Geoscience Reference
In-Depth Information
Since glacial times, trees have spread to lower altitudes
as the climate has become moister and warmer. The details
of the succession vary from location to location, and
Figure 25.6
shows the slightly different sequence in France,
Italy and Greece. The differences are due to regional
conditions, but the overall pattern is similar; first, an
invasion of northern types of coniferous and deciduous
trees (pine, birch, elm, oak); second, evergreen oaks and
chestnut become more widespread as temperatures
increase to reach their Holocene maximum levels at
5-6 ka
BP
.; and, third, lower soil moisture contents cause
northern species to retreat to higher altitudes and
northerly aspects, whilst at the lowest, hottest elevations
scrub and open steppe vegetation develops.
Copper, Bronze, Phoenician, Greek, Roman, Moorish and
modern Spanish eras. Different types of agriculture -
pastoral farming, cereals, vineyards, orchards, vegetables
- have superimposed their imprint on the coastal
landscape. Inland there is a long history of pastoral
transhumance following traditional sheep trails (
ca
~
adas
),
and of dry farming for cereals, vines and olives.
The net result of this prolonged exploitation of the wild
vegetation has been, first, to reduce the natural resource
base on which subsequent peoples could depend; second,
to introduce, whether deliberately or inadvertently, species
foreign to the area (olive, orange, cotton, sugar cane and
many other species), and thirdly to accelerate natural
rates of erosion by deforestation, grazing, burning and
cultivation. The effect of browsing by goats is illustrated
in
Figure 25.8
.
It is possible to look at a Kermes oak
(
Quercus coccifera
) and estimate how severely it is
browsed. The most intense is where the tree is bitten into
a cushion shape; less intense browsing is shown succes-
sively by columns, thickets and 'got-aways'. Thereafter the
shrub grows above the height of browsing, except where
goats can climb into the tree to produce a goat pollard
(
Plate 25.2
).
The shrubby, steppe-like vegetation so characteristic of
today's wild landscapes of the Mediterranean region is
viewed by biogeographers such as Polunin, Huxley, Eyre
and Thirgood to be the result of human pressures
superimposed upon climatic trends. The effects of these
Human impact
This simple model of climatically controlled vegetation
succession is greatly complicated by human occupation.
The great antiquity of archaeological remains in
the Mediterranean basin points to long and extensive
'attack' by human societies on a changing and emerging
Mediterranean forest. Again, the details and dates of
prehistoric and historical societies differ from region to
region.
Figure 25.7
shows the chronology of the southern
and south-eastern coastal areas of Spain. Here there is a
particularly rich history of cultural waves or sequent
occupance from the Palaeolithic through the Neolithic,
SOUTHERN
FRANCE
CENTRAL
ITALY
NORTHERN
GREECE
Ye a r s
Years
2000
2000
MAQUIS
EVERGREEN
OAK AND MAQUIS
EVERGREEN
OAK AND MAQUIS
AD
AD
0
0
EVERGREEN
OAK
MIXED OAK
FOREST
OPEN OAKWOODS
WITH FIR
4000
4000
MIXED OAK
FOREST
MIXED OAK
FOREST WITH
ASH AND
HAZEL
BC
BC
PINEWOODS
STEPPE
OAK AND PINE
8000
8000
BIRCH
STEPPE
OPEN
OAKWOODS
MIXED OAK WITH
ELM AND JUNIPER
PINE - BIRCH
STEPPE WITH
OAK
STEPPE
WITH
JUNIPER
GRASSY
STEPPE
12000
12000
PINE
STANDS
