Flora and Vegetation of Arctic Alaska, Yukon, and Northwestern Canada
EA-Plant Sciences
(A. E. Porsild)
FLORA AND VEGETATION OF ARCTIC ALASKA
YUKON, AND NORTHWESTERN CANADA
CONTENTS
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Page
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Introduction
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1
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The Flora
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3
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Types of Vegetation
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6
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Rocky Barrens or Fell-fields
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8
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Tundra
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12
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Strand Vegetation
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17
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Vegetation of Fresh Water
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18
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Bibliography
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20
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EA-Plant Sciences
(A. E. Porsild)
FLORA AND VEGETATION OF ARCTIC ALASKA
YUKON, AND NORTHWESTERN CANADA
INTRODUCTION
Floristically the North American Arctic, here taken to include the
total land area lying north of the tree line, may be divided into four major
provinces, namely (
1
) arctic Alaska and Yukon, (
2
) the arctic Archipelago,
(
3
) continental parts of arctic Northwest Territories and Ungava, and (
4
)
Greenland. The present description however, embraces only arctic Alaska–
Yukon and the arctic parts of Mackenzie-Keewatin to which has been added
the western and central islands of the Arctic Archipelago. It does not
include arctic Ungava, the easternmost islands of Ellesmere, Devon, Cornwallis,
Somerset, Baffin, or the islands of Hudson Bay. In this area the writer today
recognizes 872 species (and varieties of well-defined geographical range) of
vascular plants distributed among 60 families and 194 genera.
Although the two areas under discussion are separated by a rather strongly
marked phytogeographical boundary - the Mackenzie Valley - they have many
features in common. Approximately one-third of the species which make up the
combined floras are widely distributed, circumpolar species. Common to them
both, as the most striking feather, is the total absence of trees. There are,
EA-PS. Porsild: Flora and Vegetation
to be sure, a number of ligneous or woody plants - such as willow, dwarf
birch, and various kinds of heath and berry bushes - but even these become
low and dwarfed north of the tree line, and are generally restricted to
places where protecting snow cover is assured during the winter. In the
interior of the mainland some of the these species still are
^
a
^
dominant component
of the vegetation, but when we reach the seacoast or cross to the arctic
islands their numbers dwindle rapidly. The few woody plants that occur there
become low and creeping, with their stems partly buried in the moss, while
some of the berry bushes cease to produce fruits, or disappear entirely.
the climate of the entire region is arctic but there are, nevertheless, strong
regional differences; thus the Bering Sea shores, and also the Canadian Arctic
east of Hudson Bay, has a maritime polar climate whereas the Mackenzie and
Keewatin districts, and also the Arctic Archipelago, all have distinctly con–
tinengal types of climate with relatively warm summers and very cold winters.
This is well illustrated by the course of the 50° F. isotherm for the warmest
month, July, which in western Alaska first parallels the Bering Sea coast,
then swings abruptly eastward across the north slope of Alaska. From the mouth
of the Mackenzie, it follows the Arctic coast east to Bathurst Inlet whence, by
the cooling influence of Hudson Bay, it is deflected in a southeasterly direction,
bisecting the west coast of Hudson Bay between Chesterfield Inlet and Churchill.
Even locally the proximity of the sea strongly affects the temperature
and thereby also the vegetation. Thus, at Nome on the south coast of Seward
Peninsula, the mean temperature for July is 50° F. whereas Kotzebue, at the
head of Kotzebue Sound and
only
1 1/2 degrees farther north, but sheltered by
Seward Peninsula, has a 2-degree warmer July mean. Of much more importance,
however, is that the average numbers of days without killing frost is 52 at
EA-PS. Porsild: Flora and Vegetation
Nome but 93 at Kotzebue. The mean annual precipitation at Nome is 18 inches
whereas at Kotzebue it is only slightly over 6 inches. Barrow, on the other
hand, has an extreme polar climate; the mean for July there is 40° but the
number of days without killing frost is only 17, At Coppermine, and at
Cambridge Bay on Victoria Island, the mean for July is 10° F. higher and the
number of days without killing frost almost seven times as high as at Barrow.
