The plant cover of Sweden: a study dedicated to G. Einar Du Rietz on his 70th birthday, April 25th 1965 by his pupils

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ACTA PHYTOGEOGRAPHICA SUECICA

EDIDIT

SVENSKA VA.XTGEOG�AFISKA S.!LLSKAPET

50

THE PLANT COVER OF SWEDEN

UPPSALA 1965

ALMQVIST ^& WIKSELLS BOKTRYCKERI AB

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ACTA PHYTOGEOGRAPHICA SUECICA 50

THE PLANr-f COVER OF SWEDEN

U PP S A LA 1965

Almqvist ^&Wiksells Boktryckeri AB

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PRINTED IN SWEDEN BY

Almqvist & Wiksells

BOKTRYCKERIAKTIEBOLAG UPPSALA 1965

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ACTA PHYTOGEOGRAPHICA SUECICA 50

THE PLANT COVER OF SWEDEN

A STUDY DEDICATED TO

G. EINAR _DU RIETZ

ON HIS 70TH BIRTHDAY APRIL 25TH 1965

BY HIS PUPILS

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PREFACE

The Swedish Phytogeographical Society has taken advantage of the seventieth birthday of Professor G. Einar Du Rietz to pay respectful homage to a scientist of international distinction who has for many years lead and directed the progress of our science in Sweden and whose influence has been felt widely throughout the botanical world. This is being done by dedicating to him the fiftieth volume of the Acta Phytogeographica Suecica and within it presenting a symposium about the general fea

tures of Swedish vegetation. The scope of the book is naturally wide but problems of method, technique or classification and other specialized aspects of research have generally been left aside. We have thought it proper that the survey, although far from being a manual, should be written in an international language, so that its contents may be available to naturalists and friends of Scandi

navia throughout the world. We also wish to re

lieve ourselves of the blame for our previous re

luctance to share with the outside world the results of geobotanical investigations in our homeland, a country where, fortunately, the landscape and its plant covering is not yet so grossly worn down or destroyed as in more heavily populated or ruth

lessly exploited countries.

The "Uppsala School of Phytosociology" is now a tradition rather than a school. G. E . Du Rietz himself, in the thirties, was the first to relieve its

1 *- 652151 APhS 50

In action as a field-work instructor, G. ErNAR Du RIETZ talks phytosociology to an excursion party, Betula nana around his feet, the wide horizon of a Lapponian aapa mire behind him. Jaltonape, Lule Lappmark. July ^{1 7,}

1 945. Photo H. Weimarck.

Acta Phytogeogr. Suec. 50

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small plants such as cryptogams are not neglected, the strict delimitation and the demand for homo

geneity of sampling plots, the appreciation of domi

nance and life form as phytosociological criteria, are features associated with this school that are all still judged important in Scandinavian vegeta

tion research. In his teaching Professor Du Rietz is as broadminded as he is profound, and his imposing knowledge of almost all kinds of plants and vegeta

tion, his versatile interests and intense personality have attracted pupils highly different in outlook.

Under his guidance scientists of several generations have been inspired to undertake investigations into our natural and semi-natural vegetation.

Obviously, the present survey had to be written by a team, and for this purpose the active disciples of Professor Du Rietz were summoned. Had they all been able to respond, the field would have been covered reasonably well, except for some types of vegetation never adequately investigated. However, for various good reasons about one fourth of the team were unable to contribute, thereby causing inevitable omissions. Certain other gaps are due to the fact that on a number of subjects (such as litto

ral lichen communities) the only really competent author would have been Professor Du Rietz himself.

The endeavour to cover the field completely was thus bound to fail from the outset, and we have had to content ourselves with the more modest achieve

ment of covering the most obviously important kinds of vegetation.

The contributions are arranged under four head

ings, starting with a regional survey. The intro

ductory section on "Features of land and climate"

is included as a background to many of the succeed

ing essays, but may be omitted by readers familiar with northern environments. Regional features of the vegetation at sea, in lakes and on land are then considered. Special papers on the vegetation of the

gives a summary of the history of Swedish vegeta

tion and an account of some influences producing prominent contemporary changes. Other similar factors, such as marine and freshwater pollution and hydro-electric development, are touched upon in some of the earlier articles. We would have liked to conclude the book with a chapter on the protection of Swedish nature, a subject close to the heart of Professor Du Rietz, but limitations of space forebade it.

The extremely short time available for editorial work accounts for a certain inconsistency of treatment between the several contributions. In order that each article should be readable as a separate paper we have not insisted too rigidly on avoiding repetition, nor have we tried to impose any uniformity of style so that, for instance, some authors quote the literature in great detail while others do it sparingly, a fact to be borne in mind when using the seemingly compre

hensive bibliography.

The presentation in the English language has been a problem, for there was neither time nor money to employ a large team of expert translators and revisers.

However, the editors greatly appreciate the co-opera

tion of Mrs. Carolyn Horner, Mrs. Marianne Nordfors and Mrs. Ulla Schott. Mr. Lars Bergstrom has kindly contributed several photographs including that on the.

jacket. A few illustrations have with kind permis

sion been taken from other books, others have been drawn, chiefly by Mr. Sven Jansson. Mrs. Inga Oster

vall, Mr. Ralf Ericsson and Mr. Erik Gummesson have given much technical assistance.

Generous financial support is appreciated from H. M. King Gustaf VI Adolf's Fund for Swedish Cul

ture, The Swedish Natural Science Research Council�

The 'Langmanska Kulturfonden' and members of our own Society, including Dr. Gunnar Lohammar who has paid the extra cost of the plates that could thus be included in his paper.

Uppsala, April 25th, 1965.

