Pinus silvestris

Mountain forests with Fagus silvatica Abies alba Pinus silvestris Pinus uncinata

montane (montane-mediterranean)

Mountain forests with Cedrus atlantica Cedrus libani Abies pinsapo Abies cilicica, Pinus nigra

Pinus nigra Populus div. spp.

Pinus rndiata Pinus pinaster Eucalyptus div. spp. Populus div. spp.

Deciduous forests with

Quercus cerris Quercus pubescens Quercus faginea Carpinus orientalis

submontane (sub-mediterranean, supra-mediterranean)

Evergreen and deciduous forests with Quercus boissieri Quercus pubescens Quercus coccifera Quercus ilex, Pinus brutia

Pinus pinaster Eucalyptus div. spp.

Pinus radiata Pinus halepensis Eucalyptus div. spp.

Evergreen forests with Quercus ilex Quercus suber Pinus pinea Pinus pinaster

\ basal/foothills , \ (eu-medi- J Xterranean)/

Evergreen forests with Tetraclinis articulata Juniperus phoenicea Pinus halepensis

Pinus halepensis Eucalyptus div. spp. Tamarix div. spp.

Fig. 4.1.23. The altitudinal zones of dominant tree species of natural vegetation and the most important exotic tree species used in reforestation in the Mediterranean region. (After Müller-Hohenstein 1991)

Fig. 4.1.23. The altitudinal zones of dominant tree species of natural vegetation and the most important exotic tree species used in reforestation in the Mediterranean region. (After Müller-Hohenstein 1991)

nix dactylifera, Ziziphus spp., Lawsonia inermis), and Fabaceae (Lens culinaris, Pisum sativum, Vicia fab a).

The Phoenecians brought olives, vine, pomegranates and figs and the Romans introduced garlic, onions, apples and pears. During the Arab period the number of species from central and east Asia increased, e.g. citrus, mulberry and carob trees, hemp and sugar cane. Species from the New World followed after the discovery of America. During that time those plants now regarded as characteristic of the region reached the Mediterranean basin: agave, opuntia as well as maize, tobacco and tomato. In the nineteenth century many ornamental plants were added. Economic reasons resulted in the successful introduction of acacia and eucalyptus. About 200 exotic species are today naturalised in North Africa, corresponding to 4% of the total flora (Le Floch et al. 1990). Many species were introduced unintentionally, along with the crop plants, and became established. The number of those species originating from the New World is considerable, amongst them so-called aggressive invaders which established particularly on rud-eral sites (species of the genera Amaranthus, Cuscuta and Conyza, as well as Heliotropium curassavicum, Solanum eleagnifolium, Xanthium spinosum). The three last mentioned, as well as some shrubs (Ricinus communis and Nicotiana glauca), are expanding rapidly in North Africa at the moment.

In the segetal flora, on the other hand, indigenous species found new niches. The ca. 50 species on fields and fallow land include Ammi ma-jus, and A. visnaga, Anagallis arvensis and A. foemina, Echium italicum, Ridolfia segetum, Si-napis arvensis, Calendula arvensis, Cirsium arvense, as well as Carduncellus, Convolvulus, Cy-perus and Diplotaxis species. The number of sometimes thorny weeds on pastures is just as high (Astragalus armatus, Atractylis serratu-loides, Calycotome villosa, Scolymus hispanicus and S. grandiflorum), and also partly poisonous or at least non-edible species (Asphodelus fistu-losus, A. macrocarpus, A. tenuifolius, Haloxylon scoparium, Hertia cheirifolia, Peganum harmala, Solanum nigrum, Stipagrostis pungens and S. ca-pensis). Among the nutrient indicators (nitro-phils) are, e.g., Aizoon and Mesembryanthemum species, Calendula arvensis, Chenopodium murale, Hyoscyamus albus and H. niger, Malva par-viflora and Withania somnifera (Le Floch et al. 1990).

For the Mediterranean regions the same applies as for central Europe: Naturalisation, expansion and disappearance of individual species is closely connected to agricultural practices.

Deil (1997) showed for the areas bordering the Strait of Gibraltar, how, to a high degree of certainty, vegetational landscapes may be read as history books, and how historic and actual forms of use show religious regulation, as well as subsistence-orientated management of the indigenous population, or the market-oriented management of colonial times. Thus, even today, it is possible to demonstrate, from the spectrum of different species, an Islamic cemetery from the time before the reconquista, just as it is possible to show the different use of herbicides and mechanical control of weeds in the fields of southern Spain or northern Morocco.

The recent history of forests in the Mediterranean regions is determined by man and will be discussed in more detail, particularly as it is possible to explain essential problems of site conditions. During the Greek colonisation of Dalmatia from the eighth century b.c., forests were cleared. The Italian peninsula was predominantly deforested during Roman times, the Iberian peninsula mostly from the 6th century b.c. onwards. Consequences for vegetation and site have often been shown (Muller-Hohenstein 1973; Finckh and Deil 1989). Forest degradation often starts with structural changes (age structure, density of stand and closure of canopy); the grazing in forests leads to invasion of ruderal species, decline of rejuvenation and therefore to thinner stands.

At first forests on more favourable sites were cleared. Arable fields extended with not very productive dry land agriculture. Clearing occurred also, often supported by fires, to gain grazing areas. Le Houerou (1992) showed how and for what reasons Mediterranean dwarf shrub communities (macchie with various regionally different terms such as garrigue, tomil-lares, phrygana, matorral) and pastures differing in their floristic compositions are anthropo-genically determined (see Box 4.1.2).

Clearing was not only an intervention with irreversible consequences for vegetation, but particularly because of soil erosion down to the bed rock and resulted in sedimentation in valleys. At present, floods signal the considerable changes in water relations. The view that degradation has had negative economic consequences, and also the acute lack of wood for the last 50 years, has led to increased reforestation, at first in southern European regions and later in north African countries. Any trend to establish nearly natural economic forests is, however, hardly recognisable. Exotic, fast-growing types of trees are chosen for reforestation, in part pine species, but predominantly eucalyptus species. Figure 4.1.23 shows the most important forest spe-

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