Aportación al estudio de los pastizales leoneses

Resum

The pastures of alliance Xerobromion are developed on calcareous substratums and live in dry sunny places with Mediterranean climate. They are xeromorphic pastures living in places which climax vegetation were completely destroyed. The plants living there show hemicryptophyte biotypes that are able to support the summer dryness but in spring there are a lot of species of therophytic biotypes. They are limited to áreas with annual rain between 700 and 800»mm and get into contact with others pastures when soil depth or humidity increase. We have only located a community of these pastures in Cordillera Cantábrica and we have had problems in the differentiation with other pastures of other alliances specially Aphyllantion forming with it mosaics and transitions. There are also clear contacts with pastures of alliance Mesobromion. In the studied áreas the pasture is a tough, xerophytic, herbaceous formation filling between 50 and 60 % oí the surface, furnishing spring pastures little desirable for cows but it is a good pasture for sheep.