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Scottish Geographical Magazine Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/rsgj19 The origin and development of heather Moorland Dr. W. G. Smith Published online: 27 Feb 2008.

To cite this article: Dr. W. G. Smith (1902) The origin and development of heather Moorland, Scottish Geographical Magazine, 18:11, 587-597, DOI: 10.1080/00369220208733402 To link to this article: http://dx.doi.org/10.1080/00369220208733402

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suffices to demonstrate the exaggeration involved in this theory. Even in the semi-artificial region of industrial Scotland we have seen that if man modifies the details of his environment it is only while con- tinuing to respect its main features. This is the main geographical fact. The general conclusion, then, is that anthropo-geographical in- vestigations show that in this domain, as elsewhere, man only commands nature by obeying her.

THE ORIGIN AND DEVELOPMENT OF HEATHER MOORLAND.

By Dr. W. G. SMITH. AN important contribution on regional botanical survey has recently been published in a monograph on the Moorlahd Heaths of North-West by Dr. Paul Graebner.1 As the author has been unable to give special attention to recent work in Britain, a comparative review seems not unnecessary. The moors of have been examined by Graebner for the past ten years, and his earlier papers were used as references in preparing the scheme of botanical survey suggested by the late Robert Smith.2 Dr. Graebner's latest work finds a fitting place in the series of monographs on the vegetation of the earth issued by Professors Engler and Drude. In our opinion it ranks amongst the best of these. From the point of view of botanical survey, the vegetation of the un- cultivated moorland has a special interest, for there the influence of man is least apparent, and the natural agencies of soil and air exert their influence on plant-growth with least disturbance. The various types of moorland, where the dominant vegetation consists of heather (Calluna), with a well-marked set of associated species, are so characteristic in Northern and the mountainous parts of Europe generally, that they form an ever-present problem. The list of papers quoted by Graebner extends to twelve pages, and is evidence of the interest taken by the plant-geographer in the distribution of heather vegetation, and by the biologist in the exquisite adaptations to environment presented

Downloaded by [University of Ulster Library] at 03:58 04 January 2015 by Calluna, Erica, Vaccinium, and other associates. The area of Dr. Graebner's observations—the North German plain— has been compared to " an old Frisian mantle, made of coarse sackcloth, but fringed with silk"; the silk fringe is the grassy pastures of the Dutch and Frisian cattle country, the sackcloth is the barren heath of

1 Die Vegetation der Erde, edited by Engler and Drude : vol. v. Die Heide Norddeutsch- lands, by Dr. Paul Graebner. Reviews of the preceding volumes have already appeared in this magazine. 2 Smith, Robert, Botanical Survey of Scotland: I. Edinburgh district; II. Northern Perthshire. John Bartholomew and Co., Edinburgh, 1900.—Also Scot. Geog. Mag., July and August 1900. 588 SCOTTISH GEOGRAPHICAL MAGAZINE.

