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Fens and floodplains of the temperate zone: Present status, threats, conservation and restoration

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Fens and floodplains of the temperate zone: Present status, threats, conservation and restoration

Abstract

This Special Feature focuses on lowland fens and flood plains. In this introduction we discuss the most important mire-related terms, present status, threats and conservation and restoration attempts. Floodplains and especially lowland fens are rare and vulnerable ecosystems. They are highly threatened all over the world because of direct conversion to agricultural land and especially the lack of appropriate management and altered catchment hydrology. Finally we present a framework for the conservation and restoration of these ecosystems. This consists of (1) optimising abiotic conditions; (2) safeguarding propagule availability of the target species; (3) creating and maintaining conditions for (re)establishment of these species, and (4) appropriate management to keep the conditions suitable.
- FENS AND FLOODPLAINS OF THE TEMPERATE ZONE - 157
Applied Vegetation Science 9: 157-162, 2006
© IAVS; Opulus Press Uppsala.
Abstract.
This Special Feature focuses on lowland fens and flood
plains. In this introduction we discuss the most important
mire-related terms, present status, threats and conservation and
restoration attempts. Floodplains and especially lowland fens
are rare and vulnerable ecosystems. They are highly threatened
all over the world because of direct conversion to agricultural
land and especially the lack of appropriate management and
altered catchment hydrology. Finally we present a framework
for the conservation and restoration of these ecosystems. This
consists of (1) optimising abiotic conditions; (2) safeguarding
propagule availability of the target species; (3) creating and
maintaining conditions for (re)establishment of these species,
and (4) appropriate management to keep the conditions
suitable.
Keywords: Biodiversity; Diversity; River floodplain; Species
richness; Water table; Wetland.
Introduction
The present volume contains 16 papers on the
analysis, management and restoration of riparian
wetlands and lowland fens, 14 of which were presented
at the 7th INTECOL international wetlands conference,
held from 25-30 July 2004 in Utrecht, The Netherlands.
The theme fits the growing recognition of the value of
wetland ecosystems worldwide.
The importance of river floodplains as spawning
grounds for fish and as productive pasture for domestic
cattle is recognised since long by local people. Still, the
general attitude of marshes being wastelands comes to
expression in wetland-related words such as ʻswampʼ
and ʻmudʼ which definitely have negative connotations
in most languages. However, this attitude started to
change in the 1960s and 1970s. People began to realise
that these ecosystems did possess important values that
could be expressed even in economic terms (Pearce 1993;
Costanza et al. 1997; van den Berg et al. 2004).
Recently the biodiversity value of certain wetland
Fens and floodplains of the temperate zone:
Present status, threats, conservation and restoration
van Diggelen, Rudy1*; Middleton, Beth2; Bakker, Jan1; Grootjans, Ab1 & Wassen, Martin 3
1Community and Conservation Ecology Group, Biological Sciences, University of Groningen, PO Box 14, 9750 AA Haren,
The Netherlands; 2U.S. Geological Survey National Wetlands Research Center, 700 Cajundome Boulevard, Lafayette, LA
70506 USA; 3Copernicus Institute for Sustainable Development and Innovation, Environmental Sciences, Utrecht Univer-
sity, PO Box 80.115, 3508 TC Utrecht, The Netherlands;
*Corresponding author; E-mail r.van.diggelen@rug.nl
types was recognised. Wetlands contain a large number
of adapted organisms (Mitch & Gosselink 2000) and, for
instance, calcareous fens are among the most species-
rich ecosystems of the temperate zone which also
harbour many endangered species (Wassen et al. 2005).
In addition to biodiversity there are other reasons why
wetlands are important. Mires play an important role in
the worldʼs carbon balance. Accumulating mires store
several 10 000s of kg C per ha per year (e.g. Asada et al.
2005), whereas drained mires lose even larger amounts of
CO2 (Wösten 1997) and other greenhouse gases (Flessa et
al. 1998; Groffmann et al. 2002). The role that wetlands
play in the purification of water (Olde Venterink et al.
2006, this issue) and in dampening the effect of a large
variation in precipitation (Bragg & Lindsay 2003) is
important in many places, especially low-lying areas.
Wetlands also provide resources such as game, fish, reed
and wood (Bragg & Lindsay 2003).
