of the soil, are all factors that should be noted and put down. The dry or wet character of the soil is important, and advanced students may estimate the water content. Any points that may be noted as to the influence of one species upon another are also of the highest importance.