Except for the distinctly moister southern part of the Bering Sea region,
precipitation throughout the area is light, averaging perhaps about 10 inches
for the year. All records, however, are from stations situated along the
coast, and there is reason to believe that the annual precipitation of the
interior mainland as well as that of some of the larger islands is consider–
ably less. Most of the precipitation falls as snow during the winter but is
swept off the ground by frequent gales, so that the plant cover, moreover, is
exposed to the drying effect of the wind. The light precipitation is to
some measure compensated by the fact that 40 per cent falls as rain during the
months of June, July, and August. Of far greater importance, however, is that
owing to the presence of permafrost a few inches below the surface, moisture
derived from melt water as well as from rain is prevented from penetrating to
depths beyond the reach of plant roots. Without permafrost many areas in the
Arctic would be a lifeless desert.
THE FLORA
Arctic Alaska and Yukon — largely unglaciated during the Pleistocene —
presents the greatest variety of plant habitats; its flora is rich in isolated
and endemic species and, undoubtedly, is very old. Through its former land
connection across hypothetical Beringia, there has been a free interchange
of species so that almost one third of the present flora of 604 species of
EA-PS. Porsild: Flora and Vegetation
vascular plants is of Asiatic affinity. The much smaller number of Cordilleran
species may have reached the area by way of the Mackenzie Mountains. In the
Eastern Arctic practically all mountains areas were covered by huge ice caps
during the Pleistocene. In consequence, the alpine flora of the Eastern
Arctic is youthful, poor in species, and usually entirely lacking in rare or
endemic species. In Alaska and Yukon, on the other hand, although some of
the high mountains may
^
^
have had, or even now have, isolated ice caps, such
glaciations as existed was largely limited to cirques and valley glaciers;
during the Pleistocene many of the large mountains massifs undoubtedly acted
as refugia and, indeed, today harbor the richest floras of rare and endemic
species (5; 14; 16). Such discontinuous vertical distribution of plants is
very noticeable on the Seward Peninsula and, indeed, in most places in arctic
Alaska and Yukon wherever mountains or hills exceed one thousand feet in
elevation. Below this level the coastal flats are occupied by a wet, marshy
tundra that everywhere is inhabited by practically the same assortment of
species. The most notable change in the flora, when one travels inland,
away from the seashore, is the increasing ration of fruticose species over
herbaceous ones.
On the hills, on the other hand, above the one-thousand-foot level, a
very different and much more varied flora is encountered; here we find most
of the rare and interesting plants for which the region is famous, notably
those of Asiatic affinity or at least of bilateral Beringian range. The writer
(11) selected 88 species that, in the Bering Sea region, appear to be
restricted to levels above one thousand feet. By grouping these species
according to their general distribution it is found that, roughly speaking,
three-fourths are either Western-Cordilleran, Bering Sea endemics, or essen–
tially Asiatic species transgressing into western America, whereas but one-
EA-PS. Porsild: Flora and Vegetation
fourth are widely ranging, circumpolar, or North American species that are
common across the continent from the Atlantic to the Pacific coast. A
further breakdown discloses that 17 species are circumpolar or essentially so,
3 are essentially North American species, known from the Atlantic to the
Pacific coast, 16 are western American or Cordilleran, 15 endemics of the
Bering Sea region, and no less than 37 are Asiatic or Beringian bilateral
species transfressing into western America.
The Arctic Archipelago was formerly though to have escaped glaciations.
Recent investigations, however, indicate that at least the southern islands
have been severely glaciated and that all but the higher parts of the Archi–
pelago was submerged in Pleistocene time, (13; 20). The climate is decidedly
high-arctic, and the flora, consequently, is comparatively poor in species.
The total number of vascular plants species known to occur in the Archipelago
has recently been increased to 308, of which 226 occur in the western part
and no less than 214 in Banks and Victoria islands alone (13). Almost
one-half are widely distributed arctic species. The presence of a compara–
tively large number of isolated and endemic species offers some curious
phytogeographical problems.
The arctic Canadian mainland is characterized by a distinctly continental
and very dry climate which, together with the absence of mountain barriers,
accounts for its strikingly uniform and monotonous plant cover. Of the 651
species known to occur north of the tree line, 70 per cent are widely distri–
buted circumpolar arctic or North American species. A considerable number
of nonarctic forest species reach far north of the present tree line and,
together with tree stumps
in situ
and peat deposits, may indicate past
oscillations in the tree line. In terms of postglacial chronology, the flora is
EA-PS. Porsild: Flora and Vegetation
youthful, as indicated by unstable, preclimax plant communities and by
the general paucity of endemic and isolated species. To the west, the
Mackenzie Valley forms a strongly marked floristic boundary which has been
crossed by comparatively few species of Cordilleran or bilateral Beringian
range.
