Comparision between two tropoandean ecosystems: the chilean "puna" and the ecuadorian "paramo"

This survey is a preliminary, comparative study of the phyto-ecologic features of two great types of ecosystems of the Andes mountain range.

It deals with the Chilean "puna" in northern Chile (volcanic region of the Pallachatas, lsluga, Guallatire, and Colorado hills all of which are over 6.000 m above sea level) and the Ecuador paramos (volcanic regions of Cotopaxi and Rumiñahui in the west and the central range of the country).

Numerous samples were collected in the field according to the Canfield lineal method and

the Braun-Blanquet one. The data were used to establish the frequency percentage, prevalence, covering, and importance index of shrubs and herbaceous species representative of vegetal formations. These groups were found on the vegetal range floor of the "puna"and "paramo" fover 3.000 m above sea level). They proved to have a very similar composition in gender and family but they are different at the level of species. There were only two plants. Stipa-ichu and dense Azorella which presented a high index of common representativeness in both ecosystems.

This botanical variety is mainly due to the different ways that the definitive ecological factors affect the development of herbaceous species. In the "paramo", there are some factors that help the development of extensive shrub and herbaceous communities, such as, favourable exposition, high atmopheric humidity, and high rainfall. All of these help provide a high degree of cover and a dense physiognomy. Meanwhile, in the "puna" there are some factors, such as the high atmospheric dryness, low rainfall, and the existence of unfertile soils which are appropriate for the development of plants adapted to dryness, cold, and wind. They contribute to the formation of open intermediate altitude shrubs and rangelands lower in altitude than in the "paramo".

The comparative tables and the vegetal profiles show the predominance of herbaceous

species in the high mountain communities and the extense altitudinal distribution of these. Some are living close to the lower limit of the eternal snows of the volcanoes.

Specific, morphological, and physiological functions of the plants would explain the great

ecologic adaptability of these species to exist in mountains over 5.000 m in altitude.