Aro Wetland Environments

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A 513 OULU 2008 A 513

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SERIES EDITORS SCIENTIAE RERUM Jarmo Laitinen NATURALIUM Jarmo Laitinen ASCIENTIAE RERUM NATURALIUM Professor Mikko Siponen VEGETATIONAL AND BHUMANIORA LANDSCAPE LEVEL University Lecturer Elise Kärkkäinen RESPONSES TO WATER CTECHNICA Professor Hannu Heusala LEVEL FLUCTUATIONS DMEDICA Professor Olli Vuolteenaho IN FINNISH, MID-BOREAL AAPA MIRE – ARO WETLAND ESCIENTIAE RERUM SOCIALIUM Senior Researcher Eila Estola ENVIRONMENTS FSCRIPTA ACADEMICA Information officer Tiina Pistokoski

GOECONOMICA Senior Lecturer Seppo Eriksson

EDITOR IN CHIEF Professor Olli Vuolteenaho EDITORIAL SECRETARY Publications Editor Kirsti Nurkkala FACULTY OF SCIENCE, DEPARTMENT OF BIOLOGY, UNIVERSITY OF OULU; ISBN 978-951-42-8878-4 (Paperback) ISBN 978-951-42-8879-1 (PDF) ISSN 0355-3191 (Print) ISSN 1796-220X (Online)

ACTA UNIVERSITATIS OULUENSIS A Scientiae Rerum Naturalium 513

JARMO LAITINEN

VEGETATIONAL AND LANDSCAPE LEVEL RESPONSES TO WATER LEVEL FLUCTUATIONS IN FINNISH, MID-BOREAL AAPA MIRE – ARO WETLAND ENVIRONMENTS

Academic dissertation to be presented, with the assent of the Faculty of Science of the University of Oulu, for public defence in Kuusamonsali (Auditorium YB210), Linnanmaa, on September 19th, 2008, at 12 noon

Supervised by Professor Jari Oksanen Professor Juha Tuomi Docent Pekka Pakarinen

Reviewed by Professor Håkan Rydin Research director Heikki Toivonen

ISBN 978-951-42-8878-4 (Paperback) ISBN 978-951-42-8879-1 (PDF) http://herkules.oulu.fi/isbn9789514288791/ ISSN 0355-3191 (Printed) ISSN 1796-220X (Online) http://herkules.oulu.fi/issn03553191/

Cover design Raimo Ahonen

OULU UNIVERSITY PRESS OULU 2008 Laitinen, Jarmo, Vegetational and landscape level responses to water level fluctuations in Finnish, mid-boreal aapa mire – aro wetland environments Luonnontieteellinen tiedekunta, Department of Biology, University of Oulu, P.O.Box 3000, FI-90014 University of Oulu, Finland Acta Univ. Oul. A 513, 2008 Oulu, Finland

Abstract Gradient, which is largely considered to be related to water level in mires, is referred to as a microtopographic mud bottom to carpet to lawn to hummock level gradient or the hummock level to intermediate level (lawn) to flark level gradient. The relationship of this vegetation gradient to various physical water level characteristics was studied. The general classification used in the present summary paper divides the aro vegetation of the inland of Northern Ostrobothnia into two main groups: (a) treeless fen aro vegetation (Juncus supinus, Carex lasiocarpa, Rhynchospora fusca, Molinia caerulea) and (b) heath aro vegetation (Polytrichum commune). The first group (a) was divided into fen aro wetlands with an approximately10 cm peaty layer at most and into aro fens with a peat layer thicker than 10 cm. The treatment of the water level gradient was divided into three main groups. (1) The mean water level correlated with mire surface levels (microtopographic gradient) within mires with slight water level fluctuations and partly within mires with considerable water level fluctuations. (2) Three habitat groups could be distinguished on the basis of the range of water level fluctuation i.e. mires with slight water level fluctuations, mires with considerable water level fluctuations and the aro vegetation with extreme water level fluctuations. (3) The timing of water level fluctuations indicated that there are different types of patterns within aro wetlands, the seasonal pattern being mainly a response to yearly snow melt and the several-year-fluctuation pattern being related to the regional groundwater table fluctuation in mineral soils (heath forests). A link was suggested between the stability of the water regime and peat production in local aapa mire – aro wetland environments. From the point of view of peatland plants the direction of variation from a stable to an unstable water regime in aapa mire – aro wetland environments represents a transition towards more and more harsh ecological conditions, partly forming a gradient through natural disturbance. A qualitative functional model was provided for the mire – aro wetland systems of Northern Ostrobothnia. The model supposes differences in the characteristics of peat between two functional complexes within a mire system. Finally, the model for local mire – aro wetland systems was converted to a general from: diplotelmic (acrotelm) mires were divided into two subtypes (diplotelmic water stabilization mires, diplotelmic water fluctuation mires) and the relationship of those subtypes to percolation mires and seasonal wetlands was considered.

Keywords: diplotelmic model, ecological gradients, Ellenberg indicator values, hydrogenetic mire types, mire vegetation, peat procuction, seasonal wetlands, wetland hydrology, wetland vegetation classification

Acknowledgements

The topic of this study occurred to me when I was performing field work in Hirvi- suo in connection with drawing up my final paper in the summers 1983-85. Emeri- tus Professor Seppo Eurola had stated that there are some exceptional features in parts of the area, and when guiding my final paper, he often also took up the question of the poorly-known aro wetlands of Muhos. After that, I remained preoccu- pied with the topic of seasonal drought concerning both mires and aro wetlands. It was not until about 1998 that the actual investigation into water level measurements began. The first years of the study also involved an exhaustive search for new aro and other study localities. Later it also included vegetation sampling in addition to water level measurements, and the main part of the vegetation material for the final paper was also combined into the thesis. I wish to thank my three supervisors, Professor Jari Oksanen (Oulu), Professor Juha Tuomi (Oulu) and Docent Pekka Pakarinen (Helsinki). I would especially like to thank Jari Oksanen for his flexible attitude, quick enthusiastic response, practicalness and for not taking matters so seriously. The last mentioned attitude in particular has taught and encouraged me a lot. Collaboration with him in planning and preparing articles has always felt easy and fluent. Special thanks go to Juha Tuomi for his patience in giving me vast general guidance and support from the very beginning of the study process, which lasted ten years. Pekka Pakarinen guided me in the principles of scientific thought and writing at the beginning of the process. I also thank him for ideas and critical questions concerning mire terminology and the planning and writing of articles. Thanks are also due to Satu Huttunen, Professor of the Department of Biology, for her interest in my research and for taking care of some matters concerning the thesis. I further wish to thank all the co-authors of the study. Sakari Rehell’s contribution especially in the water level monitoring and inventory of new study localities has been decisive. I also thank him for his endless number of ideas and suggestions during the writing process and for suggesting and planning the cross- section figure for functional mire types. I especially thank Antti Huttunen for his willingness to always discuss with me practically any topic concerning the actual research, its terminology and the atmosphere generated by research cooperation. I also thank him for the vast practical help that I received from him during the long study process, for drawing figures, providing the soil photos and corresponding soil descriptions in the field etc. Collaboration with Teemu Tahvanainen has always been inspiring and challenging. Kari Kukko-oja provided valuable criticism and attended practical work on vegetation material in one of the articles,

5 while Raimo Heikkilä and Tapio Lindholm participated as co-workers in a study discussing the general mire classification of Finland. I wish to express my warmest thanks to all of them. I am grateful to the former and present staff of the Department of Biology for their practical assistance, for providing field study equipment, and recently especially for their help with the use of computer. Thanks are also due to the staff of the Botanical Museum of Oulu. I wish to thank Risto Virtanen for brief discussions clarifying important concepts in modern field-ecological research, Pekka Halonen for determining some lichens, Lassi Kalleinen for providing his photos of aro wetlands to the thesis and for preparing some figures, and Henry Väre for a common field trip with vegetation sampling. Tauno Ulvinen, Emeritus Director of the Botanical Museum, determined and checked a large number of my plant species samples over the years. I thank him for numerous, invaluable discussions of the ecology and species identification of various plants. I am also grateful to Emeritus Professor Seppo Eurola for his ideas, encouragement and support during the field work connected with my final paper (subsequently part of the thesis), and for discussing and helping me solve some problems in the classification of aro wetlands much later. His thorough teaching in the directions of variations in mire vegetation inspired me to study those topics, as did the special, critical vegetation-ecological thoughts of Emeritus Professor Paavo Havas, whom I also wish to thank warmly. Several other people have also contributed to the progress of the research. I extend my thanks to Elina Palojärvi for giving me her vegetation mapping of the northern part of Hirvisuo, and to Seppo Hellsten for discussions and help in the final phase of the investigation process. I am grateful to Vieno Seppänen, a late farm owner, for common time during my field work in Unhola and to old shopkeeper Irma Lämsä from Arkaperä for donuts and chatting during lonely field work. I especially thank my family, wife Elina for patience during the long study process, Markus for preparing some figures, Sini and Hilla for their fascination of tiny issues of human interest in the research, and for Lumi for her expression of love with father. I thank the reviewers, Professor Håkan Rydin and Research Director Heikki Toivonen for their comments on the work and Antti Rönkkö for revising the English language. The work was mainly financed by Tauno Tönning Foundation, Societas pro Fauna et Flora Fennica, Environet (Oulu), Ella and Georg Ehnrooth Foundation and the University of Oulu.

Oulu, August 2008 Jarmo Laitinen

6 List of original papers

The thesis is based on the following papers, wich are referred to in the text by their Roman numerals:

I Laitinen J, Rehell S & Huttunen A (2005) Vegetation-related hydrotopographic and hydrologic classification for aapa mires (Hirvisuo, Finland). Annales Botanici Fennici 42(2): 107-121.

II Laitinen J, Rehell S, Huttunen A & Eurola S (2005) Arokosteikot: ekologia, esiintyminen ja suojelutilanne Pohjois-Pohjanmaalla ja Kainuussa. Summary: Aro wetlands: ecology, occurrence and conservation in North-Central Finland. Suo 56: 1-17.

III Laitinen J, Rehell S & Oksanen J (2008) Community and species responses to water level fluctuations, with reference to soil layers in different habitats of mid-boreal mire complexes. Plant Ecology 194: 17-36.

IV Laitinen J, Kukko-oja K & Huttunen A (2008) Stability of the water regime forms a vegetation gradient in minerotrophic mire expanse vegetation of a boreal aapa mire. Annales Botanici Fennici 45: 00–00.

V Laitinen J, Tahvanainen T, Rehell S & Oksanen J (2007) Vegetation ecology and flooding dynamics of boreal aro wetlands. Annales Botanici Fennici 44: 359-375.

VI Laitinen J, Rehell S, Huttunen A, Tahvanainen T, Heikkilä R & Lindholm T (2007) Mire systems in Finland – spedial view to aapa mires and their water flow pattern. Suo 58: 1–26.

