The Late Quaternary History of Vegetation and Climate at Porcupine Mountain and Clearwater Bog,...

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The Late Quaternary History of Vegetation and Climate at Porcupine Mountain andClearwater Bog, ManitobaAuthor(s): Harvey NicholsSource: Arctic and Alpine Research, Vol. 1, No. 3 (Summer, 1969), pp. 155-167Published by: INSTAAR, University of ColoradoStable URL: http://www.jstor.org/stable/1550287 .

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Arctic and Alpine Research, Vol. 1, No. 3, 1969, pp. 155-167

THE LATE QUATERNARY HISTORY OF VEGETATION AND

CLIMATE AT PORCUPINE MOUNTAIN AND

CLEARWATER BOG, MANITOBA

HARVEY NICHOLS

Institute of Arctic and Alpine Research and

Department of Biology University of Colorado

Boulder, Colorado 80302

ABSTRACT

Radiocarbon-dated pollen diagrams from two sites in the southern Boreal forest of Canada have reflected aspects of the local and regional environments since 6,700 and 1,000 BP, respectively. Spruce forest near Porcupine Mountain was replaced by grassland ca. 6,700 BP, with a maximum of prairie taxa occurring just before 5,140 BP and a short-lived reduction of grass and herb pollen shortly after that date. The

grassland episode ended at 4,200 BP when

spruce forest dominated Porcupine Mountain. The site experienced very rapid Sphagnum peat growth and increased sporogenesis after 2,450 BP.

A tentative climatic interpretation is supplied which suggests that 6,700 to 4,200 BP experienced generally dry, warm summers, with a maximum of this effect just prior to 5,140 BP and a cooler spell following; after 4,200 BP the summer climate was cooler and moister, especially from 2,450 to 2,000 BP. The possibility of a regional increase in soil erosion and sheet

flooding prior to 6,700 BP is examined. Clearwater Bog is underlain by a spruce

forest horizon dated 1,200 BP which was established at a time of reduced water level in Clear- water Lake; the Picea timbers were overlain by very humified peat dated 900 BP. Unhumified Sphagnum peat later formed and continued to the modern bog surface. The climatic interpretation is that the summer climate was warm and dry at 1,200 and 900 BP, and that cooler, wetter summers characterized the period since then to the present day.

The suggested climatic sequences are synchronous at many points with the scheme previously developed for southern Keewatin and northern Manitoba, and some of the vegetational changes are provisionally interpreted as the movement of the southern limit of the Boreal forest in phase with the shifts of the Keewatin forest-tundra boundary described earlier. This correlation encourages comparison with other sites in the Northern Hemisphere.

INTRODUCTION

This work is a continuation of palynological studies of the late Quaternary vegetational and climatic history of central and northern Canada

(Nichols, 1967a-c). The two sites described below, Clearwater Bog and Porcupine Moun- tain, are in west-central and southwest Mani-

HARVEY NICHOI.S / 155

III



toba, and lie close to the 100?W meridian along which other studies farther north in Canada have been concentrated (ibid.; Nichols, unpub.; Figure 1). The Porcupine Mountain site has recorded a substantial fraction of the local postglacial period, from 6,670 + 70 BP (WIS-

271) (Bender et al., 1968b) to the present day, while Clearwater Bog has registered only the last thousand radiocarbon years, but both sites provide dated points of comparison for the se- quence already established for central Canada (Nichols, 1967c).

PORCUPINE MOUNTAIN

GEOGRAPHY

Porcupine Mountain (52?31'N, 101?15'W) is one of a series of low hills and scarps that make up the Manitoba Cretaceous Escarpment, which is the western limit of the Manitoba lowlands containing Clearwater Bog. The mountain top reaches ca. 820 m (2,700 ft) and the sampling site is at ca. 640 m (2,100 ft). The peat-filled kettle hole which was sampled was surrounded by a closed forest of Picea mariana and P. glauca, with the peat surface being dominated locally by living Sphagnum spp., with Ledum groenlandicum, Rubus chaemaemorus, and Polytrichum sp. The Glacial Lake Agassiz lowlands which lie immediately to the east of Porcupine Mountain are ex- tensively farmed; the area was settled between 1890 and 1900, and the associated felling of the lowland forest appears to have left a record in the upper horizons of the Porcupine Mountain peat (see below). The remnants of the Porcupine Mountain forest have been protected since 1906 by the Forest Preserves Act. (See Clearwater Bog section for remarks on climate.)

SAMPLING METHODS

A pit was dug into the peat-filled kettle hole by the roadside at 52?31'N, 101?15'W in September 1967. Peat blocks ca. 20 cm square were cut from one of the cleaned vertical faces of the pit to form a continuous monolith from the bog surface down to 175 cm, and then a modified Hiller-type borer was pushed into the floor of the pit to recover a single-shot sample from 175 to 225 cm. This borer had been made with a detachable sampling chamber 4 cm in internal diameter, which was removed intact at the sampling site for later laboratory examination. The equipment was made to my specifications and care had been taken to en- sure that the stainless steel outer sampling chamber was sufficiently robust to avoid the distortion which occasionally allows sample contamination in the commercially available Hiller borer.

In the laboratory, the basal core (175 to 225 cm) was frozen in its C-section aluminum liner and then removed. Vertical distortion of the sediment column did not appear to result from this freezing. The ends of the liner were tightly capped by thick polyethylene sheeting, and the expansion

due to freezing was expressed horizontally, as the sediment bulged slightly out of the open face of the C-section casing. The outer skin of the frozen organic cylinder was scraped away and discarded as melting began because this material had the greatest chance of having been contaminated during boring. The remaining core was sampled for pollen analysis and radiocarbon dating; a 5-cm slug of the basal organic material (205 to 210 cm) sufficed for the lowermost 14C determination. The peat blocks above 175 cm were cut into 2-cm horizontal slices for macrofossil examination and radiocarbon dating. STRATIGRAPHY (SUMMARIZED)

Humification values are taken from von Post (1924) and Troels-Smith (1955).

HI - very fresh, H 10 = very humified. 0-10 cm Moderately fresh Sphagnum peat,

H2-3, surface rootlets of Ericales. 10-18 cm Unhumified pale brown Sphagnum

peat, H2, Ericales roots. 18-20 cm Moderately fresh Sphagnum peat.

