Overall, 38% of lowland fen marsh and swamp features
reported are in favourable condition. This is about the
average for terrestrial habitats, but below the average for all
habitats or all features combined together. 41% of A/SSSI
features and 18% of SAC features reported are in favourable
condition. 21% of A/SSSI and 39% of SAC features
reported are unfavourable-recovering.
A sample of English fen, marsh and swamp sites was split into
topographic types. They showed that the category with the
highest proportion in favourable condition was spring fen (40%)
followed by water fringe fen (30%), then basin fen (29%),
floodplain fen (27%), and valley fen (26%). The more
favourable condition of spring fen may reflect the higher quality
of the groundwater on which they depend, as opposed to more
nutrient-enriched surface water capable of entering the other
categories. There is also the implication in the comparison
of these figures that fen condition in England is worse than
elsewhere in the UK.
The main reasons for features not being in favourable
condition are lack of remedial management, under-grazing, water
management, invasive species, and water quality. This may
reflect a number of issues commonly encountered in relation to
fens. For example, it is natural for open fens to change
spontaneously into wooded fens, and management, such as scrub
clearance and grazing, is required to prevent this. The
management of surface and groundwater is clearly crucial to
providing the surface:groundwater requirements of each type of fen,
as are its constituents, for example basic ions such as calcium,
its pH, and quantity of the plant nutrients nitrogen and
phosphorus.
Air pollution is not listed as a cause of unfavourable
condition in fens. It is likely that surveyors would
attribute its effects to other causes, such as drainage.
Critical loads of sulphur are still being exceeded for some types
of wetland, and are predicted to do so at least until 2010.
Dry deposition of ammonia is still very high in most parts of
England, Wales and Northern Ireland. Apart from the
inhibitory effect of bisulphite on some Sphagnum moss
species, deposition of nitrogen encourages rank competitors such as
the purple moor-grass Molinia caerulea. It should be
borne in mind that several fen types bear similar vegetation to
lowland raised bog and blanket mire, so that observations
appropriate to them in respect of air quality would also
apply.
Purple moor-grass and rush pastures
Under a third of purple moor-grass and rush pasture features
reported are in favourable condition (30% of A/SSSI, and 4% of SAC
features). There is some variation between countries, with
Scottish SSSIs (62% favourable) in rather better condition than
those in Northern Ireland (42% favourable) or England (22%
favourable).
The unfavourable-recovering category accounts for a
significant proportion of assessments reported (32% of A/SSSI
features, 56% of SACs), particularly in England.
Under-management is the main cause of unfavourable condition,
specifically under-grazing and abandonment. Scrub
encroachment is the common result, sometimes together with invasive
species problems.
Purple moor-grass and rush pastures are also affected by
overgrazing and nutrient enrichment. Underlying causes of
under-management are still thought to be largely due to current
agricultural economics and policies, exacerbated by e.g. BSE and
Foot & Mouth disease, leading to a reluctance to keep stock
(large stock in particular) on pasture perceived to have little
nutritional value. In addition, the extent to which
atmospheric nutrient deposition is affecting the composition of
grassland sites is a largely unknown quantity.