Tesis Maestría en Ciencias en Recursos Naturales y Desarrollo Rural El Colegio de la Frontera Sur 1997

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In the highlands of Chiapas, rapid habitat destruction and alteration threaten the survival of epiphytic populations. One of the presumed effects of the transformation of the forests is an increase in border-type and open vegetation with more severe desiccation than in the nucleus of primary forest. Hence we expect that in particular populations of mesic epiphytic species should be affected. In this study we focus on the role of water availability during the development of a population of the mesic C3 green tank-bromeliad, TiUandsia guatemalensis. that is widespread in the region. The climate in Chiapas is characterised by a pronounced dry season from November up to April with an average monthly precipitation <30 mm. It is during the dry season that the seeds of T. guatemalensis are released. Germination in the field occurred some seven weeks after the beginning of the rains and was highly successful (over 93%, an observation confirmed in the laboratory). In our field experiment many of the tiny seedlings disappeared before they could anchor themselves to the substrate and appeared to be flushed off by torrential rains. In a naturally established population of well anchored individuals over half of all seedlings died during the dry season. High seedling mortality may also be deduced from the size-class structure of a natural population. Seedling mortality on bark derived from the tree base up to a height of 1.3 m of bigger trees is similar on two species of oak as compared to two species o f pine. Bark from these origins, also showed a high water retaining capacity. In the case of oaks, however, bark derived from higher up the tree absorbed and released a larger amount o f water per surface area and released water during a longer period in the dry season than the bark of Pinus oocarpa var. ochoterenai trees from similar positions within the host tree. Inglés

Also the water retaining capacity of the bark of bigger trees was generally larger. We suggest that such differences in water retaining capacity explains, at least in part, a preference of epiphytes for oaks, for the lower part o f pine trees, and for bigger trees. After the development of the typical tank growth form, mortality in a natural population is reduced and our experiments suggest, based, however, on stressed plants transplanted out of their original habitat, that during this stage in development nutrients are limiting growth. Inglés

Manejo y Conservación de Recursos Naturales

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