the hinterland. The plain extends from the shore of the and Baltic southwards to the base of the Weserberg, , Erzgebirge, Iser- gebirge, and other hills which form the northern fringe of the South German plateau. The plain as a whole is a uniform area of rolling land of no great elevation, yet Graebner's map shows that the " Heidegebiete " is definitely concentrated into certain portions of the plain. The chief mass lies in , Oldenburg, and Schleswig-Holstein, and extends from the Zuider See pastures eastward; the southern edge includes the upper part of the Vecht, passing along the base of the Weserberg to the cities of Hanover and Brunswick, whence the eastern boundary passes almost directly north to Lubeck and Kiel Bay. Along the Baltic there is a narrow coast-zone to Dantzic Bay and the mouth of the Memel. An isolated but well-defined area lies in Lausitz on the north-east frontier of Saxony, partly in and partly in Silesia. Another outlier, with a less marked " Heide " character, lies in Mecklenburg in the Elde valley, between Schwerin and the River . The "Heide" area thus indicated is the source of most of the examples quoted by Graebner, but his general conclusions and the questions raised by them may equally well be discussed from examples nearer home. Our material is provided by the papers and maps already published by E. Smith, his notes for future work, and other information collected by us. At present we are not in a position to discuss the heath vegetation of southern moors, such as Exmoor and Dartmoor, because these have not been worked over (to our knowledge) in the light of recent developments. The moorlands of Scotland and the north of England, up to 2000 feet, may be conveniently described as dark or black moors and green moors. The former is dark, partly from the soil which is more or less peaty, and partly from the sombre aspect of the vegetation, which con- sists of heather (Calluna), heaths (Erica), and other associates of the heather vegetation. The green moors and hills have a vegetation chiefly composed of grasses. The distinction is convenient, but it is also indicative of differences in soil and other external factors which influence the growth of plants; thus heather-moor, grass-moor, and forest are three primary types of vegetation considered from a biological stand- point. The term " Heide," used by Graebner, refers to the heather vegetation, and he defines it thus :—" An area covered by a dwarf, woody vegetation, where trees are not a conspicuous element, and where con- tinuous swards of grass are absent." The word " Heide " is here given

Downloaded by [University of Ulster Library] at 03:58 04 January 2015 a scope somewhat more comprehensive than most writers allow; it corresponds to our dark moor or heather moorland in its widest sense. Such a moorland is recognised not by the occurrence of any one plant— although heather, bell-heaths, or cotton-grass (Eriophorum) are generally present—but by the nature of the whole association of plants. Lists of species are unnecessary for our present purpose; they are given in the text accompanying the published maps of the Scottish Botanical Survey, and Graebner (pp. 35-58) gives lists of species which inhabit his " Heide- gebiete," and which occur off it respectively. The heather moorland, although a well-marked type of. vegetation, includes a number of sub- types indicative of some change in the environment—for instance, wet, THE ORIGIN AND DEVELOPMENT OF HEATHER MOORLAND. 589

moist, and dry places differ in their species and in the relative frequency of the species found on them. In the maps of the Scottish Survey two subdivisions of heather vegetation are shown by distinctive colours: the drier moors with a moderate depth of peat, and heather (Callund) as the most abundant species, are distinguished from the wet of deep peat where heather is largely replaced by cotton-grass or bell-heath. Heath plants also find a subordinate place in the mixture of grasses and heather recorded on the maps; here the heather has been more or less suppressed by grazing or other causes, while Nardus, Aim, and other grasses have been favoured; the result is a vegetation with a strong admixture of heath plants, yet presenting a transition to the pure grassy type; these we distinguish as grass-heaths. The presence of heath-plants in some of the forest associations affords an example of transition from pure heath or moor to the forest type. Graebner's work thus falls naturally into two parts. The first deals with heather vegetation generally, the conditions of its existence, its relation to climate, and its development. The second part is more botanical, and deals with the subdivisions of the heather formation. In the present paper we shall consider principally the general part of Graebner's work, because his observations and suggestions, while valuable to' the botanist, are no less instructive to the geographer and meteorologist.

CONDITIONS NECESSARY FOR DEVELOPMENT OF HEATHER MOORLAND. (1)' Altitude.—One is liable, on first thoughts, to connect heather with hills, but more careful consideration may recall the fact that in Britain we have, especially on the East Coast, considerable heaths a few feet above sea-level. The maps of the botanical survey show that heather may occur at all elevations up to 2000 feet, and even higher, although there it is more frequently found that bilberry (Facciniwn myrtillus) assumes the place of dominant plant. On the other hand, the map pre- pared by Graebner shows that the " Heidegebiete " of the North-German plain exists only in the western or North Sea region, while it disappears in the eastern inland steppe region. Altitude in itself has thus no direct effect on the distribution of heather moorland, and is only of importance when considered along with other factors. (2) Climate.—Northern Germany presents an excellent opportunity