H3. 20-30 cm As above, with Ericales roots, char-

coal and wood fragments. Many Picea sp. needles at 26 cm.

30-32 cm Moderately humified Sphagnum peat, H4, large wood fragments.

32-36 cm Moderately fresh Sphagnum peat, H3, wood fragments.

36-39 cm As above, without wood. 39-44 cm Single massive timber, charred on

outside. 44-46 cm Moderately fresh Sphagnum peat,

H3, a few charcoal fragments. 46-48 cm Moderately fresh Sphagnum, H-3,

wood fragments. 48-60 cm Fresh pale brown Sphagnum peat,

H3, with embedded single massive unburned timber, peat more humi- fled (H4-5) 58-60 cm.

60-64 cm Moderately humified Sphagnum peat, H5.

64-74 cm Moderately fresh Sphagnum peat, H3-4, a little charcoal between 70- 73 cm.

74-79 cm Moderately humified Sphagnum peat, H4, burned at 75-76 cm, with much charcoal and wood fragments.

79-88 cm Moderately humified Sphagnum peat, H3, little wood. Charcoal and wood 85-88 cm.

156 / ARCTIC AND ALPINE RESEARCH



FIGURE 1. Location map showing sites mentioned in the text. Vegetational boundaries taken from Rowe (1959).

88-119 cm Moderately humified Sphagnum peat, H4. Few wood fragments and twigs 98-119 cm. Picea sp. needles 104- 106 cm, charcoal 106-110 cm.

119-123 cm Single massive log, charred on outside.

123-126 cm Humified peat, H5-6, scorched. 126-132 cm Increasingly humified peat, H6-7,

somewhat muddy. 132-136 cm Well humified muddy Sphagnum-

rootlet peat, H7-8. 136-142 cm Rootlet peat, H7-8, twigs at 142 cm. 142-148 cm Rootlet-detritus peat, H7-8, twigs

at 148 cm. 148-166 cm Crumbly detritus peat (H7-8) with

wood fragments. Carex sp. seeds 158-166 cm.

166-170 cm Coarse detritus mud, a few Carex sp. stems and leaves, Carex sp. seeds 168-170 cm.

170-175 cm Fine detritus mud. 175-185 cm Dark brown necron mud (gyttja),

with sand and occasional angular gravel. Picea sp. needle at 180 cm.

185-195 cm As above, with small pebbles (3 x 4 mm). Occasional Cyperaceae sheaths, Carex sp. seed. Salix sp. wood 189 cm, a garnet at 192 cm.

195-200 cm Sandy necron mud, Carex sp. and Potamogeton sp. seeds.

200-207 cm Sandy necron mud with clay and gravel.

207-215 cm Blue clay-silt with pebbles and Salix sp. wood fragments at 208 and 215 cm.

215-223+cm Smooth blue clay, no stones, cf. Salix sp. wood fragments at 219 cm.

The stratigraphy is illustrated in a pollen diagram for Porcupine Mountain (Figure 2).

BASE TO 6,670 BP

The lowest material recovered from the ex- cavation at Porcupine Mountain was a pale blue stoneless clay. The clay (215 to 223 cm) passed upward into blue clay-silt with pebbles and fragments of Salix sp. wood (207 to 215 cm), and then apparently conformably into sandy necron mud (gyttja) (200 to 207 cm) with some clay and gravel. There followed sandy necron mud (195 to 200 cm) with Carex sp. and Potamogeton sp. seeds, and then necron mud (175 to 195 cm) with sand, gravel, small pebbles (including a garnet), with macrofossils of Carex sp., Salix sp., and Picea sp. There seems to have been no hiatus in deposition between the clay and the overlying necron mud, but from the sand included in the lowest necron mud it seems that some disturbance of the mineral soils around the basin continued after clay deposition ceased, possibly reflecting merely local events.

The basal clay contains high percentages of Picea pollen, a large amount of Salix, with some Artemisia and Ambrosia, and much Cyperaceae. The spruce pollen values (ca. 48 to 68%) suggest the substantial presence of Picea forest in the general area, with locally disturbed or open soil, perhaps just around the site. The Salix wood and the relatively high level of Salix pollen indicate that willows grew immediately around the site, as did members of the Cyperaceae. The aquatic state of the deposit is compatible with the identification of pollen of Typha latifolia and Sparganium/T. angustifolia type. T. angustifolia is believed to have been introduced from Europe (Love and Bernard, 1959), and since its pollen grains are hardly dis- tinguishable from Sparganium by optical micros- copy it seems likely that the latter is the correct identification. The basin of accumulation was clearly occupied by a small lake in what is probably a kettle hole, formed after the main final deglaciation when a locally long-lived ice block melted to form a small steep-sided lake.

Despite the high Picea percentages at the base of the diagram and the supposition that spruce grew abundantly in the area, there are no Picea macrofossils to confirm this local presence. It is possible that the spruce pollen was secondary, having been derived from older materials by the reworking of mineral soils around the lake. Picea values are associated with the basal silts and clays and decrease swiftly above the base. However, mineral inwash (sand and pebbles) into the necron mud continued for 30 cm above the Picea fall, which does not

HARVEY NICHOLS / 157



PORCUPINE MOUNTAIN, MANITOBA, 1967

Unhumified Rootlet Fine J Sphagnum Peat Detritu eat t Detritus Mud

Sphgnum Peat Drift Peat Necron Mud

m Rootlet Peat Coarse Mud Sand Detritus Mud E': Sand

Scole Chonge

/ 2060 100 180% I I I IllI

E AP+ NAP = 300, excluding Sphagnum and Cyperaceae

20 60 100 180 260% 0 20 40 60 80 100% i1 I, , l ~ l ~ l ~ l J i ,l Jl ll ~ l ,

v v Wood Pebbles *

Charcoal L LL Clay Tr ee

FIGURE 2. Pollen diagram from Porcupine Mountain, southwest Manitoba. Vertical sampling in- terval 5 cm.



support the hypothesis of a secondary reworked origin for the spruce pollen.

