Patterns of species co-ocurrence and richness in small patches of High Andean vegetation.

NUÑEZ, C.,; AIZEN, M.; EZCURRA, C.

JOURNAL OF VEGETATION SCIENCE

Internat. Assoc. Vegetation Science

Año: 1999 vol. 10 p. 357 - 364

1100-9233

In high-elevation communities of the southern Andes,plant cover is low due to severe environmental conditionsand vegetation occurs mostly as isolated small (< 1 m2)patches.Most patches are dominated by flat cushion plants. We evaluatedpatterns of plant species co-occurrence and species affinityfor patches with and without cushion plants and differentspecies richness. We mapped and recorded species compositionof patches occurring within two 20 m x 20 m plots at theNE slope of Cerro Chall-Huaco, Nahuel Huapi National Park,Argentina. In these plots, we identified 32 and 24 plant species,and a maximum of 15 and 12 species per patch, respectively.The community was characterized by positive associationsbetween species. Patches in which either of the commoncushion plants Mulinum leptacanthum and Oreopolus glacialisoccurred sustained richer communities than patches in whichthey were absent. Patches dominated by different cushion plantsdid not differ in species composition, but species differed intheir affinities for patches with different numbers of species.Because richness increased with patch size and patch size withtime, differential affinities of plant species suggest that successionalchanges take place in the patches. Some small herbaceousspecies appear to act as late colonizers, mostly restrictedto species-rich patches. Flat cushion plants are considered ´nurseplants´; they strongly modify micro-environmental conditionsand allow establishment and survival of associated species.Keywords: Cushion plant; High-mountain vegetation; Nurseplanteffect; Southern Andes; Species association; Succession.