My interest in fens is growing. I am restructuring my posts on this subject. Dave Godfrey
1. General Introduction
Fen: a fen is a type of wetland, a 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.
Simply put: swamps and marshes have lots of water, salt or fresh. Swamps have trees. Bogs and fens have saturated soil. The water in a bog comes from rain water. The water in a fen comes from ground water and/or flowing water. Fens are rich in nutrients and can be grazed in perpetuity if proper managed.
Good video introductions to Fens
Cycling the fen: http://www.youtube.com/watch?v=cmEocg3OW1I Turn the volume down.
Dung digging: http://www.youtube.com/watch?v=XRsSGwCojBA Why grazing is good for fens.
Wild bees at Wicken: http://www.youtube.com/watch?v=445FH_RqWDs
Wicken Windmill in song: http://www.youtube.com/watch?v=EpUxFH3RfhI
2. Wetlands in General
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 often include systems of aquatic habitats such as ditches, rills and streams which can also be important for plants. Wetland complexes in the UK such as the Broads, Somerset and Pevensey Levels, form extensive networks of habitats which are rich in many other forms of wildlife. Canada has an extremely diverse set of wetlands in all parts of the country. Holland and the UK lead in Fen restoration.
3. Wetland Habitat features
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. In England, upland blanket-bogs cover more than 10,000 hectares of land and are hugely significant in the landscape.
2. 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 rushes 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.
3. Wet woodland
Mature wet woodland is a rarity, as opposed to swampy woodlands, and isoften 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.
4. 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 the most intact wetland systems.
5. Farmable wetlands.
Some wetlands, in some seasons, can be quite productive. It has been estimated that the full value of wetlands in terms of annual benefits is in the order ten to fifteen thousand dollars a hectare. The Cadboro Bay fen was used mainly for pasturing and the production of sedge-hay also termed meadow hay.
Wetlands may be seen as transitional stages moving from open water towards woodland. The technical term hydrosere is used to describe a succession which starts in water. A wetland is a transitional area between open water and dry land and may contain several stages of a hydrosere at the same time. Some studies add a fifth type: shallow open water.
In time, an area of open freshwater such as a lake or marshy sea shore may become woodland. During this process, a range of different habitats such as marshes and fens may succeed each other. Peat usually accumulates slowly, at the rate of about a millimetre per year.
This succession from open water to climax woodland is likely to take at least several thousand years although some intermediate stages will last a shorter time than others. For instance, a shallow swamp may change to marsh within a decade or less. How long it takes will depend largely on the amount of siltation occurring and whether storms and tides scour out established vegetation from time to time.
If there are five or six feet of peat beneath Gyro Park, one can be sure that it has been a long time since the area was a marsh. However, the calculation is complex since after the last Ice Age, the island rose but so did the sea levels.
5. 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. . 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.
Recently, however, analysis of methods of carbon storage have revitalized interest in the peat bogs which cover 3% of the earth’s surface and store an estimated 550Gt of carbon. Drainage of peatlands leads to mineralisation of carbon and nitrogen from the peat, releasing the greenhouse gases CO2 and N2O to the atmosphere and thus contributing significantly to global warming. It is estimated that such land use induced changes are responsible for 6 % of anthropic CO2 emissions, with well-known hotspots in south-east Asia (SEA) and central and eastern Europe (CEE). It is also well known that rewetting of drained peatlands can increase carbon storage.
The International Mire Conservation Group produces a reputable (and free) journal covering wetlands world wide. Here is a review from that journal of the carbon credits and peatland restoration question. http://www.mires-and-peat.net/map11/map_11_br_03.pdf
6. LIST OF FEN PLANTS
- Beaked sedge; Carex rostrata
- Whorl grass; Catabrosa aquatica
- Needle spike-rush; Eleocharis acicularis
- Northern spike-rush; Eleocharis austriaca
- Sweet grasses; Glyceria species.
