Estratégias funcionais e efeito da abundância de Acacia mangium Willd na riqueza de espécies nativas em um fragmento de floresta secundária em Laranjal do Jari, Amapá

Abstract

Acacia mangium Willd is a fast-growing exotic tree species that, when inserted in a different environment, can adapt and present an invasive potential in secondary forests. Little is known about the combination of functional attributes that are exhibited by A. mangium Willd in the habitat it was inserted, which predicts the different ecological strategies in relation to the conditions of nutrient availability in the soil, which guarantee an increase in abundance, which can affect the richness of native species. In this context, this study aims to understand the ecological or functional strategies of A. mangium Willd, as well as the effect of abundance of this species and edaphic factors on native species richness in a secondary forest fragment. For this, ten plots of 200 m2 (10m x 20m) were established in the forest fragment of the Ecological Trail of WAJÃPI, located behind the campus of the Instituto Federal do Amapá campus Laranjal do Jari. The maximum height of all tree individuals with diameter at breast height (DBH) ≥ 10 cm in each plot was identified and estimated. Soil samples were collected in the plots and sent for fertility and granulometry analysis. Five leaves were also collected from three to six acacia trees in the plots to measure three functional attributes related to soil resource acquisition and competition: leaf area (LA), leaf thickness (LT) and specific leaf area (SLA). A total of 145 tree individuals distributed in 16 species were sampled, with the species A. mangium Willd being the most abundant with 95 individuals. There was a negative relationship between the relative abundance of A. mangium Willd and native species richness. The species used different growth strategies to maximize its growth and abundance in more acidic and less fertile soil in the fragment, which influenced the decrease in native species richness. However, soils with higher fertility favored the increase in species richness, decreasing the abundance of A. mangium Willd, even so, the species maintained a growth strategy (larger specific leaf area) in relation to other tree individuals. It is important to develop actions for monitoring and controlling invasive exotic species such as A. mangium Willd in the analyzed forest fragment, since the species has an opportunistic character, inhibiting the regeneration of native species after local disturbances.