Geoscience Reference
In-Depth Information
Fire in the Mediterranean landscape
KEY CONCEPT
Every spring and summer, newspaper headlines proclaim the ravages caused by fires in Mediterranean regions,
whether in Europe, California or Australia. Losses of property, life and vegetation seem to mount year by year; large
conflagrations in the autumn of 1993 in California were followed by widespread mudflows in the spring of 1994, a
sign that burning had accelerated erosion. Similarly in the early 1990s a series of extensive forest fires raged throughout
Spain, Italy and Greece. Public and politicians link fires with land degradation, desertification and increased drought
due to global warming (see
Chapter 28).
Whatever the scientific reality, public and politicians certainly judge fires as
a major natural hazard, and a hazard which costs billions a year. Although the negative impacts of forest fires have
probably been exaggerated, it remains a significant environmental problem in Mediterranean regions (
Plate 25.6
).
Fire has been a common experience in the Mediterranean throughout the Quaternary era, i.e. since 2 Ma
BP
. and
indeed many Mediterranean plants have morphological adaptations to it. These take the form of thick, protective
bark, e.g. the cork oak, Quercus suber, or rapid regeneration after fire, e.g. esparto grass, Stipa tenacissima, and
dwarf fan palm, Chamaerops humilis, or by rapid regeneration from seed, e.g. the pines like Aleppo pine, Pinus
halepensis, and the rock roses, Cistus spp. Owing to high resin and oil content, many plants are very flammable,
and after the hot, dry summer the plant material and dry litter can burn fiercely to reach 800
C. The hazard increases
with the age of the vegetation, and maquisover thirty years old is extremely combustible. Thus we have the paradox
that suppression of fire leads to greater hazard, as large fires every thirty years cause far more damage and are more
dangerous than smaller fires every ten years.
Fire statistics in the Mediterranean are notoriously difficult to compile, as there is much under-reporting and also
confusion with land use practices such as stubble burning and bush clearance. Data from Sardinia suggest that 3
per cent of the maquis and 1 per cent of the woods are burned every year. Other data from France suggest there
may be 7,000 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 for the past fifty years show increased frequencies of fire,
but this could reflect better reporting. In the past only large fires were worth recording. If there has been a real
change in fire frequency, 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 build-up 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 areas where
agricultural use 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 mostly plant 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 holiday complexes, camping facilities
and suburban dwellings into the countryside has greatly increased the cost and danger of fire damage.
Fire has important effects on the ecology. Under-ground 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, Quercus coccifera, and strawberry tree, Arbutus unedo, can reach 1 m in height after two years.
The conifers like 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 generally to maintain
mixed communities, e.g. mixed pine-oak woodland rather than a monoculture of one species, of greater richness
and diversity. Thus fire stimulates ecological processes, nutrient cycling and the vigorous regrowth of vegetation. It
causes temporary bare land and therefore probably more short-term erosion, but 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.
