One of the objectives of this study was to continue the effort started in the first phase of this project to further identify peatlands in the study area by examining the literature, using our existing collective field knowledge, and using Geographic Information System (GIS).

Introduction

Within the Adirondack Park, the Adirondack Park Agency, under the authority of the New York State Freshwater Wetlands Act and the Adirondack Park Agency Act, has the responsibility for mapping wetlands, assessing their condition, and evaluating potential threats.

The EPA-sponsored Oswegatchie/Black River Wetlands and Watershed Project: Phase I completed in 1996, focused on identifying and locating wetlands and nesting them within lake watersheds using a GIS (Roy et al. 1996). One of the goals of the Phase II Project was to find out more about wetlands potentially sensitive to anthropogenic inputs from atmospheric deposition. Some scientific literature (Tickle 1992, Gorham et al. 1984) lead us to believe that of all the wetland types peatlands, particularly poor fens and bogs, have the greatest risk of suffering adverse effects from pollution inputs via atmospheric deposition. Peatlands differ from other wetlands in their chemistry, morphology, function, and plant communities. Even the New York State Freshwater Wetlands Act identifies peatlands as significant resources and the Agency's Rules and Regulations assigns a high value to them.

With this initial direction, we set out to accomplish four objectives: 1) what defines a peatland relative to our capabilities for mapping and detecting; 2) how to recognize them in the field; 3) how to distinguish differences among peatlands types and how to classify them; 4) and how GIS could be used to locate peatlands and record information. In the next part of this chapter, we discuss some of the findings regarding peatland sensitivity to increased atmospheric deposition of acidity and nutrients, particularly nitrogen.

In the presence of favorable local hydrologic conditions, climate exerts the ultimate control for the initiation of peat development. Peatlands generally develop in climates with high humidity and low evaporation which allows water-logged conditions to develop, creating an environment without oxygen (anoxic and anaerobic). This slows the rate of plant decomposition as compared to production, allowing the peat to build-up in a basin (in-filling) or even on a slope or flat area.

The organic matter deposited comes from three main plant types: grass-like plants, particularly sedges (usually Carex spp); mosses, most often Sphagnum spp (often called peat moss); and woody plants, such as various species of shrubs and trees. The grass-like plants and moss species are usually the dominant peat-formers.

The literature is quite sparse on providing a particular depth of peat before classifying a wetland as a peatland. Crum (1988) uses a minimum depth of 30cm of accumulated peat (about 12 inches). Canada uses a peat depth of greater than 40cm (about 15.6 inches), which is close to the soil taxonomy definition of a Histosol, and considers wetlands with 30-60cm of peat as "shallow organic deposits" (Halsey et al. 1997). We chose 30cm of peat deposits as constituting a peatland after Crum (1988), which will include the shallow organic deposits as defined by Halsey et al. (1997).

Peatlands: A Classification (Objectives 2 and 3)

The literature is rife with classification schemes for peatlands, with no one system widely accepted. Researchers have also used a number of colloquial terms to describe peatland characteristics. Common in the United States are the terms "bog", "poor fen", "medium fen", and "rich fen", however, even these terms have varying definitions depending upon who uses them. Other terms are often based on landscape position, trophic status, and/or hydrology of the peatland.

Terms describing peatland origins based on landscape position include: topogenous - developing in a topographic depression; limnogenous - developing along bodies of water; soligenous - developing on slopes or mineral soils (Damman and French 1987). Several schemes exist to classify wetlands based on landscape position. In particular, Damman and French (1987) developed a scheme especially for peatlands that also assumes hydrology of- and patterning within- the peatlands. The latest scheme developed by Brinson (1993) is the Hydrogeomorphic Method (HGM). This classifies wetlands based on landscape position, and infers hydrology and nutrient status. It does not, however, deal specifically with peatlands. Only the "flats" group has a separate class for organic soil, but organic soils and, thus, peatlands can form in any of the landscape positions.

Classifications based on hydrology include: ombrotrophic - rain fed peatlands that get their nutrients solely from the atmosphere (typically called bogs); and minerotrophic or rheotrophic - peatlands that have a groundwater source for their nutrients and water. Classifications based on nutrient status similar to lakes include: oligotrophic - low in nutrients; mesotrophic - nutrient status between oligo- and eu-trophic; and eutrophic or, again, minerotrophic - those rich in nutrients. Interestingly, a key parameter in peatland ecology is acidity, yet no set of terms has been developed to reflect this. Finally, many researchers have described peatland types based on plant community associations.

