The Flora of the Fuego-Patagonian Cordilleras: Its Origins and Affinities*

Revista Chilena de Historia Natural 56: 123-136, 1983 The Flora of the Fuego-Patagonian Cordilleras: its Origins and Affinities* Flora de las cordilleras de Tierra del Fuego y de la Patagonia: sus origenes y afinidades DAVID M. MOORE Department of Botany, Plant Science Laboratories, The University, Whiteknights, Reading, RG6 2AS, England ABSTRACT The cordilleras of Tierra del Fuego and southern Patagonia contain floristic elements which reflect both their histories and present conditions. The mountains to the west and south of the zone, repre- senting the southernmost extension of the Andes, are the wettest and highest of the region and their species show some Antarctic affinities. The other Fuego-Patagonian mountains are lower and drier, with their plants demonstrating many affinities with lowland Patagonia and the eastern Andes and pre- cordilleras further north. Nevertheless, the large number of orophytic species which occur at lower elevations testifies to the youth of the southern montane floras, which have moved upwards during the 16,000 years since the last glaciation. The endemic SPecies and genera in these zones indicate that they have immigrated to these areas from the south, from the east and from the north. Key words: Floras, Fuego-Patagonia, orophytic species, post-glacial. RESUMEN Las cordilleras de la Tierra del Fuego y de la Patagonia austral comprenden elementos que reflejan sus historias y, tam bién, las condiciones actuales. Las sierras a1 oeste y a1 sur de esta zona, que representan el extremo más austral de la Cordillera de los Andes, son las más humedas y las más altas de la region y sus especies ostentan afinidades antárticas. Las otras sierras fueguino-patag6nicas son más bajas y secas, y sus plantas muestran relaciones con las floras de la meseta patag6nica y con la precordillera más a1 norte. Sin embargo, el gran numero de especies orofiticas que crecen en elevaciones más bajas demues- tra la juventud de la flora de todas las cordilleras del sur que han migrado hacia arriba durante los 16.000 aiios despues de la ultima glaciaci6n. Las especies y generos presentes en estas zonas indican que elias inmigraron desde el sur, el este y el norte. Palabras claves: Floras, Tierra del Fuego, Patagonia, especies orofiticas, post-glacial. INTRODUCTION lower ground south of 44° S lat., at least west of the Andes (Briiggen 1950, Vui- Although the origin of the Cordillera llemier 1971 ). Such cover was intermit- de los Andes and its attendant moun- tent, since the glaciers advanced and re- tain ranges may be traced back some treated four times; the most recent retreat, 100 million years to the Cretaceous period, in the aftermath of which we now live, they did not attain their present altitude began about 16,000 years ago. However, until the Upper Pliocene, about 2 million the persisting glaciers in Fuegia (Cordillera years ago (Briiggen 1950, Harrington Darwin and Isla Santa Inés, for example) 1956). Subsequent to that the southern and the extensive icefields of the Hielo cordilleras, our concern here, were subject- Patagónico Sur serve as a reminder that the ed to the Pleistocene glaciations which glacial retreat is still not complete in these covered all the mountains and much of the regions. * Paper presented in the Symposium "Biogeography and Evolution of the Andean Flora" held during the IV Meeting of the Botany Section, Sociedad de Biologia de Chile, 7-10 September, 1982, Antumapu, Santiago. (Received 24 May 1983. Accepted 2S September 1983). 124 MOORE The southernmost parts of the Andes, the influence of the Hielo Patag6nico which attain maximum altitudes of about Sur and the glaciers to which it gives rise. 3300 m in southern Patagonia and about To the west of the cordillera, on the islands 2500 m in Tierra del Fuego, constitute of the west Patagonian channels, the tree- a barrier to the moisture-laden winds line becomes increasingly lower and ill- which prevailingly blow from the south defined under the effects of the exposed, and west. As a result of this there is very oceanic conditions so that towards the much more precipitation to the west and outer parts of the Chilean archipelago south of these mountains, while the lower trees are largely confined to well-drained ranges lying in the rain shadow to the east coastal sites and sheltered valleys. The of the main cordillera in Patagonia and drier mountains of the 'Marginal Cordi- to the north in Tierra del Fuego are much llera' along the Argentinian-Chilean frontier drier. to the east of Ultima Esperanza have a In addition to the differences, already tree-line at about 600-800 m in their noted, in altitude and precipitation be- southern part (e.g. Sierra Dorotea, Sie- tween the Andes and the ranges of the rra del Cazador). However, further north, Marginal Cordilleras (Kranck 1932) in in the region of the Sierra Baguales-Sierra their rain shadow, there are also geologi- Vizcachas, there are no forests and the cal differences of importance to the plant- transition