Vegetation ecology and conservation on Tuscan ultramafic soils

This article provides a review of studies concerning the floristics, vegetation description and ecology of the ultramafic (serpentine) soils of Tuscany, central Italy. After a concise history of geobotanical research on Tuscan ultramafic outcrops since the end of sixteenth century, the features of the flora are summarized. The most significant vegetation types are concisely described and their ecology discussed in the following section. The role of soil nickel toxicity in limiting vegetation development is reconsidered and appears less important than are drought and nutrient stress. Drought stress also has a special role during exceptionally dry summers, which can occasionally occur and significantly reduce vegetation structure by causing the local extinction of many late-successional species. Nutrient-addition experiments and permanent plot monitoring provided additional evidence supporting the drought and nutrient stress hypothesis. The last section of this article discusses the main threats to the conservation of the unique plant diversity of Tuscan ultramafic environments, the most significant of which are quarrying and pine plantations. Pine plantations, mostly established for soil amelioration and erosion control, determine not only the increase in vegetation cover and diversity but also a trend for serpentine endemic and rare species to disappear.