This paper presents the biotic, sedimentary, geomorphic, and climatic history of the upper part of the Roberts Creek Basin, northeastern Iowa for the late—glacial and Holocene, and compares these records with a C—O isotopic sequence from Coldwater Cave, 60 km northwest of Roberts Creek. The biotic record (pollen, vascular plant and bryophyte macrofossils, and insects) is preserved in floodplain alluvium that underlies three constructional surfaces separated by low scarps. Each surface is underlain by a lithologically and temporally distinct alluvial fill. The highest surface is underlain by the Gunder Member of the Deforest Formation, dating from 11 000 to 4000 yr BP; beneath the intermediate level is the Roberts Creek Member, dating from 4000 to 400 yr BP; and the lowest level is underlain by the Camp Creek Member, deposited during the last 380 yr. Pollen and plant macrofossils in the alluvial fill show that a typical late—glacial spruce forest was replaced by Quercus and Ulmus in the early Holocene. This early—to—middle Holocene forest became dominated by mesic elements such as Acer saccharum, Tilia americana, Ostrya virginiana, and Carpinus caroliniana as late as 5500 yr BP; in contrast, the closest sites to the west and north were at their warmest and driest and were covered by prairie vegetation between 6500 and 5500 yr BP. After 5500 yr BP, the forest in the Roberts Creek area was replaced by prairie, as indicated by a rich assemblage of plant macrofossils, although only Ambrosia and Poaceae became abundant in the pollen record. The return of Quercus ≈ 3000 BP (while nonarboreal pollen percentages remained relatively high) indicates that oak savanna prevailed with little change until settlement time. The bryophyte assemblages strongly support the vascular plant record. Rich fen species characteristic of boreal habitats occur only in the late—glacial. They are replaced by a number of deciduous—forest elements when early—to—middle Holocene forests were present, but mosses of forest habitats completely disappear when prairie became dominant. A few deciduous—forest taxa return during the late—Holocene, when oak savanna prevailed. The C—O isotopic record from stalagmite s in Coldwater Cave indicates a relatively stable environment from ≈ 8000 to 5100 yr BP, when the δ13C values indicate a change in vegetation dominated by C3 (predominantly forest) to C4 (predominantly prairie) plants. About 4900 yr BP, the rise in 18O values indicates a temperature increase of ≈ 1.5°C. The fact that the vegetational change suggested by the δ13C values preceded the temperature increase suggests that fire may have been an important factor in converting forest to prairie. Abundant charred seeds and other plant material at Roberts Creek 4830 yr BP support this hypothesis. The 18O values remain constant from ≈ 5100 to ≈ 3000 yr BP, but the δ13C values gradually rise, indicating that soil formed under forest takes at least 2000 yr for its carbon to reach equilibrium after replacement by prairie vegetation. The return of oak to form sav...

The vascular plant and bryophyte vegetation of 50 stands in nine sites from the foothills of western Alberta were quantitatively sampled in order to determine the major vegetation gradients. These fens are mostly patterned, with pools of water (flarks), alternating with raised ridges (strings), and are minerotrophically rich. Mean calcium ion concentrations of the nine fens range between 18 and 37 ppm and mean pH values range between 6.8 and 7.9, with electrical conductivities varying from 140 to 456 μmho/cm (1 mho = 1S). One string community type, dominated by Tomenthypnum nitens, Betula glandulifera, and Larix laricina. and one flark community type, dominated by Scorpidium scorpioides, Drepanocladus revolvens, and Carex limosa, are described, with three phases recognized in the flarks. (The Scorpidium scorpioides phase is most prominent in the wettest flarks, with the Campylium stellatum – Scirpus spp. phase found in slightly drier habitats.) The water chemistry and vegetation of these rich fens compares well with similar mires described from eastern Canada and Fennoscandia. Indirect and direct gradient analysis techniques illustrate a wet–dry ecological series of bryophytes rich in Amblystegiaceae and lacking in Sphagnaceae.