Many of these terms overlap in meaning and usage. For example, ombrotrophic, oligotrophic and bog are all often used interchangeably. This can cause a great deal of confusion since review of the literature makes it clear that nutrient status and hydrology and landscape position cannot necessarily be inferred from one another (Bridgham et al. 1996). The literature even throws some considerable doubt about using plant communities, pH and Ca ion concentrations as indicators of hydrology or nutrient status, as is so often done (Bridgham et al. 1996, Moore 1997, Siegel and Glaser 1987). This makes identifying peatlands, particularly those potentially sensitive to acid deposition, quite difficult.

Plant Associations

A great deal of literature exists describing plant associations in bogs, poor fens and rich fens, often looking at the plant community over environmental gradients such as pH, conductivity and calcium ion concentrations (Lynn and Karlin 1985, Crum 1988, Gorham and Janssens 1985, Worley 1982, Malmer 1986, Damman 1977, Rochefort et al. 1990, Glaser 1983). These studies do provide valuable rules-of-thumb for what plants would likely be found where, but they should be used with some caution. Recent research has suggested that the plant community association cannot reliably predict nutrient status and hydrology (Bridgham et al. 1996, Siegel and Glaser 1987). Also, plant assemblages and plant associations reflecting an environmental gradient that occur in one region may not hold true for another region. Therefore, researchers caution against transposing such indicators of chemistry, or other environmental conditions, across regions.

With all of this in mind, we developed a field data sheet (Figure IIIA.1) for the collection of certain chemistry, plant community and watershed information. Data gathered from this field sheet will go into a database to track, at a minimum, the following: a) where peatlands occur and vegetative cover type; b) peatland landscape position; c) plant community associations for peatlands along with any pH and conductivity data.

The data sheet was developed using the National Wetlands Inventory field sheet as a template and modifying it to our specific needs. Plant codes developed by the Adirondack Lakes Survey Corporation (ALSC) have been incorporated as well as watershed information, landscape position and New York Natural Heritage Program (NYNHP) plant community types.

We used concepts from several of the classification schemes previously discussed. The terms chosen refer to landscape position only with no assumption about hydrology, patterning or nutrient status.

Data sheet fields

LANDSCAPE POSITION DESCRIPTORS:

1. lacustrine fringe - fringing a lake or pond
2. riverine fringe - fringing a river or stream
3. depression
4. slope
5. flat

The natural plant community types, based on the New York Natural Heritage Program (Reschke 1990) classification, that could possibly occur in the Adirondacks include:

OPEN PEATLANDS: sedge meadow, rich sloping fen, rich graminoid fen, rich shrub fen, medium fen, inland poor fen, perched bog, patterned peatland, highbush blueberry bog thicket, dwarf shrub bog.

FORESTED PEATLANDS: red maple-tamarack peat swamp, northern white cedar swamp, rich hemlock-hardwood peat swamp, black spruce-tamarack bog.

We intend for APA staff, ALSC staff, other interested people and possibly organized volunteers to use this field data sheet to gather information on Adirondack peatlands. From the eventual database, we hope to perhaps develop a key to peatlands, improve plant community descriptions, and encourage in-depth research into peatland nutrient status and cycles and peatland hydrology.

In previous project quarterly reports, we presented a key to peatlands in the Adirondacks. This was based on literature from Minnesota, Canada and the Adirondacks. Upon continuing to search the literature, however, it became clear that a peatland key was premature. We know so little about the plant community associations in the Adirondack Park, not to mention the hydrology, nutrient status and biogeochemistry of these wetlands. We just are not sure what the presence of certain plant communities tells us. The NYNHP probably has the best data at present for plant community descriptions and the need really lies in collecting more information about our peatlands to see what, if any, inferences can be made.

The literature did shed some light on the classification of peatlands. Several researches (Crum 1988, Shotyk 1988) used 30cm of accumulated peat (at least 20% organic matter) as the minimum necessary to classify a wetland as a peatland. Also, it seemed fairly consistent that "bogs" had low pH (usually less than 4.5) and low calcium ion concentrations (usually less than 2.0 mg/l) or low conductivity, depending upon which was measured.