Downloaded by [University of Ulster Library] at 03:58 04 January 2015 for observing the effects of climate on the distribution of heaths and moors. Graebner has collected meteorological observations for his area, the general facts of which are also shown in the charts in Bartholomew's Physical, Atlas. The area of least rainfall lies in the -Weichsel basin, many parts of which do not attain 50 cm. (20 inches) per annum. Towards the Baltic there is an increase to 62-70 cm., except near the of the Oder and Weichsel; it is noteworthy that we have a Baltic " Heide " zone unbroken except in the neighbourhood, of the same estuaries. Passing southwards from the Oder-Warthe basin the rainfall increases towards the Lausitz "Heide" area, where it again reaches 60-73 cm. per annum. The chief " Heidegebiete '* west of the Elbe, and 590 SCOTTISH GEOGRAPHICAL MAGAZINE.

extending north into Holstein, shows a rainfall lowest (60 cm.) in Luneburg in the south-east, and increasing towards the North Sea coast to 60-70 cm. per annum. It is also shown that in the " Heide " area the average number of days with rain is 170 per annum, while on the plain outside this area it varies from 130 to 150 days. The monthly rainfall is greatest in the " Heide " area in these months when the greatest drought prevails in the area outside it. In regard to temperature, the " Heide " area is shown to have fewer hot days (maximum, in shade, 25° C. or more), fewer frost-days (minimum, in shade, under 0° 0.), and fewer ice-days (maximum, in shade, under 0° 0.). The " Heide " area, in short, is distinguished from the more eastern Steppe region by a moister climate, without long droughts, cooler in summer, and less intensely cold in winter. Graebner further contrasts the two areas as follows (p. 60) :— (1) The soils of the North German plain are the same in the east and the west; sandy districts occur in both areas. (2) The vegetation is quite different: in the west there are extensive heaths, with heather-bog in the moister parts; in the east meagre pinewoods, dry sand-plains and knolls, with a steppe vegetation, while the wet parts are generally swamps (Wiesenmoor). (3) The two types of vegetation inhabit distinct areas (the " Heidegebiete" has already been indicated, and boundary lines of selected species are shown on the map). (4) In North Germany a large number of species inhabit the heath area which in the east are rare or absent. (5) A still larger number of species inhabit the eastern and midland parts of North Germany which are completely absent in the western area. If we apply these climatic factors to Britain, it will be found that wherever heather and its associates are dominant the same conditions prevail: there is a considerable and constant quantity of rain or aqueous vapour, long periods of drought occur rarely, the average summer temperature is low, while the winter is variable, and icebound conditions do not last long. On the other hand, it would be wrong at once to assume that given these conditions of climate the vegetation should be heather. This is not the case. In Britain we have areas where the hills for miles are "green hills" and heather is conspicuously absent. In the published map of Northern Perthshire the Ben Lawers region stands out in sharp contrast to the surrounding typical heather area. In the Craven dales of Yorkshire it is the rule to find the valley slopes grassy and

Downloaded by [University of Ulster Library] at 03:58 04 January 2015 without heather for miles, while the plateaus and peaks of the watersheds are clad with a vegetation identical with some of Graebner's " Heide." Both the districts just mentioned have a very high rainfall which in the grassy area is not appreciably lower than in the heather area. (3) Soil-Conditions.—Graebner (p. 114) states that the chief essentials for a dominant vegetation of heather and its associates are uniformly moist atmospheric conditions and a soil poor in plant-food. E. Smith says:—"The conditions of development of the heather association, shortly stated, seem to be the presence of a peaty soil poor in mineral content, which may be dry and unretentive, or wet and stagnant." On comparing the two summaries it is apparent that the worker on the THE ORIGIN AND DEVELOPMENT OF HEATHER MOORLAND. 591

