Resumen

CASTRO HERNANDEZ, J. C; WOLF, J. H. D; GARCIA-FRANCO, J. G  y  GONZALEZ-ESPINOSA, M. The influence of humidity, nutrients and light on the establishment of the epiphytic bromeliad Tillandsia guatemalensis in the highlands of Chiapas, Mexico. Rev. biol. trop [online]. 1999, vol.47, n.4, pp.763-773. ISSN 0034-7744.

In the highlands of Chiapas, rapid habitat destruction and alteration threaten epiphytes. Presumably, forest transformation increases open and border-type vegetation, characterized by drier conditions than those prevailing deeper in the forest. If so, mesic epiphytes should be especially affected. We investigated the role of water availability during the growth of a population of the wide-ranging mesic C3 phytotelm bromeliad Tillandsia guatemalensis. Chiapas experiences a pronounced dry season from November to April when average monthly precipitation falls below 30 mm. T. guatemalensis observed in situ released seeds during this interval and high germination rates occurred about seven weeks after the rainy weather returned (over 93%, an observation confirmed in the laboratory). Many of the tiny seedlings disappeared before they could anchor to the substrate, probably flushed off by torrential rains. Over half of the seedlings comprising a naturally established population died during the dry season. High seedling mortality was also deduced from the size-class structure of natural populations. Seedling mortality on bark taken from the tree base up to a height of 1.3 m of bigger trees is similar on two species of oak compared to two species of pine. These barks also possessed high water retaining capacity. Oak bark derived from higher up the tree, however, absorbed a larger amount of water per surface area and liberated water during a longer period of time than the bark of Pinus tecunumanii taken from similar locations on the host tree. Additionally, the water retaining capacity of the bark of larger trees was generally greater. We suggest that such differences in water retaining capacity explain, at least in part, why epiphytes favor oaks, the lower parts of pine trees, and larger (older) trees. After the development of the phytotelm growth form, mortality in a natural population falls. Our experiments on phytotelm plants that appeared stressed after being transplanted out of their original habitat suggest that nutrients are limiting growth.

Palabras clave : Bromeliaceae; epiphytes; germination; host preference; phytotelm bromeliad; pine-oak forests; plant population structure; seedling establishment.