7 8 Contents

Abstract Acknowledgements List of original papers Contents 1 Introduction 11 1.1 Water level gradient of boreal mires...... 11 1.2 Aro wetlands ...... 12 1.3 Basic concepts of mire ...... 12 1.4 Functional and vegetational classification of mire systems and types.... 14 1.5 Aims of the study ...... 16 2 Study area 17 2.1 Climate and geology ...... 17 2.2 Vegetation zones and sections and the study localities...... 17 3 Material and methods 21 3.1 Vegetation study...... 21 3.1.1 Vegetation materials, descriptions and analysis in original papers ...... 21 3.1.2 Summary vegetation classification for the present paper ...... 22 3.2 Direct and indirect environmental measurements...... 22 3.2.1 Water level ...... 22 3.2.2 Peat thickness and soil profiles ...... 23 3.2.3 Application of Ellenberg indicator values ...... 23 3.3 Landscape level investigations...... 24 4 Results and discussion 25 4.1 Plant communities and aro vegetation classification ...... 25 4.1.1 Aro wetlands and aro vegetation...... 25 4.1.2 Clustering of communities and the range of water level fluctuations...... 32 4.2 Water level, vegetation and peatland processes...... 33 4.2.1 Mean water level and the mire surface levels...... 34 4.2.2 Range of water level fluctuation ...... 35 4.2.3 Timing of water level fluctuation ...... 38 4.2.4 Natural disturbance ...... 40 4.2.5 Local peat growth ...... 41

9 4.2.6 Other gradients...... 41 4.2.7 Indicator species groups for the stability of the water regime ...... 42 4.3 Towards functional models of mire systems and types ...... 44 4.3.1 Principal-water-function model for mid-boreal mire – aro wetland systems ...... 44 4.3.2 Functional subtypes of diplotelmic mires and their relatioships to percolation mires and seasonal wetlands ...... 49 References Appendices Original papers

10 1Introduction

1.1 Water level gradient of boreal mires

Boreal mire ecology has largely set out from focusing on various vegetation gradients (Tuomikoski 1942, Sjörs 1948) based on regional, extensive vegetation descriptions (Ruuhijärvi 1960, Eurola 1962). Subsequently various ordination methods have been applied (Pakarinen 1976, Pakarinen & Ruuhijärvi 1978) or scattered, complementary measurements of the central environmental variables were performed to evaluate the interpretation formed on the basis of vegetation descriptions (Havas 1961). Later the vegetation analyses and the research on environmental variables were more and more combined in vegetation classification and gradient studies (Økland 1989, Nicholson et al. 1996). Gradient largely considered to be related to water level in mires is referred to as a mud bottom to carpet to lawn to hummock level gradient (Sjörs 1948) or microtopographic gradient (Malmer 1986) in Sweden. In Finland, the corresponding direction of variation from hummock-level communities (Bültengesellschaften) through lawn communities (Teppichgesellschaften) and moss-rich flark communities (Moosreiche Rimpigesellschaften) to moss-poor flark communities (Moosarme Rimpigesellschaften) (Ruuhijärvi 1960) was later placed in three categories: hummock level, intermediate level (lawn) and the flark level (Eurola & Kaakinen 1978, Ruuhijärvi 1983, Eurola et al. 1984, 1995). The relationship of this vegetation gradient to various physical water level characteristics and the relationship of species to those characteristics in boreal Fennoscandia have been thoroughly studied especially in bog complexes (Malmer 1962, Lindholm & Markkula 1984, Økland 1989), but the measurements have been performed in a relatively narrow habitat range, and the fluctuation has even been seen as a kind of inconvenience in classifying mires on other grounds: Vitt & Chee (1990) state that in their study area in Alberta (Canada) the use of water chemistry as a basis for classifying mires may be hampered by periodic variation in water supply. Anderson & Davis (1997) even say that it is difficult to quantify peatland hydrology because of seasonal and subseasonal variability. Thus the variability has been assumed to be of negligible or minor importance as a factor structuring vegetation in northern regions, and different factors involved in the variability of the water regime have gained little attention in studies of boreal mires. Only Havas (1961), based on general observations and a measurement series, strongly stresses the ecological division of slope mires in Eastern and

11 North-Eastern Finland according to the stability of the water regime. Laitinen (1990) suggests the occurrence of the stability of the water regime as a general vegetation gradient in various mire surface levels, but the concept was not based on measurements. In global wetland research the water level fluctuation has been seen as a significant factor (Keddy 2000).

1.2 Aro wetlands

´Aro´ is a term used in local dialects of Finnish to describe small seasonal wetlands mostly characterised by a very thin peat layer, seasonal flood, seasonal drought and at least partly fen-like vegetation. Vegetation-ecological research on wetlands with a missing or very thin peat layer (e.g. Eurola 1967, Siira 1970) has been generally separate from peatland research in Fennoscandia. In the present study area, however, there are several small aro wetlands in connection with mires on flat, sandy glaciofluvial areas (II, III, V). As they are concentrated in certain areas, they have not been described in connection with the large regional mire study of Nort- hern Finland (Ruuhijärvi 1960). Little is known about their vegetational variation, vegetational position among major boreal vegetation types and the responses of the aro vegetation types to hydrology. Aro wetlands co-occur with mires in the study area so they must be treated together with mires. Such habitats also occur outside mires in various depressions in mineral soil, including the flooded heaths (tulvanummet) of Jalas (1953) and the water stagnation sites (vedenviipymät) of Helin & Leivo (2000). There seems to be a transition to mires from the flooded heaths Valpas (1964). The special ecological character of aro wetlands, strong water level fluctuations culminating in a hydroperiod and especially in a seasonal drought of the surface in summer time (Jalas 1953, Valpas 1964) make aro wetlands a fascinating research target: they are an ecological extreme end of mires partly without being mires.

1.3 Basic concepts of mire

1. Mire. In this thesis mire is viewed simply as an entity formed by vegetation and peat (e.g. Godwin 1941). The hydrological functioning of mires, then, is bound to their three-dimensional structure with various causalities and feedbacks between vegetation, hydrology, peat and the underlying mineral soil. This short mire definition allows for the water table to occasionally fall below the peat layer in extreme mire habitats, a condition previously known for some thin-peated slope fens

12 (Havas 1961). – There are many definitions for a ´mire´, depending on the context in which the concept is used. A definition mostly used in Finland, referred to as a botanical concept, postulates that mires are sites supporting peat-producing plant communities (Laine & Vasander 1996). According to Vitt (2006) peatlands are ecosystems in which the net primary production has exceeded decomposition over thousands of years, and as a result organic matter rich in carbon has accumulated over time, and peat is formed. Recently, Tahvanainen (2005) defined mire as follows, based on the main stress and resource factors concerning vegetation irres- pective of the current peat accumulation rate: In a mire, organic matter has accumulated as peat due to the anoxia caused by water-logged conditions. Tahvanainen (2005) stresses that the water-logging takes place in an organic soil layer and hence a water table can be determined in it. In the present thesis, a larger hydrological variation for mires is allowed. 2. Mire vegetation. Mire vegetation here is a large unit including (sensu Cajander (1913), Ruuhijärvi (1960), Eurola & Kaakinen (1978) and Eurola et al. (1984, 1995)) the mire expanse and mire margin vegetation, with the concepts mire margin and mire expanse (Sjörs 1948) being used in the same way as they are used in Finland i.e. by Tuomikoski (1942, 1955), Ruuhijärvi (1960), Eurola (1962) and Eurola et al. (1984, 1995). The mire expanse vegetation includes Weissmoor (treeless, lawn or flark level poor to intermediate fen or bog), Braunmoor (treeless rich fen) and Reisermoor (hummock-level pine mire) vegetation, and the mire margin vegetation Bruchmoor (spruce mire), Sumpfmoor (swamp wetland) and Quellmoor (spring and spring fen)) vegetation. Even thin-peated sites are included in mires according to this concept. 3. Mire system, mire massif and mire complex. Mire system (Masing 1972, Heikkilä R. et al. 2001) is defined in this thesis as any uniform mire area surrounded by mineral soil areas or watercourses (VI). Accordingly, the concept includes (1) the climatic, zonal mire complexes of Cajander (1913), Ruuhijärvi (1960), Eurola (1962), Eurola et al. (1984, 1995), Havas (1961) and Tolonen (1967) and (2) additionally the local, small mire complexes of Cajander (1913) (VI). Mire systems including large aro wetlands are here called mire-aro wetland systems; the occurrence of aro wetlands is a local feature in them. Mire massif (Russian terminology) is a large ´peatland block´ in climatic, zonal mire systems, characterised by a certain eco-morphology. It is a synonym for ´mire complex type´ by Yurkovskaya 1995 (see also Heikkilä R. et al. 2001) constituting a large, morphologic mire unit with a convex, plain, sloping or concave gross profile and

13 with one to several microtopographically uniform sub-areas usually situated regularly in relation to each other (VI). 4. Aapa mire. Aapa mire (Aapamoor) was originally described as a climatic mire complex type from Northern Finland by Cajander (1913) and Ruuhijärvi (1960). The concept of ´aapa mire´ may refer either to a narrower morphological mire system type characterised by flarks and strings (Cajander 1913, Pakarinen 2001) or to a broader, vegetation-ecologically determined concept (Eurola et al. 1995) with several, climatic-regional (zonal) sub-types with different morphology in the central parts (Ruuhijärvi 1960) (I). In this thesis, aapa mires are discussed according to the broad, vegetation-ecological definition: aapa mire is a mire system type whose central parts are characterised by minerotrophy and mire- inherent influence or near to such and which may receive supplementary nutrients in its central parts – besides marginal parts and brook sides – also through snow- melt water from the surroundings (translated from Eurola et al. 1995). According to this definition aapa mires include string flark fens as well as flark and lawn fens with no strings (VI). – The climatic envelopes of four main mire complex types in Fennoscandia (aapa mire, palsa mire, raised bog, blanket bog) were recently outlined by Parviainen & Luoto (2007) and the relationship between climate and a larger group of temperate to boreal (to arctic) mire complex types was summarized by Vitt (2006).

1.4 Functional and vegetational classification of mire systems and types

The hydrological, physical water function in mires includes e.g. the fluctuation of the water table level and the flow of water (Rydin & Jeglum 2005). These functions are in relation to peat characteristics and growth, and to the characteristics of the mineral soil beneath the peat (Reeve et al. 2000, 2001). They also have vegetational impacts in the form of ecological resource factors (e.g. nutrient supply to plants) and destabilizing factors (Økland 1989) or (natural) disturbance (Grime 1979, Keddy 2000). Hydrology thus affects the plant community properties of mires and other wetlands. In this way the functional mire classifications concentra- ting on physical water functions also provide a hydrological framework for vegetational mire types and classifications based on variation in the vegetation itself. Based on Russian traditions (Ivanov 1981), Ingram (1978), defines terms for general soil layers in mires (acrotelm, catotelm) and mire types (diplotelmic, haplotelmic) quite generally in order to enable the two-layer-hypotheses to be

14 more thoroughly explored and developed as a functional basis for ecological and soil-taxonomic studies. Bogs are nowadays generally regarded as diplotelmic mires; in relation to other mire types, the opinions differ more from each other (Rydin & Jeglum 2005). A hydrogenetic mire classification with several mire types was developed in continental Central Europe, intended to serve as a basis for a larger range of mires of different age and with different geologic settings (Succow & Joosten 2001, Joosten & Clarke 2002). Diplotelmic mire (acrotelm mire) is included in the system, but boreal aapa mires are not. The hydrogenetic mire classification is based on the role of water in peat formation (Schwingmoor mire and immersion mire (Verlandungsmoore), water rise mire (Versumpfungsmoor), flood mire (Überflutungsmoor)) and the role of water in the present-day mire hydrology (surface flow mire (Überrieselungsmoor), acrotelm mire, percolation mire (Durchströmungsmoor)). A Canadian wetland classification (Tarnocai 1988, Warner et al. 1997) introduces, at a very general level, a transition from peatlands (bog, fen) to various mineral wetlands (marsh, swamp) along the water level fluctuation gradient (Zoltai & Vitt 1995), and Vitt (2006) outlines various functional criteria (e.g. stability of the water table) for functional grades (wetland, peatland, fen, bog) of boreal wetlands. Vitt (2006) also attempts to present some general floristic indicators for those ´boreal wetland grades´. Any wetland type somehow referring to aro wetlands is not, however, included in that general classification. A gradient reference frame for peatlands and other wetlands, including two major peatland gradients derived from Sjörs (1959, 1963) (wetness, poor-rich), and a littoral gradient (wave exposure), was developed in Northwestern Ontario (Racey et al. 1996, based on Harris et al. 1996). This scheme considers the transition from peaty marshes with low wave exposure to marshes-on-mineral-soil with high wave exposure. Neither is any wetland type corresponding to aro wetlands included in this classification. There are many kinds of mire systems in the mid-boreal lowland area of Finland (study area), both zonal (climatic) and local mire systems (VI), which are often combined into a nearly uniform network. Mire-aro wetland systems provide opportunities for applying a mire-system-level functional classification based on the principal water function. The diversity is increased by the fact that some rare mire systems occurring in the same geographic area (Olvassuo, Pilpasuo) have vegetational and hydrological features that deviate from typical aapa mires (Rehell 1985, Rehell & Tahvanainen 2006) and refer to the percolation mires of Joosten & Clarke (2002) (Lihdholm & Heikkilä 2006b) with a very stable water regime.