THE SwEDISH PHYTOGEOGRAPHICAL SociETY Editorial Committee

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l

15 28 48 64 78

85 92 97 105

Ill

123 1 31 141 144 149 159 161

The Borderland. By Sven Fransson . . . 167

Glimpses of the Bothnian coast. By Erik Skye 176

Northern mires

Regional ecology of mire sites and vegetation. By Hugo Sjors 180

Algfloarna, a mixed mire complex in Jamtland. By Folke Bjorkback 188

Calcareous fens in Jamtland. By Yngve Nordqvist ^. . . . 193

The major rivers of Northern Sweden. By Nils Quennerstedt 198

The north-east corner

Terrestrial vegetation and flora. By Erik J ulin . ^. 205

Notes on aquatic vegetation. By Svante Pekkari 209

Lappland east of the mountains

The landscape of Lappland east of the Scandes. By Jim Lundqvist . 215 South-facing hills and mountains. By Jim Lundqvist . . . . 216

Vegetation and flora of alpine outliers. By Gunnar Wistrand 219

Regional aspects on the flora. By Sven Rune . . . 221 Cultural influence on the flora. By Gunnar Wistrand . . . . . . . 226 Notes on the vegetation of lakes in the woodland of Lule Lappmark. By Lennart Granmark . 228 Lost and living lakes in the upper Ume valley. By Gunnar Wassen . . . . 233 Subalpine tall herb vegetation, site and standing crop. By Hilmar Holmen . 240

Acta Phytogeog1·. Suec. 50

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Snow distribution. By Olav Gjrorevoll . . . . Chionophobous plant communities. By Karl-Goran Bringer Chionophilous plant communities. By Olav Gjrorevoll . The high-alpine region. By Olav Gjrorevoll . . . ^. ^.

257 257 262 267 PAST AND PRESENT

The Late-Quaternary vegetation of Sweden. By Magnus Fries Reindeer grazing problems. By Eliel Steen . . . . Botanical indications of air pollution. By Erik Skye . . . . Recent changes in flora and vegetation. By Bengt Pettersson

269 281 285 288

BIBLIOGRAPHY, compiled by Ake Sjodin . . . . 295

NORWAY

100

Acta Phytogeogr. Sttec. 50

FIN

LAND

Provinces and seas. The provinces from Skane to Dalsland constitute Gotaland, those from Sodermanland to Dalarna Svealand, those from Gastrikland to Torne Lappmark Norrland. The five Lappmarks make up Lappland. The Baltic seas include the Baltic proper, the Gulf of Bothnia, etc. For names of rivers see p . 1 99.

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R EGIONAL S U RVEY

Features of Land and Climate

By HUGO S J O R S

Geology and topography

HISTORICAL SUMMARY .-Sweden belongs to Fen

noscandia, a physiographical area consisting of Norway, Sweden, Finland and northwestern Russia (Kola and Karelia) and characterized by predo

minantly very ancient bedrock, Pleistocene glacial sculpture, and Late-glacial and Post-glacial crus

tal uplift.

The long and complicated history of Pre-Cam

brian geology cannot be treated here. At the end of this era, much of Fennoscandia was worn down

the Sub-Cambrian peneplane is still locally preser

ved-and then successively submerged during the Cambrian and Ordovician and to some extent Silurian epochs. This resulted in the deposition of very extensive sediments on top of the Pre-Cam

brian rocks. Later, near the middle of the Palaeo

zoic era, western Fennoscandia rose and was folded to form part of the Caledonian range, which also includes the Scottish Highlands. In Scandinavia these mountains, often referred to as the Scandes, were formed through a process involving great eastward overthrust of nappes that partly covered various older rocks as well as some Cambro-Silurian layers. These sediments therefore are preserved along and beneath the Caledonian border. Other sediments were included in the Scandes themselves often in a high-metamorphic state.

East of the Caledonian border the country also rose but was far less disturbed, although numerous faults occur. During hundreds of million years, Sweden was prevailingly dry land and subject to weathering and erosion which wore off the sedi

ments from most areas, except for remnants (see below), and cut a series of new or regenerated pene

planes down into the Caledonian rocks or, further

east, the Pre-Cambrian basement, all the way from the summits of the Scandes to the present coast.

Finally, during the Pleistocene, the entire country was repeatedly covered by inland ice and the bed

rock evidently strongly scoured in many places.

THE SCANDES.-Fennoscandia's western part, the Caledonian mountain range or the Scandes, has a rugged but usually not very bold topography. The Scandes are much like the Scottish Highlands but twice as high. The rocks of the Scandes are largely hard-schistose and prevailingly silicious, but they also include softer, frequently somewhat calcareous rocks, as part of the phyllites. In consequence, quite large areas in the Scandes harbour a basi

colous flora, or rather a vegetation containing various basicoles, although limestone, dolomite, and ultra-basic rocks such as soapstone, peridotite and serpentine are all very local in the Scandes.

Rocks of intermediate standard are some mica

schists, certain eruptives, and the hard amphi

bolites that form many of the high summits.

However, the majority of soils in the Scandes are rather poor, considered as substrata for plant life.

Still the general standard is far better than is usual in the eastern and southern, Pre-Cambrian parts of Fennoscandia.

Extensive regions, some alpine and some wooded (forming foothills or plateaux to the east), are built up of quartzites, sparagmites, granites, syenites, porphyries, etc., that are very low in calcium and magnesium and high in silica. In these areas, the alpine vegetation is poorer than normal in species but yet often more variable and even richer than that of adjoining high-level woodlands. Most of the latter areas, such as for instance the sparag-

A cta Phytogeog.r. Suec. 50

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Fig. I. Altitudinal map of the Scandinavian peninsula.

From Angstrom 1 958.

mites of Harjedalen, are exceedingly poor for plant life. This is true also of the J otnian sandstone of Dalarna (the Dala sandstone) which does not be

long to the Scandes geologically but forms the southernmost true alpine areas in Sweden as well as extensive wooded plateaux.

THE BALTIC SHIELD.-East and south of the Caledonian border the major part of Sweden rests on a Pre-Cambrian basement. Archaean crystalline bedrock, some of it extremely old, extends over the greater part. The prevailing Archaean rocks are granites and gneisses of varying composition, although from an ecologist's point of view the differences are mostly of little influence upon vege

tation, except for local aberrant rocks such as

BEDROCK MAP

OF

SWEDEN

- loor rocks

� Stz�?n- }S'arui-

r::-:::1 Jotnian & stones

�Cambrian

D

gnei.sses etc. ^Granites, E=3 Caledonian

� schist.s etc.