Though the above literature review suggests difficulty and problems with trying to recognize, classify, and map peatlands, we still think it useful to attempt to do so. Peat accumulates under special long-term hydrology and the literature recognizes that peatlands function differently than wetlands on mineral soils, particularly regarding their biogeochemical cycles (Halsey et al. 1997, Aandahl 1974).

Figure III.A.1 Peatland field data sheet.

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In the northwestern Adirondacks, it appears that a large percentage of the wetlands could be peatlands. This could have important implications for interpreting the water chemistry data of Adirondack lakes. Halsey et al. (1997) found that when peatlands constituted greater than 40% of a lake's watershed it greatly influenced the lake chemistry. They also found that the percentage of bog versus fen in a watershed influenced the lake chemistry differently. These points alone, regardless of peatlands' sensitivity to acidic and nutrient inputs, make them important components of the landscape and of the water chemistry of a watershed. For this reason we still want to know where peatlands are located on the landscape and to attempt to classify them. This is the goal of the Field Data Sheet and incorporating the information into a GIS database. At this time, we conclude that plant community associations and some simple chemistry appear to be the best and simplest way to characterize Adirondack peatlands.

Peatlands simply cannot be identified from existing wetland maps. The wetland classification method used in the Adirondack Park (Cowardin et al. 1979) does not specifically label wetlands using traditional common names such as bog, fen, marsh, swamp, etc. Also, peatlands cannot be readily discerned from other wetlands using conventional aerial or satellite imagery because their single most defining feature, deep peat accumulations, is not discernible by remote sensing without a great deal of field verification. Other existing collateral data layers and GIS were used to attempt separation of poor fens and bogs from all the other wetlands and from other peatlands.

The method involved subsetting the wetland coverages, created and gathered as part of the Phase I mapping project, to find the wetland types likely to be peatlands. Soil associations with an organic parent material, as defined by soil taxonomy, were selected from the general soils layer and put into a shape file, creating a separate coverage. The organic soils shape file was intersected with the wetlands layer. All intersecting organic soil and wetland polygons were selected under the assumption that these were likely to be peatlands resulting in a potential peatland data layer.

Maps for six quadrangles were printed and all potential peatlands polygons were checked against high altitude infrared aerial photography, along with some field verification, to verify whether the areas selected were likely to, in fact, be peatlands. The results were somewhat mixed. The difference in minimum mapping units between the soils layer (about 40 acres or 16.2 ha) and the wetlands layer (0.10 acres or 0.04 ha) posed a problem. While all of the resulting polygons did appear to be peatlands, however, there were many peatlands, usually of small size, that were not selected.