15 1.5 Aims of the study

The general aims of the whole thesis (I-VI) are (1) to investigate the landscape level relationships of the morphology, vegetation, water level fluctuation, peat depth-soil structure, groundwater recharge-discharge pattern and the surfical water flow pattern in mid-boreal aapa mire-aro wetland environments, (2) to evaluate the general significance of the water level gradient of boreal mires and seasonal wetlands and analyse their vegetational responses in the lowland aapa mire systems of Northern Ostrobothnia and (3) to discuss the interwoven gradients of the water level fluctuation gradient. Article VI partly considers the topics of this thesis, pla- cing the studied mire systems and their hydrological patterns into the kind of general typology proposed in that article. The specific aims of the present summary paper are (1) to summarize the vegetational variation of aro wetlands and closely related fens into a vegetational classification, (2) to arrange various aspects of the water level gradient and interwoven and parallel vegetation-ecological gradients of the water level fluctuation of boreal aapa mire-aro wetland environments in an orderly manner and (3) to present a functional, qualitative (non-mathematical) model for local mire-aro wetland systems and a general model for the subtypes of diplotelmic mires and their relationships to percolation mires and seasonal wetlands.

16 2Study area

2.1 Climate and geology

The study area is situated in a lowland area by the Bothnian Bay, Finland (Fig. 1). The mean annual temperature in the study area is + 1 to + 2 C° and snow depth in March 50–60 cm (Alalammi 1987). The permanent snow cover falls on the average on 15th–25th November and snow melts from open ground by 5th May. Annual precipitation is 600 mm, annual evapo-transpiration 250–300 mm and annual runoff 300–350 mm (Karlsson 1986). The difference between precipitation and evapo-transpiration (in cultivated areas) from the melting of snow until the end of July is about 0 mm, indicating moderate dryness of the climate during that period (Karlsson 1986). Siliceous rocks without considerable amounts of basic or carbonate minerals prevail in the study area (Korsman et al. 1997). The lowland area was deeply submerged during the Holocene in the Baltic Sea area. Isostatic land uplift gave rise to a series of sandy raised beach ridges at glaciofluvial eskers, which are often flat-topped and even plane-like in this area. Mires have spread largely over various glacial deposits. At present peatlands cover over 50 per cent of the land in the lowland area. In spite of the northern position of the study area, mires are quite extensively ditched (Lindholm & Heikkilä 2006a). Entire intact mire systems with no ditches are hardly found in any corner of the mire systems.

2.2 Vegetation zones and sections and the study localities

The study area belongs (1) to the middle boreal zone according to Hämet-Ahti (1981), Eurola et al. (1991) and Moen (1999) (Fig. 1), mainly based on the forest vegetation, and (2) mainly to the southern aapa mire zone of Ruuhijärvi & Hosiais- luoma (1988). The Kaakkurinneva locality (Fig. 1) belongs to the Kermi raised bog area of the coast of the Bothnian Bay (Eurola 1962). The largest raised beach ridge mires with large aro wetlands i.e. typical mire-aro wetland systems (Ressu- naro area, Vesisuo, Meriaro, Fig. 1) are situated south of the River Oulujoki, on the sides of the broad and flattened Rokuanvaara esker chain extending from Lake Oulujärvi to the island of Hailuoto. Those mire systems seem to lie in the border between the aapa mire area of Suomenselkä and Northern Ostrobothnia by Ruuhi- järvi (1960).

17 Fig. 1. Study area (rectangle) in the coastal lowland of Northern Ostrobothnia (upper map) and in Fennoscandia (map in the bottom part of the figure). Vegetation zones from Moen (1999).

18 Ruuhijärvi (1960: Abb. 88), however, has very few study localities just south and southeast of Oulu. In the mire zone and section division of Eurola & Vorren (1980) the above mentioned mire-aro wetland systems clearly belong to the MBs (middle boreal southern) mire area, which mainly corresponds to the aapa mire zone of Suomenselkä of Ruuhijärvi (1960) as far as the present study area is concerned. Large, typical aapa mire localities of the present study (Hirvisuo, Iso Palosuo- Kuusisuo, Kärppäsuo, Hoikkasuo) having about an equal proportion of the lawn fen (peripheral parts) and flark fen (central parts, mainly string fens) and much smaller proportions of aro wetland, are situated north of the River Oulujoki within the aapa mire area of Northern Ostrobothnia of Ruuhijärvi (1960). The MBs-MBn (middle boreal south-middle boreal north) mire area boundary of Eurola & Vorren (1980) or the boundary between the aapa mire area of Suomenselkä (dominated by the lawn) and the aapa mire area of Northern Ostrobothnia dominated by both the flark level and the lawn (Ruuhijärvi 1960) should run in the study area approximately from Oulu along the river Oulujoki and then between the Rokuanvaara and Meriaro-Vesisuo localities directed to the south to the area just west of Lake Oulu- järvi. From about there the border should turn back to the north across Lake Oulu- järvi; the more flark-level (patterned fen) dominated northern part of the southern aapa mire zone seems to form a projecting part directed to the south-west in the northernmost part of the Suomenselkä area, as the formerly unpublished map of Ruuhijärvi and Hosiaisluoma (Lindholm & Heikkilä 2006b: Fig. 3) suggests. In the mire vegetation section division of North Fennoscandia proposed by Eurola & Vorren (1980) the study area belongs to section IV (the Ledum section) and subsection IVb (Ledum palustre-Carex laxa subsection or the aapa mire subsection). This subsection is characterised by the dominance and occurrence of many continental mire plants, such as Carex globularis, Chamaedaphne calyculata (in the southeast) and Eriophorum russeolum (in the north). Certain rather oceanic species, such as Calluna vulgaris, Rhynchospora fusca and Lycopodiella inundata, however, are particularly characteristic of the mire and aro wetland sites with an unstable water regime in the study area. In the highest (most elevated) mid-boreal hill areas of Kainuu (Eurola & Kaakinen 1982, Eurola et al. 1991) to the east of the study area and in the northern boreal Riisitunturi hills of Koillismaa (Eurola et al. 1982) the hygric maritime vegetational features again increase, both in the forest and mire vegetation. These include the disappearance of Chamaedaphne calyculata and decline of Ledum palustre above 300 m a.s.l. in the hills of Kainuu (Eurola & Kaakinen 1982) and the more common occurrence of the Trichophorum cespitosum-Sphagnum compactum fen in Kainuu (Ruuhijärvi

19 1960) and in the Riisitunturi area (Havas 1961, Eurola et al. 1982, Paasovaara 1986) as compared with the study area (mid-boreal lowland area).

20 3 Material and methods

3.1 Vegetation study

3.1.1 Vegetation materials, descriptions and analysis in original papers

Vegetation studies with sample plot material were included in four of the original articles (II, III, IV, V) . These materials include (1) the primary material for the description of aro wetland types (II), (2) the material of the water level measurement points across various mire and aro wetland communities (III), (3) the large Hirvisuo vegetation material (IV) and (4) the combined material derived from the primary description of aro wetlands (II) with some additional communities from the Hirvisuo material (IV). Subjective cover estimation and relatively small sample plots were used in all the vegetation studies. The small plot size was used because of the need to exactly relate the water level fluctuation and species composition from just the same mire surface level. This procedure is in line with the view of Økland (2007) according to which several important research objectives cannot be approached without subjective elements in sampling designs and that a research strategy entirely based on rigorous statistical testing of hypotheses is insufficient for field ecological data. The sample plot designs in each material (1-4) were as follows. (1) Vegetation sampling for the primary description of aro wetlands (II) was based on sample plots of size 0.5 m that were placed subjectively. (2) Sampling for the water level measurement research (III) was performed by selecting one monitoring plot from each habitat type (community) as a sample plot (2 m) composed of four separate vegetation quadrats of 0.5 m. The quadrats were located beside the mire-water wells and observation tubes one after another so that every other quadrat was used as a vegetation quadrat. (3) In the Hirvisuo aapa mire study (IV), subjectively placed vegetation sample plots of 0.25 m were used. (4) The same material as that in the primary aro description (II), added with reference material from the Hirvisuo study,was used in the vegetation analysis of aro wetlands (V). In article II (material 1), the vegetational aro wetland types were formed on the basis of the dominant species. This seemed a highly relevant method with regard to vegetation extremely poor in species. In article III (material 2), the vegetation was ordinated using Non-metric Multidimensional scaling (NMDS). In article IV (material 3), TWINSPAN-classification and NMDS-ordination were

21 used and in article V (material 4) the cluster analysis and NMDS ordination were used.

3.1.2 Summary vegetation classification for the present paper

In this summary paper the communities of articles II (vegetation material 1), III (material 2) and V (material 4), supplemented with one additional community from article IV (material 3), are rearranged and renamed to create a more uniform vegetation classification, including the poorly-known aro vegetation. For the inland aro vegetation of Northern Ostrobothnia a multiple-entry key (vegetation, peat) is suggested (see Eurola & Kaakinen 1978, Eurola et al. 1984, 1995). New classification aspects concern the vegetation of aro wetlands and related fens. In other respects the arrangement of the study communities follows the vegetational mire classification of Ruuhijärvi (1960), Eurola & Kaakinen (1978) and Eurola et al. (1984, 1995) basically based on Cajander (1913). A clustering application, considering both the vegetation (communities of article III, material 2) and the range of water level fluctuation (main clusters arranged on the basis of the range of water level fluctuation), was performed to combine the vegetation classification and hydrology.

3.2 Direct and indirect environmental measurements

3.2.1 Water level

Article III constituted a water level monitoring series with 12 vegetation types (from hummock-level mire types to lawn fen types to flark fen types and to various aro wetland types). The concept of water level fluctuations within different types of aro wetlands was supplemented in article V by providing a reference measurement point in a heath forest. This was supposed to represent the areal fluctuation of the ground water level (Soveri et al. 2001). The fluctuation pattern of aro wetland types was compared to the areal fluctuation pattern of the groundwater table level in article V. Two methods were used to measure the superficial position of water table and the depth of groundwater level in mineral soil (III, V). The measurements were preferably made through observation wells (mire water wells) established at all the measuring plots. The diameter of the wells was 10 cm and depth 30–50 cm. To obtain water level values from deeper parts, plastic observation tubes with a

22 diameter of 2 cm and perforated bottom parts were installed in several monitoring plots. Their bottoms were placed at depth 60–100 cm from the surface. The tubes were placed at a distance of 0.5–1 m from the surface wells. In plots where the observation tube was installed in addition to the well, the tubes served as piezometers. The monitoring was carried out during snow-free periods between 1997 and 2002. The year 1998 was exceptionally wet with very large amounts of rain during the summer. In years 1999, 2000 and 2002 the autumns were drier than normal. In sites with an unstable surface moisture status, most of the measurements were carried out during the early part of the overall measuring period and the measurements of Sphagnum fen (a habitat with a stable surface moisture status) sites during the latter part. This may have a minor effect on the residence times so that the residence times of flooded conditions in habitats with an unstable water regime (aro-like habitats) are overrepresented in relation to those of stable habitats (Sphagnum fen).

3.2.2 Peat thickness and soil profiles

For article I, the approximate peat thickness pattern of the studied mire system (Hirvisuo) was shown in a map of Hänninen (1988), and for vegetation sample plots (II, III, IV, V) peat thickness was measured by means of a metal rod. The thickness of the porous surface peat layer and the tight bottom peat layer was measured on the basis of peat humification for the water level measurement points of article III. The humification of the peat profile was determined by means of Hiller boring. Porous surface peat included peat with a humification degree of H 1–3 (von Post) and the tight bottom peat with a humification degree of H 4–10. the mineral soil profiles were subsequently (November 2007) provided from two aro wetland sites for the vegetation summary classification of the present paper. Total soil profiles were not systematically investigated in this research.

3.2.3 Application of Ellenberg indicator values

For each sample plot in article V (vegetation material 4, Section 3.1.1.), the average Ellenberg´s indicator values for ´moisture´, for ´soil reaction´ and for ´nitrogen´ (Ellenberg et al. 1992) were calculated. The validity of Ellenberg´s soil reaction values for the study area was confirmed by comparing Ellenberg´s et al. (1992) result to the pH measurements obtained from Eastern Finnish fen material (Tahvanainen et al. 2002, Tahvanainen 2004). Species ecological optima along the

23 water pH gradient were estimated from the data by means of abundance weighted averaging. The estimated pH and Ellenberg´s values were then fitted into the ordi- nations. Water pH has proved to be the most reliable indicator of the poor-rich gradient (Sjörs 1952, Tahvanainen 2004) in mires. In aro wetlands, surface water fluctuation makes it difficult to assess water pH conditions without detailed seasonal monitoring. Furthermore, the pH of surface water probably does not have similar dynamics and effects in aro wetlands as in mires. However, most of the aro wetlands species are typically mire plants and therefore the calibration with pH, a chemical indicator of the poor-rich gradient in mires, is valid for exploring the poor-rich gradient in aro wetlands.