An alternative explanation is that the rapid decline of spruce pollen and the end of clay deposition marked a change in the local environment. It does not seem likely that this was a result of deglaciation. The basal organic material has a date (6,670 - 70, WIS-271) (Bender et al., 1968b) some thousands of years later than the presently accepted date for deglaciation of this area. Ritchie (1964) recovered spruce wood 9,570 ? 130 (S-129) radiocarbon years old from Riding Mountain 270 km to the south. He as- sumes, until further 14C dates are available, that the organic bases of the other deposits studied at Riding Mountain (ibid.) are also ca. 9,000 to 10,000 radiocarbon years old. A tentative iso- chrone map of Canadian deglaciation (Bryson et al., 1969) suggests that the ice sheet disappeared from the Porcupine Mountain area about 9,000 BP.

It has already been noted that this site is probably a kettle hole, and it is possible that the start of organic accumulation was delayed until the ice block had melted. Comparable postglacial events elsewhere have indicated that it might have taken thousands of years to accomplish such melting (Clayton, 1967). There would then have been ample time for closed spruce forest to occupy Porcupine Mountain, which would explain the high Picea percentages at the base of the diagram. The short lived Artemisia, Ambrosia, and Com- positae peaks at the base might then be considered to reflect very local soil disturbance around the basin as the melting ice block caused the final col- lapse into the basin of the mineral soils which had covered the ice.

An alternative and very tentative explanation is that the organic base at 207 cm does not repre- sent the earliest organic material in the basin, but that more underlies the basal clay which could not be penetrated below 223 cm. One may envisage a kettle hole in which organic lacustrine accumulation began ca. 9,000 BP shortly after deglaciation, but where some local catastrophic wash-in later occurred which brought minerogenic materials into the basin to cover the organic accumulation. This local disaster might have resulted from an increase in torrential summer rainfall which might have caused soil slipping and destruction of the plant cover just around the sides of the basin.

This hypothetical event may have been of merely local importance, but it may be significant that of the few similar Canadian deposits which have been radiometrically dated there are three others which I have sampled which have bases of essentially the same age. Lynn Lake, 530 km north of this site in northern Manitoba, started to accumulate

necron mud over a conformable clay base at 6,530 + 130 BP (WIS-72) (Nichols, 1967a). A site at Peace River, Alberta, has a basal date for necron mud overlying clay of 6,880 ? 85 BP (WIS-274) (Bender et al., 1968b); and Colville Lake, Mackenzie Territory, has mud overlying marl at 6,790 ? 75 BP (WIS-275) (ibid.). The four dates, 6,670, 6,530, 6,880, and 6,790 BP, lie remarkably close to each other.

The date from Alberta appears to be several thousand years too young to reflect deglaciation (Bryson et al., 1969). The Lynn Lake material I formerly ascribed to accumulation in a proglacial lake (Nichols, 1967a), but in view of the similarity of these basal dates this may be incorrect. There is so little known about deglaciation in northwest Canada that the date from Colville Lake can only be regarded as indicating the minimum elapsed time since glaciation. The map by Bryson et al. (1969) suggests that deglaciation was substantially earlier.

There is thus a possibility that these four basal dates reflect recovery from an environmental change which occurred on a regional scale. This would presumably have been a climatic shift toward wetter conditions, to initiate sheet flow, or toward a much colder climate, reflected in freeze- thaw movement; either of these geomorphological processes might have resulted in the transport of minerogenic materials into these lake basins. Paleoclimatic evidence suggests general climatic amelioration at this time, so freeze-thawing seems the less likely of the two mechanisms.

I have no proof at present that such in-washing has occurred in Canadian sites. I noted during fieldwork, however, that many of the younger and shallower Sphagnum bogs which occupy kettle holes throughout southern Canada are underlain by unweathered blue silty clays, which show no signs of being exposed to the air before being covered by muskeg. The basal organic dates for these bogs indicate that they formed at times of climatic deterioration (Nichols, 1969) to colder and wetter conditions. The onset of the climatic deteriorations may have been marked by locally severe erosion by heavy rainfall and sheet flow of mineral matter into basins, followed by a build- up of Sphagnum sp. mosses.

To conclude this speculation, it may be noted that similarities in the late postglacial climatic histories of parts of Canada and northern Europe have been noted previously, and that recently numerous radiocarbon determinations have established some measure of synchrony and parallelism (Nichols, 1967b). With this in mind, it is worth pointing out in a very tentative manner that in northern Europe the period prior to 6,500 to 7,000 BP was apparently characterized by rela-




tively high rainfall (Godwin, 1956; Frenzel, 1967; Starkel, 1967). In the Alps of southern Switzerland, Zoller (1960, 1964) found evidence of several short-term cold spells in the period 7,300 to 6,500 BP (the "Misox oscillations"). The early Atlantic pollen zone was marked by blanket peat growth in northern England (Con- way, 1954; Tallis, 1964), by sheetflow and increased soil erosion in northern Europe (Starkel, 1967), and by landslides (Franks and Johnson, 1964; Morariu et al., 1964). The possibility that comparable events may have occurred at the same time at some sites in Canada cannot be ignored.

The high Picea values at the base of the diagram suggest a relatively cool, moist summer climate. This brief spruce episode was followed quickly by increased Gramineae and Artemisia values and a rise in Betula; this suggests a shift from closed spruce forest to grassland with birch copses as a result of drier, warmer summers. This transition resembles the change from spruce forest to grassland reflected in the lower parts of the Riding Mountain diagrams (Ritchie, 1964), which was tentatively interpreted as marking a shift from the Anathermal to the Hypsithermal climate, though the horizon was undated. The results appear to be compatible with the hypothesis of Love (1959) in her pioneer work on the paleo- botany of Manitoba.

6,670 TO 5,140 BP The percentages of Picea were low and there

was a slight Pinus increase, while Betula rose to a peak. Gramineae and Artemisia had increases, and there was some Chenopodiaceae, Umbelliferae, and Ambrosia pollen. The numbers of Typha declined, while Cyperaceae rose.

This herbaceous episode probably saw the es- tablishment of prairie on the flat land of the former Lake Agassiz bottom which surrounds Porcu- pine Mountain. The birch pollen may have derived from trees which colonized the high ground of Porcupine Mountain as the spruce forest died. Wood referable to Betula sp. which occurred at 189 cm may indicate that the 190-cm birch pollen peak was due to local overrepresentation, and certainly provides evidence of birch colonization on Porcupine Mountain. The pine increase may have been due to some scattered colonization of the area abandoned by spruce, and also to long- distance transport of Pinus pollen.

