Dale H. Vitt

The relationships of vegetation to surface water chemistry and peat chemistry in fens of Alberta, Canada

The relationships between vegetation components, surface water chemistry and peat chemistry from 23 fens in boreal Alberta, Canada, substantiate important differences along the poor to rich fen gradient. Each of the three fen types have their own characteristic species. The extreme-rich fens are characterized by Calliergon trifarium, Drepanocladus revolvens, Scirpus hudsonianus, S. cespitosus, Scorpidium scorpioides, and Tofieldia glutinosa. Moderate-rich fens are characterized by Brachythecium mildeanum, Carex diandra, Drepanocladus vernicosus, D. aduncus, and D. polycarpus. Poor fens are characterized by Carex pauciflora, Drepanocladus exannulatus, Sphagnum angustifolium, S. jensenii, and S. majus. Moderate-rich fens have fewer species in common with poor fens than with extreme-rich fens, while species richness is highest in the moderate-rich fens and lowest in poor fens. Variation in vascular plant occurrence appears to be more associated with nutrient levels, while bryophytes are more affected by changes in acidity and mineral elements. Based on chemical criteria, the three fen types are clearly separated by surface water pH, calcium, magnesium, and conductivity, but are less clearly differentiated by the nitrogen and phosphorus components of the surface waters. Moderate-rich fens are chemically variable both temporally and spatially, whereas poor fens and extreme-rich fens are more stable ecosystems. Whereas components of alkalinity-acidity are the most important factors that distinguish the three fen types in western Canada, nutrient concentrations in the surface waters generally do not differ appreciably in the three fen types.

Fossil carbon/nitrogen ratios as a measure of peat decomposition

Net accumulation rates of carbon in a 9000 calendar year record of Sphagnum fuscum peat in western boreal Canada range from 13.6 to 34.9 g.m-2 yr-1. The depth vs. age curve is slightly convex due to generally declining net productivity at the site. Fossil carbon/nitrogen ratios of bulk Sphagnum fuscum peat and its components are used to calculate the rate and total amount of decay in the deeper anoxic peat deposits. The pro- portional rate of decay in the catotelm of the peatland declines linearly over time. Carbon loss from the catotelm is estimated at 50% after 1700 calendar years and 65% after 7500 calendar years. Carbon has been added to the catotelm at an average rate of 28.0 g.m-2*yr-1 over the last 1174 years, whereas, at present, the cumulative loss of carbon over the entire catotelm is 19.4 g.m-2*yr-1. The peatland continues to represent a sink for carbon.

Boreal Peatland Ecosystems

1 Peatlands and the Boreal Forest 2 Functional Characteristics and Indicators of Boreal Peatlands 3 The Postglacial Development of Boreal Peatlands 4 The Role of Sphagnum in Peatland Development and Persistence 5 Peatland Fauna 6 The Role of Fungi in Boreal Peatlands 7 Decomposition in Boreal Peatlands 8 Primary Production in Boreal Peatlands 9 Carbon in Boreal Peatlands 10 The Nitrogen Cycle in Boreal Peatlands 11 Phosphorus in Boreal Peatlands 12 Sulfur Cycling in Boreal Peatlands: From Acid Rain to Global Climate Change 13 The Hydrology of Boreal Peatlands 14 Modeling Ecosystem Processes and Peat Accumulation in Boreal Peatlands 15 Forestry and BorealPeatlands 16 Disturbance in Boreal Peatlands 17 Restoration of Degraded Peatlands 18 Boreal Peatland Ecosystems: Our Carbon Heritage

Disequilibrium response of permafrost in boreal continental western Canada to climate change

In the boreal forest of continental western Canada, permafrost is restricted toSphagnum-dominated peatlands on which air photo interpretation reveals the occurrence of five types of surface physiography. Concentrated in the northern part of the boreal forest, permafrost is present in peat plateaus with and without collapse scars. In the southern part of the boreal forest, continental bogs dominate, representing ombrotrophic peatlands that have never contained permafrost. In the midboreal zone, internal lawns are present in bogs and in fens. These internal lawns do not presently contain permafrost but did in the recent past, representing degradation of permafrost since the Little Ice Age. Evaluation of the distribution of these peat landforms indicates that today 30% of bogs contain permafrost at the −0.4 °C isotherm and 50% of bogs contain permafrost at the −1.2 °C isotherm, whereas in the past, 30% of bogs contained permafrost at the −1.4 °C isotherm and 50% of bogs contained permafrost at the −2.3 °C isotherm. Although spatial degradation has occurred with a shifting of permafrost northwards in response to warming since the Little Ice Age, permafrost cover has increased in any given area where present-day temperatures are between 0.5 and −3.5 °C.

