Holm Oak and Holm Oak Forests: An Introduction
5
In Spain, holm oak dominates in about 3 million ha, i.e. 25% of the area
where trees cover at least 10% of the ground (Primer Inventario Forestal
Nacional, 1965-1974), and it accounts for 16% of total wood production. Almost 1 million ha is coppices used for firewood, and another 1.3 million ha is
"dehesas", a savannah-type man-managed formation, whereas the remaining
areas consist of poorly developed coppices, practically without economic use.
The forest area dominated by holm oak is smaller in Catalonia (NE Spain),
totalling around 100000 ha (about 10% of forested lands). In the French
Mediterranean region, holm oak covers about 250 000 ha (Barbero et al.
1992). In Italy, Corsica and Sicily it is the dominant forest tree in Mediterranean climate areas at altitudes ranging from only 500 m in Liguria to 1400 m
in Calabria, the basal parts being mostly occupied by a "macchia" dominated
by holm oak. In Sardinia its climacic area spreads over most of the island, but
forests and "macchia" are strongly degraded. In Morocco, holm oak grows
between 600 and 2700 m, covering 1.4 million ha, over 30% of the natural
forest area (Braun-Blanquet and Maire 1924; Khatouri 1992), but it is declining fast through overexploitation.
1.2 History of Holm Oak Forests
Holm oak has been present in the Mediterranean Basin at least since the
Miocene (Barbero et al.1992) and its dominance has expanded from south to
north: in central and southern Spain it was abundant as early as 9500 B.P.
(before this, it was probably limited to a few warm refuges), whereas similar
proportions of Q. ilex and of the deciduous Q. humilis (= Q. pubescens) appeared in NE Spain after 5000 B.P. (Riera-Mora and Esteban-Amat 1994). In
the north-western Mediterranean Basin, holm oak has spread only in very
recent times, replacing deciduous Q. humilis forests (Pons and Vernet 1971).
For instance, in Low Provence (southern France) it became dominant only
after the SubAtlantic period (2000 B.P.), with the increase in human activity
and the spread of agriculture in Gallo-Roman times. A similar history has
been described for the Eastern Mediterranean Basin, with the increase of
Q. ilex pollen associated with an increase in human activity at the end of the
Atlantic period (4700 B.P.). In northern Africa, there were probably extensive
holm oak forests much before, but a human-related increase is also observed.
1.3 Species Composition Patterns in Holm Oak Forests
It is difficult to assess the natural diversity of forests that have been managed
over many centuries. Holm oak forests are now, in most cases, monospecific
in the tree layer (Chap. 3), perhaps as a result of human activities. The main
5
In Spain, holm oak dominates in about 3 million ha, i.e. 25% of the area
where trees cover at least 10% of the ground (Primer Inventario Forestal
Nacional, 1965-1974), and it accounts for 16% of total wood production. Almost 1 million ha is coppices used for firewood, and another 1.3 million ha is
"dehesas", a savannah-type man-managed formation, whereas the remaining
areas consist of poorly developed coppices, practically without economic use.
The forest area dominated by holm oak is smaller in Catalonia (NE Spain),
totalling around 100000 ha (about 10% of forested lands). In the French
Mediterranean region, holm oak covers about 250 000 ha (Barbero et al.
1992). In Italy, Corsica and Sicily it is the dominant forest tree in Mediterranean climate areas at altitudes ranging from only 500 m in Liguria to 1400 m
in Calabria, the basal parts being mostly occupied by a "macchia" dominated
by holm oak. In Sardinia its climacic area spreads over most of the island, but
forests and "macchia" are strongly degraded. In Morocco, holm oak grows
between 600 and 2700 m, covering 1.4 million ha, over 30% of the natural
forest area (Braun-Blanquet and Maire 1924; Khatouri 1992), but it is declining fast through overexploitation.
1.2 History of Holm Oak Forests
Holm oak has been present in the Mediterranean Basin at least since the
Miocene (Barbero et al.1992) and its dominance has expanded from south to
north: in central and southern Spain it was abundant as early as 9500 B.P.
(before this, it was probably limited to a few warm refuges), whereas similar
proportions of Q. ilex and of the deciduous Q. humilis (= Q. pubescens) appeared in NE Spain after 5000 B.P. (Riera-Mora and Esteban-Amat 1994). In
the north-western Mediterranean Basin, holm oak has spread only in very
recent times, replacing deciduous Q. humilis forests (Pons and Vernet 1971).
For instance, in Low Provence (southern France) it became dominant only
after the SubAtlantic period (2000 B.P.), with the increase in human activity
and the spread of agriculture in Gallo-Roman times. A similar history has
been described for the Eastern Mediterranean Basin, with the increase of
Q. ilex pollen associated with an increase in human activity at the end of the
Atlantic period (4700 B.P.). In northern Africa, there were probably extensive
holm oak forests much before, but a human-related increase is also observed.
1.3 Species Composition Patterns in Holm Oak Forests
It is difficult to assess the natural diversity of forests that have been managed
over many centuries. Holm oak forests are now, in most cases, monospecific
in the tree layer (Chap. 3), perhaps as a result of human activities. The main