+ Jlich rocks

' ,

/00 200KM

Fig. 2. Simplified bedrock map, showing geobotanically important rocks. +signifies local occurrence of rich rock, e.g. phyllite or marble (highly schematically), - large particularly oligotrophic areas. Material from .J. Eklund (Atlas over Sverige) and others.

marble and greenstone. As to the soils, this general uniformity was increased by the intimate mixing of all kinds of rocks in the glacial drift that covers most of the country (though the local rock is usually predominant in the tills) .

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Features of land and climate 3

Fig. 3 . Eskers (black) and sedimentary soils: sand, silt and clay (grey). From Lundegardh & al. 1 964 (adapted from Atlas over Sverige).

Fig. ^{4 .}Highest coastal line (present elevation in m) and maximum extension of ice-dammed lakes. From Lunde

gardh & al. 1 964.

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Palaeozoic (Cambrian, Ordovician, and Silurian) sediments; the largest Cambro-Silurian area is Cen

tral Jamtland, with northward extensions along the Caledonian border, and other areas are located in Skane (see below), Vastergotland, Ostergotland and Narke. A smaller, ring-shaped remnant occurs near Lake Siljan in Dalarna. Large parts of the floor of the Baltic Seas (see Fig. 5) are also for

med by these rocks, a ridge of which protrudes in the shape of the long and narrow island of Oland in the Baltic. The larger island of Gotland is formed by Silurian limestones that partly origi

nated as reefs. These two islands, although sur

prisingly dissimilar, are the two areas where the calcareous character of the total lands ea pe is most prominent, a fact largely due to the shallowness of the drift cover; frequently there is almost no soil at all on top of the limestone bedrock.

The last glaciation left Sweden covered by glacial drift. This consisted mainly of till, over large areas covered by glacial clay, and, locally, by often extensive coarse-grained sediments. The long eskers are characteristic features of the Swedish landscape, particularly in the eastern lowlands; unfortunately they are now badly damaged from more or less unplanned exploitation, their gravel being in high demand for road and building construction.

Much of the land was under water as the ice border retreated from south to north; the highest coast line consequently is much older in the southern than in the northern part of the country. Despite this, the highest absolute value (295 m) is found as far north as Angermanland, and the maximum rate of uplift (ea

l

cm per year) is still in the same area. There have been alternating periods with freshwater and brackish water in the Baltic.

The good third of Sweden that is below the highest coast line was originally covered by silt or clay sediments, probably to a very great extent, but, due to wave action at the emergence of the land· from the .water,. this material was washed away from the hills and re-deposited on the lower parts. Now, the characteristic landscape of lowland Sweden shows the topography and sediment distri

bution of an ancient archipelago: rocky hilltops

.Acta Phytogeogr. Suec. 50

and gravel from which most of the finer soil frac

tions have been removed; moderately exposed, often very extensive till areas where the surface layer has been washed and deprived of its finest material but the deeper parts have not been affec

ted; sheltered tills in part covered by thin local sediments; low -lying fields of fine-grained sediments.

The latter range from sand, fine sand or silt along

side the eskers and in the upper parts of the present river-valleys, to heavy clays in the lowland plains, e.g. around Lake Malaren.

Interesting enough, this process of landscape remodelling can still be studied along much of the western and nearly all the eastern coast of Sweden.

Nowhere is it more evident than on the coasts of Uppland, from the 50 km wide Stockholm archi

pelago northward. By the way, this area (and Aland) also shows a remarkable contrast between poor silicious rocks and soils rich in calcite (calcium carbonate); the latter originates from the calcareous Ordovician bedrock on the floor of the Bothnian Sea, from where it was transported south by the Pleistocene ice.

SKANE. -Scandina vians never regard their lands as parts of the Continent-they are as much penin

sular as the British are insular-but southernmost Sweden is physiographically much more similar to West-Central Europe than to the rest of the country.

The undulating rich agricultural landscapes of southern and western Skane (Scania), although somewhat unfortunately included by definition in Fennoscandia, deserve special mention. Together with Denmark, they form a physiographical area ( "Scanodania") that is essentially an outlier of West-Central Europe. The bedrock geology is com

plicated, due to faults; in addition to Archaean horsts and sediments of early Palaeozoic age also the Mesozoic system is well represented, in parti

cular by Liassic and Late-Cretaceous sediments (sandstones, clays and chalk) .

I n Late-glacial time, ice masses moved across Skane in different directions (one of these ice flows even partly had a north-westerly course). They left south-western Skane covered by calcareous

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Features of land and climate 5 boulder-clays with high contents of Palaeozoic and

Mesozoic sedimentary rock material. In most of north-eastern Skane, on the contrary, the till is non-calcareous and has a low clay content, being dominated by Archaean crystalline rock material, i.e. similar to the most widespread type of till in the rest of Sweden. Transitional areas have tills which contain both Archaean and sedimentary, largely Palaeozoic material, often rather rich in calcite. Extensive areas are covered by sand. Post

glacial crustal movements have been small in Skane, and in the extreme south the country is even sinking slowly.

Soils

The soils of Sweden are chiefly podsolic but there is great local and regional variation. Brown forest soils prevail in the south and along the south

eastern coast, but are also found elsewhere beneath luxuriant broad-leaved forest vegetation; a special kind is typical of rich flushed sites all over the country. The young soils at very low altitude often show various stages of incipient podsolization. The degree of podsolization increases towards the humid south-western uplands and still more towards the cool uplands of the northern interior, where typical podsols are strongly predominant both under coni

fers and mountain birch. Podsolization has an upper limit about half-way up the low-alpine belt.

The terrestrial humus cover is nearly always developed either as mull or as mor, the latter being by far the predominant type of humus cover.

Thickness is highly variable. Mull is not always combined with brown soil, for quite typical mull has been observed on podsol. On the other hand, even though mor is of course usually combined with a podsol profile, it is not rare to find mor resting on mineral soil that is only slightly or inci

piently podsolic, either because it was earlier cove

red by mull or, in the lowland, because the climate is not humid enough to favour typical podsol except in very base-deficient sites. The local and temporal variation as to the degree of podsolization is so great that up to now a detailed pedological map of Sweden has never been published, in spite of the considerable research on forest and arable soils that has been carried out.