TYPES OF VEGETATION
Land surfaces in the Arctic may be divided into three principal tyles
of landscape: (
1
) the ice desert, (
2
) the rock desert, and (
3
) the tundra.
The first, which in the form of glaciers, ice caps, or perennial snow fields,
occupy 86 per cent of the interior of Greenland, and also some smaller moun–
tain regions in Baffin, Devon, Ellesmere, Axel Heiberg, besides several
islands of the Sverdrup group, in the area under discussion occurs only as
local glaciers in the Brooks Range. The rock desert - the dominating land–
scape in heavily glaciated northern Keewatin, northeastern Mackenzie, and
the arctic islands - in Alaska and Yukon is found only at high elevations
in the mountains. In arctic Cnada the rock desert is everywhere interspersed
with lakes and ponds, or with small or large areas of tundra. The tundra,
finally, occupies a wide belt between the edge of the forest and the high–
arctic rock desert and is endowed with the richest flora. Like the rock
desert it may be divided into several distinct plant communities such as
marsh, grassland, and dwarf-shrub heath.
The present treatment deals mainly with the vascular plants. The cryp–
togamic flora of the arctic landscape is very incompletely known outside
Greenland, and its ecological aspects are practically unknown. Among the
terrestrial cryptogams, bryophytes and lichens are both very significant
EA-PS. Porsild: Flora and Vegetation
ecologically in the composition of arctic vegetation.
Thus far comparatively little progress has been made in the study of
arctic plant communities in North America. In the heavily glaciated parts
of Keewatin, Mackenzie, and the Arctic Archipelago, the comparative youthful–
ness of the flora and vegetation is evidenced by unstable plant communities,
whereas in unglaciated Alaska and Yukon, and in the coastal plain east of the
Mackenzie, climax conditions may have been attained in the lowland “niggerhead”
tundra which is so characteristic a feature of the coastal plain landscape.
Four major types of vegetation may be recognized in arctic North America,
each capable of subdivision into a number of more or less distinct ecological
associations, the composition and interrelation of which again depend on the
physiography of the landscape.
Rocky barrens or fell-fields
Vegetation of rock desert
Vegetation of unstable screes and frost-activated (congeliturbated) soils
Vegetation of gravelly river flats, flood plains, and fans
Tundra
Dwarf-shrub heath
Lichen and moss heath
Grassland
Copses and thickets
Marsh and wet tundra
Snow-flush herb mats
St
^
r
^
and vegetation
Brackish meadows and marsh subject to floods
Vegetation of sand dunes and gravel beaches
Vegetation of rocky shores
Vegetation of fresh water
Vegetation of ponds and lakes
Vegetation of brooks and rivers
EA-PS. Porsild: Flora and Vegetation
Rocky Barrens or Fell-fields
Vegetation of Rock Desert
. The fell-field, or rocky barren, has been
defined (
[:
]
^
19
^
) as having so scanty a vegetation that the ground is
only partly covered. To this should be added that the winter snow cover is
generally deficient. Fell-field vegetation is found at high elevations and
also in high latitudes and is the dominant vegetation type in the rock desert
of northern Keewatin and Mackenzie, the greater part of the Arctic Archipelago,
and the highest mountains of Alaska and Yukon.
Most striking features of the rock-desert landscape are the flat-rock
tables and ridges of pre-Cambrian crystalline rocks of the heavily glaciated
Laurentian Shield or peneplain that has been left almost completely denuded of
soil, and the extensive, flat, or slightly rolling rock-strewn plateaus of
severely weathered Paleozoic or pre-Cambr
ian sediments predominant in the
western and northern islands of the Archipelago. But although soil is every–
where scarce, these wastelands, nevertheless, are not completely lacking in
vegetation. Over large areas the rock surfaces of the acid pre-Cambrian rocks
are covered by black, brown, and gray species of the crustaceous lichens (
Rhizo–carpo
n
, Licidea
,
Lecanora
,
Buellia
, and others), or by the much larger black
and green foliose lichens, sometimes called “rock tripe” (
Gyrophora
and
Umbil–
icaria
) that all lend a rather somber and depressing color to the landscape.
