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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.
Applied Vegetation Science 9: 157-162, 2006
© IAVS; Opulus Press Uppsala.
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
Keywords: Biodiversity; Diversity; River floodplain; Species
richness; Water table; Wetland.
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
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
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)
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
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
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
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
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
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-
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
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
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
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... Most studies on extinction debts have been conducted in dry grasslands (e.g., Adriaens, Honnay, & Hermy, 2006;Bagaria et al., 2017;Cousins, Ohlson, & Eriksson, 2007;Helm, Hanski, & Pärtel, 2006;Lindborg, 2007;Olsen et al., 2018) or in woodlands (e.g., González-Varo, Albaladejo, Aizen, Arroyo, & Aparicio, 2015;Kolk & Naaf, 2015;Vellend et al., 2006). Studies about the evidence of extinction debt in other habitat types such as wetlands are still rare, even though the biodiversity of wetlands has recently declined around the world (Parish et al., 2008;van Diggelen, Middleton, Bakker, Grootjans, & Wassen, 2006) and many wetland species are threatened (e.g., Bornand et al., 2016). The main causes for this decline in wetlands are drainage, peat extraction, and intensification of agriculture (Fischer, 2015;Küchler et al., 2018;Mälson, Backéus, & Rydin, 2008). ...
... This is evidenced by our findings that, on the one hand, the expected species richness of long-lived specialist species in wetlands with a substantial loss in area was lower than their actually observed species richness and, on the other hand, that historical wetland area-besides current wetland area-explained a substantial and significant part of the current species richness of long-lived wetland specialist plant species. There is still time to take conservation measures to prevent future extinction in the wetlands of canton of Zürich and elsewhere (Kuussaari et al., 2009;Mitsch & Gosselink, 2000;van Diggelen et al., 2006). Our study also confirmed that severe habitat loss leads to extinction debt of longlived specialist species not only in dry grasslands and woodlands (Bagaria et al., 2017;Hanski & Ovaskainen, 2002;Krauss et al., 2010) but also in wetlands. ...
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Abstract Habitat loss leading to smaller patch sizes and decreasing connectivity is a major threat to global biodiversity. While some species vanish immediately after a change in habitat conditions, others show delayed extinction, that is, an extinction debt. In case of an extinction debt, the current species richness is higher than expected under present habitat conditions. We investigated wetlands of the canton of Zürich in the lowlands of Eastern Switzerland where a wetland loss of 90% over the last 150 years occurred. We related current species richness to current and past patch area and connectivity (in 1850, 1900, 1950, and 2000). We compared current with predicted species richness in wetlands with a substantial loss in patch area based on the species‐area relationship of wetlands without substantial loss in patch area and studied relationships between the richness of different species groups and current and historical area and connectivity of wetland patches. We found evidence of a possible extinction debt for long‐lived wetland specialist vascular plants: in wetlands, which substantially lost patch area, current species richness of long‐lived specialist vascular plants was higher than would have been expected based on current patch area. Additionally and besides current wetland area, historical area also explained current species richness of these species in a substantial and significant way. No evidence for an extinction debt in bryophytes was found. The possible unpaid extinction debt in the wetlands of the canton of Zürich is an appeal to nature conservation, which has the possibility to prevent likely future extinctions of species through specific conservation measures. In particular, a further reduction in wetlands must be prevented and restoration measures must be taken to increase the number of wetlands.
... Progression of species is related with sequential intermediate stages that eventually lead to the climax stage, which in a moderate climate consists of a forest. In many areas succession occurs in originally treeless systems which have lost resilience as a result of drainage and eutrophication (Van Diggelen, Middleton, Bakker, Grootjans, & Wassen, 2006). One of the stages of this process is tree and shrub expansion in non-forest ecosystems, which is often considered one of the major threats to biodiversity (Barabasz-Krasny, 2016;Hoek & Sýkora, 2009;Poschlod, Bakker, & Kahmen, 2005), also to non-forest ecosystems protected throughout the European Union (EU) as Natura 2000 habitats such as fen meadows (Kotowski, Jabłońska, & Bartoszuk, 2013). ...