A quantitative analysis of the habitats of 14 species of Sphagnum found in the Caribou Mountains of northern Alberta and a literature review are the basis for a discussion of the habitats of these species as they occur in circumboreal–subarctic regions. Despite the implication inherent in the name, the Caribou Mountains are not mountains; the formation is an extensive, elevated plateau, which is underlain by more-or-less continuous permafrost. Three habitat types predominated in our study area: an upland "treed-tundra" (which is dominant over much of the plateau) with scattered Picea mariana and a hummocky bottom layer of sphagna; rounded "thaw-pocket" depressions dominated by carpets of Sphagnum and some carices; and streams defined by a dense zone of shrubs with the narrow water channel bordered by more-or-less firm lawns of Sphagnum species. Three gradients, which are considered to have a predominant influence on the occurrence of Sphagnum species, are wet to dry, ombrotrophic to minerotrophic, and shaded to exposed. The relative importance of each of these factors varies with each species of Sphagnum. Sphagnum jensenii, S. majus, S. riparium, and S. lindbergii occur exclusively in weakly minerotrophic to ombrotrophic, aquatic habitats where populations form loose, floating carpets. Such habitats are generally not much shaded. Such species as S. angustifolium, S. teres, and S. russowii are characteristic of somewhat less moist conditions, but all have a broad amplitude along the ombrotrophic to minerotrophic gradient. However, S. angustifolium is most abundant under poorly minerotrophic conditions where there is less shade, while S. teres predominates under highly minerotrophic conditions and is more-or-less equally tolerant of shade and exposure. Sphagnum warnstorfii apparently is restricted to habitats which are highly minerotrophic, but is tolerant of both shade and exposure. The sphagna most characteristic of densely shaded, woodland habitats where there is little peat development are S. squarrosum, S. wulfianum, and S. girgensohnii. All three species generally form low mounds. Sphagnum fuscum and S. nemoreum form well-defined hummocks and are most prevalent under ombrotrophic conditions.

Concentrations of N, P, S, Na, K, Mg, Ca, Mn, Fe, Cu, Cd, Zn, Pb, Al, and AIA (acid insoluble ash) m mosses (three Sphagnum species and Tomenthypnum nitens, all hummock species) from a variety of mires, both ombrotrophic and minerotrophic, in the coastal western and central parts of Canada are considered in relation to surface water pH and concentrations of Na+, K+, Mg2+, Ca2+, Cl−, and SO42‐ Distinct west‐east concentration gradients were present for most elements in both mosses and water, but there were correlations between surface water and moss concentrations only for Ca and Mg On ombrotrophic sites and sites characterized by poor fen vegetation, wet deposition is the main source of elements in the surface water On rich fen sites, additional Ca and Mg from surrounding soils change the elemental proportions We conclude that hydrochemically the limit between poor and rich fen sites is more decisive than between bog and fen The increase in Ca may give brown mosses a competitive advantage over Sphagnum Moss concentrations of Na and Mg are the only ones decreasing inland The constancy or inland increase of moss elemental concentrations may depend on either an increasing atmospheric supply (e g Pb), differences in moss growth rates (especially N, P, and K) or site conditions related to the water regime (e g Fe and Al)

Vegetation from 133 relevés representing a broad spectrum of peatland types from the Prince Rupert area, British Columbia was divided into six relevé groups. The 210 taxa found in these relevés were classified into six species groups. In general, the species groups are related to one another along shade and height (above water level) gradients. Chemical and physiographic gradients that correlate with the relevé distribution pattern on a detrended correspondence analysis ordination are surface water chemistry, shade, and height. In particular, the major gradient influencing the first axis of the ordination is shade. The second axis of the ordination is related to a complex chemical gradient in which hydrogen ion, calcium, and sulphate are the most important components. These chemical changes are influenced by ombrotrophy. Surface water chemistry patterns show enriched ionic conditions on Graham Island (Queen Charlotte Islands), with a decrease inland. Especially important is the decrease of sodium and chloride ion. The peatlands studied include ombrotrophic bogs and soligenous fens. Raised bogs were found in basins, whereas blanket bogs occurred on gentle slopes at the most oceanic site. Pinuscontorta Loud. var. contorta is most abundant on ombrotrophic sites, whereas Chamaecyparisnootkatensis (Lamb.) Spach is dominant in soligenous fens. Soligenous poor fen, characterized by high Sphagnum abundance in lawns and forest islands and pH of 4.4–6.6, is the peatland type most frequently encountered in the study area.