Environmental Engineering Reference
In-Depth Information
20.2). 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 it is not easy to disentangle the relative importance of each. During the Glacial
Epoch (20,000-15,000 years BP) the climate was distinctly 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 conditions farther
north. Lowlands were mostly dry steppes, with or without groves of trees, depending on
location.
Since glacial times (i.e. during the Holocene) 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 26.6 shows the slightly different sequence in France, Italy
and Greece. The differences are due to regional conditions, but the overall pattern is first
an invasion of northern types of coniferous and deciduous tree (pine, birch, elm, oak),
with evergreen oak and chestnut becoming more widespread as temperatures increased to
reach their Holocene maximum levels about 5000-6000 years BP. Lower soil moisture
contents caused northern species to retreat to higher altitudes and northerly aspects,
whilst at the lowest, hottest elevations scrub and open steppe vegetation developed.
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 (Plate 26.1). Again, the details and dates of
prehistoric and historical societies differ from region to region. Figure 26.7 shows the
chronology of the southern and south-eastern coastal areas of Spain. Here there is a
particularly rich history of 'cultural waves', from the Palaeolithic through the Neolithic,
Copper, Bronze, Phoenician, Greek, Roman, Moorish and modern Spanish eras. Different
types of agriculture have superimposed their imprint on the coastal landscape - pastoral
Figure 26.6
The history of Mediterranean vegetation since
the last glacial epoch.