Environmental Engineering Reference
In-Depth Information
This gives rise to the paradox that the suppression of fire leads to greater hazard, as large
fires every thirty years cause more damage and are more dangerous than smaller fires
every ten years.
It is difficult to get a statistical picture of fires in the Mediterranean, as there is
probably much under-reporting and also probably some confusion with practices such as
the stubble burning of crops. There are some figures from Sardinia which suggest that 3
per cent of the
maquis
and 1 per cent of the woods are burned every year. Other figures
from France suggest there may be 7000 fires per year, the majority of them 'cause
unknown'. Fires can be classified into
natural
(mostly due to lightning),
occupational
(caused by grazers and farmers in order to clear and control vegetation) and
wildfires
(resulting from accidents or deliberate firing). Statistics in the past fifty years point to
increased frequency of fire but could easily reflect better reporting. In the early years
only large fires were worth recording. If there has been a real change, it is probably the
result of increasing tourism and rural recreation, with obvious increased risks of
accidental firing. Suppression of small fires could also allow the buildup of biomass and
litter which would be more susceptible to lightning strikes.
Land-use changes which cause the build-up of fuel could also contribute to increasing
fire hazard. In those areas where agricultural land has been abandoned, reinvasion by
scrub will provide more flammable biomass, as will any lessening of woodcutting, animal
grazing or animal browsing. Modern forestry practices in Mediterranean regions add to
the risk. Foresters have mostly planted fire-promoting trees of the pine and eucalyptus
genera, for example Monterey pine (
Pinus radiata
) in California, and Aleppo pine (
P.
halepensis
) and maritime pine (
P. pinaster
) around the Mediterranean itself. In Spain, for
example, 85 per cent of planting since 1950 has been of coniferous species, 13 per cent of
eucalyptus, with only 2 per cent native evergreen oak (mostly cork oak). Although
foresters deplore burning by grazers trying to increase grazing potential by stimulating
grasses and herbs, one estimate is that a third of all fires occur in Aleppo pine plantations
around the Mediterranean. It is also true that the expansion of settlement into the
countryside (holiday complexes, camping facilities, suburban dwellings) greatly increases
the cost and danger of fire damage.
Fire has important effects on the ecology. Underground plants emerge and bloom after
a fire (e.g. squill), and the following moist season usually sees a flourishing of annual and
perennial grasses and herbs which thrive on the injection of light, moisture and nutrients.
Bulbs and tuberous herbs are usually prominent.
Maquis
recovers quickly, and Kermes
oak and strawberry tree can reach 1 m in height after two years. The conifers (e.g. pines
and junipers) are killed by fire, but the pines recover quickly through seeds released from
cones on burnt trees. Oaks are usually burnt back but not killed. The effects of fire are
thus to maintain mixed communities (e.g. mixed pine-oak woodland rather than a
monoculture of one species) of greater richness and diversity. In that sense, fire
stimulates ecological processes, nutrient cycling and the vigorous regrowth of vegetation.
It causes temporary bare land and therefore probably more erosion, but the adverse
effects are short-lived. Overall, fire is a natural part of many Mediterranean ecosystems,
stimulating productivity and diversity. It is doubtful whether fire causes serious land
degradation or erosion, as its impacts are mostly temporary rather than permanent.
