Holocene climatic change and the distribution of peatlands in western interior Canada

QUATERNARY

RESEARCH

33,231-240 (1990)

Holocene Climatic

Change and the Distribution Western Interior Canada

of Peatlands in

STEPHEN C. ZOLTAI* AND DALE H. VITT? *Forestry Canada, Northern Forestry Centre, 5320 122 Street, Edmonton, Alberta, Canada, T6H 3S5, and fDepartment of Botany, University of Alberta, Edmonton, Alberta, Canada T6G 2E9 Received April 17, 1989 Dates of basal fen peat at 52 locations across west-central Canada indicate that peat deposition began ~6000 yr B.P. in a broad zone north of the present-day grassland. The isopleth of XOOO yr B.P. basal fen peat parallels the foothills of the Rocky Mountains, and extends eastward along 54”30’ north latitude. The absence of XOOO yr B.P. peat within this zone is attributed to a warmdry early to middle Holocene climate that caused severe seasonal droughts and prevented the establishment of peat-forming fen vegetation. Wetlands west (and probably north) of this line experienced lower water tables, but supported fen vegetation. As the climate became cooler and moister, stable water tables allowed the development of fens and rapid peat accumulation ensued, reaching the modem distribution of fens between 2000 and 3500 yr B.P. Projections of climatic parameters indicate that the mean annual growing degree days were 6 to 21% higher during the early and middle Holocene, and that precipitation was reduced through most of the area, resulting in much higher (by 17 to 2%) aridity than at present. o 1990 University of ~a.~hington.

INTRODUCTION Paleoecological studies and climatic reconstructions have shown that the climate of northern mid-latitudes was influenced by warmer summers and colder winters, with a summer drought period, between 12,000 and 6000 yr B.P. Pollen and diatom evidence indicate that grasslands extended north of their present extent between 9500 and 6500 yr B.P. (Ritchie, 1976). This was accompanied by lowered lake levels, indicating severe drought conditions from 9000 to 6000 yr B.P. (Schweger et al., 1981). Paleoecological data from numerous lakes in central Alberta indicate that most shallow lake basins were dry during the early Holocene and began flooding shortly after 8000 yr B.P. During the early Holocene the deeper lakes may have had their levels drop by as much as 15 m below their present level. Productivity of these warm, shallow lakes was highest between 9000 and 4000 yr B.P. (Schweger and Hickman, 1989). This warm, dry period can be related in general to the warmest part of the Hyp-

sithermal interval (also referred to as altithermal, xerothermic, or thermal maximum) that occurred during the early and middle Holocene (approx 9500 to 2500 yr B.P.) both in North America and in northem Europe (Deevey and Flint, 1957). This interval included several thermal maxima and arid phases that were not always synchronous. A maximum summer warmth period, peaking lO,OOO-9000 yr B.P., was detected in the northern hemisphere, according to the Milankovitch postulate (Kutzbach and Street-Perrott, 1985), although this net radiation maximum was not evident from most North American paleoecological reconstructions (Ritchie et al., 1983). High temperature occurred in southwestern North America during the radiation maximum, but the waning Laurentide ice sheet delayed the summertime thermal maximum in eastern North America (COHMAP, 1988). The ice sheet caused strong east-west thermal gradients that influenced the flow of air masses (Forester et al., 1987). The radiation maximum caused a world-wide shift of climatic zones, that 231 0033-5894l90 $3.08 Copyright 0 1990 by the University of Washington. All rights of repmduction in any form reserved.