3.3 Landscape level investigations

The main morphological pattern of Hirvisuo (I), Kärppäsuo (II) and Hoikkasuo (VI) mire systems (Fig. 1) was determined on the basis of aerial photographs. The vegetation pattern of the Hirvisuo mire system (mire complex in article I) was delineated on black and white aerial photographs (1: 10000), and the dominating mire site types (Eurola & Kaakinen 1978, Eurola et al. 1984) for each pattern were determined in the field. The suggestion for dividing the Hirvisuo mire system into mire areas with a stable and unstable (variable) water regime was based primarily on vegetation mapping and literature records for the hydrological instability of certain communities (Ruuhijärvi 1960, Havas 1961, Fransson 1972, Paasovaara 1986, Heikkilä & Lindholm 1988) (I). The groundwater recharge-discharge pattern for the southern part of the Hirvisuo mire system (I) was suggested mainly on the basis of the vegetation and prevailing direction of groundwater flow in the glaciofluvial formation south of the Hirvisuo mire complex (Miettunen 1994) and on the basis of the topography of the bottom of the mire basin (Hänninen 1988). The groundwater recharge-discharge pattern in a part of the Iso Palosuo-Kuusisuo mire system (II) was assessed on the basis of the groundwater table levels measured (about) simultaneously by Miettunen (1992).

24 4 Results and discussion

4.1 Plant communities and aro vegetation classification

4.1.1 Aro wetlands and aro vegetation

For the present summary paper the central plant communities of this thesis are named uniformly and placed into a vegetation classification system including aro vegetation in Table 1. The floristic composition of each community is provided in Appendices 1 and 2 and in the Appendix of article IV, and the most important Fin- nish references for previously described communities are also given in Table 1. For aro wetlands, a couple of typical vegetation types usually with a thin (not exceeding 5–10 cm thickness) peaty organic surface layer were primarily described in article II (additions in articles III and V). In this summary paper the term ´aro vegetation´ is proposed as a general name for the vegetation of aro wetlands and for corresponding vegetation in more thickly-peated sites. Aro vegetation as a group is briefly described below with a key for the main communities. The key-form is only used to indicate the principal differences between communities in a concise form and only concerns the study area. Aro vegetation is extremely poor in species. Scattered Pinus sylvestris and Betula pubescens sometimes occur as individuals or as small groups. Shrubs are scanty, except for occasional occurrences of Salix repens. Saplings of Pinus sylvestris and Betula pubescens occur temporarily, especially in sites with strong human influence on water conditions. Dwarf shrubs are generally lacking, with occasional occurrences of only Andromeda polifolia in peripheral parts. Certain graminoids (Carex lasiocarpa, Rhynchospora fusca, Molinia caerulea, Juncus supinus, Carex nigra subsp. nigra, Juncus filiformis) overwhelmingly dominate in the field layer. Carex limosa, Carex chordorrhiza, Scheuchzeria palustris, Menyanthes trifoliata and also Rhynchospora alba are lacking or scanty. Menyanthes trifoliata most clearly avoids aro vegetation. Forbs (with the exception of Drosera longifolia in some sites) are lacking. In near-seaside localities certain forbs (Lysimachia thyrsiflora, Potentilla palustris) may be included. There is a variation from a total lack of mosses to a considerable Sphagnum or Polytrichum cover in the bottom layer. The appearance and condition of dominant Sphagnum majus, S. jensenii and S. platyphyllum vary considerably according to the current moisture status of the land surface. Low-grown Sphagnum compactum is highly dominant in some sites.

25 The key: 1 Fen species Carex lasiocarpa, Rhychospora fusca, Molinia caerulea, or Juncus supinus are dominant in the field layer. Bottom layer either lacking, or dominants are Sphagnum majus or Sphagnum jensenii, which are in a varying condition depending on the current moisture status of the ground surface, or low-grown Sphagnum compactum. Soil profile in Fig. 2. – Treeless fen aro vegetation Æ 2 1 Heath species Polytrichum commune dominant in the bottom layer, certain sparsely growing sedge-like plants (Carex nigra subsp. nigra, Juncus filiformis) in the field layer. Soil profile in Fig. 3. – Heath aro vegetation Æ (Polytrichum commune community of aro wetlands) (Fig. 4) 2 (1) Peaty surface layer < 10 cm thick. Typical mire expanse flark fen species (Menyanthes trifoliata, Carex chordorrhiza, Carex limosa, Scheuchzeria palustris, Rhynchospora alba) do not usually occur. – Fen aro wetlands Æ 3 2 Peaty surface layer > 10 cm. Typical mire expanse flark fen species (mentioned above) may occur. – Aro fens Æ 5 3 (2)Dominant species evenly distributed, the habitat does not seem near-to plantless – Ordinary fen aro wetlands Æ 4 3 Almost plantless-looking, muddy ground surface (flooded at times) dominates. – Mud flats (Juncus supinus community of mud flats, e.g.) (Fig. 5) 4 (3) Dominant in the field layer Carex lasiocarpa – Carex lasiocarpa community of aro wetlands (Fig. 4) 4 Dominant in the field layer Rhynchospora fusca. Rhynchospora fusca as a uniform, dense stand. – Rhynchospora fusca community of aro wetlands (Figs. 6, 7) 4 Dominant in the field layer Molinia caerulea – Molinia caerulea community of aro wetlands (Fig. 8) 5 (2) Dominant in the field layer Carex lasiocarpa – Carex lasiocarpa community of aro fens 5 In the case with dominant Rhynchospora fusca no distinction can be made between the aro fen and mud bottom flark fen and the vegetatation is included in mud bottom flark fens. Rhynchospora fusca often occurs as dense patches surrounded by sparser stands of other sedge-like plants. Eriophorum angustifolium and Carex limosa almost constant, Carex lasiocarpa and Rhynchospora alba frequent. Trichophorum cespitosum may occur. From forbs Drosera longifolia most frequent, Menyanthes frifoliata also occurs.

26 Bottom layer scanty, only Hepaticae (Cladopodiella/ Gymnocolea) almost constant. Sphagnum compactum and S. platyphyllum scanty. – Rhynchospora fusca community of flark fens

The communities in the above key are suggested as vegetation types for Northern Ostrobothnia; Rhynchospora fusca community of flark fens belongs to the mesot- rophic mud bottom flark fens of Eurola et al. (1984, 1995). ´Vegetation type´ is here regarded as a fixed point in the multidimensional network of ecological directions of variation (Eurola 1984, 1995), not as an organism-like entity (Clements 1916), which is just to be ´found´ in the field. There are additionally numerous other communities of a smaller scope within the aro vegetation of the study area, which are not described in this study (especially in the Ressunaro area, Fig. 1, and in near-seaside areas). Vegetation sample plot material from the aro fen community (Carex lasiocarpa community of aro fens) is infrequent (III) although the water level measuring points cover several such sites. The question of distinguishing flooded treeless Carex lasiocarpa-Sphagnum dusenii fens of Valpas (1964) from aro fens remains open. By way of conclusion, the present key discerns with caution the aro communities, which are regarded as vegetation types within the climatic and geologic conditions of the study area. Considering the young successio- nal vegetation of the near-seaside areas of the Bothnian Bay and a larger regional extent, the key should be decisively altered. The types suggested above, however, probably represent vegetation types of the geographic area in which the scope of the aro vegetation is at its highest in Fennoscandia. Aro wetlands (II, III, V) and the wider group aro vegetation proposed in this thesis represent a boreal vegetation that has not been described as a uniform unit for any larger region (see e.g. Dierssen 1982, 1995, Mackenzie & Moran 2004). Aro wetlands belong to seasonal wetlands that are characterised by a semi- permanent or seasonally flooded water regime and a mineral soil substrate (Cowardin et al. (1979). Fen aro vegetation may be simultaneously viewed as belonging to mires as defined in this paper (Section 1.3.). The global distribution of the aro vegetation is unknown. Corresponding vegetation, however, is expected to be found thoughout the boreal zone, where its occurrence as a vegetation type of minor extent among dominant vegetation types (nested habitats, Palik et al. 2003) seems to be mainly determined by the topography and water-permeability characteristics of the underlying mineral soil. This special seasonal wetland type especially supposes conditions that culminate in the considerable drought of the surface (Jalas 1953, Valpas 1964).

27 Table 1. Synopsis of the central vegetation types of the study material (appendixes 1 and 2, and article IV: appendix: 5). Community name in the present table is followed by the abbreviation of the community name used in the original articles of this thesis. The reference for a previous description of the corresponding vegetation type is given, provided with a common forest or mire site type name in cases in which the community corresponds to them.

Plant communities with their division into main groups, and appen- Previous reference of the community, mire or dixes with community composition forest site type with a common abbreviation (in bold) A Paludified heath forests and pine mires (Soistuneet kangas- metsät ja rämeet) A1 Vaccinium uliginosum-Ledum palustre-Pleurozium schreberi Kalela 1961: EVT (Empetrum-Vaccinium community (App. 2: 1 pEVT, IV: App: 1) type), paludified A2 Calluna vulgaris community (App. 1: 1 Callu mire, IV: App: -- 3) A3. Empetrum nigrum-Sphagnum fuscum community (App. 1: 2 Ruuhijärvi 1960: Table 35: Sphagnum fuscum Sph fus bog Reisermoor RaR B Treeless lawn fens (Välipintanevat) B1 Trichophorum cespitosum-Sphagnum compactum community Ruuhijärvi 1960: Table 9: Sphagnum compac- (App. 1: 4 Sph com fen, 2: 2 TrScomfe, IV: App: 4) tum Weissmoore LkKaN, Sphagnum compactum fen B2 Trichophorum cespitosum-Eriohorum valginatum-Sphagnum Ruuhijärvi 1960: Table 6: Kurzhalmige Sphag- papillosum community (App. 1: 3 Sph pap fen) num papillosum Weissmoor LkKaN, S. papillosum fen C Treeless flark fens (Rimpinevat) C1 Scheuchzeria palustris-Carex limosa-Sphagnum majus Ruuhijärvi 1960: Table 12: Sphagnum dusenii community (App. 1: 5 Sph fen) Rimpiweissmoore SphRiN C2 Carex limosa-Menyanthes trifoliata community (App. 1: 6 Ruuhijärvi 1960: Table 16: Oligotrophe Meny fen, App. 2: 3 ClimMnfe) moosarme Rimpiweissmoore, Table 17: Mesotrophe moosarme Rimpiweissmoore RuRiN C3 Rhynchospora fusca community of flark fens (see especially -- article IV: App: 5 Rhynchospora fusca, App. 1: 7 Rhy fu fen) D Aro vegetation (Arokasvillisuus) Da Treeless fen aro vegetation (Neva-arokasvillisuus) I Edaphic groups: Ia Fen aro wetlands (Neva-arot) – peaty surface layer < 10 cm Ib Aro fens (Aronevat) – peaty surface layer > 10 cm thick II Vegetational groups Daa Carex lasiocarpa community group Daa1 Juncus supinus community of mud flats (App. - 2: 4 Mud flat) Daa2 Carex lasiocarpa community of aro wetlands Jalas 1953: Table 11: 3 Carex lasiocarpa-Erio- (App. 1: 10 Car las aro, 2: 5 Car las aro) phorum angustifolium Heidevegetation (Saisonhydrophile Heidevegetation) Daa3 Carex lasiocarpa community of aro fens (App. -- 1: 9 Car las fen) Dab Rhynchospora fusca community group Dab1 Rhynchospora fusca community of aro -- wetlands (App. 1: 8 Rhy fu aro, 2: 6 Fhy fu aro) Dab2 Rhychospora fusca community of flark fens, -- see C3 Dac Molinia caerulea community group Dac1 Molinia caerulea community of aro wetlands (App. 1: 11 Mol aro. 2: 7 Mol aro) -- Db Heath aro vegetation (Kangasarokasvillisuus) Db1 Polytrichum commune community of aro wetlands (App. Jalas 1953: Table 11: 1–2 Saisonhydrophile 1: 12 Pol com aro, 2: 8 Pol com aro) Heidevegetation, Valpas 1964: Table 4: 28–33 Juncus filiformis-Carex nigra-Poly- Dc Other plant communities of aro wetlands trichum commune flooded heaths Dc1 Carex nigra community (App. 2: 9 Car nig aro) --

28 Fig. 2. Podsolic soil profile of a fen aro wetland (Carex lasiocarpa community of aro wetlands). Organic layer of thickness 4 cm (a loose, detritus-like layer of about 1 cm in the top and below it a dark well-decomposed peaty layer of 3 cm), an eluvial horizon of grey-whitish sand (about 8 cm), and lowermost an illuvial horizon partly merging into sandy parent material. Hämeenjärvi area near Oulu. Photo: Antti Huttunen 7.11.2007.