- Common reed; Phragmites australis
- Swamp meadow grass; Poa palustris
In typical fen
- Flat sedge; Blysmus compressus
- Great fen sedge; Cladium mariscus
- Lesser tufted sedge; Carex acuta
- Lesser pond sedge; Carex acutiformis
- Davall’s sedge; Carex davalliana
- Dioecious sedge; Carex dioica
- Brown sedge; Carex disticha
- Tufted sedge; Carex elata
- Slender sedge; Carex lasiocarpa
- Flea sedge; Carex pulicaris
- Greater pond sedge; Carex riparia
- Common spike-rush; Eleocharis palustris
- Few-flowered spike-rush; Eleocharis quinqueflora
- Slender spike-rush; Eleocharis uniglumis
- Broad-leaved cotton sedge; Eriophorum latifolium
- Reed sweet-grass; Glyceria maxima
- Yellow flag iris; Iris pseudacorus
- Brown bog [sic] rush; Schoenus ferrugineus
In fen carr
- Narrow small-reed; Calamagrostis stricta
- Purple small-reed; Calamagrostis canescens
- Tussock sedge; Carex paniculata
- Cyperus sedge; Carex pseudocyperus
- Wood club rush; Scirpus sylvaticus
General article on sedge: carex: http://en.wikipedia.org/wiki/Carex
7. Canadian Expertise.
Canada has a large percent of the world’s peatlands.
Despite continued detrimental impact to wetlands, Canada still has over 127 million hectares of wetland comprising
an estimated 24% of the total world wetland base.
For a long time, Canada was a leader in wetland research, but this expertise is now in decline. One great book from the golden era is this one:
To get an idea of plants you can grow for your own wetland, check out this great (Australian) site on Facebook.
Or this one in California: sedge plants available:
List of grasses and sedges in the Fraser Valley:
9. British Columbia
Environment BC has done some good work on wetlands, but again, in the past decade, this seems to have fizzled. The following excerpts are from a useful document: http://www.env.gov.bc.ca/wld/documents/WEG_Oct2002_s.pdf
Although British Columbia has large areas of natural wetlands, the situation in urbanized areas is critical.
Wetlands are one of the most important life support systems on earth. Currently comprising about 5.6% or 5.28 million hectares of British Columbia, they provide critical habitat for fish, birds, and other wildlife. Most wildlife in the province use wetland habitat at some point in their life cycle, and many red- and blue-listed species are wetland-dependent.
Wetlands provide for commercial and recreational use of wetland-dependent fish and shellfish, enhance agricultural productivity, and support a variety of scientific , educational and recreational opportunities. Environmental economists such as Robert Costanza have used various methods to estimate the economic market and non-market values of the goods and services of various ecosystems. For wetlands, the total value is estimated to be $19,580 hectare/year (1994 US$). Using this figure to estimate the goods and services value of wetlands, British Columbia’s total wetland surface area of 5.28 million hectares would yield a potential value of over $100 billion/year. At a local level such as the Fraser Valley, the total wetland surface area of 41,906 hectares would yield a potential goods and services value to society of over $800 million/year.
There is a growing concern over the escalating rate of wetland losses in British Columbia. In the Fraser Vancouver Island, it is estimated that 50% to 70% of the original wetland habitat has disappeared. In the ecologically critical South Okanagan, wetland losses have reached 85%.
Action is required to help reduce wetland losses and provide for coordinated conservation and management efforts. Because wetlands occur across a range of ecosystem types and can be affected by various land use activities, a comprehensive approach is needed to ensure the protection and management of wetlands. It is intended that several initiatives currently under development, including the Biodiversity Strategy, Species At Risk Strategy, the Living Rivers Strategy, as well as ongoing Land Use Planning and Protected Areas management, will all play an important role in protecting, maintaining and restoring wetlands.
10. Capital Region District
Another good summary. http://www.crd.bc.ca/watersheds/ecosystems/wetlands.htm
Mystic vale and Hobbs Creek.
There were once salmon here. A great detailed study is here: http://www.urbanecology.ca/documents/Student%20Technical%20Series/Oliver%20hannah%20final.pdf
A local report from 2005: http://www.islandnet.com/~thelynns/cbra/minutes/cbramin_2011_01_10_mystic_pond.pdf
Another summary of what could/should be down with Mystic Vale and Hobbs Creek: http://web.uvic.ca/enweb/undergraduate/pdf/MysticVale.11.09.pdf
Another group doing interesting work on communities: http://mapping.uvic.ca/welcome/committee
Some other very interesting comments are in comments below.