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ZOLTAI

varied in timing and extent due to sea ice/ landmass/land ice distribution (COHMAP, 1988). In the interior of Canada, modern vegetation was established as the climate became cooler and moister about 5000 yr B.P. in the northwest (MacDonald, 1987) and about 3000 yr B.P. in central Manitoba (Ritchie, 1983) and central Alberta (Vance et al., 1983). In northern Alberta the present climatic conditions may have been established as early as 7500 yr B.P. (Vance, 1986). There are few peatlands in the present grasslands of interior Canada, although occasional fens may occur under exceptional circumstances (Adams, 1988). The near absence of peatlands can be attributed to the general aridity of the area, where evapotranspiration exceeds precipitation, and water tables fluctuate greatly both seasonally and annually. Small ponds (sloughs), filled with runoff during the spring, frequently become dry during the summer, and the water table often sinks lower than 1 m below the surface (Adams, 1988). In some areas, the evaporation of the water concentrates various salts on the dried surface. Within wetland ecosystems, large fluctuations in groundwater levels favor increased decomposition (Damman, 1979; Malmer, 1986), resulting in little peat formation. As a result, marshes predominate in areas of drought stress. Across the modern grasslands of interior Canada, only marshes and shrub thickets can exist in the depressions and around the open water of sloughs. The marshes form concentric zones around the centers of the depressions, with vegetation related to depth of submergence, extent and frequency of desiccation, and salinity. Dominant species in this marsh vegetation are emergents and grasses, including Scirpus spp., Typha latifolia, Phragmites australis, Juncus spp., and some sedges (Carex aquatilis, C. rostra&z, C. atherodes) (Adams, 1988). Under

AND

VITT

such conditions the thin peaty layer consists only of highly decomposed (humic) organic material, often mixed with mineral soil. Fens are peatlands in which organic material accumulates due to decreased decomposition. The vegetation is dominated by sedges, especially species of Carex and Eriophorum, and the ground layer has abundant bryophytes, mostly of the Amblystegiaceae (brown mosses) or, under lower pH, Sphagnum (peat mosses). The water table is at or above the surface for most of the growing season (National Wetlands Working Group, 1988). Thus positive precipitation to evaporation ratios and stable water level regimes are necessary for the fens to form and for fen peat to be deposited. The objectives of this paper are to (1) determine the initial dates of rapid peat accumulation and fen initiation; (2) examine the resultant pattern of distribution; and (3) on the basis of these patterns, suggest early to middle Holocene climatic factors that may have been related to fen development in the study area. METHODS Peatlands were investigated and cored throughout the Low- and Mid-Boreal Wetland Regions of Alberta, Saskatchewan, Manitoba. Samples were taken from the basal portion of the fen peat column for 14C analysis with a Macaulay peat corer. In some cases, samples were also taken from the basal peat that consisted of organic limnit sediments, deposited in ponds, and from highly humified peats characteristic of modern-day prairie marshes. The samples were submitted for dating at the radiocarbon laboratories of Brock University (BGS), Saskatchewan Research Council (S), or Alberta Environmental Center, Vegreville (AECV). The reported dates are uncorrected years before 1950 (yr B.P.). Plant fragments from the dated peat were

CANADIAN

HOLOCENE

identified under a dissecting microscope. Further details of macrofossil analysis are found in Kubiw (1987) and Nicholson (1987). The present climatic records of stations located within 20 km of the southern limit of fen development and the 6000 yr B.P. fen isopleth were compiled from the current climate normals (Canadian Climate Program, 1982) to show mean annual growing degree days (5°C base), mean July temperature, mean annual precipitation, and the mean thermal season aridity index (TSAI). The aridity index (based on Tukhanen, 1980) was derived as follows:

TSAI

Mean annual precipitation (mm) = Mean April-October temperature (“C)

’

RESULTS We emphasize the initiation of rapid peat accumulation. This peat was deposited in fens in which the main peat-forming plants were Carex spp. and brown mosses of the genera Drepanocladus, Calliergon, Scorpidium, Meesia, and Tomenthypnum, as shown by macrofossil analyses. This peat accumulated either directly on mineral soil or was underlain by 5-30 cm of highly humilled marsh peat that was mixed with mineral soil particles. Some fen peat deposits are underlain by organic limnic sediment, composed of pasty detrital material, with a larger proportion of mineral soil grains and small mollusk shells. Such limnic peat is found in small ponds throughout the present-day grasslands. Basal peat dates are available from 54 localities across west-central Canada (Tables 1 and 2; Fig. 1). Most of the dates (49) were obtained from cores taken by the authors, the rest (13 dates) were from the literature. Basal fen peat that accumulated over limnit peat was dated at 18 locations (Table 2)

