Fens AA

FENS

1.  General Introduction

Fen: a fen  is a type of wetland, broad expanse of nutrient-rich, ground-fed  shallow water in which dead plants do not fully decay, resulting in a flora of emergent plants growing in saturated peat. The other 3 types of wetlands are bogs, swamps, and marshes.

Fens can be drained but this can cause problems. Some major English fens were drained in the 1600`s. However, their early success was short-lived. Once drained of water, the peat shrank, and the fields lowered further. The more effectively they were drained, the worse the problem became, and soon the fields were lower than the surrounding rivers. By the end of the 17th century, the land was under water once again. While drained, however, fens are very productive in agricultural terms.

Wicken Fen

The best example in England of an undrained (but managed) English Fen is the Wicken Fen established by the National Trust in 1899. On 1 May 1899, the National Trust purchased two acres (8094 m²) for £10.

Although it is often described as a natural wilderness, it is neither—humans have been closely involved in this fen for centuries and the reserve is managed intensively to protect and maintain the delicate balance of species which has built up over the years. Much of the management tries to recreate the old systems of fen working which persisted for hundreds of years, allowing species to become dependent on the practices. For example the Sedge plant, Cladium mariscus, is harvested every year and sold for thatching roofs. The first recorded sedge harvest at Wicken was in 1414. Ever since then, sedge has been regularly cut. This has allowed a pattern of plants and animals to build up who depend on regular clearance of the sedge to survive. Many plants and animals are dependent upon regular management of vegetation in this way to keep their habitats going. Konik Ponies and Highland cattle have now been introduced to parts of the fen to prevent scrub from regrowing as a part of the management plan.

The present appearance of Wicken Fen is the result of centuries of management by human beings. Many of the practices now undertaken have changed little since medieval times. In surrounding areas, the landscape has changed so completely that it is almost impossible to imagine how it must once have all looked. Only a very few places survive where it is possible to experience this primitive landscape first hand; Wicken Fen is one of these.

Tracks in and around Wicken Fen became visible on Google Street View before many towns and urban areas in Britain were covered. Try it: http://maps.google.co.uk/maps?rlz=1C1GGLS_en-GBGB360GB360&sourceid=chrome&q=wicken%20fen&um=1&ie=UTF-8&sa=N&hl=en&tab=wl

170px-Wicken_Fen_Windpump

The National Trust aims to acquire further land as it becomes available, paying the market prices.[7] As a result of the increased area of wetlands, the populations of skylarks, snipe, grey partridge, widgeon and teal have all increased with a major increase in barn owls and short-eared owls. Buzzards, hen and marsh-harriers have returned, and bitterns began breeding by 2009 for the first time since the 1930s.[9]

The Wicken Fen Vision has great support from many people and organisations. Large sums of money have been raised from grant-awarding bodies, and from individual donors.

A Carr Fen is swampy.

carr, the name of which is derived from the Old Norse kjarr, meaning a swamp, is a type of waterlogged, wooded terrain that, typically, represents a succession stage between the original reedy swamp and the eventual formation of forest in a sub-maritime climate.[1]

The carr is one stage in a so-called hydrosere: the progression of vegetation beginning from a terrain that is submerged by fresh water along a river or lake margin. In sub-maritime regions, it begins with reed-swamp. As the reeds decay, the soil surface eventually rises above the water, creating fens that allow vegetation like sedge to grow. As this progression continues, riparian trees and bushes appear and a carr landscape is created–in effect a wooded fen in a waterlogged terrain. At this stage the pH is not too acidic and the soil is not too deficient in mineral elements. Characteristic trees include alderwillow and sallow.[1]

FEN MANAGEMENT

ONE: General.  from plantlife.org

Wetland

{habitat_image_alt}

Wetlands form over any land whose soil is either seasonally or permanently waterlogged. This can happen alongside rivers, across floodplains, where there are springs and seepage, a high water table or tidal incursion.

Water-logging tends to exclude oxygen from the soil and plants have evolved many ways to deal with this, leading to the evolution of hundreds of specialist wetland and waterside species.

