Florística, fitossociologia e dinâmica de duas florestas secundárias antigas com histórias de uso diferentes no nordeste do Pará-Brasil. / Floristic, phitosociology and dinamic of two old secondary forests with different history of use in the northeastern Pará-Brazil.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2004

RESUMO

The increase of the substitution from process amazonic forest by agricultural areas and their desertation afterwards have caused an increasing number of secondary forest fragments to happen. Aiming to contributing with the understanding of the diynamics of these areas, the floristic composition, the phitosociology, the ingrowth rate, the mortality rate, the growth of the individuals, and the soil relations whith the gowth in diameter, density and total basal area from secondary forests (Marituba and Bragança, NE, Pará) whith different hystories of abandonment, were analyzed. Four permanent plots measuring 50x50m, subdivided into 25 sub-plots with 10x10m in each area, were installed. All trees with DBH >5cm were sampled. The measures made in Marituba took place in 1997, 2000, 2001, and 2002; yet, in Bragança, 1999, 2000, 2001 and 2002. The soil sampled were collected at lake depth of 0-5cm, 5- 15cm, 15-25cm on the even part of the areas. In the first survey made in Marituba, 1,257 individuals and 185 species were found. In the last survey, the was a reduction of 4.1% in the number of individuals and an increase 8.1% of the species, with H´ = 4.42nats/indivíduo. In Bragança, 1,819 individuals and 136 species were found in 1999. In the last survei, there was a reduction of 6,2% of the individuals and 1,5% of species, with H´ = 4.08nats/indivíduo. Between both studied areas, the was a low floristic similarity (Jac = 12%). Marituba had an increase of 0.23cm/year, ingrowth of 2.1%/year, and a mortality rate of 3.2%/year. Bragança had a increase in DBH of 0.25cm?year, ingrowth of 1.2%/year, and a mortality rate of 3.6%/year. Both forests presented a characteristic floristic balance of communities under secondary succession, whit mortality rates higher than. The ingrowth, which indicated the recovering phase. The areas showed distinct soil fertility: Bragança´s soil fertility was higher. Bragança was different from Marituba, for PCA analysis, mainly in relations to CTC, P, MO, Clay, and %Al. The canonical correspondence analysis (CCA) did not show correlation between the soil fertility and the growth in diameter, density, and total basal area. The dynamiocs of the forest in Bragança was more ntense, indicating a less advanced successional phase, wich was a result of successive cutting-burningólanting-resting cycles. For Marituba, the richness values, diversity, and basal area were compatible whit those of primary forests´, as a function of lighter degradation characteristics (selective logging). The results confirmed the hypotesis that the succession process characteristics in both secondary forests with the same age and on the same type of soil. However, oney the age itself is not an adequate feature for forecasting the recovering rates and the successional phases of secondary forests.

ASSUNTO(S)

florestas secundárias regeneração natural natural regeneration comunidades vegetais dynamics of communities secondary forests dinâmica de comunidades vegetal communities floristic composition composição florística

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