Ecologia de populações de Lytocaryum hoehnei (Burret) Toledo (Arecaceae) na Reserva Florestal do Morro Grande, Cotia, SP

AUTOR(ES)
DATA DE PUBLICAÇÃO

2004

RESUMO

The present study has investigated aspects of the natural history and ecology of palm Lytocaryum hoehnei. The palms were accompanied in three sites at the Reserva Florestal do Morro Grande, Cotia, SP, approximately 4 km apart from each other, during 2000, 2001, and 2002. Four ontogenetic stages were identified: 1) seedling: individuals with entire leaves, 2) infant: plants with at least one leaf of intermediate form between entire and pinnate, 3) juvenile: plants with pinnate leaves, without visible stem and without reproductive structures, 4) adult: individuals with pinnate leaves and with visible stem and/ or reproductive structures. These stages corresponded to cohesive groups of individuals that shared similar characteristics within groups and different ones among groups. The plants size increased continually during ontogeny, while leaf size and complexity of form increased with plant size up to a limit reached by the biggest adults. The fate of plants in 2002 depended on plants size in the preceding year: plants that died were the smallest ones and plants that were recruited to the next stage were the tallest ones. Individuals of the same ontogenetic stage presented slow and variable growth, which resulted in the variability of age and stage duration estimates. Plants which started to reproduce presented an increase in leaf production rate, which seems to be related to the beginning and the maintenance of the reproductive activity. On the whole, plants of all studied sites presented similar ontogeny, which suggests that there is a major ontogenetic pathway in L. hoehnei. However, the size of seedlings, juveniles and adults was different among plants from the three sites. The crown exposure increased during ontogeny, suggesting a decrease of shade tolerance with the palm development. Plants of the same stage under different lighting levels had similar size, indicating that greater photosynthesizing efficiency could be attained by controlling plant traits more sensitive to light variations. Ontogenetic shifts in leaf morphology, from entire to pinnate leaves, should result in decreasing costs for leaf support with increasing leaf size. The increase of complexity in leaf form seems to represent a continual growth and adjustment to the environment s increased lighting. The presence of spatial structure on palm density and on some environmental variables were studied in the microscale, and the relationship between palm density and environmental heterogeneity was also investigated in local and mesoscale. Neighbour sub-plots presented similar palm densities, in nine out of the twelve plots analysed. At least one out of the seven environmental variables presented spatial structure, in all plots. In five plots, palm density was related to the level of declivity, the canopy height and/ or the density of bamboos. Negative density effects on seedling mortality and positive density dependence on new seedlings were detected when analysing data from all plots. No significant correlation was found between palm density and the environmental variables neither in the local scale nor in the mesoscale, what can indicate the major importance of processes occurring in microscale in regulating the palm distribution in the reserve. The spatial variation in population structure and dynamics of L. hoehnei was studied in the local and the mesoscale during 2001 and 2002. The number of plants decreased in the second year of study, in all sites. The stage structure was practically the same between years, but different among sites. Survivorship was higher than 80 %, and increased with ontogeny. The finite rate of population increase ( ) did not differ from 1 in populations of all sites as well as in the reserve as a whole. These results can indicate stability in population numbers and persistence of the species in the reserve if environmental conditions remain constant. The sensitivities of to life cycle events varied spatially. The absence of a significant increasing population among those studied here may indicate the need of management actions in order to conserve the species in the reserve, what must be planned according to a metapopulation perspective.

ASSUNTO(S)

ontogenia palmeira demografia

ACESSO AO ARTIGO

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