Environmental Engineering Reference
In-Depth Information
and soils are limited to small areas exposed to the north where the forest is better
conserved. The soils are predominantly of clay texture, with a lumpy and multi-
faceted subangular and angular aggregation, and a good content of organic matter in
the upper horizons where the natural vegetation is present, providing a useful depth
of moisture and good fertility. The balance between soil, vegetation and erosion in
these areas is very delicate. Any alteration due, for example, to fire, cutting or over-
grazing, results in an intense and often irreversible degradation, leading to deserti-
fication phenomena. Land use in these areas is mainly forestry while pastoral activ-
ities are limited. Agriculture can only be practised on the gentler slopes and larger
colluvial areas. These landscapes are mainly found in the eastern Mediterranean
Basin in the mountain massifs of Greece and Lebanon, but also in western Sardinia.
4.4.2 Landscapes of the Palaeozoic metamorphic rocks
The landscapes that have developed on metamorphic rocks are characterized by a
remarkable variety of forms reflecting differences in lithological nature and the in-
fluence of morphological changes. The vegetation presents a number of different
forms, depending on exposure, altitude, microclimate and anthropogenic activity.
Generally we find less developed soils (Lithic, Typic and Dystric Xerorthents) on
more siliceous rock types because of their greater resistance to alteration. The tex-
tures vary from sandy to medium clay; the organic matter content is high only in
the presence of bush or scrub forest. On sandstone and shale sandstone, landforms
are gentler and the soils show greater development, especially in areas most heavily
conserved. We find Typic and Lithic Xerochrepts where the slopes are less steep or
there is more vegetation cover.
On these formations debris slopes are quite extensive and soils are generally
highly evolved (Palexeralfs), with a relatively high erodibility due to the weak ag-
gregation and low content of organic matter. The Pyrenees, Baetic chain and the At-
las mountains are all characterized by outcrops on Palaeozoic metamorphic rocks.
4.4.3 Landscapes of intrusive rocks (granite, granodiorite, etc.)
Intrusive rocks are more homogeneous but the landscape is almost always charac-
terized by steep slopes, deep valleys and rugged topography. Where the granite is
altered it forms slope deposits, or cones, the landscape becomes gentler and less
steep so that the land may be used in places for extensive or intensive agriculture.
In this case, the most common soils in areas with steep slopes are Xerorthents (lithic
and typic subgroups). More evolved soils lie beneath forest and generally belong to
Typic or Dystric Xerochrepts. The degradation of these landscapes through erosion
is particularly intense because of the fires, forestry operations and pasture improve-
ment. These landscapes are present in both Sardinian and Corsican mountains.
