natural revegetation and restoration of drained and cut-over ......primary mire type: →...

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Global Environmental Research ©2007 AIRIES 11: 205-216 (2007) printed in Japan

Natural Revegetation and Restoration of Drained and Cut-over Raised Bogs in Southern Germany — a Comparative Analysis

of Four Long-term Monitoring Studies

Peter POSCHLOD1*, Christina MEINDL1, Jan SLIVA2, Udo HERKOMMER3, Matthias JÄGER4, Ulrike SCHUCKERT5, Andreas SEEMANN1, Anja ULLMANN3 and Teresa WALLNER1

1Institute of Botany, Faculty of Biology and Preclinical Medicine, University of Regensburg,

D-93040 Regensburg, Germany 2Department of Ecology, Technical University of Munich, D-85350 Freising-Weihenstephan, Germany

3agl Ulm (Working group Landscape Ecology Ulm), Marlene-Dietrich-Strasse 1, D 89231 Neu-Ulm, Germany 4Institute of Animal Ecology and Tropical Biology, Faculty of Biology, University of Würzburg,

D-97074 Würzburg, Germany 5Im Weizen 47, D-71636 Ludwigsburg, Germany

*corresponding author

Abstract Mires and peatlands have become the focus of nature conservation and restoration management policy

due to their multiple ecological functions such as accumulation, disposal, retention and conservation, as well as their possible role in global climate regulation. In this paper we present the results of four long-term stu-dies on spontaneous as well as directed revegetation of peat-mining areas in raised bogs situated in the foot-hills of the Alps in southern Germany. The results clearly show that

(1) peat mining techniques affect spontaneous revegetation, peat-cutting being a technique which may allow peat-forming vegetation to reestablish itself after abandonment of peat-mining. In contrast, peat milling leads to mono-dominant successional stages of certain species that remain stable in their respective stages over decades,

(2) hydrological conditions after renewed inundation (rewetting) affect the reestablishment of peat-forming vegetation. In our case study, rewetting caused the flooding of large peat-mined areas, result-ing in the extinction of trees, shrubs and dwarf shrubs. However, it also supported the establishment of float-ing mats consisting mainly of fen species which may initiate, in the long-term, the reestablishment of the former peat-forming raised bog vegetation and

(3) reintroduction of vascular plants typical of raised and transitional bogs by sowing and planting may accelerate the establishment of a dense vegetation cover as a prerequisite for the establishment of other spe-cies. However, the establishment of a Sphagnum cover with typical peat-forming species such as Sphagnum magellanicum has not been successful on a short- or mid-term basis and remains a major challenge in restoring cut-over raised bogs.

Key words: mires, peatlands, peat-mining, re-wetting, succession

1. Introduction

Mires have multiple functions on global, regional

and local scales (Poschlod, 1994; Kapfer & Poschlod, 1998; Joosten & Clarke, 2002; Joosten, 2003). Globally, they play an important role in the carbon cycle (accumu-lation function; Gorham, 1991, 1995; Franzén, 1994; Roulet, 2000), regionally they buffer pollution by nutri-ents, heavy metals, etc. (disposal function; Succow & Jeschke, 1986), as well as mitigating heavy rainfall events (retention function; Schmeidl et al., 1970;

Ingram, 1983). Locally they provide habitats for a lot of specifically adapted, ice-age relict, rare and threatened species (conservation function; Kapfer & Poschlod, 1998). Furthermore, mires are an archive of climate, vegetation and even pollution history (archive function; Frenzel et al., 1991; Görres, 1991).

Despite these multiple functions, mires have been strongly affected by agriculture, forestry and industry in all countries of the northern temperate and boreal zones. However, in southern Germany (Table 1), melioration of mires for agricultural purposes started only at the end of

206 P. POSCHLOD et al.

the 18th century when the human population increased, which in turn resulted in the need to produce more food. A famous South German example is the drainage and cultivation of the large geogenous “Donaumoos” near Ingolstadt from 1790, where elector Karl Theodor estab-lished new settlements and introduced potato cultivation (Pfadenhauer et al., 1991). Only at the end of the 19th and beginning of the 20th century, large-scale peat mining started in ombrogenous mires, first for fuel (rail-ways, heating, etc.) and locally for litter (Poschlod, 1990). From the 1960s on, peat was mined on a large scale only for horticultural purposes (Göttlich, 1990). Today, there are no mires left which have not been influ-enced by any type of the above-mentioned land-uses. Furthermore, mires were, until recently, affected by atmospheric acid depositions, namely acidic sulphur (Ferguson et al., 1978; Ferguson & Lee, 1980) followed by an ombrotrophication of minerotrophic mires (Zoller & Seeldorf, 1989). Nitrogen (Lütke-Twenhöven, 1992a,b; Frankl, 1996) and dust (Pakarinen, 1977) are also deposited in mires. Nitrogen depositions in ombrogenous mires may result in a better growth of peat followed by surface desiccation and tree invasion (Frankl, 1996) but also in a shift towards species which are not able to form peat (Lütke-Twenhöven, 1992a,b), especially species from the Sphagnum recurvum group. In Southern Germany, the occurrence of Sphagnum angustifolium was not reported from raised bogs before the 1980s (Poschlod, 1990).

