Arctic and Alpine Research, Vol. 26, No. I, 1994, pp. 1-13
The Bog Landforms of Continental Wesrern Canada in Relation to Climate and
Permafrost Patterns
Abstract
Dale H. Vitt and
In continental western Canada, discontinuous permafrost is almost always re­
Linda A. Halsey
Devonian Botanic Garden and De­
partment of Botany, University of Al­
berta, Edmonton, Alberta T6G 2E9,
Canada.
stricted to ombrotrophic peatlands (bogs). Bogs occur mostly as islands or pen­
insulas in large, often complex fens or are confined to small basins. Permafrost
may be present in extensive peat plateaus (or more locally as palsas) and was
preceded by a well-developed layer of Sphagnum that served to insulate the peat
and lower the pore water temperatures. Air photo interpretation reveals the oc­
currence of bogs with five types of surface physiography. Concentrated to the
Stephen C. Zoltai
south are bogs without internal patterns that have never had permafrost. Dom­
Canadian Forest Service, Northern
Forestry Centre, Edmonton, Alberta
T6H 3S5, Canada.
inating the mid-latitudes are bogs with internal lawns and fens with internal lawns
(mostly representing former bogs) that had permafrost lenses in the past that have
recently degraded. Concentrated in the northwest are peat plateaus without internal
lawns or distinct collapse scars, but with permafrost; dominating in the north­
ernmost area are peat plateaus with extensive permafrost and collapse scars.
Relationships are apparent between the current -1°C isotherm and the southern
occurrence of peat plateaus and between the OOC isotherm and the southern edge
of bogs and fens with internal lawns. We interpret bogs and fens with internal
lawns to represent areas where permafrost degradation is currently occurring at a
greater rate than aggradation, seemingly in response to warmer regional climate,
although fire frequency may also be of local importance.
Introdudion
Peatlands are ecosystems that sequester carbon through peat
boreal forest, as well as in the high arctic tundra and semideserts
north of the low arctic shrub tundra (but see LaFarge-Engiand
et aI., 1990).
accumulation. These ecosystems are unbalanced, with primary
Bog development and formation in western Canada have
production greater than decomposition. Two types of peatlands
been examined by Kuhry et al. (1992, 1993), and were recently
can be recognized based primarily on hydrological and chemical
reviewed by Vitt and Kuhry (1992). In eastern Canada, Damman
properties. Fens are geogenous peatlands that are influenced by
(1979) reviewed how bog landforms are related to geography and
waters that have been in contact with surface and/or ground­
climate. Glaser and Janssens (1986) presented a comprehensivt!
water. Fens contain minerotrophic vegetation, and are charac­
model of bog development in eastern North America. More
terized by a dominance of true mosses (rich fens) or mesotrophic
recently, Glaser (1992a) and Janssens et al. (1992) have sho"
species of peat mosses of the genus Sphagnum (poor fens) and
in detail how bog landforms have developed in northern Min­
sedges (species of Carex). Fens may be alkaline or acid and range
nesota. Additionally, considerable work on peatland develop­
0
from mesotrophic to oligotrophic (Vitt and Kuhry, 1992). Bogs
ment in general has shown that peatlands can develop by either
are ombrogenous peatlands where the surface is influenced only
terrestrialization or paludification (Miller and Futyma, 1987;
by water derived from precipitation. Bogs contain ombrotrophic
Foster et aI., 1988; Kubiw et aI., 1989; Warner, 1989; Nicholson
vegetation dominated by oligotrophic species of Sphagnum and
and Vitt, 1990). Kuhry et al. (1993) presented data that corrob­
the lack of sedges and true mosses. In continental areas of the
orates the developmental model of Glaser and Janssens (1986)
Northern Hemisphere, bogs always contain a well-developed
and showed that in general coastal peatlands are relatively old
shrub layer of ericaceous shrubs and are wooded to forested with
and early in their development become dominated by Sphag­
Picea mariana. Chemically, bogs are acidic, cation poor, and
num, yielding bogs that have relatively deep deposits of Sphag­
oligotrophic. Characteristic features of bogs and fens in western
num peat. In comparison, continental peatlands are mostly rel­
North America have been outlined by Vitt et al. (1990) (coastal
atively young and become dominated by Sphagnum relatively
areas), Vitt and Chee (1990), and Vitt (1990) (inland areas).
late in their development, yielding bogs with comparatively shal­
Bogs develop in areas where available precipitation exceeds
lower deposits of Sphagnum peat. Although there is considerable
evapotranspiration. In general, bogs may be present in areas
variation due to local edaphic conditions and regional fire and
where precipitation exceeds 500 mm annually, where the bio­
climatic histories, continental bogs are younger than coastal ones
temperature is less then 8°C, and where evapotranspiration/pre­
with autogenically controlled succession often delayed. Although
cipitation ratios are less than one (Gignac and Vitt, 1993). In
few data are available, it appears that many more northern bogs
western Canada, bogs are found from the southern boreal forest
are also older than more southern ones (Nicholson and Vitt,
northward into the subarctic forest tundra. They are not present
1990; Kuhry et aI., 1992, 1993; Nicholson, 1993; Zoltai, 1993).
in the interior grasslands, and are rare in the southern aspen­
In terrestrialization, peat formation begins through the de­
dominated parkland and woodland zones south of the southern
velopment of minerotrophic vegetation. When climatic condi-
© 1994 Regents of the University of Colorado
D. H. VITI ET AL.
/ 1
1972; Zoltai et aI., 1988). The influence of permafrost on peat­
land surface morphology has been known for some time (Hop­
kins, 1959; Tedrow and Harries, 1960; Tarnocai, 1972; Zoltai
and Tarnocai, 1975). Permafrost formation causes volume ex­
pansion of the freezing water, raising the surface well above the
water table. This creates drier conditions with the dense growth
of conifer trees taking place in the south, and open canopied,
lichen-dominated woodlands developing in the north. Peat ac­
cumulation virtually ceases under such conditions, and oxida­
tion of the surface peat may occur.
