Homage to Ramon Marga/ef,' or, Why there is such p/easure in studying nature 351 (J. D. Ros & N. Prat, eds.). 1991 . Oec% gia aquatica, 10: 351 -366 THE SUBANTARCTIC NOTHOFAGUS FORESTS OF TIERRA DEL FUEGO: DISTRIBUTION, STRUCTURE AND PRODUCTION 1 2 2 2 EMILIA GUTIÉRREZ , V. RAMÓN VALLEJ0 , JOAN ROMAÑA & JAUME FONS 1 Departament d'Ecologia. Facultat de Biologia. Universitat de Barcelona. Av. Diagonal, 645. 08028 Barcelona. Spain. 2 Departament de Biologia Vegetal. Facultat de Biologia. Universitat de Barcelona. Av. Diagonal, 645. 08028 Barcelona. Spain. Received: August 1990. SUMMARY Evergreen Nothofagus betuloides and deciduous N. pumilio form the main forest types in Tierra del Fuego. These forests were sampled along two altitudinal gradients to study their structure and dynamics and assess the causes of their distribution. The distribution pattems of the two species of Nothofagus seem to respond to different climates and soils. The dornÍnant soil processes are hydromorphy in the evergreen forest and podzolization in the deciduous one. N. betuloides is an evergreen resilient to short-term environmental fluctuations, due to its ability to retain nutrients. 2 Leaves on the tree may last up to years, with an average density of mg cm, . In contrast, the leaves of 7 2 17 N. pumilio are shed in autumn and reach only 8 mg cm, . In both types of forests the following features can be outlined. Old-growth forest stands develop in the middle and lower slopes. The distribution of diameter sizes of the trees usually shows a pronounced bimodality. Recruitment is discontinuous as shown by the spatial pattem of tree sizes, and regeneration is vegetative in the upper slopes. 2 2 2 2 Leaf area indices range between and m m, for the deciduous forest and from to m m, for 2.3 2.8 2.5 2 4.5 the evergreen forest. It appears that tree standing biomass ranges between and kg e m' in the deciduous 2 6.0 13.6 forest, and between and Kg e m, in the evergreen forest. Production varies from to g e 2 10.5 15.6 2 l 148.0 372.1 m , yr ,1, and from 204.6 to 346.4 g e m , yr, , respecti vely. In relation to boreal forests, biomass can be considered high, but production is medium to low. The relation of wood production to leaf biomass shows that N. betuloides be ha ves similar to coniferous forests and N. pumilio as hardwood forests. There is much accumulation of organic matter on the forest floor, especially coarse wood debris, reflecting the stage of development of these forests and the unfavourable conditions for litter decomposition. KEY WORDS: Nothofagus, production, forest structure, regeneration, forest soils, Tierra del Fuego. INTRODUCTION (Mirb.) Oerst. is the main constituent of the evergreen Magellanic forest, whereas N. The forests of Tierra del Fuego extend pumilio (Poepp. and Endl.) Krasser forms along the southernmost foothills of the the deciduous forest. The third species, N. Andes, between 53° 30' and 56° South (Fig. antarctica (Forstf.) Oerst., also deciduous, 1). They are formed by three broad-Ieaved is restricted to the 1east favourable habitats. species of Nothofagus. N. betuloides The forest ecosystems of Tierra del Fuego 352 GUTIÉRREZ, VALLEJO, RO MAÑA & PONS are poorly known, with the possible and l.7 oC in winter (Fig 2). Thus, the exception of their floral composition. average annual variation is less than 8 oC. Geographical location and climate have Strong winds are the other climatic both contributed to this lack of studies, characteristic of the zone. Climatic even though peculiar environmental subzones are caused by the mountains of conditions make this region a place of the Andes, which in Tierra del Fuego considerable scientific interest. It is the change direction and run from west to east, closest area to the South Pole not covered bordering the westem and southem coasts. by ice. The influence of the Andes, The Andes, as in the rest of the South Quatemary glaciations and the nature of the American continent, are the great structural substrate formed mainly by metamorphic element of the landscape. The distribution and vo1canic rocks, have shaped a unique and type of ecosystems are, to a great landscape. extent, determined by the presence, Tierra del Fuego is a group of islands to arrangement and elevation of the the south of the Magellan Straits, and only mountains, which were lifted in the 1,170 km from Antarctica. The disjunctive Pliocene. The altitude of the Andes in distribution of living Nothofagus attests to Tierra del Fuego is not great, yet sufficient an ancient trans-Antarctic forest belt. to slow down the clouds from the Pacific Nowadays, the proxirnity to this continent ocean. is reflected in the climate, which is much Gradual preclpltation has created a colder than that of the Northem gradient ending in steppes. Consequently, Hernisphere at the same latitude. The