Invasion of Acacia mangium in Amazonian savannas following planting for forestry

Background: No studies have examined the invasion of exotic species used for forestry purposes in the savannas of the Brazilian Amazonia. Aims: We investigated the invasion process of Acacia mangium in savanna areas adjacent to large-scale forestry plantations in north-eastern Roraima State, Brazilian Amazonia. Methods: A tree inventory to record the presence of all A. mangium and native tree individuals was carried out in of 14 plots (each 50 m in width and 1500 m in length) established at five plantation sites. Biometric measurements were taken for all individuals to identify their structure and maturity. Distance categories were created for determining frequency of occurrence in 100 m sections along the plots for all individuals. Correlations and goodness-of-fit tests for discrete data ordered in categories were applied to verify the occurrence of A. mangium plants in relation to distance from the plantation. Results: Individuals of A. mangium were dispersed up to 900 m from the plantation edge 8-9 years after the plantation was established. Although most recorded individuals were in the juvenile stage, reproductive adults were found in two establishment patterns: non-nucleated and nucleated under native tree species. Crown cover of the savanna's most abundant native tree species facilitated the regeneration of A. mangium. Conclusions: Planting of A. mangium in Amazonian savannas provides a source of continuous dispersal, and invasion by the species is facilitated by environmental conditions.