O trabalho é apresentado em três partes, tratando dos principais tipos de vegetação da Amazônia. Considerando que a floresta de terra firme abrange cerca de 90% da área, este tipo de vegetação foi tratado de maneira mais completa. Mesmo com esta restrição, o assunto ainda fica muito amplo e, por isso, o estudo foi particularizado a dois pontos do estuário do Amazonas, isto é, Belém (Parte II) no seu trecho inferior e Baixo Jarí (Parte III), no seu limite superior. Inicia-se por uma parte geral (Parte I) em que é analisada superficialmente a literatura relevante e apresentado um esboço dos principais tipos de vegetação da Amazônia. Na Parte II foram estudadas três reservas florestais do IPEAN, comparando-se as formações de terra firme, igapó e várzea e fornecendo dados sobre composição florística, estrutura, dispersão na área, distribuição da biomassa por classes de diâmetro, incremento e sucessão nas condições naturais da mata. A Parte III contém informações sobre a região do Baixo Jarí (abaixo das cachoeiras), contendo dados sobre composição florística, estrutura da floresta, biomassa, focalizando-se também o problema sob o ponto de vista econômico relativamente aos recursos madeireiros.

The estuary of the Amazon River is the zone between the mouth of the Xingu River and the Atlantic. The present study is in three parts. Besides a general section the study refers mainly to two regions: one near Belem, in the lower estuarine region and the other on the lower Jari River at the upper extreme of the region. Part I:: The major types of vegetation of Amazonia are sketched briefly. Since forests of "terra firme" or the uplands, cover about 90 percent of the region, the report considers these forests for the most part; Part II:: The forest reserves of IPEAN (Instituto de Pesquisas Agropecuarias do Norte) at Belem, totaling some 500 hectares, were studied: upland forests of "terra firme", "igapó" or swamp forest, and "varzea" or tidewater forest. After a general description of the whole area, three smaller sections a re examined in detail: 5.7 hectares of upland forest, 4.8 hectares of "igapó", and 5 hectares of "varzea". The three types of vegetation are compared and then, the study concentrates on upland forest for the following subjects: Chapter 7 presents the most numerous of the characteristc species which mainly determine the appearance of the landscape. Chapter 8 analyzes the horizontal distribution of species. Each vegetational community is a product of the superposition of differing distributions for different species, a fact that makes the concept of uniformity of vegetational formations very relative. Rarity and abundance of species are commented on. Chapter 9 emphasizes the role of biomass in the tropical rain forest. Biomass, cover, and penetration of light through the canopy are intimately linked elements. In dense tropical forests, there are many associated species because the niches for acoomodation are very varied, requiring great variability and flexibility of species. In regions where the climate is drastic at some seasons of the year, great specialization is required so that the number of species is greatly reduced. In tropical rain forests, natural selection is strongly influenced by the light economy. The distribuition of plants by classes of trunk diameter is very different for shade-tolerant and light requiring species. Chapter 10 considers the results of 6 messurements of growth in girth on an area of 2 hectares, over a period of 15 years: 1956, 1958, 1960, 1966, 1968 and 1971. In each species considered, the trunk grouth is very divergent for trees of a given diameter class, with a high percentage of plants that do not grow (null increment). To explain this curious fact, the importance of position in the forest is suggested; a plant, according to its relations to other plants, can receive greater or lesser amount of light. Adverse conditions can halt growth. If there is a natural clearing, plant grow is activated. Natural clearings are very important in regeneration and succession. Ages and mortalities of plants are commented on. A high number of trees died in the 15 years, in part because of a storn in 1965. Chapter 11 presents a profile-diagram for a 10 x 60 m sample of forest. Our data do not show forest stratificatiçm, or layering in strata according to height above grownd. Part III: Field studies are conducted on the lower Jari River: between Almeirin and Santo Antonio Falls. Because this is a virgin region where there has been little human disturbance, the study emphasizes the economic aspect of resources of useful timber. Chapter 5 presents data on three samples of one hectare each, one in the Serra de Almeirin, one in Serra Azul, and one at Pilão (Planalto A). Mainly the composition of the three areas was studied. Chapter 6 relates the floristic composition of a transect of about 60 kilometers from Munguba to Repartimento. Five studied sample areas along this transect totaled 11.3 hectares: at Munguba 0.15 ha of varzea; 2.5 ha between Munguba and Mont Dourado; 2.5 ha on Planalto A; 2.15 ha between Planalto A and Boca do Braço and Repartimento. The floristic composition was the major subject of study in the five sample areas. Chapter 7 presents data on 11 samples of 50 x l00 m, mainly of volume of timber in boles (trunk to the first branch) over 30 cm in diameter. In the 5.5 hectares, all the trees over this diameter were cut and the volume in the boles noted as well as the presence of such defects as splits, holes, twisting, trunk irregularities and other faultes that make the wood unusable for commerce. Although the areas studied were relatively close together, there was great variation among them. The areas are indicated by numbers 1 to 11 in the map fig. 59. Chapter 8 reports total biomass of a sample of 50 x l00 m, in wich truks and foliage are chopped up and volumes calculated. Plants less than 5 cm in circunference were discarded as their volumes were calculated by class of trunk circumference. Plants of 60 cm or more circunference were identified. Data obtained are compared with those of Pires Skoury (1959), Pires (1966) and Klinge S Rodrigues (1972). Chapter 9 analyzes the relationships between height and trunk girth of trees. All the individuals of 11 common species in the Jari, down to 15 cm height, were tabulated for a transect of 10 x 6000 m. Graphs show that there are species that are shade-tolerant and others that require light. The first group is represented by many individuals of small bulk, seedlings, saplings, poles; and smaller the plant, the greater the number. Those requiring light are not represented by small individuals in the mature forest, and their reproduction depends on the existence of natural clearings. This study on Jari complements that at Belem, treated on chapter 9.3 cf PART II. Supplementing the three parts of the study, there are photographs with legends, illustrating, interesting aspects of the ecosystem of the regions studied.