Estrutura populacional e desenvolvimento da fase esporof&iacute;tica de Cyathea delgadii Sternb. (Cyatheaceae, Monilophyta) no sul do Brasil  <span class="so-article-trans-title"> Translated title: Population structure and development of the sporophyte phase of Cyathea delgadii Sternb. (Cyatheaceae, Monilophyta) in Southern Brazil </span>

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Abstract

Cyathea delgadii Sternb. é uma samambaia arborescente que ocorre em florestas primárias e secundárias da região nordeste até o sul do Brasil. O presente estudo discute a estrutura populacional e o desenvolvimento da fase esporofítica (crescimento do cáudice, produção de frondes, fenologia da produção de esporos) de C. delgadii, em floresta secundária, no Estado do Rio Grande do Sul, Brasil, baseado na observação de 41 plantas, durante 13 meses. A espécie apresentou padrão espacial agregado e uma freqüência expressivamente alta de indivíduos de menor altura, indicando um grande potencial de regeneração da população. O cáudice das plantas cresceu, em média, 4,65 cm ano-1, sendo que as maiores taxas de crescimento foram registradas em plantas mais altas. As taxas de produção de frondes novas (5,75 frondes ano-1) e de senescência (4,92 frondes ano-1) similares evidenciaram uma capacidade de manter um número de frondes estável. Poucas plantas formaram frondes férteis, sendo que a produção e liberação dos esporos ocorreram assincronicamente.

Translated abstract

Cyathea delgadii Sternb. is a tree fern that grows in primary and secondary forests from Norhteastern to Southern Brazil. This study discusses the population structure and development of the sporophytic phase (caudex growth, frond production, phenology of spore production) of C. delgadii in a secondary forest in the State of Rio Grande do Sul, Brazil, based on observations of 41 plants during a 13 month period. The species had an aggregated spatial distribution pattern and higher frequency of smaller individuals, indicating high potential for population regeneration. On average, the caudex of plants grew 4.65 cm year-1, and the highest growth rates were recorded for taller plants. The similar frond production rate (5.75 fronds year-1) and senescence rate (4.92 fronds year¹) reflect the capacity to maintain a stable number of fronds. Only a few plants formed fertile fronds, while spore production and liberation occur in an asynchronous pattern.

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Predicting population trends from size distributions: a direct test in a tropical tree community.

R Sukumar, R Condit, D S HUBBELL … (1998)

Forest ecologists often evaluate how well the species composition of saplings in the understory matches that of the canopy: absence of juveniles suggests that a tree species is suffering population decline. Here we offer a theoretical and empirical test of this assertion using data from a 50-ha census plot in Panama. Theory indicates that higher rates of population change, lambda, lead to more steeply declining size distributions (more juveniles relative to adults). But other parameters also affect the size distribution: lower growth rate of juveniles and lower survival at any size produce more steeply declining size distributions as well. Empirical evaluation of 216 tree populations showed that juvenile growth was the strongest predictor of size distribution, in the direction predicted by theory. Size distribution did correlate with population growth, but weakly and only in understory species, not canopy species. Size distribution did not correlate with the growth rate of larger individuals nor with survival. Results suggest that static in formation on the size distribution is not a good predictor of future population trends, while demographic information is. Fast-growing species will have fewer juveniles in the understory than slow growing species, even when population growth is equal.