Some permafrost peat bodies are underlain by several me­
ters of ice, creating small peat hills, termed palsas (Zoltai, 1972),
but most are only about I m above the fen level. These low,
relatively flat-surfaced permafrost peatlands, termed peat pla­
FIGURE 1. Location of study area in continental western Can­
ada with place names mentioned in text. The southern limit of
discontinuous permafrost (Brown. 1967) is shown as the dashed
line. The southern limit of coniferous forest (Zoltai. 1975) is
shown as the stippled line.
teaus, can cover several square kilometers, but many are much
smaller. Often the larger peat plateaus have small, isolated, in­
ternal wet depressions, collapse scars (Zoltai, 1971; Thie, 1974)
or thaw pockets (Horton et aI., 1979). Similar collapse scars often
occur on the margins of the wooded peat plateaus and palsas,
but they are devoid of trees or tall shrubs in contrast with the
adjoining fen (Zoltai, 1971).
tions are suitable, autogenic processes (such as peat build up,
Collapse scars invariably show evidence of subsidence, such
acidification, and oligotrophification) yield conditions amenable
as dead trees protruding from their surface (Horton et aI., 1979),
to bog development (Vitt and Kuhry, 1992). The key develop­
slumping peat banks (Zoltai, 1971), layers of woody debris in
mental process is the establishment of species of Sphagnum.
the peat profile (Zoltai, 1993), or plant macrofossils indicating
Although both fens and bogs may exist in relatively stable form
drier previous conditions than the current collapse scar surface.
for long periods of time, the change from rich fen to poor fen
Such collapse scars are without permafrost, although in more
and bog occurs over a relatively short time period of about 100
northern areas permafrost aggradation may take place (Zoltai,
to 200 yr. This change can be documented in the macrofossil
1993). Many authors have interpreted them as indications of
record and is characterized by particular species of Sphagnum
permafrost degradation resulting from climate warming (Ker­
(Janssens et aI., 1992; Kuhry et aI., 1993). Once Sphagnum­
shaw and Gill, 1979; Chatwin, 1981; Dionne and Seguin, 1992),
dominated peatlands are established, several chemical and phys­
or have attributed them to the effects of fires (Thie, 1974; Zoltai,
ical changes occur, in particular acidity increases, decomposition
1993) or to a cyclic evolution of aggradation and degradation
decreases yielding high CIN ratios, and temperatures of the peat
(Tarnocai, 1972; Seppalli, 1988).
column decrease. Temperatures of surface waters in bogs have
The objectives of this paper are to ( I ) determine the distri­
been documented to be about 56% colder than those averaged
bution of bogs in continental western Canada, (2) identify the
from a variety of nearby fens (Vitt et aI., submitted). These lower
landform features present on bogs of this area, (3) determine
temperatures seemingly result from the insulating properties of
patterns in the distribution of bog landform features, and (4)
Sphagnum (Brown, 1966; Seppala, 1988; Vitt et al., submitted).
I
Glaser ( l 992b), working in eastern Canada and northern
relate these landform features to present-day climatic factors and
regional landscape features.
Minnesota, described distinctive landform features associated
ith bogs that occur in large fen complexes. He recognized ovoid
islands as forested, ombrotrophic areas; these islands may or
Study Area
may not have wet drains originating near the center of the island
draining water towards the edges. Some islands are horseshoe
shaped with wetter interior areas mostly surrounded by drier
marginal areas. These ombrotrophic islands are also found west­
ward in continental Canada (Nicholson and Vitt, 1990) but are
lacking in oceanic areas. Eastward to Quebec, Glaser and Jans­
sens (1986) described bogs without trees that contain distinctive
pool and ridge patterns. These eccentric and concentric, pat­
terned, open bogs are almost exclusively restricted to subcon­
tinental and oceanic areas. Studies by Zoltai and Johnson (1985),
Glaser and Janssens (1986), Glaser (1987), and Nicholson and
Vitt (1990) show that ombrotrophic islands in continental and
subcontinental areas form primarily due to changes in hydro­
logical patterns that occur in large complex fens. In particular,
The study area lies in west-central Canada in parts of Al­
berta, east of the higher elevations (greater than 900 m) of the
Rocky Mountains, and in Saskatchewan and Manitoba, south
of continuous permafrost (Fig. I , here termed continental west­
ern Canada). Wetlands in the three provinces form ten zones of
which bogs are common in the northernmost seven (NWWG,
1986). The total land surface of the three provinces is ( l .7
X
108 ha), (west of 95°W longitude) with peatlands occupying ap­
proximately 3.4
x
107 ha or 20%. Bogs cover 1.3
x
107 ha or
8% of the land surface, with permafrost peatlands covering an
estimated 6.7
x
106 ha or 4% (based on Zoltai et aI., 1988; Vitt,
1992; Vitt and Halsey, unpublished data).
stagnation, water track divergence, and regional water-table fluc­
tuations are among the important factors that contribute to the
Methods
development of continental bog islands.