... The process of expansion of trees and shrubs was additionally promoted by drying of some sections of the Biebrza Valley as a result of land reclamation by draining carried out in the 19th and 20th centuries (Grygoruk et al., 2011) and climate change (Maksymiuk, Konrad, Ignar, Krupa, & Okruszko, 2008). Land reclamation resulted in expansion of trees and shrubs in originally treeless systems (Van Diggelen et al., 2006). Listing the Biebrza fens as protected sites in 1993 by establishing a National Park (Journal of Laws of 1993 No. 86, Item 399) did not change the situation. ...
Succession caused by agricultural land abandonment is one of the most serious threats to the biodiversity of non-forest ecosystems in Europe. The aim of the study conducted in the Biebrza National Park (NE Poland) was to develop a remote sensing method to analyze the process of tree and shrub encroachment into the open peatland area of the Lower Biebrza Basin of 245 km². The study covered a period of 50 years, from 1966 to 2015. Tree and shrub coverage was analyzed independently on the basis of airborne imagery acquired in 1966, 1980, 1997, 2006, 2010 and hyperspectral and ALS data from 2015. The method used, which consisted in assigning the area covered by trees and shrubs to permanent reference areas in a grid of squares enabled us to analyze the succession process by integrating various types of airborne data retrieved from various sensors with different geometric, radiometric and spectral resolutions. Owing to this, the process of succession could be characterized on the map by illustrating the spatial distribution of tree and shrub area and the dynamics and directions of their changes in time, and quantitatively by calculating the area of trees and shrubs as well as the dynamics, pace and directions of its change over time. It will be possible to integrate the results of the analysis of archived data with those acquired in the future, which will contribute to even wider use of remote sensing in succession process monitoring. The findings suggest that in the study period the area covered by trees and shrubs increased by 3020 ha, and the open areas decreased from 75.78% of the study area in 1966 to 63.31% in 2015. During the last study period (2010–2015) encroachment of trees and shrubs was inhibited to the rate of 2.7 ha/year as a result of the conservation program being implemented in the Lower Biebrza Basin.
... In past decades, however, rich fens have started to perish widely, becoming one of the 10% most endangered and red-listed habitats within European Union countries (Janssen et al. 2016), which has mainly occurred due to drainage, hydrological changes in landscapes, and acidification Van Diggelen et al. 2006). Additionally, eutrophication due to increased nitrogen deposition and intensive use of fertilizers on surrounding land or water bodies (Kooijman 2012;Marrs 1993;Navrátilová, Navrátil, and Hájek 2006), along with climate changes (Essl et al. 2012;Küttim et al. 2019) continue to impoverish rich fen ecosystems and drive succession towards other habitats. ...
An undesired succession of rich fens leads to the formation of dense Sphagnum carpets that outcompete brown mosses and some vascular plants, resulting in biodiversity loss in fen habitats of high conservation importance. Small‐scale Sphagnum removal is a rarely implemented conservational measure, whose success may depend on soil alkalinity and fertility (i.e., nutrient availability). Therefore, characterizing the effects of pH and fertility levels would potentially allow for the development of better Sphagnum removal strategies. Two experiments were conducted across 24 rich fens of different alkalinity and fertility located in an area of approximately 32,000 km2 spanning from the Bohemian Massif to the Western Carpathians (Europe). We hypothesized that high alkalinity and low fertility support the restoration of rich fen vegetation after Sphagnum removal. Our study focused on four different Sphagnum groups. In Experiment 1, the treatment plots remained unfenced. In Experiment 2, the treatment plots were fenced off and target brown mosses were transplanted from the surroundings to overcome dispersal limitations. A repeated measures design was used, with vegetation composition recorded over a 5‐year period. High alkalinity rather than fertility facilitated species richness and the appearance of target brown mosses. High alkalinity generally hindered Sphagnum recovery, while high fertility supported the recurrence of S. teres and S. recurvum agg. Under high pH conditions, enhanced fertility further correlated with the spread of non‐sphagnaceous generalist bryophytes of low conservation value. Despite sustaining a significant overall reduction, all Sphagnum taxa began to recover throughout the experiment, albeit less obviously in fens with S. warnstorfii. Sphagnum removal may reverse biodiversity loss and allow for the restoration of brown mosses in rich fens where Sphagnum cover had increased due to slight eutrophication, acidification, or a decrease in the water table. In alkaline and nutrient‐poor conditions (e.g., S. warnstorfii fens), the effect is evident and long‐lasting and the intervention may not be extensive. In fens dominated by S. teres or S. recurvum agg., repeated or large‐scale removal may be needed if high nutrient availability (potassium, phosphorus) or low alkalinity supports Sphagnum recolonization. Treatment plots with S. subgenus Sphagnum exhibited the least promising brown‐moss restoration prospects.