extensive North German plain gives precedence to abundant atmospheric moisture, a factor which the restricted area of Britain does not reveal. Both agree that the soils are poor, while E. Smith, from British and Norwegian experience, gives peat an important place. From Graebner's evidence it seems to us that the prime essential for a heather vegetation is a constant and abundant atmospheric moisture. The poor soil characteristic of heather moorlands follows as a result of the climate. Graebner attempts to demonstrate the poverty of the soil by chemical analysis, especially those made by Ramann. An interesting comparison is given of the soils of heaths and adjacent forests, also between heath- soils and adjacent grass-soils. • These support the view that heaths occupy the poorer soils, but as at present chemical analysis is a doubtful guide in showing the true available food-materials for plants, it is desirable to obtain other evidence. It is characteristic of all heath-plants that the annual growth in length and weight is small, an indication that this vegetation is meagre in its requirements. A rich soil carries a vegetation with a large annual increment. In farm cultivation it is well known that the crops should follow in rotation, while loss by removal of crop must be made up by manuring. In meadow, wood, or garden it may be observed that plants of large growth change their position, the young shoots seeking out fresh soil which has not been exhausted by parent plants. When the vegetation of an area is dwarfed and slow in growth it is less migratory and better suited to occupy the same land for long periods. This is the case on heaths and heather-moors. It is not the result of immortality of the heath-plants, since heather, for example, dies out after ten to fifteen years' growth, yet the heath is repopulated again and again with it. The intrusion of heath-plants on an abandoned farm is also evidence that although the land has become too poor to support plants of large growth, it is still fit for the dwarf moor vegetation. A similar replacement of forest by heath will be considered later. Do the heath-plants prefer a poor soil, or are they driven to it by rival forms of vegetation ? An interesting solution of this question is given by Graebner. He states (p. 143) that if a heather area be manured the characteristic vegetation disappears. That this is not entirely due to successful competition of other plants is shown by cultivating heath-plants under conditions of rich nutrition. A slight excess in food results in enlarged growth, more foliage, and less flower; the critical periods of drought and winter are, however, less successfully met, and the plants Downloaded by [University of Ulster Library] at 03:58 04 January 2015 tend to die off. Large excess of food produces premature leaf-fall, defective root-growth, and an early death. These effects are probably due to the small leaf area of Ericacece and other heath-plants, which renders the utilisation of food-materials slow, and favours the accumula-l tion of unassimilated materials in the plant. The manuring of land! by sheep would thus partly account for the development of grass-moorl from heather-moor so often observed in enclosed areas, though here the\ grazing and treading of the sheep also tend to eradicate the heath-plants I and to promote the growth of grasses. Th e view that heather and its associates occur on poor soil is supported in a general way when the geological survey maps are compared with the 592 SCOTTISH GEOGRAPHICAL MAGAZINE.

vegetation maps of Britain. Rocks which on weathering yield a poor soil generally bear some form of heath vegetation or pine forest, while over rocks producing a rich soil we find farm-land, deciduous forest, or good grazing moors. The ordinary geological maps are not, however, soil maps, hence where a good soil might be anticipated from the nature of the underlying rock, it is not uncommon to find vegetation of a heath character. Poverty of soil may result from various causes, of which we give the more important:— • (1) Natural poverty due to derivation from a poor rock. (2) Exhaustion of soil by water. (3) Exhaustion of soil by vegetation. (4) The presence of glacial or river deposits. (5) The formation of peat, humus, and other deposits. (6) Human agency. The discussion of these in detail would take us beyond our present limits, but the necessity of distinguishing them will be apparent if, with Graebner, we trace the development of some of the common forms of heather moorland. Development of Heaths on Bare Sand.—At the present day, this can only be traced on recently deposited sand, but the course of events may also be taken as an indication of what occurred on the sands deposited at the close of the European glacial period. In North Germany there are considerable areas of recent and glacial sands. In Britain the frequent presence of heather and other heath plants on sandy soils must be familiar to most readers. In the course of the Scottish work, the vegetation of sandy areas has frequently been examined. Sand recently deposited, after prolonged exposure to water, must be very deficient in soluble plant food, and several changes are necessary before such a soil becomes covered with vegetation. The first step towards a heath vegetation is the consolidation of the loose drifting sand and the pro- vision of soil-moisture. On a coast area like that north and south of the Tay , the sands from high-water limit and inland for some distance form loose sandy dunes arranged in ridges and intervening hollows approximately parallel to the coast-line. The vegetation is scanty, and consists of sand-binding grasses and salt-loving plants, but heather and its associates are entirely absent. Away from the sea, the dunes become less shifting and the sand consolidates. This is especially the case in the hollows where rain-water forms occasional pools, and fine dust and organic matter collects. The catch-water has as its first vegeta- Downloaded by [University of Ulster Library] at 03:58 04 January 2015 tion evanescent growths of slimy blue-green and green algae, which aid in consolidating the bottom and add to the organic matter, till the soil is impervious enough to retain water throughout the winter and spring. Pools of this kind soon prepare a substratum moist enough for certain mosses, the forerunners of the heather vegetation. Thus proceeds the production of a somewhat peaty soil, with a supply of moisture, scanty, but fairly constant. In time, the pink bell heath (Erica telralix), dwarf willows, mosses, and other moisture-loving associates of the heath vegetation establish themselves in the hollows, while heather (Calluna), with other associates, clothe the ridge slopes more liable to short periods THE ORIGIN AND DEVELOPMENT OF HEATHER MOORLAND. 593