The aquatic element in the pollen record de- creased as Sparganium/Typha angustifolia type and T. latifolia declined, but the stratigraphy still consisted of an open water necron mud, with sand and pebbles. This suggests that the soil around the site was incompletely occupied by grasses and birches (perhaps due to summer dryness) so that

minerogenic materials were still being washed or blown into the pool. The increase in sedge pollen toward 5,140 BP may have reflected the increasingly stable state of the lakeshore, suggested by the absence of coarse mineral matter in the mud above 175 cm.

The total herb pollen count reached its highest values at the top of this zone, where Gramineae had a peak and spruce was at its minimum. This perhaps indicated a maximum of summer dryness (and possibly summer warmth) just before 5,140 ? 75 BP (WIS-308) (Bender et al., unpub.). If the suggested similarity between the climatic histories of parts of central Canada and northern Europe (Nichols, 1967b) has any validity, then it is interesting to recall the possible maximum of summer warmth prior to 5,000 BP which was discussed by Tauber (1965). This period (6,670 to 5,140 BP) was marked in southern Keewatin and northern Manitoba by a northward movement of the Boreal forest limit during summers which were substantially warmer than the present (Nichols, 1967c). The Porcupine Mountain seems to have recorded a synchronous northward movement of the southern limit of the Boreal forest and the immigration of the prairie, as indicated by the diminution of spruce pollen and the increase of herbs. This was perhaps also a response to increased summer warmth and possibly dryness.

5,140 TO 4,180 BP There was a slight Picea increase, but its per-

centages were still low (30% or less). Pinus declined quite progressively from the bottom to the top of the zone. Betula had moderate values and A lnus rose halfway through this period. The herbs, especially Gramineae and Artemisia, maintained their moderate values (5 to 10%) until 4,180 ? 75 BP (WIS-286) (Bender et al., unpub.) when they fell to zero or very low values. Representa- tion of Typha ended, there were high counts of Cyperaceae pollen, and Sphagnum began to be represented toward the end of the zone. The total of nonarboreal pollen was relatively high and steady until the sharp decline at 4,180 - 75 BP (ibid.) where tree pollen rose. In the stratigraphy necron mud changed to drift mud at the base, and this ceased at the top of the zone.

The small increase in spruce was possibly due to a general movement of spruce forest toward Porcupine Mountain, rather than the growth of Picea in small numbers at the site. This may have been the first small southward shift of the Boreal forest from its far northern limit, reached between 6,670 and 5,140 BP, resulting from a short-lived period of cooler summers. The herbaceous element remained strong after its peak

160 ()'ARCTIC AND ALPINE RESEARCH



before 5,140 BP, and probably reflected the continued dominance of grassland on the plain around Porcupine Mountain, while birches grew on the mountain or in patches on the prairie. The summer climate was still quite warm and dry, but less so than in the preceding zone.

The disappearance of Typha, the high sedge values, and the appearance later of Sphagnum spores show that the basin was filling in with terrestrial vegetation, and this is confirmed by the stratigraphic transition to drift mud and finally to rootlet-detritus peat.

At Lynn Lake and Ennadai Lake (Nichols, 1967a) the northern edge of the Boreal forest experienced its first temporary southward retreat (at 5,140 ? 100 BP (WIS-112) and just before 4,800 + 90 BP (WIS-166), respectively), in response to a short-lived period of summer cold; but after ca. 4,500 BP there was a recovery to warmer summers. These three dated events (5,140, 5,140, and prior to 4,800 BP) are close in time to the much-debated "Ulmus decline" of northern Eur- ope of about 5,000 BP. There has recently been an increase in the evidence for climatic cooling at this period (Mercer, 1967; Frenzel, 1967).

4,180 TO 2,450 BP

After an initial short-lived fall (matched by a Betula peak) the Picea values rose to almost 70%. Pinus was very low, with a late rise. Herbs were low, while Sphagnum spores were very numerous. In the stratigraphy the deposits were now terrestrial and included Sphagnum spp. mosses.

The recovery of spruce values was initially masked by the local overrepresentation of birch, probably resulting from the thin woody fen (carr) horizon at 140 to 142 cm. Then closed spruce forest dominated Porcupine Mountain and shaded out the local herbs and shrubs. The lowland, as well as the mountain, was probably covered by spruce forest. The climate was probably cooler and wetter than before. The change to a Sphag- num peat bog may have been a merely coincidental stage of the local hydrosere, but the shift to om- brogenous peat would have been promoted by the increased precipitation/reduced evaporation and may even have been controlled by it. The temporary decline of spruce pollen at 120 cm coincided with a charred Picea log in the peat: a fire swept the local forest, and pine briefly colonized the burned ground.

At Colville Lake, Mackenzie (Nichols, unpub.), there was a similar rise of Sphagnum spores to ex- tremely high values at the same time (4,130 -+ 55 BP (WIS-294)) (Bender et al., unpub.), associated with a change from very humified to very fresh Sphagnum peat which was attributed to a

cooler, wetter summer climate. The start of peat growth at 4,200 ? 130 (GSC-494) and 4,350 + 70 BP (WIS-280) (ibid.) in Saskatchewan and Alberta was ascribed to cooler, wetter summers (Nichols, 1969). No major climatic change was detected in the Ennadai or Lynn Lake diagrams (Nichols, 1967a) ca. 4,200 BP; there was a major cooling ca. 3,600 BP at the first site.

2,450 TO 2,000 BP Picea was high and irregular, while Pinus in-

creased after 2,270 ? 60 BP (WIS-303) (Bender et al., unpub.). Herbs were low, with small short- lived peaks at times of low Picea count. Sphagnum spores began to rise at 3,450 + 60 BP (WIS-306) (ibid.) to a peak at 2,270 ? 60 BP (WIS-303) (ibid.) and after 2,000 ? 55 BP (WIS-289) (ibid.). The peat was composed primarily of Sphagnum spp. and was fresh and unhumified.