... Due to a larger content of mineral component (thin layers of sandy sediments as well as clay) in drained brook systems, Histomoders can develop into Hydromulls by way of oxidation and mineralization of the organic fraction (Stortelder et al., 1998). Like in fens, drainage does not always lead to better circumstances for decomposing organisms (Oliver et al., 1999;Van Diggelen et al., 2006). Isolation from the rather rich brook water can lead to a growing influence of rainwater, especially when it stagnates on a loamy layer with low permeability, which occurs quite often in these systems. ...
Technical Report
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In Europe an abundance of humus taxonomies exists starting with early approaches in the late 19 th century. Frequently used in an international context, they do not cover all site conditions in the European area. Although having basic concepts and general lines, the European (and North American, Canadian) classification systems differ in important parameters used for the description and classification of humus forms. These discrepancies result in incongruities, so require adjustments when exchanging partially compatible soil data, even between nearby countries. In 2003, 26 European specialists in humus forms met in Trento (Italy) and decided to formulate rules of classification based on morphogenetic descriptions and diagnostic horizons, adapted to European ecological conditions. Taking into account old and new European and North American systems of humus forms classification, six main references (Anmoor, Mull, Moder, Mor, Amphi and Tangel) were defined, each of them further dividing into detailed categories. This inventory assigned a strong discriminatory power to the action of the pedofauna. Both semiterrestrial (anoxic) and terrestrial (aerated) topsoils were classified. The descriptors of the diagnostic horizons were conceived in accordance with the spirit of recent international soil classifications. Assigning an "ecological value" to each main humus form along a gradient dividing those characterized by accumulation of poorly transformed organic matter, from very biologically active forms degrading and incorporating all organic remains, this European system of classification avoids a hierarchical structure and allows an elastic approach open to additional ecological contributions and renditions.
... of overfertilization with phosphates that have accumulated in the environment is a huge practical challenge 48 . Mining the soil P by harvesting and exporting above-ground vegetation and removing the biomass (hay removal) is applied as a nature management measure in many protected herbaceous ecosystems in western Europe, and is common practice in many protected wetlands [49][50][51] . According to nutrient budget calculations for western European herbaceous ecosystems, annual hay removal seems to result a,c,e,g,i,k, Estimated species niches, distinguishing between non-threatened (purple) and threatened species (red) and sorted by optimum along nutrient gradients. ...
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The greater bioavailability of nitrogen (N), phosphorus (P) and potassium (K) in the Anthropocene has strongly impacted terrestrial plant communities. In northwest Europe, because high N deposition is considered the main driver of plant diversity loss, European Union (EU) legislation to reduce N deposition is expected to promote plant species recovery. However, this expectation is simplistic: it ignores the role of other macronutrients. Analysing the relationship between plant species pools and species stoichiometric niches along nutrient gradients across northern Eurasia’s herbaceous ecosystems, we found that both absolute and relative P availability are more critical than N or K availability. This result is consistent with stoichiometric niche theory, and with findings from studies of hyperdiverse forests and shrublands at lower latitudes. We show that ecosystems with low absolute and relative P availability harbour a unique set of threatened species that have narrower nutrient-based niche widths than non-threatened species. Such ecosystems represent a conservation priority, but may be further threatened by latent effects of relative P enrichment arising from reduction of N availability without simultaneous reduction of P. The narrow focus of EU legislation on reducing N, but not P, may therefore inadvertently increase the threat to many of Europe’s already threatened plant species. An EU Phosphate Directive is needed.
... Peatlands of the boreal-temperate ecotone (BTE) have high conservation values in part because they provide habitats for boreal vascular plant species in landscapes otherwise dominated by temperate forest vegetation and greatly modified by human activities (Moore 2002;van Diggelen et al. 2006;Pellerin et al. 2009). Large peatlands near their southern range limits in eastern North America are particularly important for biodiversity conservation because (1) they are nested in a relatively intact biome (Evans and Brown 2017) and (2) they represent potential refugia for many disjunct boreal species at their southern range limits (Bedford and Godwin 2003;Raney et al. 2016;Glennon et al. 2019). ...