Wetland habitats include marshes, fens, bogs, water-meadows and any muddy place by water; they are found all across the UK and often include systems of aquatic habitats such as ditches, rills and streams which can also be important for plants. Wetland complexes such as the Broads, Somerset and Pevensey Levels, form extensive networks of habitats which are rich in many other forms of wildlife.

Habitat features

Bogs

Upland and Lowland bogs are characterised by the dominance of Sphagnum moss species, which lay down layers of bog peat as they grow. Sphagnum acidifies its own environs and so bog systems are populated with plants that can cope with base-poor, acid waters. English upland blanket-bogs cover more than 10,000 hectares of land and are hugely significant in the landscape. Lowland bogs are much less extensive, are more fragmented and prone to damage; our largest extent, in the Humberhead levels, has been badly damaged in recent decades as a consequence of peat removal at an industrial scale

Fens and reedbeds

This kind of habitat occurs in river valleys and floodplains that are not conducive to the development of Sphagnum dominated vegetation. Sedges and ruches tend to dominate and common reed is a prominent species, although its abundance is greatly affected by management; fens and reedbeds have a very long history of traditional management, some being grazed but many cut for ‘fen litter’ or ‘marsh-hay’, a product that went for feed and bedding for the many thousands of horses that once populated our towns and cities. Fen-litter and saw-sedge, another traditional fen product, are both cut in late summer, which suppresses reed growth; however winter cutting encourages reed growth and leads to such dominance that the reed can be harvested in bulk for thatching. Most fens are small, isolated and restricted to the margins of larger wetland systems; however large areas are still to be found in the Broads and the Cambridgeshire Fens.

Wet woodland

Mature wet woodland is a rarity in the UK and where it does exist it is often restricted to the margins of fens and marshes and the fringes of slow moving rivers. Typically dominated by alder or willow, it can be a species-rich habitat, especially where it occurs at one end of a complete transition from open water to woodland; a few such examples can be found in the Broads. Wet woodland also occur away from obvious water supplies, for instance in Suffolk where alder woods occur on the poorly drained plateau clays.

Water meadows and wet grasslands

Although often badly affected by agricultural improvement, these grasslands can form extensive systems in river valleys and the lower parts of river floodplains. Associated with traditional extensive grazing regimes, where intervening ditches are maintained as ‘wet-fences’, such grassland networks form some of our most intact wetland systems. Good examples can be found all around the country and include the Pevensey and Somerset Levels, the floodplains of the Itchen and Test rivers in Hampshire and the Thames in Oxfordshire and parts of the Broads in Norfolk and Suffolk. Many such systems support the last of our species-rich lowland meadows but even where these are not as good as they once were, the ditch networks that divide them up can still be rich in aquatic and marginal plants

Key issues

Perhaps the single most influential factor in the loss of wetlands is drainage. Wetland soils, particularly fen peats, make fine agricultural soils if the water can be got rid of. This has of course already happened across many tens of thousands of hectares of former wetland habitat, with unfortunate consequences in terms of soil loss through oxygenation and shrinkage, windblow and carbon release.

The flower-richness of wetland habitats is dependent also on good water quality. Where wetlands are fed by rivers which pass through towns and cities and intensively farmed agricultural areas, high nutrient concentrations in the water cause a few species to outgrow the majority, leading to a rapid decline in floral diversity.

Abstraction of water from underground sources can reduce supplies of water to spring fed systems such as valley fens and chalk-stream margins. This leads to a gradual drying out, loss of water-dependent species and ultimately to complete loss of the wetland habitat. Water-levels can often be restored quite quickly, with the withdrawal of abstraction, but this does not necessarily lead to a restoration of former vegetation, mainly due to the oxygenation and breakdown of formerly water-logged soils.

Changes in agriculture and the way people live their lives has led to a decline (and in some cases almost complete loss) in markets for traditional fen produce. This has led to fens becoming uneconomic to manage in the traditional way, leading to conversion to agriculture or abandonment.

