SUMMARY AND CONCLUSION
OUR TRAVELS in search of the flowers of chalk and limestone have taken us into almost every part of the British Isles. From the Isle of Wight to Sutherland, from Dover to the Burren, calcareous soils are scattered over our islands. They occur over rocks of various geological ages and range from sea-level to mountain-tops. They agree only in having a high proportion of calcium carbonate and certain physical characteristics. Apart from this their plants grow under a wide range of ecological conditions.
The presence or absence of lime in the soil determines more than any other chemical factor the nature of the flora to be found on it. Examples have been given in almost every chapter of striking differences between the vegetation of calcareous soils and adjoining acid areas. It has been demonstrated that locally chalk and limestone have characteristic flowers different from those of soils formed over rocks deficient in calcium carbonate. A few species like Hairy Violet are found on calcareous soils everywhere. Others, like Common Rock-rose and Dropwort, are to be seen over a very wide area. The great majority are limited in varying degrees to particular parts of the country. Climate as well as edaphic factors decide where they grow.
The limestones of the British Isles were laid down most extensively in Cretaceous, Jurassic, Permian, Carboniferous and Devonian times. Rocks of these ages differ considerably in hardness and purity, and one might expect that these differences would be reflected in the floras of the soils over them. It would seem that in general this is not the case. There are well-known contrasts in scenery between, for example, the massive limestones of the Carboniferous and the softer rocks of the Cretaceous and Permian ages. But the geographical separation of the outcrops of different geological formations entails important variations in climate which are of greater significance. Where outcrops of more than one age occur close together—as with the Cretaceous and Jurassic in Dorset, and the Permian and Carboniferous in north Yorkshire—there is scope for detailed work in comparing their floras. Any differences found to be due to soil variations between outcrops of different ages are likely to be slight. On the other hand, it has been shown in earlier chapters that widely separated calcareous soils, even of the same geological formation, each have their own characteristic selection of the less common plants.
The importance of geographical situation is well shown in the case of the Permian Limestone, on which the species of southern distribution are gradually replaced by northern plants along its range of some 300 miles. A similar south-to-north comparison can be made between the Carboniferous of the Derbyshire Dales and Craven. Along the Chalk there is a marked contrast between flowers of western and eastern distribution. The Jurassic combines south-to-north with west-to-east tendencies.
With such a wide range of climatic conditions over such a geographic spread it is not surprising that the flora of the chalk and limestone is extremely rich. A certain amount of alkalinity in the soil is favourable to plant life, and the great majority of British flowers will grow under such conditions. This applies even to some marked calcifuges provided they are not subject to competition from species which are better adapted to such places than themselves. Nevertheless I was astonished to find that I listed 585 species for inclusion in this book as having been seen by me on calcareous soils. All micro-species and most sedges and grasses were excluded. It is probably not an over-estimate to say that more than half of the 15501 British species of seed-plants and ferns are to be found on chalk and limestone.
This estimate of some 775 species includes not only a high proportion of attractive flowers but also an exceptionally high percentage of rare species. As Professor Good has shown, the term “rare” is used variously to cover sparsity in space, sparsity in number of individuals, and sparsity in time. Spur-lipped Coralroot, Epipogium aphyllum, is probably our rarest British plant. It has been found only in two small areas of Britain, and only a small number of individuals have been recorded at intervals since it was discovered in 1842. It is therefore rare on all three counts. Late Spider Orchid, Ophrys fuciflora, is found only over a few square miles in south-east Kent; the number of plants each year is small, but it never misses a season. It is rare on two counts. Lady Orchid, Orchis purpurea, is almost restricted to Kent, where it is in scattered colonies averaging perhaps 50 individuals which come up every year. It can only be said to be rare on two scores, and even then it is less so than the other two orchids. Every chapter contains examples of rarities. Some are found only very locally, some in small numbers, a few only occur in certain years.
Many of these rare plants might easily become extinct from a number of causes. Their life often hangs on a thread and this thread may be extremely thin. It can break under the slightest change in the conditions under which they exist. The most obvious threat comes from the unscrupulous collector. Such people are not botanists (or very rarely so) but rather persons with an adolescent mentality who derive pleasure from the possession of a specimen of a rare plant and will go to any lengths to secure it. Because such people exist I have been compelled to exercise discretion in describing places where scarce plants grow. For the same reason I must refuse to give any additional information to correspondents.
Secrecy is a purely negative method of protecting flowers. Positive action requires much more careful study, and a study of the associated vegetation as well as of the rarity concerned. Since we seldom know enough about any species to assess the ecological factors which are important to its existence, it is preferable to try to conserve whole communities in their present condition rather than particular plants. If the habitat is stabilised and saved from destruction the rarities it contains are likely to persist. Often the best way to protect communities is as parts of larger areas on which agricultural, pastoral or other uses are carried on as before.
Fortunately this approach to plant conservation has received official recognition. The Nature Conservancy was founded by Royal Charter in 1949 and it ranked as one of the four official Research Councils under the supervision of the Privy Council1. It was created “to provide scientific advice on the conservation and control of the natural flora and fauna of Great Britain; to establish, maintain and manage Nature Reserves in Great Britain, including the maintainance of physical features of scientific interest; and to organize and develop the research and scientific services related thereto.” By 1962, the total acreage of National Nature Reserves was over 190,000 acres, of Forest Nature Reserves over 4,100 acres, and of Local Nature Reserves 6,650 acres. These include some of the best chalk and limestone habitats such as Colt Park Wood, the Gower Coast, Kingley Vale, Knocking Hoe, and Wye and Crundale Downs, and permits are needed to visit some of these. Many more of the areas mentioned in this book have been scheduled as “Sites of Special Scientific Interest” (S.S.S.I.’s), which is recognition of their importance but in practice offers only very limited and inadequate protection.
Conservation, important though it is, is only one aspect of the work of the Nature Conservancy. Reserves require management, and scientific management must be based on research. In the long run the investigation of the complex interrelationships between plants, and between plants and animals, is likely to prove just as important as the initial step of saving downland from destruction. One example of this is the study of the changes in chalk grassland which followed the destruction of nearly the whole rabbit population in some areas by the 1954–55 epidemic of myxomatosis. It is essential to find ways of replacing the work of rabbits and other grazing animals if short downland turf with a varied flora is to be maintained.
The Conservation Corps of the Council for Nature is doing valuable work in clearing scrub on some of our chalk grassland. Naturalists’ Trusts are also taking an active part in conserving important chalk and limestone areas, both by acquiring land and by advising on its management. There are now twenty-seven of these Trusts, some concerned with more than one county, and it is likely that the whole of England and Wales will soon be covered by their activities. The Botanical Society of the British Isles is amongst the other bodies taking an active part in conservation work, and helped to oppose recent threats to Teesdale and Berry Head. Work on the wider problems is being co-ordinated by the Society for the Promotion of Nature Reserves, which advises and assists the County Trusts, and by the Council for Nature, which represents natural history societies.
Chalk and limestone country takes a high priority in the programme for conservation. Our heritage of calcicoles—often beautiful and sometimes rare—deserves priority. There is no more interesting group in the British flora.