�

��;;i�c�ei�g��u;d Kalkrikare jordarler Soils rich in lime

1 / 1 Kalkmaterialets lransporlriktning

I I Transport direction o(

disintegrated rocks rich in lime

2001..m '---"---'

Fig. 5. Calcareous rocks and soils, with arrows showing the dispersal of disintegrated limestone by glacial drift.

From Magnusson & al. 1963 .

About one sixth of Sweden is covered by peat.

The percentage ranges from almost none in some agricultural areas (where the original wet and some

what peaty alderwoods and marshy meadows have

Acta Phytogeog.r. Suec. 50

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continuous mire (peatland area) is the Sjaunja in Lule Lappmark, with about 400 sq.km (nearly 150 sq. miles). Fen peats (woody fen, sedge, sedge

Sphagnum or even sedge-Bryales peats) prevail both in the north and in the lowlands, whereas true (ombrotrophic) bog peats (chiefly woody bog, Sphagnum and Sphagnum-Eriophorum peats) are predominant in the western parts of south Sweden and are common in several other areas as well. In the southern and eastern lowlands, the peatlands originated chiefly or even almost exclusively from filling-in of shallow lakes by vegetation (or in some cases directly from coastal marshes), but elsewhere, and in particular in the western and northern up

lands, the present vast peat areas largely resulted from paludification of terrestrial soils.

The directions of vegetational and pedogenic succession are manifold in Sweden, and natural development of ecosystems seems to lead to no equalization of the existing diversity. Some sue

cessions however, if not broken by unpredictable irregular events such as forest fires, seem to end in steady states, or edaphic climaxes. In other cases, no stability at all can be detected, and the course of development is then not given from the primary factors alone, but influenced by the bio

coenosis itself. For instance in the case of the often divergent development in the mires, the vegetation and its substrate will even become increasingly diversified.

Climate

GENERAL.-Through the prevailing south-wes

terly air currents, bringing in moisture-laden air masses of Maritime Tropical origin, and through the Gulf Stream, great quantities of heat are carried towards north-western Europe. The Scandinavian countries therefore enjoy a much higher annual temperature than is normal at their high latitude.

Both diurnal and annual temperature amplitudes are moderate, but only the western coastal areas have a truly oceanic climate. Air humidity and cloudiness are often high, especially in late autumn, but the air is usually clear and not so hazy as in more southerly regions.

warm ("Tropical") Atlantic air masses and cold Polar or even Arctic air. In summer and autumn the former usually prevail but cool air is frequently added from the north either directly or via the North Atlantic cyclonic tracks. The Swedish sum

mer has three prevailing weather types: spells of dry, often comparatively warm and sunny weather of a continental type; moisture-laden south-western air currents with frequent rainstorms; and unplea

santly cool, either damp or dry weather under the influence of North Atlantic or even Polar air. There is a great variation regarding the relative import

ance of these and other components in various summers. Hot and dry summers are rare (about one in five to ten) but exert a considerable influence on vegetation in a country where almost bare rock and other dry sites are widespread. Not only warm but also cool periods can be rather dry, a type of weather frequently experienced in spring and early summer. On the other hand more than a third of the summers are exceedingly wet and usually rather cool (a constant cause of complaint during the vacation period); the rest are intermediate, but a summer that in its entire length is "normal" in the sense of meteorological statistics, both with respect to temperature and precipitation, is almost exceptional in Sweden.

Nevertheless, the Swedish summers, especially with regard to the northern part of the country, are among the better experienced at these fairly high latitudes. It is true that at its peak, the sum

mer is cooler in Scandinavia than in more conti

nental areas, but this is compensated for by the longer period of growth. Along the parallels on each side of the Arctic Circle, only in central Siberia and in the Mackenzie River region of Canada is the climate better for forest than in northern Fenno

scandia, but the nearly total absence of permafrost and the higher precipitation in Fennoscandia lead to a superior production of the forest and even to possibilities for agriculture. There is no other part of the world where considerable agriculture exists around the Arctic Circle, and locally even farther north.

This great northward extension of summer

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Features of land and climate 7

f

^se"

,.

^ss

56° 56

16° 18° 20" 22° 16° 18° 20" 22.

Fig. 6. The distribution of summe-r warmth, as shown by the number of days with maximum temperature over + 20°C. Less marked pattern, different from that on next figure.

Fig. 7. Isolines for the number of days when maximum tempera

ture exceeds + l 5°C illustrate the strong northward decrease in duration of the favourable season.

Fig. 8. The number of days without frost (not to be confused with the much shorter frost-free season). Coa

stal areas are strongly favoured.

Figs. 6-8 from Atlas over Sverige.

warmth is related to the most unusual feature of Scandinavian summer climate, viz. the small dif

ference between south and north. This equality is .still more marked along the Baltic and Bothnian shores of Sweden and Finland than on the Atlantic

�oast of Norway. All the way from Skane to Norr

botten (12 degrees difference in latitude), the mean temperature of July is about + 1 7° to + 15°0 in the lowland; it is about + 15° to + 12°0 in the

adjacent upland.

As in other northern countries, the light climate of late spring and the early part of the summer is of a decidedly long-day type. At midsummer, only southernmost Sweden has a night that is dark for a few hours, whereas in middle Sweden twilight prevails even at midnight, and in the extreme

north, midnight sun is visible for several weeks.

A large portion of the favourable light period coincides with the earlier part of the growth period, in particular with the times for shoot elongation and for maximum volume increment in forest trees.

WINTER.-In winter as well as in summer, the Norwegian coast has only a slight difference between south and north; it is in its entire length quite remarkably winter-mild for its high latitude.

Northern Sweden and Finland, on the contrary, are in winter within easy reach of the great Con

tinental cold air mass of northern Eurasia (the winter-time extension of the Polar air mass, with exceedingly low temperatures) . There is often in

tense cold for long periods in the northern interior

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of Scandinavia, even though temperatures below -45°0 are exceptional. Low temperatures occur in particular after large parts of the Bothnian waters and coastal parts elsewhere have bece>me frozen in late winter, but there is always enough open water left in the Baltic proper to have a mitigative effect on the winter temperatures of coastal south

east Sweden. Still more important, especially in the south and south-west, where the coast has mean temperatures about or only slightly below freezing even in January and February, are the effects of frequent invasions of mild and moist

Fig. 9. The length of daylight, twilight and nocturnal darkness, as dependent on latitude, for each month of the year. The twilight in winter is longer in practice due to multiple reflexion between snow and sky. From Angstrom 1 958.

