Navegando por Assunto "Savana"

Agora exibindo 1 - 3 de 3

Acesso aberto (Open Access)
Avifauna do estado de Roraima: biogeografia e conservação
(Universidade Federal do Pará, 2005) SANTOS, Marcos Pérsio Dantas; SILVA, José Maria Cardoso da; http://lattes.cnpq.br/6929517840401044
Acesso aberto (Open Access)
Caracterização de regimes de umidade em regiões tropicais: comparação entre floresta e savana
(Universidade Federal do Pará, 2008-08-11) SILVA, Ludmila Monteiro da; SÁ, Leonardo Deane de Abreu; http://lattes.cnpq.br/0107976161469463; MOTA, Maria Aurora Santos da; http://lattes.cnpq.br/5817549281617240
This study aims to investigate a method to classify humidity regimes based on different "states" characterization of the Tropical Atmospheric Boundary Layer (TABL), both above a forest area and above a savanna area, according with the methodology proposed by Mahrt (1991). Starting this classification, an improvement is performed while incorporates both the analysis of the thermodynamic stability of TABL for a forest area and the variation in Convection Available Potential Energy (CAPE). In these analyses, radiosonde data and data from micrometeorological towers obtained during field experiments have been used, collected during the less rainy period in each area. For the forest area (Caxiuanã) data from the COBRAPARÁ experiment were used (spanning the period from 06 to 13/11 of 2006), while for the savanna area (Daly Waters) data from the “KOORIN” experiment were used (spanning the period from 15/07 to 13/08 of 1974, in Australia). The comparison of humidity regimes of each area suggests that, should the Amazon rainforest be replaced with savanna, this would result in a drier atmosphere, with most of the energy used for the heating of that atmosphere, reduced evapotranspiration, decreased precipitation and the inexistence of CAPE. On the other hand, the analysis of the stability of the atmosphere in Caxiuanã showed that, contrary to observations in the Western Amazon, during the COBRA-PARÁ Experiment, the largest values of CAPE occurred at 18:00 local time due to the humidity convergence that occurs in the bay of Caxiuanã through the land-breeze circulation, indicating that in that area the maximum values of CAPE were associated predominantly with the humidity fields and not with temperature. Under such a “disturbed” TABL conditions, the phase space proposed by Mahrt (1991) doesn’t characterize well moisture regimes associated with great CAPE values.
Acesso aberto (Open Access)
Environmental changes during the last millennium based on multi-proxy palaeoecological records in a savanna-forest mosaic from the northernmost Brazilian Amazon region
(Universidade Federal do Pará, 2015-09) MENESES, Maria Ecilene Nunes da Silva; COSTA, Marcondes Lima da; ENTERS, Dirk; BEHLING, Hermann
The environmental changes and the dynamics of the savanna-forest mosaic, over the last 1050 years, have been reconstructed by pollen, charcoal, radiocarbon dating mineralogical and geochemical analyses of sediment cores taken from three different Mauritia flexuosapalm swamps in the northernmost part of the Brazilian Amazon region (northern state of Roraima). Studies on the relationship between the modern pollen rain and the regional vegetation provide additional information for the interpretation of the fossil pollen records. The fossil pollen assemblages and geochemical results indicate relatively wet climatic conditions throughout the recorded period. Despite these moist conditions, fires were frequent and are one of the reasons for the dominance of a grassy savanna instead of forest expansion in the study area. Considering the generally wet climatic conditions, these fires were most likely caused by human activities. Even today, fires hinder forest expansion into savanna areas. Sandy hydromorphic soils may also act as an edaphic control to maintain the current sharp boundary between forest and savanna ecosystems.