Analisi multitemporale del consumo degli oliveti periurbani nel nordovest della Sardegna: il caso di studio della città di Sassari

In Sardinia the presence of olive stands plays an important role in economic business and landscape planning. In particularly, since the 16th century, the Miocene calcareous plateau of North- West is covered by an olive stand system mainly for olive oil production. These olive groves actually are composed by a local variety (Bosana) of which the oil is rich in antioxidant and flavour compounds and for this reason appreciated by the consumer. In the same region is located the city of Sassari, the second biggest city of Sardinia, which territory contains 50% of the whole olive stands of North Sardinia, most of them are concentrated in a “ring” around the city. The survey was conducted with historical and spatial explicit data of land-use and land-use change from the half of 19th century to the present (2007), to test the hypothesis that during the 20th century the area of olive stands decreased against urban expansion. In fact, changes in land-use (in particular those regarding agriculture lands) are a widespread phenomenon in Mediterranean regions and particularly intensive along urban borders. Historical land use data were derived from a variety of sources including cadastral data, maps and aerial photographs. A GIS was necessary to store, manipulate and analyse the digital information and to carry out land use change analysis. The historical analysis started by analysing the cadastral data of 1860, 1920 and 2007. The first one shows a higher density of olive groves in the ring around the city than the present. They were associated with vineyards, pasture and ploughed land. From 1860 to 1920 the olive stands increased due to destruction of the vineyards affected by Grape phylloxera. The information regarding the period between 1920 and 1977 and from 1977 to 2007 is given by aerial photographs that allow determine high resolution details in a spatial complex landscape. From 1960’s the city of Sassari had had the major expansion characterized also by an uncontrolled diffusive urbanization (sprawl) for the leak of a specific legislation. Between 1920 and 1977 the urban development caused the decline of the olive stands due cover density reduction or land use change, with the final result of disappearance of almost 100,000 olive trees in fifty years. The decline operates along the internal limit of the ring caused by urban expansion, and in several locations within the ring due the realization of small villages and the transformation of the olive grove in a garden. The former pattern is the principal factor of the olive landscape fragmentation. Despite the decline, in the external limit of the ring was verified the increase of olive groves but with lower magnitude than the decrease. Similar trends were evaluated for the period 1977-2007 using cadastral data, and digital land use maps. The main causes of olive stand decrease can be summarized in the request of lands for the realization of new industrial and 12 residential areas; in the people movement from the city to the rural area motivated by the better life condition; in the absence of a specific legislation for landscape protection and regulation. Finally the research gives some guideline for management and recovery of the olive groves in Sardinia which rule in Mediterranean ecosystems is recognized in a wide range of studies.