Fig. 3. Podsolic soil profile of a heath aro wetland (Polytrichum commune community of aro wetlands). Organic layer of 5–8 cm in the surface, an eluvial horizon of grey- whitish sand (25–30 cm thick) below it, and lowermost an illuvial horizon partly merging into sandy parent material with some stones. Hämeenjärvi area near Oulu. Photo: Antti Huttunen 7.11.2007.

29 Fig. 4. Polytrichum commune community of aro wetlands in the foreground and Carex lasiocarpa community of aro wetlands in the background. Peukaloperä, Kärppäsuo area, northern half of the southern aapa mire zone of Finland. Photo: Lassi Kalleinen 25.7.2007.

Fig. 5. Juncus supinus community of mud flats in the foreground, Carex lasiocarpa community of aro wetlands in the background. Hepolampi seasonal pond, Ressunaro (Hepolampi) area, south of the River Oulujoki. Photo: Lassi Kalleinen 2.9.2006.

30 Fig. 6. One of the largest Rhynchospora fusca communities of aro wetlands in Northern Ostrobothnia. Hepolampi mire-aro wetland system in Ressunaro (Hepolampi) area, south of the River Oulujoki. Photo: Lassi Kalleinen 2.9.2006.

Fig. 7. Rhynchospora fusca community of aro wetlands to the left, sparsely-grown Carex lasiocarpa community to the right. Some sand on the ground surface near the bottom of the picture. Typical scenery from a large mire-aro wetland system south of the River Oulujoki: long raised beach ridges (heath forests) border the narrow and long part of the mire-aro wetland system. Meriaro locality. Photo: Lassi Kalleinen 2.9.2006.

31 Fig. 8. Molinia caerulea community of aro wetlands. Peukaloperä, Kärppäsuo area, northern half of the southern aapa mire zone of Finland. Photo: Lassi Kalleinen 25.7.2007.

4.1.2 Clustering of communities and the range of water level fluctuations

Three main clusters of plant communities were formed by means of a clustering application considering both the vegetation (communities of article III) and the range of water level fluctuation (main clusters arranged according to the range of water level fluctuation). Aro wetlands were scattered into the two uppermost clusters in the graph (Fig. 9) so that the uppermost main cluster was mainly composed of aro communities, while the second uppermost of three main clusters had one aro community (Carlasaro), one evident aro fen community (Carlasfen) and three treeless fen communities (Rhyfufen, Menyfen, Sphfen). Mud flat was not included in this vegetation material. Instead of distinguishing clearly aro vegetation from ordinary fen vegetation, this minor clustering distinguishes the peripheral and threshold communities of mire-aro wetlands systems (vegetation types in the uppermost main cluster) from those the central parts of mire-aro wetland systems and ordinary aapa mire systems (vegetation types in the middle-situated main clus-

32 ter). Thus this vegetational division stresses the significance of the location of different communities of aro vegetation-ordinary fens within the wetland basins, mainly indicating differing hydrological conditions between the peripheral and central parts of the wetland basins. Valpas (1964) also describes a zonation of ´drogs´ (having aro-like communities) in Köyliö, Western Finland, which much resembles the zonation of aro wetlands in Northern Ostrobothnia. Anderson & Davis (1997) report differing water level fluctuations between the central and peripheral parts of Maine fens.

Fig. 9. Clustering of the communities of article III. Explanations for the community abbreviations in Table 1.

4.2 Water level, vegetation and peatland processes

Water table is an important gradient in mires having links to vegetation and peatland processes, especially peat production. According to the review of Wheeler (1999), various aspects of the water level gradient may affect the species composition and community limits of wetland vegetation. The aspects are here divided into three main groups: (1) the mean water level, (2) the range of water level fluctua-

33 tion and (3) the timing of the fluctuation. The results of this thesis suggest that in various parts of mire-aro wetlands systems, too, various aspects of the water level gradient are ecologically relevant (cf. Wheeler 1999).

4.2.1 Mean water level and the mire surface levels

The result in article III suggests that the hummock-flark peatland vegetation gradient (Eurola et al. 1984, 1995), i.e. the gradient of mire surface levels (IV) or microtopograhpic gradient (Malmer 1986), largely predicts the mean water level across mire communities with slight water level fluctuations (four community types out of 12 measured) and to some extent across mire communities with considerable water level fluctuations (three community types). Accordingly, the ecological relevance of this physical average parameter seems to be restricted to a part, though to the main part, of mire communities within the monitored habitat group, but not to aro wetlands. Instead, the physiognomic or vegetational gradient (mire surface levels) is highly applicable across all the mire communities. Økland (1990) found a close correlation between median depth and water table and species composition in a SE Norwegian bog complex (see also Økland et al. 2001). Also Singsaas (1989) and Moen (1990) stress the major significance of mire surface levels as a vegetation gradient in two Norwegean fen complexes, while Nicholson et al. (1996) indicate that the most important gradients affecting peatland bryophyte vegetation in the large Mackenzie watershed (Canada) are surface water chemistry and height above the water table. Clearly the importance of the mean (or median) water level and the gradient of physiognomic mire surface levels as its central vegetational response in mires seems well-established in boreal peatland research. In article V, the Ellenberg´s Indicator value for moisture almost followed the NMDS 1 dimension in a vegetation series from paludified heath forests to lawn fens, flark fens and aro wetlands, and the indicator value could easily be interpreted as a physiognomic gradient of the vegetation or general landscape wetness. MacKenzie & Moran (2004) outline the ´soil moisture regime´ with three broad categories (very wet, wet, very moist) across all the known wetland vegetation types of British Columbia, Canada: wetlands other than peatlands also have been classified into moisture categories related to well-established, north- European mire surface levels of peatlands.

34 4.2.2 Range of water level fluctuation

The water level measurements in this study (III, V) indicate that the range of water level fluctuation forms a gradient from peatlands to aro wetlands and that it is generally smaller in peatland habitats than in aro wetlands (Fig. 10). The result is in line with the Canadian wetland classification (Tarnocai 1988, Warner et al. 1997), in which the water level fluctuations form one of the two principal gradients (pH, water fluctuation) along which five wetland categories (bog, fen, marsh, swamp, shallow water) have been arranged (Vitt 1994, 2000, Zoltai and Vitt 1995). The present results (III) also suggest that there is a gradient from small to relatively large water level fluctuations within peatlands as well, and that the vegetation of all the mire surface levels (hummock, intermediate and flark levels) seems to respond to the range of fluctuations (also articles I and IV, Laitinen 1990) (cf. Lindsay et al. 1985). Thus the stability of the water regime may be regarded as an independent vegetation gradient also in boreal Fennoscandian mires particularly if vegetation material includes steep slope fens (Havas 1961) and thin-peated mires on sand (I, IV). Accordingly, the stability of the water regime may be regarded as a mire gradient of local importance in boreal Fennoscandia on the basis of the gradient-importance categories of Økland et al. (2001). As far as the fluctuations of water table level are concerned, Wheeler & Proctor (2000) are right in claiming that there has been little attempt to categorize mires quantitatively into ´wetness types´. The community-based division to (1) mires with slight water level fluctuations, to (2) mires with considerable water level fluctuations and to (3) wetlands with extreme water level fluctuations according to the water level residence curves (III) is evidently valid in most of boreal Fennoscandia. Mires with considerable water level fluctuations are evidently bound to ´non-average´ geological settings that allow water level drawdown in typical boreal climatic conditions with a generally positive water balance (e.g. Vitt 2006) or to hygrically oceanic local climates allowing mires to form on such steep slopes (Eurola et al. 1982) that even temporary desiccation is possible in spite of the oceanic climate.

35 Fig. 10. Communities of article III arranged according to the range of water level fluctuation (standard deviation). Explanations for the community abbreviations in Table 1. In mid-boreal aapa mire – aro wetland environments four water –level fluctuation groups of species can be presented according to the results of article III: 1. Range of fluctuation 0–25 cm. Species of (ordinary) mires with slight water level fluctuations. The group corresponds most to the Vaccinium uliginosum, Sphagnum papillosum and Carex limosa groups of article IV and to the Carex globularis, Menyantes, Eriophorum vaginatum and Empetrum groups of Havas

36 (1961). The species are mire margin to mire expanse species, fen to bog species and characteristically species representing all the mire surface levels. 2. Range of fluctuation 26–50 cm. Species of mires with considerable water level fluctuations, thin-peated sites on permeable sand in flat sites. The group corresponds most to the Cladonia-Sphagnum compactum group of article IV and to the Molinia group of Havas (1961), although Molinia caerulea in itself belongs to group 3 in the current division. According to Havas (1961) the Molinia group above all indicates seasonal drought, while Auer (1922) reports the compact, periodically desiccated peat of Molinia and Trichophorum cespitosum sites in slope fens in the Kuusamo area. The occurrence of typical hummock level and lawn species in the same species group (Cladonia-Sphagnum compactum group, IV) is in line with the statement of Havas (1961) that the occurrence of species from various mire surface levels is a characteristic feature in slope fens with an unstable water regime. 3. Range of fluctuation 51–100 cm. Species of fen aro wetlands: all the central dominating species of the fen aro wetland types described in this study (Molinia caerulea, Rhynchospora fusca, Carex lasiocarpa) are within this group. The group corresponds most to the Rhynchospora fusca group of article IV, having no close correspondence to species groups for the slope fens described by Havas (1961). This highlights the difference of this species group as compared with group 2: the species within group 3, apart from Molinia, are characterised by flat, temporarily flooded aro fen and fen aro sites, not seasonally dry slope fen sites. 4. Range of fluctuation over 101 cm. Species of heath aro wetlands. The species of this group (Carex nigra, Juncus filiformis, Polytrichum commune) belong to mire margin disturbance indicators (Störzeiger) of Dierssen (1982). The huge range of water level fluctuation is caused by the deep groundwater table level in the mineral soil (permeable sand and gravel); considerable surface-water flooding may also occur in these sites. The depth of flooding, according to the water level measurements (III, V), seems to be an ecologically relevant aspect of water level fluctuation within mid- boreal aapa mire-aro wetland environments, too: the species composition and community boundaries partly follow it especially within aro wetlands, but also within the transition from mires to aro wetlands. Traditionally, the depth of flooding has not been specifically considered in peatland research unlike in global wetland research (Keddy 2000). Ellenberg´s indicator values for ´moisture´, applied for a long series of vegetation types from paludified heath forests to lawn and flark fens and to aro wetlands including mud flats (V), indicated vegetational

37 response to the depth of flooding (from total lack of flooding to a high flood). The species dominances (various aro wetland types) within fen aro wetlands respond to the increasing depth of flooding in the order from Molinia caerulea to Rhynchospora flusca to Carex lasiocarpa. Trichophorum cespitosum mainly occurs outside the flood depression (aro wetland) proper. While discussing water level fluctuation, the complex nature of the water level gradient (water level-soil moisture complex gradient, Wheeler 1999) should be considered in particular: in situations where the water table lies below the surface, the near-surface moisture conditions, including the forces retaining water (pF- values), are decisive particularly for mosses, and near-surface seasonal drought may be destructive (disturbance by Grime 1977) in mud bottoms although the water table level is not located very deep. Important moisture conditions in the soil have not been measured in this thesis, and a specific study should be conducted with the aid of time domain reflectometry (TDR), e.g., (Pepin et al. 1992, Myllys & Simojoki 1996). In a global perspective, different types of water dynamics in wetlands (including peatlands) are of utmost importance (Keddy 200). A descriptive dynamics-division has been applied to a large number of wetlands in Canada. Mackenzie & Moran (2004) suggest a hydrodynamic index with five categories (stagnant (St), sluggish (Sl), mobile (Mo), dynamic (Dy), very dynamic (VD)) to classify the magnitude of the vertical fluctuation and lateral movement of water in British Columbian wetland communities. A corresponding hydrodynamic gradient in the case of the vegetation continuum from mires to aro wetlands in Northern Ostrobothnia (III) essentially represents the gradient from small to strong water level fluctuations, and the magnitude of lateral water movements across this gradient is of minor importance. Instead, the gradient reference frame of Racey et al. (1996) for wetlands in northwestern Ontario, Canada, (see Rydin & Jeglum 2006) seems to outline the hydrodynamic gradient as a wave exposure gradient (e.g. Wilson & Keddy 1988) from sheltered, peaty marshes to exposed mineral marshes, e.g.

