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    Wild Flowers of Chalk and Limestone
    Wild Flowers of Chalk and Limestone
    Wild Flowers of Chalk and Limestone
    Ebook526 pages5 hours

    Wild Flowers of Chalk and Limestone

    By J. E. Lousley

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    Wild Flowers of Chalk and Limestone will urge many to follow in the author’s footsteps in search of the rich flora which make our chalk downs and limestone cliffs so fascinating to explore. This edition is exclusive to newnaturalists.com

    Few areas can boast so many rare and beautiful wild flowers as those of the chalk and limestone. Few areas, too, have so much lovely scenery in which to search them out. Mr. Lousley’s vivid and authoritative presentation of his subject shows that he has made full use of these opportunities. His special affection is for the woods and chalk downs of south-eastern England, of which he has a knowledge almost unsurpassed.

    Nevertheless, in this book he has also given us an admirable survey of all the important limestone regions in the country from the Devonian formation at Berry Head to the oolite of the Cotswolds and the great carboniferous stretches of the north. This book will urge many to follow in the author’s footsteps in search of the rich flora which make our chalk downs and limestone cliffs so fascinating to explore.

    LanguageEnglish
    PublisherHarperCollins UK
    Release dateMay 31, 2012
    ISBN9780007406142
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      Wild Flowers of Chalk and Limestone - J. E. Lousley

      EDITORS’ PREFACE

      DURING THE last two hundred years, successive armies of amateur field botanists have, by their exertions, helped to make the wild flora of Britain the best known of any country in the world. Mr. J. E. Lousley is one of the leading present-day representatives of this great amateur tradition. He lives and works in London and has developed a special affection for—and a unique knowledge of—the chalk downs and beech woods so typical of South-eastern England. Knowing this weakness of his we decided to ask him to undertake the first of a series of NEW NATURALIST books on the wild flowers of particular habitats—and the present volume on chalk and limestone is the result. Though the south-eastern chalk is a favourite week-end field of operations for Mr. Lousley, it is obvious that he has also visited and studied most of the other important limestone areas in Britain, from the Devonian limestones of Devon to the Oolite of the Cotswolds and the great areas of Carboniferous Limestone in the north. He has revisited most of the areas described while writing his book. During his wanderings he has been fully awake to the ecological background against which any worth-while study of plants must be made, as is well brought out in his book, but it is the flowers themselves—the peculiarities of their distribution, the characters which distinguish them from their allies, and the history of their discovery in Britain—that fill the centre of his vision and provide the inspiration of his book.

      Very few types of habitat can boast a larger proportion of rare and beautiful wild flowers than the limestone—nor more lovely scenery in which to search them out—and Mr. Lousley has undoubtedly taken hold of his opportunities with both hands. His book will, we hope, inspire many to follow in his footsteps across the thyme-scented chalk uplands, through the green shades of the Cotswold beechwoods, or across the limestone pavements of the north, and to learn something of the rich flora that makes them so fascinating to explore.

      THE EDITORS

      AUTHOR’S PREFACE

      I HAVE WRITTEN this book as an amateur for amateurs in the belief that first-hand experiences are likely to be of greatest interest to field naturalists. Most of the places described have been revisited since the end of the recent war to confirm or elaborate earlier notes which in some cases proved to be out of date.

      Limits of space have dictated the omission of much that I wished to say and the task of selection from the available material has proved difficult. If I appear to have given undue prominence to rarities it is because these so often provide the most suitable examples of plant geography and illustrate differences between the habitats better than subtle variations in the proportions and behaviour of the commoner species.

      The title has been regarded as including trees and shrubs, since to botanists these are as much flowers (phanerogams) as are the herbs. It would be invidious to omit the few ferns closely associated with calcareous soils. Some maritime flowers have been included as growing on chalk or limestone sea cliffs but, in general, species found on limy soils or rocks at an altitude of over 1000 feet have been treated as mountain flowers and therefore as coming within the scope of another book in the NEW NATURALIST series.

      Every effort has been made to select one of the places where it is most plentiful for the discussion of each species. This selection has been based on my personal experience and it does not follow that visits in other seasons would produce the same displays as those I have described. It must also not be assumed that failure to mention a plant at any particular place implies that it does not grow there: the accounts of many of the habitats would have become mere lists if all the species had been included.