References

• Aandahl, A.R. 1974. Preface p.xi In: Histosols: their characteristics, classification, and use. Eds. A.R. Aandahl, S.W. Bud, D.E.Hill, and H.H.Bailey. Soil Science Society of America, Madison, Wisconsin.
• Bridgham, S.D., Johnston, C.A., Pastor, J. 1995. Potential feedbacks of northern wetlands on climate change. BioScience 45(4):262-274.
• Bridgham, S.D., Pastor, J., Janssens, J., Chapin, C., and Malterer, T. 1996. Multiple limiting gradients in peatlands: A call for a new paradigm. Wetlands 16(1):45-65.
• Brinson, M. 1993. A hydrogeomorphic classification for wetlands. Technical Report WRP-DE-4. Waterways Experiment Station, Army Corps of Engineers, Vicksburg, Mississippi.
• Cowardin, L.M., Carter, V., Golet, F.C., and LaRoe, E.T. 1979. Classification of wetlands and deepwater habitats of the United States. U.S. Fish and Wildlife Service FWS/OBS-79/31, Washington, D.C., 103 pp.
• Crum, H. 1988. A focus on peatlands and peat mosses. The University of Michigan Press, 306 pp.
• Damman, A.W.H. 1977. Geographical changes in the vegetation pattern of raised bogs in the Bay of Fundy region of Maine and New Brunswick. Vegetatio 35(5):137-151.
• Damman, A.W.H. and French, T.W. 1987. The ecology of peat bogs of the glaciated northeastern United States: A community profile. U.S. Fish Wildl. Serv. Biol. Rep. 85(7.16). 100 pp.
• Glaser, P.H. 1983. Vegetation patterns in the North Black River peatland, northern Minnesota. Canadian J. of Botany 61:2085-2104.
• Gorham, E., Bayley, S., and Schindler, D. 1984. Ecological effects of acid deposition upon peatlands: A neglected field in "acid rain" research. Can. J. Fish. Aquat. Sci. 41:1256-1268.
• Gorham, E. and Janssens, J. 1992. Concepts of fen and bog re-examined in relation to bryophyte cover and the acidity of surface waters. Acts Soc. Botan. Polon. 61(1):7-20.
• Halsey, L.A., Vitt, D.H., and Trew, D.O. 1997. Influence of peatlands on the acidity of lakes in northeastern Alberta, Canada. Water, Air, and Soil Pollution 96:17-38.
• Lynn, L.M. and Karlin, E.F. 1985. The vegetation of the low-shrub bogs of northern New Jersey and adjacent New York: Ecosystems at their southern limit. Bull. Torrey Bot. Club 112:436-444.
• Malmer, N. 1986. Vegetational gradients in relation to environmental conditions in northwestern European mires. Can. J. Bot. 64:375-383.
• Moore, P.D. 1997. Bog standards in Minnesota. Nature 386:655-657.
• Reschke, C. 1990. Ecological communities of New York State. NY Natural Heritage Program, NYSDEC, Latham, New York. 96pp.
• Rochefort, L., Vitt, D.H., and Bayley, S.E. 1990. Growth, production and decomposition dynamics of Sphagnum under natural and experimentally acidified conditions. Ecology 71: 1986-2000.
• Roy, K.M., Curran, R.P., Barge, J.W., Spada, D.M., Bogucki, D.J., Allen, E.B., and Kretser, W.A. 1996. Watershed protection for Adirondack wetlands; A demonstration-level GIS characterization of subcatchments of the Oswegatchie/Black river watershed. Final Report. EPA Grant No. X-002777-01, 49+pp.
• Shotyk, W. 1988. Review of the inorganic chemistry of peats and peatland waters. Earth Science Reviews 25:95-176.
• Siegel, D.I. and Glaser, P.H. 1987. Groundwater flow in a bog-fen complex, Lost River peatland, northern Minnesota. J. of Ecology 75:743-754.
• Tickle, A. 1992. Critical loads for nitrogen. Acid News 3:8-9.
• Worley, I.A. 1982. The natural significance and protection priority of New York's largest open peatlands. Report to the Adirondack Conservancy, 29 pp.

One of the objectives of this study was to investigate the idea of peatlands as critically sensitive wetlands with respect to additions of acidity and/or nutrients from anthropogenic sources. Another objective was to do a comparative examination of the deposition loading literature and to try to determine if Adirondack Park wetlands were receiving significantly more or less inputs than other wetland ecosystems examined primarily in northern Europe.

Introduction

Atmospheric deposition has long been recognized as a problem in the Adirondack Park and its effects on aquatic resources in particular are not likely to be abated soon (USEPA 1995). In recent years the deposition of sulfates has been decreasing in the Northeast and the Adirondacks, while the deposition of nitrates is increasing. The recovery of lake chemistry as measured by ANC has been variable (Driscoll and vanDreason 1993). For nitrogen, the concern is two-fold because it contributes acidity and also acts as a fertilizer. The Adirondack Park is an area believed to contain naturally low nutrient ecosystems, for example, ombrotrophic peatlands which are wetland ecosystems that depend solely on an atmospheric supply of elements. While lakes and streams have been considered the key critical receptors of added acidity and nutrients in the Adirondack Park, some scientists have advised that wetlands, particularly peatlands that form inseparable linkages with both aquatic and terrestrial ecosystems have been neglected or under-studied in the Northeast (Gorham et al. 1984).

Findings

The proposal for this project presumed that particular types of wetlands, namely poor fens and bogs, had a higher sensitivity to atmospheric deposition from both the addition of acid as well as nitrogen. This presumption was based primarily on literature from England that showed high levels of acidic deposition and nitrogen addition proved toxic to Sphagnum species (Tickle 1992), potentially killing the moss and subjecting the peat to erosion and loss of built-up organic matter. Review of the literature reveals that extending this presumption to other areas, including the U.S., may not be appropriate or so simple. The literature review follows.

