Jan A. Janssens

Multiple limiting gradients in peatlands: A call for a new paradigm

Peatlands often have readily apparent gradients of plant species distributions, biogeochemistry, and hydrology across several spatial scales. Many inferences have been drawn about the colinearity of these gradients, and these assumptions have become ingrained in the terminology that describes and classifies peatlands. We review the literature and present some of our own data that show that many of these inferences are either wrong or correct only under a limited set of ecological conditions. We examine historical classification schemes of peatlands and, in this context, gradients of alkalinity, pH, nutrient availability for plant growth, nutrient mineralization, hydrology, and decomposition. We further suggest a strictly defined set of terms to describe separate gradients of hydrology, alkalinity, and nutrients that limit plant growth in peatlands. Specifically, we make the following suggestions concerning terminology. (1) The suffix “-trophic” should only be used when referring to nutrients that directly limit plant growth at natural availabilities (e.g., eutrophic and oligotrophic). (2) Terms such as circumneutral, moderately acid, and very acidic (or alternatively strong, intermediate, and weak) should be used to describe the pH of peatlands. (3) Ombrogenous and geogenous (or limnogenous, topogenous, and soligenous) should be used to describe the hydrology of peatlands. (4) The terms bog and fen should be defined broadly based on water/soil chemistry and dominant plant species without accompanying assumptions regarding hydrology, topography, ontogeny, nutrient availability, or the presence or absence of nondominant indicator plant species. Better yet, the generic term peatland be used when possible to avoid confusion about conditions that may or may not be present at a particular site.

THE RESPONSE OF VEGETATION TO CHEMICAL AND HYDROLOGICAL GRADIENTS IN THE LOST RIVER PEATLAND, NORTHERN MINNESOTA

SUMMARY (1) Two peat mounds have developed in the Lost River peatland of northern Minnesota. One has the chemical and physical properties of an extremely rich fen and the other has the properties of a raised bog. The two mounds are separated by a water track with poor-fen vegetation and chemistry. (2) The vegetation at Lost River can be divided into five noda that correspond to landform units: spring-fen channel, spring-fen forest, marginal swamp forest, water track, and raised bog. These vegetation types have well-defined ranges for pH and calcium concentration. (3) Ordinations of the vascular plant and bryophyte data indicate a close relationship between the vegetation and both moisture and chemical gradients. The link between vegetation and chemistry is also supported by plots of species richness vs. pH and calcium concentration in which the peak in species numbers occurs within the rich-fen range. (4) The chemistry of the surface waters at Lost River is largely determined by the mixing of alkaline groundwater with precipitation, because the entire peatland is located at least seasonally within a discharge zone for groundwater. Mixing models indicate that the amount of groundwater within the surface waters ranges from 50% in the spring-fen channels to 1 % on the raised bog. (5) The development of the two peat mounds was reconstructed from peat cores collected near the crests of the spring-fen mound and raised bog. The raised bog developed over a depression, which was first filled in with fen peat before minerotrophic sphagna invaded the site around 2625 B.P. By 2200 B.P. all fen indicator species had disappeared and the site was dominated by assemblages similar to those in the present raised bog. (6) The spring-fen mound, however, developed over a rise in the mineral substrate, which was not covered by peat until 3000 B.P. The mound was quickly colonized by Sphagnum and no fen indicators appeared until 1160 B.P. At this time the bog vegetation was replaced by a sedge fen containing assemblages similar to the present spring-fen channel. (7) This sharp reversal from bog to fen under the spring-fen mound can best be explained by the discharge of alkaline groundwater at the peat surface in sufficient quantities to convert the bog vegetation to a spring-fen channel.

Palaeoclimatic studies in South Shetland Islands, Antarctica, based on numerous stratigraphic variables in lake sediments

The hitherto longest found lake sediment sequence on Byers Peninsula, Livingston Island, South Shetland Islands, was analysed with respect to lithology, chronology, diatoms, Pediastrum, pollen and spores, mosses, mineralogy, and sediment chemistry. During the ca. 5000 year long development the sediments were influenced by frequent tephra fall-outs. This volcanic impact played a major role in the lakes history during two periods, 4700–4600 and 2800–2500 BP, but was of importance during the lakes entire history with considerable influence on many of the palaeoenvironmentally significant indicators. The large and complex data set was analysed and zonated with different types of multivariate analysis. This resulted in a subdivision of the sequence into 8 time periods and 21 variables. Redundancy analysis (RDA) of this data set, both without and with the tephra periods, and with 4–6 of the variables as explanatory environmental variables, reveal that climatic/environmental signals are detectable. The palaeoclimatic picture that emerged out of the tephra ‘noise’ suggests that the first 100 years were characterized by mild, humid conditions. This was followed by a less mild and humid climate until ca. 4000 BP when a gradual warming seems to have started, coupled with increased humidity. These mild and humid conditions seem to have reached an optimum slightly after 3000 BP. At ca. 2500 BP a distinct climatic deterioration occurred with colder and drier conditions and long seasons with ice cover. This arid, cold phase probably reached its optimum conditions at ca. 1500 BP, when slightly warmer conditions might have prevailed for a while. Except for the modern sample with rather mild climate, the last 1400 years seem to have been fairly arid and cold, and the effects of the frequent volcanic activity during this period is only vaguely seen in the records.

