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Abstract
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.
Acknowledgements
This study was supported by the project “Ecology and Management of Natural Resources of the Roraima Savanna” (PPI/INPA 012/18) and National Council for Scientific and Technological Development of Brazil (CNPq/306286/2008-4), under a fellowship for R.I. Barbosa. We thank FIT Manejo Florestal Ltda. for providing us with free access to the five plantation sites. Roraima State University (UERR) and Roraima State Foundation for the Environment and Water Resources (FEMARH-RR) academically supported the first author to carry out the research. Flavia Pinto (INPA) and Ciro Campos (ISA) collaborated with initial discussions on the study. We thank R. Khorsand-Rosa (Florida International University), P.M. Fearnside (National Institute for Research in Amazonia), D.M. Richardson (Stellenbosch University), C. Delnatte (Institut de Recherche pour Le Développement) and two anonymous reviewers for their useful comments to improve the final version of the manuscript.