PEATLANDS

233

and in some cases the age of the underlying basal limnic peat was also determined. At two locations, the age of the basal marsh, below the fen, was determined (Table 2, Sites 51 and 52). The geographical distribution of the basal fen dates across west-central Canada is shown in Fig. 2. The occurrence of Mazama ash (dated between 6600 and 6000 yr B.P.; Zoltai, 1989) in peat and in limnic peat is also plotted (Fig. 2). These data indicate that the oldest basal fen dates (>8 100 yr B.P.) are consistently found in the foothills and along the eastern slopes of the Rocky Mountains. The isopleth separating the XOOO yr B.P. from younger basal fen peat ages is located at approximately 54”30’N latitude, extending almost due east from the Swan Hills, Alberta across Saskatchewan and Manitoba. Two basal fen dates in the Peace River area in northwestern Alberta, an area in which aspen parkland vegetation now exists, are less than 6000 yr B.P., indicating conditions similar to those in the main grassland area. The approximate extent of present peatland vegetation along the prairie margin, based on the occurrence of Picea mariana and Lark faricina (Zoltai, 1975), is shown in Fig. 2. The southern extent of fens in Alberta compares well with floristic data based on the distribution of the two major peatland trees (D. H. Vitt, unpublished data). The ages of basal fen peat are youngest near the margin of modem fen occurrence, and the basal fen ages become progressively older with increasing distance from the prairie margin. The present climate was determined along the present fen-grassland boundary (Table 3a) and along the 6000 yr B.P. fen isopleth (Table 3b). Climatic variability along this boundary was accounted for by grouping the stations into three elevatioual regions as follows: (1) a western section, the Alberta Plain (Bostock, 1970), generally above the 2000-ft (610-m) contour; (2) a middle section, the Saskatchewan Plain,

234

ZOLTAI TABLE

Location 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 34. 36. 37. 39. 54.

52‘27’N 52”51’N 52”50’N 53”20’N 55”03’N 54’45’N 56”ll’N 55=‘08’N 53”33’N 54”37’N 54’58’N 55”54’N 56”12’N 54”38’N 55”54’N 54”OO’N 54”43’N 53”58’N 55”OS’N 54”51’N 54”36’N 54”18’N 54”16’N 53”28’N 53”18’N 52”22’N 51”25’N 49”24’N 55“09’N 54”22’N 54”55’N 54”36’N 52”53’N 54”lO’N

& 115”12’W L 116”28’W & 116”51’W & llP28’W & 117YlO’W & lls”52’W & 115”2O’W & 114”Ol’W 6’1, 1139O’W & 112”09’W & 112”OO’W L 112”07’W t lll”31’W &c llo”43’W & lOs”35’W & 105“52’W & lOs”28’W & 104”52’W & lOl”36’W & 98”3O’W & lOl”26’W L lOl”16’W & 99’09’W h lOl”29’W L 99Y6’W & 102”37’W & %“53’W & 95”22’W L llS”43’W t 115”06’W JL 103”23’W & 98”34’W & 99=08’W & lll”28’W

u A. B. Beaudoin

(1989).

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VITT

I. 14C DATES OF BASAL FEN PEAT OVER MINERAL Depth of sample (cm)

Radiocarbon age (Yr)

331-337 352-357 361-368 502-510 220-23 1 548-554 41@21 224-229 267-274 236241 288-294 203-218 192-200 180 42M25 320-325 373-379 239-245 329-334 332-338 209214 271-279 238-243 332-337 278-284 19&195 459-465 350-355 135-140 180

6380 f 8600 f 8480 f 8400 k 4740 2 8940 * 5960 -+ 6800 f 3870 + 2900*160 69005240 7170 k 7510 f 3400 + 6855 a 3470 f 6240 2 3750 2 4550 2 7600 * 2970 * 4640*100 4900 2 4550 k 4180 -t 3415 ? 4340 * 3685 2 6770 5 4850 5 5900280 4500 2 4670 -+ 4350 *

260 150 195-200 Personal

200 250 190 270 1Ofl 240 160 150 80

130 110 160 160 230 165 120 100 150 100 loo 100 120 165 155 240 440 130 120 130 70

