SEASONAL FLORISTIC AND VEGETATIONAL CHANGE IN THE PRE-ANDEAN MOUNTAIN IN PUTRE COUNTY (I REGION OF TARAPACA, CHILE), DURING 2002 AND 2003

Abstract

The pre-andean mountains of the northern Chile (18º 15´S – 69º 33´W) corresponds to a narrow strip which is affected
by the desert at lower altitud to the west, and the Altiplano, a higher plateau at the east. The vegetation in the area also
presents an altitudinal variation, and the pre-andean mountains constitutes the second of four altitudinal floors, commonly
called tolar or pre-altiplano shrubland (sensu Gajardo). Ten sampling sites were studied for life forms of plants, absolute
and relative vegetal cover, plant diversity and species richness of vascular plants before and after summer rainfall (dry and
wet season) in four expeditions during 2002 and 2003 by using transects. The summer rainfall in 2002 was 203 mm,
considered a normal precipitation for the region, whereas the following year presented a lower amount of rain of 84.7 mm
(less than 50% of normal summer rain for the area). The majority of the species of plants (92,9 %) were native (total n=98
species) and the most abundant life forms were chamaephytes, nanophanerophytes and hemicryptophytes. The results
of the transects showed patterns of seasonality; they presented higher vegetal cover, species richness and biodiversity in
wet season. In the dry season nanophanerophytes and chamaephytes, mainly tolas (shrubs in Aymara language), are the
most abundant life forms. Whereas in the wet season therophytes and hemicryptophytes herbs also are present. The
proportional change of vegetal cover between wet and dry season and the presence of terophytes community were lower
in the wet season during 2003, which was dryer than 2002.