of drought. Simultaneously with the above changes, the dune-ridges are levelled by wind and rain, in many cases assisted by the excavation of rabbits; the dune-grasses are replaced by low sward-forming grasses which accompany the heath plants in this association. Whether the dunes will become grassy or heathery depends chiefly on the presence or absence of grazing on them. The landward part of Tentsmoor (Fife) was at one time a heather moor of the wet type, but drainage has made it drier; it is now covered with luxuriant heather on a moderate depth of peat, and is preserved as a grouse moor. As a rule, the coast heath vegetation is dry, the heather being short and stunted, while the soil contains little organic matter. Development of Heather Vegetation from Forest.—The development of heath on bare sand is probably the more primitive mode, yet Graebner considers that the majority of the existing heath areas in North- have been developed on the sites of former forests. This is admitted by most observers, and although the German plain is an area of low altitude, the results are worth considering in regard to the origin of British heather moorlands. R. Smith decided to adopt 2000 feet (608 metres) as the approximate upper limit of the heather moor; above this limit the heather either ceases or becomes a subordinate element in the blaeberry (Vacdnium myrtillus) type of vegetation. The birch wood or thicket also ceases about this altitude, and is the highest of our forest zones. Woods of larch and Scots pine occur in Northern Perthshire up to 1800 feet, but White's Flora of Perthshire gives isolated pines up to 1900 feet altitude. In Aberdeenshire, Dickie's Flora gives 2200 feet, and quotes from Watson's Cybele the finding of a pine trunk, 8 feet girth, in peat at 1650 feet. Geikie1 says that pine trunks in peat are not uncommon from 1800 to 2500 feet altitude. The agreement between the upper limit of the principal heather area and the higher forest zones in Scotland is suggestive of a possible origin of the heaths from forests; in many cases this was doubtless so, but more evidence is required before this course of development can be admitted as universal. In North Germany the conversion of forests of a high national value into heather wastes of little value is an important economic question. The problem has naturally attracted much attention, and Graebner had it before him as one of his chief objects. The explanation most widely accepted is that of Krause and Borgreve; the forests have been exploited by man for the timber, and the failure to re-establish them is the result of errors in

Downloaded by [University of Ulster Library] at 03:58 04 January 2015 cultivation, of which the chief is the destruction of seedling trees con- sequent on the grazing of forest land by cattle and sheep. Graebner differs from most of his contemporaries. He regards the above view as too narrow, and considers that the climate and impoverishment of the soil are the chief causes. His arguments are here summarised. The rainfall of the " Heide," as already stated, is higher than the adjacent Steppe area of Northern Germany, and the soils are generally sandy. Rainfall on a heavy clay, or other soil of close texture, results chiefly in erosion, because the rain-water flows over the surface; on a sandy soil

