Estructura básica generada por el arbolado en pastos semiáridos (ecosistemas de dehesa)

A study was made of the effect on spatial distribution of species from semiarid grasslands. The basic structural aspects considered were: num- ber of species, exclusive species, and dominant species. Comparisons were made among the sites: under crown, canopy edge, and open grassland; in all three cases the N-S orientation was taken into account. The reduced number of species below the crown contrasts with the much higher number found at the canopy edge. However, in the latter case there were almost no exclusive or dominant species present since, owing to its intermedíate position, the most contrasted ecological charac- teristics correspond to the location receiving the most direct influence of the tree canopy and to the open spaces. Additionally, the similarity between the locations under the crown and the N exposure of the edge, and between the open spaces and S exposure of the edge leads to different results, according to whether orientation is considered or not