Abstract

This is a study of Chilean arid Altiplano and Puna vegetation (24-25°S) using Braun-Blanquet phytosociological methodology. New altitudinal limits for bioclimatic belts are proposed: supratropical (3.400-3.800 m), orotropical (3.800-4.200 m), criorotropical (4.200-4.700 m), athermic (>4.700 m). As a result of the phytosociological analysis, the following main vegetation units were identified: Ambrosio artemisioidis-Atriplicion imbricatae all. nov. (desert scrubland), Calamagrostietea vicunarum Rivas-Martinez and Tovar 1982 (xeromorphic grasslands and dwarf scrubland), Anthochloo lepidulae-Dielsiochloetea floribundae Rivas-Martinez and Tovar 1982 (vegetation of solifluxional gravelly slopes) and Plantagini rigidae-Distichietea muscoidis Rivas-Martinez and Tovar 1982 (high-Andean mires and bogs). Twelve floristic associations were identified. Each was characterised in terms of floristic composition, general physiognomy, geographic distribution, altitudinal range and environmental conditions. The study area is in a climatic transition zone. However, the hypothesis of a resulting floristic transition is not sustained since the flora and vegetation of the study area reveal strong affinities with subtropical Andean, not with Mediterranean Andean. One alliance, Ambrosio artemisioidis-Atriplicion imbricatae all. nov. has been created to identify the Andean Atacama desert dwarf scrubs, which at the moment cannot be included in any order or class. In addition, six new associations were typified for the study area: Acantholippio deserticolae-Atriplicetum imbricatae, Adesmio melanthis-Artemisietum copae, Fabiano bryoidis-Adesmietum erinaceae, Adesmietum frigido-echinoris, Mulino crassifolii-Deyeuxietum crispae and Puccinelio frigidae-Calamagrostietum eminentis. Also, four provisional associations are proposed: Stipo frigidae-Adesmietum caespitosae, Nicotianetum petunioidis, Senecionetum chrysolepidis and Lycietum humilis; a provisional alliance, Lycion humilis, is proposed for the latter. In the phytosociological units, the floristical components are relevant at alliance level. The supratropical alliances have desertic characteristics, while the orotropical and criorotropical alliances have principally Puna characteristics. Cosmopolitan plants predominate in the azonal alliances. The study area is located in a transitional climatic zone despite the fact that the hypothesis of a consequent floristical transition is not supported because the flora and vegetation of the study area reveal a strong affinity with Andean-subtropical, not with Andean-Mediterranean.