1 Geikie, J., Trans. Roy. Soc. Edin., xxiv., pp. 363-384, 1865-66. VOL. XVIII. 2 U 594 SCOTTISH GEOGRAPHICAL MAGAZINE.

of loose texture there is more percolation. Rain-water sinking through the soil carries with it dissolved substances, which are either absorbed by the roots of plants or pass below into the subsoil. This action will in time reduce a sandy soil, moderately rich in soluble matter, to a con- dition when little soluble matter remains. According to Graebner, this condition is indicated by the spontaneous appearance of a heath vegeta- tion. If the area be under forest, the trees assist in the removal of mineral food, but this will be returned to the soil if the trees fall and rot in situ. The exploiting of timber will reduce the material returned, and it is generally assumed that one-third of the mineral matter taken up by the tree is thus removed. Tables are given to show that there is a loss by removal of timber, and analyses by Ramann are quoted to show that fallen leaves do not replenish the soil for tree growth so much as is frequently stated. Graebner ascribes the disappearance of forest to impoverishment of a naturally open soil by rain, assisted by removal of timber, so that the materials necessary for vigorous growth are no longer available. Thus beech forest, with its subordinate vegetation of plants requiring a rich soil, gives place to a heath vegetation of dwarf growth and meagre needs. In the transition it is not uncommon to find a phase with Scots pine or spruce forest, since either of these is less demanding than beech. Graebner (p. 70) admits that the process of impoverishment in the way just described must be slow, and is limited to open soils poor in plant food to begin with. The development of heatb from forest may be accelerated by other changes which produce a condition of poverty in the part of the soil available for plant growth ; the most important changes of this kind are accumulation of humus and the formation of moor-pan. Humus consists of the debris of plants which being returned to the soil become incorporated with it. The soil of a heavily manured garden or farm is rich in humus which is rapidly disintegrated.and decomposed, largely through the agency of bacteria. In forests and under close masses of vegetation (e.g. heather) the plant remains decompose slowly and tend to accumulate as raw humus. Under such conditions light and air are deficient, and physical disintegration proceeds slowly, while bacterial action is largely replaced by the slower action of true fungi. The leaf mould of gardeners is raw humus collected in woods, while peat of various kinds is the raw humus accumulated under heather, cotton-grass, bog- moss, or other moorland plants. Raw humus may be formed on soils

Downloaded by [University of Ulster Library] at 03:58 04 January 2015 naturally rich or poor, and in all cases it masks the true action of the soil. The effects of raw humus on vegetation have been described by Grebe.1 A layer of moderate thickness cuts off the underlying soil from oxidation and other atmospheric action, so that roots of plants are imperfectly aerated. Under heath vegetation the raw humus combined with the roots of plants forms a felted mass which interferes with the circulation of air and water in the soil; it hinders evaporation of super- fluous water in spring, while in summer it forms a dry felt which pre- vents dew and light rains from reaching the soil. The raw humus, in

