Variation in the oaks and beeches

While both are in the beech family (Fagaceae) and occupy large areas of the world's warm temperate forests, the beech Fagus has only 8-13 species depending on the authorities consulted, whereas oak Quercus has more than 250 in the western hemisphere alone. Indeed, Mitchell (1974) states that over 800 oaks have been described, including many hybrids. The beeches are a closely related group of trees with rounded spreading canopies that reach heights of 30-45 m. Their trunks are strikingly cylindrical in form, the annual rings of the upper parts of the trunk being wider than those near its base. The bark is grey, relatively thin and very smooth, so the appearance of these trees is in great contrast to that of the oaks with their typically furrowed bark and more tapering trunks. Fresh cohorts of beech Fagus sylvatica (Fig. 3.23) usually arise after mast years in which fruiting has been exceptionally heavy (Section 4.4.1). European and

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Figure 3.23 Two dicotyledonous tree seedlings (a) pedunculate oak Quercus robur, whose germination is hypogeal with its cotyledons remaining below ground (and largely concealed within the remains of the acorn) and (b) beech Fagus sylvatica, contrasted with that of a conifer (c) Scots pine Pinus sylvestris in which the hypocotyl has elongated and the tips of several cotyledons are still trapped within the testa. Three single needles borne on the developing plumule can just be seen. Like the Scots pine, beech has epigeal germination, the two semi-circular cotyledons are raised above ground and remain photosynthetically active for a considerable period. (Drawn by John R. Packham. From Packham and Harding, 1982. Ecology of Woodland Processes. Edward Arnold.)

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Figure 3.23 Two dicotyledonous tree seedlings (a) pedunculate oak Quercus robur, whose germination is hypogeal with its cotyledons remaining below ground (and largely concealed within the remains of the acorn) and (b) beech Fagus sylvatica, contrasted with that of a conifer (c) Scots pine Pinus sylvestris in which the hypocotyl has elongated and the tips of several cotyledons are still trapped within the testa. Three single needles borne on the developing plumule can just be seen. Like the Scots pine, beech has epigeal germination, the two semi-circular cotyledons are raised above ground and remain photosynthetically active for a considerable period. (Drawn by John R. Packham. From Packham and Harding, 1982. Ecology of Woodland Processes. Edward Arnold.)

Japanese beeches both coppice when cut down. In contrast the American beech F. grandifolia develops from suckers arising from its widespread roots (see Fig. 10.8b) so it is ecologically very different, its reproduction being much less influenced by seed predators. Beeches occur in forests spreading from central and eastern USA, through the UK and across to western Asia with a gap before the final occurrences in China and Japan. Though their forests are very extensive, beeches show much less variation than either the pines or oaks so it is not surprising to find that the range of conditions they can endure and the area they cover is considerably less than those of the other two groups.

The oaks, of which roughly half are evergreen, belong to three groups: the red and white oaks (both of which have some evergreen species), and an intermediate group all of whose species are evergreen. All three groups possess both tree and shrub species; the Mediterranean Kermes oak Q. coccifera (normally <2m tall) being an example of the latter. Some oaks are semi-evergreen, dropping all their leaves in spring and replacing them within a week from rapidly developing buds. This is seen in the long-established Turner's oak Q. turneri, a hybrid between the pedunculate Q. robur and evergreen Q. ilex oaks, which has long grown in Gibraltar. Sexual reproduction in the oaks involves the production of acorns (Fig. 3.23), which occur in only one other genus (Lithocarpus densiflorus, the closely related tanbark oak), and possess a cupule of bracts. Until late in the nineteenth century North American Indians collected acorns, removed the shell, ground them into a flour, leached this of tannins with running water and then used it to make a variety of foods. Beech nuts are also edible; their oil has been used for cooking.

Unlike the beeches, oak trees vary greatly in form, the trunks of some being very tall and upright while others are repeatedly forked from quite a low level. Oak leaves are usually cut or lobed, whereas those of beeches tend to be ovate. Oaks are found in a great variety of situations, from coastal plains to altitudes as great as 4000 m in the Himalayas. In regions where many species of oaks and other trees are present together, there is considerable interest in the precise attributes which lead to a species dominating a particular ecological niche while being absent from another. Contrasts between annual variations in temperature and moisture regimes between the eastern, central, western, northern and southern regions of the USA are very great and so is the range under which particular species are found. The ecological amplitude of the humid temperate Oregon white oak Q. garryana is very different from that of the semi-desert Gambel oak Q. gambelii of the south, for example. The same is true of the various species, including both oaks and pines, shown in Fig. 3.19.

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