Canadian wetlands: Environmental gradients and classification

The Canadian Wetland Classification System is based on manifestations of ecological processes in natural wetland ecosystems. It is hierarchical in structure and designed to allow identification at the broadest levels (class, form, type) by non-experts in different disciplines. The various levels are based on broad physiognomy and hydrology (classes); surface morphology (forms); and vegetation physiognomy (types). For more detailed studies, appropriate characterization and subdivisions can be applied. For ecological studies the wetlands can be further characterized by their chemical environment, each with distinctive indicator species, acidity, alkalinity, and base cation content. For peatlands, both chemical and vegetational differences indicate that the primary division should be acidic, Sphagnum-dominated bogs and poor fens on one hand and circumneutral to alkaline, brown moss-dominated rich fens on the other. Non peat-forming wetlands (marshes, swamps) lack the well developed bryophyte ground layer of the fens and bogs, and are subject to severe seasonal water level fluctuations. The Canadian Wetland Classification System has been successfully used in Arctic, Subarctic, Boreal and Temperate regions of Canada.

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

Abstract Dates of basal fen peat at 52 locations across west-central Canada indicate that peat deposition began 6000 yr B.P. basal fen peat parallels the foothills of the Rocky Mountains, and extends eastward along 54°30′ north latitude. The absence of >6000 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 modern 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 29%) aridity than at present.

Organic matter accumulation, peat chemistry, and permafrost melting in peatlands of boreal Alberta.

Abstract In the discontinuous permafrost zone of boreal western continental Canada, permafrost is limited almost exclusively to ombrotrophic peatlands. Permafrost in peatlands recently has been degrading and continues to degrade at its southern limit across western Canada, with no evidence of regeneration. The melting of permafrost could have dramatic effects on organic matter accumulation, organochemical properties, and nutrient status in peatlands. Our objectives are to quantify differences in peat chemistry (i.e., concentrations of organic fractions, N, P, and S) and rates of organic matter accumulation over the past 200 years between a site with permafrost, a site with degraded permafrost (internal lawn), and three sites with no evidence of permafrost since the last glaciation (continental peatlands: two bogs and one poor fen). Results indicate that peat chemistry may differ according to the presence, absence, or degradation of permafrost. Recent rates of organic matter accumulation follow similar trends over the past 100-200 years in the permafrost and continental bogs; however, net rates of organic matter accumulation are accelerated by 60% in the internal lawn. As decomposition in peatlands is influenced by nutrient limitations and organic matter quality, peat chemistry is likely to be a critical factor in the carbon balance response of boreal peatlands to climate change.

Patterns of bryophyte diversity in peatlands of continental western Canada

In continental western Canada, 62% of the 110 species found in 96 peatlands occur in Sphagnum-dominated bogs and poor fens, whereas 71% occur in brown moss-dominated rich fens. Alpha (site) diversity is remarkably uniform over the bog-rich fen gradient. Gamma (landscape) diversity is highest in extreme-rich fens, which are the most variable of the five peatland types surveyed. Species richness at the site level is most highly correlated with habitat heterogeneity. Climatic factors are not as important; however, habitat heterogeneity (46%) and temperature (15%) together explain 61% of the variation. When the five peatland types are examined individually, species richness in poor fens increases with pH, in extreme-rich fens decreases with pH, and in peat plateaus, continental bogs, and moderate-rich fens remains relatively constant regardless of pH. Peat plateaus consistently have greater species richness than continental bogs due to limited carpet and pool habitat heterogeneity in the latter. Twenty-five percent of the species were found only once; these species are considered rare in the region. Sixty percent of these occurred only in extreme-rich fens. Habitat heterogeneity, plus pH or temperature in some peatland types, can be effectively used to predict site biodiversity. Patterns of species richness have long been of interest to biogeographers. Attempts to explain these patterns of species occurrence have been varied, ranging from those that are historically oriented (Fischer 1960) to those that are equilibrial and argue that richness patterns are attributable to current conditions (Rosenzweig 1975). Among processes that have been hypothesized to account for richness patterns are productivity, habitat harshness, climatic stability, interspecific competition, and habitat heterogeneity. Peatlands are unique ecosystems that accumulate carbon, as peat, due to unequal rates of plant production and decomposition. Peatlands can be easily separated from non-peat-forming ecosystems based on hydrological and physiographic criteria, and they posess a largely unique bryoflora. Within peatlands, there exist strong gradients in ecosystem age, productivity, stability, and habitat heterogeneity, and peatlands occur under a diversity of regional climates. Peatlands have been considered by many to be stressed ecosystems and in general have relatively low species richness when comparisons that utilize only vascular plants are made to other habitats. Based on hydrology, peatlands can be classified either as bogs ombrotrophic systems, or fens-minerotrophic systems. Wheeler (1993) has compared species richness between these two hydrological types in Britain and found 464 vascular plants and 189 bryophytes in fens, totalling 653 species, whereas in bogs he found only 109 vascular plants and 84 bryophytes with a total of 193 species. Clearly fens have more species than bogs; however, this is an unequal comparison. Fens and bogs are hydrological units, not vegetational units. When peatlands are classified on the basis of vegetation, four types have long been recognized (Sj6rs 1952; Vitt & Chee 1990). In western Canada, where permafrost can have a strong influence, bogs can be divided into two types based on vegetation, namely those largely underlain with permafrost, termed peat plateaus, and those without permafrost called continental bogs (Belland & Vitt 1995). Fens can be divided into three types, namely poor fens, moderate-rich fens (which some incorrectly term intermediate fens), and extreme-rich fens. Thus in continental western Canada, the comparisons of species richness need to be made using five vegetation types, not two peatland hydrological types. Three of the five vegetation types are Sphagnum-dominated (peat plateau, continental bogs, and poor fens) whereas the other two are brown-moss dominated (moderateand extreme-rich fens). When DuReitz (1949) originally proposed that fens can be divided into what he termed poor fens and rich fens, he based his terminology of poor and rich on the number of indicator species present in the fen. Poor fens have fewer indicator species than do rich fens. If this indicator species concept is continued along the bog-fen gradient to bogs, then sup0007-2745/95/218-227

