The nurse-plant effect of Prosopis flexuosa D.C. (leg-mim) in a dry valley of the Bolivian Andes

Abstract

The role of Prosopis flexuosa D.C. (Leg-Mim) as a nurse plant for establishment of other plant species was evaluated in an Andean semiarid dry valley of Bolivia (Mecapaca, La Paz). It is the first study that evaluates possible plant-plant positive interactions in these xeric environments. Abundance and species richness under the crown of P. flexuosa were recorded and compared to those in open spaces lacking the influence of any kind of canopy. In all, 21 species between woody plants and big perennial herbs were recorded under the canopy of P. flexuosa (3-4 species/tree), while 17 species occurred in open areas (13species were common to both; Sörensen index = 0.34). The abundance of three Asteraceae species: Baccharis boliviensis, Viguiera australis and Verbesina cinerea was significantly higher beneath the canopy of P. flexuosa than in open spaces, which suggests quantitative rather than qualitative benefits of P. flexuosa as a nurse plant. Moreover, individuals of Corryocactus melanotrichus (Cactaceae), Dodonaea viscosa (Sapindaceae) and Krameria lappacea (Krameriaceae) were more abundant outside than underneath shrubs, suggesting that these species can establish in open areas. We postulate that P. flexuosa may modify the spatial pattern of small shrubs affecting species replacement rather than species enrichment. We discuss how species replacement may contribute to increase the local diversity and, mainly, to a possible dynamic patch structure