Some of the Silurian and Paleozoic rocks of the arctic islands, on the other
hand, almost completely lack lichen cover.
On loose rocks and gravel grow a number of fruticose species among which
may be mentioned the coral-like
Stereocaulon
, black and gray
Alectoria
, and
yellow, gray or brown species of
Cetraria
and
Cladonia
. On cliffs, below
EA-PS. Porsild: Flora and Vegetation
ledges providing nesting sites for gulls, hawks, falcons, or ravens, or on
isolated boulders that, in the Arctic, are favorite perches for snowy owls
and other birds, the dung-loving orange or vermilion lichen (
Calopaca elegans
)
often grow in great profusion and lend a touch of color to the otherwise
bleak landscape
Flowering plants, however, are not entirely missing in the arctic rock
desert, for the rock-strewn barren flats or cliffs that from the air may look
entirely devoid of vegetation, on closer inspection from the ground may dis–
close small or large patches, or “islands,” of vegetation composed of mountain
avens (
Dryas integrifolia
), yellow arnicas, several species of locoweed (
Oxy–tropis arctica
,
O. pygmaea
,
O. Maydelliana
, and
O. arctobia
), or saxifrages.
For a short time each summer these flowers transform these cases of the rock
desert into incredibly gas miniature rock gardens.
A number of plants that grown on windswept, stony soil develop tussocks
or dense, flat, hemispherical cushions, that by their shape provide protection
against evaporation and mechanical abrasion by wind, drifting sand, or snow.
Examples of such plants are the moss pink (
Silene acaulis
),
Diapensia lapponica
,
Loiseleuria procumbens
, a number of saxifrages,
Draba Bellii
, and many others.
In rock crevices grow a number of species that, like the foregoing, are all
strongly xerophytic. Among them are several saxifrages (
Saxifraga nivalis
and
S. reflexa
), tufted fescue (
Festuca brachyphylla
), several sedges including
Carex rupestris
, and the rock ferns
Woodsia ilvensis
,
W. glabella
, and
Dryopteris fragans
.
On gravelly slopes or in shelter of rocks where some soil has accumulated,
the showy, white-flowered avens (
Dryas
) forms large, flat cushions, often many
feet in diameter, sometimes to the exclusion of other species. In such places
EA-PS. Porsild: Flora and Vegetation
we may also find mats of crowberry (
Empetrum
), clumps of the purple-flowered,
broad-leaved willow herb (
Epilobium latifolium
) or the vetch
Hedysarum
Mackenzii
, whose showy purple flowers are scented like sweet clover. Other
colors are added by the lilac-flowered vetch (
Astragalus alpinus
), by yellow
arnicas and locoweeds (
Oxytropis
), by blue campanulas, bluish-white anemones
(
Anemone parviflora
), white chickweeds (
Stellaria
and
Cerastium
), or by the
large-flowered and very fragrant
Pyrola grandiflora
. In the southern part of
the arctic rock desert occur a number of dwarf shrubs, including several species
of willow, Lapland rho
^
do
^
dendron (
Rhododendron lapponicum
), dwarf azalea (
lois–eleuria procumbens
), Labrador tea (
Ledum decumbens
), and bilberry (
Vaccinium
uliginosum
). These are always low and prostrate with their stems bent and
gnarled. Furthermore, their shape is often contorted by wind action so that
the prostrate crown grows away from the root by which it is anchored. Some
of them grow espalierlike against south-facing rocks or cliffs from which they
obtain added warmth. The roots of these dwarf shrubs are spread horizontally
in the upper layers of the shallow soil, avoiding the permafrost. The majority
are evergreen, and in the structure of their leaves possess special features,
such as hair covering and concealed stomata to prevent loss of water.
Vegetation of Unstable Screes and Frost-activated (congeliturbated) Soils
.