Terminology and definitions
In the literature on wetland ecology there is much
confusion about terminology and especially about the
distinction between wetland, mire, fen, fen meadows and
similar terms. This calls for a section with definitions on
how we use some of these terms in this issue.
ʻWetlandsʼ are defined as ʻareas of marsh, fen,
peatland or water, whether natural or artificial, permanent
or temporary, with water that is static or flowing, fresh,
brackish or salt, including areas of marine water the
depth of which at low tide does not exceed six metresʼ
(Convention on Wetlands in Ramsar, Iran, 1971).
There are essentially two schools of thought with
respect to the definition of mires. The first one states that
a ʻmireʼ is a peatland together with peat communities
(Godwin 1941), sometimes called a peat-producing
ecosystem (Godwin 1956; Gore 1983; Joosten & Clarke
2002) or an area that supports at least some vegetation
known to form peat, and usually includes a peat
158 VAN DIGGELEN, R. ET AL.
deposit (Bragg & Lindsay 2003). The second view
includes also some non-peat-producing ecosystems
such as groundwater-fed calcareous fens (Ratcliffe 1964;
Mörnsjö 1969) where the main deposit consists of tufa.
We follow Joosten & Clarke (2002) and use the word
mire in a strict sense for peat producing ecosystems.
Mires can be subdivided into bogs, fens and
floodplain mires. The definition of ʻbogʼ has always been
straightforward: a bog is a mire system that is entirely
dependent on precipitation for its water and solutes (Du
Rietz 1954).
There is more uncertainty about the definition of
fen. Originally this term was simply used to describe
those types of mires which are not bogs (Du Rietz
1954). Soon people felt the need to make a distinction
between poor fens and rich fens, mainly based on
vegetation composition. Wheeler (1988) included similar
vegetation types on mineral soils also in the definition,
whereas Wheeler & Proctor (2000) used pH – and also
productivity to some degree – as criteria. All mires with a
pH > 5.5 were defined as ʻfensʼ. Recently there has been
a tendency to narrow the definition of fen to ground-water
fed wetlands (Bedford & Godwin 2003). We agree with
this approach and use the word fen to mean all mires
that are pre-dominantly fed by groundwater. Note that
wooded wetlands (sometimes called ʻcarrʼ) are included
in this definition of fen.
The third type of mire is a floodplain, sometimes also
called ʻflood mireʼ (Succow & Joosten 2001). We define a
ʻfloodplainʼ as a mire that is predominantly fed by surface
water. This definition includes the tall sedge fens and reed
swamps from the European literature (e.g. Wheeler &
Proctor 2000) and most of the sedge meadows from the
American literature (Curtis 1959). These communities
are open wetlands dominated by sedges and grasses, and
consist mainly of tussocks of large helophytes.
The semi-natural communities ʻfen meadowsʼ and
ʻwet grasslandsʼ have developed after human mani-
pulation with water tables. Fen meadows have usually
developed from undrained fens after a modest lowering
of the water table to increase productivity. Wet grasslands
is a more general term that could include fen meadows,
but in a strict sense is used to describe managed (drained)
floodplains.
Distribution and present status
At present there are no exact data available on the
distribution and status of temperate fens and floodplains.
Nevertheless some rough figures exist. Lappalainen
(1997) and co-authors estimated that an area of slightly
less that 4 million km2 of mires exist throughout the entire
world and another 2.5 million km2 for other wetlands.
The great majority of these peat deposits are found in the
northern hemisphere, especially in the boreal zone, and
consist mainly of bogs. The sparse data available suggest
that bogs cover a much larger surface area than do fens,
which also occur in most countries of the temperate zone.
A study by Bragg & Lindsay (2003), however, shows the
opposite to be true in eight countries in central-eastern
Europe. Here, the majority of the mires consist of fens
with 78% of a total of ca. 73 000 km2 (5% of the total
surface of these countries). The authors estimate that
43% of this surface is still in a nearly natural state.
The situation in North America is rather similar to
Europe. The great majority of mires consists of bogs,
and fens are mainly found in localized areas with
groundwater outflow. In the United States, these areas are
found especially in the glaciated Midwest and Northeast,
as well as portions of the Appalachian Mountains and
mountainous West (Bedford & Godwin 2003). Only
fragmented information exists on the present state, e.g.
