Banca de DEFESA: KESID RAFAEL CAVALCANTE PAIXÃO

Study of soil and vegetation in degraded areas in the north of the state of Rondônia.

Degraded area, Amazon, soil, Rondônia, floristics

Deforestation in the Amazon intensified from the 1970s onwards, when government incentives influenced the occupation of the Amazon. As a negative consequence of economic cycles in Rondônia, the native forest has been intensely exploited over the years. Since the 1980s, the state has deforested more than 66,100 km² of native forest, which corresponds to 28% of its territory. It is common in the Amazon region for areas that gradually lost their natural fertility to stop being economically exploited and, over time, to observe the growth of secondary forests. These forests are related to the maintenance of biodiversity, and play a role in mitigating the impacts generated by deforestation. Secondary forests in the Amazon are home to 56.6% of the country's secondary formations. Due to their importance in preserving the environment, knowing them represents an important step in our strategies to mitigate the damage caused by deforestation. The objective was to describe the diversity of secondary forests in a portion of the territory of Rondônia and to understand the occurrence and relationship of arboreal flora in secondary formations with soil attributes in degraded areas. This work is organized into two chapters. In the first, we approach the flora of plantations and secondary forest formations, describing their composition and ecological characteristics. The information used was obtained from specialized bibliographies, online botanical platforms and various studies carried out by the authors in areas of secondary forests in the northern region of Rondônia. A total of 56 species from 50 genera and 24 families made up the list. Of the total species, 43% are pioneers, 50% are secondary and 5% are climax species. For the planting group, 51% are diversity and 31% are cover. For the dispersal syndrome, 69% of species are zoochoric, 18% anemochoric and 11% barochoric. In the second chapter, the structure of a secondary forest and the influence of soil attributes on the density of some of its tree species were studied. For the floristic and phytosociological studies, 22 plots of 10 m x 100 m were implanted randomly. As an inclusion criterion, DBH ≥ 5 cm was used. The soil was approached from composite sampling obtained inside each of the plots at three different depths: 0-10 cm, 10-20 cm and 20-40cm. 2818 individuals were sampled, distributed in 172 species, 115 genera, 44 families and with an unidentified taxon.The floristic similarity between the three areas, estimated through an exploratory analysis by NMDS. The influence of soil attributes on vegetation was studied through the correlation between soil attributes and the density of the seven species with the highest density of individuals. The Shannon-Weaner (H') specific diversity index was 3.44 nats.indˉ¹. The Pielou evenness index was 0.82. NMDS showed the formation of two floristic groups. The soils in the study area had low natural fertility values and high acidity, with all plots having low pH (3.9 to 5.4). Most soil attributes showed no relationship with species density.