Ecologia, manejo e conservação de Pentaclethra macroloba (Willd.) Kuntze (Fabaceae) em floresta de várzea estuarina do Rio Amazonas

Abstract

Pentaclethra macroloba (Willd.) Kuntze (pracaxi) is a species of multiple utilities and hyperdominant in the Amazon estuary. Little is known about the natural history of P. macroloba in the Amazon region, which is worrying, as this species is largely exploited in the Amazon estuary to extract the medicinal oil from its seeds. We studied a broad aspect of P. macroloba autoecology to assist in management and conservation plans of its resources and in understanding its dominance in the estuarine floodplain of Northeast Amazonia. Adult individuals have adapted structures in response to daily flood, such as adventitious roots to increase respiratory efficiency and lenticels in the trunk, serving as a connection point for oxygen transport between the root and the aerial part. Dried fruit favor the activation of the explosive dehiscence mechanism, allowing the seeds to reach long distances. The deltoid shape of the seeds allows their fluctuation and more efficient dispersal. The seedlings are phanerocotylar hypogeal with a pair of reserve cotyledons that provide an extra source of energy for the seedlings to escape the flood. Germination rate was 78 % and the speed was 0.2 seeds.day-1. Circular buffer method revealed the presence of 123 subpopulations of P. macroloba distributed in a radius of 5.699.943 km² across the Neotropical region. Flowering was synchronized in the dry season (flower buds: βtemperature =1.30, p <0.01 and flowers in anthesis: βtemperature =1.84; p <0.001). Immature fruits appeared during the dry season (βtemperature =0.67; p <0.01) and ripen in the rainy season. Seeds were dispersed during the rainfall (βrainfall =0.0051; p <0.01) and flooding of the river (βwater =0.12; p <0.001). There was no relationship between leaf change and hydrometeorological variables. The main floral visitors were wasps, bees and ants. 33 trees produced 261 fruits (9 ± 8 fruits) and 380 seeds (54 ± 50 seeds). The predation rate was 5% (18 seeds), with most of the seeds predated by moth larvae (50%). During the period of seed production, the diametric growth of P. macroloba decelerates (r = - 0.76; F = 12.7; p < 0.01) and the number of seeds increases during the period of forest flooding (r = 0.90; F = 40.3; p < 0.001). In an area of 136.59 ha, 2,072 adult trees (15 individuals ha-1) were registered. The regenerants showed negative exponential pattern of diameter distribution and adult trees have a log-normal pattern. The mean height of the regenerants was 0.63 m (± 0.55 m) and adults 12.7 m (± 5.4 m). Regenerants and adults had aggregate spatial pattern. The analysis of the growth rings of 38 trees revealed mean age of 60 years (± 20 years), with minimum age of 28 years and maximum of 102 years. Dendrometric bands installed on the tree trunk in different topographies, showed that in the low floodplain growth stagnation occurred during the rainy season (R2 = 0.41; t = -2.62; p < 0.01) and higher water levels of the river (R2 = 0.47; t = -3.01; p <0.01), the formation of growth rings may be associated with the seasonality of these phenomena. The high synchrony of P. macroloba with climatic seasonality and with the daily tide of the Amazon River, explain its high dominance and adaptability in the Amazon estuary. The result of this research will be fundamental to seek public policies for the good management and conservation of estuarine P. macroloba trees and to strengthen the productive chain of non-wood products as a generator of income and social inclusion of riverside populations along the Amazon River.