to an orophytic zone is marked life. The main mass of the southern Andes by less obvious changes in the structure is composed of strongly deformed and met- and floristic composition of the vegeta- amorphosed Palaeozoic to Jurassic mica- tion. and quartz-schists, penetrated in many places by lower Tertiary granites and grano- THE VEGETATION diorites, and flanked by dark slates (grey- wackies), marls and quartz-porphyries. The orophytic zones of Fuego-Patagonia, West and south of these the Jurassic-Low- as circumscribed above, contain a rela- er Cretaceous igneous greenstooes and tively small number of vegetation-types; the Jurassic 'Andean diorites' form the however, they intergrade so frequently Fuegian and western Patagonian archipel- that it is often difficult to obtain a clear agos. All these rocks· weather rather slow- picture, particularly in view of the nume- ly to give only skeletal lithosols initially. rous local variants. Nevertheless, by consi- In contrast, the 'Marginal Cordilleras' derable simplification, 6 principal structur- are largely composed of Cretaceous sedi- al types of community can be seen to ments -sandstones, clay-slates, marls and form the basis of the montane vegetation conglomerates- which are strongly folded, in these austral regions -cushion heath, with the beds often vertical. These softer grass/cushion heath, dwarf-shrub heath-, rocks erode to give deeper, clayey soils, montane meadows and two quite different which are very subject to solifluction at kinds of feldmark or 'desierto andino', higher elevations. depending upon the substrate. Although not entirely satisfactory, the delimitation of an orophytic flora and Cushion Heath. Throughout much of vegetation in most Fuego-Patagonian Tierra del Fuego, except the southern mountains can be achieved by basing it and western parts of the archipelago, on the upper limit of the forests (Moore and in the southern parts of the 'Mar- 1975). The timberline, usually comprising ginal Cordillera' in Patagonia, a cushion a dense belt of 'Krumholz' formed by heath dominated by Bola:x gummifera Nothofagus, commonly, but by no means is common at, and extending some dis- always. N. antarctica, lies at an average tance above, timberline. Since this formation altitude of about 550-600 m in Tierra del is rather frequent at lower elevations, it Fuego, though it may be lower on the is not surprising to find that it contains smaller drier sierras and higher {up to many widespread species, both cushion- 700 m) on the larger mountain masses. forming (e.g. Abrotanella emarginata, Azo- North of the Estrecho de Magallanes the rella lycopodioides, Colobanthus subulatus situation is somewhat more varied. Along and Drapetes muscosus) and not (e.g. the flanks of the Cordillera de los Andes Acaena magellanica, Empetrum rubrum, the tree-line lies at about 640-750 m, Festuca contracta, Luzula alopecurus, Ly- though it may be greatly depressed under copodium magellanicum and Pernettya FLORA OF FUEGO-PATAGONIAN CORDILLERAS 125 pumila). This community provides a ha- in which Empetrum rubrum and, to a lesser bitat for the endemic Tetrachondra pata- extent, Pernettya pumila, are important gonica ssp. fueguina and Onuris alismatifo- occur widely in the orophytic zone, espe- lia in Tierra del Fuego, while such rela- cially where the soils are relatively shallow tively restricted Fuego-Patagonian species as and well-drained with adequate available Saxifragodes albowiana and Acaena te- moisture. Such communities intergrade nera are also largely confined to it. in a complex fashion with the various facies of the cushion heaths referred to Grass/Cushion Heath. In the northern earlier and with the true feldmark to be parts of the South Patagonian 'Marginal mentioned next. In the higher rainfall Cordillera, the Sierra Baguales-Sierra zone of the Cordillera de los Andes and on Vizcachas region, where there is no forest, the mountains of the canales and archi- the lowest orophytic vegetation consti- pelago further to the west, various commu- tutes a grass/cushion heath. In this, Festuca nities of the dwarf-shrub heath occur im- gracillima, which dominates the grassland mediately above the timberline and, prevalent at lower altitudes, is associated indeed, where this is ill-defined or non- with Bolax gummifera. Such communi- existent, grade into the non-montane ties also replace the cushion heath above vegetation in which Empetrum rubrum timberline in several areas further south is also frequently important (Moore in the 'Marginal Cordillera', as on Cerro 1979). The dwarf-shrub heath is probably Solitario and Cerro Castillo, and also further richer in species and includes more com- west on the mountains of Peninsula Anto- munities than any other physiognomic nio Varas. Amongst the most common vegetation-type present in the montane and conspicuous of the communities in- zones of the Fuego-Patagonian mountains. cluded in the grass/ cushion heath may It is, of course, impossible to detail here be noted Acaena magellanica, A.

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