Geoscience Reference
In-Depth Information
Brown
Mediterranean Soil
'terra fusca'
Red
Mediterranean Soil
'terra rossa'
Alluvial Soil
'vega'
cm
0
Dark brown
Red brown
clay; blocky
Black clay;
prismatic
Ah
A
Ah
Brown clay;
blocky
A
30
Red clay;
prismatic
Bt
Brown clay
loam;
prismatic
Yellow
brown clay;
prismatic
Bt
B
60
C
White
R
Brown clay
loam;
massive
100
C
Crystalline
Marble
R
Green
130
Metamorphic
Schist
160
Alluvium
optimum range for many plant nutrients. The soils have
high contents of calcium and magnesium, and a cation
exchange complex that is base-saturated. However, the low
organic matter content (typically between 1 per cent and
2 per cent at the soil surface) is a result of the high rates
of mineralization and decomposition during the summer
months. Unfortunately this leads to deficiencies of
nitrogen and phosphorus, both major plant nutrients.
Native vegetation has to adapt to these deficiencies, whilst
agricultural management depends upon the application
of suitable chemical fertilizers or the use of legumes in the
crop rotation. From the point of view of physical
properties, the soils show large water-holding capacities,
owing to their clayey textures, if rain is able to infiltrate.
Summer desiccation of the soil surface usually forms a
cracking pattern, which can be especially deep in the case
of alluvial soils. Such soils have high content of expanding
lattice, montmorillonitic clay minerals. However, rehydra-
tion after the first autumn rain causes the clays to swell,
thus closing the cracks and shutting off infiltration.
OF VEGETATION
The vegetation of the Mediterranean region has experi-
enced many changes during the past 15 ka, i.e. roughly
during the time since ice sheets in Europe were at their
Würm (Devensian) maximum. Vegetation is dynamic,
and plant communities change rapidly in response to
factors which control their structure and productivity. In
the Mediterranean region there have been significant
prehistoric and historical changes in the two most
powerful controlling factors, namely climate and human
land use, and, as already noted, it is not easy to disentangle
the relative importance of each. During the Glacial Epoch
(20 ka to 15 ka
BP
) the climate was cooler and drier.
Mountains surrounding the Mediterranean became refugia
for trees of both southern and northern European species
which were unable to cope with the harsh glacial condi-
tions farther north. Lowlands were mostly dry steppes,
with or without groves of trees, depending on location.
