Structure and species diversity of Bromus erectus grassland of biancana badlands

Species richness, diversity and structure were studied in Bromus erectus grasslands on the top of biancana landforms of the Orcia Valley, Tuscany (central Italy). Three community types were recognized : uneven B. erectus grasslands on less stable morphologies, and compact B. erectus grasslands and B. erectus grasslands colonized by Spartium junceum scrub, both on more stable morphologies. The main difference between them was a dramatic decline in species richness and diversity from the former to the latter. The number and cover of annual herbs, many of which are low-growing species (e.g. legumes and graminoids), also decreased significantly in the same order. The frequency of B. erectus was constant (100%) in all three types of community, whereas percentage cover increased sharply (54.2 vs. 85.5%) between uneven and compact grasslands, remaining high in the scrub communities (83.8%). Cover of phanerophytes showed low values in the uneven and compact grasslands, but reached 80% in the scrub communities. The increase in cover of B. erectus caused the disappearance of species typical of the pioneer vegetation of Pliocene clay soils with Artemisia cretacea. Colonization of the compact grasslands by S. junceum induced a reduction in grassland species of the class Festuco-Brometea. The implications of these findings for the conservation of B. erectus grasslands and biancana badlands are discussed.