Accona Desert

The Crete Senesi lie on top of Plio-Pleistocene silty-clay over consolidated marine deposits rich in sodium. Deep, narrow cracks (joints;[14]) cut the deposits to about 10m from the surface, favoring localized water infiltration and the excavation of subterranean tunnels. In natural, unstressed conditions, soils can develop as deep as 1.5 m, with removal of sodium by the leaching action of infiltration water. The present situation is characterized by the presence of eroded or poorly developed soils especially in the badlands.[15] Intense animal activities (trampling, overgrazing) and anthropic activities (deforestation, tillage operations, exposure of bare soil surface to weather agents on excessively sloping grounds) favor surface soil erosion, causing small rivulets, rills and gullies. The rate of soil erosion[1] varies from zero to 1–2 mm of soil removed yearly. If gullies are excavated by concentrating overland flow, erosion values in a field can attain 2–4 mm of soil loss in a single rain event. Excessive animal grazing facilitates gully erosion, soil slips and mass movements. Cropland management requires tillage (deep ploughing, seed bed preparation) and sometimes large earth movements. All these activities[16][17] cause a net movement of soil from the upslope side of the field to the downslope side. Soil in the upslope side of the field is lost at rates between 1 and 4 cm yearly. For medieval tilling techniques, the estimated erosion rate would have been around 2 cm/year. Considering an alternation of years with and without ploughing, 300 years would have been enough to expose the subsoil still rich in sodium. Sodium gives dispersive characteristics to the clay, making it very erodible, hence increasing the velocity of rain-induced erosion.

The first half of the fourteenth century was characterized by social unrest due to the transformation from farmers who owned their land to large land holdings with the property subdivided into poderi. Each pderi was managed by a farmer (mezzadro) and his family living on the fields in a crop sharing system.[18] At the same time foreign armies (e.g. Henry VII's, mercenaries) passing through the Sienese territory interfered with normal activities in the countryside. Hence, erosion and floods are testified in several documents,[19] including t Lorenzetti's Buongoverno frescos (1340) that show biancanas while severe floods are reported.[19] The climate was characterized by droughts and extreme events[19][20] that led to a shortage of food in Italy and necessitated imports from abroad. This forced Siena to invest a large part of its wealth in facing these difficulties, and divert funds from other priorities such as flood prevention.

In the second half of the 14th century the abrupt and large demographic decrease due to the plagues resulted in the farming population of small owners and mezzadri needing to manage twice as much livestock and land per capita. With no resources for maintenance, the only use for a severely eroded field was animal grazing. Hence, the eroded fields became irrecoverable. The lack of personnel persisted for about two centuries during which the eroded areas expanded, reaching a maximum in the 19th century.

This picture is substantially confirmed by soil denudation rates estimated using average erosion in the basin of the river Ombrone, which drains the area, and on the denudation rates of the two largest biancanas of the Leonina site and the gully in between.[1]

Biancana badlands reclamation began at the end of the 19th century and ended during the second half of the 20th century when bulldozers removed almost all the biancanas and some of the smallest calancos, encouraged by EU subsidies then available under the Common Agricultural Policy.[21][22] Thus it can be said that damage mainly due to an epidemic (Black Death) was eventually solved by the EU-CAP of 1960-2000.

The natural and social history of the Crete Senese does not leave much room, either temporal or spatial, for any physical desert. Nevertheless, there certainly were large areas that progressively became severely eroded and devoid of vegetation. The Accona podere when Bernardo Tolomei retired there in 1313 may have been in poor condition, certainly without any mezzadro. Hence, in all likelihood, the desert of Accona referred at first to the absence of farmers in Accona and/or the lack of strong spiritual leadership, a role that the Olivetans had filled. Later, between 1830 and 1850 when the badlands were at their maximum, the label "Accona desert" was adopted by scholars and learned persons[23][24] to convey the feeling of desolation felt when in the midst of the biancana fields or the calanco gullies.