      The English names used, with few exceptions, are taken from Rayner’s Standard Catalogue of English Names of our Wild Flowers. Although some of these names are not particularly well chosen it seems better to follow a list already in use than to adopt a miscellaneous selection which may mislead. Usually the scientific names are taken from J. E. Dandy’s invaluable List of British Vascular Plants (1958), to which the reader is referred for synonyms and author’s names. The use of scientific names has been reduced as much as possible and after the first mention they are usually not repeated for very common trees and flowers to which there is frequent reference. In the case of rarer species they are repeated at intervals for the benefit of readers not familiar with the English names.

      Although the public have free access to most of the chalk and limestone habitats described, it must be made clear that no statement or description in this book should be taken as implying that any Right-of-way exists in these places. Permission to trespass is very rarely refused to genuine botanists and should always be requested as a matter of courtesy.

      The experiences described in the following chapters are in large measure due to the companionship, help and encouragement of many botanical friends over a number of years. To mention some and leave out others would be invidious, but their assistance is not appreciated less because it must remain anonymous. Parts of the manuscript at various stages have been read by Messrs. J. D. Grose, R. H. Hall, J. E. Prentice, E. C. Wallace and Drs. W. A. Sledge and J. F. Hope-Simpson, and I am most grateful for their help; although it must not be assumed that they are in any way responsible for the text as printed. The first proof has been read by Messrs. R. Graham, D. McClintock, John Raven and E. C. Wallace, who have all assisted with valuable suggestions. I am also greatly indebted to the Editors of the NEW NATURALIST series for much help and encouragement.

      PREFACE TO SECOND EDITION

      Considerable changes have taken place in some of the habitats, and in many of the names given to plants by botanists, since publication of the first edition of this book in 1950, and the text has been heavily corrected. I am grateful to Mr. David McClintock for reading the proof and making many valuable suggestions.

      J. E. L.

      CHAPTER 1

      FLOWERS, AND CHALK AND LIMESTONE SOILS

      I MAKE NO apology for being an enthusiast over the flowers of chalk and limestone. As a schoolboy I soon realised that I found a greater variety of plants on the chalk than on other soils, and most of my botanising was done on the North Downs within cycling distance of my home in South London. An annual stay with grandparents near Reading offered opportunities of getting to the Berkshire Downs. Holidays in Somerset and Devon provided an introduction to the joys of the flora of the older limestones. Later on, when choice of places to visit was entirely my own, I found that chalk and limestone areas were automatically selected for a very large proportion of my field work.

      Although chalk is a limestone—indeed the white Upper Chalk is one of the purest British limestones—it differs in its softer nature from the other, usually older, British limestones. Hence the sense in which chalk and limestone are used in this book is in accordance with popular usage.

      My preference is by no means unusual. The majority of the thousands of people who flock to Box Hill or Ivinghoe Beacon, the Great Orme or Berry Head, Cheddar or Ingleborough, are not botanists, but many of them find the flowers in these places an additional attraction. Some of them doubtless realise that the plants differ from those of other soils. The botanist is so well aware of it that he may travel right across England to make for one particular bit of chalk or limestone where he knows that certain rare flowers are to be found.

      Many of these rarities have never been found in Britain on other soils. The only places where the Monkey Orchid and the Military Orchid, Orchis simia (Plate 14b) and O. militaris (Plate 26), have been seen are on chalk. All our localities for the White Rock-rose, Helianthemum apenninum, are on limestone. A very long list might be given of scarce and beautiful wild flowers which are similarly restricted; they will be discussed in later chapters.

      There are also a great many more widespread plants which are almost limited to chalk and limestone. Good examples are Chalk Milkwort, Polygala calcarea, and Round-headed Rampion, Phyteuma tenerum, which are locally abundant on much of the southern chalk though never found in the north of England. Conversely the Dark-flowered Helleborine, Epipactis atrorubens (Plate 41), is widespread on the limestone of the north and west. Horseshoe Vetch, Hippocrepis comosa, and Clustered Bellflower, Campanula glomerata (Plate 4), are plentiful on both chalk and limestone. In addition there are many flowers such as Salad Burnet, Poterium sanguisorba, and Carline Thistle, Carlina vulgaris, which are specially abundant on soils over these rocks but are also sometimes found on others. Finally there are numerous common species which are not exacting in their soil requirements—such as Common Birds-foot Trefoil, Lotus corniculatus—abundant there just as they are elsewhere.

      Thus the flowers found on chalk downs like Box Hill or limestone crags such as the Great Orme are a mixture. Some could be seen equally well in many other places, but a great many, and this applies particularly to the rarities, grow specially on soils containing a high percentage of lime. These plants are called calcicoles—a word made up from the Latin calx, chalk, and colo, I inhabit, i.e. plants dwelling on chalky soils. The derived adjective is calcicolous. Botanists generally use these terms in a very much narrower sense than one might suppose from their literal meanings. They only include as calcicoles those plants which show not only the positive characteristic of thriving on calcareous soils but also the negative attribute of avoiding soils deficient in lime. Those which grow equally well elsewhere cannot be regarded as chalk or lime lovers. They are not calcicoles.

