Phytosociology and the timber potential of transitional ecosystems from forested campinarana to dense forest in the south of Roraima, Brazil

Resumo

Transitional forest ecosystems in the south of the state of Roraima show great heterogeneity of tree species and represent different volumes of timber stock in projects of vegetation suppression requiring Deforestation Licences (DL). The aim of this study was to evaluate the phytosociology and standing timber volume in ecosystems of Submontane Dense Ombrophilous Forest (Ds) and transitional Campinarana/Ombrophilous Forest (LOt₁ and LOt₂) in the district of Rorainópolis, Roraima. The DL were issued and authorised from 2011 to 2016 by the State Foundation for the Environment and Water Resources of Roraima (FEMARH) and the Brazilian Institute of the Environment and Renewable Natural Resources (IBAMA). A total of 9,391 timber-yielding trees were analysed, with a DBH ≥ 45 cm in 646.5 hectares; these belonged to 21 botanical families, 73 species and 8 taxa identified at the genus level. Diversity and evenness were greater in Ds (H’ = 3.34; J = 0.82) compared to LOt (H’ = 1.92 to 2.20; J = 0.55). The floristic similarity was greater between Ds and LOt₂, of different forest typologies, showing that transitional environments can be complex in terms of floristic composition and diversity. However, the larger volumes of timber stock in LOt₁ and LOt₂ compared to Ds may be related not only to natural processes, but also to the influence of deforestation and illegal selective logging in the surrounding area. There is a strong need for studies on transitional forest ecosystems in the Amazon, due to the complexity of the ecological relationships, the influence of environmental gradients, and anthropogenic factors.