Ombrogenous mires of southern Germany, which are mostly situated in the foothills of the Alps where pre-cipitation is higher than 1,000 mm/year, have been mainly affected by drainage followed by peat mining. Only small areas were afforested or put to agricultural use. Therefore, these peatlands today often represent a mosaic of drained, small or large peat mining sites with more or less intact areas of peat forming communities. Due to the above-mentioned multiple functions it is now an aim of the federal not only to maintain more or less

intact areas – permission for drainage and peat mining have not been granted since the end of the 20th century – but also to restore drained and mined areas (Pfadenhauer, 1988). However, is restoration management necessary at all? Comparing successional stages of abandoned peat- mining areas in nine peatlands in the foothills of the Alps, Poschlod (1990, 1994) suggested that vegetation development without management depends on (1) the peat mining technique that was used, with peat cutting being more suitable for the reestablishment of peat- forming vegetation than peat milling, and (2) the thick-ness and quality, also (3) water quality as well as (4) the hydrological regime. Restoration management methods have been deduced from these comparative studies (Poschlod, 1990) which involved rewetting of heath and forests in dry peat- cut areas as well as manipulation of the surface topography, rewetting, sowing of seeds and transplanting of plant material on peat-milled areas (Maas & Poschlod, 1991; Sliva, 1997; Sliva & Pfadenhauer, 1999; Pfadenhauer & Grootjans, 1999).

Until now, the hypotheses concerning successful vegetation development without management were never proven through long-term observations of these sites. Only short-term studies existed which did not allow for adequate assessment (Pfadenhauer & Klötzli, 1996; Gorham & Rochefort, 2003; Vasander et al., 2003). However, long-term monitoring of restoration sites is necessary to confirm that restoration manage-ment practices are appropriate.

In this paper we present new results (“Wurzacher Ried,” “Wieninger Filz,” “Wendlinger Filz”), and re-consider already published results (“Kendlmühlfilz”; Sliva, 1997) regarding the following questions and case studies in ombrogenous peatlands in the foothills of the Alps: (1) Is spontaneous revegetation in abandoned peat-

mining areas towards peat-forming vegetation (in-cluding peat growth) possible without restoration management (case studies “Wieninger Filz,”

Table 1 Historical and current impacts by agricultural, forestry and industrial use and the current situation of mires/peatlands in Southern Germany (Pfadenhauer, 1988; Poschlod, 1996). Nomenclature of mire/peatland types according Joosten and Clarke (2002). In bold – names of case study mires/peatlands in this paper.

Type of mires Historical and actual impacts and actual situation Geogenous mires (developed from rising ground-water after the ice age – primary mire type: water-rise mires, secondary type: percolation mires) in the valleys of the Danube and rivers joining it (e.g., “Donaumoos” at Ingolstadt, “Osterried” near Ulm)

Cultivated as early as in the 18th or beginning of the 19th century (“law of derelict land”); partly peat cutting for land owners’ purposes; today mostly intensive agriculture (corn, potatoes or grassland)

Large complexes of geo- and ombrogenous mires in former glacier basins (primary mire type: → terrestrialisation mires, secondary type: → raised bogs) in the foothills of the Alps (e.g., “Kendlmühlfilz” southeast of Munich, “Wurzacher Ried” south of Ulm)

Heterogenous character of more or less intact centres of the raised bog part (however, often affected by drainage), large areas of peat mining (formerly by peat cutting, today by peat milling); along the borders, agricultural use (formerly mostly litter meadows once cut only in autumn, today intensive grasslands cut three to five times per year)

Small geo- and ombrogenous mires in small basins within end/ground moraine landscape (developed mostly from lakes; primary mire type: → terrestrialisation mires, secondary type: → raised bogs) in the foot-hills of the Alps (e.g., “Wieninger Filz” near Traunstein, “Wendlinger Filz” southeast of Munich)

Large numbers of this type, therefore relatively many more or less intact but also intensively agriculturally used (or left fallow); ombrogenous peatlands often mined at the beginning of the 20th century, mostly through peat cutting by hand or machine; borders mostly cultivated

Small geogenous mires on slopes (sloping mires, spring mires) in ground/end moraine landscape (developed from springs) in the foothills of the Alps

Formerly used as litter meadows, today drained and intensively used as grasslands or abandoned, resulting in an overgrowth by shrubs such as Frangula alnus

Natural Revegetation and Restoration of Drained and Cut-over Raised Bogs in Southern Germany 207

“Wendlinger Filz”)? (2) Is rewetting management of drained and peat-cut

areas useful/successful (case study “Wurzacher Ried”)?

(3) How useful/successful is restoration management of milled areas not only through rewetting but also through sowing and planting (case study “Kendlmühlfilze”)?