Pearson & Loeschke (1992) estimated that approximately
40% of the fens in Iowa were lost. Bedford & Godwin
(2003) wrote: “Few estimates of loss and current extent
exist, but where estimates are available, they indicate
extensive loss, fragmentation, and degradation”.
Changes in the status
Direct conversion
Probably the most important factor affecting fens
and floodplains is their conversion into agricultural
fields. These wetlands were drained from medieval times
onwards and used for grazing cattle and making hay. In
the 20th century, drainage technology developed to such a
level that even crop production became possible on these
wet soils, especially (but not only) in former communist
countries. This conversion has resulted in substantial
emissions of carbon dioxide and other greenhouse gases,
making peat drainage a significant contributor to global
warming (Flessa et al. 1998; Groffman et al. 2002).
Compared to bogs, fens are less often used for fuel
extraction, but the absolute surface used for this purpose
is probably a large threat, especially in somewhat more
southern regions where bog peat is rare. The total surface
affected is unknown, not in the least because this type
- FENS AND FLOODPLAINS OF THE TEMPERATE ZONE - 159
of peat extraction is not well-administered and mostly
carried out in small-scale excavations by one-man
companies. In bogs, large companies do most of the
digging.
Effects of hydrological changes
Fens are especially sensitive to relatively small
changes in the hydrological system. Human activities
such as groundwater abstraction, large-scale drainage
of the surroundings for agricultural purposes and use
of groundwater for irrigation lead to a diminished
groundwater flow to the fen, even when conducted at
large distances from the fen. The effects of groundwater
abstraction may often not be visible in the water table
inside the fen, but it always leads to an increase in the
relative importance of rainwater and finally to acidi-
fication of the top layer (Wassen et al. 1996; van Diggelen
1998; Grootjans et al. 2006, this issue). This process may
take many decades (van Diggelen et al. 1996; van der
Hoek & Sýkora 2006, this issue) and go unnoticed for
a while (van Belle et al. 2006, this issue). The factors
that control the acidification rate are not completely
understood yet, but the speed certainly depends on the
amount of acid produced (Kooijman & Paulissen 2006,
this issue) and the buffering capacity of the soil (van
Diggelen 1998; van Bremen & Buurman 2002).
Water tables in fens and floodplains are lowered due
to the more intensive drainage pressure, and this leads
to increased mineralisation rates. Most often increased
mineralisation rates result in higher biomass production,
but they may also lead to a shift in the limiting nutrient
(Wassen & Olde Venterink 2006, this issue; Higgins et
al. 2006, this issue; van Belle et al. 2006, this issue).
Productivity gradients and vegetation patterns change
accordingly, in response to altered competition intensity
for nutrients and light (Kotowski et al. 2006, this
issue).
The opposite situation as to water tables may occur as
well, although less often; fens and especially flood-plains
sometimes become wetter because of changing water
regimes, building of dams and similar activities. Under
such conditions, the surface water component increases
and nutrient dynamics change, depending on water
chemistry and sediment load. Sedimentation is normally
the most important nutrient source in floodplains
(Olde Venterink et al. 2006, this issue), and increased
sedimentation leads to higher nutrient availability
(Werner & Zedler 2002) and affects vegetation patterns
through shifts in competitive interactions (Kotowski et
al. 2006, this issue). However, sedimentation rates vary
greatly between vegetation types with different structure
(Olde Venterink et al. 2006, this issue).
Conservation and restoration
Fens and floodplains are among the most species-
rich habitats but at the same time biodiversity decline
has been more intense in these areas than in many other
ecosystems. Conservation of existing fens and flood-
plains and restoration of degraded ones, therefore, is a high
priority (Resolution VII.17 of the San José Conference
7th Meeting of the Conference of the Contracting Parties
to the Convention on Wetlands (Ramsar), 10-18 May
1999; Final Resolution Adopted at the 7th INTECOL
International Wetlands Conference, 25-30 July, 2004).
Van Diggelen & Marrs (2003) categorized essential steps
for conservation and restoration into four groups:
1. Establishing or re-establishing the necessary abiotic
conditions;
2. Supplying (sufficient) propagules of constituent spe-
cies of the target communities;
3. Creating and maintaining suitable conditions for the
(re-)establishment of target species;
4. Appropriate management to keep the conditions
suitable.