Atlantic air. They reach a variable way to the north and exert an influence even in northern Sweden, as evident from the fact that the winters are far warmer over all Sweden than would be expected from latitude.

The winter climate has a strong south-to-north gradient, quite contrasting to the equalized mean temperatures in summer. But the gradient is not uniform, for there are secondary effects involving differences between the milder coasts and the more severe inland, and to some extent also between lowland and upland. Above all, in the shelter of

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Features of land and climate 9 the highest mountains in the southern Scandes, a

distinct minimum exists in the areas on both sides of the Swedish-Norwegian frontier, in the provinces of Hedmark and South Trondelag in Norway and Dalarna and Harjedalen in Sweden. Farther north, westerly to north-westerly invasions of Atlantic air frequently cross the low mountains of North Trondelag and break in into Jamtland. In conse

quence the winters are considerably milder here, but on going still farther north winter temperatures again decrease strongly and reach their lowest values for Sweden in interior northern Lappland (they are still lower in Finnish Lappland and adja

cent parts of Finnmark, in Norway).

The Scandes have much lower summer tempera

tures ( + 1 1 oc and lower) than the rest of Sweden, but in winter the lowest temperatures are not in the mountains but to the east of them.

The winter temperatures seem to have their greatest botanical importance in the southern coast areas, where they are mild enough to allow many of the suboceanic species of western and central Europe to grow wild (e.g. Hedera helix) and still more to be cultivated (e.g. flex aquifolium, the few spontaneous occurrences are unstable and doubtful as to their origin) . In the rest of the country, only strongly frost-hardy species can survive in a natural environment with normal competition, but the upper limits of cultivation of numerous cold-sensi

tive plants are good indications of the increasing severity of the winters towards the inland and the north. Mostly, however, other factors than low temperatures in winter seem to be responsible for out-wintering, such as too short autumns for bud and bark development or lignification of shoots, or the trying weather typical of early spring especi

ally in central Sweden, with local warmth on sunny days, dry cool winds, still frozen subsoil often covered with a sheet of re-frozen ice or with a layer with congeliturbation at the very surface, and with heavy radiation frost almost every night. A long, late autumn but a not too prolonged period of early spring therefore are to be regarded as fa

vourable.

Soil freezing (tjiile in Swedish) occurs all over Sweden but penetrates to much greater depths in the north. Contrary to common belief, the frozen

100 200 KM

Fig. ^l0. Growth period: number of days with mean tempera

ture exceeding + 6°C, according to Langlet. From Skogen och skogsbruket .

soil is often permeable to thaw water, except when repeated re-freezing occurs. Permafrost is not recorded with certainty in mineral soils except at high altitude and it may also exist under areas blown snow-free in winter at somewhat lower

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60'

58°

1600 1400 1200

1000 900 800

2'

60'

f

^58'

200 km 56'

Sthlms o' mcrid, 2' 40

Fig. 1 1 . Annual precipitation in Sweden. From Angstrom 1 958 (adapted from Atlas over Sverige) .

elevations in the mountains. In the northern mires (see the section on them) local permafrost occurs in the form of palsas.

GROWTH PERIOD .-For the regional features of Swedish indigenous vegetation, the mentioned traits of the climate may have considerable importance.

Another important set of factors is related to the length of the growth period. Unfortunately it is customary in Sweden to give the "vegetation

or + 4°0 (HULTEN 1950, p. 39*). Both temperatures are chosen too low, because they will give iso-lines of duration that show up strongly oceanic areas as too favourable. It is well known that at least for many crops and for forest vegetation, too great an oceanity of climate is unfavourable. With iso-lines of duration of a period above + 6°0 (or perhaps even higher) we obtain a climatic picture (LANGLET 1937, p. 373) that corresponds fairly well to the zonation of major vegetational regions although the favourable autumnal effect of the Gulf of Bothnia is not fully accounted for; still, such a comparison cannot be made in sufficient detail at present due to lack of reliable data on local climate and vegetation.

In the mountains, the actual vegetation period is also checked by snow accumulation, and late

snow areas have a much shorter season of growth than the normal, which is anyway no longer than about three months at the timberline in Lappland, and still shorter at higher altitude. The adaptation of some mountain plants to grow at very low air temperatures (but heated internally from solar irradiation) will cause some growth even at altitudes where there is no growth period at all in the meteo

rological sense.

PRECIPITATION AND RUN-OFF.-Precipitation in Sweden is not so unevenly distributed as in Norway, but still there are great differences. Low figures (about 400 to 500 mm) are found in the archipe

lagos, along some parts of the coastline itself, and on part of the Baltic islands; further near the large lakes, in sheltered valleys in the northern upland and, locally, the eastern Scandes; finally in a large area in the north-north-east. Medium precipitation (about 500 to 700 mm) prevails for instance in many eastern and central parts, and in most of the northern uplands, with considerable increase with altitude. High figures (about 700 to 1000 mm) are typical of the. western half of south Sweden and of the western elevated upland from Varmland and Narke to northern Dalarna; still higher amounts of precipitation (frequently 900 mm to about 2000 mm) evidently fall within the Scandes, at least in

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Features of land and climate l l their highest and their west-exposed parts, to judge

from run-off determinations.

The maximum of precipitation is nearly always in late summer, but in the west there is also much rain or snow in autumn and early winter; elsewhere winter is drier, and late winter and spring precipi

tation is low in all parts. Therefore, even in the north most precipitation falls as rain. The period of snow cover is extremely variable; because the snow is nearly always unreliable in the extreme south and on the south-west coast, there this period is only about 40-50 days, but it rapidly increases in length inland. The average duration of snow near Stockholm is about 3 months but there is a variation from a few weeks to about four months between various years. Four to six months of snow are typical of much of northern Sweden, but in the extreme north the time with snow exceeds seven months. In the Scandes the cover is too uneven to allow an estimation of duration; this would vary from almost none on windy ridges to all year round in permanent snow-beds at high altitude.

