SILVOARABLE SYSTEMS

The tree species that form traditional agroforestry systems are the various species of oak, cypress and poplar. Of the various oak species, the valonia oak (Quercus ithaburensis subsp. macrolepis) stands out; it is found in various regions of mainland Greece as well as in many islands with a typical Mediterranean or subMediterranean climate. In various areas of its range, the valonia oak grows in or on the borders of fields usually cultivated with cereals, and forms silvoarable systems or agrosilvopastoral systems, if the fields are also grazed by livestock after the grain harvest (Papanastasis 2015). Also, the Macedonian oak (Quercus macedonica or trojana), which is mainly founds in the Region of Western Macedonia, occurs in agricultural crops, in or on the borders of fields planted mainly with cereals and forms the same systems as the valonia oak (Mantzanas et al. 2006). Other oak species such as Quercus pubescens, Quercus frainetto and Quercus petraea, form silvoarable and agrosilvopastoral systems in extensive areas in the semi-mountainous and mountainous zone of the mainland. Among the coniferous tree species, the cypress (Cupressus sempervirens) is planted on the borders of cultivated fields with cereals or other agricultural crops for the natural marking of fields or for wind protection of crops, forming silvoarable and agrosilvopastoral systems (Papanastasis 2015).

Various productive clones of poplar trees (Populus sp.) are cultivated or planted within arable lands that have relatively deep and fertile soils, are irrigated or have good water conditions near canals and riverbanks. The most common system, however, is around arable land with vegetables or other summer crops. This planting scheme results in the creation of silvoarable systems, which are traditional in several parts of the country, particularly in Northern Greece. Poplars are used for timber production but also serve other purposes such as boundary marking or as windbreaks (Papanastasis 2015). The most important among the evergreen fruit trees, is the olive tree (Olea europea), which is found almost all over Greece and especially in the plains and coastal areas. According to Papanastasis (2015), the olive tree has been one of the most widely cultivated species in the Mediterranean zone of Greece already since the 1st century BC. The area covered by olive groves in our country amounts to 700,000 hectares, of which approximately 125,000 hectares are agroforestry systems, either silvopastoral or silvoarable (Papanastasis et al. 2009). In olive agroforestry systems the trees are usually old and come from wild olives grafted to produce edible olives and olive oil. The characteristic of these trees is that they branch at a remarkable height above the ground (1.5-2 m.) and this is due to the fact that the grafting was done at this height to avoid the eating of the new shoots by goats. Under the trees, various crops can be found such as cereals, maize, alfalfa, vineyards, or vegetables such as potatoes, onions, tomatoes and beans. Another type of tree in this category is the carob tree (Ceratonia siliqua), which occurs in very limited areas in the Southern Peloponnese and Crete. Its fruits were used in the past as fodder for livestock, while some crops can be found in the understory (Schultz et al. 1987). In recent years there has been a strong interest in carob honey and carob flour and products derived from them such as nuts (rusks).

Walnut tree (Juglans regia) and almond tree (Amygdalus communis) belong to the

Of the broad-leaved fruit tree species, the most extensive silvoarable systems are made up of walnut and almond trees broad-leaved fruiting species that form extensive silvoarable systems. Walnut systems are found throughout the country, mainly in the semi-mountainous zone, but also in the mountainous. Trees may be scattered or in rows within agricultural plots. They are used for walnut production as well as for highquality timber, while in the understory there may be cereals, alfalfa, vineyards, cotton, tobacco, etc. Walnut silvoarable systems combining walnuts with vines, cereals, alfalfa, vegetables or dry beans have been recorded in the Municipality of Voio, in the Regional Unit (RU) of Kozani, Greece (Mantzanas et al. 2006). Silvoarable systems with almond trees are found mainly in the dry areas of the country and on the islands. The almond tree grows alone or in a mixture with other species such as olive, fig, walnut and pistachio (Papanastasis 2015). Traditionally, almond is intercropped with various agricultural crops such as cereals, tomato, legumes, and hay crops. Almond tree silvoarable systems have been recorded in the Voio Municipality of Kozani RU, where almond trees are co-cultivated with vineyards, tobacco and alfalfa in addition to cereals (Mantzanas et al. 2006). Other planted broadleaf tree species that form silvoarable systems on a smaller scale are the chestnut (Castanea sativa), the mulberry (Morus alba), the fig (Ficus carica), the pseudoacacia (Robinia pseudoacacia), the cherry (Prunus avium), the apple (Malus domestica) and the pear tree (Pyrus communis).

Conclusions

Silvoarable systems are formed by a wide variety of trees (forest or fruit bearing) and with various combinations of agricultural plants both in mainland and insular Greece. Among them, the silvoarable systems of olive, walnut and the various species of oak, which are traditional forms of land use, cover the largest areas.