introduction - Ecologia Mediterranea

PHENOLOGY AND GROWTH OF QUERCUS ILEX IN DIFFERENT ENVIRONMENTAL CONDITIONS IN SICILY u
The former assumptions are consistent with theories
assessing that leaf growth dynamics and turn-over depend
on climatic and micro-climatic conditions, as like as on
the adaptive ability of the species to external factors
(Gratani, 1996). Thus, a larger leaf area as observed at
Mt Pellegrino (table 2), generally reflects an increase in
resource availability.This means that the larger is leaf area,
the higher is the photosynthesis rate (Chabot & Hicks,
1982; Jurik, 1986). The relationship between leaf turnover
and the photosynthesis features is strictly related to
that. Results of several studies (Reich et al., 1992;
Kikuzawa, 1995) indicate that a shorter leaf longevity, i.e.
an accelerated turn-over, usually corresponds to a higher
photosynthetic rate, rapidly decreasing through time as
leaf area decreases. Such a characteristic generally involves
a high growth rate.
In the view of general considerations, comparisons can
be attempted between the Sicilian stands and other case
studies. For instance, very high leaf area values (about
16 cm 2) were recorded at Castelporziano (Gratani, 1996).
At Supramonte di Orgosolo (Sardinia), mean leaf area is
close to values from Mt Pellegrino (Susmel et al., 1976). It
must be added that the Supramonte holm oak stands, for
their structural features and the mean size of trees, are ascribed
among the best examples of Quercus ilex forests in the
whole Mediterranean area. Finally, data our from Mt Etna
confirm the values previously recorded by Poli and Leonardi
(1974), Poli et al. (1974a, b), and Leonardi (1982) at Mt
Minardo (north-western slopes of Mt. Etna), a site just few
kilometres afar from the present investigated stand.
In conclusion, holm oak in Sicily shows a varied behaviour
according to different environmental conditions. Some
peculiar aspects were observed at Mt Pellegrino, the most
“oceanic” site among the investigated ones. Moreover, they
are specially enhanced in the south-eastern side of the trees
crown, where the particular micro-environmental conditions
surely play a major role. In that site, polycyclic growth
and flowering, global higher growth performance, shorter
leaf turn-over and higher leaf area seems to indicate that
holm oak is prone to profit of more favourable conditions
than those characterising its usual habitat.
General results show that Quercus ilex has a certain
ecological plasticity, being able to adapt to different environments.
This can just reflect a phenotypic characteristic,
but the existence of a genotypic blueprint can not be
excluded at all. On the other hand, its behaviour in special
situations strengthens the idea that Quercus ilex has a
certain suitability to a tropical-type climate, and this can
be very likely a consequence of the atavistic environment
where the species originated.
ecologia mediterranea, tome 29, fascicule 1, 2003, p. 15-25
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