Spruce forest continued to dominate the area, but there was a considerable element of pine after 2,270 BP, which was perhaps encouraged by the fires recorded by charcoal horizons in the peat and temporary decreases in spruce pollen. The herbs were shaded out by the closed forest except for brief expansions at times of forest fires.

The Boreal forest cover indicated relatively cool moist summers, and this is supported by the very rapid unhumified growth of Sphagnum peat and the production of very large quantities of Sphag- num spores, particularly at 2,270 and 2,000 BP.

At Ennadai Lake a cold period followed 2,670 + 105 BP (WIS-93) (Bender et al., 1966) and the northern limit of the Boreal forest moved south; at Lynn Lake the cooling was marked by a great increase in Sphagnum spore numbers shortly before 2,170 + 80 BP (WIS-113) (Nichols, 1967a) which reached its maximum at that date. At Pelly Lake in northern Keewatin (Nichols, unpub.), the southward retreat of the forest was reflected in minima of Picea and Pinus pollen windblown into the tundra at about 2,080 + 60 BP (WIS-292) (Bender et al., unpub.). From 3,180 -- 65 BP (WIS-314) (ibid.) to 1,810 + 60 BP (WIS-297) (ibid.) Colville Lake had summers which were too cold and dry to allow peat growth (Nichols, unpub.). At 2,380 + 90 BP (WIS-1) (Bender et al., 1965) peat growth began at Root Lake in central Manitoba, and almost simultane- ously at four other sites in Canada; these events have been ascribed to wetter and colder summers (Nichols, 1969).

2,000 TO 1,170 BP Picea counts were initially low and were domi-

nated by Pinus, but this position was sharply re- versed above 65 cm. Sphagnum percentages were




very high and sustained after 2,000 ? 55 BP (WIS-289) (Bender-et al., unpub.), then fell, and achieved a new peak at 1,170 + 60 BP (WIS- 287) (ibid.). The generally unhumified Sphagnum peat was particularly fresh above 60 cm.

The beginning of this period saw a mixed pine- spruce forest at the site, with the former genus dominant. The change to spruce forest at 65 cm may have marked a shift to a slightly wetter climate, which may explain the very unhumified Sphag- numn peat above 60 cm. The switch from pine to spruce at 65 cm is estimated to have occurred ca. 1,600 BP. Some of the early low values for spruce may be explained by the traces of fire (charcoal) found in the peat, but pine percentages were high and sustained, somewhat different from the earlier episodes of brief fire climax for pine. Herbs had very low values.

At Ennadai Lake and Lynn Lake (Nichols, 1967a) environmental changes were registered at 1,510 ? 80 (WIS-88) and at 1,550 ? 50 BP (WIS-225), but their climatic significance was unclear.

1.170 BP TO PRESENT DAY SURFACE

Picea percentages were high and sustained up to 25 cm, where they fell sharply and gave way to Pinus until Picea again rose to dominance at the surface. Shrubs and herbs were low up to 25 cm, and then they rose. The Ericaceae rose briefly at the Picea decline at 25 cm. Cerealia appeared for the first time at 20 cm and had low values. Alnus rose after 25 cm. Sphagnum declined from its peak at 1,170 BP and had a brief rise of 25 cm, dated "modern" or less than 250 BP (WIS- 301) (Bender et al., unpub.), followed by low values at 20 and 15 cm, and then a sustained increase up to the present day surface. The Sphag- num peat was unhumified, and contained Erica- ceae roots and Picea wood and needles.

There was closed spruce forest around the site, with some pine which benefited from the fire recorded by charred Picea wood at 39 to 44 cm. At 20 cm, just after the "modern" ]4C assay, the spruce forest was partially destroyed at the same time as cereal pollen first appeared. Herbs benefited from the opening of the forest; Ericaceae and Ambrosia increased, and alder was able to colonize waste ground. This event has all the characteristics of human clearance of the forested Agassiz lowlands for agriculture, including cereal

cultivation. Dr. J. H. Warkentin has informed me that farm settlement occurred in the decade 1891 to 1901 in the area north of Bowsman and west of Birch River, at the foot of Porcupine Mountain; sawmilling accompanied this settlement, and there were mills on the southern and eastern slopes of the mountain in the 1890s. Pro- fessor Warkentin suggests that the destruction of trees and planting of cereals recorded in the Por- cupine Mountain pollen diagram may have occurred ca. 1900 A.D. (written communication, Mar. 10, 1969).

The Sphagnum peat was still growing quickly under wet conditions, but the reduced Sphagnum spore counts and presence of Ericales roots perhaps suggest some drying of the surface of the bog. The modern peat surface has numerous members of the Ericales associated with recently desiccated fresh Sphagnum mosses.

The low Sphagnum spore counts at 20 and 15 cm, just after the "modern" 14C determination and the European clearance of the forest (ca. 1890), followed by the maintained rise at 10, 5, and 0 cm, may be of merely local significance, and too much cannot safely be read into these changes. However, in view of the known sensitivity of Sphagnum sporogenesis to environmental and especially climatic alterations, it is permissible to refer to the meteorological instrumental records which are available for this recent period. From scattered Canadian records (Canada Year Book, 1914, 1960; Kendrew and Currie, 1955), it appears that summers in southwest Manitoba were perhaps warmer and drier in the late 19th/early 20th century. From then to the present day the summer climate has been somewhat colder and wetter. After the forest destruction referred to the 1890s (at 20 cm) the Sphagnum percentages were low (at 20 and 15 cm), a phenomenon sometimes associated with desiccation; the rising Sphagnum numbers at 10, 5, and 0 cm may have reflected wetter conditions. It is tempting to attribute these variations to the climatic changes known to have occurred at the same time. The palynological observations by Bartley and Matthews (1969) at a site in Arctic Quebec may be relevant: in modern (surface) peat they encountered high Sphagnum spore percentages which they tentatively attributed to the climatic amelioration of ca. 1880 to 1950 (Lamb and Johnson, 1961), which in that area had the effect of a warmer and wetter summer climate.

CLEARWATER BOG

GEOGRAPHY

Clearwater Bog is the unofficial name for the muskeg peat which lies on the side of Clearwater

Lake, near the town of The Pas, west-central Manitoba, at 53?59'N, 101?12'W. The mire rests on the gently sloping lacustrine sand, formerly the




beach of Clearwater Lake; former shorelines can be discerned around the lake.