The first question was identifying peatlands. This is discussed more extensively in the previous section (Peatlands-Identification). Many of these terms historically used to categorize peatlands overlap in meaning and usage, for example, ombrotrophic, oligotrophic and bog are all often used interchangeably. This can cause a great deal of confusion since review of the literature makes it clear that nutrient status, hydrology, and landscape position cannot be inferred from one another (Bridgham et al. 1996). The literature even throws some considerable doubt about using plant communities, pH and Ca concentrations as indicators of hydrology or nutrient status, as is so often done (Bridgham et al. 1996). This makes identifying peatlands potentially sensitive to acid deposition quite difficult.

The next question was what is the evidence in the literature that added acidity or nutrients are detrimental to peatlands? Williams and Silcock (1997) report that the main source of nitrate to ombrotrophic bogs is atmospheric deposition, and any nitrate is utilized mainly by vegetation. In their paper, the role of ammonium N is discussed along with consideration of other nutrients in the peat profile, such as phosphorus and potassium, on microbial activity associated with the decomposing litter. They conclude that "...the effects of added inorganic N on rates of decomposition of organic matter are not clear, and it is uncertain if N alone can cause increased decomposition rates....Phosphorus and the concentrations of base cations may well have a controlling influence on the processes of assimilation and retention of inorganic N in peatland ecosystems".

Several studies have looked at the effects of both sulfate and nitrate additions on peatlands with mixed results (Aerts et al. 1992, Urban and Bayley 1986). There are two aspects to the issue: acidification and fertilization. Urban and Bayley (1986) report that short term effects of acid deposition on peatlands in Ontario and Minnesota, largely attributable to nitrate, will be slight, while longer term effects attributable to sulfate, remain possible.

Bryophytes appear to be the key plant group to focus on for this study because in many semi-natural ecosystems the atmospheric supply may represent only a small proportion of the total available nitrogen. But since at least the bryophyte component of the vegetation is often dependent on an atmospheric source of solutes, those should be the most affected by an increase in atmospheric nitrate deposition unless they are nitrate tolerant. One of the few wetland ecosystems in which bryophytes dominate is in peatland types commonly called poor fens and bogs. These plants depend absolutely on an atmospheric supply of elements which are usually also at low concentration. These peatlands thus may provide ideal sites for evaluation of the potential ecological importance of an increase in atmospheric nitrogen supply (Press et al. 1986).

Rochefort et al. (1990) added nitrate at 0.46 g/m²/yr [4.6 kg/ha/yr] and sulfate at 1.8 g/m²/yr [18 kg/ha/yr] to a mire complex characterized as a poor fen at both minerotrophic zone and oligotrophic zones to simulate acidic rain equivalent to precipitation pH in eastern U.S. and Canada (pH = 4.0). The control was lake water. They measured growth and production for three of the dominant Sphagnum spp: S. fuscum, S. magellanicum and S. angustifolium for four years. They concluded that though nitrate additions stimulated growth in two of the three Sphagnum species in the first two years, by the fourth year, there was no difference in acidity or production as compared to pre-acidification conditions. The community structure of Sphagnum remained the same. This would support the notion that many peatland systems may be phosphorus limited (Bridgham, 1996 pers. com.). The loads used by Rochefort et al. (1990) were lower than the additions shown to cause toxicity to Sphagnum in England (6 g/m2/yr) [60 kg/ha/yr].

Press et al. (1986) report that southern Pennines blanket mires have been extensively modified by air pollution. They found that even small increases in nitrogen concentration reduced the growth of Sphagnum cuspidatum in the laboratory and found growth at the Pennines site significantly lower than at the unpolluted North Wales site. They concluded that the nitrogen regime at an unpolluted North Wales site would be more favorable than a polluted site at south Pennines where the volume weighted mean annual concentration of nitrate was more than two times greater (estimating from above that same site equivalent to 3.6 g/m²/yr) [36 kg/ha/yr]. They suggest "that increasing nitrogen deposition may be affecting the growth and metabolism of ombrotrophic Sphagnum species and hence the ecology of mires more widely than has previously been envisaged. It may also be affecting at least the bryophyte component of other ecosystems".

