Studio geologico e pedologico dell’area di Macchia di Blera (provincia di Viterbo) a supporto di un piano di gestione del bosco

This study constitutes the necessary base for the forest management and its double goal is to stimulate and to increase the synergy among Earth Sciences, Forest Sciences and Pedology, not yet well developed in Italy. The starting point was the need of the Commune of Blera (province of Viterbo) to carry out a forest management plan of the Commune forests, in particular the Macchia di Blera area. The vegetation is constituted by a mosaic of woods, brushwoods, and pastures. The forest stands are primarily formed from oak (Quercus cerris L.) with maple (Acer monspessulanum L., Acer campestris L.) and ash (Fraxinus ornus L.). The evolution of the forest systems has been limited by anthropogenic disturbances such as cutting, grazing and fires. Therefore, the new management plan aims at restoring degraded forest stands and considering the different goods and services the forest produce: fuelwood, soil protection, recreation, biodiversity. The lithological substratum of Macchia di Blera consists mainly of the Late Cretaceous-Eocene Tolfa Flysch or Tolfa Formation (ABBATE & SAGRI, 1970; FAZZINI et alii, 1972), that is made up of a calcareous-marly member and a member and a varicoloured argillite member. Some limited outcrops of the Tufo Rosso a Scorie Nere Unit are also present; this unit is connected to the last eruptive phase of the Vico Volcanic District, active between 0,7 and 0,25 Ma. The two units are frequently covered by eluvial-colluvial deposits and slope debris. From the morphological point of view the Macchia di Blera area has a topography of hills with gently inclined slopes, affected by slope movements in the zones where the argillite member outcrops. Some slope consist of prevailingly V-shaped small valleys, and structural forms in the Tufo Rosso a Scorie Nere Unit showing characteristic vertical walls affected by topless landslides have been recognized. The pedological cover suggests that an alternation of stable and erosional phases has been active. As an effect of the most recent erosional phase, thin soils, with a high content of coarse lithic fragments, are widespread. They show fine texture and are uniformly calcareous. This last phase of colluvial cover deposition could be connected to the last intensive exploitation of the area with consequent reduction of the vegetational cover. The short term risks for soil conservation are limited, even though erosional processes have been active in the recent past. The record of the past shows, however, that this stability is not intrinsic, but rather due to the present status of high vegetation cover. In conclusion, for correct landscape planning, the forest heritage of Macchia di Blera needs active action of reconstitution and improvement, since it has an environmental value able to improve the quality of human life quality.