The area is underlain by Paleozoic limestone, which is generally mantled by the silts and clays of Glacial Lake Agassiz, with local accumulations of sands and gravels from former beach ridges. This level area of the Manitoba Lowlands lies about 160 km north of the southern edge of the Boreal coniferous forest, where it grades into decid- uous forest, mainly Populus and Quercus, mixed with grassland. Closed coniferous forest stretches north of Clearwater Bog for about 300 km before the trees become less dense in the lichen wood- lands of northern Manitoba.

Around Clearwater Lake the level, ill-drained land, often covered by shallow muskeg peat, is occupied by woodland patches of Picea mariana and Larix laricina. Sand or gravel ridges are occupied by Pinus banksiana, which has also invaded burned forest areas, along with Populus tremu- loides.

Meteorological records from The Pas (53?59'N, 101?15'W) are relevant to Clearwater Bog and are given in Table 1. Such data are not available for Porcupine Mountain, but the figures from The Pas may be taken as a guide to the latter site,

TABLE 1

The Pas (elevation: 270m)a

Mean daily Mean monthly temperature precipitation

Month (?C) (mm)

January -22.8 15

April 0.6 21

July 18.3 56

October 1.7 28

Mean annual total precipitation: 381 mm.

aThese figures refer to 40 years of observations prior to 1955 (Kendrew and Currie, 1955).

which is estimated to have a somewhat higher precipitation total for the year. Summer tempera- tures are probably very similar at the two sites, while the higher winter and spring figures around Porcupine Mountain (warmer by only a few de- grees) are offset by the cooling effect of altitude at the site itself (640 m).

SAMPLING METHODS

The peat bank was sampled for the author by Dr. R. A. Bryson in August 1964. Blocks of peat ca. 13 cm square were cut from the cleaned face

of a roadside exposure to provide a continuous peat monolith from the present bog surface down to the sand at 82 cm. The peat blocks were sampled for pollen analysis in the laboratory by the author and were then cut into 2-cm horizontal slices to facilitate the search for macrofossils and the submission of material for radiocarbon assay.

STRATIGRAPHY (SUMMARIZED)

Surface- 0.5 cm Secondarily humified dark brown

Sphagnum peat, with Ericaceae roots and Picea needle.

0.5-21 cm Unhumified Sphagnum peat; unidentified wood fragments 6-6.5 cm, a few Cyperaceae stems 6-12 cm.

21-27 cm Moderately humified Sphagnum with humified leaves and roots of Cypera- ceae and Ericaceae. Oxycoccus cf. quadripetalus ssp. microphyllus (or O. cf. macrocarpus) leaves at 22 cm, Ledum sp. leaf at 26 cm. Numerous Cyperaceae leaves 24-27 cm.

27-33 cm Very marked change to very humi- fled dark brown Sphagnum peat with oxidized Cyperaceae leaves.

33-43.5 cm Very fresh unhumified pale brown Sphagnum peat, with occasional Cy- peraceae stems.

43.5-45 cm Moderately humified mid brown Sphagnum peat.

45-52.5 cm Unhumified Sphagnum peat; cone and needle of Picea mariana at 50 cm; rhizomes of Equisetum cf. palustre 48-50 cm.

52.5-58 cm Moderately humified Sphagnum peat. 58-63 cm Unhumified Sphagnum peat; oc-

casional Cyperaceae leaves, one Equi- setum cf. palustre rhizome at 62 cm.

63-69.5 cm Very humified dark brown peat. 69.5-72.5 cm Unhumified Sphagnum spp. with

oxidized unidentified other plant material.

72.5-80 cm Very dense humified dark brown peat, with unidentified wood fragments; small piece of wood charcoal at 80 cm.

80-82 cm Section of large timber of Picea sp. 82 cm+ Coarse gray quartz sand.

THE BEHAVIOR OF SPHAGNUM

The peat profile is composed primarily of Sphag- num spp. bog mosses in varying states of humification. The importance of the precipitation-evaporation budget to the growth of Sphagnum spp. makes these mosses potentially valuable indicators of past climate, though at present the thresholds of growth and sporogenesis in the different species are not fully understood.

The variation in the degree of humification of the peat is particularly marked in this profile. Con-




tinuous samples of the peat cut from the monolith were laid out contiguously and allowed to dry, enhancing the color differentiation and allowing more accurate description of the humification values.

There is a pronounced correlation between the degree of peat humification and the number of Sphagnum spores recorded from the peat. The dark brown, very dense peat which lacks recogniz- able macrofossils had very low (relative) percentages of Sphagnum spores. The very fresh, pale brown, unhumified peat composed almost entirely of Sphagna had very high Sphagnum spore counts, and the moderately humified peat contained inter- mediate Sphagnum percentages.

The similarity of the behavior of Sphagnum at Clearwater to that reported by Tallis (1964) from Britain and Nichols (1967c) from Keewatin has encouraged me in this account to regard the variations in Sphagnum spore values as reflecting changes in climate. Clearwater Lake is not far from the junction of the southern Boreal forest with the aspen parkland, which is also a climatic boundary (Bryson, 1966). The variation in Sphagnum peat humification may have been in response to the changing intensity of Pacific air- mass dominance at the site during summer.

THE POLLEN DIAGRAM

There is little systematic change in the diagram (Figure 3) apart from the peaked representation of Sphagnum spores. This is not surprising in view of the small time span represented by the deposits: the basal peat is only 940 ? 60 radiocarbon years old (WIS-173) (Bender et al., 1967).

The peat monolith was underlain by a com- pressed massive timber of Picea sp. (identified by Dr. R. C. Koeppen) which covered the basal lacustrine sand. The origin of the spruce wood, dated 1,280 ? 75 BP (WIS-146) (ibid.), was unclear when the peat bank was sampled for the author in 1964 by Dr. R. A. Bryson; accordingly, the site was reexamined in 1967 by Dr. Bryson and myself. The same peat bank was cleaned and scrutinized, and it became clear that the Picea sp. wood lying between the peat and the sand in the 1964 monolith was not an isolated fragment, but that for scores of meters along the roadside exposure the sand was covered by a layer of flattened spruce logs. Dr. Bryson drew my attention to a faint fossil podzol horizon just beneath the wood layer. The colors were faded but the zones of leaching and accumulation were still discernible.