      There are certain flowers which avoid the chalk and limestone. One of the best examples is Foxglove, Digitalis purpurea, which is common on other soils in most parts of the British Isles. Similarly, Broom, Sarothamnus scoparius, is practically absent from calcareous soils. These two plants are such excellent soil indicators that on train journeys it is often easy to tell immediately the line leaves chalk or limestone by their presence on the railway banks. The term applied to plants which avoid lime is calcifuge, from the Latin calx and fugio, I flee. It is the converse of calcicole.¹

      Every serious gardener is well aware that some plants have these strong soil preferences. Even under the artificially easy conditions of cultivation, which frees flowers from the competition of their neighbours, they may often be a matter of life or death. It is hopeless to try to grow most members of the Heath Family, Ericaceae, on chalk, and if Rhododendrons or Ling, Calluna vulgaris, are planted in such situations they will probably soon die. On the other hand Buddleia, Buddleja davidii, and many other plants thrive on the shallowest of chalk soils; and limestone is commonly used for rockeries. Gardeners select the plants they grow according to the nature of their soil. This they can modify over a limited area by adding lime if it is too acid, or peat if too mild. Thus by taking the appropriate measures they can grow species which are quite unsuited to their natural soil.

      Soils found in the country show contrasts similar to those of gardens. On moorlands and heaths they are acid, or, as gardeners would say, sour. Those formed where chalk or limestone are close to the surface are usually basic or mild. These differences are primarily due to the nature of the rocks from which the soils are derived.

      Limestones are rocks which contain at least 50 per cent of carbonate of lime, which is known to chemists as calcium carbonate, CaCO3. This is a basic (alkaline) substance which neutralises acids, and farmers spread ground limestones on their fields to prevent the soil from becoming sour. Chalk has been used for this purpose since very early times and many small chalk-pits remain to remind us of the practice. The net result is similar to that attained by the use of lime (oxide of calcium, CaO) though there are important differences in the action. Calcium carbonate effervesces vigorously with cold dilute hydrochloric acid, and this is one of the tests by which limestones can be recognised.

      Another characteristic of these rocks is that they are all soft enough to be scratched with a knife. This is true even of the hardest forms (known as marble). The purest of the limestones, such as much of the Upper Chalk which is commonly 95–98 per cent calcium carbonate, are white. Others are greyish, or stained yellow or red.

      Flowers which grow on chalk and limestone do so because the conditions suit them better than those elsewhere, but the particular reasons are complicated and not yet fully understood. Some plants seem to be restricted by the chemical characteristics of the soil in which they grow. One example is the Privet, Ligustrum vulgare, which thrives equally on the driest of chalk downs and in wet East Anglian fens. In spite of the great contrast in other conditions both localities agree in being strongly basic owing to the presence of calcium carbonate. But the more common reasons are probably due to the physical characteristics of the ground. Limestones are dry, well aerated and warm. Plants which grow on them never have their roots waterlogged. They are able to commence growth early in the spring and many of them flower in May and June and remain more or less dormant during the driest summer months which follow. Others send their roots deep down into the well aerated soil to a level where they are assured of a more constant water supply even in times of drought: these include some of the later flowers like Wild Thyme, Thymus drucei, Perforate St. John’s Wort, Hypericum perforatum, and Small Scabious, Scabiosa columbaria.

      Some of the finest scenery in the British Isles is to be found on chalk and limestone. The broad outlines of the views which attract and delight visitors are directly due to the nature of the rocks. Where these are soft, as in the chalk areas, the hills are rounded and undulating. Even the steepest escarpments, like those of the North Downs and Ivinghoe Beacon, have all their edges smoothed off. Cliffs are never formed naturally except by the sea, and the soft outlines of the chalk make ideal walking country. Here the wild flowers have often been preserved from destruction by the use of the land as sheep walks throughout the centuries. This, in turn, has produced a short dense springy turf with orchids and other characteristic flowers.

      On the harder limestones there are cliffs and steeper slopes. Cheddar and the Avon Gorge (Plate XV), parts of the Wye Valley, and the Great Orme (Plate XVI), are examples which are particularly well known. In such places the choicer flowers grow on ledges where difficulty of access and immunity from any threat of cultivation has served to protect them.