What we’re doing about it

Plantlife’s Fenlands Project, supported by Esmee Fairbairn and Natural England, conducted experimental management at a range of sites in the East of England to a) enhance populations of priority fen species and b) encourage the reappearance of fen plants at degraded fens. Experimental work finished in 2009 but monitoring work continues to track the response of plants to the experiments over time.

TWO: Technical

A good manual illustrates how complex this can be:

The Fen Management Handbook Edited by Andrew McBride, Iain Diack, Nick Droy, Bobbie Hamill, Peter Jones, Johan Schutten, Ann Skinner and Margaret Street

Introduction and Basic Principles
Fens are magical places; they are an essential part of our
cherished landscape. They support a rich variety of wildlife, and
are often a repository of evidence of many generations of past
economic use and management. With so much in their favour, it is
perhaps surprising that fens are one of the least well recognised
habitats, and a part of our countryside which most people
understand little about.
This handbook has been produced to improve understanding
of fens and how they function, to explain why fens need
management and to provide best practice guidance. Case
studies are included at the end of most sections as practical
examples of the principles and techniques outlined in the text.
The handbook is aimed at anyone interested in fens, or who might
become involved in fen management, creation or restoration from
a practical, policy or planning perspective.
Key points and good practice are highlighted in green boxes.
Cautions about activities which might be legislatively controlled
or which might potentially damage the interest of fens are
highlighted in red boxes.

Snapshot case studies in the text to
illustrate specific points are highlighted in yellow.
1.1 What are fens?
The word ‘fen’ is derived from the old English word ‘fenn’ meaning
marsh, dirt or mud.

A fen is a wetland that receives water and nutrients from surface and/or
groundwater, as well as from rainfall.

Differentiating between fens and bogs
Fens receive most of their water via rock and soil which contain
dissolved minerals creating growing conditions that allow more lush
vegetation than bogs.
Bogs receive water exclusively from rainfall which is acidic and contains
very few minerals; consequently rain-fed acid bogs support a less
diverse range of vegetation than fens.
Fens are found from sea level up into the hills, across the whole of the British
Isles. They range in size from tiny flushes of only a few square metres, to extensive
floodplain fens covering hundreds of hectares, forming important features in the
wider landscape and river catchments. 8
1.2 What’s so special about fens?

Fens were prized by our ancestors for the range of products they yield: reeds and
sedge for thatching, willow for basketry, hay and lush aftermath grazing for cattle.
It is the past management and human interaction with fens for such purposes that
has created the extremely diverse and ever-changing habitat which attracts and
supports a rich variety of plants, insects, mammals and birds, and which explains
why fens are described as semi-natural rather than natural habitats.

Section 2:
Fen Flora and Fauna explains more about the flora and fauna which make fens so
special from a wildlife perspective.
The UK contains a large proportion of fen types found in Europe, the surviving
fragments of previously much more extensive wetlands. ‘

In his book The Illustrated History of the Countryside, Oliver Rackham suggested that “about a quarter of the
British Isles is, or has been some kind of wetland.”

As in other parts of Europe, the
quality and extent of wetlands including fens has declined dramatically as a result
of drainage, development and neglect. Some of our best agricultural soils have
been provided by fens, following drainage and decades of tillage. However, the
organic component of the soil that makes it so suitable for root and other crops has
gradually broken down releasing carbon and lowering the land level, making the
land more difficult to drain.
It is estimated that of 3,400 km2
of fen present in England in 1637, only 10 km2
remains today.

In intensively farmed lowland areas of England, fens now occur less
frequently, are smaller in size and are more isolated than in other parts of the UK.
Despite these losses, the UK still boasts some large fens such as the 300 ha Insh
Marshes in the floodplain of the River Spey in Scotland, the calcareous rich-fen and
swamp of Broadland covering 3,000 ha in Norfolk and Suffolk, and the Lough Erne
system in Northern Ireland with extensive areas of fen and swamp. In some lowland
areas, such as the Scottish Borders and southern parts of Northern Ireland, there
are large numbers of fens which although small (many less than 3 ha in size), are
still of European importance for the rich wildlife they support.