Clearwater Bog rests on the shallow slope of the former beach of Clearwater Lake. Fossil shorelines at higher elevations circumscribe the site. The colonization of the exposed lacustrine sand


clearly involved some fall in lake level from a previous high stand marked by the old shorelines. This may presumably have resulted from local geomorphological factors, such as river downcut- ting, or from a reduction in the precipitation-evaporation budget. The possibility of climatic desiccation is strengthened by the regional evidence for warmer, drier climates at this time. Palynological and peat stratigraphic evidence from Ennadai Lake, southern Keewatin, indicates warmer summer weather between 1,500 and 700 BP (Nichols, 1967a), at a time when there is macrofossil evidence for a northward movement of the Boreal forest limit in the same area due to climatic warming (1,140 ? 90 BP or 1,050 + 180 BP) (WIS- 17) (in Bryson et al., 1966). The same climatic amelioration was registered at Pelly Lake, northern Keewatin by maxima of Picea and Pinus pollen windblown from the forest to the south, dated 900 ? 75 BP (WIS-245) (Bender et al., 1968a), and by the growth of peat in a dry cold desert situation between 1,060 ? 55 and 940 ? 60 BP (WIS-263 and 278) (ibid. and Nichols, unpub.). The date of the spruce log underlying Clearwater Bog (1,280 + 75 BP) (WIS-146) is compatible with the dates quoted above for regional summer climatic warming. This amelioration coincides with the Scandinavian settlement of Greenland and the early medieval North European summer warming (Lamb, 1966; Nichols, 1967b).

At the base of the diagram Picea had low but rising values. Alnus had a small peak while Pinus percentages were low, as were those of Sphagnum, and nonarboreal pollen was hardly represented. Spruce appears to have been the dominant tree locally, with lesser numbers of pine. The local presence of spruce is supported by the identification of the large timbers below the peat as Picea sp. There were very low percentages of Sphagnum spores at the base, and the Sphagnum peat was very humified: this suggests a dry climate during the growing season and is compatible with the data in the preceding paragraph.

At 72 cm the dark brown peat is less humified, perhaps as a result of wetter climatic conditions, and at 70 cm the percentage of Sphagnum spores was very high. Humified peat and lower Sphag- num values followed (69 to 63 cm), perhaps indicating a drier climate; a peak of Cyperaceae pollen may have reflected the colonization of shorelines exposed by lower lake levels. The decline of Picea and Pinus pollen at 65 cm was probably a result of the fire registered by the charcoal horizon in the peat. The subsequent peak of Pinus seems to reflect the colonization of the burned area by pine, which is the pioneer of burned woodland in this area (Ritchie, 1956). It was not until the 50-cm level that Picea pollen recovered,



Depth 2 Cm

ALNUS

CLEARWATER BOG, MANITOBA, 1966 ZAP + NAP = 300, excluding Sphagnum

/0% 10% 20% 40% 60% 20% 40% 60% 20% 40% 200% 400% 600% 800% 1000%

2 < l l l l t t l l l l l l ' C l, r l c lr h a 4UclQ

j I L I J I I

I L_, I

, j i I ~ ] I , I i I ~ I I ~ I

iZ O 4-. O,s

, . PICEA PIUS 4 CYPECEE , 4 SPHUM ,

'6^ 4-c 5 414 p O (

ANAL.- H NICHOLS

Decomposed Fresh Moderately Humifie d

L J c - Surface Sp nu Pea t r Sphagnum Peat Sphagnum Peood harcoal

FIGURE 3. Pollen diagram from Clearwater Bog, The Pas, west-central Manitoba.



indicating that finally spruce dominated the Clear- water scene again. Picea pollen outnumbered that of Pinus throughout the rest of the diagram, probably reflecting a predominantly spruce forest with pines.

Picea declined between 35 and 25 cm at a time when humified peat and low Sphagnum spore values may have indicated a drier climate. At 30 cm there were low peaks of Alnus and Betula pollen and a rise of Chenopodiaceae and Am- brosia. The drier conditions may have lowered the lake level, allowing the spread of chenopods and ragweed and perhaps alder around the exposed beach, and perhaps encouraging alder and birch to colonize the desiccated peat bogs around the lake. It may be that the decline of Picea at 25 cm and the rise of Pinus reflected a thinning out of spruce forest and colonization by pine, or maybe desiccation encouraged the spread of pine onto new territory, perhaps dried peat, which reduced the relative abundance of Picea pollen without an alteration in the spruce cover.

An alternative, anthropogenic interpretation is possible; 19th-century European settlement of the area was associated with some destruction of the spruce forests and the introduction or spreading of weeds (especially Ambrosia). The "modern" radiocarbon dates (i.e., less than 250 BP) at 62 to 63 cm and 26 to 30 cm (WIS-153 and 170) (Bender et al., 1967) are compatible with the sug- gestion that this was a 19th-century event, and the

similarity to the signs of European settlement at the top of the Porcupine Mountain diagram sup- ports this hypothesis. An initial agricultural settlement was located at The Pas, near Clearwater Bog, by 1850 (Morton and Martin, 1938).

At the top of the diagram Picea values recovered dominance over Pinus, Sphagnum counts increased, and the Sphagnum peat was very fresh. A predominantly spruce forest with pines flour- ished under the wetter climate indicated by the behavior of Sphagnum, a situation probably very similar to that of the present day. The upper Sphagnum peat is unhumified and there are living Sphagnum spp. growing nearby. A sample of peat from 62 to 63 cm was assigned a "modem" date (less than 250 BP) (WIS-153) (Bender et al., 1966), so that it is suggested that the palynological record ends close to the present day.

The suggested evidence for a drier summer climate (humified peat and low Sphagnum counts) between 35 and 25 cm, followed by wetter conditions, appears from the "modern" radiocarbon dates and suggests evidence for settlement to have occurred sometime during the 19th and 20th cen- turies. It is possible that these phenomena were synchronous with the parallel changes experienced by Porcupine Mountain during the last century and were expressions of the climatic warming of ca. 1880 to 1940 and the subsequent cooling (Lamb, 1966).

