Plant responses after drainage and restoration in rich fens

Transkript

1 Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 439 Plant responses after drainage and restoration in rich fens KALLE MÄLSON ACTA UNIVERSITATIS UPSALIENSIS UPPSALA 2008 ISSN ISBN urn:nbn:se:uu:diva-8882

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3 Hemulen körde under hög jämmer ner sin nos i den våta sanden. Nu går det för långt! sa han. Varför kan inte en stackars oskyldig botanist få leva sitt liv i frid och ro! Livet är inte fridfullt sa snusmumriken förtjust. Tove Jansson, Trollkarlens hatt Till min familj

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5 List of papers The thesis is based on the following four papers, which will be referred to in the text by their Roman numerals. I. Mälson, K., Backéus, I. and Rydin, H Long-term effects of drainage and initial effects of hydrological restoration on rich fen vegetation. Applied Vegetation Science 11: II. III. IV. Mälson, K. Rydin, H. Interspecific competition among rich fen bryophytes. Manuscript. Mälson, K. Sundberg, S. and Rydin, H. Ditch blocking, soil disturbance and mowing as tools in rich fen restoration. Manuscript. Mälson, K. and Rydin, H The regeneration capabilities of bryophytes for rich fen restoration. Biological Conservation 135: Paper I and IV are printed with kind permission from the publishers.

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7 Contents Introduction...9 Study system...10 Rich fens...10 Biodiversity...11 Drainage...11 Other causes behind degradation of rich fens...12 Restoration...13 Aim of the thesis:...14 Material and Methods...15 Long term study: Effects of drainage and rewetting (I)...15 Greenhouse and garden experiments: competition among rich fen bryophytes (II)...16 Evaluation of different restoration measures (III)...17 Artificial introduction of bryophytes (IV)...18 Results:...20 Discussion and implications for conservation...23 Acknowledgements...25 Svensk sammanfattning...27 Rikkärr ett viktigt livsrum för många arter...27 Dikningens effekter och möjligheter till restaurering...27 En kombination av restaureringsåtgärder är nödvändigt...28 Spridningsbegränsning och konkurrens...29 References

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9 Introduction From a plant-ecological perspective, mires are highly interesting as study objects. Their properties of peat as growth substrate for plants, with partially anoxic environments in combination with fluctuating water levels, low nutrient concentrations and a wide spectrum on the ph-scale, make them a superior arena for discussions about theoretical ecological questions. The specific ecological properties also make these ecosystems vulnerable to drastic environmental changes, and this gives rise to practical questions and conservation issues. Among mires, rich fens are the ones with the highest species richness (Rydin and Jeglum 2006; Sundberg 2006), but have also been heavily utilized for human purposes. There is a long history of influential work done in plant ecology in mires in Sweden during the 20 th century, but still several questions remain unsolved and the exchange of knowledge between theoretical ecological and practical restoration issues needs to increase. Sweden is the country within the European Union with the largest area of rich fens (approximately ha or 2-3 of the total land area; Sundberg 2006). Many of these rich fens have been affected by drainage during the last two centuries during the 19th century mainly for agricultural purposes and during the 20th century for forestry (Vasander et al. 2003). 9

10 Study system Rich fens The study system in this thesis is boreal and boreo-nemoral rich fens. These are minerotrophic mires with high mineral concentrations (principally calcium but also iron and magnesium) and high ph-values. The rich fens are divided into moderately rich fens (with a ph between 6-7 and a Caconcentration of approx mg/l) and extremely rich fens (with a ph > 6.8 and Ca-concentrations of approx mg/l; Sjörs and Gunnarsson 2002). The term rich refers to the concentrations of these cations but also to the number of plants species occurring within this biotope, but not to the overall nutrient status since rich fens are generally low in nutrients (Du Rietz 1942, 1949; Sjörs 1950, 1985; Rydin et al. 1999, Rydin and Jeglum 2006). Sweden is a country rich in wetlands in general (9.3 million ha or approximately 20 % of the total land surface) and open mire habitats in particular (53 % of the wetland area; Rydin et al. 1999). The largest areas of rich fens are found where bedrock with limestone is present or where lime occurs in the upper morainic soil layers. Rich fens can also be found in areas with a specific mineral composition of the bedrocks (often with alkaline minerals) and in areas with seashell deposits (Sundberg 2006). The rich fens are in general small in the southern parts of Sweden, and increase in size towards the north. In the province of Jämtland, 95 rich fens with an area over 100 ha have been reported (Nystrand 2004). Rich fens are most easily defined by plant species indicators, usually species associated with high humidity, high ph and low nutrient demands (sensu Ellenberg et al. 1991). These species include both vascular plants (such as several specialized sedges and orchids) and bryophytes (mainly pleurocarpous species in the families Amblystegiaceae and Calliergonaceae; see Vanderpoorten et al. 2002). Among the vascular plants, the species indicating rich fens differ between the northern and the southern parts of Sweden, whereas among bryophytes the indicator species occur across the country (Rydin et al. 1999; Sundberg 2006). The presence of rich fen indicating species also differ between sites due to abiotic and biotic properties of each site, such as influence of spring water, amounts of cations such as calcium and iron etc. 10