FEN PLANTS

Yellow Flag

220px-Iris_pseudacorus_001

Greater Pond Sedge: carex riparia800px-Carex_riparia_(Ufer-Segge)_IMG_22812

Common Spike Rush

In pools

[edit]In typical fen

[edit]In fen carr

Kjarr

carr, the name of which is derived from the Old Norse kjarr, meaning a swamp, is a type of waterlogged, wooded terrain that, typically, represents a succession stage between the original reedy swamp and the eventual formation of forest in a sub-maritimeclimate.[1]

The carr is one stage in a so-called hydrosere: the progression of vegetation beginning from a terrain that is submerged by fresh water along a river or lake margin. In sub-maritime regions, it begins with reed-swamp. As the reeds decay, the soil surface eventually rises above the water, creating fens that allow vegetation like sedge to grow. As this progression continues, riparian trees and bushes appear and a carr landscape is created–in effect a wooded fen in a waterlogged terrain. At this stage the pH is not too acidic and the soil is not too deficient in mineral elements. Characteristic trees include alderwillow and sallow.[1]

Canadian Expertise.

http://www.gret-perg.ulaval.ca/fileadmin/fichiers/fichiersGRET/pdf/Doc_generale/Wetlands.pdf

4 thoughts on “Fens AA

  1. VERSUS BOGS

    Bogs are rain fed (ombrotrophic). They need poorly-drained areas, a climate where precipitation exceeds evaporation, and a nutrient-poor environment that favors peat mosses in their ecologic competition against higher plants. Growth of higher plants is also curbed by peat mosses themselves because they bind available nutrients and render the bog water acidic, with a pH of 3-4. Bog peat consists almost exclusively of partly decomposed Sphagnum; its ash content is low (about 3%). Peat depth of bogs is 2-10 meters.
    Because the water surface is trapped among a dense network of Sphagnum stems and leaves, water movement is almost completely lacking, and temperature exchange between water and air is severely restricted. This results in an extreme microclimate, with temperature differences of more than 30º C between day and night. In summer, even if the sun heats up the plant cover, the water temperature hardly exceeds 10º C, and night frosts are common all year round. As compared to the surrounding areas, the vegetation period of bogs may be shortened by 2-3 months.

  2. Pingback: FENS. Part 1. | DGLIKES

  3. Russian data: http://encyclopedia2.thefreedictionary.com/Peat+soil
    Peat Soil
    any one of a group of soil types formed under conditions of excess moisture from precipitation or from stagnant fresh or slowly running groundwaters that have some mineral content. Peat soils are the upper portion of peat bog deposits, formed below a layer of particular types of vegetation that thrive under conditions of excess moisture. They are distributed primarily in the temperate zone of the northern hemisphere.

    The basic processes characteristic of peat soil are the initial stages of peat formation—the accumulation of partially decomposed plant remains. With the accretion of new layers of peat soil, the lower layers become biologically less active; the number of microorganisms in the lower layers decreases sharply, and the soil becomes less fertile as it is transformed into peat-forming soil. The lower boundary of peat soil approximately coincides with the depth to which water in the soil descends in summer (from 30 to 50–60 cm, sometimes deeper).

    Peat soils differ from underlying rocks in their higher coefficient of filtration and greater permeability to water. Two types are distinguished: high-moor and low-moor. High-moor peat soils are formed under conditions in which precipitation provides the required moisture. Vegetation characteristic of these soils includes sphagnums, highly compressed pine (more rarely, spruce), ledum, Chamaedaphne, bog bilberry, cloudberry, Oxycoccus, Scheuchzeria, and cotton grass. The soils are highly acidic (pH 2.5–3.6) and have a low ash content (2.4–6.5 percent), a very high moisture capacity (from 700 to 2,000 percent of the dry weight or more), anda bulk density of 0.10–0.15.

