Environmental Engineering Reference
In-Depth Information
zone is present only in the highest mountains of the Basin such as the Atlas
Mountains. This zone is devoid of vegetation apart from a range of widespread
alpine species in rocks and screes.
In addition to the formations described above, many mountain habitats and plant
communities are independent of this elevation gradient but instead are associated
with geomorphological or hydrological processes and features. Cliffs are a conspic-
uous feature of the Mediterranean Basin, whose presence is often associated with
mountains. The main characteristics of cliffs are vertical surfaces, lack of a well-
developed soil layer, severe drought effects and extreme diurnal temperatures, and
their importance for the flora has long been recognized (Turland
et al.
, 1993). Ac-
cording to Snogerup (1971), there are no sharp limits between communities on a
single cliff, and while the species composition in two adjacent cliffs can be entirely
different the vegetation formation can be identical. Cliffs have provided habitats for
some highly specialized plants, many of which lack the competitiveness to survive
elsewhere. Those plants able to tolerate harsh cliff conditions are termed chasmo-
phytes. Moreover, cliffs serve as refuges and may host a high number of relict en-
demic species, such as
Petromarula pinnata
in Crete, protecting them from grazing
and environmental change.
Another feature that dominates the highest mountain summits are scree slopes
consisting of angular blocks of various shapes and sizes, which provide habitats for
many plants. Scree formation in hot and dry regions of the world is driven by the
sudden expansion and contraction of the rock. Rupicolous chasmophytic vegetation
is more diverse in calcareous than siliceous rocks on the High Atlas Mountains
(Quezel, 1981c) while there is differentiation in community composition between
fixed and mobile screes (Vogiatzakis and Griffiths, 2006). In the Lefka Ori of Crete,
calcareous scree formations resulting from limestone weathering are also abundant
above 1900 m. Some of the species adapted to life on screes are
Cicer incisum,
Peucedanum alpinum
and the endemics
Silene variegata
and
Viola fragrans
.
In depressions where water and soil accumulate from snowmelt there are summer
dry meadows (e.g. in the Pindos and Mount Olympus in Greece and in the High At-
las in Morocco), with species such as
Festuca, Trifolium
and
Plantago
, while the im-
permeable nature of siliceous bedrock gives rise to waterlogged pozzines or mires
with distinct plant communities (Nagy and Grabherr, 2009). The Taurus Moun-
tains of Turkey are a good example, with high plant community richness due to the
variety of geomorphological and hydrological processes occurring. Some of these
communities include the vegetation of hilltops and exposed ridges, snow-beds and
meltwater communities and azonal hydrophytic units (Parolly, 2004). In the moun-
tains of Crete, the Dinaric Alps and Spanish Sierras, the abundance of carbonate
rocks has led to the development of karstic formations (Figure 6.4; see Chapter 4).
Typical features include dolines, poljes, deep gorges and extensive cave systems.
In the Lefka Ori massif of Crete there are numerous dolines, for example, mainly
dominated by the evergreen shrub
Berberis cretica.
They support more perennial
than annual plants and are rather poor in endemic species confined strictly to this
habitat compared to scree slopes and mountain pastures (Egli, 1991). Waterlogging