Unstable rock screes and stone creeps, together with soil sorting and heaving,
usually result from frost action in the soil and are features of high-arctic
climates such as are found in high latitudes or at high elevations. The un–
stable soil conditions of these habitats make them unsuitable to many plants,
especially such as have woody stems or horizontal thizomes, whereas those with
superficial runners, strongly developed taproots or adventitious root systems
are able to persist. A number of xerophytic species, particularly in the
EA-PS. Porsild: Flora and Vegetation
families
(
Cruciferae
and
Compositae
(
Erysimum pallassii
,
Lesquerella arctica
,
Smelowskia calycina
,
Draba
spp.,
Arabis
spp.,
Crepis nana
,
Artemisia
spp., and
Taraxacum
spp., to mention only a few) by their growth form seem especially
well adapted to slide-rock habitats. In the strongly frost-activated soil of
polygon fields in Banks and Victoria islands, avens (
Dryas integrifolia
),
cinquefoil (
Potentilla rubricaulis
), and the locoweed (
Oxytropis arctica
) are
extremely common and frequently comprise 90 per cent of the plant cover.
Vegetation of Gravelly River Flats, Floodplains, and Fans
. Floodplains,
river flats, and fans are inhabited by plants whose growth form, like that of
the scree plants, permit them to endure unstable soils, but they must also be
able to withstand water erosion and inundation. Because the soil movements
are less violent and water is abundant, a few woody species, notably willows
and several hemicryptophytes with sell-developed rhizomes may grow here as well.
[:
]
The broad-leaved willow herb (
Epilobium latifolium
), the vetches (Hedysarum
alpinum
and
Astragalus alpinus
), besides several grasses and sedges, are ubiquitous
in these habitats.
The predominance of alpine and arctic species on erosion fans and flood–
plains has sometimes been taken to indicate that these plants were washed down
from adjacent mountains by glacial torrents during spring freshets, and that
they were able to gain a foothold only because lowland species are not so well
adapted to the edaphic conditions which are peculiar to these habitats. Per–
haps the primary reason why alpine and arctic plants frequently dominate flood–
plains and erosion fans, is that huge masses of overflow ice (crystocrene)
accumulate there in winter and frequently persist until late in the summer,
thereby shortening the season to such an extent that only truly alpine or
arctic plants can survive.
EA-PS. Porsild: Flora and Vegetation
Tundra
Dwarf-shrub Heath
. The tundra differs from the rock desert by having
a closed or continuous cover of vegetation and in having a protective cover
of snow in winter. The dwarf-shrub heath of the tundra is essentially a
continental lowland plant association and reaches its best development in the
interior coastal plain of the north slope of Alaska at some distance from the
sea, in northern Mackenzie, and in central Keewatin. Its principal components
are low willow (
Salix
spp.), dwarf birch (
Betula glandulosa
, Labrador tea
(
Ledum decumbens
, and
L. groenlandicum
), Lapland rhododendron (
Rhododendron
lapponicum
), bearberry (
Arctostaphylos alpina
and
A. rubra
), besides white
heather (
Cassiope tetragona
), bilberry (
Vaccinium uliginosum
), and the alpine
cranberry of cowberry (
Vaccinium Vitis-Idaea
). Ubiquitous also are a number
of sedges and grasses such as
Carex lugens
,
Arctagrostis latifolia
, and
Festuca
altaica
, but notably cotton grass (
Eriophorum vaginatum
) which forms huge
tussocks that are known in Alaska as “niggerheads.” These solid, turfy
hummocks may stand a foot or a foot and a half above the surrounding ground
and are notorious as the chief impediment to travel across the tundra in
summer or winter. When viewed from a distance the “niggerhead tundra” has
the appearance of a slightly uneven grassy plain, and in mid-July, when the
“cotton” matures, may look completely white as if the land were covered
with snow.
Among the smaller herbaceous plants growing on the tundra are several
fernweeds (
Pedicularis labradorica
,
P. lanata
,
P. arctica
, and
P. sudetica
),
baked-apple (
Rubus Chamaemorus
), groundsel (
Senecio atropurpureus
and
S
.
lugens
),
Saussurea angustifolia
, blue lupine (
Lupinus arcticus
), wintergreen
(
Pyrola grandiflora
), the knotweed (
Polygonum Bistorta
ssp.
plumosum
), the
EA-PS. Porsild: Flora and Vegetation
root of which is edible, yellow saxifrage (
S. Hirculus
),
Spiraea Beauverdiana
,
and many others. Many of these have brightly colored flowers and for a short
time in early summer the dwarf-shrib heath is gay with color, but during the
rest of the year presents a dreary and desolate aspect.