11 Biodiversity Rich fens are very important from a conservation point of view and are biodiversity hotspots in the landscape (Wassen et al. 2005; van Diggelen et al. 2006). Several factors contribute to the high species richness in rich fens. One major factor is the high amounts of calcium that binds available phosphorus, thus limiting phosphorus uptake by plants (Tyler 1999; Koerselman and Verhoeven 1995; Wassen et al. 2005). This limitation of the nutrient prevents expansion of a few dominants (sensu Grime 2001) and favours a high diversity of specialized, stress tolerant species. Rich fens contain a large proportion of threatened species of various groups of organisms (including vascular plants, bryophytes, land snails and insects): 160 red listed rich fen species occur (30 vascular plants and 14 bryophytes) in the Swedish red list and among these 74 are considered as threatened (Gärdenfors 2005; Sundberg 2006). Among plants, bryophytes function as good indicators of the ecological status of rich fens, since they respond more rapidly to changes in the abiotic and biotic environment than do vascular plants. Bryophytes also contribute to a large part of the floristic diversity in rich fens (see e.g. Sjörs 1948). Among the bryophytes, the ecologically defined group brown mosses (with species of several genera such as Calliergon, Scorpidium, and Warnstorfia) are often dominant in rich fens, whereas poor fens and bogs are dominated by peat mosses, Sphagnum spp. Drainage Among the different threats to wetlands in general and mires in particular, drainage is the most severe and drastic. In Sweden one fourth of the wetland area has been destroyed, while two thirds of the remaining wetland area is affected by drainage (Kjellsson et al. 2005). Approximately one million ha of the peatland area in Sweden have been drained for forestry and, roughly estimated, equally large areas have been drained for agriculture (Rydin et al. 1999). Among mires, a higher proportion of the rich fens have been affected by drainage than other mire types during the last two centuries. The reason why rich fens have been considered to be more easily converted to agricultural land or forest production is probably their higher ph-values and lower peat depths with more easily mineralized peat, compared to poor fens and bogs. The largest loss of rich fen areas has been in the southern parts of Sweden and losses decrease further to the north. Even moderate hydrological changes in these ecosystems or in the surrounding landscape may have a drastic, negative impact on the biodiversity, not least among vascular plants and bryophytes, but continuous, long-time monitoring of these processes in boreal rich fens is still lacking. 11

12 Drainage and the abiotic and biotic changes in the ecosystem that follow, will cause severe drawbacks for several specialized species occurring in the biotope for several reasons. Lowering of the water table in the peat initiates peat subsidence, oxidation and mineralization, which results in lowered ph and leakage of cations and a shift in limiting nutrient from P to N (Heathwaite et al. 1993; Naucke et al. 1993; Zak et al. 2004; van Diggelen et al. 2006). Following theses changes in the hydrology and peat chemistry, important biological attributes such as invasion of dominant and strongly shading species follows. These changes lead to a rapid loss of rich fen specialists. For the rich fens, not only direct effects of drainage will have effects, but also large-scale changes at the landscape level, such as altered regional water table and outflow of groundwater in the surroundings (Grootjans and van Diggelen 1995; van Diggelen et al. 2006). Other causes behind degradation of rich fens Looking at rich fens at a landscape level, a general depletion of available habitats and fragmentation leads to lowered connectivity among sites which may, at least at longer time perspectives, influence the species richness of the sites (Taylor et al. 1993; Middleton et al. 2006). Whilst drainage is the most severe and drastic threat to rich fens, other factors also leads to habitat degradation. Reduced management such as haymaking (Elveland 1978; Moen 1995; Moen et al. 1999; Øien and Moen 2001), eutrophication and acidification (Kooijman and Bakker 1995; Sjörs & Gunnarsson 2002; Paulissen et al. 2004; Wassen et al. 2005; Kooijman and Paulissen 2006; Wassen and Olde Venterink 2006) may also cause drastic changes in the rich fen flora. The eutrophication processes can be either internal (due to mineralization following drainage) or external (deposits of airborne nitrogen). Eutrophicated surface peat may also prevent recolonization of locally extinct rich fen specialists. A drastic, but expensive measure is to remove the eutrophicated upper soil surface, which has been tested in a degraded rich fen in Sweden (Kjellsson et al. 2005) but also with successful results in other wetland habitats in Europe (Patzelt et al. 2001; Holzel and Otte 2003; Rasran et al. 2007). The effects of acidification are more obvious in less buffered systems (Wheeler and Shaw 1995). Hence, these effects are more pronounced in moderately rich fens than in extremely rich fens, where the latter have a higher buffering capacity due to high concentrations of calcium. Acidification effects are also smaller in naturally acid mires such as poor fens and bogs (Gunnarsson et al. 2000). Establishment of peat mosses (Sphagnum spp.) may also speed up the floristic changes in the flora of rich fens due to the acidifying properties of the Sphagnum species (see Clymo 1963, 1964). A treatment to counteract acidification effects on the flora in rich fens and the effect of leached cations, is addition of lime. 12