ACKNOWLEDGMENTS

I thank Dr. R. A. Bryson for his help in excavat- ing peat samples and Dr. M. Bender for the radiocarbon assays. Field work and analyses were supported by NSF GP5572X, Meteorology De-

partment, University of Wisconsin, Madison, and preparation of the manuscript by the Institute of Arctic and Alpine Research, Boulder. Dr. Doris Love provided helpful criticism of the manuscript.

REFERENCES

Bartley, D. D. and Matthews, B. 1969 : A palaeobotanical investigation of post-

glacial deposits in the Sugluk area of northern Ungava, Quebec. Palaeobot. and Palynol., (in press).

Bender, M. M., Bryson, R. A., and Baerreis, D. A. 1965 : University of Wisconsin radiocarbon

dates, I. Radiocarbon, 7:399-407. 1966 : University of Wisconsin radiocarbon

dates, II. Radiocarbon, 8: 522-533. 1967 : University of Wisconsin radiocarbon

dates, III. Radiocarbon, 9: 530-544. 1968a: University of Wisconsin radiocarbon

dates, IV. Radiocarbon, 10(1): 161- 168.

1968b: University of Wisconsin radiocarbon dates, V. Radiocarbon, 10(2): 473- 478.

Bryson, R. A. 1966 : Air masses, streamlines, and the Boreal

forest. Geog. Bull., 8(3): 228-269. Bryson, R. A., Wendland, W. M., Ives, J. D., and

Andrews, J. T. 1969 : Radiocarbon isochrones on the disinte-

gration of the Laurentide Ice Sheet. Arctic and Alpine Res. 1(1): 1-14.

Canada, Government of: 1914 : Canada Year Book, 1913. Queen's

Printer, Ottawa. 1960 : Canada Year Book, 1960. Queen's

Printer, Ottawa. Clayton, L.

1967 : Stagnant-glacier features of the Missouri Coteau in North Dakota. In Clayton, L. and Freers, T. F. (eds.), Glacial geology of the Missouri Coteau and ad-




jacent areas. North Dakota Geol. Sur- vey, Misc. Series 30: 25-46.

Conway, V. M. 1954 : Stratigraphy and pollen analysis of

southern Pennine blanket peats. J. Ecol,. 42: 117-147.

Franks, J. W. and Johnson, R. H. 1964 : Pollen analytic dating of a Derbyshire

landslip: the Cown Edge landslides, Charlesworth. New Phytol., 63(2): 209-216.

Frenzel, B. 1966

Godwin, H

:Climatic change in the Atlantic/sub- Boreal transition on the Northern Hemisphere: botanical evidence. In World Climate from 8,000 to 0 B.C., Proc. Int. Symp. Roy. Met. Soc., Lon- don, 99-123.

Gowi. 1956 : History of the British Flora. Cam-

bridge Univ. Press, Cambridge, 384 pp. Kendrew, W. G. and Currie, B. W.

1955 : The Climate of Central Canada. Queen's Printer, Ottawa.

Lamb, H. H. 1966 : The Changing Climate. Methuen, Lon-

don, 236 pp. Lamb, H. H. and Johnson, A. I.

1961 : Climatic variation and observed changes in the general circulation, II. Geog. Annaler, 43: 363-400.

Love, D. 1959 : The postglacial development of the

flora of Manitoba: a discussion. Can. J. Bot., 37: 457-585.

Love, D. and Bernard, J. P. 1959 : Flora and vegetation of the Otterburne

area, Manitoba, Canada. Svensk. Bot. Tidskr., 53(4): 335-461.

Mercer, J. H. 1967 : Glacier resurgence at the Atlantic/sub-

Boreal transition. Quart. J. Roy. Met. Soc., 93(398): 528-534 .

Morariu, T., Diaconeasa, B., and Girbacea, V. 1964 : Age of land-slidings in the Transyl-

vanian Tableland. Revue Roumaine Geol., Geoph. et Geogr., Serie de Geogr., 8: 151.

Morton, A. S. and Martin, C. 1938 : History of Prairie Settlement and "Do-

minion Lands" Policy. Macmillan, To- ronto.

Nichols, H. 1967a: Pollen diagrams from sub-arctic cen-

tral Canada. Science, 155: 1665-1668. 1967b: Central Canadian palynology and its

relevance to northwestern Europe in the Late Quaternary period. Rev. Palaeobot. and Palynol., 2: 231-243.

1967c: The post-glacial history of vegetation and climate at Ennadai Lake, Kee- watin, and Lynn Lake, Manitoba. Eiszeitalter und Gegenwart, 18: 176- 197.

1969 : The chronology of peat growth in Can- ada. Palaeogeog., Palaeoclimatol., Pal- aeoecol., (in press).

Post, L. von 1924 :

Ritchie, J.

Das genetische System der organogenen Bildungen Schwedens. Com. Int. Pedo- logie, IV. Commission 22.

1956 : The vegetation of northern Manitoba. I. Studies in the southern spruce forest zone. Can. J. Bot., 34: 523-561.

1964 : Contributions to the Holocene palaeo- ecology of westcentral Canada. I. The Riding Mountain area. Can. J. Bot., 42: 181-196.

Rowe, J. S. 1959

Starkel, L. 1967

Tallis, J. H. 1964

Tauber, H.

Zoll

:Forest Regions of Canada. Canada Dept. Northern Affairs and National Resources, Forestry Branch, Ottawa, 71 pp.

: Postglacial climate and the moulding of European relief. In World Climate from 8,000 to 0 B.C., Proc. Int. Symp. Roy. Met. Soc., London, 15-33.

: Studies on southern Pennine peats III. The behaviour of Sphagnum. J. Ecol., 52: 345-353.

1965 : Differential pollen dispersion and the interpretation of pollen diagrams. Danm. Geol. Unders., 11(89): 69.

er, H. 1960 : Pollenanalytische Untersuchungen zur

Vegetationgeschichte der insubrischen Schweiz. Denkschriften Schweiz Natur- forsch Ges., 83(2): 45.

1964 : Zur postglazialen Ausbreitungsgeschich- te der Weisstanne (Abies Alba Mill.), in der Schweiz. Schweiz A. Forstwesen, 11: 681.

Ms suhmitted March 1969




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