Large peatland complexes at the boreal-temperate ecotone are essential habitats for boreal species at their southern range limits where they are threatened by tree encroachment accelerated by climate change and nitrogen deposition. To inform vascular plant and biodiversity conservation, we studied tree encroachment patterns in a large (> 400 ha) boreal peatland complex in the northeastern United States across vegetation types and environmental gradients. We characterized vascular plant composition, environmental drivers and tree demography on 50 plots (each 25 m2). We used non-metric multidimensional scaling (NMS) to identify two main drivers of vascular plant composition in the herbaceous layer—pH and tree canopy openness—that described three broad plant community types (open bog, forested bog, and fen). Tree demography suggested that woody encroachment (i.e., tree seedling recruitment) varied across these community types; open bog was colonized by Picea mariana seedlings, while forested bog and fen (dominated by evergreen conifers, Picea mariana and Thuja occidentalis, respectively) were colonized by deciduous tree species (Acer rubrum and Betula alleghaniensis). Our findings provide early warning signs of vegetation change in boreal peatlands near their southern range limits caused by the encroachment of temperate tree species into forested peatlands and expanding tree cover in open bogs.
... The colonization by organisms with specific adaptations makes mires very important for nature conservation [351,356]. Generally, they are threatened by various direct impacts (e.g., land reclamation, peat extraction, drainage, organic pollution and eutrophication; [50,357,358]) that cause their fragmentation, loss of specialized organisms [359], or even complete destruction. One per cent of the land area of the planet is covered by peat bogs, and Europe has lost about 62% of this habitat type in recent decades [360]. ...
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In this overview (introductory article to a special issue including 14 papers), we consider all main types of natural and artificial inland freshwater habitas (fwh). For each type, we identify the main biodiversity patterns and ecological features, human impacts on the system and environmental issues, and discuss ways to use this information to improve stewardship. Examples of selected key biodiversity/ecological features (habitat type): narrow endemics, sensitive (groundwater and GDEs); crenobionts, LIHRes (springs); unidirectional flow, nutrient spiraling (streams); naturally turbid, floodplains, large-bodied species (large rivers); depth-variation in benthic communities (lakes); endemism and diversity (ancient lakes); threatened, sensitive species (oxbow lakes, SWE); diverse, reduced littoral (reservoirs); cold-adapted species (Boreal and Arctic fwh); endemism, depauperate (Antarctic fwh); flood pulse, intermittent wetlands, biggest river basins (tropical fwh); variable hydrologic regime-periods of drying, flash floods (arid-climate fwh). Selected impacts: eutrophication and other pollution, hydrologic modifications, overexploitation, habitat destruction, invasive species, salinization. Climate change is a threat multiplier, and it is important to quantify resistance, resilience, and recovery to assess the strategic role of the different types of freshwater ecosystems and their value for biodiversity conservation. Effective conservation solutions are dependent on an understanding of connectivity between different freshwater ecosystems (including related terrestrial, coastal and marine systems).
... They may further shift towards more productive tall herb, shrubland and woodland ecosystems if nutrient availability is improved and disturbances are missing (Jensen and Schrautzer, 1999;Koch and Jurasinski, 2015;Jamrichová et al., 2018). Drainage and eutrophication lower environmental extremity of fens and trigger succession towards the more widespread wetland communities of lower conservation importance (Wołejko, 2002;Middleton et al., 2006;van Diggelen et al., 2006;Hájek et al., 2015). This development has been frequently documented by the resurvey studies of fen vegetation after decades (Fojt and Harding, 1995;Bergamini et al., 2009;Kapfer et al., 2011;Moradi et al., 2012;Pedrotti et al., 2014;Seer and Schrautzer, 2014;Koch and Jurasinski, 2015;Pasquet et al., 2015;Navrátilová et al., 2017). ...