13 Drier summers have been observed in south east Sweden during the late 20 th century (Lindström and Alexandersson 2004), which also most probably has affected hydrology, species composition and dynamics in the mires. It has previously been suggested that vegetation changes after drainage in mire ecosystems resemble effects of global warming (Laine et al. 1995). Restoration There has been an increased interest and focus on restoration methods of mire ecosystems during recent years (Pfadenhauer and Klötzli 1996; Vasander et al. 2003; van Diggelen et al. 2006) and there is a particular need of scientifically evaluated practical restoration experiments in fens, since most efforts so far have focused on bogs and fen meadows (see for example Rochefort et al. 2003; Klimkowska et al. 2007). Several restoration studies have been performed in wetland ecosystems in western-central Europe, but the dissimilarities in wetland types, climate and species composition often make comparisons with boreal mire ecosystems difficult. In the Nordic countries, Finland is the country where most restoration activities in mire habitats have been performed. There, approximately ha of drained peatland have been restored, but only a very small proportion of this area is rich fens (appr. 200 ha; Sundberg 2006). Practical restoration of mires includes efforts both at the species level and at the ecosystem level (Aapala et al. 1996). Failure of the original plant species to recolonize hydrologically restored mire habitats can be due to two major reasons - dispersal limitations and substrate degradation. Several studies have focused on restoration of plant populations and communities in minerotrophic mire ecosystems (see e.g. Kooijman et al and Cobbaert et al. 2004). Despite the fact that there are large mire areas in the Nordic countries that are directly or indirectly highly influenced by drainage, only few scientifically evaluated restoration projects have been carried out in these countries (although several studies of vegetation changes after drainage have been performed; see Backéus 1981 for a historical review). In Sweden, there is a large need for restoration of rich fens from a national point of view; 67 % (1067 objects) of the class 1 objects (highest conservation value) in the Swedish wetland inventory (Larsson and Löfroth 1995) are affected by drainage (Sundberg 2006). There is also a need for long-term vegetation monitoring after restoration to evaluate the effects of the measures. 13

14 Aim of the thesis: The general aim of this thesis has been to study different aspects of restoration of rich fens, but also to discuss reasons for and effects of degradation of these habitats. My interest has been to link practical conservation with ecological questions such as dynamics, establishment and competition among rich fen plants. More specifically, I addressed the following questions: Paper I: Which floristic changes occur and develop after drainage of rich fens? Are these changes irreversible, and what initial trends can be seen in the flora after rewetting? This work gives important background information concerning major driving forces behind floristic changes and status change of rich fens in the landscape. Paper II: How does competition among brown mosses function under altered abiotic conditions at a detailed scale? Can a competitive hierarchy be demonstrated among the dominant species in boreal rich fens? Insights of competition are of importance when predicting the outcome of restoration activities and for the understanding of the mosaic pattern of species occurrences in rich fens. Paper III: Can practical restoration activities such as rewetting, mowing and soil disturbance lead to spontaneous re-establishment of an ecologically functional flora in previously drained rich fens and how large are the effects of such treatments in the initial restoration phase? Paper IV: Is it possible to re-introduce locally extinct rich fen bryophyte species to rewetted sites by active addition of moss fragments, and which treatments are needed to optimize establishment and survival of these species? 14

15 Material and Methods Long term study: Effects of drainage and rewetting (I) To evaluate floristic changes after drainage and after rewetting, we analyzed vegetation changes over a time period of 24 years after drainage and 4 years after rewetting. The study site, which was drained for forestry purposes during , is located in the province of Gästrikland, i.e. in the southern boreal vegetation zone (Sjörs 1999) in east central Sweden. The vegetation before drainage was dominated by brown moss species such as Scorpidium scorpioides and Campylium stellatum and sedges, such as Carex rostrata, C. panicea and C. livida in the wetter parts. Rewetting was performed in 2002 by blocking the main ditch at four positions (separated by a distance of 50 metres) with of a wooden dam in combination with peat and mineral soil that was compacted by an excavator three metres upstream of the wooden dam (Fig.1). Figure 1. The dam construction in the main ditch, with compacted peat upstream of the wood construction. 15