      The details of the scenery are supplied by the trees and flowers, and the vegetation in turn is dictated, like the topography, by the nature of the rocks. Visitors sometimes fail to appreciate how much the beauty of Box Hill owes to its famous Box Trees, Buxus sempervirens, or Selborne Hanger (Plate VIII) to its Beeches, Fagus sylvatica, or Cheddar (Plate 32) to its Yews, Taxus baccata, and Whitebeams, Sorbus aria. The downland turf is made up of plants which only grow together in this way on calcareous soils, and the association of flowers differs from those found on all other soils. With a little practice places where chalk or limestone is near the surface can be recognised immediately; the plants collectively give characteristic detail to the scenery.

      In my travels all over the British Isles I have been impressed with the very gradual changes in the flora when the various chalk and limestone districts are compared. They are like a length of cinematograph film. Each frame differs only in detail from its neighbours, just as the chalk flowers of Reigate Hill, Box Hill and Hackhurst Downs are very similar. Pictures farther apart show much greater differences, and if the distance is sufficiently great they may at first sight seem to have little in common when examined as stills. Thus the chalk flowers of the Dover cliffs and the limestone plants of the Burren in Co. Clare may seem to be quite unconnected. But when the cinematograph film is projected and the pictures are shown on the screen in quick succession they are shown to form a continuous story. The links which form a series between the scattered frames are seen in their proper place. The chapters in this book cover habitats scattered all over the British Isles and each place described has its own characteristics. By bringing them all together in one volume they can be compared as a series gradually changing from east to west, and from south to north. It is the first time this has been attempted for the calcareous soils of any country.

      The reasons for these differences between the flowers of various districts can be distinguished under two heads—variation in climate and the incidence of the geographical distribution of species. The second is to a great extent dependent on the first.

      image 1image 2

      Even in a small area like the British Isles the climate varies considerably and the differences are more important to some kinds of flowers than to others. Just as the human species is adaptable and can live under conditions varying from tropical heat to polar cold, so there are some plants which can endure a considerable range of climate. Flowers like Common Birdsfoot Trefoil, Horseshoe Vetch, and Clustered Bellflower, are to be found growing just as well on the limestone of the north of England as they do on the chalk of the south. But many others are much more exacting. For example, the much wetter conditions of Westmorland and west Yorkshire suit Birds-eye Primrose, Primula farinosa, and Globe Flower, Trollius europaeus, which would never grow on the dry chalk of the South Downs even if they were planted there. Then there are plants like Maidenhair Fern, Adiantum capillus-veneris (Plate 48), which cannot stand much frost. They thrive on limestones of the west coast of England and Ireland but would be killed under the extreme conditions of the average east coast winter. There are many contrasts of this kind and they will be emphasised in later chapters.

      But in addition there are plants which are so local that present climatic conditions can hardly be the only explanation of their rarity. For example, there are three small Sandworts, Arenaria ciliata, A. gothica, and A. norvegica. In Britain the first is found only on a short length of cliff in Ireland (see Chapter 15), the second occurs only on a few limestone tracks on the side of a Yorkshire mountain (see Chapter 13), while A. norvegica is restricted to small areas in north-west Scotland, the Hebrides, Shetland and Ireland. It seems certain that there must be other places where each of these plants could find the conditions under which it thrives, and the explanation of their present rarity must be looked for in the past history of the species. In this particular case the three Sandworts belong to a group with a circumpolar type of distribution. The scattered localities where they are now found are likely to be relics of a time when they were more widespread. Although we do not know for certain why they have disappeared from the intervening districts, it is highly probable that they were destroyed during periods of glaciation in past ages. Thus to explain the present distribution of plants in Britain it is necessary to plot the places where they occur elsewhere and also to study the geological and climatic history here and overseas.

      From a careful study of the areas over which each species is found in Britain and abroad it has become clear that our country has been invaded by plants from more than one direction. For example, some probably came in from the south-east (see Chapter 4). Others found in the west of Ireland also grow in Spain and Portugal and the Mediterranean district (see Chapter 15). In some cases plants have not spread far from the districts where they entered our country; in others they have extended over more or less wide areas. Plants, and especially rare plants, become very much more interesting if we know something of the climatic conditions under which they can live and of how they have come to the places where they grow. Such facts are most conveniently considered if their habitats are arranged geographically.

      But a purely geographical arrangement would not suffice. Limestones (including chalk) are rocks which are mainly composed of the base calcium carbonate. Such rocks can occur in strata of all ages and, far from being uniform, they vary widely in degrees of impurity and hardness. Limestones are sedimentary¹ and mostly of marine origin, though some were laid down in fresh water, and sand, mud and other impurities as well as calcium carbonate were involved in their formation. The purity of much of the Upper Chalk (often 98 per cent or more) is exceptional; most limestones are far less pure. It is obvious that these differences may be reflected in their floras, and although very little scientific work has so far been done on this subject it is one which deserves attention.

