Most of the Amazonia is covered by the lowland evergreen rain forest (LERF) formation. A small proportion of the region (5-6% in total) is covered by heath forest, which is particularly common in the Rio Negro basin on Spodosols - white sand soils with a layer of mor humus. The smaller facies of heath forest (SHF) is called 'Camping' in Brazil and often lacks the mor humus; the taller facies (TBF) is called 'Campinarana'. The present study was made in central Amazonia, on a gradient from SHF through THF to well developed LERF. Soil, vegetation, and nutrient dynamics were studied in three 50 m x 50m plots in each type of forest. Litterfall was measured during one year and litter standing crop was measured three times a year. Three decomposition experiments, using bagged leaf litter, were made using leaves of two common species from the heath forests and one from the LERF. Fertiliser addition experiments in the field and in the laboratory were carried out to determine the potential nutrient limitations for plants in the three forest types. Annual litterfall was highest in the dry season and was 3.8 t ha-1 yr-1 in the SHF, 6.3 t ha-1 yr-1 in the THF and 7.8 t ha-1 yr-1 in the LERF. The rates of weight loss of the enclosed leaf litter were most rapid in the LERF and slowest in the SHF. The leaves of the LERF species Clitoria racemosa decomposed faster than those of the heath forest species. Fine roots penetrating litter-bags differed significantly among forest types and leaf species, and increased the decay rates. There were no significant differences in decomposition rates between the wet and dry season experiments. Significant differences in the release of chemical elements were observed: higher immobilization of iron and aluminium in the LERF; higher potassium and copper release in THF; and lower calcium, but higher boron release rates in SHF. Significantly higher immobilization of iron and aluminium (mainly in LERF) was found in bags penetrated by fine roots, while release of magnesium, calcium, manganese and zinc was significantly increased by fine roots, particularly in the TI-IF. Leaf mass loss and nutrient release were mostly controlled by abiotic factors in the SHF, but organisms were more active in the THF and LERF. Diplopoda were the dominant decomposers, particularly in the THF. Fertiliser addition showed an overall positive effect of liming, especially in heath forest soils. Nitrogen and phosphorus additions did not induce higher biomass production, while calcium chloride addition invariably induced a high mortality. 11÷ ion toxicity, together with a higher concentration of soil phenolics are suggested as causes of the poor growth in the heath forests, but in the SHF, where it lacks mor humus, limitation by nutrients, especially basic cations, may occur.

The Amazon region is one of the richest areas on the planet in terms of its biodiversity and natural resources. The large scale harvesting of trees in this region is a relatively new activity, and it is uncertain whether the exploitation of timber species will result in depletion of forest genetic resources. To examine this, I have assessed levels of inbreeding, gene flow, and genetic diversity in populations of Amazonian forest trees undergoing logging. Because of their high variability within populations, microsatellite genetic markers were chosen for the study, and it was verified through an initial sampling experiment that this class of markers is sufficiently stable within somatic tissue of large and long-lived trees such that population studies could be undertaken with them. By sampling adult trees and seed progenies at several microsatellite loci, high levels of gene flow and low levels of inbreeding were found within populations of Sextonia rubra and Carapa guianensis, two important insect-pollinated Amazonian forest tree species. Comparing seed progeny collected before versus after selective logging of a population of Carapa guianensis, no measurable evidence was found that that the population genetic dynamics is impacted by logging. In particular, levels of inbreeding, gene flow, and population substructure were the same before and after logging. Comparing different populations distributed over the Amazon basin, a phylogeographical structure in the chloroplast DNA of Carapa guianensis that corresponds to major tributaries of the Amazon river was discovered, suggesting that seed dispersal through rivers may contribute to genetic connectivity among populations. Overall, the results of this thesis suggest that the large effective population sizes, the high levels of gene flow, and the low levels of inbreeding in exploited Amazonian tree populations may allow them to counteract potential negative genetic impacts of selective logging, at least at the levels of harvesting carried out during this study, and for the Carapa guianensis population investigated.

Thesis (Ph.D)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2009. / Committee Chair: Fu, Rong; Committee Member: Dickinson, Robert E.; Committee Member: Nenes, Athanasios; Committee Member: Webster,Peter J.; Committee Member: Yu, Hongbin. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (Ph. D.)--University of California, Berkeley, 1976. / Includes bibliographical references (l. 319-356).

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

No description available.

No description available.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1980. / Microfiche copy available in Archives and Science. / Vita. / Includes bibliographies. / by Robert Forster Stallard. / Ph.D.

One of the primary challenges facing researchers and practitioners in their efforts to address issues of poverty and environment is the need to deepen our understanding of the logic that guides local people's decisions over resource use, particularly among the rural poor whose livelihoods depend on fragile and dynamic environments. This study seeks to identify the set of factors that influences how rainforest people respond to abrupt natural disturbances and resource scarcity through changes in livelihood and resource management practices in two rural poor communities of the Peruvian Amazon. Data were gathered through in-depth survey interviews (n=95 households) between June and December 2003 in the Amerindian community of Arica Viejo (Ucayali River) and the mestizo (ribereno) community of Roca Fuerte (Maranon River). The results reveal that socioeconomic characteristics such as forest experience and knowledge, and access to agricultural land explain striking differences among households in livelihood responses to environmental change, particularly concerning resource use behavior, resilience to disturbance, and the propensity to adopt sustainable resource management strategies.

No description available.