SOIL

Radiocarbon lab. No. BGS 768 BGS 772 AECV 206C BGS 775 AECV 926C BGS 778 BGS 786 BGS 789 AECV 18C BGS 784 BGS 780 AECV 178C AECV 182C AECV 97C S-2582 S-2575 S-2578 S-2573 BGS 859 BGS 870 BGS 864 BGS 856 BGS 868 BGS 852 BGS 854 S-2570 S-2473 S-2468 AECV 468 GSC-752 s-1065 GSC-1958 GSC-410 WIS-280

Source This paper This paper Kubiw et al., 1990 This paper This paper Zoltai et al., 1988 This paper This paper This paper Zoltai et al., 1988 Zoltai et al., 1988 Nicholson and Vitt, 1990 This paper Kubiw et al., 1990 Zoltai et al., 1988 This paper This paper Zoltai et al., 1988 Zoltai et al., 1988 This paper Zoltai et al., 1988 Zoltai er al., 1988 Zoltai et al., 1988 Zoltai et al., 1988 Zoltai et al., 1988 Zoltai et al., 1988 Zoltai et al., 1988 Zoltai et al., 1988 A. B. Beaudoin” Lowdon and Blake, 1968 Schreiner, 1983 Lowdon et al., 1977 Klassen, 1%7 Bender et al., 1969

communication.

generally above the lOOO-ft (305-m) contour; and (3) an eastern section, the Manitoba Plain, generally below the lOOO-ft (305 m) contour. Stations along the 6000 yr B.P. fen isopleth were divided into corresponding sections. Climatic data (Table 3a) show that considerable differences exist in temperatures from east to west along the present-day fen limit. The summers are cooler, but the winters warmer, in the western section than in the middle and eastern sections. The warmer summers result in higher growing

degree days in the east than in the west. Precipitation is the lowest in the Saskatchewan Plains section. However, the aridity index shows only a 5.2-point spread between the most arid Saskatchewan Plains section (40.0) and the least arid Alberta Plains section (45.2). DISCUSSION Temporal patterns of initial fen peat accumulation indicate that fens were not present south of about 54”30’N latitude and

CANADIAN TABLE

2. l’C DATES OF BASAL

HOLOCENE

FEN PEAT ABOVE LIMNIC Depth of sample

(cm)

Location 30. 49”49’N & Same core: 31. 50”04’N .!k Same core: 32. 50’35’N & Same core: 33. 51”57’N & 35. 52’31’N & Same core: 38. 52”28’N & 40. 50”40’N & Same core: 41. 51’04’N & 42. 53’4O’N & Same core: 43. 54”28’N & 44. 54”15’N & 45. 54”49’N & 46. 55”ll’N & 47. 55=20’N & 48. 55”32’N & 49. 54’53’N & Same core: 50. 54’33’N & 51. 56’17’N & Same core: 52. 49”39’N & 53. 52”54’N dc a Dated

95’18’W basal limnic 95’33’W basal limnic 95”27’W basal limnic lOO”58’W lOl”15’W basal limnic lOl”2O’W 114’33’W basal limnic 115‘03’W 112’51’W basal limnic 107”51’W lOY57’W 105’33’W 105”2O’W 104’55’W 104’48’W 102”05’W basal limnic 99”47’W 117”2O’W basal limnic %“19’W” 99?5’W’

material

was marsh

peat peat peat

peat

peat

peat

205-210 470476 172-177 230-236 390-395 590-596 238-246 17&175 205-210 213-220 640 930 50 18&187 552-564 360-365 275-28 1 485-490 360-366 360-365 545-55 1 308-314

peat

peat

355-360 130-132 171-173 235-240 227-233

peat beneath

PEAT, WITH

Radiocarbon age (yr) 3240 4980 3210 5400 4275 6120 2300 5140 6670 4280 8220 18,400 1140 2020 6170 4215 5215 7400 8010 6405 5270 5975 7255 6500 4510 6880 7670 7600

235

PEATLANDS

+ f + 2 2 + 2 + -+ f. 2 -c 2 k + k + f f k -t * f f f f + +

SOME BASAL

Radiocarbon lab No. 235 270 130 170 255 310 215 75 70 140 80 1090 70 230 190 175 140 170 170 255 205 210 250 150 70 85 190 110