In arctic Canada, permafrost dominates the landscape and
forms a continuous permafrost zone; however, farther southward
REMOTE SENSING
permafrost becomes discontinuous, and is almost always re­
Aerial photographs taken from 1949 to 1952 at a 1:40,000
stricted to ombrotrophic peatlands (Brown, 1970; Zoltai, 1971,
scale were examined for continental western Canada. Bogs great-
2 / ARCTIC AND ALPINE
RESEARCH
Arctic and Alpine Research
Top. Oblique photograph
riew
with infernal lawns north
bog with an in/crna! lawn from rWrih
,<;andy lake, A/hcrw. BO/lOm. Ground
Sandv Lake, .. Uberla. (Photos by Dale ViII, Devonian
Botanic Garden and Department olBolany, C'nircrsitr olAlberla. See p. 1.)
4
3
2
1
TO5
TO4
TO3
TO2
o TO1
-1 TO0
-2 TO-1
-3 TO-2
-4 TO-3
-5 TO-4
< -5
NOT
MAPPED
F/(JUR1,' 2,
FlGC'RE j,
clJean anllual ICmpCrtllllrc ill "(" corrcclcd/or dcration,
,S'ummcr prcc/piraliol1 in millimeters,
��l
:; :1<15
15-20
20-25 WI25-30 0::30-35 u9
wo::
>35 0<1:
NOT
MAPPED
9
:::r::
<
�
!::l
�
w
<250
250-300
300-350
350-400
400-450
> 450
NOT
MAPPED
F/(il'RE -"
FIGLR1,' 4,
,"'UIl1IllCl' {,\fay rlmmgh Scptember} aridily index,
northeastern ,j/herra,
bug islands III
a
wei,
e'f
than 0.5 km' were idemitied by (I) thL' presence of a uniform
U)\l'f
of !'!ce(J
murtuna
and (2) a uniform topography of the bog
surbce. Forested to wooded ti.:ns were identitied by (I) the pres­
ence of l'!cca mariana and Lui.\" lartClIW and (2) uniform to­
pography of the fen surface. Open fens were identified by their
high rc!kctance due to the presence ora continuous Care.\" cover.
used in the past
Similar methods hah� been
lO
map
peatlaml distribution in Olllario (Pala and Boissonneau. 1982:
Riley. 1987; Bobbette and Jeglum. 19(0). Quebec (Buteau. 1989).
Ne'w Brunswick (Keys and Henderson. 1(83). and Alberta (Vilt.
19(2).
The' occurrence and type of bog landforms were identified
and plotted on I:1.000.000 scale maps. The number of land­
l(m1lS in a I Y latitudinal
30'
(I :50.000 map
TFR.i! /sor.ou r
have usc:d for many years
Scandinavian pemland
a series of terms indicating the relative height of the ground­
layn surj�iCe
lO
the water sudllce. Each of these levels has dis­
along the bog-poor len-rich ten gradient.
tincti\c
Open pools have only submerge'd
gent vegetation
carpets havc emer­
on loosely consolidated peat: lawns
have wct. flat areas oClittle relicf with vcgclation
from
well consolidated underlying peat: and hummocks have undu­
lating areas with the driest wgctation uf peatlands. This pool­
carpL'l-lawn-hummock sequence is well establisht'd in the Eu­
ropean and North American peatland literature and portions uf
it will be used here.
sheet) were tallied and assigned an abundance class on a five
point scale (rarc
< 5.
Results
occasional 6-1 S. common 16-25. frequent
26-50. and abundant /50). Bog landform !.Ones were developed
from visual inspection of the data.
(IIi/I'lL Fl(TOR'"
�'1can annual temperatures. currected for ckvation. rangc
ti·om ·
CUJf.UF IARllBLF.'>'
Summer data for precipitation and temperature variables
arc available from numerous climate stations in Alberta for the
1951-1980 period (Atmospheric Environment Service. 1(82).
Many of these stations arc present in northern upland areas and
arc maintained only during the icc-free scason: hence thl:Y lack
year-long data. The lack of yearly data makes it dillieult to es­
timate the distribution of mean annual temperatures in Alberta.
especially in areas where elc\'ational dil1erences arc present. For
this rcason. a model of mean annual temperature was generated
that utili/cd ele\·atiol1. summer only stations. and yearly stations.
