Revista Chilena de Historia Natural 82 (2): 171-184, 2009
RESEARCH ARTICLE
Floristic changes in alpine plant communities induced by the cushion plant Azorella
madreporica (Apiaceae) in the Andes of central Chile
It is well known that the number of plant species associated with nurse plants increases
with elevation. However, studies conducted so far have largely ignored the effect of nurse plants on other community attributes, such
as the species abundances, diversity and evenness. Moreover, changes in these community attributes along environmental gradients
have also been seldom examined. The present study evaluates the effect of the cushion plant Azorella madreporica
(Apiaceae) on species richness, species abundance, diversity and evenness of vascular plants at two elevations in the Andes of
central Chile. Theoretically, the impact of this nurse cushion plant on these community attributes should be grater at a higher elevation.
Results showed that the proportion of plant species associated with cushion plants increases with elevation, and the abundance of
some species is also greater within cushions than on bare ground. Although the proportion of species growing within cushions
increased with elevation, diversity and evenness were higher on bare ground. This is due to some few species that attained very high
densities within cushions, generating assemblages highly dominated by some few species. Ordination analyses indicated differences
in species assemblages within and outside A. madreporica at the higher elevation. Therefore, the influence of cushion
plants on community structure changes with elevation. Accordingly, we suggest that attributes other than species richness must be
included in future studies in order to analyze the impact of nurse species on community structure along environmental gradients.
Key words:
positive associations,
community structure, elevation, environmental gradients, nurse effect