16 Nine permanent subplots (1 x 1 m) were arranged in each of two plots. Each plot was investigated annually and the analysis was resumed in 2002 (before the hydrological restoration) and continued to All vascular plant and bryophyte species were recorded, and their cover in percent was estimated. We used the multivariate method analysis DCA (Detrended Correspondence Analysis) to illustrate the vegetation changes. Average cover values of subplots were used for analysis of changes over time. Also, to evaluate the effects of drainage and restoration and facilitate comparisons with other studies (with a different set of species), the species were classified into nine ecological groups based on life form and affinity to rich fens in the region. Greenhouse and garden experiments: competition among rich fen bryophytes (II) To evaluate if a competitive hierarchy and different competitive strategies can be demonstrated among brown mosses under altered habitat wetness, we used a factorial setup with three species-combinations (species pairs) combined with two water levels. The studied species were Campylium stellatum S. cossonii and Scorpidium scorpioides (Fig. 2). These species are three of the most abundant and widespread in rich fens in northern Europe (Rydin et al. 1999; Hedenäs 2003; Sundberg 2006). They represent slightly different morphology and occur at somewhat different heights in relation to water in mires, where S. scorpioides grows under wetter conditions (Ericsson, 2006). Rich fen peat was distributed into 30 plastic containers with perforated bottoms to enable free exchange of water. Each treatment combination was replicated five times (3 species combinations x 2 water levels x 5 replicates; in total 30 containers). The experiment lasted from November 2004 to November During June October, the containers were placed under garden gauze (to avoid extreme temperatures and desiccation) in the Botanical Garden of Uppsala University. During the period October - June, the containers were placed under controlled light conditions inside the greenhouse (16 h light, 8 h darkness). 16

17 Figure 2. The three studied bryophyte species; Campylium stellatum (left), Scorpidium cossonii (middle) and Scorpidium scorpioides (right). To assess the competitive outcome we measured the area expansion of one species into the part of the container covered by the competing species (cf. Rydin 1997). The area measurements were performed with the Image J software (Abramoff et al. 2004) in which a visual outline and demarcation of each species was drawn on digital photos. The spatial expansion into the competitors side of the container was quantified. Evaluation of different restoration measures (III) To evaluate re-colonization and practical restoration activities in rewetted rich fens, we performed an experiment at two sites in east central Sweden, one moderately rich fen and one extremely rich fen. Both sites were drained in the 1950s for forestry. In 2002, some 50 years after drainage, the secondary vegetation in the bottom layer at the moderately rich fen was dominated by Sphagnum spp. and Polytrichum spp., whereas Betula pubescens had formed the tree layer. The drained extremely rich fen was dominated by graminoids (such as Molinia caerulea and Schoenus ferrugineus) in the field layer and low grown Pinus sylvestris and Betula pubescens in the shrub and tree layers. At both sites, the tree layer was removed in late 2002 to recreate the light regime of an open rich fen. Two experimental blocks with 16 plots each were arranged at both sites, one block in the rewetted part and one in the still drained part. Peat disturbance and mowing was applied to the plots in a factorial design (Fig. 3). In the disturbed plots, all vegetation was removed, and surface peat was turned to a depth of 1-2 dm once in September - October

18 Figure 3. Restoration experiment. To the left are sample plots in the moderately rich fen at the experimental start in 2002 (plots with peat disturbance and controls). The vegetation was dominated by Sphagnum and Polytrichum. To the right are the sample plots at the extremely rich fens site in 2003, after annual mowing. The vegetation is dominated by Molinia caerulea. Vegetation was analysed with species abundance estimated before the treatment in 2002 and in 2005 as percent cover and as rooted frequency in 16 subplots. The area of bare peat was also estimated. Mowing was performed annually at the end of the vegetation season (August - October) and the biomass was removed. The species composition and species changes in individual plots between 2002 and 2005 were visualized with DCA (Detrended Correspondence Analysis) ordinations. Directional changes in vegetation caused by the treatments (rewetting, peat disturbance, mowing), i.e. the movement over time of each plot (sample scores) in the ordination diagram, was analyzed with GLM ANOVAs. We tested both movement distances along the most influential axis (axis 1) and along the four main axes of the ordination space. Artificial introduction of bryophytes (IV) Experiments were performed to evaluate if addition of gametophyte fragments can re-establish viable populations of locally extinct species in drained rich fens. A field experiment was performed in the same moderately rich fen site as that used in paper III. The effects of liming, and a gauze cover (desiccation protection) were tested in a factorial design replicated in four blocks at different locations along the ditch. Experimental plots (0.25 x 0.25 m) were cleared of all above-ground living plants, to create gaps of bare peat. Apical gametophyte fragments (1 cm) of four bryophyte species (Campylium stellatum, Pseudocalliergon trifarium, Scorpidium cossoni and Scorpidium scorpioides) were added in early summer. After one field season, the 18