Establishing and safeguarding necessary abiotic
conditions in affected wetlands almost always involves
raising the water table (Timmermann et al. 2006,
this issue), (re-)establishing the major water source
(rainwater, groundwater and surface water) for the
wetland under consideration and creating the necessary
productivity level regime (van Belle et al. 2006, this
issue). Rewetting is in itself technically not so difficult to
achieve (Timmermann et al. 2006, this issue; Bodegom
et al. 2006, this issue), but conserving and/or restoring
the two other parameters may be much more difficult.
Restoration is comparatively easy in floodplains,
especially along the edges of water bodies such as larger
rivers and lakes where the appropriate water type is
nearby. The productivity of the typical vegetation is high,
and this makes floodplain vegetation much less sensitive
to increased nutrient availability in water and air than are
low-production communities (Verhagen & van Diggelen
2006). In the case of fens, it is much more difficult and
often impossible to conserve the necessary groundwater
feeding. The hydrology of the surrounding landscape
has often completely changed (Barendregt et al. 1995;
Grootjans et al. 2006, this issue), and groundwater is
replaced by rain or surface water. Critical parameters
such as productivity, limiting nutrient, light penetration
and pH shift outside the limits typical/necessary for fen
vegetation, and the characteristic species disappear (van
Bodegom et al. 2006, this issue).
Even if the critical abiotic constraints lie within the
tolerance of the target vegetation, this vegetation will
not necessarily contain all target species, nor will they
quickly reappear. Many species do not form a long-
160 VAN DIGGELEN, R. ET AL.
persistent seed bank and have to rely on dispersal to reach
a site after local extinction. Other authors (e.g. Novak &
Prach 2003; Galatowitsch 2006, this issue) found a clear
relationship between immigration rate and isolation of
a site, which suggests that dispersal is a constraint for
many species. There are also differences between modes
of dispersal. Soons (2006, this issue) showed that wind
dispersal is of limited value for most wetlands and is
negatively affected by increased productivity. Dispersal
by water (in flooded parts) and by large herbivores (in
grazed parts) seem to be more efficient dispersal vectors
(van den Broek et al. 2005; Middleton et al. 2006a, this
issue). Of course the latter implies that sites must be
connected to each other by a water course or by moving
animals.
Species establishment after restoration, (or, in the case
of annuals, yearly establishment) is a process that shows
many similarities to that of alien species that have to
establish in existing vegetation. Presently, we are not able
to predict which species will re-establish, and whether
or not these species will be invasive. Nevertheless, we
do know some of the constraints for establishment.
Kotowski et al. (2006, this issue) showed that competition
for light was the major factor that kept many species out
of the high-productive zone, whereas Bartha et al. (2003)
showed that colonisation rates increased significantly
after extreme weather events when total species cover had
decreased considerably. Chirino et al. (2006, this issue),
on the other hand, showed that the relative establishment
success was independent from weather conditions but
did depend on species identity. All these results suggest
that interspecific competition is a major bottleneck for
establishment.
Unlike the term ʻnatural areaʼ suggests, most fens
and floodplains are not capable of surviving without
regular human intervention. We know from palyno-
logical evidence (e.g. van Diggelen et al. 1991; Succow
& Joosten 2001; Grootjans et al. 2006, this issue) that
large surfaces of base-rich fens were present in natural
landscapes at one time. We know also that all over
Europe the remaining ʻnatural fensʼ are in fact ʻfen
meadowsʼ that were slightly drained (Wassen & Joosten
1996) and used for hay production and sometimes
grazing. The same was true in North America, except
that grazing was much more common there than it was
in Europe. These activities declined in the second half
of the 20th century, and the effects were the same in
both continents: shrubs and large helophytes started to
invade the sites and gradually took over, outcompeting
the original fen vegetation with many light-demanding
species (Kotowski et al. 2006, this issue). The situation
is much less dramatic in the more productive floodplains,
but abandonment also leads to shrub invasion in these
areas (Jensen 1998).
Nature management tries to counteract these un-
wanted developments by applying certain management
techniques that mimic traditional agricultural manage-
ment. The objective of all techniques is to remove exces-
sive nutrients and create recruitment gaps for low-com-
petitive species. The techniques used include mowing
and removing hay (Slotte 2001), grazing (Littlewood et
al. 2006, this issue) and also burning (Middleton 2002).