Calcareous fens represent an endangered type of peatlands, acting as refugia for stress-tolerant species in the currently changing landscapes. The resurveys across many regions have reported their recent disappearance or deterioration despite both the extreme habitat conditions (carbonate richness, presence of calcareous tufa, nutrient limitation, high water level) and conservation management. To test the stability of their biotic communities in different environmental and management configurations, we repeatedly sampled molluscs (terrestrial and aquatic), vascular plants, and bryophytes at 30 calcareous fens in the Inner Western Carpathians (Slovakia, Poland) after 13-17 years of warm summers and land-use changes. We found a small yet statistically significant effect of sampling period (old versus new survey) on the species composition of all three groups of organisms when the effect of various positions of sites along ecological gradients was controlled for. The compositional changes, interpreted with the help of Ellenberg Indicator Values, suggest an incipient succession towards grasslands and shrublands, driven by decreasing soil moisture and increasing nutrient availability. Although the number of habitat specialists did not change, the number of matrix-derived vascular plant and bryophyte species significantly increased, with six ubiquitous species of productive habitats being significantly more represented currently, while the richness of aquatic molluscs significantly decreased. Fens in which potentially strongly competitive plant species were less stressed because of less intense management and lower habitat extremity were more prone to such succession. There was no single factor that could predict the magnitude of composition changes; instead, tested factors were found to act synergistically. Conservation management was predominantly important for bryophytes, while extreme habitat conditions were predominantly important for terrestrial snails. We suggested a way how nature conservancy authorities can prioritise the management needs by applying an abiotic indicator system, with less environmentally extreme fens requiring more intense conservation management.
... For the purpose of this study, it is important to characterise the complexities and uncertainties related to the biophysical and socio-economic aspects of these fenlands. For at least two millennia, humans have used them mainly for low-intensity agriculture and, for relatively shorter periods (200-300 years), for peat excavation (Joosten and Clarke, 2002;Trepel and Kluge, 2002;Schleyer, 2004;Van Diggelen et al., 2006;Owens, 2008;Rawlins and Morris, 2009). These and other forms of human intervention have changed the landscape through successive historical periods. ...
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This dissertation began with a desire to better understand the conceptual and empirical contexts for governance for sustainable development. How does current research define and explain governance for sustainable development? In line with established research, the present study takes up sustainable development as conceptualised and implemented using modes of governance which differ in character and in orientation towards steering and the goal of sustainable development. Like sustainable development, the concept of governance is under debate. Here, the 1987 WCED Brundtland Report definition is taken as a starting point: “Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs” (1987, p. 1 of Chapter 2). Governance is understood as the act or manner of steering societal developments by public and/or private actors towards collective goals. A mode of governance for sustainable development is defined here as a type of steering arrangement with a certain institutional configuration (including public and/or private actors and different types of institutional relations) that is intended to influence societal changes towards sustainable development. The research focuses on three such modes of governance: adaptive management, transition management and payments for environmental services (PES). These have been selected due to their prominence in the discourse on governance for sustainable development. Adaptive management refers to efforts to enable a social-ecological system to maintain itself over long periods through learning-by-doing and cooperation, and efforts to enhance the adaptive capacity of a system to respond to changing circumstances. Transition management is based on innovation, experimentation and learning, with an orientation towards a long-term vision; it aims to fundamentally alter the structure of a socio-technological system in order to prevent environmental crisis. PES describes efforts to make environmental conservation economically viable by accounting for and preventing negative environmental externalities and by contributing to sustainable livelihoods. Research for this dissertation has found no academic studies that have comparatively examined the selected modes of governance for sustainable development based on empirical analysis. Such analysis can help to understand how the selected modes work in practice and whether they assist in a real-world context in moving towards sustainable development. This study achieves this by examining practical experience with 216 interventions in accordance with the three selected modes of governance as applied in the Dutch fen landscape. Research aim The present study aims to gain greater insight into the key challenges arising in steering towards sustainable development. It achieves this aim by:  Analysing three different modes of governance – adaptive management, transition management and PES – according to their steering mechanisms and orientation towards sustainable development;  Evaluating the three modes according to a set of criteria for governance for sustainable development;  Analysing practical experiences with the selected modes in the Dutch fen landscape.