This model was established by regressing monthly mean tem­
peratures ft)f summer-only stations against monthly mean tem­
5° to! 5°C, and form relatively discrete lones oriented
frum the southL'ast
10
the northwest (Fig. 2). Toward the north­
west (Alherta). temperatures arc related to elevation. with the
northern Alberta highland areas having colder temperatures than
the surrounding lowlands. Elevation gradually increases west­
ward and becomes more uniform eastward. Summer precipita­
tion is greatest in west-central Alberta and decrL'ascs both north­
ward and westward (Fig. 3). Summer aridity (Fig. 4) is highest
along the foothills. northeastward to Lesser SlavC' Lake. Albena
and in centrallv!anitoba. Aridities of about 20 detine the bound­
ary between the boreal forest and grassland. When aridities great­
er than 20 are considered. lowest arc along the southern boundary
of the boreal forest in Saskatchl'\van and !\lanitoba extending
nonln\!ard in central Saskatchewan.
perature�s from the closest yearly station for the 1951-1980 pe­
riod. Using these regressions. mean annual temperatures for
summe'r stations were gL'nerated. /\ linear model was then es­
tablished using these generated mean annual temperatures for
summer-only stations coupled with mean annual temperatures
from yearly stations and station elevation in blocks of 4° latitude
and 8° longitude for western Canada. Grid nodes were estab­
lished in the center of a 15' latitudinal and 30' longitudinal grid
(a 1.50.DOD map sheet). Elevation for each grid node was then
determined. Using these elevations. mean annual temperatures
were generated with the linear elevation model.
Summer precipitation (l'v1ay-September) was estimated us­
ing all available climatic stations from the 1951-1980 period
and contoured using MaeGridlO (RoekWare Inc.. 19(1). a grid­
generated contour program. A 5-mo summer aridity index (May­
September) was determined for these stations by dividing the
total 5-mo summer precipitation by the monthly mean 5-mo
summer temperatures (Gignac et al.. 1(91). These values were
contoured using MacGridzo.
BOU LIXJ)FOIUfS
Bogs (Fig. 5) occur only in forestt'd portions of the study
area north of the Transitional Mid-Boreal Wetland Region
(N\VWG. 1(86). Centers of abundance arc in extreme nor1hern
Albena. especially in the northern uplands: eastern AJberta from
Lesser Slave Lake north to Lake Clair: in western Saskatchewan
north of Buffalo Narrows. and cast and north of Lake Winnipeg.
Manitoba. Areas of lcast occurrence arc in western Alberta along
the Rocky Mountains and in central Saskatchewan/western
'\:1anitoba (Fig. 6).
Five types of bog landforms can be recognized in continental
western Canada. Each of these has distinctive surface features.
All bogs arc either wooded (open canopy) or forested (closed
canopy) with Picca mariana and have abundant ericaceous shrub
cover of LcriulIl groen/andfcuIn. while many bogs also have ('/zilKa/lIlia
I'acciniulfl O.i.)'CUC(OS.
I'. l'iliHdac1i and Ruhus ciJalllaCIIlOI'llS as conspicuous species.
Bogs \l'ithoul [merna/ Lawns
1'1:'1 T .<;TFCI T/GR.ll'ffY
Bogs without associated internal lawns arc uniformly wood­
Peat cores were collected using a Macaulay peat corer from
ed and occur as islands within large complex fens or as peninsulas
unfrcllen peat deposits and with a small diameter permafrost
protruding into large fens (Fig. 7). Bogs confined to small basins
probe from perennially frozen peat. Samples of known volume
arc also present. but not abundant. Stratigraphically. we have
were taken for macrofossil analysis. Some samples were detloc­
examined these bogs extensively with results presented partially
culated with a 5'l'b KOH solution. sieved through a 150-11111 sieve
by Zoltai et al. (1988). Vilt and Nicholson (1990). Kuhry et al.
and macrofossils remaining on the sieve were determined. Other
(1992. 19(3). and Nicholson (1993). In no case has evidence of
samples were dispersed in distilled water and examined for ma­
permafrost been j(Jund. either through extensive probing of in­
crofossils.
dividual sites or through stratigraphic analyses: however. thin
4!
ARCTIC AND ALPINE RESEARCH
NONE
RARE
OCCASIONAL
COMMON
FREQUENT
ABUNDANT
NOT MAPPED
FlU( RI:' 7.
Fj(iCRf:' 6.
Occurrcl1ce o{hogs.
Aerial pholograplz
(h) ;1"11170111 interna!/mms/;"OI)]
c{,lIlral Allwrra.
NONE
RARE
OCCASIONAL
COMMON
FREQUENT
ABUNDANT
NOT MAPPED
9
:r:
<
�
ttl
...;
�
v,
F!(j[ 'Rl:' Y.
FlU!. 'R!:' 8.
Occurrcl1«'
\j'ilhUI!I ill/cma//(1)l?Is.
/Iliernal IU\l'lls
Aerial photographs showillg !A) hugs w/lh tii.lt/I1Ct. rar/wtlllg
!i; Film lIun/wastcm .·llh('l'/a,
(I-um H'I'SI(Clllra! .\Jalli{()ha.