19 survival of the added species was used as a measure of gametophyte establishment. After two field seasons, the cover of each species was analyzed to quantify the spatial expansion of the introduced species. Greenhouse experiments were used to evaluate the effect of liming on the same four species used in the field experiment. As in the field study, 1 cm long apical fragments were tested for survival and growth. As an addition to this experiment we also tested the non-apical part of the gametophytes (the 1-2 cm section below the apex). The cultivation of the fragments was performed in greenhouses at the Botanical Garden of Uppsala University under controlled light conditions. To be able to perform multiple measurements of growth, non-destructive size measurements were made: the shoot size included the summed length of the stem and side branches. After 5 months, survival rate and shoot size were measured. To test the growth of gametophyte fragments under different (but constant) water levels in the peat, an experiment was performed within the main ditch in the hydrologically restored part of the mire. We used plastic boxes that were kept floating in the ditch by air-filled plastic cans tied up to the sides (cf. Rydin 1986, Sundberg and Rydin 2002). Plastic cylinders were filled with peat from the surrounding mire (with lime added). Gametophyte fragments (1 cm) of Campylium stellatum and Scorpidium cossonii were added to the peat surface of eight cylinders per species and box. Since a preliminary analysis of the greenhouse experiment indicated that the four species responded rather similarly, the small water level niche separation of Campylium stellatum and Scorpidium cossonii (Ericsson, 2006) made them interesting for this more detailed experiment with controlled water levels. The experiment was arranged as a factorial combination of water levels and gauze cover. The floating depth of the boxes was fixed to three levels. After 4 months, the shoots were harvested and biomass was used as response variable. 19

20 Results: In paper I, three successional stages in the vegetational changes after drainage were observed in both investigated plots. In the first stage (<5 yrs) there was a rapid loss of rich fen bryophytes. The second stage showed an increase of sedges and early successional bryophytes, which was followed by the third stage with an increase of a few emerging dominants, such as Molinia caerulea, Betula pubescens and Sphagnum spp. Depending on, for instance, initial species composition, different routes of vegetation change were observed in the flora after drainage, although after 24 years, species composition became more homogenous and dominated by a few species with high cover. After rewetting, there are indications of vegetation recovery (such as drawback of the cover of Molinia caerulea), albeit at slow rates (Fig. 4). Figure 4. Change in common species during the investigation period for both investigated plots (average values of nine subplots). 20

21 In paper II, we found that the competitive abilities were very similar among the three species with similar ecological demands (Campylium stellatum Scorpidium cossonii and S. scorpioides). Given the seemingly weak effect of interspecific competition and the knowledge that these species may show spatial microtopographical niche separation, the results indicate that competitive exclusion among these species may be rare, not occur at all, or be a very slow process under natural conditions. The possibility for coexistence of these species may be further enhanced by disturbances caused by shifting water levels during the growing season. In the case of clonal spread of species into the area of its competitor, C. stellatum and S. cossonii show exceptionally similar patterns of spatial expansion. In paper III, the effect of rewetting, mowing and peat disturbance in a moderately rich fen and one extremely rich fen were evaluated. The results indicate that rewetting alone will not have drastic effects on the vegetation. In plots with peat disturbance, several rich fen characteristic species established (that were not present prior to disturbance treatment), probably from a persistent seed bank. The establishment rate was low in disturbed plots (with over 90 % bare peat in disturbed, rewetted plots), but on the other hand this treatment prevented a rapid re-establishment of undesirable dominants. Late season mowing alone appeared not to be a very strong treatment in the initial restoration phase, but seemed to re-enforce the effect of peat disturbance. The results point towards the necessity of combinations of several treatments to achieve good restoration results in drained rich fens. However, the results are tentative, since a longer time period is required to fully evaluate the restoration methods. In paper IV, we found that it is possible to re-introduce locally extinct rich fen bryophytes to rewetted sites by the use of gametophyte fragments. We found a strong positive effect on survival and growth with addition of lime. Protective cover, especially with gauze, had a significant positive effect on shoot establishment. The establishment rate did not differ among the tested species (Fig. 5). Furthermore, a positive effect of liming on growth was observed also under controlled greenhouse experiment for all tested species. An additional finding from the study was that liming directly, or via increased ph and increased nitrification will favour the growth of brown mosses, and probably also give them an advantage against potential dominants such as Sphagnum, Polytrichum and tall vascular plants. 21

