Estrutura populacional, padrões ecológicos e polinização de Bertholletia excelsa Bonpl em áreas antropizadas

Abstract

The reproduction of Brazil nut tree is allogamous, dependent on specific pollinators with enough force to enter the ligule of its flowers. There are no records of the monitoring of the pollination process in deforested areas with occurrence of Brazil nuts tree even though there are already studies of low flowering and fruiting in these areas. The study area was developed in the extension of the BR-163 highway, in the Copaíba branch, near the rural community of Santa Maria, municipality of Oriximiná (PA). This is a region of plateau dominated by deforested areas fruit of the expansion of cattle ranching activity. The objective of this work was to evaluate the population structure, ecological patterns and the pollination of Brazil nuts tree in anthropic areas. For the study of the population structure, 51 Brazil nut trees were recorded in the deforested area (DA) in 33.6 ha with 13 years of deforestation and 77 Brazil nuts trees in the forest fragment area (FF) at 30.3 ha. The density was 1.5 tree / ha (DA) and 2.5 tree / ha (FF). The soil samples showed acidity with pH below 5, loam texture and similar density in both areas. The mean height of the trees in both areas was 47.4 m, with DAP 166.4 ± 46.4 cm in DA and 180.7 ± 50.4 cm in FF and crown area with no significant difference (p = 0, 5). The population is composed of senescent trees (DBH> 160 cm), 53% in DA and 65% in FF. Brazil nut trees with DBH (80-160 cm) considered as most productive were 34% in FF against 45% for DA. The population in general appears to suffer from problems in pollination and fruiting, with low yield in the sampled trees (n = 22 in DA and n = 16 in FF). The mortality rate in the tree population was significantly higher in DA (18%) than FF (5%) in two years of monitoring. The mean distance between brazil nuts trees was significantly higher in DA (mean of 40.6 m) compared to FF (mean of 28.0 m), but fruit yield was 2.6 times higher in DA than in FF. In contrast, 9% of the DA seeds were not fertilized against 5% FF. There were no significant correlations between fruit yield and canopy area or with Brazil nut trees diameter. In relation to pollination, 5 species of bees of two families were captured and identified: four (4) Apidae (Xylocopa ordinaria and X. frontalis, Centris superba and Eulaema nigrita, and one (1) Megachilidae (Megachile spp) under cloudy conditions with higher activity between 07:30 and 08:30, at 25.3° C, relative humidity of 89.2% and wind velocity of 0.9 m / s. Of the captured bees, two potentially new species were identified pollinators of Brazil nut tree flowers: ordinary Xylocopa ordinaria and Centris superba.