To answer these questions, we installed permanent plots (1) in abandoned peat-mining sites in which observations were made in 1986 and 2005 or 2006, (2) in a peat-mined area in 1992 before initiation of rewet-ting management, which started in 1993, with observa-tions repeated in 2002 and (3) in large peat-milled fields where sowing, planting and transplanting of peat- forming plants were applied and vegetation develop-ment was monitored from 1987 to 1994.

As a measure of restoration success we use the reestablishment of peat or peat-forming vegetation or species, since this parameter is connected to all the eco-logical functions of mires mentioned above – accumula-tion, disposal, retention, conservation and archive. Peat- forming species in ombrotrophic mires in the foothills of the Alps are the peat mosses Sphagnum magellanicum (up to 90% of the ombrogenous peat), S. papillosum, S. capillifolium, S. cuspidatum (all less than 10% of the ombrogenous peat) and the vascular plant Eriophorum vaginatum (Paul & Ruoff, 1932). Under minerotrophic conditions, sedges and other members of the family Cyperaceae as well as “brown mosses” may generate peat.

2. Study Sites, Restoration Management and

Monitoring

2.1 Study sites without restoration management after drainage and peat mining

The “Wendlinger Filz” is situated in southeastern Bavaria about 40 km east of Munich (Fig. 1). It is a raised bog in a depression on the end moraine of a glacier of the last ice age which probably developed from melting ice blocks. Peat was extracted only after the Second World War by local farmers who milled the surface to produce litter for cattle kept in stables (Fig. 2b). This was done until the 1960s. Very few areas re-mained under peat extraction until the mid 1980s. After abandonment, the open peat surface remained bare with only slow establishment of a few dominant species (Poschlod, 1990). Seven transects along which perma-nent plots (4 m2 in size) were irregularly arranged were established in 1986. Vegetation and hydrological param-eters were recorded at each permanent plot in 1986 and 2006. Additionally, all transects were levelled, peat profiles were taken and peat composition studied by macro-remains analysis in 1986.

The “Wieninger Filz” is also situated in southeastern Bavaria near Traunstein (Fig. 1). Like the “Wendlinger Filz,” it is one of the typical small raised bogs at the border of an end moraine of the last ice age. In contrast

to the “Wendlinger Filz,” peat extraction here was done by hand cutting since the beginning of the 20th century as fuel for the brewery “Wieninger.” The upper rooted horizon of newly mined areas was deposited into the area which had been exploited (Fig. 3a) so that most of the typical raised-bog species were present on the formerly mined area after its abandonment. They persisted either as vegetative parts or in the diaspore bank (Poschlod, 1990, 1995). In 1960, peat-mining ended. No management has occurred since, except that the central ditch was dammed during the winter season to provide an open water surface in winter for the traditional Bavarian winter sport “ice stick shooting” (Poschlod, 1990). In late summer of the following year the down was opened to allow cutting of reeds.

The peatland was mapped first in 1986 along three levelled transects (Poschlod, 1990). Peat profiles were taken every 20 to 50 m. Permanent plots (4 m2 in size) were irregularly arranged along these transects, accom-panied by hydrological measurements (water level, water quality). Vegetation and hydrological parameters were recorded in 1986 and 2005 at these permanent plots.

2.2 Study sites with restoration management after

drainage and peat mining The “Wurzacher Ried” is situated in Upper Swabia,

south of Ulm (Fig. 1). It represents one of the largest raised bog complexes in southern Germany. Growth of the mire started after the last ice-age from a shallow lake in a basin closed by the glacier’s end moraine. Origi-nally, the mire consisted of seven raised bog shields (Fig. 4a; Schwineköper et al., 1991). Drainage and local peat-mining started in 1730. In 1880, industrial peat mining by means of cutting started and was intensified after the First World War in 1920 when fuel was limited. In 1946, a glass industry was established in Bad

W

S

K WiWe

M

BavariaBaden-Wuerttemberg

Fig. 1 Location of the study sites (●) in Baden-Wuerttemberg

and Bavaria (Southern Germany). K – Kendlmühlfilz, W – Wurzacher Ried, We – Wendlinger Filz, Wi – Wieninger Filz, S – Stuttgart, M – Munich.


Wurzach which was followed by further intensification of peat mining (Gremer & Poschlod, 1991). However, despite several trials the different owners of the peatland did not succeed at draining the entire peatland due to its situation in the basin (Schwineköper et al., 1991; Krüger & Pfadenhauer, 1992). Today, only two of the seven raised bog shields are left, with the largest central shield being partly affected by peat mining and drainage. How-ever, the largest part of the central shield remained unaf-fected, although a road has been cut through it (Fig. 4b). Although peat-mining continued until 1995, part of the Wurzacher Ried became a nature reserve in 1959 (more than 4 km2). The protected area was increased in 1981 to a size of nearly 14 km2 and in 1996 to more than 18 km2. In 1989, the Wurzacher Ried was awarded the European Diploma, and a detailed plan was developed. One measure of this management plan was the rewetting of the drained and mined areas of the central shield.