A Quantitative Method for Stratigraphic Analysis of Bryophytes in Holocene Peat

(1) A new method of analysing the changes in amounts of bryophytes in autochthonous peats is developed. Bryophyte concentration changes (expressed as number of fragments per 100 ml of peat) and percentages of types are calculated and presented in continuous stratigraphical diagrams. (2) A formula used to calculate Sphagnum concentrations is based on counts of Sphagnum plants, branches, and leaves. This makes it possible to present Sphagnum together with other bryophytes in the same diagrams. (3) As an illustration of the method a 3.8-m deep peat core was analysed from Red Lake Peatland, on the bed of Glacial Lake Agassiz in northern Minnesota. Peat accumulation began at this site about 3500 years ago. (4) Scorpidium scorpioides and Calliergon trifarium are the major peat formers during several recurring episodes of peat accuimulation. Seven other species of the Amblystegiaceae are recorded. One or more of six Sphagnum species dominate other periods of the accumulation. Four additional types belong to the Bryaceae, Meesiaceae, Aulacomniaceae and Polytrichaceae. (5) Five local bryophyte zones are sharply delimited in the late Holocene peat of this Red Lake Peatland site. The four lower zones reflect either changes in the water level in a non-patterned fen system or fluctuations in the size of low hummocks formed by emergent, minerotrophic bryophytes in a patterned fen. The uppermost zone indicates the formation of less minerotrophic vegetation on top of the fen peat and periodic advances of the bog margin over the fen at the coring site. (6) Bryophyte concentration data are useful in interpreting peat ontogeny and the local hydrological environment during peat accumulation. The bryophyte assemblages reflect shifts along a minerotrophic-ombrotrophic gradient of one of the dominant components of the local wetland vegetation.

Relationships of bryophytes and lichens to environmental gradients in Maine peatlands

The most important environmental gradients of Maine peatlands are geologic substrate and alkalinity. Other gradients are coastal-inland climate, moisture content of the peat, P and K concentrations, and shade. Abundance weighted means of pH, Ca, and moisture content of peat are given for the 48 most frequently occurring bryophyte and lichen species. A TWINSPAN differentiated twenty associations. Environments of the first four TWINSPAN dichotomies differed largely by pH and related variables, though Fe, %H2O, shade, microtopography, and degree of humification were also significant. A CCA with forward selection entered pH, P, Fe, Na, %H2O, shade, and a climate factor as the minimum number of variables which best account for the species variation. Bryophyte and lichen distributions are determined primarily by edaphic and hydrologic factors, which determine the kinds and amounts of mineral solutes in peat interstitial water. Two independent chemical gradients were identified: (1) the acidity-alkalinity gradient related to base cation concentrations, and (2) a gradient of Fe, Al, Mn, and Si related to shallowness of peat and inputs from granitic lithologies.

On Diettertia, an isolated mesozoic member of the Jungermanniales

Abstract The fossil genus Diettertia does in no way support a radial ancestry for all bryophytes. It is totally bilaterally organized. Diettertia is presented here as a uniquely isolated member of the Jungermanniales (suborder Diettertiineae) and we postulate that the triradial original organization of the Jungermanniales underwent rapid evolution, so that by the time Diettertia evolved, hepatics had already undergone a long and complex phylogenetic history. Only very few Mesozoic fossils belonging to the Jungermanniales are known and they are mostly highly derivative. These Laurasian records support the assumption that the early evolution of the Jungermanniales occurred in Paleozoic time in Gondwanaland and few of the primitive types ever spread into Laurasian regions.

Late Pleistocene and early holocene bryophytes from Battle Ground Lake, Washington, U.S.A.

Abstract Battle Ground Lake is located in a volcanic crater outside the limit of the last glaciation in the southern Puget Trough, Washington. Fossil bryophyte fragments extracted from sediment-cores provide information on the local vegetation between 20,000–4500 yr B.P. and complement existing interpretations based on pollen and macrofossil data. Species belonging to three ecological groups were identified. Wetland taxa and species present in exposed upper-slope habitats during the Late Pleistocene were replaced by epiphytes and forest-dwellers when the crater walls became forested in the Holocene. All the species found as fossil fragments grow in the Pacific Northwest now and most present-day phytogeographical elements of this region have a Pleistocene record.