The ground under and between the stems of the dwarf bushes and between
the tussocks is everywhere covered by a dense carpet of mesophytic mosses
and lichens into which the foot of the traveler sinks ankle deep at every
step, making traveling on foot exceedingly wearisome.
Lichen and Moss Heath
. Near the timber line, in drier and better drained
parts of the tundra, the dwarf-shrub heath imperceptibly passes into lichen
and moss heath. The place of mesophytic species of mosses is here taken by
gray and brown fruticose lichens of which the so-called reindeer mosses
(
Cladonia rangiferina
,
Cl. alpestris, Cetraria nivalis
) and Iceland moss
(
Cetraria islandica
) dominate to such an extent that the landscape may appear
as if snow-covered. In time most herbs and the low dwarf shrubs become sub–
merged in the lichen carpet, and only dwarf birch, rhododendron, and willow
remain.
Grassland
. Extensive grassland or natural meadows are occasionally found
in the tundra regions, especially in central Keewatin, on alluvial flats
formerly occupied by large glacial lakes. These meadows are still wet in
spring but there is reason to believe that they will, in time, be invaded
by tundra shrubs and eventually change to dwarf-shrub heath. The principal
meadow-forming species are
Carex saxatilis
and
C. membrancea
,
Arctophila
fulva
,
Arctagrostis latifolia
,
Deschampsia caespitosa
,
Juncus balticus
,
Carex
stans
and
C. canescens
, besides a number of herbaceous tundra herbs.
Copses and Thickets
. Willow and alder thickets, with their accompanying
EA-PS. Porsild: Flora and Vegetation
flora of herbaceous species, are found chiefly on the continent, in well–
drained soils along streams, on south-facing slopes, and on the sloping banks
of lakes and rivers where protection against wind and consequent accumulation
of snow is assured. The alder (
Alnus crispa
), although it does not extend far
north of the tree line, form thickets 18 feet high with trunks up to six
inches in diameter, along the lower courses of rivers flowing into Bering
Sea. At some inland villages, where timber or driftwood is not available,
alder is the principal source of fuel. The principal thicket-forming willows
are
Salix arbusculoides
,
S. pulchra
,
S. Richardsonii
,
S. glauca
,
S. planifolia
,
and
S. alaxensis
. Only the last may occasionally assume tree like growth, whereas
the rest are shrubs that rarely exceed 8 feet in height. In protected places
with abundant snow cover, willow thickets may be found even in the arctic islands.
Thus, on the south-facing slope at Walker Bay, on the west coast of Victoria
Island, in latitude 71° 30′,
Salix Richardsonii
forms six-foot-high thickets.
Some of the common herbs growing inside the thickets are fireweed.
(
Epilobium angustifolium
), horsetail (
Equisetum arvense
), the anemones (
Anemone
parviflora
and
A. Richardsonii
), buttercup (
Ranundulus lapponicus
), coltsfoot
(
Petasites frigidus
), groundsel (
Senecio lugens
), wintergreen (
Pyrola grandiflora
),
and a number of grasses and sedges. Among the latter, cotton grass (
Eriophorum
angustifolium
), blue joint grass (
Calamagrostis canadensis
var.
Langsdorffi
i),
and
Arctagrostis arundinacea
are the most important.
Marsh and WetTUndra
. Wet, grassy tundra predominates on low coastal flats
of the unglaciated arctic coast of Alaska and probably is a climax type found
on thick deposits of raw humus or peat that here often rests on a massive
thickness of fossil ice. The often very great thickness of frozen, raw humus
suggests that this lowland tundra formation is very old. It was probably
EA-PS. Porsild: Flora and Vegetation
formed during a period with a climate wetter than the present and may be
considered a postclimax relic which is no longer being actively formed. A
characteristic feature of thus tundra is the presence of numerous ponds and
lakes that have formed in places where the fossil ice below the tundra has
melted. Such local erosion is actively going on everywhere in the tundra
today; it frequently starts by the widening and cutting, by meltwater, of a
frost crack or when, in some other manner, the insulating cover of humus is
removed by water or wind erosion. Such tundra ponds usually have steep,
slumping banks in which may usually be seen a wall of pure ice (10; 11).
