4
Jaume Terradas
developed later in this book, but I will try here to relate them to some more
general aspects of holm oak ecology. Other characteristics will be outlined
now as an introduction for those readers who are unfamiliar with Mediterranean forests.
1.1 Biogeography of Holm Oak
In the Mediterranean Basin and the Middle East, holm oak is present over a
large area extending 6000 km longitudinally (Debazac 1983), from Portugal
to Syria, and 1500 km latitudinally from Morocco and Algeria to France. It
has been frequently considered as a typical Mediterranean plant due to its
evergreenness, sclerophyllous leaves, and drought resistance. Nevertheless,
many authors consider that the typical Mediterranean vegetation types are
not forests, but dense evergreen shrub formations, such as maquis or garrigue in the Mediterranean Basin, chaparral in California, fynbos in South
Africa, matorral in Chile or mallee in Australia. Holm oak can be present in
maquis and has leaves quite similar to those of evergreen shrub oaks
(Quercus coccifera, Q. calliprinos), but its optimum lies on the geographical
periphery of maquis and garrigue formations. Holm oak is mostly found
from cold semi-arid to temperate humid Mediterranean bioclimates (Emberger 1955), whereas maquis and garrigues are more frequent from temperate semi-arid to warm humid bioclimate zones.
Biogeographical aspects of holm oak have been reviewed by Barbero et al.
(1992). They describe the species as a circum-Mediterranean one, more
abundant in the western part of the Basin. It is distributed mainly in the
thermo-, meso- and upper Mediterranean altitudinal "etages" and in semiarid to humid Mediterranean climates (Rivas MartInez 1987). It is absent
from those parts of the Mediterranean Basin where summer drought is too
long. In North Africa, southern Spain and southern Greece, holm oak is
rarely found at altitudes below 350 m and it can be found up to 1500-1800 m,
reaching even 2700 m on the Atlas range. It can compete with deciduous oaks
and some conifers in the coldest and moistest limits of its distribution range,
or with other sclerophyllous evergreen oaks or conifers near its driest border.
Its limits of distribution have been modified by management practices favouring holm oak, or by different livestock uses. Overuse by agriculture and
grazing for many centuries and frequent fires have contributed to a gradual
degradation of forests and soils and increased aridity. This, in the moister
parts of the holm oak range, has sometimes favoured the spread of evergreen
forests over deciduous forests (Debazac 1983), whereas in the drier parts it
has favoured pine forests with xerophytic shrubs or maquis. In most parts of
Iberia, holm oak is largely indifferent to soil reaction, whereas in the northern areas it prefers calcareous soils and southern slopes where it competes
successfully with deciduous species.
Jaume Terradas
developed later in this book, but I will try here to relate them to some more
general aspects of holm oak ecology. Other characteristics will be outlined
now as an introduction for those readers who are unfamiliar with Mediterranean forests.
1.1 Biogeography of Holm Oak
In the Mediterranean Basin and the Middle East, holm oak is present over a
large area extending 6000 km longitudinally (Debazac 1983), from Portugal
to Syria, and 1500 km latitudinally from Morocco and Algeria to France. It
has been frequently considered as a typical Mediterranean plant due to its
evergreenness, sclerophyllous leaves, and drought resistance. Nevertheless,
many authors consider that the typical Mediterranean vegetation types are
not forests, but dense evergreen shrub formations, such as maquis or garrigue in the Mediterranean Basin, chaparral in California, fynbos in South
Africa, matorral in Chile or mallee in Australia. Holm oak can be present in
maquis and has leaves quite similar to those of evergreen shrub oaks
(Quercus coccifera, Q. calliprinos), but its optimum lies on the geographical
periphery of maquis and garrigue formations. Holm oak is mostly found
from cold semi-arid to temperate humid Mediterranean bioclimates (Emberger 1955), whereas maquis and garrigues are more frequent from temperate semi-arid to warm humid bioclimate zones.
Biogeographical aspects of holm oak have been reviewed by Barbero et al.
(1992). They describe the species as a circum-Mediterranean one, more
abundant in the western part of the Basin. It is distributed mainly in the
thermo-, meso- and upper Mediterranean altitudinal "etages" and in semiarid to humid Mediterranean climates (Rivas MartInez 1987). It is absent
from those parts of the Mediterranean Basin where summer drought is too
long. In North Africa, southern Spain and southern Greece, holm oak is
rarely found at altitudes below 350 m and it can be found up to 1500-1800 m,
reaching even 2700 m on the Atlas range. It can compete with deciduous oaks
and some conifers in the coldest and moistest limits of its distribution range,
or with other sclerophyllous evergreen oaks or conifers near its driest border.
Its limits of distribution have been modified by management practices favouring holm oak, or by different livestock uses. Overuse by agriculture and
grazing for many centuries and frequent fires have contributed to a gradual
degradation of forests and soils and increased aridity. This, in the moister
parts of the holm oak range, has sometimes favoured the spread of evergreen
forests over deciduous forests (Debazac 1983), whereas in the drier parts it
has favoured pine forests with xerophytic shrubs or maquis. In most parts of
Iberia, holm oak is largely indifferent to soil reaction, whereas in the northern areas it prefers calcareous soils and southern slopes where it competes
successfully with deciduous species.