Beziehungen zwischen mikroklimatischen Faktoren und natürlicher Verjüngung araukano-patagonischer Nothofagus-Arten

Abstract

Summary Climatic conditions under which Nothofagus species regenerate spontaneously were investigated. For this purpose, temperature and relative humidity of the air in the herb layers of numerous habitats in Southern Chile were recorded between the latitudes 37°30′ and 42°30′. In the North of the above region, summer climate is determined by radiation and irradiation processes, strongly modified by topographic factors. The influence of maritime winds increases southward, and for these reasons, the mosaic of microclimates and plant communities manifold in the North, become more simple to the South Daily temperature fluctuations were used to appraise continentality of the stands. To caracterize the thermic requirements of the species, temperature averages of complete days (from 0 to 24 hrs.) and of the warmer half-day (from 10 to 20 hrs.) were used. The latter values in relation to saturation deficit of the air were used to describe xerothermic conditions of the regeneration habitats The above values are used to determine ranges of tolerance of the different species. To characterize optimal conditions of the latter, daily average temperature curves were calculated. By means of a statistical analysis, probability of the occurrence of nocturnal freezing in the summer season was determined for typical habitats of the species Results are discussed, relating them with climatic and fitogeographic aspects: Nothofagus obliqua proved to be extraordinarily thermophilic with a certain continental tendency. This species is characteristic for occasional dry zones, even invading the region of sclerophyllous forests, but it does not reach up to the litoral zone. The regeneration habitats of Nothofagus antarctica present strong daily amplitudes and therefore, are considered as relatively continental. Nocturnal freezings are frequently observed during the summer. Similar to the former species, it also supports considerable dryness. Accordingly with these characteristics, N. antartica reaches up to the Patagonic grasslands. Nothofagus procera is a tree of the subandine region. This species, with respect to its climatic requirements, occupies an intermediate place. In relation to continentality, it coincides with N. obliqua , and relative to its thermic requirements is comparable to N. dombeyi . Preferring habitats with deep soils, in these conditions the tree even supports considerable deficits of air saturation. N. procera shows greater affinity with evergreen species than the other decidous Nothofagus . In the “typical habitat” of this tree, the frequency of freezings is relatively low, due to nocturnal warm air currents. Nothofagus pumilio , as N. antarctica , is an andine, subantarctic species, although it displays less marked continentality. Its ecological range is clearly displaced towards low temperatures. It requires rather high relative humidity and regenerates with preference in shadowy sites. Compared with the decidous Nothofagus mentioned before, following evergreen species present a more distinct tendency for oceanic climate. Nothofagus dombeyi , which possesses the greatest ecological range, occurs optimally on humid slopes of the West side of the Andes. Nevertheless, in an oceanic climate, it is also able to propagate in sporadically dry and warm stands The range of tolerance of Nothofagus nitida is more reduced than the above species. It is the only tree not present at the Eastern side of the Andes. This species regenerates in stands with constant humidity and intermediate thermic conditions. It shows a special adaptation to wet soils, and this property is essentially the ecological difference between this species and N. dombeyi . Nothofagus betuloides forms the “maritime timberline” in Southern Patagonia. Their habitats are characterized by relatively low temperatures, reduced thermic fluctuations and strong winds. Relative to their climatical ecological range, it is evidently inferior to that of N dombeyi and superior to N. nitida