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Accueil du site → Master → Brésil → 2008 → Fitossociologia, diversidade e sua relação com variáveis ambientais em florestas estacionais do bioma cerrado no planalto central e nordeste do Brasil

Universidade de Brasília (2008)

Fitossociologia, diversidade e sua relação com variáveis ambientais em florestas estacionais do bioma cerrado no planalto central e nordeste do Brasil

HAIDAR, Ricardo Flores

Titre : Fitossociologia, diversidade e sua relação com variáveis ambientais em florestas estacionais do bioma cerrado no planalto central e nordeste do Brasil

Auteur : HAIDAR, Ricardo Flores

Université de soutenance : Universidade de Brasília

Grade : Mestrado em Ciencias Florestais 2008

Résumé partiel
In open formations which predominate in the Cerrado biome, seasonal dry forests deserve distinction as they occupy 30% of its territorial area and constitute the most endangered physiognomy by human interference. The fine quality timber obtained from some of its species, its high fertility lands and due to limestone mining in some areas are the main factores of forests degradation. The wide distribution of these formations within the Cerrado’s various land units, under different temperature, precipitation, and drought period regimens, as well as under distinct soil and topographic characteristics, propitiates floristic and structure variations of the tree layer. The present study was carried out in three Cerrado seasonal dry forests, two of which located at “Planalto Central” (Goiás State and the Federal District) and the other at Piauí State.In Goiás, sampling was carried out at Altamiro Moura Pacheco State Park (PEAMP), in fragments which there remain after human interference before the park’s foundation. In the Federal District, sampling took place at a limestone outcrop site known as Fercal, on a hillside continuously covered by forests. In Piauí it was carried out in some of this physiognomy’s disjunctly distributed natural spots, along Sete Cidades National Park’s (PNSC) savanna. The purpose was to study tree communitarian diversity and structure, as well as to try to relate substrate and relief variations with its tree species distribution. A characterization survey with focus on environmental variables (temperature, precipitation, drought period duration and soil’s physical and chemical properties) was carried through, as well as a floristic and structure comparison between the three studied seasonal dry forests, in order to test the hypothesis that, even when subjected to a wide range of environmental variations, these forests show floristic and structural similarities within their tree layer. A standardized methodology for tree layer data collection based on “two-stage casual sampling” was used, as proposed by the “Rede de Parcelas Permanentes dos biomas Cerrado e Pantanal”, where twenty-five 400m2 sample plots were installed in each site, and all tree individuals with DBH > 5,0 cm were measured and registered. Standardized soil collection and analysis were carried out in accordance to EMBRAPA’s recommendations. Regardless the amplitude of the richness (78 to 115 species), density (1059 to 1840 ind.ha-1), basal area (18,08 to 22,72 m2.ha-1) and alpha diversity (3,36 a 4,05 nats.ind-1) values found for the three forests, they are all within the value range which has been obtained in other Brazilian seasonal dry forests. The communities exhibited a self-regenerating structure, with diameter distribution following a reversed-J shape. A consistent soil fertility and texture variations was found under the three forests, as well as strong temperature and drought period duration variations among the two Cerrado biome sectors where the studied sites were implanted (Planalto Central and Rio Parnaíba’s watershed sectors). Soils at the Fercal site showed silt-clay texture and are relatively the most fertile. The ones at PNCS are extremely sandy and nutrient lacking, while the ones at PEAMP are sand-clay and show intermediate levels within the fertility gradient. Vegetation classification and ordering results show high beta diversity among the seasonal dry forests, even along PEAMP’s forest fragments and PNSC’s natural forest spots, due to substrate texture and fertility variations and land topography changes, denoting a highly floristic and structural heterogeneity of the vegetation at local level. In Fercal’s seasonal dry forest beta diversity found was low, due to the high density of species, which showed a wide distribution in the sample, bringing forth greater floristic and structural homogeneity.

Assunto(s) : florística, mata seca, Cerrado, savana, fitogeografia, solos, ENGENHARIAS, floristc, dry forests, Cerrado, savanna, phytogeography, soils

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