S-2466 S-2467 S-2469 S-2470 S-247 1 S-2472 S-2477 WIS-308 WIS-271 s-2479 GSC-2851 GSC-2670 Beta-1282 AECV 442C AECV 441C S-2584 S-2574 S-2579 S-2576 S-258 1 S-2577 S-2571 S-2572 BGS 866 WIS-311 WIS-274 S-2465 BGS 858

LIMNIC

PEAT DATES

Source Zoltai et al., 1988 Zoltai et al., 1988 Zoltai et al., 1988 Zoltai et nl., 1988 Zoltai et al., 1988 Zoltai et al., 1988 This paper Nichols, 1%9 Nichols, 1%9 This paper Lowdon and Blake, Lowdon and Blake, MacDonald, 1982 This paper This paper This paper This paper Zoltai et al., 1988 Zoltai et al., 1988 This paper This paper Zoltai et ul., 1988 Zoltai et OZ., 1988 This paper Bender er al., 1%9 Bender et al., 1%8 This paper This paper

1979 1979

fen peat.

east of the foothills of the Rocky Mountains prior to 6000 yr B.P. in west-central Alberta. Basal dates on limnic and marsh peat within this area show that ponds and marshes did exist, as they do in the presentday prairie. The extent of ponds was probably restricted. Small lakes did not fill with water until 6000 to 5000 yr B.P. in southeastern Manitoba, as suggested by basal limnic peat dates (Sites 30, 31, and 32). North and west of the 6000 yr B.P. fen line, fens were present at least 3000 years earlier. The oldest basal fen peat dates are from the foothills and eastern slopes of the Rocky Mountains, generally above the 1067-m (3500-ft) contour. Temporally, there is a tendency for the initiation of fen

peat accumulation to become progressively younger south of the 6000 yr B.P. line. The present fen limit was reached between 3500 and 2000 yr B.P. Fen peat development in northern Minnesota, south of the study area, began about 2700 yr B.P. (Griffin, 1977), although prairie marshes began forming about 3100 yr B.P. Janssens et al. (1990) reported major fen peat accumulation only after 5000 yr B .P. in northern Minnesota. The 6000 yr B.P. fen limit follows the 54”30’ N parallel, with small local deviations. The northern extent of grasslands at 6500 yr B.P. also follows this line, but dips farther south in Manitoba (Ritchie, 1976). According to Ritchie (1976), boreal forest

236

ZOLTAI

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VITT

SASKATCHEWAN

FIG. 1. Location of 54 sites with 14C dated basal dates. Site numbers are as in Tables 1 and 2. Resent-day vegetation zones are adapted from Rowe (1972). (WI Major cities.

persisted east of Lake Winnipeg, although this may reflect a lack of data from that area. A pollen study in adjacent Ontario suggests a vegetation of open, grassy Pinus banksiana-Pop&s tremuloides woodland that terminated about 3600 yr B.P. (McAndrews, 1982). Peatlands existing north and west of the 6000 yr B.P. isopleth were also affected by the Holocene climatic change. Kubiw et al. (1990) reported accumulation of limnic peat deposits around Muskiki Lake in the Rocky Mountain Foothills prior to 9000 yr B.P., with fen peat initiation about 9000 yr B.P. Extensive paludilication of this site began about 8000 yr B.P. and pattern formation within the fen began about 5000 yr B.P. Macrofossil evidence suggests that a marked vegetation change indicating drier conditions took place between 7500 and 5000 yr B.P. in the portion of the peatland influenced by the associated lake.

Although the earliest peat accumulation surrounding a small lake in northeastern Alberta began at 8200 yr B.P., extensive regional paludification was initiated about 6000 yr B.P. (Nicholson and Vitt, 1990). In the following 3000 years the entire peatland of about 7 km2 was paludified. Landform development, including bog islands, watertracks, and forested fens, occurred gradually, beginning about 5000 to 4500 yr B.P. Thus, in areas to the north and west of the 6000 yr B.P. fen isopleth, peat accumulated via terrestrialization surrounding small lakes before about 6000 yr B.P. Only after 6000 to 5000 yr B.P. did extensive paludification and landform development take place. Associated with complex landform development is the succession of many peatlands to a Sphagnum-dominated, acidified bog ecosystem. In central Alberta, north of the 6000 yr B.P. isopleth, the presence of Sphagnum is dated about 4500 to

CANADIAN

HOLOCENE

237

PEATLANDS

FIG. 2. t4C dates of basal fen peats. Dotted line is the southern limit of fens; solid line is the southern fen limit at 6000 yr B.P. Line with “?” delimits a possible extension in western Alberta. (0) Basal fen peat <6000 yr B.P.; (0) basal fen peat >6000 yr B.P.; (A) Mazama ash present in limnic peat; (A) Mazama ash present in fen peat. Numbers are basal fen peat ages to nearest 1000 yr B.P.

