High-Elevation Andean Ecosystems orthophylla and Stipa spp Prominent genera include Adesmia, Mulinum, Anthobryum, Baccharis, Chersodoma, Cortaderia, Fabiana, Lampaya, Lophopappus, Margyricarpus, Oreocereus, Parastrephia, and Urmenetea A strong floristic break has been detected between desert puna and southern Andean steppe on the Chilean side of the Andes, whose strongest manifestation is seen in the lower puna belts This has been attributed to extreme aridity at very high elevations at latitude 24–251 S (Villagra´n et al., 1983) Central Andean Dwarf Polylepis Forest More than 20 species of Polylepis can be found in humid puna, many with restricted distributions (Kessler and SchmidtLebuhn, 2006; Schmidt-Lebuhn et al., 2006) However, species such as P tarapacana found in Bolivia, Peru, and Chile and P tomentella found from Colombia to NW Argentina have wider distributions Polylepis dwarf forests in puna are encountered from about 3700 to 4600 m and in some places they can cover entire high-elevation slopes as on Volca´n Sajama in Bolivia In wet puna the trees are often festooned with mosses, vines such as Bomarea, Loasa, Mutisia, and Passiflora, mistletoes (Tristerix spp.), and many epiphytic flowering plants (Gala´n de Mera et al., 2003) Cushion Bogs and Salar Vegetation Extensive high azonal elevation bogs (bofedales) are found throughout puna becoming progressively smaller, more widely spaced, and floristically impoverished toward the southern puna limit (Arroyo et al., 1988) Bofedales in humid puna tend to intergrade with the zonal vegetation, whereas in dry and desert puna they become more conspicuous on account of their dark green color contrasted against the more zonal puna vegetation The flora of these bogs tends to be more uniform latitudinally than the surrounding zonal vegetation (Arroyo et al., 1988), and includes cushion species of Oreobolus, Distichia, and Oxychloe, together with species of Scirpus, Juncus, Calamagrostis, Lachemilla, Colobanthus, Werneria, Aa, and Gentiana The large latitudinal distributions of bog taxa have been attributed to good dispersal and the availability of similar azonal conditions along the Andean chain independently of macroclimatic differences Large saline deposits representing ancient lakes are also common throughout dry and desert puna (Arroyo et al., 1988) Some of the typical cushion bogs species are able to survive on their edges where there is still some water, but such species as Distichlis humilis, Muhlenbergia fastigiata, Salicornia pulvinata, Lampaya spp Suaeda foliosa, Tessaria absinthoides, and Triglochin maritima tend now to be more common (Beck, 1985) 105 lacking From 311 to 341 S on the western side of the Andes, an open treeline of Kageneckia angustifolia (Rosaceae) is found South of 35–371 S closed-canopy forest forming a well-defined treeline appears Treeline species can be deciduous or evergreen species of Nothofagus, evergreen Austrocedrus chilensis, Araucaria araucana, and Pilgerodendron uviferum, depending on precipitation level and degree of continentality N betuloides may form krummholz on the wetter western maritime mountains in the southern canal zone (Wardle, 1998), while N antarctica does so on drier easterly mountains Southern Andean steppe develops over a large range of precipitation conditions Most precipitation (which falls mainly in the winter as snow) derives from a southwesterly Pacific source, and in parts of Argentina, from an Atlantic source Because of the strong west to east rainshadow, the western side of the southern Andes generally receives more rainfall than the eastern side, and this source increases southward to diminish again in the far south The western side of the Andes is still quite arid at 301 S (242 mm at 3700 m; Squeo et al., 1993) and 331 S (445 mm at 2500 m; Santiban˜ez and Uribe, 1990) (Figure 4), but even more so in adjacent areas in Argentina where mean annual precipitation at Puente del Inca (2720 m) is approximately 200 mm (Me´ndez et al., 2006) Southward at 401 S precipitation reaches 1746 mm above a treeline situated at 1350 m (estimated from Hijmans et al., 2005) and occurs in both summer and winter Further south (461 S), but on the eastern side of Patagonian Andes, at an altitude of 1310 m (just above treeline), annual precipitation drops to approximately 717 mm Based on treeline and climatic characteristics, southern Andean steppe should probably be subdivided into a more northerly section to around 35–371 S and a southerly section extending to the end of the continent Southern Andean steppe is mostly dominated by a mixture of perennial herbs, low rounded shrubs and cushions plants, with accompanying grasses, the latter rarely as dominant as in puna Plants of this high-elevation Andean vegetation zone have developed numerous adaptations for survival, including some the highest tolerance levels to freezing temperatures ever reported, these involving different physiological mechanisms (Squeo et al., 1996; Sierra-Almeida et al., 2009, 2010; Southern Andean Steppe Southern Andean steppe occurs south of the puna to the extreme end of the continent The lower altitudinal limit is found at approximately 3200 m at 281 S and at 500–600 m in the extreme south In northern areas a treeline is entirely Figure Tropaeolum polyphyllum in the subandean vegetation belt, southern Andean steppe, 321 S, 2400 m, Valle de Juncal, Chile