22 Figure 5. The effect of lime and cover treatments for survival of individual shoot fragments during the first year of the field experiment. Bars represent pooled mean values for the tested species Campylium stellatum, Pseudocalliergon trifarium, Scorpidium cossonii and Scorpidium scorpioides. Error bars show SE. 22

23 Discussion and implications for conservation For restorations of rich fens, improvement of the biodiversity must be considered as the major reason. Wetlands in general are considered as highly important for diversity, and rich fens in particular are of great importance for species richness in boreal mire ecosystems. The restoration measures in drained rich fens must be divided into activities at several scales, from a landscape perspective, where sufficient number of suitable patches of undisturbed and ecologically functional rich fens are required, to a local scale, where hydrological restoration, cutting of trees and shrubs are performed, and to small scale where disturbances to create suitable substrate properties and to prevent dominant species to outcompete low grown specialist species are essential. Also, the dispersal potential of source material of rich fen species must be considered. The extinction of several rich fen specialists after drainage is a rapid and drastic process, and the accelerating succession raise challenges in applying appropriate restoration measures. Among plants, the changes are most drastic among bryophytes, because they respond quickly to changed chemical and hydrological conditions (due to their lack of roots and vascular tissue), and hence species composition can give hints to the stage of degradation of drained rich fen site. The best results of restoration in fen ecosystems are obtained shortly after drainage (Grootjans and van Diggelen 2005; Vasander et al. 2003) or where the damage is spatially limited, where the chemical properties of the substrate are more intact and where the target species for restoration are still present at the site or in the near vicinity. Hydrological restoration to achieve pre-drainage conditions is the basic demand for an ecologically functional rich fen to re-develop. The results in this thesis indicate that this measure will affect the species composition in rich fens already after a few years, but long term effects must be monitored further and more closely in the future. An overall conclusion is that the loss of species from a degraded rich fen site is a quick process but recolonization and establishment of species is a much slower one. Single restoration measures (such as rewetting) might not be enough to promote establishment of viable populations of rich fen plant species, and it seems that a combination of several activities is needed to obtain good results. The finding that even small water level differences may affect the outcome of competition among rich fen specialists stresses the importance of a detailed evaluation of the hydrological conditions prior to rewetting. To cre- 23

24 ate suitable habitats for a diversity of species, a spatial heterogeneity of wetness within the mire is desirable. Gap creation by removal of litter, or even removal of the peat surface layer, in combination with a small initial addition of lime to raise the ph are actions that should be considered if reestablishment of lost species are the main objectives for the restoration. This is also valid if the chemical conditions have been heavily changed. Further, repeated activities, such as mechanical peat surface disturbances, grazing or mowing may be necessary to counteract degradation of the substrate caused by expanding dominants such as grasses and peat mosses. The absence of the original species in hydrologically restored mire habitats can be due to either dispersal limitations or substrate degradation and hence both these causes must be taken into account when considering suitable restoration measures. Even though our experiments with gap creation, liming, and desiccation cover are small scaled and performed at an experimental basis, the methods should be feasible to scale up to practical conservation methods. It should be kept in mind that individual rich fens in Sweden often are small (median 2.1 ha in southern Sweden; Sundberg 2006). A creation of a mosaic of bare peat patches that are limed and covered in a hydrologically restored area may due to this be a way to reintroduce lost species into degraded sites. 24

25 Acknowledgements First of all I would like to thank my supervisor Håkan Rydin. When I started my career as a PhD-student, I did not fully understand the great importance of having a good supervisor. I do that now Håkan, you are the best! You have encouraged me during the whole process from my first written sentences to the final ones. I am deeply grateful for all your help and support. My warmest gratitude also to my assistant supervisor Sebastian Zebbe Sundberg. I tried to combine the words wetland, sphagnum, researcher and enthusiast - I got the word Wetlandsphagnumresearcherenthusiast - and that is what you are. Thanks for all the help along the way. Many thanks also go to: Ingvar Backéus, for the pleasure of writing a manuscript together with you, for the photo on the cover of this thesis and for lots of jolly conversations during the years at Växtbio. Magnus Larsson, Joachim Strengbom and Jon Ågren for valuable comments on earlier versions of manuscripts and on this thesis. Bengt Carlsson and Stefan Gunnarsson for help with technical questions about illustrations and pictures. My friends in VäxtBio! We had a lot of fun together and I am sure that this funny phenomenon helped us to achieve better results as researchers. Everyone at the Department of Plant Ecology no one mentioned, no one forgotten. Jerry Skoglund for introducing me to the joy of Plant Ecology. Lennart Norell, Morgan Emtner and Staffan Karlsson for statistical advice. Willy Jungskär, Stefan Björklund and Ulla Johansson for helping me out with practical issues. 25