      The problem is complicated by the fact that the occurrence of plants is influenced by the characteristics of the soil round their roots rather than by the geology of their habitats. The latter determines such features as steepness of slopes produced under given climatic conditions, and drainage. Geology provides the outline of the picture but other factors are also involved in deciding whether soil conditions are acid or alkaline.

      Soil is the superficial unconsolidated layer of the earth’s crust and is a highly complicated mass of organic and inorganic material. The latter is itself the weathered products of rocks. It follows that in general limestone rocks are likely to give rise to calcareous soils, but there are many exceptions to this assertion. Examples will be given in later chapters, but perhaps the one which impressed me most was a shallow depression on the top of a block of limestone in Westmorland. This contained peaty soil only 1½ in. deep in which grew calcifuges, in marked contrast to the calcicoles on the adjacent rock. Although the example just given is an extreme one, less sudden soil changes due to various causes are very common, and hence it is only practical to produce reasonably accurate soil-maps of small areas. The distribution of the chief geological formations (which influence the soil in a general way, but not always in detail) is shown on the small-scale maps (Fig. 1) and in the Table.

      It has already been explained that limestone rocks are largely sedimentary. At certain periods in the ancient past conditions in our part of the globe were particularly favourable to their formation, and for this reason strata of some ages are richer in limestones than others. The geologist marks his maps primarily according to the times when the rocks near the surface were made, and this he is able to do by a careful study of the fossils they contain and the sequence in which they occur. For example, there is the well-known Cretaceous system of some eighty million years ago. At the beginning of the period the fine sands and clays of the Wealden Beds were laid down in fresh water in the south of England. Then sea invaded the area and the sands and clays of the Greensands and Gault were deposited. These include only very local and small areas of calcareous rock (e.g. Kentish Rag), but towards the end of the period the sea advanced still farther and an accumulation of calcareous ooze formed the Chalk.

      Geological maps show this as outcropping over considerable areas (Fig. 1a). In some places it can be seen as the familiar soft white rock of the Upper or White Chalk, which is often almost pure limestone. At others it outcrops as the less pure Middle Chalk, while some exposures of the Lower Chalk (and Chalk Marls) are very muddy and impure. Not only does the Chalk itself vary but also the higher ground is frequently covered with superficial deposits of very different rocks (see below). It will be evident that the indication of Chalk on small-scale generalised geological maps covers a wide variety of rock conditions. Nevertheless areas so marked indicate where limestone habitats are likely to be found and serve to link together in an orderly fashion the places where they occur.

      Next in botanical importance to the Cretaceous, the Carboniferous is the period of geological time when limestones were laid down over wide areas of our country. Sands and shales were also deposited and much of the land-surface shown as Carboniferous has outcrops of these rocks (and very impure limestones) on which acid soils form. But once more the map is a useful guide. Its markings include all the places where limestone of this period comes to the surface and is the basis of calcareous soils.

      Similar considerations apply to the Permian, which is the period which produced the Magnesian Limestone. They also apply to the Jurassic. There are smaller outcrops of calcareous rock in the Devonian and other systems. The lithological divisions shown on the following maps include all places where extensive limestones of botanical importance are to be found in the British Isles.

      Reference has already been made to superficial deposits which cover large areas of the limestone-bearing divisions of small-scale generalised maps of solid geology such as those just mentioned. These are rocks (often gravels, sands or clay) which may give rise to neutral or even acid soils. They have been formed in the following ways:

      Residual Deposits. In the formation of these the original limestone rock has been broken up by frost and dissolved away by rain-water (in which it is soluble to the extent of about 1 in 16,000 parts). When the calcium carbonate is removed the impurities are left as sands or clays on which grow plants different from those of calcareous soils.

      Drift Deposits derived from extraneous sources. These consist of material removed from other areas during the Ice Ages and dropped by the glaciers. Sometimes the drift has been carried for very great distances, and is very unlike the limestones over which it is deposited. Other drifts are calcareous.

      Superficial deposits of both kinds are to be found on various limestones, but perhaps the Chalk is the best-known example to use as an illustration. This is the softest of all our limestones and weathers most quickly. When all the calcareous material has been removed the residue sometimes consists of fine particles of very sticky clay mixed with angular flints. The latter are similar to those which are often to be seen in chalk-pits or in cultivated fields on the downs. When this residue accumulates to any depth it gives

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