1 Zeitschrift für Forst- und Jagdwesen, xxviii. (1896), pp. 513-542. THE ORIGIN AND DEVELOPMENT OF HEATHER MOORLAND. 595

short, renders the soil unfavourable to plants which require fresh soil, active aeration, and sustained moisture. The formation of humus is accompanied by the development of organic acids, which in the case of raw humus are imperfectly oxidised, and their accumulation gives rise to • changes prejudicial to the growth of most plants. The heath vegetation is adapted to growth in moor-humus by its modified xerophytic character and by the shallow growth of underground parts. The adaptations of heath-plants are dealt with in a paper by L. C. Miall (Nature, lviii., 1898, pp. 377 and 401), and in this or the special works of Warming or Kerner the details will be found. Two forms of heather vegetation are recorded on the Scottish maps, of which the one with shallow peat is the drier, the other is the bog or moss with deep peat. The formation of moor-pan may precede or follow on the accumula- tion of raw humus. Its effect is to assist in masking the true fertility of the soil. Graebner's account of moor-pan is the best we have seen, and throws considerable light on the formation of heaths and peat. Moor- pan, as we translate the German word "Ortstein," may frequently be seen in drain-trenches or other exposures on our moors. It is a layer of humus-sandstone which may be recognised at the base of the peat if one probes with a long knife-blade downwards from the peat into the soil beneath; if pan is present, a distinct hard layer is met which turns the knife like a soft sandstone, and when exposed it can be removed as cakes of a dark brown stony material. A form of pan is familiar to farmers on certain classes of soil as a hard layer just beneath the ploughed soil; its effects are to stunt the root-growth of crops, hence it has to be periodically broken up by deep ploughing. Graebner's account of the development of moor-pan is as follows: The removal of soluble salts and the accumulation of raw humus lead to the exhaustion of the upper soil, which loses its powdery, crumbly texture and becomes caked to- gether. The percolation of rain-water carries humus compounds and dissolved salts in solution downwards through the poorer layers of the soil to layers below as yet unexhausted, and here ensues a precipitation of both humus and mineral matter. The process may be seen when a deep trench is freshly dug in a heath area; water flows in from the peaty soil, and on reaching the bottom of the trench it meets the subsoil richer in mineral matter; there then occurs a precipitation of a gelatinous brownish layer which when dry is insoluble in water. Graebner also succeeded in making an incipient pan in a glass tube filled with heath

Downloaded by [University of Ulster Library] at 03:58 04 January 2015 sand. The occurrence of moor-pan in heaths has been proved by borings, and Graebner gives several of these. One locality may be given as an. example: (a) heath-peat, 15 cm. (i.e. 6 inches); (b) bleisand, 20 cm.; (c) moor-pan, 4-10 cm ; (d) marl-sand, 40 cm.; (e) diluvial sand. This arrangement of the layers is almost constant, though the thickness varies ; the moor-pan is always deep enough to be protected from the action of frost, which breaks it when shallow. Chemical analysis of borings shows that below the moor-pan there is always a marked increase in the amount of soluble mineral matter. A well-developed moor-pan may resist the penetration of the roots of young trees or other plants, hence it cuts off the best part of the soil, and limits the plants to the upper impoverished 596 SCOTTISH GEOGRAPHICAL MAGAZINE.

layers. In replanting the heaths of .North Germany with forest trees, it is now considered necessary to break up the moor-pan by deep subsoil ploughing, previous to planting. Minor causes of disforestation occur locally. Thus the influence of man in digging drains, building reservoirs, and otherwise disturbing the existing conditions of drainage, may favour one vegetation at the expense of another. Wind-borne sand may also overwhelm forests or other vegetation and lead to the development of heath or other sand types. One of the objects of the Scottish botanical survey is to ascertain the extent of our primeval forest, hence the importance of Graebner's obser- vations. The origin of the heather moorlands in Scotland has a very direct bearing on the afforestation of our moors, a prominent item in the work of the Scottish Arboricultural and kindred societies. In many instances it has been proved that, with proper treatment, our moors may be converted into forests of Coniferse. This would indicate that the soil of our moors, especially the drier types of heather moor, is not yet too exhausted to carry forests. The extensive and successful conversion of heather moor into farmland in earlier times also points this way. At present we consider that a large proportion of the heather moorland in Scotland has been derived from ancient forest, but in the Pennine chain in England there is less evidence of this. Tlie_heath_vegetati_on_is-the^ result_of_a_moist climate, which favours the accumulation of raw humus cutoff from the true soil by a moor-pan or an imperviou¥Jlayer~oT~fine clayT JN atural poverty of soil in itself is~ohly1reiponiibleln a few~cases^ such^as the thin stunted heaths of sand-dunes. Other causes of convert] sion are the influence of man through sheep-grazing and drainage, andjj . in a less degree, through the favouring of heather and its associates by the regular burning of grouse-moors. Development of Peat mosses.—Graebner traces the development of " Heide-moor," the peat bog vegetation of cotton grass (Erioplwrum), crowberry (Empetrum), heather, blaeberry, etc., which is indicated on the Scottish vegetation maps by a special colour. The wet boggy moors of this kind may be developed in water, on bare soil, or from forest. His conclusions will prove useful to workers in such localities, but we defer discussion of them at present. Extensive areas of this type of vegetation have been examined in the Pennine chain of the north of England, and E. Smith has left field maps which show that the western part of Scot- land is largely of this nature. Downloaded by [University of Ulster Library] at 03:58 04 January 2015 The development of heather and its associates on limestone is not a . question which affects the heaths of North Germany. Graebner, however, has contributed some useful work on this. He has confirmed, along 1 with other workers, that bog moss (Sphagnum), heather, and other typical heath-plants may grow in soils containing a large amount of lime-salts. The well-knownf absence of heath-plants on limestone soils is thus not due to any prejudicial effect of the limestone, but to the absence of the particular soil-conditions necessary to heather and its associates. In the course of our wanderings in North-West Yorkshire, we have frequently found heather closely associated with the carboniferous mountain lime- atone. In one case, near Settle, a summit-plateau of considerable area THE ORIGIN, AND DEVELOPMENT OF HEATHER MOORLAND. 597

