Influência da distância geográfica e de filtros ambientais sobre a diversidade de espécies arbóreas na Amazônia

Abstract

The Amazon is home to the largest tropical rainforest in the world and presents a complex species richness. Despite its ecological importance, the Amazon biome has been suffering from deforestation and environmental degradation, increasing the need for research on its tree biodiversity. The objectives of this study were i) to evaluate the influence of geographic distance and distance from the river on species composition; ii) to describe the modules and plots to assess how environmental and spatial filters can influence species composition and diversity; and iii) to evaluate the effects of environmental filters and spatial characteristics, such as altitude and distance from the river, on forest structure, species richness, abundance of individuals and the health of tree vegetation. The methodology was based on biodiversity data available in the RAPELD system from 2015 to 2017 for the southern Amazon region. In the data collection, 500-meter-long linear transects were installed, arranged transversely in relation to the river bank and at different geographic distances. Along each transect, sample plots of 50 x 40 meters (total of 2,000 m²) were established, respecting the distance of 100 meters between the plots of each transect, to collect data on biotic and abiotic variables. To respond to the first objective, estimates of species similarity were calculated and multivariate analyses were performed to verify the species composition in relation to the modules (geographic distances) and to verify the species composition in relation to distances from the river. To respond to the second objective, descriptive analyses of the environmental and spatial variables were performed. To respond to the third objective, several Generalized Linear Models were created to evaluate the effect of environmental and spatial filters on the vegetation structure (diameter, height and basal area of ​​tree species), on species richness, on the abundance of individuals and on the number of healthy plants in the studied area. The results showed that the geographic distance reduced the species similarity between the evaluated modules, on the contrary, the distance from the river did not influence the species composition. Forest structure was positively correlated with the soil variables silt, nitrogen and magnesium, and with the spatial variable altitude. However, phosphorus and distance from the river showed a negative relationship. Richness was lower in areas with greater amounts of sand and clay and was lower in areas far from the river; however, areas at higher altitudes showed greater richness. The abundance of individuals was higher in areas with less clay and in areas at higher altitudes. The percentage of healthy plants was higher in areas with greater amounts of sand, silt and phosphorus. Different ecological and geographic aspects interact to define the composition, diversity and structure of vegetation in southern Amazonia. In addition, the research concludes that stochastic factors that occur in vegetation should also be considered to complement the explanation of ecological patterns.