Fen Management Handbook - Scottish Natural Heritage

6.4.1 The risks of burning
Plant litter is an important part of many animals’ environment. Species of
invertebrate live or lay eggs in dead stems of reeds and other tall graminoids, grass
snakes and adders seek shelter in plant litter, mammals such as water vole may
pass through plant litter, and birds nest in and above it. In addition, purple moorgrass
litter provides cover for field voles and its removal exposes them to predation.
Therefore, burning litter is not selective and can be lethal to many vertebrates and
invertebrates living or hibernating in the dead or live vegetation. For example, the
rare Annex II species, Desmoulin’s whorl snail (Vertigo moulinsiana), may overwinter
in dead litter. There is no guarantee that burned areas will be re-colonised
from surrounding areas.
The natural growth sequence in fens is for much of the partially rotted remains
of plants growing each year to accumulate as peat, which locks up atmospheric
carbon. Although burning may appear useful as a management tool in preventing
peat accumulation and thus slowing hydroseral succession, burning releases
carbon and nutrients that would otherwise remain bound in the peat. Another
hazard of burning vegetation on peat is that the peat itself may ignite and smoulder
for days or even weeks as a deep-seated fire, bursting into flames whenever fanned
by the wind, and releasing large amounts of carbon dioxide into the atmosphere.
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The extract below from Wicken Fen management plan explains why on
many fens managed for conservation, other more reliable methods have
been favoured over burning.
There is no tradition of the use of burning at Wicken Fen. Extensive
fires have generally been considered a hazard on Sedge Fen, although
burning has been proposed from time to time as a management tool.
It has been used to assist in localised bush clearance, normally of very
small areas, since the war.
Major accidental fires occurred in 1929 and 1952. In April 1980, the
standing litter in one compartment was burned, but the fire got out of
control and spread across Cross Dyke to another compartment. Much
of the northern third of this was burnt-out, many trees and bushes
were killed and the sedge crop lost. In 1989 and 1991, a smouldering
litter heap flared up after hours, and led to major fires in two additional
compartments.
The deliberate burning of standing vegetation is likely to be a rare
event, and should only be considered for specific areas with careful
precautions and when no other management is appropriate.
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6.4.2 When and how to burn
Where burning is chosen as a last resort management tool, it should preferably be
undertaken in winter when peat, if present, is more likely to be waterlogged and is
therefore slower to ignite. Even so, winter burning can kill hibernating animals such
as grass snakes and over-wintering invertebrates. Spring is the poor second choice,
but standing reed should not be burned after March 31 st .