Verbreitung und Wasserhaushalt araukano-patagonischer Proteaceen in Beziehung zu mikroklimatischen Faktoren

Abstract

To determine ranges of climatic tolerance under which Proteaceae regenerate spontaneously, thermohygrograph records were carried out in the herb layers of numerous habitats. To characterize optimal conditions of the different species, 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. To characterize ecologic amplitudes, habitational variation of other values was used: Temperature averages of complete days (general thermic requirements), daily temperature fluctuations (continentality), temperature averages and atmospheric saturation deficit of the warmer half-day (xerothermic adaptation). To characterize water relationships, measurements of relative transpiration were carried out and compared with saturation deficits of the leaves. Results are discussed, relating them with phytogeographic aspects. Furthermore a former investigation is taken into account, related with drought resistance of Patagonic evergreen species. Embothrium coccineum being a “facultative tropophyte”, is distinguished by low thermic requirements. Notwithstanding it also invades habitats presenting rather warm conditions during the light period. The frequency of freezings is high in its typical open biotopes. Distribution on small scale is strongly controlled by the light factor. Embothrium is a typical heliophyte with reference to its rapid transpiration. However, stomatal regulation is slow even under considerable water losses. This feature is equalized by a pronounced plasmatic drought resistance as well as by the ability to shed the leaves. Gevuina avellana is a true evergreen tree like all the following species. Its optimum habitat is characterized by warm conditions, rare nocturnal free zings and reduced thermic fluctuations. By all means the ecological range is relatively wide. Corresponding to its ability for establishing themselve in open habitats of convenient climatic conditions, Gevuina — just as well as the preceding species — is one of the most important pioneers following the forest destruction. The water relationships recall to that of Lomatia hirsuta (see below). This is accordant with the fact, that both trees possess extraordinary thermophilic features, considering the phytogeographic region in question. Optimum habitats of Lomatia dentata are similar to that of Gevuina . However, its ecological ranges are much more reduced with reference to the temperature and humidity factors. On the other hand, this species regenerates and competes very succesfully in shadowy stands. Its typical biotopes are situated in the interior of deciduous Nothofagus forests. Because of that corresponding microclimates are little similar to their regional climate, whic is characterized by moderate continental features. Lomatia ferruginea is the only species restricted to climatic conditions of the temperate rain forests. Correspondingly, the optimum biotope presents low average temperature, small thermic fluctuations and high atmospheric humidity. This species represents a typical example for the drought resistance relations of subantarctic evergreen trees: Stomatal transpiration is suspended when saturation deficit reaches up to 10 % or so. Nevertheless, the subletal deficit lies much higher (76 %). This surprising wide safety range is explained as a compensation for reduced efficacy of the cuticle in permanent humid and windy conditions. Lomatia hirsuta forms a prominent contrast to the preceding species. In relation to continentality, it coincides with Embothriurm , and relative to its thermic requirements is comparable to Gevuina . This tree possesses a special aptitude to occupy xerothermic habitats. Drought resistance is chiefly based on diffusion resistance of the cuticle, and transpiration is very strongly reduced when water losses arrive at a critical value.