Apart from many similarities, there are also considerable
differences between these techniques (van Diggelen &
Marrs 2003; Middleton et al. 2006b, this issue). Mowing
creates a spatially homogeneous situation that is highly
heterogeneous in time with high selection pressure on
species for exact timing of the life-cycle. Low-intensity
grazing, on the other hand, often results in a spatially
heterogeneous pattern that is stable in time because
herbivores create and maintain intensively used graz-
ing lawns adjacent to hardly used spots (Bakker et al.
1984). There are still many uncertainties about the role
of fire in managing fens and floodplains. It is obvious
that prescribed burning removes dead vegetation and, at
least temporarily, results in an increase of biodiversity
but winter fire does not control shrubs.
Although not exhaustive, this introduction should
point to many research questions concerning the
maintenance and restoration of fen and floodplain
biodiversity in the temperate zone. This special issue of
Applied Vegetation Science is a first attempt.
Acknowledgements. We thank Jarita Davis for editorial
comments.
- FENS AND FLOODPLAINS OF THE TEMPERATE ZONE - 161
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... Nevertheless, even twice-a-year mowing might not be sufficient for fen restoration in the case of strongly damaged fens, e.g., fens entirely overgrown by shrubs or even trees Sundberg, 2012;Galvánek et al., 2015), intensely fertilised fens (Berendse et al., 1992), fens invaded by Phragmites australis (Güsewell et al., 2000) or drained fens (Kołos and Banaszuk, 2018). More intensive restoration measures such as tree cutting or sod removal with consequent mowing should be applied in such cases (Singh et al., 2021;van Diggelen et al., 2006). If the water regime is severely disturbed, it is crucial to restore it first and then apply conservation management (Kołos and Banaszuk, 2013). ...
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While the importance of conservation mowing for mesic grasslands is generally accepted, its use for fens and fen grasslands interspersed within agricultural land is still controversial. Although fens may persist naturally, ongoing environmental changes increase productivity and accelerate succession. These processes can be mitigated through conservation management with appropriate settings. However, long-term management experiments are challenging and provide only locally valid results. Here, we analysed vegetation data (bryophytes and vascular plants) from seven management experiments (spanning 3–20 years) conducted in Central European poor, moderately-rich, and calcareous spring fens (Czech Republic, Slovakia). Two of these experiments examined the effects of restoration of abandoned fens, while five experiments examined changes in mowing regimes in managed fens (cessation, intensification, delay to autumn, and litter removal). Data were analysed using unidimensional and multidimensional methods separately for the initial, extended, and entire period. Mowing had a statistically significant effect on species composition except for the shortest (3-year) experiment. Litter removal did not compensate for mowing. Mowing twice or delayed mowing significantly affected the species composition of calcareous fens. In all cases, cessation of mowing significantly reduced the richness of species, especially those of conservation importance. In contrast, any mowing of abandoned fens increased species richness. The effects of mowing intensification or cessation on species richness and composition of a restored calcareous fen were evident in the first 2–3 years. Other effects were initially weak or nonsignificant but later became stronger, such as mowing delay and restoration removal of litter, which became significant only after nearly 20 years. We found that cessation or restoration of mowing usually triggers a rapid vegetation change, whereas it can take decades to detect the response caused by changes in mowing timing. Importantly, mowing can stabilise or even restore vegetation of fen ecosystems that have been weakened by their fragmentation in the temperate agricultural landscapes.
... Par comparaison avec les travaux menés dans d'autres zones de l'Ouest Européen comme les Pays-Bas par exemple ( Van de Plassche, 1981 ;Van Geel et al., 1996 ;Diggelen et al., 2006 ;Meijles et al., 2018 ;Van Geel et al., 2020 ;Grootjans et al., 2021), les études sur le bassin sédimentaire de la Somme ont débuté beaucoup plus tôt, dès 1840 dans la région d'Abbeville avec les travaux de Traullé (1796) ; Picard (1834) ou Boucher de Perthes (1847). Ces recherches ont cependant connu des longues périodes d'abandon ainsi qu'un développement irrégulier dont ressortent essentiellement les contributions fondamentales de V. Commont (1910) puis de F. Bourdier (Bourdier, 1969 ;Bourdier & Lautridou, 1974). ...