The depth of snow is equally variable but its maximum (exceeding l m on an average and occasionally as much as

1.8

m, according to AGER 1964) is in the mountain valleys of southern Lapp

land and not in the extreme north; again, there is

· great local variation, especially above the timber

line of conifers (the birchwoods above the latter do not check the snow-drift to the same extent as does coniferous forest).

Precipitation in excess of evapotranspiration (i.e. run-off per unit area) is regarded by 0. TAMM (l959b) as the best expression of humidity (of the ground), giving a picture superior to, for instance, that of DE MARTONNE's index (HESSELMAN 1932)^.

0. TAMM developed an empirical formula for a fairly accurate calculation of run-off from precipi

tation and temperature data, although only valid for the forested parts of Sweden. The distribution of surplus precipitation is similar to that of total precipitation although the diminishing due to eva

potranspiration is greater in the south; this, in turn, gives a better correlation with distribution and strength of podsolization, tendency to paludifica

tion and types of peatland. But it should be remem

bered that most of the paludification took place

58°

Fig. 12. Average number of days with snow cover. From Angstrom 1958.

at a time long ago when distribution of surplus precipitation was not necessarily equiformal to the present one, and that mire types are strongly dependent on the type of terrain and not only on the climate.

Except in the extreme south, the maximum run

off comes after the snow has melted. In rivers coming from the mountains, this period is prolonged and there may even be a second maximum in early summer. In late summer and autumn water-levels tend to be sinking except in periods with great

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autumn or winter are usual. The difference in flow is exceedingly great in those northern rivers which have not yet been regulated, with about 50 to

lOO

times greater flow at high waters than at the late winter minimum. This also leads to great amplitu

des in water-level of rivers and lakes, in extreme cases nearly 6 m difference between highest and lowest water-level.

LocAL CLIMATE.-Little is known about local variation of Swedish climate. Among important factors for vegetation, warmth of insolation and frequency of low minimum temperatures at night (including frosts) are known to be much affected by situation and exposure. It should be observed that Sweden (especially the north) is at such a high latitude that the difference in insolation between slopes towards the south and those facing west or east is diminished; contrary to true Polar condi

tions, however, north-facing slopes are still highly inferior. Data by JIM LuNDQVIST (see his contri

bution) and others seem to show that the most important climatic feature of an elevated strong slope, when compared with a valley situation, is the higher temperature during cool nights, perhaps also the early melting of the snow cover in favour

ably exposed steeps.

Lakeside situations in the north are characterized by lower frequencies of frosts but also by lower temperatures on bright summer's days. In combina

tion with direct influence of wind and scarcity of protecting snow in winter, this leads, in the upper subalpine region, to an "inversion" of the tree line

A cta Phytogeog1·. Suec. 50

large mires. Similar effects are probably partly responsible for the poor growth of several woody species on the outer islets in the Baltic archipelagos, but the extremely late spring and other factors may also be of importance. The reducing effect on precipitation of large bodies of water has already been mentioned; an opposite, increasing effect is due to the forest which slows down the wind and thus forces the air to rise.

As elsewhere, the micro climate deviates often strongly from the general and local climate treated in this article, but few data are available.

SoURcEs.-Data on which this article was based were taken from several works, the chief source being

"ATLAS OVER SVERIGE", which has legends and sum

maries in English . A large handbook for international use is "A GEOGRAPHY OF NORDEN". Pre-Quaternary geology is treated by N. H. MAGNUSSON et al. (1960) and the Quaternary by G. LUNDQVIST (1959a, 1961). The book on North Swedish soils by 0. TAMM occurs in an English translation (1950) as well as the Swedish original (1940). For the soils, see also a short paper in German by ScHLICHTING (1955). Among works in Swedish, special reference is made to MAGNUSSON, G. LuNDQVIST & REGNELL (1963), to P. H. LuNDE

GARDH, JAN LUNDQVIST and M. LINDSTROM (1964), and to articles by JAN LUNDQVIST and T. TROEDSSON in "JORD" (1963) for geology and soils, to ANG

STROM (1958) for climatology, and to AGER (1964) regarding winter climate of the northern part; but maps are also found in HULTEN (1950), SELANDER (1955), various atlases and encyclopaedias etc. Com

plementary data for special areas will be found in several articles in this book. - The author is indebted to Dr. B. COLLINI of Uppsala University for advice on geology.

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Fig. l. Vigorous infralittoral shrubs of Fucus vesiculosus, ! ^mhigh, without vesicles, cradled by the swell and thus kept clean and free of sediments. Top of photograph shows dense tufts of Ceramium tentoicm·ne, bleached by the sun.

Aland Sea, Halsaren, steep rock slope, heavily exposed, at 5 m. July 17, 1944. Submarine photo Mats Wrern.

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(27)

A Vista on the Marine Vegetation

By MATS W LE R N

Perpetual motion and permanent rest in submarine environments

It is easy to observe the algal growth on a rocky shore, particularly at ebb tide or, in the tideless seas, at low waters. To some degree we are also able to extend our inspection downwards through the superficial layers of water, a penetration at

tempted at when we wade in the modest surf on a calm summer's day or lean over the gunwhale while hugging the shore at the edge of islands or skerries. Except in the calmest coves, what we see are clean plants without a coating of sediments.

The "fucoid" algae appear, we may say, regular, and the "confervoid" tufts are short and dense.

An impression of almost universal, deep-reaching cleanness will be perceived especially by those algologists who explore the cliffs on the exposed edge of archipelagos or promontories. Beaten by the waves or cradled by the swell, this is the vegetation that forms the basis of our general idea of marine growth.

The diver meets more shifting views. The vegeta

tion has quite a different aspect when one is stand

ing amidst it, than the way it looks when watched from above with downward fading sharpness. The most striking feature of submarine observation, at least inshore, is however the experience of the complete quietude in the landscape on the lower side of the reach of the waves. When walking in an area of extreme calmness, the diver stirs up a cloud of finely divided mud which obscures his sight until it is carried away by some sluggish current. The water itself, if undisturbed, is generally clearer here than in the surf region above where the waves cradle the algae to and fro, and lots of particles whirl around.

