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due to the lack of rainfall, the short persistence of snow and the relatively small extension of
the catchment basins.
Numerous peculiar habitats and microhabitats contribute to regional landscape disconti-
nuity, hence to species-richness. This is the case of the naturally dynamic and disturbed river-
beds and screes, of the wide karstic areas of the inner island, of the humid areas such as rock
pools, temporary and permanent ponds, saltmarshes and coastal lagoons. Other portions of
Sicilian territory are characterised by extremely hostile soils issuing from the pedogenesis on
gypsum, dolomia or salty clays or characterized by impressive seasonal changes in terms of
water flow (e.g. braided streams flowing towards N and NE Sicilian coastlines), soil humidity
(e.g. badlands), etc.
Because of the few or null frosty days, and because of the relatively scarce rainfall, the
weathering of rocks is relatively slow in Sicily and the soils reflect with unusual fidelity the
chemical composition of the mother rocks (FIEROTTI 1988). Different soil chemistry and tex-
ture are selecting remarkably different species assemblages, as it happens, for instance, in the
three orders belonging to the class Tuberarietea guttatae: Tuberarietalia guttatae on acidic
soils, Stipo-Trachynietalia distachyae on alkaline to neutral soils and Malcolmietalia on
sandy soils.
Local speciation due to habitat heterogeneity may be common in plants due to random
genetic drift and the selection of novel variants if they happen to have an adaptive advantage
in novel ecological conditions, or if they happen to attract with higher frequency a pollinator
different from that of the ancestors (LEVIN 1993). This two-fold process may be particularly
important in peripheral populations due to their small size, potential isolation, inbreeding,
wider numerical fluctuations in the population than in the barycentre of the range. Genes with
no major impact on fitness in large populations may confer a selective advantage in the novel
conditions experienced by smaller, isolated populations (LEVIN 1970). In Sicily, the abundan-
ce of micro-species of Ophrys, Allium, Centaurea, Helichrysum, Brassica may be the result
of local differentiation driven by niche heterogeneity and/or diversification of pollinators in
small sized populations.

4. Human influence on habitat fragmentation
Over the centuries, Sicily has attracted many human cultures and civilizations, leaving
behind a unique blend of natural and cultural heritages all over the island. The Sicilian lands
have been a time Phoenician-Carthaginian or Greek, Roman, Byzantine, Arab, Norman, Swa-
bian, French and Spanish, just to name the origin of some of the most influential settlers of
the island. Human presence in Sicily knows no pauses since 14-13 millennia (MANNINO et
al. 2012), and not only species but entire plant assemblages were probably erased - or at least
intensively shaped - by the early onset of agro-silvo-pastoral practices, especially during the
past three millennia (TINNER et al. 2016, and references therein).
Through the centuries, rural communities have managed their environment and farmed the
land in their own natural way, creating a rich diversity of landscapes, choral representation of
historical identity of the territory and cultural human heritage (Fig. 3).
Until the recent past, agro-silvo-pastoral practices induced the prevalent imprint on the
Sicilian landscapes. Traditional small-scale farming contributed to the development of highly
complex socio-ecological systems, which are only partially known and investigated. The vege-
tation of the island shows almost everywhere the traces of a long-lasting exploitation of the
land.

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