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Dans le bassin de la Somme, les importants dépôts tourbeux des fonds de vallée suscitent l'intérêt des archéologues et géolo-gues depuis plus de cent cinquante ans. Que ce soit pour la richesse des traces du passé conservées ou pour la compréhension des processus de formation, les hypothèses sur les conditions environnementales de développement des tourbes ont fait l'objet de nombreuses investigations dès le xix e siècle. Un large panel de spécialistes s'est mobilisé pour étudier ces questions. La multiplication des découvertes archéologiques, la synthèse géoarchéologique, la naissance de nouvelles techniques analytiques (datation absolue 14 C) et le développement des connaissances sur l'Holocène contribuent, dans la seconde moitié du xx e siècle, à la mise en place d'un modèle global d'évolution morpho-sédimentaire lié aux occupations humaines (principalement Paléolithique supérieur et Mésolithique). Cependant, des incertitudes persistent dans ce modèle et nécessitent des précisions et investigations supplémentaires pour caractériser avec précision les évolutions au cours de l'Holocène moyen et récent. Il s'agit de la chronologie de développement des principaux faciès de tourbe, du cadre paléoenvironnemental contemporain de ces dépôts et des causes d'interruption de la turfi-genèse (voire de dégradation des tourbes) dans la vallée. ABSTRACT PEAT SEQUENCES OF THE SOMME BASIN VALLEY FLOOR (FRANCE): HISTORY OF RESEARCHES, DIVERSITY OF CONCEPTS AND PERSPECTIVES In the Somme Basin, the large peat deposits at the bottom of the valley have been of interest to archaeologists and geologists for more than a hundred and fifty years. From the abundance of preserved remains of the past to the understanding of the formation processes, hypotheses on the environmental conditions of peat development have been the subject of numerous investigations since the xix th century. A wide range of specialists has been working together to study these questions. The increase of archaeological discoveries, the geoarchaeological synthesis, the emergence of new analytical techniques (absolute 14 C dating) and the development of knowledge on the Holocene contributed in the second half of xx th century to the realization of a general model of morpho-sedimentary evolution linked to human occupations (mainly Upper Palaeolithic and Mesolithic). Nevertheless, some uncertainties remain in this model and require further clarification and investigations to accurately characterize the Middle and Recent Holocene evolutions. These include the chronology of the development of the main peat facies, the palaeoenvironmental setting in which they were deposited and the causes of the interruption of turfigenesis (or even the degradation of peat) in the valley.
... Flood events impact the structure of plant and animal communities due to changes in the populations of most living organisms within the affected ecosystem. The scientific literature is rich in examples related to flood-induced changes in the populations of plants (e.g., van Diggelen et al., 2006), birds (e.g., Vaughan et al., 2007), fishes (e.g., Lasne et al., 2007) aquatic creatures (e.g., Bunn and Arthington, 2002), among others. On the contrary, less attention has been paid to the impacts of flooding on the diversity, abundance, and community structure of terrestrial invertebrates in riparian areas (Truxa and Fiedler 2012). ...
... Mires and peatlands are ecosystems with many highly specialized species (Joosten and Clarke 2002, 87-90). There is clear empirical evidence that conventional farming on organic soilsmainly on drained peatlandsnot only leads to heavy greenhouse gas emissions, but also has negative consequences for biodiversity (van Diggelen et al. 2006). The only way to stop both the emissions and the loss of biodiversity is to rewet the peatlands. ...
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Biosphere integrity and securing biodiversity is one of the most important environmental challenges facing the world today and a core problem of sustainability. Starting with an overview of the development of nature conservation and biodiversity protection, this chapter analyses the relationship between democracy and biodiversity. We summarize theoretical arguments and empirical findings on the question of whether democracies perform better than autocracies in biodiversity protection. Additionally, we refer to the discussion of democratic legitimacy in nature conservation projects and possible trade-offs between participation and scientific rigor. We take a look at biodiversity protection in biosphere reserves and outside protected areas. A key finding is that evidence for an impact of democracy on biodiversity protection is contested. Furthermore, there is no consensus on which form of democratic legitimacy is best for nature conservation. We conclude by pointing out several fields of future research on the relationship between democracy and biodiversity protection.
