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.
If the relation of the meadows and pastures to the drainage of the country be studied, it will be seen that streams and rivers are arranged upon a definite system. In many cases the streams may be found to run in parallel series. And between one system of streams and another there may be seen to be dividing ridges which determine the areas of drainage of each system. This will be at once connected with the natural slope of meadows on either bank of the stream. The influence of such slopes may be regarded as the cause of distribution of certain plants at certain points. The aspect of the slopes will be found to have an important bearing again upon the occurrence of a plant, some species preferring a north, south, west, or easterly aspect.
These facts may be illustrated by the drawing up of a list of the plants found to grow on the different aspects. The same thing will be noticed in regard to the banks of a ditch or hedge, and it will be recognized that banks or slopes are the special habitat of some plants, as Ivy, Ground Ivy, etc.
Effect of Grazing: of Animals. - In addition to the effect of enclosure, which has been pointed out, there is the effect of the grazing of animals. Enclosure has resulted in this case in limiting the area to be grazed or browsed. Consequently the influence of this factor today is much greater than in the past. It is readily appreciated in a pasture. In times of drought the surface is almost entirely dried up and parched where animals are in the habit of grazing.
Several effects are produced by all classes of animals. The flowering stems and the later fruits are necessarily reduced in number by the browsing of animals. The normal struggle for existence, it may be pointed out, is thereby also greatly accentuated. For the tenderer succulent plants are liable to disappear, or to retreat to the hedgerow, where they are more or less protected, owing to the possession of thorns and prickles or spines by the Hawthorn, Bramble, Sloe, Rose, and other plants. Such fodder plants as Furze are protected by their needle-like spines. Trees in the hedgerow, as the Elm or Ash, are protected by their hard bark and by the tree habit, which raises the main branches and foliage above the reach of animals that relish the leaves, etc.
Among herbaceous plants, thistles and Rest Harrow are protected by their sharp spines, the Sow Thistle by its prickly leaves. The Dandelion and Goat's Beard possess a bitter juice which is distasteful to cattle as a rule. Some plants, as Alkanet, Comfrey, and Borage, are provided with stiff bristly hairs. The Nettle, found also in fields, which protects the other plants below it, is provided with stinging hairs containing a poison.
The White Dead-nettle has a bristly calyx which may assist it in being protected. Some plants that are poisonous, as Hemlock, grow in fields. This latter has a nauseous smell and spotted stem. The Bittersweet is also poisonous, and the flower a purple colour, with a central yellow cone, which is also a warning sign. The common Buttercups, owing to their acridity and power of blistering, are thus protected.
Grasses and Sedges in meadows are often protected by the sharpness of the leaf margin in the former, e.g. Tussock Grass, or by the triangular sharp-edged stem, as in the latter. These are only a few of the facts that may very usefully be pointed out, or better, discovered by the pupils, in studying the relation of grazing to the meadow or pasture.
Apart from these general features, it may be seen that it makes a great deal of difference what class of animal grazes a meadow. For instance, when sheep are continually grazing it may be noticed that crested Dog's Tail grass, Sheep's Fescue, and other grasses with sharp or filiform flower-stalks, have the bottom leaves alone browsed, and the flower-stalks are left. Where cows or horses browse such grasses are eaten entirely. Where donkeys are kept in meadows by the sea, thistles and other plants are eaten, whereas inland where donkeys are rarer they are left.