Arquitetura de copas de árvores decíduas e sempre-verdes em cerrado sentido restrito no Distrito Federal

Dissertação (mestrado)—Universidade de Brasília, Instituto de Ciências Biológicas, Departamento de Ecologia, Programa de Pós-Graduação em Ecologia, 2014.Diferenças funcionais entre árvores de cerrado sentido restrito com fenologia vegetativa distinta têm sido investigadas em nível foliar e de indivíduo. Dados da literatura indicam que atributos foliares das espécies decíduas configuram uma estratégia menos conservativa de uso dos nutrientes, com maiores taxas de assimilação máxima de carbono (tendo como base a massa foliar) e maior área foliar específica e que a arquitetura das copas também diverge entre decíduas e sempreverdes. O presente estudo testa a hipótese de que espécies sempre-verdes apresentam maior razão de copa (proporção da altura total do indivíduo ocupada pela copa) e maior densidade de folhagem (m² de folhagem por m³ de copa) em comparação com espécies decíduas. A influência que características da copa exercem sobre as propriedades do ecossistema é função da contribuição relativa dos grupos fenológicos em termos de biomassa. Assim, foi testada a hipótese de contribuição equitativa dos grupos para a estrutura vegetação arbórea. O estudo foi conduzido entre junho de 2012 e dezembro de 2013 no Parque Nacional de Brasília, onde um módulo para estudos de longo duração composto por duas linhas de 5 km separadas por 1 km foi instalado. Para avaliar possíveis relações entre a distribuição de decíduas e fatores edáficos e topográficos, variáveis ambientais foram caracterizadas nas parcelas amostrais (n=10). A intensidade do último evento de queima e a concentração de nitrogênio total no solo foram as variáveis significativas para explicação da razão de copa, sem diferenças significativas entre grupos fenológicos. No entanto, sempre-verdes apresentaram maior densidade de folhagem. As espécies decíduas predominaram na área de estudo, correspondendo a cerca de 72% da biomassa lenhosa do compartimento arbóreo. As formações vegetais nas parcelas foram classificadas em cerrado ralo, cerrado típico e cerrado denso. Além dessa diferença na cobertura de arbóreas, as parcelas diferiram principalmente quanto à distância até a mata ripária e quanto à magnitude da variação interna de características do solo. A distribuição das espécies decíduas mostrou relação positiva com os valores mais baixos de pH do solo, o que parece estar relacionado a variações das características de solo em áreas de transição cerrado para vegetação ripária. _______________________________________________________________________________________________ ABSTRACTFunctional differences between Cerrado tree species with different vegetativephenology were investigated at both leaf and individual levels. Previous results inthe literature indicate that leaf traits of deciduous trees are related to a lessconservative nutrient use strategy, with higher values for maximum carbonassimilation rates (on a mass basis) and higher specific leaf area; and that crownarchitecture also diverge between deciduous and evergreen species. This study teststhe hypothesis that evergreen species presents higher values for crown ratio(proportion of individual total height occupied by the crown) and foliage density (m2of foliage per m3 of crown) in comparison to deciduous species. The influenceexerted by crown architecture attributes on ecosystem properties is a function of therelative contribution of each group in terms of biomass. Hence, the hypothesis ofequitable contribution of both groups to woody vegetation structure was tested. Thestudy was conducted from june 2012 to december 2013 in the Brasilia NationalPark, where a module for long-term studies composed of two lines of 5 km separatedby 1 km was installed. In order to evaluate possible relations between thedistribution of deciduous trees and edaphic and topographic factors, environmentalvariables were characterized in the sampling plots (n=10). Intensity of the previousfire event and soil N content were significant variables to explain crown ratio butdifferences between phenological groups were not observed. However, evergreenspecies showed higher foliage density. Deciduous species prevail in the study site,corresponding to approx. 72% of total dry wood biomass. Within study plots,vegetation was classified in to three formations along a gradient of increasing treecover: cerrado ralo – cerrado típico – cerrado denso. In addition to this differencein tree cover, plots in the study area differed mainly with respect to their position inthe terrain (distance to nearest riparian forest) and to the magnitude of internalvariations in soil attributes. Deciduous species distribution showed a positiverelation to higher values of soil pH, apparently due to shifts in soil characteristics intransitional areas between Cerrado and riparian forest

Reconstructing Three Decades of Land Use and Land Cover Changes in Brazilian Biomes with Landsat Archive and Earth Engine

Brazil has a monitoring system to track annual forest conversion in the Amazon and most recently to monitor the Cerrado biome. However, there is still a gap of annual land use and land cover (LULC) information in all Brazilian biomes in the country. Existing countrywide efforts to map land use and land cover lack regularly updates and high spatial resolution time-series data to better understand historical land use and land cover dynamics, and the subsequent impacts in the country biomes. In this study, we described a novel approach and the results achieved by a multi-disciplinary network called MapBiomas to reconstruct annual land use and land cover information between 1985 and 2017 for Brazil, based on random forest applied to Landsat archive using Google Earth Engine. We mapped five major classes: forest, non-forest natural formation, farming, non-vegetated areas, and water. These classes were broken into two sub-classification levels leading to the most comprehensive and detailed mapping for the country at a 30 m pixel resolution. The average overall accuracy of the land use and land cover time-series, based on a stratified random sample of 75,000 pixel locations, was 89% ranging from 73 to 95% in the biomes. The 33 years of LULC change data series revealed that Brazil lost 71 Mha of natural vegetation, mostly to cattle ranching and agriculture activities. Pasture expanded by 46% from 1985 to 2017, and agriculture by 172%, mostly replacing old pasture fields. We also identified that 86 Mha of the converted native vegetation was undergoing some level of regrowth. Several applications of the MapBiomas dataset are underway, suggesting that reconstructing historical land use and land cover change maps is useful for advancing the science and to guide social, economic and environmental policy decision-making processes in Brazil