Rewetting management was initiated in 1993. Monitor-ing of permanent plots (4m2 in size) that were regularly arranged along three transects (Gremer & Poschlod, 1991) and ran from the peat-mined to the drained part of the raised bog shield was carried out in 1992, before the initiation of the management, and in 2002. Hydrological parameters along these transects were measured to gain baseline data for the management plan. After rewetting, hydrological measurements were only carried out in ditches which were blocked.

The “Kendlmühlfilz” is one of the largest raised-bog complexes in Bavaria, situated in a basin south of Lake Chiemsee (Fig. 1). The basin was formed by the Inn-Chiemsee Glacier during the last-ice age. Today, the peatland represents a complex of arable fields, grass-lands and afforested areas at its borders, with peat- mining areas and a remaining part of the former raised bog shield, which is partly affected by drainage

c

b

d

a

Fig. 2 Wendlinger Filz: a – location of the milled fields (grey) in the peatland (black line = border of

the peatland), red line = Transect 2; b – actually milled field (1985); c – milled fields at the eastern part of Transect 2 in 1986 with dominant Calluna vulgaris; d – milled fields of the eastern part of Transect 2 in 2006 with dominant Rhynchospora alba.

ba

Fig. 3 Wieninger Filz: a – diagram of peat cutting (from Poschlod, 1996); b – peat forming vegetation in a former peat-cut area in 2005 with Eriophorum vaginatum and Sphagnum papillosum (Permanent Plot 3).


(Fig. 4c). Until the end of the 19th century peat was cut locally

or extracted for litter by farmers. Large-scale drainage started only in 1885. Peat was cut for industrial purposes, namely for salt production. After the First World War, peat was extracted from an area of 2.4 km2 by the Bavarian peat company for fuel, first still by hand but later by machine. In 1976, a private company started peat extraction in an area of about 0.4km2 by milling for horticultural purposes. Peat mining stopped in 1985 (Pfadenhauer et al., 1990).

Restoration of the milled areas, where ombrogenous peat layers about one meter high remained, started in 1986 by surface re-configuration of the nearly 1.5 km-long milling fields into polders, a method described in detail by Eggelsmann (1987). After rewetting the polders, reestablishment of typical mire vegetation according to the peat and water quality in the polders was initiated by planting and sowing specific vascular plant species in 1987 (Maas & Poschlod, 1991). Later on, fertilizer was applied to accelerate vegetation development, and Sphagnum species were reintroduced by transplanting small pieces of Sphagnum lawns (Sliva, 1997). The success of restoration management practices was monitored in permanent plots of 100 m2 (vascular plants) and 1 m2 size (bryophytes) which were situated along a transect running along Field 6S (Fig. 8). Here, we present only results of sowing and planting selected vascular plants in the summer of 1987 (Carex rostrata,

Eriophorum angustifolium; only sown: E. vaginatum) and introduction of Sphagnum (S. magellanicum, S. capillifolium – hummock/lawn species; S. cuspidatum – hollow species) sods in summer of 1992. For the entire experimental approach see Maas and Poschlod (1991) and Sliva (1997).

2.3 Vegetation and hydrological monitoring

Vegetation was recorded according to the dominance scales of Schmidt or Braun-Blanquet (Pfadenhauer et al., 1986). Nomenclature follows Ehrendorfer (1973) for vascular plants and Frahm and Frey (1983) for bryo-phytes except for Sphagnum spp., which follow Daniels and Eddy (1985).

Hydrological parameters were measured using plas-tic tubes of 1 or 2 meters length (Poschlod, 1990). Measurements of water levels and water chemical parameters such as pH and ions were carried out monthly from May to September during 1985 in the “Wieninger Filz” and “Wendlinger Filz.” In 2005, meas-urements in the Wieninger Filz were made only every other months in the same period. In 2006, hydrological parameters in the “Wendlinger Filz” were measured only once, in September. To compare data from the different years we used data from these months where measurements were made in 1986 and 2005 and 2006, respectively. Since in the “Wurzacher Ried,” measure-ments of water level and water chemical parameters before and after rewetting were carried out at different

Fig. 4 Wurzacher Ried: a – historical situation (horizontal lines – ombrotrophic parts (raised bog shields), horizontal broken lines –

minerotrophic parts); b – current situation (air photograph from Schuckert et al., 1997; c – unaffected part of the central raised bog shield cut through by the road; m – mined areas of the central raised bog shield).

Kendlmühlfilz: c – infrared coloured aerial photograph from the central part in 1986: in the south the more or less unaffected part of the raised bog shield, in the north peat-mined areas (red: by peat cutting until 1971, black: by peat milling from 1976 to 1985).


sites (see above), they were not evaluated for this paper. In the “Kendlmühlfilz,” data on hydrology have already been presented by Sliva (1997). They will, therefore, only be used for the discussion. Vegetation development was analysed by applying a variance analysis to compare changes in the dominance of single species followed by a Mann-Whitney-U-test, available in WinStat, and multivariate statistical methods, available in the software package PC-Ord (McCune & Mefford, 1999) to compare changes in the vegetation.

