Diversity, composition and biomass of native vascular plants regenerating under Acacia mangium Will. plantations in northern Amazonia

Abstract

It is imperative that studies can be developed to assess the role of homogeneous tree plantations in biodiversity conservation and the ability to store atmospheric carbon. This study aimed to evaluate the effects of Acacia mangium Will. plantations established in areas originally occupied by savanna (locally termed “lavrado”) on the establishment success of vascular plants, by analyzing three attributes of the community—diversity, composition and biomass. All plants with base diameter ≥ 1 cm were measured in 28 0.05-ha plots (11 plots allocated in natural areas of “lavrado” and 17 under A. mangium plantations). Species diversity was much higher in A. mangium plantation than in the natural areas of “lavrado”. There was a clear floristic differentiation between A. mangium and “lavrado”, with high density of forest species and low density of “lavrado” species growing under A. mangium plantations. “Lavrado” plots presented high floristic similarity, but plots under A. mangium plantations were far less similar, indicating a more heterogeneous vegetation. Biomass of vascular plants in A. mangium plantations was about one-fifth of that found in natural “lavrado” sites, but in “lavrado” 92.6% of the total biomass was allocated in only two species, whereas in A. mangium plantation two species comprised only 43% of the total biomass. In A. mangium plantation, species classified as forest species and typical “lavrado” species accounted for 72.8% and 27.2% of total biomass, respectively. Our results showed that A. mangium plantations resulted in high alpha and beta plant diversity due to the invasion of alien forest species. Also, biomass of “lavrado” species in plantations was smaller and species relative abundances completely different from natural “lavrados”. Therefore, we conclude that forest plantations established in savannas cannot be used to meet conservationist purposes.