4.2.3 Timing of water level fluctuation

Environmental factors generally arise from various factors that may correlate over different time scales (Yu 2006). Fluctuation occurs in flooding and drying in aro wetlands over a longer scale, dominated by two patterns, i.e. a seasonal fluctuation pattern with a spring flood (in some years prolonged) and a longer term fluctuation

38 pattern with hydroperiods and dry periods even longer than one snow-free period (V). The seasonal pattern is mainly a response to yearly snow-melt, and aro wetlands dominated by this pattern (Polytrichum commune type etc.) are here called surface water aro wetlands (perched water aro wetlands) (Fig. 11) (V). The longer term pattern mainly reflects the areal, long-term fluctuation in the groundwater table level of mineral soils, because aro wetlands dominated by this pattern (mud flat, Rhychospora fusca aro) have a several-year-fluctuation pattern equal to that of a reference site i.e. a dry heath forest (large sand area) (see Soveri et al. 2001). The aro wetlands dominated by this fluctuation pattern are here called groundwater aro wetlands (Fig. 11) (V). It seems that the timing and duration of hydroperiods and dry periods, which are a highly important environmental factor especially for various temporary wetlands of more arid and warm environments of the world, such as the vernal pools of Mediterranean climate regions (Keeley & Zedler 1998) and for tropical wetlands (Müller & Deil 2005, Müller & Wezel 2006), also have some local importance in boreal wetlands. This is true for the study area (mid-boreal lowland area of Finland), which has locally large sandy areas with the groundwater table near the surface: here some the local aro wetlands are mainly characterised by the irregular several-year-fluctuation in groundwater table level, and some (situated well above the groundwater table level) by the annual snow-melt-induced fluctuation.

Fig. 11. Main vegetational and hydrological types of aro wetlands of the inland of Northern Ostrobothnia in relation to some hydrologic factors and in relation to the intensity of disturbance caused by flooding and desiccation.

39 4.2.4 Natural disturbance

In the present study (V) the total cover of plants was regarded as an indirect measure of natural disturbance. The total cover of plants formed a gradient along the Ellenberg´s indicator value for ´moisture´ and was smallest in habitats with the highest moisture indicator values . This suggests a connection between disturbance and water level in general. Ellenberg´s indicator value for ´moisture´ also largely follows the depth of flooding, suggesting specifically the significance of disturbance through flooding. The intensity of disturbance within aro wetlands, as suggested by the total cover of plants, increases as a result of the increasing depth of flooding and the duration of each hydroperiod and dry period (V) (Fig 11), the almost bare mud flats being the striking extreme end in ecological terms. Accordingly, the aro wetlands seem to demonstrate that both the range and timing of water level fluctuation are agents within the disturbance (V). The number of species diminished (V) along the increasing Ellenberg´s indicator value for ´moisture´ and along the depth of flooding. Only the rarer Carex nigra aro slightly deviated from the general pattern by being more species rich. Thus in this case, the number of species decreased with the increasing intensity of disturbance, and disturbance did not affect the temporal occurrence of ruderals, which is contrary to the basic idea of Grime´s (1977, 1979) model. Instead, tree seedlings occurred and acted as ruderal-like plants in aro wetlands: the repeated loss of small tree seedlings is the most evident floristic effect of the natural disturbances caused by inundation in aro wetlands. Accordingly, repeated inundation seems to have a marked landscape-level effect on aro wetlands in keeping them in a treeless state. Natural disturbance (Grime 1979, Keddy 2000) has been discussed little in connection with mires and discussion of disturbance has more stressed perturbations by man, e.g. as in Turetsky & St. Louis (2006). Nekola (2004) found an axis correlated with moisture and disturbance level in a comprehensive gradient analysis of Iowa fens, without explaining the concept disturbance level. Mires are generally ecosystems in which natural disturbance in the sense of Grime (1979) (removal of biomass) or Keddy (2000) (a short-lived event that causes a measurable change in the properties of an ecological community) is not as evident as in littoral wetland ecosystems, for example. In addition to drought and water erosion (Økland 1989), it may include frost upheaval and lateral pressure from expanding ice in the flarks (Rydin & Jeglum 2005: 215).

40 4.2.5 Local peat growth

The occurrence of communities with unstable water regimes in thin peat layers in Hirvisuo (IV) indicates a stagnant state in peat growth, which is also indicated by the presence of highly humified peat in such sites (e.g. Huttunen 1987). Fransson (1972) relates the unstable water regime to the regressive developmental stage of mires, represented e.g. by the occurrence of Cladopodiella fluitans, Gymnocolea inflata and Cladonia squamosa and the Sphagnetum compacti association. Sphag- num majus, S. fuscum, S. magellanicum and S. papillosum, on the other hand, are ´progressive species´ (Fransson 1972). Økland (1989, 1990) discusses a peat productivity gradient (coenocline associated with the peat producing ability of the bottom layer, Økland 1990), but does not suggest any environmental factors as a reason for this. The strongly peat producing species of Økland (1990) and progressive species of Fransson (1972) correspond quite well to species that do not occur abundantly in the extremely thin-peated sand flat of Hirvisuo, and the weakly peat producing species of Økland (1989, 1990) and regressive species of Fransson (1972) correspond well to species that occur in the extremely thin-peated sand flat of Hirvisuo. However, peat thickness in general does not directly indicate the net peat accumulation rate; the age of the basal peat should be known in order to make comparisons. With caution, the peat productivity gradient of Økland (1989, 1990) may thus be regarded as a gradient much dependent on the stability of the water regime.

4.2.6 Other gradients

According to Ellenberg´s indicator values for available nitrogen, all the communities studied in research into the aro vegetation gradients (V) are extremely to moderately poor with regard to available nitrogen. The indicator value, however, increases from the Trichophorum cespitosum-Sphagnum compactum fen to all the aro wetland communities (and to nearly mossless Carex limosa-Menyanthes trifoliata fen). Vitt (1994, 2000) and Zoltai & Vitt (1995) suggest in a schematic pre- sentation of Canadian wetlands that nitrogen and phosphorous in surface water are parallel gradients to water level fluctuation and increase across a transition from moss-dominated peatlands to non-moss-dominated wetlands (marshes, swamps). Thus the nitrogen gradient and the water level fluctuation gradient both in the general Canadian wetland scheme and in the gradient from mires to aro wetlands seem parallel. However, available nutrients (nitrogen, phosphorus) are abundant

41 and vascular plant production is high in typical marshes (Zoltai & Vitt 1995, Keddy 2000). In addition, marshes are characterised by high amounts of water flow. Aro wetlands, instead, more resemble isolated wetlands (Leibowitz & Nadeau 2003) with typically stagnant, seasonal flood water.

4.2.7 Indicator species groups for the stability of the water regime

The indicator species groups (Pakarinen 1995) of various ecological directions of variation (Tuomikoski 1955, Sjörs 1948, Ruuhijärvi 1960, Eurola et al. 1984, Mal- mer 1986, Ruuhijärvi & Lindholm 2006) have been commonly proposed in Scan- dinavian and Finnish mire-ecological traditions. Laitinen (1990) summarized the influence of the unstable water regime of mires and aro wetland sites, characterised by seasonal drought and seasonal flood, as ´flood and desiccation influence´. This can be seen as the extreme end of water regime instability in aapa mire-aro wetland environments and could be called áro influence´. The concept refers at least to two different ecological factors i.e. to partial or total submergence of plants and to the moisture conditions of the soil. The ´flood´ in question here refers to locally inundated conditions with stagnant water without solid particles in suspen- sion (Jalas 1953) and poor in nutrients. As a conclusion, three water regime stability species groups corresponding to the habitat groups obtained on the basis of water level measurements are here concluded to exist for mid-boreal, poor to intermediate minerotrophic aapa mire- aro wetland environments (Table 2) (I–V). The species groups are further subdivided into mire margin and mire expanse species using a corresponding Finnish species division (Tuomikoski 1955, Ruuhijärvi 1960, Eurola 1969, Eurola & Kaakinen 1978, Eurola et al. 1984, 1995, Eurola & Huttunen 2006). The species group éxpanse – extremely unstable´ (Table 2) contains peatland species, but hummock level and lawn species are lacking because of strong seasonal flood. The group ´margin – extremely unstable´ (Table 2) is characterised by mineral soil species and mainly coincides with the Störzeiger species group separated by Dierssen (1982) from the Finnish Sumpf species group of Tuomikoski (1955) and Ruuhijärvi (1960). The point of the group éxpanse – transitionally unstable´ (Table 2) is that the species of typical carpets (mjukmatta) of Sjörs (1948) are lacking: seasonal drought compacts the peat of such sites by allowing strong decomposition (IV). The group éxpanse – stable´ (Table 2) consists of peatland species from all the mire surface levels: the species of mud bottom, carpet, lawn and hummock level within the division of Sjörs (1948).

42 Table 2. Water regime stability species groups for poor to intermediate minerotrophic aapa mires and mire-aro wetland systems of flat Northern Ostrobothnia within the mid- boreal zone. Species are further divided into mire margin and mire expanse species according to the Finnish mire margin (supplementary nutrient influence) – mire expanse (inherent nutrient influence) division.

Water regime (1) EXTREMELY (2) TRANSITIONALLY (3) STABLE stability spe- UNSTABLE UNSTABLE cies groups Habitat group (1) Aro vegetation (2) Mires with unstable (3) Mires with stable water water regime regime Presence/ Most species may be present in Species are lacking or scanty Species are lacking or scanty absence of spe- habitat groups 2 and 3 in aro vegetation (1) but occur in mires with unstable water cies in/from other in mires with stable water regime (2) and principally habitat groups regime (3) lacking from aro vegetation (1) (a) MIRE 1a Éxpanse – extremely 2a Éxpanse – transitionally 3a Éxpanse – EXPANSE unstable´ unstable´ stable´

(inherent nutrient Juncus supinus Rhynchospora alba Menyanthes trifoliata influence) Carex lasiocarpa Carex livida Utricularia intermedia Eriophorum angustifolium Trichophorum alpinum Carex limosa Rhynchospora fusca Trichophorum cespitosum Carex chordorrhiza Lycopodiella inundata Drosera rotundifolia Carex rostrata Molinia caerulea Drosera longifolia Scheuzeria palustris Andromeda polifolia Vaccinium microcarpum Eriophorum vaginatum Calluna vulgaris Carex pauciflora Sphagnum compactum Vaccinium oxycoccos Sphagnum platyphyllum Sphagnum tenellum Rubus chamaemorus Sphagnum jenseni Sphagnum capillifolium Sphagnum majus Cladonia Sphagnum angustifolium Warnstorfia fluitans Sphagnum balticum Sphagnum papillosum Sphagnum pulchrum Sphagnum subsecundum Sphagnum magellanicum Sphagnum fuscum (b) MIRE MAR- 1b ´Margin – extremely unsta- 3b ´Margin – stable´ GIN ble´ Potentilla palustris (supplementary Juncus filiformis Lysimachia thyrsiflora nutrient influ- Carex nigra subsp. nigra Calla palustris ence) Agrostis canina Pedicularis palustris Salix repens Carex diandra Equisetum fluviatile Polytrichum commune Equisetum sylvaticum Carex globularis