carries heather vegetation resting directly on the limestone. The con- ditions which here favour the heath-plants are of two kinds : on the one hand, shallow deposits of peat have formed, a thing not common over limestone; on the other hand, the topography of the area renders it unsuitable for sheep-grazing. Part ii.. of Graebner's monograph is an analysis of the biological types of vegetation included in his " Heide formation." The associations are distinguished by their habitat, and full lists of the species in order of their dominance are given. This portion of the work is of the utmost value to botanical workers on the heather vegetation, and as it becomes more widely known amongst botanists, it will assist towards a clearer recognition of what types of vegetation are. It is satisfactory to see a close agreement between Graebner's scheme and the plan adopted in the Scottish survey; comparisons are thus easy. In conclusion, the monograph of Dr. Graebner is one of the standard books of reference on heather vegetation, and will repay careful reading.

THE RETURN OF PEARY AND SVERDRUP. As already briefly noticed in our last issue, the Windward, with Commander Peary on board, arrived at Sydney, Cape Breton Island, on September 18, and the Fram, with Captain Sverdrup, at Stavanger, Norway, on September 19. It is now possible to give some account of the work done by these two gallant explorers and their respective parties. Data are hot yet available from which maps may be constructed, but reference should be made to the map illustrating Professor Nansen's article in vol. xiii. p. 246 of this magazine. In regard to this map it may be well to point out that while on the American side it still practi- cally represents the present state of our knowledge till the new results be fully available, on the opposite side of the Polar area Captain Cagni of the Duke of the Abruzzi's expedition made two years ago a notable advance, reaching 86° 33' N. lat., the highest point yet attained by any explorer. Commander Peary set out on his great journey in the summei oi 1898, but his movements have been already chronicled up to the time when the Erik left him at a temporary camp in the vicinity of his Downloaded by [University of Ulster Library] at 03:58 04 January 2015 quarters at Payer Harbour, near Cape Sabine in Smith's. Sound, at about 78° 45' N. This was on the 29th of August 1901. The winter was spent at Payer Harbour, which the expedition reached on September 16. A week later the Eskimo with the expedition began to sicken, and not one escaped illness. Six adults and a child died in camp, and early in the following January news was brought of a fatal epidemic among the Eskimos of Anvalik. The first start was made on March 3rd, when Henson with six sledges set out for Fort Conger in charge of an advance party. Three days later the main party started with eighteen sledges, leaving Percy in charge at Payer Harbour. Fort Conger lies about 81° 30' N., and the