Illlcma! lum/s ii}
and fBi /lOI!S H'ill! inliislillc/
[WI],' 1
i mCr/wl lawns
Is!alliL
Site
Site A
POh."ntial macrofossil
55°50''',,,
conh,,�nt
IOS"I)'W
Sphugnurn rtparium
Light yellowish-green
Site C
Sandy Lake, AI13,
Amount
55"5()'N,
Amounl
56"04'N,
lOS"15W
("'0)
112"55'W
f)-II
lUO
(}'-8
11-40
l(j(i
8,,25
40-55
K5
25-34
iO(j
Amoulll
(}.-s
!lIO
itnuJsiJ,"pilupercula
fibril' \'phagnutn peat
,\/)ha�nUfn npariunl
Ycllov.'ish-brov;n fibflc
,\'rhagmun
B
Patuanak, Sask,
Patuanak, SasL
Stratigraphy
Depth (em)
Depth (em)
Depth (em)
('arcx linwsa"-paupercu!a
peat
spp. remams
Dark
bn)\,.,n rncsir
PICt'>.l
\voody pta!
nl'Coh.'s
!O
Wood
Ericacl'l.)us roots
Pi.J!ytrU"hUlfl .\!rli'[Uffl
.-luiacomniurn pafusfrc
7i)!F!t'Jilh.vpnurn nl/ens
,)'phagnum angusI{f'u!ilun
Lcdunl grtJcniaruilnun
Dark owwn humic
woody fk'at
34--227
!O
Ericaceous roots
75
Picco needles
lO
5
5
2()
Wood
54-2(j(h
Plt>uro:::iu!n schreheri
S-. magef/anlClHn
70
5
10
10
.\', angusq(oinan
20
Charcoal
P(Jiyzric/WHl
Sf nC! am
10
layers of seasonal frost can be present well into the summer,
indicates that substantiall'hangL' oCL'llrred from a relatively dry,
especially below hummocks, Bogs without internal lawns are
wooded bog habitat to a wet open lawn condition, and that this
most abundant along the southern edge of bog occurrence and
change was rapid, without transitional phases, Such changes are
are especially abundant in central Alberta west of Edmonton and
consistent with the thermal subsidence of permafrost peatland,
also northeast of Lesser Slave Lake and in eastern Manitoba to
Growth rings of four trees growing on thc edge of internal
lavills in central Alberta were examined, The rings show that the
the east of Lake Winnipeg (Fig, 8),
efleets of subsidence reached the trees between 1925 and 1945,
when they began leaning towards thl' center of the intGrnal lawn,
Bugs \l'iltz Internal Lml'ns
One trce growing ncar the center of an internal lawn started
This catcgory of bog landform is characterized by the pres­
leaning in 1893,
ence of open, \vet S'r'!w gnu m-Carcx - dominated lawns often con­
These bogs occur mostly in the mid portion of the occur­
taining partially buried stands of dead trees within a uniformly
rence of bogs and arc most abundant in cast-central Alberta and
wooded bog island or peninsula (sec frontispiece), Common spe­
to the northcast of Lake Winnipeg, Manitoba (Fig, 10),
cies of ,')'phagnullI occurring in these internal lawns are ,')', ail-
S,
and ,)', ripariul1l, On the drier parts of
these lawns, near the bog margins, hummocks of S.
or
') magellanicutn may be found supporting small black spruce
Bogs often occur as discrete, dry, wooded islands surrounded
trees, These hummocks provide a transition between the bog
by weI, open, complex fens (Fig, II), The most notable of such
, ',
and the lawn, obscuring the division between them, The internal
"islands" have a pennafrost core (peat plateaus, palsas), In some
lawns arc less than 50 cm lower than the surrounding wooded
fens, wetter areas can be found that are slightly depressed (Fig,
bog surface and may oecur in extensive patterns radiating from
12), In such lawns, dead trees, partially buried in peat are com­
the bog island center (Fig, 9a) or in indistinct, nonradiating
mon (Fig. 13), Stratigraphic c\idence often shows a woody layer
patterns (Fig, 9b), Although permafi'ost is absent. or restricted
at a depth of 20
to small wooded areas that occur marginally to the lawns of these
under drier conditions, such as Picuro:::illlll schrebcri or 1'0111(,11-
bogs, thin seasonal frost layers can last well into late summer.
IhYfJl1l11f1 nili'll.\' have been found in this woody debris layeL
to
40 em, In some cases, plants usually growing
Stratigraphic analyses of bogs with internal lawns frolll Al­
Aerial overnights also re veal the presence of dead trees tilted in
berta and Saskatchewan reveal an uppermost layer of about 3D
random directions in the ten lawns, indicating the [i)fmer exis­
to 50 cm of weI, oligotrophic species of
tence of densely treed, small permafrost bodies, In some cases,
underlain
by a thin layer of sedges followed by a thin layer dominated by
remnants of such wooded "islands" are still present in the lawns
slrictulII or P/euro::!lI1Il schrebcri, and abundant wood
giving a "ghost" or "shadow image" of their former extent (Fig,
and/or black spruce needles, Beneath this last layer is a thick
12), Such internal lawns arc often observed ncar the periphery
layer of a variety of more decomposed macrofc)ssils, all indi­
of peat plateaus, indicating thermal subsidence,
cating a habitat of dry wooded bog (Table 1), Such stratigraphy
6 / ARCTIC AND ALP[NE RESEARCH
These landforms occur in the mid-portion orthe occurrence
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VrTT ET
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7
of bogs and arc found in the same lone as arc hogs with internal
and !ens \\iilh internal lawns as well as bogs that contain no
lawns. Fens with internal lawns arc most common in central
internal lawns. Zone.1 is sporadically present
Manitoba north of Lakc Winnipeg. and hecome increasingly less
Slave Lake. Alberta. Tv,;o areas of lone 3 occur as outliers in
common westward (Fig. 14).
the Pasquia and Porcupine hills of Saskatchewan. �1ean annual
kmperatures range from
PCa! Pia!calls H'Il/lOut
to
the cast of Lesser
1 to 0°(' as cstimated Ii'om the ele­
vation model. and summer aridity indiccs arc greater than 20.