3. Results

3.1 Sucession in milled areas without restoration

management – the “Wendlinger Filz” case study Vegetation within the milled areas developed

towards mono-dominant stages of vascular plant species. The water level as well as pH, which depended on the remaining peat layer, determined vegetation develop-ment. In 1986, Eriophorum vaginatum was dominant at wet (annual average water level between 10 to 0 cm below surface) and acidic sites, Rhynchospora alba at wet acidic to subneutral sites and Carex rostrata, Eriophorum angustifolium or Phragmites australis at wet or flooded sites with subneutral to neutral pH. On all dry sites (average water levels lower than 10 cm below the surface), Calluna vulgaris dominated (Poschlod, 1990; Fig. 2c). In 2006, no changes could be observed. The same species were still dominant at the respective sites and no Sphagnum species had invaded except at flooded sites with Carex rostrata where Sphagnum cuspidatum became dominant and formed a close layer. No peat growth could be observed. However, many of the sites formerly dominated by Calluna vulgaris were invaded by Rhynchospora alba, the latter

becoming the more dominant species despite the fact that water levels remained the same as in 1986 (Figs. 2d, 5).

3.2 Succession in peat-cut areas without restoration

management – the “Wieninger Filz”case study Vegetation development in the “Wieninger Filz” dif-

fered strongly from that in the “Wendlinger Filz.” In 1986, non-mined areas were affected by drainage which became more obvious in 2005 when the dominance of indicators of drained ombrotrophic peatlands such as Pinus mugo or Calluna vulgaris increased. Depending on the water level and water and peat quality, peat form-ing vegetation was already established in 1986, either with Eriophorum vaginatum and Sphagnum papillosum or with Scheuchzeria palustris, Sphagnum papillosum, S. cuspidatum and S. angustifolium. In 1986, fresh peat layers of more than 80 cm could be observed. Due to continuing peat growth only a few permanent plots with peat forming vegetation (Fig. 6 – Permanent Plots 1a, 1b, 3 and 4) could be found in 2006. In the case of Perma-nent Plots 1a and 1b, where apart from Eriophorum vaginatum, Sphagnum angustifolium was also dominant, there was no increase in the peat layer. However, in Permanent Plots 3 (Fig. 3b) and 4, Sphagnum magellanicum and especially S. papillosum contributed to further peat growth of 28 and 30 cm, respectively, since 1986.

3.3 Succession in peat-cut areas after rewetting

management – the “Wurzacher Ried” case study Rewetting management of the peat-mined areas in

the Wurzacher Ried caused not only raised water levels within drained as well as mined areas, but extensive flooding of the peat-cut areas. It was followed by large

Fig. 5 Wendlinger Filz: Ordination of the permanent plots which were classified in 1986 as stages dominated by Calluna vulgaris

(DCA, main matrix: 12 plots, 27 species; second matrix: 12 plots, 27 species [highly correlated species, red; R² > 0,30] and 4 abiotic parameters [WLev = water level; pH; Cond = conductivity; Ca = Calcium content mg/l water]; however, R² for all abiotic parameters was < 0,30).

Pic abi = Picea abies, Cal vul – Calluna vulgaris, Vac uli – Vaccinium uliginosum, Eri vag – Eriophorum vaginatum, Rhy alb – Rhynchospora alba, Dic cer – Dicranella cerviculata, Leu gla – Leucobryum glaucum.


vegetation changes: however, they were not on the peat ridges between the peat-cut areas, but in the peat-cut areas, where a large-scale die-off of trees, dwarf shrubs and other indicators of drainage or degradation such as Molinia caerulea was noticeable due to flooding (Table 2). Reestablishment of or increase in peat-forming raised-bog species such as Eriophorum vaginatum and Sphagnum species occurred only through the establish-ment of floating mats (Fig. 7, Table 2). In contrast, Sphagnum magellanicum lawns which had already been established before the water level rose, disappeared after rewetting due to flooding (Table 2). Where peat was mined into the geogenous peat layers or the former drainage ditches touched the mineral underground, peat-forming fen species such as Carex rostrata or Phragmites australis became established or spread (Table 2).

3.4 Succession on milled areas after rewetting

management and reintroduction of vascular plants and Sphagnum spp.–the “Kendlmühlfilz” case study

Establishment of success differed between sowing and planting vascular plants, planting being more suc-cessful than sowing (Fig. 8a). Planting of Carex rostrata achieved a cover of 100% in four years after planting and it managed to become established along nearly the whole transect, except in the middle of the first half and at the end of the second half of the transect during the monitoring period (Fig. 8a). Eriophorum angustifolium

became established after sowing and planting except on the first planting plot. In contrast to Carex rostrata, its occurrence remained restricted to the sown and planted plots even seven years after introduction (Fig. 8a). Eriophorum vaginatum became established only on the sown plot but was more successful in establishing itself in the first half of the transect, where no introduction management took place (Fig. 8a). Transplantation suc-cess of Sphagnum sods differed strongly as well. Irrespective of their ecology, all three species showed similar behaviour within the same plots. Sods increased in diameter and cover in five plots (Fig. 8b) but died in four other plots.

