THE SUBANTARCTIC TIERRA DEL FUEGO: NOTHOFAGUS FORESTS OF DISTRIBUTION, STRUCTURE AND PRODUCTION

加泰罗尼亚语； 瓦伦西亚语. 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. Leaves on the tree may last up to 7 years, with an average density of 17 mg cm,2 . In contrast, the leaves of N. pumilio are shed in autumn and reach only 8 mg cm,2 . 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. Leaf area indices range between 2.3 and 2.8 m 2 m,2 for the deciduous forest and from 2.5 to 4.5 m 2 m,2 for the evergreen forest. It appears that tree standing biomass ranges between 6.0 and 1 3.6 kg e m'2 in the deciduous forest, and between 10.5 and 1 5.6 Kg e m,2 in the evergreen forest. Production varies from 148.0 to 372.1 g e m ,2 yr , 1 , and from 204.6 to 346.4 g e m ,2 yr,l , 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.