Scars
Zone -l contains all hog landform types and is present as a con­
Peat plateaus without collapse scars have a relativel" flat.
tinuous. wide band from north of Lesser Slave Lake eastward.
- 3 to (Joe as
raised surLlCe with an abundance of lichen cover and a hetero­
Mean annual temperatures generally range from
geneous cover of Picea manalla. No distinct internal lawns or
estimated from the elcvation modeL while summer aridity in­
.
collapse scars arc present. They occur as peninsulas at the edges
dicl's arc generally greater than 25. Zone 5 commonly contains
of tCns or in broad depressions. often grading lalaally into peat
peat plateaus with and without collapse scars and is found to
platc'Clus with collapse scars. On aerial photographs. they possess
the north of lone 4. Mean annual temperatures estimated from
a coarse texture. resulting from a combination of their lichen­
the elevation model range li'om
dominated surface and a heterogeneous tree co\'er (Fig. 15). Peat
aridity indices arc greater than 25. Abundant peat plateaus with
3 to
lee I(lr IOnc 5, and
plateaus without collapse scars occur in the nonhern ponion of
and without collapse scars charactcri/e zone 6. which is present
bog occurrence. and arc especially common in the northwestern
in the lower Hay River drainage basin of northern Alberta. Mean
and Ilorthcentral regioIls of Albena (Fig. 16). They are rare or
annual tl�mpc�ratures. estimated fmm the c!C\'ation model. range
generally not present in the eastern portion of the provinccs.
from
4 to
.'IcC, while summer aridity indices arc greater than
25. Zone 7 is an area in which bogs are not common due
Peal Platealls with Collapse 5,'cars
nantly peat plateaus with collapse scars. Mean annual temper­
These landforms are clearly delineated by aerial photogra­
phy (Fig. 17). Peat plateaus arc forested.
to
edaphic factors, but when bogs arc present. they are predomi­
Of
more commonly
atures estimated from the elevation model rangc from
3 to
la C with summer aridity indices generally below 25. Zone R
wooded, bogs that have a ground layer dominated by lichens
is characterized by extensive tracts of peat platcaus with collapse
(mostly species of Cladina, ('ctraria, and ('ladonia): sometimes
scars and is found in the northern uplands of Alherta and in
interspersed with Plcuro::iulIl schrchcri,
and
nonheastern Manitoba. Zonc 8 has mean annual temperatures.
slrictzlIIl. Collapsl� scars. which arc dominated by
estimated from the elevation modeL that arc generally less than
Sphagnum allgusli{olium, S'. jcnsenii. 5,'. majlls, ,')'. Oi>IIISUfII. or
.';. ripariutn. arc present as internal depressions (carpets or lawns)
'4° C and summer aridity indices of greater than 25. Climatic
variables are gin'n in Table 2 for each of the IOnes.
and arc typically 100 em lower than the surrounding bog surface.
They may be present as isolated. circular areas or as intercon­
Discussion
nected. elongated. drainage channels (Fig. 18). Often they haw
dead. dying,or leaning trees present on one or more sides (Fig.
In general, bogs occur in areas where the summer aridity
19). Although permafrost is not present in collapse scars. the
index is greater than 20: howl�wr. greatcr aridity indices (e.g..
collapse scars arc always surrounded by permafrost. Stratigraph­
increascs in available moisture) have little clrcct on bog distri­
ic evidencc shows that many collapse scars have a previously
hution. Summer prccipitation below 25() mrn appcars 10 inhihit
dry surface that has heen covered by the present wet surface.
bog development and mean annual temperatures abcne 2°(' arc
thus indicating degrading permafrost. In some cases, the per­
associated with the absence of bogs. Thus a combination of low
mafrost degradation was initiated by tire (Zoltai. 1993). or hy
precipitation and high annual tcmperatures appear to hinder bog
allogenic changes. Other collapse scars. especially those con­
development. The lack of bogs in north-central Saskatchewan
nected to a channel. show no evidence of previously drier sur­
and along the east slope of the Rocky Mountains is almost cer­
faces in their stratigraphy. In these cases the "collapse scars"
tainly due to edaphic features (sandy soils in Saskatchewan and
may never have held permafrost but were formcd as the per­
calcareous ground water in Alherta). not climatic ones.
mafrost closed in around them (Kuhry. pers. comm., 1992). Peat
The surface and internal morphology of hogs are affected
plateaus occur in the northern portion of bog occurrence (Fig.
by additional ProCl:SSCS related to climate: notably. permafrost
20). They arc most abundant in northwestern and eastern Albena
development. Both the absence of permafrost and the aggrada­
and nonheastern Manitoba.
tion and degradation dynamics of permafrost in bogs leave spe­
citic imprints on the bogs. The dominance of a process or a
combination of these can be used to establish climatically sig­
BOO LLVDFORM /.ONFS
nificant lones.