4400 yr B.P., whereas in eastern Alberta, just north of the isopleth, Sphagnum appears between 2200 and 560 yr B.P. (S. C. Zoltai, unpublished data). Thus, in fens that were initially dominated by brown moss, conversion to an acidified, Sphagnumdominated system was delayed until the TABLE

Section

No. of stations

3. PARAMETERS Mean growing degree days

present-day climatic and hydrologic conditions became prevalent. The absence of fens in the expanded Holocene grassland area implies that the extreme water table fluctuations presently inhibiting the development of fens in the prairies also inhibited fen development at that OF CURRENT

CLIMATE

Mean July temperature CC)

Mean annual precipitation (mm)

Mean thermal season aridity index

(a) Climatic stations in sections along the southern-most fen occurrence (with SE) Alberta Plain 9 1339 f 17 16.2 k 0.1 468 f 11 45.2 f 1.2 Saskatchewan Plain 12 1458 2 26 17.3 f 0.1 422 + 10 40.0 + 1.1 Manitoba Plain 1.5 1574 2 21 18.4 2 0.1 4% + 12 43.8 + 0.9 Alberta Plain Sakatchewan Plain Manitoba Plain

(b) Climatic stations in sections along the 6000 yr B.P. fen limit (with SE) 9 1252 f 25 15.8 + 0.6 531 + 11 4 1243 + 16 16.8 f 0.2 481 % 12 5 1255 f 34 17.4 f 0.3 473 f 24

53.1 + 1.0 51.5 ” 2.3 51.1 + 3.8

238

ZOLTAI

time. The same climate that now prevents fen development in the prairies may have prevailed then. It follows that the climate at the margin of present-day peat development may be comparable to the climate at the Holocene limit of peat development. Acceptance of this postulate permits an estimate of the minimum change in climate at the present fen distribution limit, by subtracting the modem climatic parameters at the 6000 yr B.P. fen limit (Table 3b) from the corresponding climatic data of the modern fen limit. The differences can be expressed as percentage change, either greater (+) or lower (-) at 6000 yr B.P. than at present (Table 4). These comparisons show that although the mean July temperatures were only slightly higher 6000 yr B.P. than at present, the growing degree days were considerably higher (6 to 20% higher). This was possibly the consequence of a longer growing season, as well as somewhat higher summer temperatures. Precipitation was generally lower 6000 yr B.P. than at present (about 19% lower on the Saskatchewan Plain, but about 5% higher in Manitoba). Higher growing-season temperatures combined with lower precipitation resulted in increased aridity. The aridity index was much lower in all sections, indicating greater aridity by 17 to 29%. These estimates agree with those derived drom pollen studies. Ritchie (1983) estimated that mean July temperatures in the middle Holocene were 18” to 2 1“C in central Manitoba, a rise of about 2°C. He also estimated that the effective precipitation was

TABLE

4. DIFFERENCE FEN LIMIT,

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VITT

10 to 20% less than at the present. Although the term “effective precipitation” was not defined, it appears to be an estimate similar to the aridity index used here and intended to indicate the ecologically effective precipitation. CONCLUSIONS

Wetland distribution across the western interior of Canada has dramatically changed over the past 10,000 years. Fens and the accumulation of extensive peat were restricted to the Rocky Mountain foothills and north of about 53”30’N in early Holocene time. In the middle and late Holocene (~6000 yr B.P.), fens expanded southward to their present distribution. During this time, the decrease in aridity seems to have been an overriding climatic factor, controlling the accumulation of peat and the distribution of peatlands. The changes in the distribution of peatlands during the Holocene gives an indication of the response of this large segment of the landscape to climatic changes. This information can be used to anticipate changes in the wetland ecosystems due to any future climatic changes. ACKNOWLEDGMENTS This research was supported in part by Grant A6390 from the Natural Sciences and Engineering Research Council to D. H. Vitt. We thank Dr. Charles Schweger for critical comments on the manuscript and Dennis Gignac for ideas on climatic indices.