Sphagnum riparium Sphagnum squarrosum Sphagnum teres Sphagnum fimbriatum Warnstorfia exannulata Helodium blandowii Cinclidium subrotundum Hamatocaulis lapponicus

It also consists of both the Weissomoor (poor to intermediate treeless fen) and Reisermoor (hummock-level pine mire) species included in the classifications of Ruuhijärvi (1960), Eurola & Kaakinen (1978) and Eurola et al. (1984, 1995). The group ´margin – stable´ (Table 2) specifically contains species of all the subtypes

43 of the Finnish mire margin species group, indicating Sumpfigkeit (surface water influence), Quelligkeit (groundwater influence) or Bruchmoorigkeit (spruce mire influence) or the mixture of Sumpfigkeit and Quelligkeit (Ruuhijärvi 1960, Eurola & Kaakinen 1978, Eurola et al. 1984, 1995). From the point of view of peatland plants, the direction of variation from stable to unstable water regime in the aapa mire-aro wetland environments of Northern Ostrobothnia represents a transition towards more and more harsh ecological conditions. The transition may be compared to the transition from minerotrophy to ombrotrophy in that the ´indicators of stable water regime´ disappear along the transition (Laitinen 1990). The stability of the water regime, however, rather forms a disturbance gradient (Day et al. 1988, e.g.) than a resource gradient (Austin & Smith 1989) and the ability of the species to grow on and within the vital, dense but (often) quite loose Sphagnum layer currently accumulating peat may be of significance. Few specialists adapted to the (extremely-transitionally) unstable water regime within Finnish mid-boreal aapa mire-aro wetland environments (Juncus supinus, Rhychospora fusca, Lycopodiella inundata) are quite rare species, which do not thrive in a vital Sphagnum layer currently forming peat. In British plant communities with Lycopodiella inundata, studied by Rasmussen & Lawesson (2002), Sphagnum compactum and Sphagnum tenellum are almost the only Sphagnum species and the proportion of bare soil in those Bristish communities is large. Rhynchospora fusca occurs in the same communities of Rasmussen & Lawesson (2002). Rhynchospora fusca is regarded as a disturbance-dependent rare species in Central Europe, the disturbance being caused by a fluctuating water level (Kesel & Urban 1999).

4.3 Towards functional models of mire systems and types

4.3.1 Principal-water-function model for mid-boreal mire – aro wetland systems

Landscape level relationships complying with the morphology, surficial water- flow pattern, stability of the water regime and the groundwater recharge-discharge pattern of mid-boreal mire-aro wetland systems (I, II, III, VI) show that it is possible to set forth various parts in them in relation to the principal water function. Part of the hydrogenetic mire classification of Central Europe (Succow & Joosten 2001), with an addition for the origin of water (Joosten & Clarke 2002), and the gradient reference frame of the Canadian wetland classification system (Vitt 1994,

44 2000, Zoltai & Vitt 1995) provide a framework to which those functional parts can be placed. In mire-aro wetland systems an evident primary division follows the stability of the water regime (Figs. 12, 13) leading to two main functional parts, a water stabilization complex and a water fluctuation complex. This division supposes differences in the characteristics of the peat (organic) layer between the water stabilization and the water fluctuation complex, i.e. the existence vs. lack of an elastic, poorly humified peat (layer), respectively. The purpose of this layer is to allow the flow of excess water (mainly) within this peat layer, thus diminishing the fluctuations of the water table level in relation to the mire surface (Ingram 1978, Ivanov 1981). Water table instability has been reported in many damaged raised bogs (Money & Wheeler 1999), but as far as the present water fluctuation complex is concerned it is the question of a concept derived from mire system parts that are supposed to be mainly in a natural state. The lack of a reasonably thick, poorly humified peat layer capable of stabilizing the water table level by regulating the flow of water, and the existence of a well-decomposed organic layer in water fluctuation complexes, are a response of mineral soil characteristics and surface topography: Flat, sandy areas with very low, flat-bottomed depressions – typical localities for aro wetlands (II), or flat sand terraces in the peripheral parts of large mire basins – the Hirvisuo case (I, IV), allow a thin peat layer to form but also permit its repeated desiccation and oxidation leading to strong decomposition. This seems a stagnant state in peat growth (Section 4.2.5). One may suppose that the disappearance of a seasonal flood water layer from the surface of the well-decomposed and supposedly poorly water-permeable peat layer takes place, besides evaporation, also along fractures and other deformations in the tight, dry organic layer, i.e. aided by the secondary porosity of the peat (Siegel & Glaser 2006). The weak downward direction of water flow was detected in some measurements within a few localities in water fluctuation complexes and also in a Sphagnum fuscum bog locality situated in sandy mineral soils. This is in line with the presumption and results of Reeve et al. (2000, 2001) that vertical flow systems develop within peatlands that cover porous sand and gravel deposits, whereas horizontal flow systems are associated with peatlands underlain by less permeable soils of clayey silt. The occurrence of a podsolic profile in aro wetlands also partly refers to the downward movement of water in them (Section 4.1.1). The water fluctuation complex (Figs. 12, 13) is further subdivided into water fluctuation mires and into aro wetlands, aro wetlands being the very extreme end of the gradient, i.e. flat, seasonally flooded and seasonally dry depressions with an

45 extremely thin peaty layer on water-permeable sand. Water fluctuation mires differ from aro wetlands in terms of a thicker (over 10 cm) peat layer and the decreasing depth of flooding and the decreasing depth of the lowest water table level. They were called mires with considerable water level fluctuations in the measurements of article III and formed the intermediate group in relation to the range of water level fluctuations.

Fig. 12. Water stabilization complex (A) and the water fluctuation complex (B) within the Kärppäsuo aapa mire system in the northern half of the southern aapa mire zone of Finland. 1 sand and gravel, 2 till, 3 aapa mire peripheral parts, 4 aapa mire central parts with strings, 5 water fluctuation mire, 6 aro wetland, 7 direction of water flow. Vegetation types within the water fluctuation complex (B) from the distal end of the aro wetland towards the water stabilization complex: Polytrichum commune community of aro wetlands, Carex lasiocarpa community of aro wetlands, Molinia caerulea community of aro wetlands, Carex lasiocarpa community of aro fens.

Fig. 13. Principal-water-function model for mire – aro wetland systems in Northern Ostrobothnia. Functional parts of the local mire – aro wetland system type are related to hydrogenetic mire types of Central Europe and to seasonal wetlands. The origin of water is classified according to Joosten & Clarke (2002).

Water fluctuation mires also differ from aro wetlands (articles II, III, V) and from the whole aro vegetation unit (Section 4.1.1) in that they include the whole gradient of mire surface levels, i.e. the gradient from hummock level (Calluna vulgaris community I, III, IV) to lawn (Trichophorum cespitosum-Sphagnum compactum community I, III, IV, Ruuhijärvi 1960, Fransson 1972, Dierssen 1995) and to flark level including at least the Rhynchospora fusca community of flark fens (III, IV) and the Eriophorum angustifolium community of mud bottom flark fens (Ruuhi- järvi 1960). Topographically the water fluctuation mires form a series from seasonal flood depressions (equal to aro wetlands) to threshold sites: they are either parts of receiver segments or parts of donor segments in flat (raised bog)-aapa mire systems, as demonstrated in the Hirvisuo area (I, VI). Water-fluctuation-lawn-fens are the essence of water fluctuation mires as they also clearly differ physiognomically from the aro wetlands. Such mires occur outside the study area especially within the subalpine belt of the boreal zone of Northern Europe

47 (Dierssen 1995: Trichophoro cespitosi-Sphagnetum compacti) and in slope fens in Northeastern Finland (several communities described by Havas 1961). Plant community composition and the ecology of these habitats have been discussed (Havas 1961, Dierssen 1995), but their occurrence as parts of functional mire systems still awaits further scrutiny. From the hydrogenetic mire types of Succow & Joosten (2001) and Joosten & Clarke (2002), the water fluctuation mires are most closely related to surface flow mires (Überrieselungsmoore), in which evaporation and run-off periodically exceed the water supply, the water level drops, oxygen penetrates the peat and the decomposition of peat accelerates causing water to increasingly overflow the peat (Joosten & Clarke 2002). According to Joosten & Clarke (2002), blanket bogs and part of slope fens belong to the hydrogenetic mire type ´surface flow mires´, while Holden & Burt (2003) perceive blanket peat from the point of view of the acrotelm-catotelm model. The water stabilization complex is subdivided in the present model into two main parts, which are in proportion to (1) the percolation mires of Succow & Joosten (2001) and to (2) the acrotelm mires of Cowenberg & Joosten (1999) (Fig. 13). The functional mire type ´groundwater-fed outlet fen´ refers to the central parts of aapa mires partly resembling the percolation mires of the hydrogenetic classification (see Lindholm & Heikkilä 2006b). They are characterized by the groundwater discharge from deep mineral soil, as described by Heikkilä H. et al. (2001) and Rehell & Tahvanainen (2006) for parts of the large Olvassuo aapa mire massif in Northern Ostrobothnia. According to Joosten & Clarke (2002) percolation mires are found in landscapes where the water supply is large and evenly distributed: the water table levels remain almost constant. In Pilpasuo (Oulu), which contains features of a percolation mire, the poorly humified surface peat is relatively thick (Rehell 1985) and small water level fluctuation takes place in the upper part of the porous surface layer. Percolation mires proper are characterised by peat which remains mostly weakly decomposed and elastic, allowing substantial water flow through the whole peat body (Joosten & Clarke 2002). The vegetation of the outlet-fen-part of Olvassuo (Heikkilä H. et al. 2001) varies from meso-eutrophic flark fen with surface water (swamp) influence to Calliergon richardsonii rich fen (following the classification of Eurola et al. 1995). There is an indication of both surface water influence and ground water influence (Eurola et al. 1984, 1995) in the vegetation of that groundwater-fed outlet fen.

48 The other main part of the water stabilization complex, related to acrotelm mires in the present model (Figs. 12, 13), covers the whole morpho-hydrological range of the most common type of zonal mire systems in the study area. Ordinary aapa mire systems and aapa mire systems with raised bogs (VI) in the study area practically invariably have two main parts in relation to mire water flow pattern in the surface layer, drier donor segments and wetter receiver segments (I, VI) – segments easily recognizable in aerial photographs. The donor segments within these mire systems (raised bog massifs, peripheral parts of aapa mire massifs) easily relate to diplotelmic mires (Ingram 1978) or acrotelm mires (Couwenberg & Joosten 1999) in terms of their general peat structure and water behaviour (Ingram 1978, Ivanov 1981). Receiver segments (central parts of aapa mire massifs) are here also proposed as belonging to diplotelmic mires because of the diplotelmic structure in (part of) aapa mire strings, in the same way as in the hummock ridges of raised bogs (Ivanov 1981). It can be stated by way of conclusion that the local model presented above considers some factors of the physical behaviour of water in mires, combined with the interpretation of the large-scale (aerial photograph) morphology of the mire systems. The general, functional fork-like model by Vitt (2006) for main boreal wetland (swamp, marsh) and peatland types (poor to extremely rich fen, oceanic to continental bog, bog with internal lawns, palsa bog, peat plateau) attempts to consider more widely the ecological, hydrological and general floristic criteria for various habitat types. The model of Vitt (2006) does not, however, consider any large wetland groups comparable to aro wetlands or water fluctuation mires. Vitt (2006) states that in the boreal zone there is climatically a regionally positive water balance at least during the growing season; this allows local water tables to stabilize within peatland ecosystems. This is a general view not considering the diversity in the geological settings (topography, mineral soil) of mires.