Abundanccs of bog landforms furnish a basis for synthesiz­
The bogs without internal lawns show no e\'idencc of having
ing thc occurrence of the bog landform features described above
bcen aITected by permafrost. These bogs de\eloped on fens from
(Fig. 21). Zone I contains no ombrotrophic landforms. Mean
initial ."·phagnlllll layers that eventually led to acidification. in­
annual temperatures as estimated from the elevation model arc
creascd oligotrophy. and decreased surface water temperatures.
generally above 1° C,except in nonh-central Alberta where tem­
This combination of factors reduced production of vascular plants
peratures may be as low as
2°('. Summer aridity indices for
and decrcased decomposition rates and nutrient turnover, thus
lone I arc below 25. Zone 2 contains bogs without internal lavins
increasing the rate of peat accumulation. However, the thermal
�
and is present in central Alberta and to the west and cast of the
regime of these bogs was not sut1lcicntly cold to initiate per­
southern part of Lake Winnipeg. Manitoba. In Alherta, zone 2
matrost de\·elopmcnt.
has mean annual temperatures that range from 0 to 2°(' and
The stratigraphy of bogs with internal lawns. however. in­
summer aridity indices of gcnerally greater than 25. In Manitoba.
dicates that small areas within these bogs have been aflectcd hy
I to 2°(' and summer
permafrost development in the past. \Vhcn pcrmafrost is estab­
aridity indices below 25. Zone 3 contains an abundance of bogs
lished in a pcatland. the surface is elevated abc)\e the water table.
zone 2 has mean annual temperatures of
8 / ARcrlC AND ALPINE RESEARCH
NONE
RARE
OCCASIONAL
COMMON
FREQUENT
ABUNDANT
NOT MAPPED
FIG CRl�' I5.
FJ(a RF 14.
OCCllrrl'lIc(' O(./£'IIS 1I'ilh illiernal lawlls.
Aerial phO/ograf,h s/iOll'i IIg peal pia/caliS \\'i/ h011l
lIon/III'es/ern Alherta.
NONE
RARE
OCCASIONAL
COMMON
FREQUENT
ABUNDANT
NOT MAPPED
v
::r:
<
�
!::j
;p.
f'
'Co
Ff(i( 'RF 16.
FIG1'RE 17
Occurrence (J(Pi'i1i pla/cLilis lI'iillUU/ collapse scars.
Aerial phu/ographlhoH'il1g pca/ pla/caus H'i/h colla.lll(' scars
lIorthwestem .J/her/a.
T.IBU:· ::
('iinlL1tic variahle,\'
\kan annual
temperature
fvh'an Annual
Contoured
Temperature
index
range
�
>
2.0
ST
19.4-19.6
25
34
2
0.6
.\
�25
31
20.CJ..-45.6
17
·20
28
18 .7-44.3
Ul3
8
20
26
I X.8-40.2
2.14
0.1
44
20
.,�
- ,
I8.CJ..-41.1
0.1
416
25
20
114-38.5
2.0
dry to permit dense tree growth, nourished by
n
26
11.3
creating a drier habitat. At its full de'velopment the surElCe be­
comes
("e)
2.
0.7-2.1
l.i
Range
(OCi
aridity index
climate normals
3.'l"'(1.O
1.2"'(1.6
I...()
25
Mean
··25
0.9
.,
.J
195 I-I980
aridi I)
S.E.
1
!
Summer
summer
Normals
1951-1 980 Climate
36
12
54
0.2
427
developml'nt of collapse scars, which under severe conditions,
may coalesce and become large.
the decomposing surface peat, and pear development virtually
Peat plateaus without distinct collapse scars contain per­
ceases (Zoltai and Tarnocai. 1971). The rl'lati\'(: elevation of
mafrost. except occasionally in hollows. They occur mostly in
areas h;ning permafrost is largely dependent on the thickness of
the' northwestern ponion of the area, often in association with
the permafrost. When the permafrost thayvs, the surf2lCC subsides
peat plateaus containing collapse scars. Thesc arc peat plateaus
below the level of the bog. due
that have undergone little or no disturbance (e.g. tire) for a rel­
to
low peat accumulation rates
and partial oxidation of the peat on the pan previously uplifted
by the permafrost. This creates a depression that is occupied by
atively long time period.
Comparisons bCl\v('en the current distribution of bog land-
lawn (or carpet) species, until the bog can fe-invade the depres­
forms and present-day climate,
sion. These internal lawns are aI'e'as, which were once affected
the following
(I)
temperature, reveals
fens vvith internal lawns occur in areas with
] and [j0C, (2) most bogs with
by permafrost, but \vhere permafrost is no longer present. The
annual temperatures between
elevation, alllollnt of wetness. and hence species that occur in
internal lawns occur in areas with temperatures between
the lawn arc largely dependent on the original thickness of the
(l"e (3) peat plateaus with no collapse scars occur in areas with
ice lens before
temperatures between
Fens with internal lawns arc peatlands in which permafrost
3 and
2 and
I0('; and (4) peat plateaus with
collapse scars occur mostly in areas with temperatures colder
provided uplift to a part or all of the peatland. The "ventual
than
partial or complete thawing of the permafrost creates lower areas
ernmost limit ncar a temperature between () and
2°C. Whereas bogs with internal lawns have their south­
in the peatland that are weHer than their surroundings and have
plateaus hav'c their southernmost limit ncar O"e. Peat plateaus
developed lawn vegt'tation. Remnants of the vegetation of the
in areas of annual temperatures around
former permafrost peatlands (dead, tilted trees: \v()ody debris
to climatic change; these peat plateaus arc those in landform
layers in the peat) indicate the rapid change from permafrost to
zone 4.