Williams and Silcock (1997) report that "...average values for wet deposition [of N] vary geographically and range in Europe from approximately 2 kg/ha/yr in northern Scandinavia to 80 kg/ha/yr in the Netherlands...In North America, values of inputs of N to wetlands in wet deposition of up to 12 kg/ha/yr have been reported". Ollinger et al. (1993) estimated a total nitrogen deposition range of less than 6.7 to greater than 10.75 kg/ha/yr in the Oswegatchie/Black study area and predicted the annual wet deposition of nitrate at higher elevations (i.e., greater than 1200 m) in the Adirondack mountains can be as much as 30 kg/ha/yr. One of our questions was are there such elevations in the Oswegatchie/Black study area and do peatlands occur there? The southwestern portion of the study area approaches that upper range.

Williams and Silcock (1997) conclude that "peatland ecosystems behave as sinks for inorganic N inputs, and provided these amounts are small, the N is assimilated by the vegetation. At high inorganic N input rates from atmospheric deposition, the composition of bog vegetation may change, and sensitive species, such as Sphagnum mosses, may be damaged". They do not offer a specific value for what would be considered high, however.

A fairly extensive search of the literature found no studies which compared peatland sensitivity to atmospheric deposition (either from acid additions or nitrate additions) to other wetland types.

As a result of this preliminary examination of the scientific literature on peatlands and atmospheric deposition, we found the evidence mixed. At this time, therefore, we find it inconclusive as to whether Adirondack peatlands are being negatively impacted by the current loads of acidity and nitrogen.

In this preliminary work, we recognize the importance of improving how peatlands can be identified and located in the Adirondack Park. This project has created a framework for identifying parameters of concern (key wetland indicators) as well as a system of mapping and retrieval with GIS. It is now possible to advance our regional understanding of wetlands by advising on academic research and incorporating these and other findings into our GIS system. This also allows us to share the information with others more easily.

Recommendations for future work

1. Continue literature work on peatland nutrient work.
2. The wetland literature should be examined to determine whether wetlands other than peatlands are sensitive to additions of nutrients or acids.
3. Predicting the location of wetlands in areas of the Park where wetland mapping is unavailable should be investigated using other GIS layers like muck soils from the general soils coverage.

References

• Aerts, R., Wallen, B., and Malmer, N. 1992. Growth-limiting nutrients in Sphagnum-dominated bogs subject to low and high atmospheric nitrogen supply. Journal of Ecology 80:131-140.
• Bridgham, S.C. 1996 personal communication.
• Bridgham, S.C, Pastor, J., Janssens, J.A., Chapin, C. and Malterer, T.J. 1996. Multiple limiting gradients in peatlands: A call for a new paradigm. Wetlands 16(1):45-65.
• Driscoll, C.T. and vanDreason, R. 1993. Seasonal and long-term temporal patterns in the chemistry of Adirondack lakes. Water, Air, and Soil Pollution 67:319-344.
• Gorham, E., Bayley, S.E. and Schindler, D.W. 1984. Ecological effects of acid deposition upon peatlands: A neglected field in "acid-rain" research. Can.J.Fish.Aquat.Sci.41:1256-1268.
• Ollinger, S.V., Aber, J.D., Lovett, G.M., Milham, S.E., Lathrop, R.G., and Ellis, J.M. 1993. A spatial model of atmospheric deposition for the northeastern U.S. Ecological Application 3(3):459-472.
• Press, M.C., Woodin, S.J., and Lee, J.A. 1986. The potential importance of an increased atmospheric nitrogen supply to the growth of ombrotrophic Sphagnum species. New Phytol. 103:45-55.
• Rochefort, L., Vitt, D.H., and Bayley, S.E. 1990. Growth, production and decomposition dynamics of Sphagnum under natural and experimentally acidified conditions. Ecology 71(5):1986-2000.
• Tickle, A. 1992. Critical loads for nitrogen. Acid News 3:8-9.
• Urban, N.R. and Bayley, S.E. 1986. The acid-base balance of peatlands: a short-term perspective. Water, Air, and Soil Pollution 30:791-800.
• U.S. Environmental Protection Agency 1995. Acid deposition standard feasibility study report to Congress. Air and Radiation (6204J), EPA 430-R-95-001a, pp.120+.
• Williams, B.L. and Silcock, D.J. 1997. The effects and fate of inorganic nitrogen inputs to oligotrophic peat soils. In: Northern Forested Wetlands - Ecology and Management, eds. Trettin, C.C. et al. CRC Lewis Publishers, New York, pp.353-365.