26 The staff at the Botanical Garden of Uppsala University that helped me and kept me company during my studies in the greenhouses. Jesper Hansson, Therese Eriksson, Linda Ljungdahl and Bu Zhaojun for field assistance and company out on the mires. All my good friends (Mange, Palmen, Åke and the Boasters fishing society [fiskeföreningen Skrävlarna] among others), for helping me to understand that there is more to life than measuring bryophyte growth. Knut och Alice Wallenbergs forskarstipendiefond, Liljewalchs stiftelse, Stiftelsen Exstensus and Bertil Lundmans fond for financial support. I also would send many, many thanks to my family Gun, Tomas and Johan. Thanks for being there as a true and confident support for me! I am grateful for having the opportunity of being with you. Last, but not least, I thank Monica. You are the one that always believe in me. You have also put up with me during the final stages of putting this thesis together, which is admirable! Now, let s take care of little Assar together! 26

27 Svensk sammanfattning Rikkärr ett viktigt livsrum för många arter I min avhandling har jag specialstuderat en viss typ av myrar - de så kallade rikkärren. Sverige är ett land rikt på våtmarker och en tiondel av den totala landarealen upptas av olika typer av myrar, det vill säga torvbildande våtmarker. Benämningen rikkärr syftar på den höga artrikedomen av arter inom dessa myrar samt på deras rikedom på mineralämnen (främst kalcium). De i rikkärren höga halterna av kalcium gör att det viktiga näringsämnet fosfor komplexbinds och därmed blir svårtillgängligt för växterna. Detta leder bland annat till effekten att storvuxna arter inte kan dominera och konkurrera ut småväxta arter. Myrarna fyller många viktiga funktioner i landskapet. I min avhandling har främst rikkärrens betydelse för den biologiska mångfalden och som livsrum för många specialiserade och hotade arter varit i fokus. Rikkärren är de mest artrika myrarna och i Sverige förekommer minst 160 av Sveriges rödlistade arter i dessa myrar, ett 70-tal av dessa arter klassas som hotade. Rikkärren har historisk även spelat en viktig roll för höproduktion. Då slåttern upphörde kring förra sekelskiftet försvann också en viktig faktor för utformningen av floran i de svenska rikkärren. Även om andelen rikkärr i Sverige endast utgör en liten andel av den totala myrytan (1-2 %), så har Sverige de största arealerna rikkärr inom hela EU. Rikkärren förekommer spritt över landet men förekommer företrädesvis i områden med kalk i berggrunden eller i lösa jordlager. De största arealerna av rikkärr i Sverige finns i landets norra delar och där företrädesvis i Jämtland och i fjällkedjan, men även i exempelvis Skåne, Uppland och Gotland förekommer många rikkärr. Jag har under mitt avhandlingsarbete studerat vilka effekter dikning har haft på vegetationen och olika metoder att restaurera rikkärr. Dikningens effekter och möjligheter till restaurering För att studera effekter av dikning på rikkärrsvegetation användes data från ett rikkärr i Gästrikland där en växtekologisk långtidsstudie initierats 1979, 27