4. Discussion

4.1 Spontaneous revegetation

Our comparative analysis of peat-cut and peat-milled areas without restoration management clearly shows that the peat-mining technique affects the spontaneous re-establishment of peat-forming vegetation. Peat-forming vegetation became established only in peat-cut areas but not in milled areas, as was already stated by Poschlod (1990) in a analysis of nine peatlands in the foothills of the Alps. Monitoring of the formerly mined peat- forming areas in the Wieninger Filz indicates that in peat-cut areas (1) the process of peat-formation is continuing and (2) that the accumulation rates are enormous, about 30 cm in 20 years, confirming the assumptions of Poschlod (1990). In the Wendlinger Filz,

Fig. 6 Wieninger Filz: Ordination of selected permanent plots recorded in 1986 and 2005, abiotic parameters and plant species correlated (DCA, main matrix: 22 plots, 65 species; second matrix: 22 plots, 65 species [highly correlated species, red; R² > 0,30] and 4 abiotic parameters [blue; WLev = water level; pH; Cond = conductivity; Ca = Calcium content mg/l water]; R² > 0,30); green circle – peat forming vegetation at high water level (WLev) in former peat-cut areas with Eriophorum vaginatum (Eri vag), Sphagnum magellanicum, S. papillosum, S. angustifolium a.o.; red circle – vegetation at low water level with dominant Pinus sylvestris, Picea abies and Calluna vulgaris in the peat-cut area (Permanent Plots 2a and 2b) or with dominant Pinus mugo and Calluna vulgaris on drained sites in the unmined area; brown circle – alder carr vegetation with Alnus glutinosa (Aln glu), Frangula alnus (Fra aln), Typha latifolia (Typ lat), Angelica sylvestris (Ang syl), Caltha palustris (Cal pal), Lycopus europaeus (Lyc eur), Peucedanum palustris (Peu pal) a.o.


however, the original peat forming vegetation has not reestablished even more than 40 years after mining activities ended of mining.

Studies in North America recently reported by Lavoie et al. (2003) and Poulin et al. (2005) have also shown that Sphagnum establishment occurs only in block-cut (= peat-cut) peatlands whereas at milled sites only vascular plants were able to establish. Lavoie et al. (2003) saw as a positive example the invasion of cotton grass (Eriophorum vaginatum) as a positive develop-ment which in our opinion, however, represents no

success, as 20 years of succession at the Wendlinger Filz were insufficient for the establishment of Sphagnum species in a successional stage of Eriophorum vaginatum. Not even has the cover of Eriophorum vaginatum in-creased from 1986 to 2006. The only effect which could be measured was the invasion of Rhynchospora alba in formerly Calluna vulgaris-dominated successional stages. In all milled and vacuum harvested areas, Sphagnum could reestablish only under flooded con-ditions. After 20 years, these Sphagnum mats still contained only Sphagnum cuspidatum or in rare cases

Table 2 Significant changes in dominance of potential peat forming species in peat-mined areas of the Wurzacher Ried after rewetting management (Indicator species: first group – peat-forming bog species; second group – peat-forming fen species; third group – species of dry/degraded sites; Habitat: PR – un-mined peat ridges between the peat-cut areas; PCA – peat-cut areas; Significance (Mann-Whitney-U-test; p < 0.05): ↑ – increase; ↓ – decrease; - no significance).

Indicator species Habitat Significance Remarks Eriophorum vaginatum PR - - PCA ↑ Establishment of floating mats Sphagnum magellanicum PR - - PCA ↓ Decrease due to flooding Sphagnum papillosum PR - - PCA ↑ Establishment of floating mats Sphagnum capillifolium PR - - PCA - - Sphagnum cuspidatum PR - - PCA ↑ Highest increase of all peat-forming species;

establishment of floating mats Carex rostrata PR - - PCA ↑ Increase due to flooding Phragmites australis PR - - PCA ↑ Increase due to flooding Trees and dwarf shrubs PR - - (Betula spec.; Vaccinium myrtillus; V. vitis-idaea a.o.)

PCA ↓ Decrease due to flooding

Molinia caerulea PR - - PCA ↓ Decrease due to flooding

Fig. 7 Wurzacher Ried: Transect levelling profile, location of the permanent plots and cover (% – y-axis) in 1992 as well as changes

in cover (%) of Eriophorum vaginatum and Sphagnum magellanicum from 1992 to 2002.