] 0(', peat
1 "C arc most sensitive
nonpermafmst conditions. This process indicates that in the
Large areas of permafrost (> 0.5 km ') arc no! found in areas
zone where these features arc abundant. the permafrost bodies
where the mean annual temperature is above O°e. In areas where
the mean annual temperature is between -- 1 and
arc unstable and are vulnerable to degradation.
On the basis of stratigraphic data, it appears that in some
(re per­
mafrost that was once present has now generally degraded, Brown
cases fens developed into bogs, followed by permafrost aggrading
(196 7 ) places the limit of discontinuous permafrost at the
to develop peat plateaus. These peat plateaus than entirely col­
mean annual temperature isotherm, generally corresponding to
1.1°C'
to permafrost melting, leaving at present at shadow
the boundary between fones 3 and 4. Zone 4 docs contain ev­
of thc [i:mner peat plateau (Fig. 121. Although in most cases the
idence of permafrost degradation, particularly in the south of
laps"d,
original area of pennafi'()st was bog, occasionally dry fen vege­
this zone, with peat plateaus and thus permafrost distribution
tation underlies the present-day wet. kn lawn. In these cases
common in areas with temperatures below
permafrost lenses developed within treed fens dominated by
l'!clIro::ium schreheri,
nirells.
2°C.
Two relationships arc evident from Figures 1{J, 14, and 16.
First, landforms interpreted as having degraded permafrost (fens
These lenses have since
and bogs with internal lawns) arc concentrated to the cast. If
melted with the subsequent collapSe' and replacement of the dry
climate is the overriding inf1uencc on the formation of these
CUIIl.
and
by the current wet fen species kg.
;,;i;,;ilIllCIIIII,
spp., 5,'corpi-
han scorpioides, and Cari'): spp.) (Fig. 13).
Extensive peat plateaus with collapse scars occur in the
patterns, then the eastern part of the study area was considerably
colder in the recent past.
It has been estimated by authors working in other regions
of Canada that the Little lee Age (A.D. 1550-1850) was ap­
northe'rIl portions of the study area where the regional trend is
proximatv,ly 1°C cooler than the present day (Wilson [1992),
for bogs
develop permafrost. Local disturbances such as ilrc
eastern/central Canada; Jacoby and D'Arrigo []989], North
(Zoltai, 1993). rise of water table, and windthrow (Zoitai et aL
American boreal treeline). Based on comparisons of modern
to
1988). howey'C!'. can disrupt the insulating surfi:lce layer and the
landf()rm distribution and present day temperature zonation, a
thawing of permati-ost may he initiated, This results in local
drop in mean annual temperature of 1"C is sullleient to explain
10. ARcnc AND ALPINE RESEARCH
..- N C') '<t U"HO r-- co
WWWWWWWW
Cl
w
c...
ZZZZZZZZI-c...
OOOOOOOOO �
NNNNNNNNZ"",
'"
,...
;:-
��
.� "":"'
�
;i
f�
'--
;::
:3
::>' ...:.
-.
;::
��
?:= S
s�·
'.
-.
-.,
-J:;::
�
�
�::::..
'"
'"
'--
�
c5
.g
�
..::::;
a
:.C
-.,
�
..,
:--..)
'-'
:--:...
.�
i
:::)
'"
-,
"'
--:
-:;::
=<
�
�
'"'
:--:...
'�
-;:::
,�
D. H.
VITI
ET AL
! 11
the distribution of past permafrost landforms observed in the
eastern part of the study area. This suggests that during thL' Little
Icc Age. permafrost occurred farther south than it docs today.
Similar suggestions have been made to explain the presence of
"rdict" permafrost in bogs of eastern Quebec (Dionne. 1984:
Dionne and Seguin. 1992). Thie (1974) estimated that most of
the permafrost in peatlands at the north end of Lake \Vinnipeg
funl1ed less than 600 yr ago. and rapid thawing of pL'rmafrost
began about 170 yr ago. The ages of leaning trees around internal
fens in Alberta tend to conlirm this estimate.
Second. landforms interpreted as having little or no de­
graded permafrost (peat plateaus without collapse scars) arc con­
centrated in the northwest. Comparing climatic parameTers of
this region with thost.' eastwards rewals that northwestern Al­
berta has a steep temperature gradient (the
I to DoC area is
nearly absent) and a steep aridity gradient. The combination of
rdatively high temperatures and high aridity prevents bog for­
mation to the south (55-56°N,(,ramic Prairie area) and restricts
bogs to small. relatively isolated basins northward 57-58°N. Still
farther northward (59-6()ON), peatlands eowr large areas and
almost all bogs contain permafrost. Thus southward in this area,
bogs arc rare and ha ve never contained permafrost while north­
ward they contain perma!i'ost that due to mean annual temper­
atures ranging between
3°e and
1° C have not degraded.
Acknowledgments
This research was supported by The Natural Sciences and
Engineering Research Council of Canada through Operating Grant
r\-6390..·\dditional support \vas provided from a joint research
agreement between Forestry Canada and the University of Al­
berta. Much (lf the basic aerial photographic interpretation was
done while completing maps of the pL�atland distribution in Al­
berta through funding Ii-om Employment and Immigration, Can­
ada.
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