To GrsLEN (1929) who was perhaps the first bio

logist to have a direct physical contact with sub

marine sedimentation, this confrontation was im

pressive, and he was astonished to observe its pro

found and far-reaching effects in all its stages (p. 99):

"One of the things which is most surprising when we make a comparison between bottoms from the inner and outer parts of the fjord is the increasingly pronounced layer of dirt covering the plants and stones towards the interior. While outside the fjord one walks on hard bottoms without having the view spoilt by the whirling up of any detritus or sedimentary par

ticles, in the inner parts one cannot take a step on the seabottom without a thick cloud of dust, one is tempted to say, whirling up. "

H e also described observations o n the opacity o f a thin stratum of fresher water, not rare to occur in the interior Gullmar Fjord, quoting a diver's statement that it was dreadfully dark working in the algous belt

"but lightened farther down".

The possible nutritional effect of the "dust" on the algae was also commented on by GrSLEN (p. 100):

"The rich sedimentary deposit on the algae and the absence of strong motions of the waves, make it pos

sible for certain epiphytes to flourish here which never, or very rarely, appear beyond or in the outer parts of the fjord. To what extent they are nitrophile or not I cannot decide, but it seems probable that such is the case.' '

The coarser algae, when growing dust-covered in the calm, acquire distorted, bizarre shapes and thus appear as a "warped" formation. The fucoid species, when identical with those of the "cradled"

facies (e.g. Halidrys siliquosa, Chondrus crispus, Phyllophora membranifolia, Furcellaria fastigiata), grow large and look different, and are surrounded by tuft algae in big but thin clouds. Within some fjord-like inlets in Bohuslan, e.g. the Gullmar Fjord, a typical ·warped formation may begin only a few

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never L. digitata.

Starting from the pure organic mud as one ex

treme, the "warped" vegetation forms a series of transitional stages leading to vegetation in a

"cradled" position, the extreme type of the latter being the crystal clean barnacle facies on the most exposed rocks, with small red algae growing close to the surface.

Broad archipelagos occupy large parts of Swe

den's coasts, and a great work remains to be done until we know the varying vegetation of these wide waters. As one sails inshore, the ceasing of the swell and the decrease of the transparency of the water as well as the increased deposition of sedi

ments have a great influence on the distribution and composition of underwater vegetation.

In archipelagos of the Baltic the most profound change in the vegetation may set in already when one is passing the outer fringe of an archipelago.

The sheltered sides of even the outermost skerries, at a moderate depth, lose the freshness typical of the shores that are absolutely unprotected. This contrast is not so striking in that part of Bohuslan which receives the rough long waves of the North Sea over the open Skagerrak.

Outside of the isolated off-shore group of islets and skerries called Vaderoarna, the sea may during heavy westerly gales break over banks at a depth of about 18 m (probably Laminaria hyperborea bottoms) . Further south, the coast is protected by the spit of Skagen which acts as a breakwater. In the Baltic, the exposed shallows break the waves only at a much lesser depth, but here a new factor must be taken into account: the pack ice which has been observed to run aground on rocks at a depth of many metres (cf. ice map, Fig. 3).

It is probable that tidal currents contribute to keep the vegetation clean of sediments in the archi

pelagos of Bohuslan. In the Baltic, however, desti

tute of a real tide, the currents are due to outflows or influenced by changes in water level related to the shifts in wind direction and air pressure. U nfor

tunately we know too little about the currents within the archipelagos, especially the bottom currents, and are too dependent on deduction from

Along certain Baltic coasts a submarine archipe

lago, off-shore of the skerries, has been observed to act as a screen in front of the visible skerries, as for instance, off the coast of SmiUand and in the outer Stockholm Archipelago. Although the effect of this screen may escape notice near the water surface around these outer skerries, which carry a vegetation seemingly typical of strong exposure, the shelter is perceptible in the deeper infralittoral.

Where we would have expected a beautiful and strong-growing vegetation of Rhodornela subfusca, Polysiphonia nigrescens, Sphacelaria arctica with Aglaothamnion roseum, and outside Sma1and Fucus serratus, instead Furcellaria fastigiata is found to grow with entangled, loose individuals of Phyllo

phora Brodiaei, Ph. membranifolia, Rhodomela sub

fusca, together with a great amount of the Baltic small-sized Mytilus edulis. This indicates a some

what sheltered aspect of the infralittoral algal growth of the Baltic, and constitutes a "warped"

vegetation, to be compared with the above-men

tioned "warped" vegetation of Bohuslan as found in the Gullmar Fjord, as a matter of fact even with some dominant species in common.

This "warped" vegetation of the Baltic is not restricted to growth on the rocks. In its more shel

tered aspects, it covers even certain bottoms of clay or of clay with fine sand in the "fjards", either as loose-lying or as loose-and-entangled in the byssus of clusters of Mytilus. A similar wavering transition between an attached and a loose-lying way of living is also characteristic of the warped vegetation of Fucus vesiculosus in the inner Baltic archipelagos (we have to realize that Fucus vesicu

losus is an infralittoral plant in the Baltic, growing on the rocks from about 0.5 down to 10 m and more). Even on the rock one may find a mixture of attached and loose plants, and on the clay or the organic mud occurs a dense cover of loose-lying comparatively big warped plants. In these mats of loose-lying Fucus may sometimes be found shoots of loose-and-entangled Zostera marina. They grow erect, looking as if they were attached, but their roots are black, affected by the decomposition of the lower stratum of the thick Fucus cover.

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A vista on the marine vegetation 17

Vegetation on debris

The reach of the swell into the archipelagos (cf.

WlERN 1952, Fig. 48), and the system of currents are factors governing the transport of large par

ticles, their sorting and final deposition. Shell frag

ments, tubes of polychaetes, remains of Litho

thamnion and other coastal debris, and even coke and refuse originating from ships, etc., occur in a shifting assortment, with a variable amount of fine-grained sediments mixed in. These fragments of firm bodies offer substrates to an interesting se

ries of algal communities, ranging from vegetation moved by currents to warped types, as on the rocks.

