Abstract
The floristic composition and species richness of the western (moister) and eastern (dryer) areas of the high Andean region of Nahuel Huapi National Park (Argentina) were compared. Species lists were compiled for the two sectors from collections in the alpine area of 20 mountains of the Park (10 from each sector) from 1993 to 1997. A total of 232 species, 111 genera and 48 families were recorded. Asteraceae (with 70 species), Poaceae (17), Apiaceae (12), Fabaceae (11) and Scrophulariaceae (11) are the predominant families in the area, and Senecio (with 22 species), Nassauvia (12), Acaena (7), and Perezia (7) are the best represented genera. There are six endemic species in this protected area. The most frequent life forms are perennial herbs and subshrubs, followed by shrubs, and annual species are nearly inexistent. Species richness was found to increase in relation to the precipitation decrease from west to east: 149 species were found in the moister westem sector and 220 in the dryer eastern sector. Some families and genera are more represented or appear exclusively in one of the two sectors. We discuss current ecological and past historical factor s that could explain this variation in spedes diversity and composition.
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