Fen Management Handbook - Scottish Natural Heritage

12.1.3 Biomass energy and Biofuels
The high productivity of some fen vegetation, combined with winter dieback or
leaf loss, makes it potentially useful as feedstock for biomass boilers or anaerobic
digestors. The sustainability benefits of these crops should not be ignored, since
they require little mechanical work and no fertiliser, making them a near carbonneutral
form of solar energy capture. Willow on short coppice rotation can achieve
yields of above-ground dry matter in the order of 12 tonnes/ha, while common
reed may be able to produce 15 tonnes/ha. Commercial bulk production of willow,
reed and sedge is effectively a short rotation monoculture which is not ideal for
biodiversity, but harvesting material as a cash crop can help to fund re-wetting and
the progressive extension of wetland, such as that proposed around Wicken Fen.
The harvesting of long-rotation willow coppice from wetland sites in west Wales is
currently being investigated.
Wood taken from small areas of scrub control, channel clearance and restoration
undertaken as part of overall management to maintain or improve fen biodiversity
can also generate useful income as a source of biofuel, subject to a local market
or processor. Summer-cut material has the added advantage of removing excess
nutrients which have entered the site as biomass.
Large-scale commercial agricultural production of elephant grass species is
developing, for processing to produce fuel in shredded or pellet form. This sugar
cane-like grass can yield up to 20 tonnes/ha with exceptionally efficient metabolism,
but monoculture production of an exotic species such as this has little or no direct
biodiversity benefit. However, as a perennial crop requiring little or no fertiliser
or herbicide input, elephant grass could be of indirect benefit where sensitively
incorporated in catchment-sensitive farming schemes, and it could also provide
a buffer against intensive agriculture for sensitive wetlands. Giant reed (Arundo
donax) is increasingly grown as a biofuel, mainly in developing countries and the
United States, but this species could be invasive and harmful in UK wetlands.
Using fen products as biofuel
The feasibility of using locally harvested reeds to heat the Wildlife Trust of South and West
Wales’ visitor centre was investigated by Metcalfe (2007). Reeds have a similar calorific
content (19.6 MJ/kg dry matter) to Miscanthus, and ashing properties that are acceptable
within modern biomass boilers. It was found that 27 tonnes of air-dry reed would be
needed annually to heat the centre and some adjacent buildings. This mass of reed could
be obtained from winter harvesting of 2.7 ha of reedbed from the immediate reserve (Teifi
Marshes NNR), with possible augmentation from nearby reserves. Initial discussions
with the site manager suggested that this rate of harvesting could be sustained whilst
maintaining biodiversity. The capital cost of the biomass boiler and associated heating
infrastructure was estimated at c. £50,000, and the payback period was between 5
and 10 years, after which the centre would benefit from much cheaper heating than that
offered by the current liquid petroleum gas system.
The Wildlife Centre
at Kilgerran (www.
welshwildlife.org)
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