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Universidade de Brasília (2007)

Efeitos de queimadas em áreas de cerrado Stricto Sensu e na biomassa de raízes finas

Neves, Beatriz Moreira de Castro

Titre : Efeitos de queimadas em áreas de cerrado Stricto Sensu e na biomassa de raízes finas

Auteur : Neves, Beatriz Moreira de Castro

Université de soutenance : Universidade de Brasília

Grade : Doutorado em Ecologia 2007

This work is part of Projeto Fogo, coordinated by University of Brasilia with support of the Reserva Ecológica do Instituto Brasileiro de Geografia e Estatística. The project aims to asses the effects of prescribed burning in the cerrado vegetation, a type of Brazilian savannas. There are several publications on savannas of Central Brazil and a few comparisions of root biomass in different phytophisiognomies ; this study focuses on cumulative effects of prescribed burning in cerrado stricto sensu. Results from 15 years of Projeto Fogo show that different seasons and frequencies of burning have influence on fire characteristics, on its effects and on the capacity to resist fire or recover from it. Fire regimes (treatments) used in four study areas were : bienal precoce (every two years burning, in June), bienal modal (in August), bienal tardia (in September) and quadrienal (every four years burning, always in August). These four areas are under these regimes since 1990 and before the burning treatments, there were at least 65% similarity among them. Fine root biomass (5mm diameter) was determined at 0-10 cm, 10-20 cm, 20-30 cm and 30-50 cm depth and analysed with 5% significance analysis of variance. Aboveground biomass - tree-and-shrub layer, litter, tree cover and groud layer : herbaceous and non herbaceous contents - were determined in order to establish biomass profiles for all four areas. Biomass for bienal precoce was 16,1±9,9 Mg/ha (tree-and-shrub), 6,7±2,6 Mg/ha (ground layer), 15,3±7,0 Mg/ha (core root biomass) and 21,5±15,6 Mg/ha (fine root biomass) ; tree density were 1742 (diameter ≥ 5,0cm) and 3740 (diameter ≥ 1,0cm) and tree cover was 16,5%. For bienal modal, values were 23,8±12,6 Mg/ha (tree-and-shrub), 6,2±0,9 Mg/ha (ground layer), 20,2±5,3 Mg/ha (core root biomass) and 25,3±8,8 Mg/ha (fine root biomass), tree density were 1106 (diameter ≥ 5,0cm) and 6644 (diameter ≥ 1,0cm), tree cover was 13,6%. Para a bienal tardia, 17,2±5,2 Mg/ha (tree-and-shrub), 7,0±1,1 Mg/ha (ground layer), 20,1± 2,2 Mg/ha (core root biomass) e 19,6±10,4 Mg/ha (fine root biomass), tree density were 1014 (diameter ≥ 5,0cm) and 6405 (diameter ≥ 1,0 cm), tree cover 7,8%. For quadrienal, 18,2±5,6 Mg/ha (tree-and-shrub), 10,4±2,2 Mg/ha (ground layer), 19,9±4,8 Mg/ha (core root biomass) and 22,0±8,0 Mg/ha (fine root biomass), tree density were 1074 (diameter ≥ 5,0cm) e 4456 (diameter ≥ 1,0cm), tree cover was 10,0%. Results show difference among study areas in aboveground biomass, but not in fine root biomass. Fine root biomass results are in the upper limit of values described for the cerrados sensu stricto, and, for the modal area, fine root biomass values are above registered values. One might think that this could be related to greater biomass of grass in burned systems, but fine root biomass did not show correlation (R2 < 0,2) neither with groud layer biomass nor with grass biomass.

Mots clés : Efeito de queimada Biomassa de raiz Efeito cumulativo do fogo no cerrado


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