IN CLIMATIC PARAMETERS BETWEEN THE PRESENT FEN LIMIT AND THE 6000 B.P. EXPRESSED AS PERCENTAGE OF PRESENT CLIMATIC PARAMETERS

Section

Growing degree days

Mean July temperature (YY)

Mean annual precipitation

Thermal season aridity index

Alberta Plain Sakatchewan Plain Manitoba Plain

+87 or +6.5% +215 or + 14.7% + 324 or + 20.6%

+0.4 or +2.5% +0.5 or +2.% + 1.0 or +5.4%

-63 or - 13.5% - 59 or - 14.0% +23 or +4.6%

-8.3 or - 18.4% - 11.5 or -28.8% -7.3 or - 16.7%

CANADIAN

HOLOCENE

REFERENCES Adams, G. D. (1988). Wetlands of the prairies of Canada. In “Wetlands of Canada” (C. D. A. Rubec, Co-ordinator), pp. 156198. Polyscience, Montreal. Bender, M. M., Bryson, R. A., and Baerreis, D. A. (1!%8). University of Wisconsin radiocarbon dates V. Radiocarbon 10,413-418. Bender, M. M., Bryson, R. A., and Baerreis, D. A. (1969). University of Wisconsin radiocarbon dates VI. Radiocarbon 11, 228-235. Bostock, H. S. (1970). Physiographic subdivisions of Canada. In “Geology and economic minerals of Canada” (R. J. W. Douglas, Ed.), pp. 11-30,5th ed. Geological Survey of Canada, Economic Geology Report No. 1. Canadian Climate Program. (1982). Canadian climate normals 1951-1980. Vol. 2, Temperature; Vol. 3, Precipitation; Vol. 4, Degree days. Atmospheric Environment Service, Downsview, Ontario. COHMAP Members, (1988). Climatic changes of the last 18,008 years: Observations and model simulations. Science 241, 1043-1052. Damman, A. W. H. (1979). Geographic patterns in peatland development in eastern North America. In “Classification of Peat and Peatlands” (E. Kivinen, L. Heikurainen, and P. Pakarinen, Eds.), pp. 42-57. Proceedings of the Symposium of the International Peat Society, Hyytiala, Finland. Deevey, E. S., and Flint, R. F. (1957). Postglacial Hypsithermal interval. Science 125, 182-W. Dyck, W., Lowdon, J. A., Fyles, J. G., and Blake, W., Jr. (1966). “Geological Survey of Canada Radiocarbon Dates V.” Geological Survey of Canada, Paper 66-48, 32 p. Forester, R. M., Delorme, L. D., and Bradbury, J. P. (1987). Mid-Holocene Climate in northern Minnesota. Quaternary Research 28, 263-273. Griflln, K. 0. (1977). Paleoecological aspects of the Red Lake Peatland, northern Minnesota. Canadian Journal ofBotany 55, 172-192. Janssens, J. A., Hansen, B. C. S., Glaser, P. H., and Bamosky, C. W. (1990). Development of a raisedbog complex in northern Minnesota. In “Patterned peatlands of northern Minnesota” (H. E. Wright, Jr., B. Co&r, and N. Aasing, Eds.). Univ. of Mmnesota Press, in press. Klassen, R. W. (1%7). “Surticial Geology of the Waterhenarand Rapids Area, Manitoba.” Geological Survey of Canada, Paper 66-36, 6 p. Kubiw, H. J. (1987). “The Development and Chemistry of Muskiki and Marguerite Lake Peatlands, Central Alberta.” Unpublished MSc. Thesis, University of Alberta, 140 p. Kubiw H, Hickman, M., and Vitt, D. H. (1990). The developmental history of peatlands at Musk&i and Marguerite lakes, Alberta. Canadian Journal ofBotany, in press. Kutzbach, J. E., and Street-Perrott, F. A. (1985). Mi-

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