Eriophorum vaginatum – 1992

Eriophorum vaginatum – difference between 1992 and 2002

Sphagnum magellanicum – 1992

Sphagnum magellanicum – diff. 1992 and 2002


representatives of the Sphagnum recurvum group (S. recurvum var. mucronatum, S. angustifolium). However, the typical peat-forming bog species have not yet invaded the Sphagnum cuspidatum mats and, therefore, peat growth towards raised bog communities has not yet occurred. This confirms hypotheses that all mining practices that result in bare peat areas cannot be assumed to enable spontaneous revegetation towards the former peat-forming raised-bog vegetation, at least not in southern Germany, but this has also been noted in other countries. Price et al. (2003) state that suitable loci for Sphagnum recolonization are absent at milled and vacuum-harvested sites. They attribute this fact to the loss of capillary water flow to the surface, resulting in quick desiccation of the surface peat layers and to the huge extent of the mined sites which decreases the likelihood of the arrival of plant propagules. However, there are more causes for non-successful spontaneous re-vegetation of milled sites after abandonment. One of the key factors is not only dispersal, but also establishment and growth of the respective Sphagnum species (Rochefort, 2000; Chirino et al., 2006). Neither dispersal of spores nor establishment from spores have been observed so far, which is not surprising e.g. for the

main peat- forming species in the foothills of the Alps, Sphagnum magellanicum. Records of individuals with spore capsules are extremely rare (Poschlod, 1990). In contrast, vegetative fragments may be dispersed (Poschlod, 1995) and would be able to regenerate a new Sphagnum plant (Poschlod & Pfadenhauer, 1989; Spencer-Famous & Taylor, 2005). However, reestablish-ment of larger patches of peat-forming species at non- flooded sites was successful only after active reintroduc-tion (Sliva, 1997; see below).

Conditions for successful spontaneous reestablish-ment of peat-forming vegetation in peat-cut areas have been summarised by Poschlod (1994; Table 3). The main factor is the conservation of the surface layer as a valuable source for peat-forming species either vegeta-tively or in the propagule bank (Rhynchospora alba, Sphagnum spec. a.o.); the latter, however, is maintained only when stored under moist or wet conditions (Poschlod, 1989, 1990, 1995). Furthermore, the top spit may be a more suitable microsite for germination and establishment than a bare milled peat surface (Roderfeld, 1992; Roderfeld et al., 1993). Successful germination and establishment in milled areas depend on seed size and growth rate, limiting the recolonization potential of

Fig. 8 Kendlmühlfilz: a – development of cover of selected vascular plant species along the transect through milled field 6S from 1988 to 1994. Outlined arrow: sown plots, solid arrow: planted plots; b – development of the diameter (cm; outlined dot) and cover (%; solid dot) of transplanted Sphagnum sods at site J (Sliva, 1997).

Table 3 Comparative analysis of two peat-mining techniques – peat cutting and peat milling (vacuum mining) – from a restoration point of view.

Peat mining by cutting Peat mining by milling / vacuum extraction Vegetation (rooted) horizon (or surface layer, top spit) is maintained (potential for regeneration – whole plants, seeds, spores and bud banks)

Vegetation (rooted) horizon is destroyed

Mining vertically (1.5 to 3 m per year) → mined area is relatively small

Mining horizontally (vertically only 6 to 8 cm per year) → mined area is extremely large

Mined area will be abandoned after one year – possibility of fast regeneration also from adjacent areas

Mining of the same area over several decades depending on the depth – no possibility of fast regeneration because of the large mined areas and destruction of most of the adjacent areas during the mining period

Mining can also be done “under water” – re-wetting management in many cases not even necessary

Mining only under dry conditions possible – huge efforts for rewetting management necessary (including the construction of polders to minimize erosion)

Sphagnum magellanicum

Sphagnum capillifolium

Sphagnum cuspidatum

Carex rostrata

Eriophorum angustifolium

Eriophorum vaginatum

a b


typical raised-bog species (Campbell & Rochefort, 2003).

4.2 Restoration management

As the case study “Wurzacher Ried” shows, rewet-ting alone will not be followed by the reestablishment of peat-forming vegetation, at least not in the short or medium term, although succession after peat-mining but before local rewetting management leads to the reestab-lishment of the original peat-forming vegetation. Due to the extremely heterogeneous surface of the peat-mined area with un-mined ridges and mined areas of up to more than four meters in depth (Fig. 7) large parts of the peat-mined areas were flooded. As Rochefort et al. (2002) have shown, only shallow and short-term flood-ing may enhance the growth of most Sphagnum species. Nevertheless, according to Schouwenaars (1982) and Beets (1993), the establishment of floating mats as in some of the peat-cut areas of the Wurzacher Ried may initiate the establishment of peat-forming vegetation, however, mostly of fen species. Some bog or transition mire species such as Eriophorum vaginatum and Sphagnum papillosum may use these floating mats to increase their dominance (Beets, 1993).