4.3.2 Functional subtypes of diplotelmic mires and their relatioships to percolation mires and seasonal wetlands

Considering that water level fluctuations set the conditions governing the rates of the oxidative decomposition of peat (Ivanov 1981, Joosten & Clarke 2002), the model presented above (Fig. 13) can be converted to a general form not confined to the mid-boreal zone of Finland. The model schematically considers the gradual transition of four wetland types (percolation mire, two subtypes of diplotelmic mires, one mineral wetland type) to each other along three gradients. i.e. 1) along

49 the depth gradient of the soil layer in which water level fluctuations occur, 2) along the gradient of the changing proportions of poorly decomposed, water-permeable vs. well-decomposed, poorly water-permeable peat layers, and 3) along the gradient from peat to mineral soil (Fig. 14). The present model relies on the diplotelmic soil-layer hypothesis of mires (Ingram 1978), but supplements the concept by dividing the diplotelmic mires into two subtypes (diplotelmic water stabilization mires, diplotelmic water fluctuation mires) and by schematically considering the transition from diplotelmic mires to percolation mires and to seasonal wetlands. There is a general consensus among mire ecologists (Rydin & Jeglum 2005) that bogs may be viewed as diplotelmic mires (Ingram 1978), i.e. acrotelm mires (Couwenberg & Joosten 1999), with the surficial peat layer (acrotelm) and the main body of peat (catotelm) differing in several respects (Ivanov 1981). In this thesis (article III) typical aapa mires are regarded as diplotelmic mires because the lawn and the hummock-level dominated aapa mire periphery in poor aapa mires have a diplotelmic structure, and because strings of aapa mire centres may have the same kind of diplotelmic structure as the hummock ridges of bogs stated by Ivanov (1981). The concept of a diplotelmic water stabilization mire used here (Fig. 14) refers to the diplotelmic mire suggested by Ingram (1978) and referred to by many authors (e.g. Holden & Burt 2003, Couwenberg & Joosten 2005). This diplotelmic mire subtype has a considerable surface peat layer (acrotelm) with high hydraulic conductivity decreasing with depth (Ivanov 1981, Rydin & Jeglum 2005), i.e. possessing a relatively clear change from acrotelm to catotelm (III). The new subtype diplotelmic water fluctuation mire (Fig. 14), which in article III was placed outside diplotelmic mires proper, refers to mires in which there is a very distinct diplotelmic peat structure within a thin peat layer, but the behaviour of the water table differs from that of normal diplotelmic mires: the water level fluctuation does not remain in the superficial poorly-decomposed peat layer, occasionally reaching the mineral soil in thin-peated sites (III). The thin-peated Trichophorum cespitosum-Sphagnum compactum fen of mid-boreal lowland aapa mires (I, III, IV) is a characteristic community: the superficial, poorly-humified peat layer is thin, composed mainly of living Sphagnum compactum, and changes abruptly into a thin, well-humified bottom peat layer. Because of the shallowness of the porous surface peat, the diplotelmic water fluctuation mires are hydrologically close to the surface-flow mires of Succow & Joosten (2001) and Joosten & Clarke (2002) (Fig 13). Generally, the compact, poorly permeable peat near the surface facilitates the formation of rainwater lenses (Schot et al. 2004) and leads to stronger water level fluctuations (Schipper et al. 2007).

50 Fig. 14. Schematic soil profile across a continuum from percolation mires to diplotelmic mires (two functional subtypes) and to seasonal wetlands. Along the transition from diplotelmic water stabilization mires to percolation mires (Fig. 14) the proportion of relatively poorly humified, elastic peat (Joosten & Clarke 2002) of the whole peat column increases, allowing a substantial flow of water through a thicker peat column and the very stable water table level. The abundance of flowing water, partly derived from groundwater from deep mineral soils, additionally keeps the water table level near the surface. Actually, the functioning of the whole peat body of percolation mires may be related to the functioning of the acrotelm in diplotelmic mires. The continuum from diplotelmic water fluctuation mires to seasonal wetlands (Fig. 14) is a pattern demonstrated in the field by the gradient from water fluctuation mires to aro wetlands in mire-aro wetlands systems in Northern Ostrobothnia (Fig. 13). According to the peat -profile model (Fig. 14), the porous, water permeable surface-peat layer becomes thinner and is finally absent. Also the

51 well-decomposed, poorly water-permeable peat layer becomes thinner and thinner. Thus there is also an intermediate form between diplotelmic water fluctuation mires and seasonal wetlands (Fig. 14). Within this intermediate form the well- decomposed bottom peat reaches the surface and the whole peat column is thin. Mud-bottom-water-fluctuation mires (Rhynchospora fusca community of flark fens, other corresponding the communities of article IV, the Eriophorum angustifolium flark fen of Ruuhijärvi (1960) and part of aro fens (Section 4.1.1.)) fall into this category. Heath aro wetlands are a very extreme case within this scheme, having no peat layer proper, and with a seasonal flood water table perched one to a couple of metres above the regional aquifer in the glaciofluvial formation (see Dempster et al. 2005).

52 References

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61 62 Appendices

63 64 Appendix 1. Plant communities of article III (abbreviations) with general community names and main groups according to the vegetation classification of the present thesis: 1 Calluna vulgaris community, 2 Empetrum-Sphagnum fuscum community, 3 Trichophorum cespitosum- Eriophorum vaginatum-Sphagnum papillosum community, 4 Trichophorum cespitosum-Sphagnum compactum community, 5 Scheuchzeria palustris- Carex limosa-Sphagnum majus community, 6 Carex limosa-Menyanthes trifoliata community, 7 Rhynchospora fusca community of flark fens, 8 Rhynchospora fusca community of aro wetlands, 9 Carex lasiocarpa community of aro fens, 10 Carex lasiocarpa community of aro wetlands, 11 Molinia caerulea community of aro wetlands, 12 Polytrichum commune community of aro wetlands.

Main group Pine mires Treeless Treeless flark fens Aro vegetation lawn fens (aro wetlands and aro fens) Community number 123456789101112 Community type

Molaro Sph fen Meny fen Meny Callu mire Callu Rhy fu fen fu Rhy Rhy fu aro Car las fen Car las aro Pol com aro Sph fus bog Sph pap fen Sph com fen com Sph Tree layer Pinus sylvestris (X)------Shrub layer Salix repens ------7- Saplings Pinus sylvestris 0.1--0.2-----0.13- Dwarf shrubs Andromeda polifolia 40.30.710.1-----0.1- Betula nana 0.510.10.2------Calluna vulgaris 15--0.4------Chamaedaphne calyculata -2------Empetrum nigrum 0.116-0.5------Ledum palustre 0.11-0.1------Vaccinium oxycoccos --0.3-0.1------Vaccinium microcarpum -1------Vaccinium uliginosum -4------Graminoids Carex chordorrhiza -----0.1--1--- Carex lasiocarpa - - 0.2 - - 0.3 - - 18 14 - - Carex limosa ----710------Carex nigra subsp. nigra ------7 Carex pauciflora --3------Eriophorum angustifolium - - 0.9 - 0.1 0.3 14 0.4 4 0.8 - - Eriophorum vaginatum 12103------

65 Juncus filiformis ------0.3 Molinia caerulea ------25- Rhynchospora alba ---10.30.914----- Rhynchospora fusca ------2658---- Scheuchzeria palustris ----9------Trichophorum cespitosum 0.8-2318-0.1------Forbs Drosera rotundifolia -0.50.10.1------Menyanthes trifoliata -----3------Pedicularis palustris -----0.1------Rubus chamaemorus 0.119-0.1------Utricularia intermedia ----0.1------Sphagnum mosses Sphagnum angustifolium -4------Sphagnum annulatum --0.1------Sphagnum balticum --110.1------Sphagnum capillifolium 130.1------Sphagnum compactum - - 0.6 95 - - - 76 0.1 - 2 - Sphagnum fuscum 189------Sphagnum jensenii ------0.1--- Sphagnum majus ----93--3---- Sphagnum papillosum --8536------Sphagnum platyphyllum ------30.20.3- Sphagnum tenellum --0.22------Other mosses Dicranum polysetum 0.8------Pleurozium schreberi 0.1------Polytrichum commune ------97 Polytrichum strictum -40.1------Polytrichastrum longisetum ------0.1 Warnstorfia fluitans ----0.3------Hepatics Gumnocolea inflata & --0.50.1--0.10.5--20.2 Cladop. flu. Hepaticae spp -0.2-0.1------Mylia anomala -2------Lichens Cladina arbuscula 380.1-0.3------Cladina rangiferina + stygia 250.3-0.1------Cladina stellaris 4.5------Cladonia cenotea 0.1------Cladonia crispata 0.1--0.1------Cladonia fimbriata 0.1------Cladonia cracilis 2------Cladonia sulphurina 0.1------Cladonia uncialis 0.5------Community number 123456789101112

66 Appendix 2. Plant communities of article V (abbreviations) with general community names and main groups according to the vegetation classification of the present thesis: 1 Vaccinium uliginosum-Ledum palustre-Pleurozium schreberi community, 2 Trichophorum cespitosum- Sphagnum compactum fen, 3 Carex limosa-Menyanthes trifoliata community, 4 Juncus supinus community of mud flats, 5 Carex lasiocarpa community of aro wetlands, 6 Rhynchospora fusca community of aro wetlands, 7 Molinia cauerulea community of aro wetlands, 8 Polytrichum commune community of aro wetlands, 9 Carex nigra community. Sphagnum aggr. refers to S. majus and S. annulatum (incl. S. jenseni).

Main group Paludified heath forests, Aro wetlands treeless lawn and flark fens (1–3) (4–9) Community number 123456789 Community type

aro aro pEVT Car nig Mol aro Pol com Mud flat Mud ClimMnfe TrScomfe Car lasaro Rhy fu aro fu Rhy Tree layer Pinus sylvestris X------Shrub layer Salix repens 0.1 Saplings Betula pubescens -0.1-0.3- Pinus sylvestris 0.1 0.1 0.1 0.1 0.1 Dwarf shrubs Andromeda polifolia -1--0.40.1--- Betula nana 0.50.1------Calluna vulgaris 0.20.1------Empetrum nigrum 4------Ledum palustre 18------Lycopodiella inundata ------0.2-- Vaccinium microcarpum -0.1------Vaccinium myrtillus 5------Vaccinium oxycoccos -0.1------Vaccinium uliginosum 24------Vaccinium vitis-idaea 5------Graminoids Agrostis canina ------0.12 Calamagrostis epigejos ------0.2 Carex chordorrhiza --4------Carex elata ------0.7 Carex globularis 0.5------Carex lasiocarpa - - 0.2 0.2 15 0.2 5 0.1 0.1

67 Carex limosa --15------Carex nigra subsp. nigra ------0.116 Carex pauciflora -5------Eriophorum angustifolium - 0.1 2 - 0.8 0.4 - - 0.2 Eriophorum vaginatum -10------Juncus filiformis ----0.1-0.42.5- Juncus supinus ---1----- Molinia caerulea ------33-- Rhynchospora fusca -----56--- Scheuchzeria palustris --2------Trichophorum cespitosum -15----0.6-- Forbs Drosera longifolia - 0.1 0.1 - - 0.1 0.1 - - Drosera rotundifolia -0.1------Menyanthes trifoliata --4------Utricularia intermedia --0.1------Sphagnum mosses Sphagnum aggr. ----150.20.10.3- Sphagnum balticum -0.2------Sphagnum capillifolium 2------Sphagnum compactum - 89 - - 0.4 21 0.9 0.8 - Sphagnum papillosum -1------Sphagnum platyphyllum ---0.10.11--- Sphagnum rubellum -0.1------Sphagnum tenellum -10------Other mosses Dicranum polysetum 3------Hylocomium splendens 0.1------Pleurozium schreberi 72------Polytrichum commune ----0.2-17814 Polytrichum juniperinum 0.1------Ptilidium ciliare 1------Straminergon stramineum ----0.3---- Warnstorfia fluitans ----0.1-0.4-- Hepatics Hepaticae spp. - 0.1 0.4 - 10 - 2 - - Community number 123456789

68 Original papers

I Laitinen J, Rehell S & Huttunen A (2005) Vegetation-related hydrotopographic and hydrologic classification for aapa mires (Hirvisuo, Finland). Annales Botanici Fennici 42(2): 107–121.

V Laitinen J, Tahvanainen T, Rehell S & Oksanen J (2007) Vegetation ecology and flooding dynamics of boreal aro wetlands. Annales Botanici Fennici 44: 359–375.

VI Laitinen J, Rehell S, Huttunen A, Tahvanainen T, Heikkilä R & Lindholm T (2007) Mire systems in Finland – spedial view to aapa mires and their water flow pattern. Suo 58: 1–26.

The permission of the Finnish Zoological and Botanical Publishing Board (I, IV, V), Finnish Peatland Society (II, VI) and Springer Science and Business Media (III) to reprint the original papers is gratefully acknowledged.

Original publications are not included in the electronic version of the dissertation.

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