This form of tundra occurs only in unglaciated parts of arctic North America
but has its counterpart in arctic Eurasia.
Another feature of special interest in the low wet tundra is well-developed
patterns of irregular polygonal ridges of peat which have formed along frost
cracks. Another
peh
phenomenon caused by frost action are the conical hills
or
pingos
formed in former lake basins by the local upheaval due to expansion
following the progressive downward freezing of a lens or body of water or
semifluid mud or silt trapped between the frozen surface soil and a lower
permafrost layer. East of the Mackenzie delta some
pingos
, formed in this
manner, are several hundred feet high (10). Around the bases of these hills
are concentric peat ridges separated by moatlike ribbons of water.
The flora of the wet, lowland tundra is more varied and far richer in
species than is the dwarf-shrub tundra. In the wet tundra back of Atkinson
Point on the Arctic Coast, east of the Mackenzie Delta, the writer (8)
noted 150 species of flowering plants, more than a third of them grasses
and sedges. Dwarf shrubs are almost entirely absent and represented chiefly
by creeping willows. Fruticose lichens, too, are scarce whereas bryophytes
are well represented.
EA-PS. Porsild: Flora and Vegetation
Snow-flush Herbmats
. An association of particular interest is found
in places where large snowdrifts accumulate during winter. Mountain country,
especially if the snowfall is heavy, favors the formation of large drifts,
but even in the lowland where the snowfall is generally light, large drifts,
favorable for the formation of snow-flush vegetation, may be formed by the
prevailing wind in river valleys, on sheltered slopes, at the base of cliffs,
and along lake shore
.
s. Such habitats are late, for the snowdrift may last
well into the summer or, indeed, may not disappear entirely before winter
starts. The snowdrift, on the other hand, throughout the summer provides an
unfailing supply of water and, besides, contains a very considerable amount of
potential plant food in the form of wind-transported inorganic dust or loess
mixed with seeds and plant remains. The accumulation of fertile soil which is
often found on screes and slopes is deposited in this manner.
The principal difference between the willow thicket and the snow-flush
association is due to the duration of the snowdrift: too deep snowdrifts
shorten the season too much for willows. For this reason willow thickets
usually are found on the edge of snow-flushes, thus giving the impression that
the willows are invading the herbmat area. The assembly of species that occupy
snow-flushes are almost entirely herbaceous, and chiefly of the hemicryptophytic
type in which the wintering buds are placed below the surface of the soil. The tiny
willow (
Salix herbacea
) in the East, and (
S. pseudopolaris
) in the West are
among the few woody plants found on snow-flushes. Characteristic, and very
necessary for snow-flush plants is their ability to persist vegetatively for
several seasons, when thick snowdrifts reduce their growing season to a minimum.
Many snow-flush plants may not flower and fruit for a period of years and may
even survive several unfavorable seasons completely buried under snow and ice.
EA-PS. Porsild: Flora and Vegetation
Whereas the general aspect of snow-flush vegetation is similar everywhere
in the Arctic, its floristic composition varies greatly according to geo–
graphical position. For example, snow-flushes in Greenland and in the
Mackenzie Delta have almost no species in common. Examples of widely distri–
buted snow-flush plants are the alpine spear grass (
Poa alpina
), sedge (
Carex
scirpoidea
), mountain sorrel (
Oxyria digyna
), dwarf buttercup (
Ranunculus
pygmaeus
), and alpine club moss (
Lycopodium slpinum
).
Strand Vegetation
Brackish Meadows and Marsh Subject to Floods
. Salt marshes subject to
floods are found chiefly on the low continental strand flats of western and
northern Alaska, and from the delta of the Mackenzie extend east to the mouth
of Anderson River. Along this shelving coast large, shallow, and brackish
bays or lagoons are cut off from the open sea by long sandspits or by narrow
sand or gravel islands formed by sea currents and by ice-push. Rivers empty–
ing into the lagoons speed up the silting process, which is further favored by
the almost neglibible tide. Back of the lagoons are vast meadow-covered flats
that, as one travels away from the coast, imperceptibly change into low tundra.
