The distribution of plants over large areas is determined by climate, but within a climatic region variation in the nature of the vegetation is caused by the occurrence of different kinds of soil. This fact is borne out by the distribution of the woods, heaths, moors, etc., that occur in Great Britain. In England there are three main types of woodland, which are dominated by oak, beech and ash respectively.
The oak wood is the most widely distributed of these woods, and is the climax stage of the plant sucoession over most of the British Isles except the North of Scotland. Damp oak woods are dominated by Quercus robur, and are found on the deep loams and clay soils of the lowlands of the South and Midlands of England. Dry oak woods dominated by Quercus sessiliflora occur on the shallow siliceous soils of the Pennine uplands to a height of about 1,600 ft. The two species of oaks may be distinguished by their, which in Quercus robur have little or no stalk and have an ear-like fold at the base of the blade, called an auricle. The of Quercus sessiliflora have stalks to 1 in. long and have no auricles.
The ground flora of the two types of oak wood is different, with the exception that bracken, briars and brambles are found in both.
Plants found in Damp Oak Woods
These include lesser celandine, dog ’s mercury, wood, primrose, lady ’s smock, wood spurge, red campion, yellow deadnettle, early purple , wild strawberry, wood sanicle, dog violet, bugle, wood avens.
Plants found in Dry Oak Woods
Soft grass, bluebell, wood sage, foxglove, tormentil, heath bedstraw.
Beech and Ash Woods
Beech woods are mainly found on chalk in the south of England, while ash woods occur on the limestone hills of Derbyshire, Somerset and Yorkshire. Beech trees cast a far denser shade than oak trees, and on account of this and because of the shallow rooting nature of beech trees, very few shrubs and herbaceous plants are found in beech woods. A few shade-loving plants, such as wood sanicle and enchanter ’s nightshade, occur in the more open spots, and the two saprophytes, yellow bird ’s nest and bird ’s nest, are sometimes found in beech woods. Ash woods are not so shaded as beech woods, and have an abundant and varied ground flora which includes the herb paris, wild garlic and small scabious.
Moorland and Heath
Moorland and heath are developed on acid soils, and are characterized by xerophytic vegetation. Heaths are common in the South of England and are typically found on poor and gravelly soils which are covered by a few inches of peat. In many cases the heaths have resulted from the degeneration of areas once populated by oak and birch, and which have been deforested by man. Moors are found in regions such as the Pennine uplands, Dartmoor and North-West Scotland, where the conditions are cold and moist. They are characterized by a deep layer of peat, which may vary in thickness from 5 to 30 ft.
Gorse, broom, brambles and briars are common on heaths, but ling is the most widely spread plant. Bell heather frequently occurs among the ling, and the cross-leaved heath grows in the damper parts. Other plants also found on heaths are mat grass, sheep ’s fescue, waved hair grass, heath bedstraw and wild thyme.
On the damp moors of the Pennines and Dartmoor, the cotton grass is often the dominant plant. When in fruit the cotton grass can be recognized by the white tufts of hair which occur on the hanging spikelets, and which help in the dispersal of the fruit. The purple moor grass is commonly found with the cotton grass, together with many rushes and sedges. The wettest parts of a moor are occupied almost entirely by the bog moss. The vegetation of a dry moor is very similar to that of a heath. On the lower slopes of the Pennines, where the conditions are drier, large areas are covered by the bilberry, while in places ling is dominant and gives rise to true heather moor. Many of the so-called heather moors of Yorkshire and Scotland have only a few inches depth of peat, and so are really heaths.