Environmental Engineering Reference
In-Depth Information
climax vegetation is evergreen oak woodland (holm oak,
Q. ilex
; cork oak,
Q. suber
)
which will degenerate into
maquis
scrub under light exploitation.
Maquis
is typically 1-3
m high, and today is more widespread than 'relict' evergreen forests. Many plants that are
present in the forest but which prefer more open habitats grow abundantly in
maquis
(tree
heath, buckthorn, holly oak, strawberry tree, myrtle, juniper). The net result is a dense,
almost impenetrable shrub community, with plant species varying in different parts of the
Mediterranean. Excessive exploitation leads to the formation of a low mixed heath,
garrigue
, which is a very diverse community of low shrubs and flowers, typically less
than 1 m high. The community is colourful and aromatic, with species varying according
to local conditions. However, common plants are rosemary, thyme, lavender, sage, broom
and rock rose. The common feature of
garrigue
plants is their resistance to grazing by
sheep and goats on account of their poisonous, thorny or 'oily' nature. Prolonged
degeneration can lead to the almost complete disappearance of shrubs and the formation
of steppe grassland and stony pasture (Plate 26.2). Such eroded, rocky terrain supports
only grasses (esparto), annuals (clovers) and bulbs (asphodels, tulips). Figure 26.9 also
indicates the pathways of regeneration should the human impact cease, for example
through the abandonment of agricultural land. However, regeneration of
garrigue
to
maquis
and then forest is clearly a much slower process than degeneration, as soil erosion
will have reduced soil depth, water-holding capacity and nutrient content. Extreme
degeneration can make regeneration impossible.
A view of vegetation dynamics which differs from the above has recently been
advocated by Rackham, Grove and Moody. They question the use of terms such as
'potential climax' and 'degradation', and point out that there is often little evidence that
maquis
,
garrigue
and steppe can be turned from one into another. The fact that a hillside
is treeless may mean that it has never been suitable for trees. It is clearly important in the
light of these new studies to treat each local area as an individual entity with its own
ecological history before accepting deforestation unthinkingly across the entire region.
Plate 26.2
Overexploitation for millennia has produced this
Mediterranean heath (garrigue) in northern Libya.
Vegetation is being removed by overgrazing and collection
for firewood.
Photo: Ken Atkinson.