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Peat growth is a frequent phenomenon in European river valleys. The presence of peat in the floodplain stratigraphy makes them hotspots of carbon storage. The long-term dynamics of alluvial peatlands are complex due to interactions between the peat and the local river network, and as a result, alluvial-peatland development in relation to both regional and local conditions is not well understood. In this study, a new modelling framework is presented to simulate long-term peatland development in river floodplains by coupling a river basin hydrology model (STREAM – Spatial Tools for River basins and Environment and Analysis of Management options) with a local peat growth model (modified version of DigiBog). The model is applied to two lowland rivers in northern Belgium, located in the European loess (Dijle (Dyle) River) and sand (Grote Nete River) belts. Parameter sensitivity analysis and scenario analysis are used to study the relative importance of internal processes and environmental conditions on peatland development. The simulation results demonstrate that the peat thickness is largely determined by the spacing and mobility of the local river channel(s) rather than by channel characteristics or peat properties. In contrast, changes in regional conditions such as climate and land cover across the upstream river basin have been shown to influence the river hydrograph but have a limited effect on peat growth. These results demonstrate that alluvial-peatland development is strongly determined by the geomorphic boundary conditions set by the river network and as such models must account for river channel dynamics to adequately simulate peatland development trajectories in valley environments.
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.
Until the late fifties of this century species rich wet meadows were characteristic of the swampy alluvial plains in SchleswigHolstein (north-western Germany). Today many of these meadows undergo successional changes due to abandonment. The vegetation development after abandonment can be characterised as a sequence of different successional stages. After an initial phase(successional stage I) follows a phase of clonal expansion of highly competitive species (successional stage II) and a phase of immigration and establishment (successional stages III and IV). In the course of succession species richness decreases and highly productive vegetation-stands develope. Species contributing to successional changes can either be present in the initial aboveground vegetation, in the soil seed bank or in the seed rain.
The 464 plant species recorded in the survey are segregated into those (153) for which fens are a major habitat (principal fen species), those (203) that are as well or better represented in other habitats as in fens (affiliated species) and those (108) essentially atypical of fens (accidental species). Occurrence of principal fen species of low frequency (occurring in <5% of samples) (ie rare species) is analysed. Many rare species occur mainly in just a few distinctive herbaceous vegetation types of low crop mass. Most do not occur at all in fen carr. Very species-rich stands are infrequent and referable to just a few vegetation types. These are the ones that also contain most rare species. Individual fen plant species (principal and affiliated species) occupy a discrete range of vegetation species-richness (the "associated-richness') in herbaceus fen vegetation samples. Those species which show only small variation in the associated-richness values (interquartile range <50% median associated-richness value) are "richness indicator species'; their occurrence can be used to predict the species-richness of herbaceous fen vegetation. The present infrequency of species-rich vegetation (and its associated rare species) in undrained fens is probably mainly due to increase in vegetation crop mass at many sites, caused by the abandonment of traditional management regimes perhaps exacerbated by increased net productivity caused by fertilizer run-off from the catchments. Four possible indices, based on richness and rarity, for evaluation of fen sites for conservation are proposed and 15 sites are evaluated using these. -from Author
Questions: Various floodplain communities may differ in their relative abilities to influence water quality through nutrient retention and denitrification. Our main questions were: (1) what is the importance of sediment deposition and denitrification for plant productivity and nutrient retention in floodplains; (2) will rehabilitation of natural floodplain communities (semi-natural grassland, reedbed, woodland, pond) from agricultural grassland affect nutrient retention? Location: Floodplains of two Rhine distributaries (rivers Ussel and Waal), The Netherlands. Methods: Net sedimentation was measured using mats, denitrification in soil cores by acetylene inhibition and bio-mass production by clipping above-ground vegetation in winter and summer. Results: Sediment deposition was a major source of N and P in all floodplain communities. Highest deposition rates were found where water velocity was reduced by vegetation structure (reedbeds) or by a drop in surface elevation (pond). Sediment deposition was not higher in woodlands than in grassland types. Denitrification rates were low in winter but significantly higher in summer. Highest denitrification rates were found in an agricultural grassland (winter and summer) and in the ponds (summer). Plant productivity and nutrient uptake were high in reedbeds, intermediate in agricultural grasslands, ponds and semi-natural grasslands and very low in woodlands (only understorey). All wetlands were N-limited, which could be explained by low N:P ratios in sediment. Conclusions: Considering Rhine water quality: only substantial P-retention is expected because, relative to the annual nutrient loads in the river, the floodplains are important sinks for P, but much less for N. Rehabilitation of agricultural grasslands into ponds or reedbeds will probably be more beneficial for downstream water quality (lower P-concentrations) than into woodlands or semi-natural grasslands.