28 samma år som kärret dikades för skogsändamål. Analys av förekommande växtarter genomfördes årligen mellan 1979 och Resultaten visade på en mycket snabb och drastisk förändring av den karakteristiska rikkärrsfloran efter dikning. Inom loppet av fem år hade de för rikkärren typiska mossarterna som varit talrika innan dikningen försvunnit. Den sänkta vattennivån gynnade några av rikkärrens halvgräs, som expanderade tillfälligt och uppnådde sin högsta täckning cirka 10 år efter den genomförda dikningen. Drygt 20 år efter dikningen hade huvuddelen av de naturligt förekommande karakteristiska rikkärrsarterna av såväl mossor och kärlväxter försvunnit. Vegetationen i kärret utgjordes till stor del av några få dominanta arter, främst glasbjörk och gräset blåtåtel. År 2002 återskapade vi det ursprungliga vattenståndet i kärret med hjälp av dämmen i diket. De sedan tidigare etablerade provytorna undersöktes återigen årligen fram till 2006 för att undersöka initiala effekter av dämningen. Under denna period noterades en långsam tillbakagång av de dominanta arterna även om återkolonisationen av de typiska rikkärrsarterna var låg. En kombination av restaureringsåtgärder är nödvändigt För att skapa förutsättningar för livskraftiga populationer av rikkärrsarter vid restaurering krävs en kombination av åtgärder. Att dämma diken för att återfå en funktionell hydrologi är en grundförutsättning vid restaurering av dikade rikkärr, men ytterligare åtgärder som exempelvis störning i form av slåtter eller bete kan komma att krävas för att uppnå positiva resultat. Bäst resultat och kostnadseffektiva lösningar ges i relativt nyligen dikade kärr där många av de ursprungliga rikkärrsarterna fortfarande finns kvar. Ju längre tid ett kärr har varit under påverkan av diken, desto mindre är chansen att med enkla medel vända de negativa processerna. Många rikkärrsspecialister har svårt att återkolonisera restaurerade kärr. Markytan i dessa är ofta täckt med några få, helt dominerande växtarter av buskar, gräs och vitmossor och i dessa bestånd har de ofta konkurrenssvaga rikkärrsarterna svårt att etablera sig på nytt. I en studie i hydrologiskt restaurerade rikkärr har jag visat att man med hjälp av andra fysiska störningar (blottläggning av torvytor, årlig slåtter och huggning av de träd som etablerat sig i kärret efter dikningen) kan påskynda processerna för att återfå livskraftiga populationer av rikkärrsarter. Genom att skapa ytor av bar torv ökar förutsättningen för etablering från frön eller sporer. I mina försök noterade jag etablering av arter som varit försvunna från de dikade rikkärren under en lång period. En trolig förklaring till att arterna återkommer är att de funnits kvar i kärrens torvlager i form av en fröbank som väckts till liv till efter markstörningen. För att ytterligare skapa goda förutsättningar för rikkärrsarterna och knyta an till gamla brukningsmetoder kan man utföra slåtter för att 28

29 minska skuggningen från mer storvuxna arter. Genom slåtter minskar man tillgången på den näring som frigjorts i kärren då torven syresatts efter dikningen. Resultaten från mina studier visar också att en kombination av störningsåtgärder och vattenståndshöjning förbättrar möjligheterna för återhämtning av rikkärrsarter. Spridningsbegränsning och konkurrens I och med att många rikkärr omvandlats till skogs- eller jordbruksmark så har spridningsavstånden och isoleringen mellan enskilda kärr på landskapsnivå ökat. Vid restaurering av rikkärr kan problem med återetablering av arter uppstå på till följd av detta. Ett alternativ kan då vara att aktivt tillföra växtmaterial och på så sätt skapa livskraftiga populationer av rikkärrsväxter. Jag har visat att man kan återföra rikkärrsmossor till restaurerade kärr med hjälp av små mossfragment. Försöken visar att blottläggning av bara torvytor genom att avlägsna vegetation, i kombination med en initial kalkgiva och ett uttorkningsskydd i form av odlingsduk under de första två åren, ger en god överlevnad och etablering av mossorna. Vidare visar försöken att olika delar av mossplantorna kan användas för etablering av mossor från fragment, inte endast den översta skottspetsen av mossplantan där normalt den största tillväxten sker. Detta resultat är viktigt, då man vill använda så lite insamlat mossmaterial som möjligt för spridning till restaurerade kärr. Fragmentförsöken visar att små skillnader i markens fuktighet kan ge tillväxtskillnader hos olika mossarter. Resultaten är intressanta, då olika arter kan ges olika förutsättningar beroende på hur väl man lyckas med den hydrologiska restaureringen. Rikkärr utgörs ofta av en mosaik av småmiljöer, med högre och lägre liggande partier, dvs. växtplatser med olika avstånd till vattenytan i marken. De vanligaste rikkärrsmossorna förekommer ofta blandade på ett mosaikartat sätt i kärren. För att undersöka orsaken till denna mosaikartade utbredning hos tre av de vanligaste mossarterna i svenska rikkärr (guldspärrmossa, korvskorpionmossa och späd skorpionmossa) utförde jag ett konkurrensexperiment i växthus. Resultaten visar att ingen art hade blivit helt utkonkurrerad under tvåårsperioden, även om två av arterna (späd skorpionmossa och guldspärrmossa) var mer framgångsrika under de betingelser som gavs i försöken, med periodvisa uttorkningar. Att samtliga tre arter förekommer i rikkärr utan att någon av arterna konkurreras ut beror sannolikt på att det i kärren förekommer en bred variation av ekologiska förutsättningar i tid (såsom översvämningar och uttorkningsperioder) och i rum (såsom gradienter av fuktighet och ljus). Rikkärr utgör komplexa miljöer och restaurering av dessa våtmarker kräver därför en förståelse av de bakomliggande orsakerna till förändringarna 29

30 efter dikning. Resultaten i min avhandling visar på effekter av dikning och olika restaureringsåtgärder, men fler långsiktiga studier och praktiska restaureringsåtgärder kommer att behövas för att få en bättre bild av hur arbetet ska optimeras i framtiden. 30

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