Changes caused by forest logging in structure and floristic diversity of natural regeneration: Relationship between climate variables and forest dynamics in the eastern Amazon

Several studies indicate that the Amazon rainforest is home to the greatest biodiversity of tree species on the planet. The unique quality of this forest typology is under constant threat of change owing to the behavior of climate variables and different anthropic activities that occur in the biome itself. Therefore, it is essential to conduct studies that clarify the factors that affect the formation of forests in this ecosystem and to validate the use of forest resources by society through appropriate forest management practices. Thus, this study aimed to answer how the structure, composition and floristic diversity of the forest are influenced by forest logging in different phases of development of a local Amazonian forest, and whether there is a relationship between these attributes and regional and global climate factors. This study assessed the dynamics of natural regeneration of 36 permanent plots over 33 years after logging in the Tapajos National Forest in Belterra, State of Para, Brazil. The plots studied were measured in 1981, 1983, 1985, 1987, 1992, 1997, 2007, and 2012. All individuals with height greater than 30 cm and diameter at breast height <10 cm were monitored in three regeneration strata (seedlings, saplings, and small trees) and three forest classes (gap-phase forest, growing forest, and old-growth forest). Density, floristic similarity according to the Sorensen Index, and floristic diversity according to the Hill series were analyzed. Climate variables such as mean annual compensated temperature; total annual precipitation, and Oceanic Nino Index were correlated with the mortality, recruitment, and density of growing trees. An ANOVA for count data verified that the density of individuals differed over time since logging among the regeneration strata and forest classes analyzed. Likewise, the diversity profiles generated from the Hill series were significantly different from each other, and the floristic similarity varied between regeneration strata over time. For the forest classes, the similarity values ranged between 50% and 96%. The gap-phase forest areas had the lowest similarity values, with some 100% dissimilar surveys. However, there was an exponential reduction in similarity over time in the different forest classes. The results indicate that logging promotes significant changes in floristic structure and diversity in different strata of natural regeneration and forest classes over time. Additionally, no correlation was found between climate variables and the natural regeneration dynamics in the Tapajos National Forest.