    Low-moor peat soils are formed in areas fed by abundant underground waters and surface runoff. Eutrophic vegetation flourishes on these soils. Characteristic plants are sedges, hyp-nums and sphagnums, reed grass, shrubs, and trees (spruce, birch, and pine). Low-moor peat soils are weakly acidic or neutral. The ash content is 6–12 percent in normal soils and 30–50 percent in high-ash types. The moisture capacity is 500–700 percent of the dry weight, and the bulk density is 0.15–0.20.

  4. Academic Emporia good illustrations in original

    http://academic.emporia.edu/aberjame/wetland/define/define.htm

    The classification scheme outlined above deals mainly with the surficial, two-dimensional aspects of wetlands. As most wetlands exist in topographic depressions, they tend to accumulate sediment through time. Furthermore, wetland soils are typically anaerobic, which often leads to the preservation of organic remains, namely peat. The term peatland denotes those wetlands in which substantial peat accumulation–at least one foot (30 cm)–has taken place (Charman 2002). The peatland substrate is in reality an organic structure built by biological activity. This gives peatland depth–a third dimension that contains a record of past environmental conditions.
    Peat is intrinsic to many wetlands around the world. Peat is partly decomposed plant remains that consist of more than 65% organic matter (dry weight). Moss, grass, herbs, shrubs and trees may contribute to the buildup of organic remains, including stems, leaves, flowers, seeds, nuts, cones, roots, bark and wood. Through time, the accumulation of peat creates the substrate, influences ground-water conditions, and modifies surface morphology of the wetland. Several factors are considered important for classification of peatland types (Charman 2002).

    Floristics — Plant composition of vegetation communities, which may be used as proxies for environmental factors.
    Physiognomy — Structure of the dominant plants, particularly used in Scandinavian and Russian schemes.
    Morphology — Three-dimensional shape of the peat deposit and geomorphology of the wetland surface.
    Hydrology — Source of the supply and flow regime for surface and ground water.
    Stratigraphy — vertical layering, composition, and nature of underlying peat deposits.
    Chemistry — Chemical characteristics of surface water, particularly acidity and content of nutrients.
    Peat characteristics — Botantical composition, nutrient content and structure, or human applications–fuel, horticulture, etc.
    From these diverse criteria, the water supply and nutrient status are the most fundamental elements for classifying peatlands. A gradient exists from nutrient-rich, alkaline water (fens) to nutrient-poor, acidic water (bogs), and so peatlands are generally divided in two broad classes (Charman 2002).
    Ombrotrophic — Raised or blanket bogs that receive all water and nutrients from direct precipitation. Neither ground water nor runoff from surrounding land reaches the surface of the bog. Rain and snow provide the water source, and nutrients are derived from whatever blows in–dust, leaves, bird droppings and feathers, spider webs, animal fur, etc. Water chemistry tends to be acidic, and nutrients for plant growth are in short supply. Few plants can survive such extreme conditions, namely Sphagnum (peat moss) and pine.
    Vertical airphoto over Teosaare Bog, a small raised ombrotrophic bog in east-central Estonia. Reddish-brown vegetation is moss (Sphagnum sp.) in hollows and around pools. Dwarf pines grow on hummocks. White survey marker at bottom center of view is one meter square. Kite aerial photo date 9/01, © J.S. Aber.
    Closeup view of blanket bog at Rjúpnafell, southern Iceland. Moss forms a spongy cushion over volcanic rocks. Swiss army knife for scale. Photo date 8/94, © J.S. Aber.

    Minerotrophic — Fens located in depressions that receive surface runoff and/or ground-water recharge from surrounding mineral-soil sources. Nutrients are more abundant and water is more alkaline–conditions that are suitable for a wide range of plants and which give rise to greater floralistic diversity compared to bogs. The terms oligotrophic and eutropic refer to more nutrient-poor and more alkaline, calcium-rich fens respectively.
    Spring-fed fen, Sangre de Cristo Mountains, near Cuchara, southern Colorado. Oligotrophic conditions prevail, as ground water is derived from silica-rich sandstone bedrock. Note the diversity of vegetation. Photo date 8/02, © J.S. Aber.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s