Most common in the meadows are grasses, sedges, and rushes, among them
Arctophila
fulva
,
Deschampsia caespitosa
,
Dupontia psilosantha
,
D. Fisheri
,
Puccinallia
paupercula
var.
alaskana
, and
P. phryganodes
,
Carex aquatilis
,
C. glareosa
var.
amphigena
,
C. maritima
, and
C. rariflora
, besides
Eriophorum Scheuchzeri
and
E. angustifolium
,
Juncus balticus
and
J. castaneus
. Among the more common
herbs growing in the meadows are the chickweed (
Stellaria humifusa
), scurvy
grass (
Cochlearia
),
Chrysanthemum arcticum
, the sweet-scented white buttercup
(
Ranunculus pallassii
), the white cowslip (
Caltha natans
), and marsh fleabane
(
Senecio congestus
).
EA-PS. Porsild: Flora and Vegetation
Vegetation of Sand Dunes and Gravel Beaches
. Along the shores, on raised
beaches and sandspits, are extensive dunes inhabited by lyme grass (
Elymus
arenarius
ssp.
mollis
), fescue (
Festuca rubra
var.
arenaria
), spear grass
(
Poa arctica
and
P. eminens
), and
Carex Gmelini
— the last two do not enter
Canada — brome grass (
Bromus Pumpellianus
var.
arcticua
), seabeach sandwort
(
Arenaria peploides
), stonecrop (
Rhodiola integrifolia
), blue lungwort (
Mertensia
maritima
), wormwood (
Artemisia Tilesii
),
Aster sibericus
and several species
of dandelion (
Taraxacum
spp.). On the edge of the dune, in wet sand near the
beach, is often found the delicate blue gentian (
Lomatogenium rotatum
), creep–
ing buttercup (
Ranunculus gymgalaria
) and the dwarf sedges,
Carex subspathacea
and
C. ursina
.
Vegetation on Rocky Shores
. On cliffs and boulder beaches that are not
too exposed to the open sea may be found dense swards of
Puccinellia phryganodes
and similar grasses that occupy crevices and crannies between rocks. Here also
grow scurvy grass (
Cochlearia
), chickweed (
Stellaria humifusa
), and a few other
seashore plants.
Vegetation of Fresh Water
Vegetation of Ponds and Lakes
. Nearly all large and deep lakes in the
Arctic are too cold for vascular aquatic plants, but they possess a rich flora
of microorganisms such as green and blue-green algae, desmids, diatoms, and
flagellates. Different species of these mostly microscopic plants often impart
a distinctive colorto the waters of the lakes. This is
the
best seen from the
air, when it is at once noticeable that, apart from the difference in color
caused by the depth of the water and the nature of the bottom, the water
itself in no two lakes is exactly alike.
EA-PS. Porsild: Flora and Vegetation
Shallow ponds and lakes that remain water-filled throughout the summer,
on the other hand, sustain a surprisingly rich plant life. Because of their
shallowness, the water of these ponds warms up more quickly and becomes free of
ice long before that of the large and deep lakes. The short season prevents
many species of aquatic plants in the Arctic from reproducing by seed, but
they maintain themselves successfully, nevertheless, by the production of
wintering buds (
Potamogeton
spp.,
Utricularia
spp., and others). The most
common aquatic plants here are pondweeds (
Potamogeton filiformis
), the arctic
buttercup (
Ranunculus hyperboreus
), and mare’s-tail (
Hippuris vulgaris
).
Floating and submerged mosses are abundantly represented, as are freshwater
algae.
Vegetation of Brooks and Rivers
. Small, sluggish lowland streams in the
Arctic may sometimes be inhabited by aquatic plants similar to those of fresh–
water ponds. Most arctic streams, however, are too cold or too turbulent for
vascular species, but a number of marsh plants - chiefly sedges and grasses -
inhabit protected and sheltered places on stream margins and flood plains. A
number of dark-colored mosses (
Grimmia
spp. and
Hygrophypnum
) and blue-green
and brown algae grow on the rocks of most arctic brooks, even in water that
is but a few degrees above freezing. The brown, slimy flagellate (
Hydrurus
foetidus
) flourished on the rocks of clear pools in ice-cold meltwater below
snow fields.
EA-PS. Porsild: Flora and Vegetation
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Flora of Alaska and adjacent parts of Canada
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^
é
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A. E. Porsild