Fen Management Handbook - Scottish Natural Heritage

Mowing is usually best undertaken in late summer after the main breeding bird
period, and when vegetation biomass is at its peak. Removal of cut vegetation and
litter is best delayed for a few weeks to allow material to wilt, reducing the volume
of material which needs to be handled.
Cut material should be transported off the fen for composting or burning rather
than allowing the material to compost on site, which would result in nutrients
feeding back into the system. Locations for burning/composting should ideally be
of no (or very limited) conservation interest, and positioned at least 10 m from any
watercourse, spring head, flush or seepage zone. Where there is no other option,
on-site burning might be required but should be done on a metal sheet to enable
ashes to be collected and removed off-site (see section 6.4).
This management is suitable for sites with moderate to high levels of enrichment as
the stores of nutrients are depleted over time, and should be completed annually
for best effect. Removal of cut litter and vegetation is highly desirable to achieve
nutrient off-take and prevent smothering of lower plants. Mowing and removal
of vegetation and litter are best undertaken on a rotational basis to allow regular
removal of nutrients while disturbing only small areas of the fen habitat at any one
time. Grazing is strongly recommended as a follow-on treatment. Cutting is usually
combined with attempting to reduce the external inputs of nutrients where possible
(see local and catchment scale management).
Litter removal is similar to cutting and removal, but slightly less labour intensive.
Again, the aim of this technique is to remove annual litter production before it
begins to decompose thereby reducing the nutrients released back into the system.
Litter removal in autumn is therefore preferable. It does not reduce those nutrients
that are already translocated to the roots, so this technique is better for fens with
low to moderate enrichment problems. As for material produced by cutting, the
litter should be removed off site for disposal.
An accumulation of litter affects the plant community by altering temperature,
nutrient availability and light availability to the soil. In an experiment on a fen in
northern Minnesota, litter removal increased peat temperature, increased light
availability at soil level, increased the phosphorus content of above-ground plant
material, and altered the plant species composition. The phosphorus results may
have been due to stimulation of microbial activity following litter removal. Therefore
this technique would not be suitable for sites that are P-limited, as an increase in
phosphorus availability may enable excess nitrogen to be used, resulting in greater
enrichment issues.
Both litter and vegetation removal are best undertaken on a rotational basis to allow
regular removal of nutrients while disturbing only small areas of the fen habitat at
a time. This also means the technique is likely to be more manageable in terms
of labour costs. Research also indicates that on drier sites where water may be
a limiting factor or on bare areas where there is no canopy cover, the retention or,
in cases of significant bare ground cover, the addition of litter can aid seedling
germination and establishment. Therefore, litter removal as a nutrient management
tool appears to be best suited to wetter sites with good vegetation cover. Drier
sites with good vegetation cover may be better suited to vegetation cutting (but
retention of some litter) and sites with significant areas of bare soil are likely to
benefit from the addition of litter/cut vegetation to improve re-establishment of
vegetation.
8.4.3 Turf removal and soil stripping
Another option for reducing excessive nutrients on fens is to remove the enriched
surface layer in which nutrients have accumulated in plant and peat material by turf
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