the coastal strip occupied by evergreen climate is cold-temperate without forest has a cold-temperate climate with pronounced thermal oscillations during the high humidity (Cfk' c, according to the year. Koppen classification; PISANO, 1981). The Measurements taken at Ushuaia, area occupied by N. pumilio runs between representative of the forest area, show an the steppe and the evergreen forests. The average temperature of 9.4 oC in surnmer climate in this zone is cold-temperate with TIERRA DEL FUEGO *¡Ushuaia � + -�Wil��_ O. o 10 Km PACIFIC t::::-.. OCEAN Cape Horn FIGURE L . Location map. General distribution of Nothofagus forests on Tierra del Fuego. The striped area corresponds to the deciduous N. pumilio forest and the unstriped coast to the evergreen N. betuloides forest. The samples were taken in the Valle de Andorra (*) and the Costa de Moat (+). NOTHOFAGUS FORESTS OF TIERRA DEL FUEGO 353 steppe degeneration (Dfk'c; PISANO, than 50 cm and N. antarctica usually 1981). Both types of forest are situated appears as an accompanying species. within the c1imatic limits of conifer forests Studies on the forests of Tierra del (Fig. 3) (HAMMOND, 1972). Fuego have been mainly descriptive, The flora and fauna of the different especially biogeographic and taxonomic. terre s tri al ecosystems of Tierra del Fuego Outstanding works are those of PISANO reflect the past and present effects of recent (1975, 1977, 1981) and DIMITRI (1982). glaciations, c1imatic changes, and Fluctuations in the extension of the forests exogenous disturbances. This last factor is based on pollen profiles as well as on other cited by PISANO (1975) as a lack of paleoecological features have been homeostasis. described by AUER (1960), MARKGRAF On the forested mountain slopes (1977) and VUILLEUMIER (1971). The numerous landslides bring ab<?ut strong c1imatic conditions, rainfall and temperature geomorphological and soil dynamism on patterns have been analysed by ZAMORA different scales. Strong winds and shallow & SANTANA (1979 a, b) and SANTANA rooting cause many tree falls, creating gaps (1984). Special reference should be paid to of different sizes and with the soil churned the work of SCHMIDT & URZÚA (1982) up and disturbed to varying degrees. Large on the structure and production of N. quantities of wood debris are accumulated pumilio, focused on forest management and on the forest floor, in relation with the timber production. The foliar anatomy of old-growth forest stand s in sorne areas, and the species of Nothofagus has been studied the unfavourable conditions for by RAGONESE (1981) and the xylem decomposition. anatomy by RIVERA (1987, 1988). We The severity of the c1imate marks an recently presented the first results on sorne altitudinal gradient in the vegetation. The aspects of soil-plant relationships for both tree line rarely surpasses 700 m a.s.l. at types of forest (GUTIÉRREZ et at, 1989). these latitudes. There is, however, a lack of quantitive The morphology and degree of studies on most of the ecological aspects of development of the trees are related to the these forests. The results of comparative altitudinal gradient. In the upper part of the studies carried out in the N. pumilio and N. forest and along a strip of more than 40 m betuloides forests are presented in this aboye the timberline, trees take on a study. We have analysed the possible bushlike aspect, known as krummholz. At the tree line the height of the trees is less � GRASSLAND PICAL f'OREST -----t:::::¡;:� HZ § %W7P USHUAIA T = 4.5 "­ � m p= 550 E f'OREST Alt. 14 5 � � 50 100 ---/// 40 80 {.ZZ. 30 60 Nothofagus pumi1 io forest 1II N. betuloides f"orest 20 40 10 20 O O MEAN ANNUAL PRECIPITATION (cm) F M A M A S O N D FIGURE 3. The ecoclimatic position of Nothofa gus forests of Tierra del Fuego among the major terrestrial FIGURE 2. Climatic diagram according to the data ecosystems in the ecoclimatic space defined by from Ushuaia, Tierra del Fuego, 54° 48'S and 68° average temperature and precipitation (modified from 19'W. HAMMOND, 1972). 354 GUTIÉRREZ, VALLEJO, ROMAÑA & PONS causes of the distribution of the two species the higher slopes of the mountains. of Nothofagus, the forrner deciduous and The evergreen forest was sampled in the the latter evergreen. area of Costa de Moat where the Beagle Climatic conditions are considered to be Channel exits towards the Atlantic, at the primary cause of the distribution of around 110 km east of U shuaia. Although these Nothofagus species, but other factors c1imatic data are not available for this site, may also come into play. Soil it is wetter and warmer than the Valle de characteristics may have a relevant role as Andorra. The area receives between 700 well. On the other hand, apart from the and 1000 mm of rainfall annually research carried out by SCHMIDT & (ZAMORA & SANTANA, 1979a).