The influence of pine plantations on typical ultramafic plant communities of Tuscany was investigated by means of thirty 5 #xD7; 5 m plots in three environmental situations with different pine canopy cover. The main changes in natural vegetation were an increase in species richness and ground cover, resulting from the spread of alien grassland and woody species, and the almost complete disappearance of therophytes and some of the serpentine plants. The typicalArmerio-Alyssetum bertolonii, an endemic garigue-steppe association characterized by large areas of bare soil, was modified into a grassland community with almost complete ground cover. The main soil changes associated with the presence of a pine canopy were found to be increases in depth and organic matter. Exchangeable cation concentrations increased with pedological evolution and were positively correlated with organic matter content. The positive relationships between soil metal ion content, species richness, and ground cover suggest that hydrological and nutritional soil characteristics were more determinant for typical ultramafic vegetation than soil metal toxicity. Artificial pinewoods may be a serious threat to biodiversity conservation, because the #x3B1;-diversity increase found at the spatial scale of the present study would correspond to a #x3B2;- and #x3B3;-diversity decrease should pine plantations spread to all ultramafic areas.
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