Due to the slow recolonization of milled bare peat areas, sowing and planting of vascular plants as well as reintroduction of vegetative Sphagnum propagules or even transplanting Sphagnum sods were recommended to initiate re-vegetation (Maas & Poschlod, 1991). As already mentioned above, sowing was not successful but planting, especially of clonal plants with long rhizomes, has been a successful tool (Fig. 8, see also Sliva, 1997; Sliva & Pfadenhauer, 1999). However, an appropriate hydrological management plan including blocking ditches, constructing bunds and reconfiguring the sur-face is a prerequisite for applying these methods (Price et al., 2003; Campeau et al., 2004). Although hydrologi-cal management was carefully planned in the case of the Kendlmühlfilz, the reconfiguration of the surface re-sulted in upwelling of mineral water and accumulation of peat mud in some of the polders, followed by inva-sion of Phragmites australis and Typha latifolia but also Carex rostrata. Nevertheless, in most of this area other species have become established, Eriophorum vaginatum, E. angustifolium and Carex rostrata being the most suitable to cover rapidly the bare peat areas. Transplants of Sphagnum sods did not spread at all sites and many even died. If spreading occurred it was extremely slow (Sliva, 1997; Sliva & Pfadenhauer, 1999). Therefore, this technique will rarely be an option. Rochefort et al (2003) applied another technique, the spreading of vegetative parts of Sphagnum spp. (collected from a natural bog) as a thin layer on bare peat surfaces. After they were spread, the Sphagnum propagules are covered with straw mulch, including phosphorus fertilization, resulting in a low Sphagnum cover after three years. Despite these first successful steps in Sphagnum establishment, reestablishment of Sphagnum carpets still remains a big challenge in bare peat areas.

4.3 Conclusions The application of specific peat-mining techniques

determines the direction of spontaneous revegetation after mining activities end. We compared revegetation of abandoned areas mined by cutting and milling. However, there are more techniques which are applied throughout temperate regions worldwide. Future work, therefore, should include comparisons of all techniques in order to understand the factors that influence spontaneous re-vegetation. Furthermore, it might also be useful not to aim for the regeneration of pristine mires, but for the regeneration of certain functions as mentioned in the introduction. E.g., Vasander et al. (2003) state that after restoration, mined peatlands may return to a functional status close to that of pristine mires within a few years, taking into account, however, only the carbon-sink func-tion. Some successional stages of milled areas where the water level is at the surface may serve as suitable habitats for many hollow species such as Drosera spp. or Lycopodiella inundata, all species of the Red Data Book of Germany (Korneck et al., 1996).

The above-mentioned aspects should be included in a new edition of “Wise use of mires and peatlands” (Joosten & Clarke, 2002). Restorability of ecosystems is one of the central criteria in nature conservation (Riecken, 1992). However, this aspect is rarely con-sidered before ecosystems are altered. Principles 5 and 6 of the Convention on Biological Diversity state (5) “conservation of ecosystem structure and functioning, in order to maintain ecosystem services, should be a priority target” as well as (6) “ecosystems must be managed within the limits of their functioning,” but this has been, until now, completely ignored in the case of mires. Furthermore, Principle 11 says, “the ecosystem approach should consider all forms of relevant informa-tion, including scientific, indigenous and local know-ledge, innovations and practices.” However, since this knowledge does not yet exist with respect to the restoration of mined raised bogs, such a principle does not help. Even if the knowledge existed, who would be responsible for collecting and reviewing it? This is in our opinion another dilemma of the scientific com-munity, that textbooks or handbooks which summarize and review the state of art on actual problems are rarely supported by independent funding institutions. We should also take into account that mires or peatlands are individual entities and existing knowledge on one mire type or in one region cannot be transferred to another mire type or another region or even to the same mire type in the same region. As Price et al. (2003) state for peat-mined areas: “No standard management prescrip-tion can be made, because each site presents unique challenges.” Therefore, the establishment of a database with data on peat harvesting techniques, long-term monitoring research and scientific findings on the re-sults of spontaneous and directed revegetation processes or restoration management would be helpful in deciding on appropriate mining techniques when the aim after peat mining is the reestablishment of the functions of a


pristine mire. However, it should be also clear to every-one working on the restoration of peatlands that theoretical (scientific) considerations are often not suit-able to be implemented into practice. This is especially true for hydrological management practices, as the stud-ies at the “Wurzacher Ried” and the “Kendlmühlfilz” have shown.

Finally, further efforts should be undertaken to look for alternatives to Sphagnum peat for its respective pur-poses (Schmilewski, 2001) and also for ways of producing Sphagnum as a renewable resource, either in peat-mining areas or even outside of mires and peat-lands (Gaudig & Joosten, 2002; Grantzau & Gaudig, 2005; Krebs & Gaudig, 2005).

Acknowledgements We thank the governments of Bavaria and Baden-

Württemberg as well as all institutions which were involved in these studies for their support. Special thanks go to Prof. Jörg Pfadenhauer, Technical Univer-sity of Munich, who initiated more than 20 years ago the first studies on wetland restoration; to the nature con-servation centre in Bad Wurzach, which has been ensur-ing that continuous monitoring is taking place after the establishment of rewetting management; and finally to Kathrin Bylebyl, who corrected the English version of the text.

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(Received 13 August 2007, Accepted 6 September 2007)

natural revegetation and restoration of drained and cut-over ......primary mire type: →...

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