Following on from the species-rich grassland survey, a friend and I were asked to survey nine wetland sites as part of a similar project on fens. This time, there was no previous survey data and our mission was to map vegetation and establish new locations for quadrats which, we hope, someone will come back to in a few years’ time to find out what has been happening to the vegetation.
Technically speaking, a fen is any wetland which is fed by streams or groundwater, so fens include valley mires, basin mires and floodplain mires and, stretching the definition somewhat, flushes, usually on peaty soils. This definition includes vegetation of both basic and acidic conditions. Acidic conditions produce vegetation communities which can be difficult to distinguish from rain-fed blanket bog and in many upland areas blanket bog rich in Sphagnum grades directly into valley mire fed by the acid waters running off the blanket bog above. It can be almost impossible to say where one ends and the other begins when the vegetation looks more or less the same. There is a tendency, then, amongst botanists, to bracket acidic fens under the term “bog” and use the term fen to mean a wetland fed by neutral or basic streams and groundwaters.
Using this habitual definition, then, fens are vegetation communities on peaty soils which are fed by neutral or basic groundwater or streams. This might include: fen-meadows dominated by purple moor-grass or blunt-flowered rush; flushes dominated by mixtures of small sedges; tall-herb dominated vegetation; and swampy vegetation with large sedges or grasses such as reed sweet-grass.
Fens (and wetlands of all kinds) are a rare habitat generally and it was quite conspicuous that a high proportion of the sites I surveyed were in SSSI – so in locations already recognised as of national importance for nature conservation. It is quite gratifying to know these are managed in Higher Level Stewardship so that the owner can have some reward for managing with nature conservation in mind.
I did enjoy this survey although I have to say I did make full use of my waterproofs during this project !