... The discontinuation of traditional practices endangers high value habitats and their biodiversity [46,57]. In the case of wetlands, the common drainage practice for agricultural intensification is the major threat [24,[58][59][60] along with natural succession caused by land use abandonment [32,61]. First, these processes degrade wetland vegetation and their biodiversity [58,62,63]. ...
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... Unfortunately, floodplain ecosystems have been massively declining in extent and integrity on a national and even global scale (Aishan et al. 2015, Kingsford 2000, Klimo and Hager 2001, Knutson and Klaas 1998, Rood et al. 2005, Stromberg 1993). Threats to floodplain forests include alteration of flow and sediment regimes by dams, levees, channelization, land clearing for agriculture, and urban development (Brinson and Malvárez 2002, Malmqvist and Rundle 2002, Tockner et al. 2008, van Diggelen et al. 2006, Wang and Wang 2016. In response, efforts to restore remnant floodplain ecosystems have been initiated over a wide variety of settings and geographies (Ebert et al. 2009, Hughes et al. 2012, Mondal and Patel 2018, Moss and Monstadt 2008, Opperman et al. 2010, Rood et al. 2005, Stanturf et al. 2000. ...
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Calcareous fens are peat-wetlands fed mainly by groundwater, located in topographic hollows and served by springs or seepages of water derived by contact with base-rich mineral ground. In the European Union they are protected habitats requiring special conservation measures. To better understand the environmental supporting conditions of alkaline fen habitat found in Ireland, a 2-years hydrological and hydrochemical monitoring programme was carried out on four contrasting fen sites that covered an ecohydrological gradient representing intact to highly degraded conditions. This paper presents a methodology (and its limitations) of how the evaluation of the temporal and spatial variability of the quality and hydrological dynamics associated with different representative vegetation communities within the four fens can be used to develop ecohydrological metrics for fen habitat. The conditions supporting fen habitat in “good” ecological condition, indicative of a functioning alkaline habitat, were determined and contrasted with conditions found in habitats deemed to be in “poor” ecological condition. Results indicate that an annual water level always above the ground surface within a threshold depth envelope of between 0.030 and 0.28 m is required for at least 60% of the year for healthy fen vegetation. In terms of hydrochemistry, higher concentrations of nutrients were found in the sediments at depth and the groundwater feed compared to the phreatic water table. This suggests the fens may be incorporating the incoming nutrients into their internal biogeochemical cycles and that there is a net accumulation of nutrients within the wetlands. Although envelopes of nutrient concentrations in the surface water of the fen associated with habitat in good ecological condition can be defined (e.g., dissolved reactive phosphorus concentrations of between 6 and 37 µg-P/l for PF1 habitat), these levels should be regarded as the water quality after the fen vegetation has effectively interacted with the higher incoming nutrient levels in the groundwater. Moreover, the local hydrogeological conditions that define groundwater pathways (and associated water quality impacts) in such calcareous fens, allied to the localized nature of these measurements in these field studies, makes it difficult to define groundwater water quality threshold values with any confidence.
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We assessed biodiversity effects of disturbance in meadows and rich fens. We hypothesized that disturbances and their timing affect plant and bryophyte species richness and other indicators of conservation success. More specifically, we expected conservation status to improve with disturbances that mimic natural grazing processes, i.e., that extensive year round grazing with trampling had a more positive effect than intensive summer grazing or mowing. Kastbjerg wetlands, Jutland, Denmark. In a 3‐year field experiment, we applied trampling, season‐specific defoliation with biomass removal and burning in a randomized design in nine wetland sites. We recorded species richness and community composition. Bayesian generalized linear mixed‐effects models were built with treatment as fixed effect, site as random effect and species richness or species composition as responses. Leaf N and P, and soil moisture were included as co‐variables. Further, a quadratic discriminant analysis (QDA) was applied to test for discrimination between treatments based on a set of biodiversity indicators. Environmental and biotic differences among sites were considerable and significant indicating a considerable effect of historical contingency (local species pool). We found only minor and mostly insignificant effects of disturbance on vegetation. However, a QDA revealed significant differences among treatments based on five indicators for conservation status. Simulated grazing and trampling were generally associated with higher vascular plant richness, bryophyte richness, number of indicator species and stress tolerant species and decreasing abundance of competitive species. We found small, but positive effects of disturbance on biodiversity indicators of wetland vegetation after three years of experimental treatments. Initial site differences explained most variation, indicating strong historical contingency. Our results support the need for restoration of disturbances in fens and meadows, and the importance of prioritizing areas with near‐natural biotas.
