OUP CORRECTED PROOF – FINAL, 06/29/2013, SPi 1 Peatland habitats Th is book deals with the diverse, beautiful, and fascinating world of peatlands. Th ey represent very special kinds of transitional, amphibious ecosystems with habitats between uplands and water, where organic matter tends to accumulate because of the waterlogged, oft en poorly aerated conditions. Here we encounter Sphagnum peat mosses with an infi nite variety of col- ours—greens, reds, browns; insect-eating plants and beautiful orchids; reeds, sedges, and cotton grasses; low, oft en evergreen shrubs; fl oating plants and emergents at the water’s edge; quaking mats; vast wetlands with spectacular surface patterns; springs and soaks; thickets, sparsely treed woodlands, and tall forests. As a consequence of their diverse vegetation, peatlands also house a multitude of microorganisms, insects, birds, and other animals. Peat accumulations are oft en several metres thick, sometimes even more than ten metres, and provide material that can be harvested and used as fuel and for horticulture. Aft er drainage, large areas have been converted to ara- ble land, meadows, or forests. Th e peats are also valuable archives of past vegetation and climate, where we may fi nd the buried remains of ancient set- tlements, trackways, fi elds, and even preserved humans—the so-called ‘bog people’ of northern Europe ( Coles and Coles 1989 ; Turner and Scaife 1995 ). Th e aim of this chapter is to provide the reader with an understanding of the main terms and concepts used in peatland science, and a general apprecia- tion of the main peatland habitats. It is essential at the outset to provide a basic language of peatlands which, even if not universally agreed upon, will defi ne the usage for this book. Th e variation in terminology refl ects the great diversity and complexity of habitats and ecosystems. Unfortunately several terms are not consistently used, even in the same country or language. Th is refl ects traditional diff erences in understanding and comprehension among specialists, and diff erences between geographical areas. Table 1.1 lists a select set of peatland types in several languages. Many glossaries and defi nitions are available; particularly useful are IPS ( 1984 ) and Joosten and Clarke (2002). Th e Biology of Peatlands. Second Edition. Håkan Rydin & John K. Jeglum © Håkan Rydin & John K. Jeglum 2013. Published 2013 by Oxford University Press. OUP CORRECTED PROOF – FINAL, 06/29/2013, SPi 2 THE BIOLOGY OF PEATLANDS Table 1.1 Peatland terminology. It is diffi cult to fi nd exact translations, and the terms are sometimes used inconsistently, even within the same language. English German Russian French Finnish Swedish Wetland Nassboden, Заболоченная Milieux humides Kosteikko Våtmark vernässter местность, Boden, З. земля Feuchtgebiete Peata Torf Торф Tourbe Turve Torv Peatland Torfmoor Торфяник, Tourbière Turvemaa Torvmark торфяное болото Mire Moor Болото Tourbière, Suo Myr tourbière vivante Bog Regenmoor, Болото Tourbière Ombrotrofi nen Mosse Hochmoor атмосферного ombrotrophe, suo, rahkasuo питания, верховое tourbière haute болото Fen Niedermoor Низинное Tourbière Sarasuo, Kärr болото minérotrophe, tourbière minerotrofi nen basse, bas-marais suo Marsh Marschmoor Марш b Marais Marskimaa – c Swamp Bruchwald, Болото лесное Marécage, forêt Korpi Sumpskog forest Moorwald marécageuse a An English word related to the word used for peat in other languages is ‘turf’ (often used in old literature, e.g. King 1685 ). b Rarely used term, usually used for translation and in plural form (‘марши’). c No commonly used term since marshes are usually classifi ed as shore vegetation. ‘Mad’ or ‘raning’ are used locally for grazed or mown marshes. 1.1 Wetlands, peatlands, and mires Th e three main terms used in the current literature to encompass the subject are wetlands, peatlands, and mires. Th ese terms are defi ned somewhat diff er- ently, although there is considerable overlap ( Fig. 1.1 ). Th e broadest concept is that of wetlands. 1.1.1 Wetlands Wetlands are ‘. neither fi rm “lands” in the conventional sense, nor bodies of open water; hence they occupy a transitional position between land and water. Th e ecosystems that develop on such lands are dominated by the per- sistent presence of excess water’ ( National Wetlands Working Group 1988 ). Wetlands include shore, marsh, swamp, fen, and bog. Scientifi cally, we can characterize wetland by the following points: • Th e water table is near the ground surface. • As a consequence, the substrate is poorly aerated. OUP CORRECTED PROOF – FINAL, 06/29/2013, SPi PEATLAND HABITATS 3 Thin peat or mineral soil Peatland swamp conifer Moderately swamp Forested wet deciduous wooded swamp bog wooded Sparsely Wet fen forested bog Very open fen wet rich bog poor fen Open fen marsh Open