Population dynamics of Pentaclethra macroloba, a hyperdominant tree in the Amazon River estuary

Abstract

Pentaclethra macroloba is a hyperdominant tree of the Amazon estuary and highly exploited in the region, because the oil of its seeds has medicinal properties. Little is known about the influence of the flood polymodal cycle on the population dynamics of trees in the Amazon estuary. We evaluated the influence of tree diversity, climate, soil properties and flood level on the population dynamics of P. macroloba. During five years of monitoring (from 2011 to 2015), population density and mortality, recruitment and growth rates data were obtained of three populations of P. macroloba (Mazagão Velho, Maracá and Ajuruxi areas). Four transects were used in each area and 20 permanent plots were installed in each transect to study the population dynamics. Linear models were used to evaluate the relationship between biotic/abiotic factors and population density of P. macroloba. The population density of the three populations analyzed showed a significant decrease between the period from 2011 to 2015 (F = 381.3; p < 0.001). The Maracá area had a higher mortality rate (4.50% year−1) compared to Mazagão Velho (3.24% year−1) and Ajuruxi (1.96% year−1). The recruitment rate in Ajuruxi and Mazagão Velho were 1.05% year−1 and 0.32% year−1, respectively, and in Maracá there were no recruits. Annual growth rate of the Maraca area was higher (0.93 cm−1 year−1) compared to Ajuruxi (0.75 cm−1 year−1) and Mazagão Velho (0.65 cm−1 year−1) populations. The flood level had a negative and significant correlation with the population density of P. macroloba in the Maracá (F = 39.7; p < 0.01), Ajuruxi (F = 9.9; p < 0.05) and Mazagão Velho (F = 19.6; p < 0.05) areas. Only the Ajuruxi area had a positive and significant correlation with arboreal richness (β = 0.14; p < 0.05). The flood gradient is an environmental driver that regulates the population growth of P. macroloba. The hyperdominant characteristic of this species is the result of its adaptability and interactions between soil fertility and tree diversity.