Estrutura e dinâmica de uma floresta tropical submetida à exploração de impacto reduzido em Belterra, Pará

Abstract

The Amazon harbors a stunning biodiversity, which currently needs research efforts that secure its development while preventing the extinction of natural resources. This work aims to contribute to knowledge about variation floristic composition variation, horizontal structure and dynamics (recruitment, growth and mortality) of a primary forest submitted to reducedimpact logging for approximately six consecutive years. Data originated from sampling conducted along permanent plots (PP) of a forest management project established by Cooperativa Coomflona (Ambé Project), located in Floresta Nacional do Tapajós, within the municipality of Belterra, Pará State, from where information was collected on all trees that had DBH 10 cm. It was chosen the UPA 2, with a total area of 300 ha, along which six 50 X 50 m sampling plots were settled, in order to sample a total 1,5 ha. Positioning of plots was determined according to a completely randomized model. Data analysis used MFT (Monitoramento de Florestas Tropicais) and BioEstat 5.0 softwares, and involved analysis of variance and T tests considering a 5% significance level in order to test for differences in forest behavior before and after forest logging, between 2006 and 2012. During the first survey (2006) 129 tree species were identified, whereas 136 were detected in 2012. Along the monitored time span between 2006 and 2009, the number trees decreased 6,46%, and between 2009 and 2012, this figure increased 5,78%. The basal area varied only slightly among the three years when it has been measured, starting from 30,36 m2/ha in 2006, 29,35 m2/ha in 2009, and reaching 29,19 m2/ha in 2012. The tree volume decreased 3,16% between 2006 and 2009, and 1,68% between 2009 and 2012. Along the complete survey, Pouteria guianensis (Abiurana) dominated the area in terms of abundance, frequency and dominace. The periodic annual increment (PAI) in diameter between 2006 and 2012 was 0,38 cm/year. Considering all species, the growth rates for basal area and volume between 2006 and 2012 were 0,4921 m2/ha/year and 6,06 m3/ha/year, respectively. Considering the complete duration of the survey, the forest presented a negative balance (0,09%), with a number of dead trees of 12,46 trees/ha/year and recruitment of 11,90 trees/ha/year.