bog water pool Hydrological Ombrogenous Minerogenous Limnogenous regime: 8 pH 6 4 Nutrient Oligotrophic Oligotrophic Mesotrophic regime: or mesotrophic or eutrophic Fig. 1.1 A general scheme to defi ne the position of broad wetland types in an ordination based on the two most important environmental gradients. Wetness, or distance between vegeta- tion surface and water table, varies along the vertical axis, and the complex gradient with variation in pH, base saturation, and nutrient status is depicted along the horizontal axis. Wetland is an even broader category than shown here, since it includes various habitats of shore and shallow waters. • Inundation lasts for such a large part of the year that the dominant plants and other organisms are those that can exist in wet and reducing conditions. Th e Ramsar Convention provides a very wide defi nition: For the purpose of this Convention wetlands are areas of marsh, fen, peatland or water, whether natural or artifi cial, permanent or temporary, with water that is static or fl owing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres ( Ramsar 1987 ). Th e Canadian Wetland Classifi cation has a narrower defi nition, extending to water depths up to two metres, and which is more ecosystemic in character: A wetland is defi ned as: land that is saturated with water long enough to pro- mote wetland or aquatic processes as indicated by poorly drained soils, hydro- phytic vegetation and various kinds of biological activity which are adapted to a wet environment ( National Wetlands Working Group 1997 ). OUP CORRECTED PROOF – FINAL, 06/29/2013, SPi 4 THE BIOLOGY OF PEATLANDS Th ere are a multitude of wetland defi nitions used for scientifi c, inventory and regulatory purposes. Considerable work has been done in the USA to defi ne wetlands by length of time of surface fl ooding during wet periods, and to defi ne upland limits to wetlands with the use of indicator plants (see Tiner 1998 ; 1999 ). Much of this work in the USA has emphasized the marsh and open water communities, in contrast with other wetland inventories that are broader and include bogs and fens (e.g. in Canada and Sweden). 1.1.2 Peat and peatland In order to defi ne peatland we must fi rst defi ne peat. Peat is the remains of plant and animal constituents accumulating under more or less water- saturated conditions owing to incomplete decomposition. It is the result of anoxic conditions, low decomposability of the plant material, and other com- plex causes. Peat is organic material that has formed in place, i.e. as sedentary material, in contrast to aquatic sedimentary deposits. Quite diff erent plant materials may be involved in the process of peat formation, for instance, woody parts, leaves, rhizomes, roots, and bryophytes (notably Sphagnum peat mosses). Most of the material originates above ground as photosynthetic organic material, and is deposited as litter on the surface to be buried by new layers of litter. However, some of the photosynthate is translocated to roots or rhizomes beneath that eventually die and are added to the peat, and a certain fraction of the dead plant material is recycled by invertebrates, bacteria and fungi, before they too die and add to the peat material. Peatland is a term used to encompass peat-covered terrain, and usually a minimum depth of peat is required for a site to be classifi ed as peatland. In Canada the limit is 40 cm ( National Wetlands Working Group 1997 ), but in many countries and in the peatland area statistics of the International Mire Conservation Group it is 30 cm ( Joosten and Clarke 2002 ). For purposes of clarity and uniformity, we will use 30 cm to defi ne peatland. 1.1.3 Mire Mire is a term for wet terrain dominated by living peat-forming plants (e.g. Sjörs 1948 ). Th e concept of ‘peat-forming plants’ is, however, somewhat problematic. Even if some species more commonly give rise to peat than oth- ers, peat formation is a process that can befall most plant materials. Both peatland and mire are narrower concepts than wetland, because not all wet- lands have peat as substrate. In one sense mire is a slightly broader concept than peatland, because peat accumulation can occur on sites that have not accumulated the required depth of peat to qualify as peatland. In another sense peatland is broader—a drained site, for instance a site being used for peat harvesting, is still a peatland, but having lost its original peat-forming vegetation it is no longer a mire. A reason OUP CORRECTED PROOF – FINAL, 06/29/2013, SPi PEATLAND HABITATS 5 for the seemingly confl icting defi nitions is that the terms are used for diff erent purposes. Mire is a term oft en used in botanical and ecological investigations of the vegetation types, and then oft en used collectively for fens and bogs (see sections 1.4.3 and 1.4.4 ).