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Four Vertigo species are covered by special forms of protection under Annex II of the Habitats Directive. The habitats of these snails are currently rare in Europe. Since typical conservation practices are ineffective for this ecosystem, support mechanisms for measures maintaining biodiversity have been incorporated into agriculture in the form of agri-environmental schemes (AES). However, an inappropriately designed AES may threaten the survival of populations of globally endangered species such as Vertigo moulinsiana (Dupuy) as mowing and swath removal dates coincide with the snails’ activity period in the upper parts of the mown plants, the majority of their population will be removed from the area along with the harvested swath. In addition, mowing instantaneously and radically alters the habitat’s microclimate. The policy of mowing the total area thus leads to unprecedented habitat homogenisation across the landscape, especially when machine mowers are used. In the case of V. moulinsiana, the best approach would be not to mow the whole area but to leave a part unmown where these snails could live unhindered. Instead of machines, traditional mowing could be implemented, which entails cutting at a greater height above the sedge clump level. This would not destroy the tussock structure and would allow the habitat to recreate itself. In combination with the designation of unmown refuges, the effects of this approach could be quite beneficial to the snails.
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High-capacity wells (HCWs) are known to reduce groundwater discharge to fens and impact their floristic quality, but whether HCW impacts have become predictive of fen floristic quality across large areas has not been studied. Here we used Thiem-equation-estimated drawdown as an indicator of regional HCW impacts to predict floristic quality, floral richness, and community composition in fens throughout their Wisconsin (USA) range. This indicator of HCW influence (HCWinfluence) was associated with a strong decline in floristic quality measures and native-species richness, while non-native-species richness increased sharply. Fuzzy Set Ordination of community data suggested estimated drawdown was associated with the loss of high coefficient-of-conservatism graminoids and forbs, specialist species, and state-listed rare species. The abundance of non-native species and weedy natives increased with increasing HCW impact. The fact that our indicator of HCW influence has become predictive of fen quality and community composition statewide suggests that HCWs are a driver of floristic quality across large areas, and that possible declines in fen quality due to cumulative impacts should be addressed before siting wells.
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A landscape-ecological analysis of the Gorecht-area in the northern part of the Netherlands was performed in order to assess the hydrological conditions. Since the area was too heavily influenced by man, it was impossible to use vegetation indications, so a vegetation reconstruction was made, based on peat-remnants. In total 50 peat-profiles were described along four transects. Results were aggregated into so called "hydro-ecological mire systems', which made it possible to reconstruct hydrological conditions during peat-formation. -from English summary
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Closed canopy vegetation often prevents the colonization of plant species. Therefore the majority of plant species are expected to appear at the initial phase of post-agricultural succession in mesic forest environment with moderate levels of resources. This hypothesis was tested with data from the Buell-Small Successional Study, NJ, USA, one of the longest continuous fine-scale studies of old-field succession. The study started in 1958, including old fields with different agricultural histories, landscape contexts, and times of abandonment. In each year of the study, the cover values of plant species were recorded in 48 permanent plots of 1 m2 in each field. We analysed the temporal patterns of colonization at plot scale and related these to precipitation data and other community characteristics. The number of colonizing species decreased significantly after ca. 5 yr, coinciding with the development of a continuous canopy of perennial species. However, species turnover remained high throughout the whole successional sequence. The most remarkable phenomenon is the high inter-annual variation of all studied characteristics. We found considerable temporal collapses of vegetation cover that were synchronized among fields despite their different developmental stages and distinctive species compositions. Declines of total cover were correlated with drought events. These events were associated with peaks of local species extinctions and were followed by increased colonization rates. The transitions of major successional stages were often connected to these events. We suggest that plant colonization windows opened by extreme weather events during succession offer optimum periods for intervention in restoration practice. Nomenclature: Gleason & Cronquist (1991). Abbreviation: BSS = Buell-Small Succession Study.
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