Unstable shell bottoms form a counterpart to the

"cradled" epilithic vegetation, though different and sometimes much richer in species composition.

From this, every transitional stage occurs towards the loose mud.

The coastal debris series may be exemplified from BohusUin. In the outer part the Arthrocladia villosa

Sporochnus pedunculatus association with Dudres

naya consists of more than 90 species; in waters of intermediate position we find a Griffithsia flosculosa association with Antithamnion plumula (bilateral type) and about 50-65 species; and on muddy bottoms in narrow waters grows a Sphacelaria as

sociation with Sph. radicans and a small number of species. The literature on these bottoms is sparse (F. L. EKMAN 1857, KJELLMAN 1878, KYLIN 1907, pp. 233-234, W lERN 1958) .

The shell bottoms are reservations for weakly competitive species often living on the fringes of their distribution ranges. A shell bottom offers an unstable substrate, which prevents the establish

ment of a dense biocoenocis of plants and animals.

New and free shell surfaces are continually offered for colonization. This reasoning is directly inspired by ideas forwarded by BENGT PETTERSSON regard

ing frost-heaved soils on the limestone alvar pave

ments of Gotland.

On the marine shell bottoms, Dudresnaya verti

cillata colonizes only grains of gravel covered by remains of Lithothamnion. Silicious unstable gravel is comparatively poor in species, and it seems likely that the vegetation on shells is not simply a product of mechanical conditions.

So far we have no counterpart to shell bottoms in the Baltic. The last traces of shell bottoms with algal growth are found in the northern entrance of the Oresund.

Northern species with an Arctic character

There is a group of northern species, though not large and not uniform, that may be noticed within Norwegian as well as Swedish fjords (the Gullmar Fjord). They are common in the Polar Seas, some

times also showing a preference for brackish water.

We think of the southward extension of occurrence of Antithamnion boreale, Sphacelaria arctica, and to a certain degree A udouinella efflorescens, Sphacelaria (Chaetopteris) plumosa, Phyllophora Brodiaei, Phyco

drys sinuosa. The latter are, so far, interesting more for their abundance in the fjords than for their mere presence. In fjords of Norway, especially in the north, with the contrasting Gulf Stream water off-shore, to this list may be added such species as Omphalophyllum olivaceum, Turnerella Pennyi, Ptilota pectinata, Cruoria arctica, and Stictyosiphon tortilis.

It is of interest to note that there are several phenomena in common between a bottom within the archipelago in Bohuslan inshore of the Skager

rak, and a bottom of the open sea, at the northern entrance to the Oresund. At the inner end of Katte

gat we meet again with Antithamnion boreale and Sphacelaria arctica, and a rich occurrence of A udoui

nella efflorescens, Sphacelaria plumosa, Phyllophora Brodiaei, Phycodrys sinuosa, etc. When travelling south towards Oresund and the Baltic, one ap

proaches a vegetation that has a touch of "Arctic"

character. The algal flora of Oresund carries a

"High Boreal impression" (L6NNBERG 1898, p. 76).

In this connection also the occurrence of Fucus edentatus in Oresund should be mentioned, though growing in polluted areas, as it does in certain other parts of the West Coast (see LINDGREN's contribu

tion to this volume) .

I n the Baltic itself the occurrence of "Arctic"

algae is a well-known fact. Here species of "Arctic"

character form an important part of the bio

coenosis, among algae Sphacelaria arctica, Litho

derma Rosenvingii, A udouinella efflorescens and Stictyosiphon tortilis, the last one especially corn-

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We may focus our attention on those factors which a fjord in Bohuslan and the Baltic (including Oresund) have in common. In this connection we may emphasize the ice cover (see the map, Fig. 3) and its consequences, such as shelter, dep:>sition of sediments, reduced light and temporary reduction of the oxygen content, as well as lower water temperatures, and particularly more marked changes in temperature.

The Baltic-a cul-de-sac

We might well compare the Baltic to a gigantic threshold fjord, with the shallower of its thres

holds in the southern part of the Oresund, between Copenhagen and Malmo, at a depth of

8-7

m. The main entrance to the Baltic is however through

Fig. 3. Maximum extension of sea ice in an average winter.

In hard winters, the pack ice becomes largely frozen to

gether and extends seawards over the floe II).arked areas and even more. From Atlas of Finland, with additions by Dr. C. J. Ostman, in Angstrom 1 958.

A cta PhytogeogT. Suec. 50

ice and floes Pack"ice Ice floes Open water

100 km ...__...___ ...

the Great Belt, which has a deep central furrow, whereas the threshold is here at the Darsser Schwelle (ea. 1 8 m) between Denmark and Ger

many. The typical Baltic conditions thus begin only east of the Darss and south of the Oresund thresholds.

The outward influence of Baltic waters reaches far beyond its thresholds, affecting Kattegat and even Skagerrak, mainly with regard to the surface waters. As to the hydrology of the transitional seas, see JENSEN (1940), STEEMANN NIELSEN (1940) , BRATTSTROM ( 1 941 ).

The South Norwegian and entire Swedish coast forms a continuous gradient from oceanic to fjord

like and finally rock-pool and near-freshwater con

ditions, a gradient regarding several factors, apart from the two most obvious ones, the salinity and the tide.

Even on the part of the West Coast bordering the Skagerrak, the interior waters, as we have

The plant cover of Sweden: a study dedicated to G. Einar Du Rietz on his 70th birthday, April 25th 1965 by his pupils

ACTA PHYTOGEOGRAPHICA SUECICA

SVENSKA VA.XTGEOG�AFISKA S.!LLSKAPET

THE PLANT COVER OF SWEDEN

THE PLANr-f COVER OF SWEDEN

THE PLANT COVER OF SWEDEN

G. EINAR DU RIETZ

PREFACE

TABLE OF CONTENTS

l

Ill

R EGIONAL S U RVEY

Features of Land and Climate

BEDROCK MAP

SWEDEN

� Stz�?n- }S'arui-

D

' ,

l

�

f

,.

f

1.8

lOO

A Vista on the Marine Vegetation

8-7

G. EINAR _DU RIETZ