Water and peat chemistry comparisons of natural and post-harvested peatlands across Canada and their relevance to peatland restoration

1.15/0 This content downloaded from 157.55.39.100 on Wed, 06 Jul 2016 05:30:35 UTC All use subject to http://about.jstor.org/terms 1995] VITT ET AL.: PEATLAND DIVERSITY 219 posedly bogs have the least number of indicator species. These indicator species concepts have often been misapplied to chemical conditions and to overall species richness. Hence, many researchers have considered rich fens to have greater species richness than poor fens based on an incorrect interpretation of the concepts of rich and poor. Also, these apparent patterns in overall plant species richness are often based only on the vascular plant component, excluding bryophytes. Environmental factors important to bryophytes differ from those important to vascular plants. Vitt and Chee (1990) used multivariate methods to suggest that whereas bryophyte patterns largely follow the gradients of acidity and alkalinity, vascular plant patterns tend to follow nutrient gradients (especially nitrogen and phosphorus). It might be expected that species richness patterns of these two groups of plants also show different patterns. This is evident along gradients of elevation and latitude (Vitt 1991), wherein bryophyte diversity increased along elevation gradients and remained relatively stable along latitudinal ones. Although Glaser (1992) has recently examined vascular plant diversity in bogs at a regional scale in eastern North America, no one has examined the species diversity patterns of bryophytes along the bog-fen gradient using a comprehensive regional data set, and no one has suggested why patterns found in these peatlands might occur as they do. Our objectives here are to answer the following questions: 1) How does bryophyte species richness of a landscape (i.e., gamma diversity) vary along the bog-rich fen gradient? 2) Does bryophyte species richness correlate with environmental factors considered important in peatland classification? 3) How does bryophyte species richness at the site level (i.e., alpha diversity) vary when bogs, poor fens, and rich fens are compared? 4) Can bryophyte species richness be predicted using appropriate factors?

Patterns of retention and utilization of aerially deposited nitrogen in boreal peatlands

Water and peat chemistry comparisons of four post-harvested and neighboring, undisturbed peatlands across Canada show that harvesting alters chemical conditions. Commercial harvesting removes the surface peat and exposes layers farther down the peat deposit. The newly exposed peat layers that were formed in earlier developmental stages of the peatland can be more minerotrophic and/or more variable in chemical composition than undisturbed bog peat. All the harvested sites were originally bogs. Only one site, which had minimal peat removed, presently has chemical conditions somewhat similar to the original surface, with low elemental levels typical of bogs. Two sites are now chemically similar to poor fens and one site is similar to a moderate-rich fen. Levels of sodium, potassium, calcium, magnesium, sulphate and chloride in three of the harvested sites are higher than normal values found in natural, unharvested bogs, and result from the exposure of fen peat. Higher levels of ammonium-nitrogen and nitrate-nitrogen in the peat and water of all the harvested sites are present, with higher ammonium associated with wetter sites and higher nitrate levels associated with drier sites.