Late quaternary vegetational and climatic changes in cerrado and palm swamp from central Brazil

Geochemical and palynological analyses of core CR1 from Crominia, Goias, provided information on the paleoenvironmental history of central Brazil. The records show that prior to 32,400 yr B.P. the vegetation of the Crominia region was similar to the present one characterized locally by a complex of cerrado, gallery forest and palm swamp, indicating a semi-humid tropical climate. A palm swamp occupied the coring site. From 32,400 to about 20,000 yr B.P. a treeless grassland replaced the arboreal cerrado and the gallery forest suggesting that humidity increased but temperature probably decreased. The site was a shallow lake between ca. 27,000 and 20,000 yr B.P. Humidity started to decrease at ca. 18,500 yr B.P. was very dry. A sparse vegetation was growing in the region during that time. The dry climate continued until 6500 yr B.P. and the core site probably dried out several times. At ca. 5000 yr B.P. humidity increased again, the palm swamp vegetation returned to the site and cerrado vegetation and gallery forest started to grow in the region. The abundant charcoal particles prior to 20,000 yr B.P. and from 10,500 to ca. 3500 yr B.P. document a long history of fires in the region. Results are compared with those from other sites in central Brazil and with the climate sequence of the last glacial maximum and postglacial time in the tropical Andes. (Résumé d'auteur

Late quaternary vegetational and climatic changes in cerrado and palm swamp from central Brazil

Geochemical and palynological analyses of core CR1 from Crominia, Goias, provided information on the paleoenvironmental history of central Brazil. The records show that prior to 32,400 yr B.P. the vegetation of the Crominia region was similar to the present one characterized locally by a complex of cerrado, gallery forest and palm swamp, indicating a semi-humid tropical climate. A palm swamp occupied the coring site. From 32,400 to about 20,000 yr B.P. a treeless grassland replaced the arboreal cerrado and the gallery forest suggesting that humidity increased but temperature probably decreased. The site was a shallow lake between ca. 27,000 and 20,000 yr B.P. Humidity started to decrease at ca. 18,500 yr B.P. was very dry. A sparse vegetation was growing in the region during that time. The dry climate continued until 6500 yr B.P. and the core site probably dried out several times. At ca. 5000 yr B.P. humidity increased again, the palm swamp vegetation returned to the site and cerrado vegetation and gallery forest started to grow in the region. The abundant charcoal particles prior to 20,000 yr B.P. and from 10,500 to ca. 3500 yr B.P. document a long history of fires in the region. Results are compared with those from other sites in central Brazil and with the climate sequence of the last glacial maximum and postglacial time in the tropical Andes. (Résumé d'auteur

Long-term spatial changes in the distribution of the Brazilian Atlantic forest

The aim of this study is to represent simultaneously changes in the spatial distribution of the Atlantic forest during the last 17,000years. To characterize such changes, here we focused on three different forest physiognomies, evergreen, semi-deciduous, and Araucaria, and we provide a list of indicator taxa for each class retrieved from the original published datasets. A review of the published fossil pollen records allowed us to classify regional behaviors in three main areas of distribution, north of 15 degrees S, between 15 degrees and 23 degrees S and south of 23 degrees S latitude that correspond to three climatic geographical barriers. Statistical probability density function method was used to illustrate changes in forest physiognomies throughout the three distribution areas. We show that the three modern barriers also functioned through the past. Asynchronous patterns of forest physiognomies are linked to an antiphasing pattern of monsoon precipitation between the northern and central area, whereas in the southern area, it is linked to the frequency and intensity of the polar advection in the subtropics. Our results attest to strong climate forcing on forest distribution between the late glacial and the interglacial period. They call into question the common reference to the last glacial maximum as a major (and sometimes as the only) driver of forest-related vicariance and genetic diversity patterns, but suggest that instead, orbital cycles were the main drivers of the successive expansion/contraction of the Atlantic forest throughout the Quaternary. Resumo Mais conhecimento sobre a historia bioclimatica da Mata Atlantica (brasileira) - um dos ecossistemas Neotropicais mais diversos e ameacados - politicas de conservacAo adequadas as mudancas climaticas devem ser urgentemente avaliadas. Direcionamos nosso foco para tres tipos diferentes de fisionomias florestais: floresta perene, floresta semi-decidua e floresta com Araucaria, alem de fornecer uma lista de taxons indicadores para cada um dos tipos florestais obtida de bancos de dados originais publicados. Uma revisAo de registros palinologicos e de espeleotemas publicados datando desde o ultimo maximo glacial nos permitiu distinguir comportamentos regionais em tres principais areas de distribuicAo: ao norte de 15 degrees S, entre 23 e 15 degrees S e ao sul de 23 degrees S de latitude. Estas areas de distribuicAo correspondem a tres barreiras climaticas definidas pelo periodo e duracAo da estacAo chuvosa (permanente na regiAo mais ao sul, curta e durante o verAo na regiAo central e durante o inverno na regiAo mais ao norte). Usamos entAo o metodo da funcAo de densidade de probabilidade estatistica para ilustrar mudancas na fisionomia florestal, fragmentacAo e deslocamentos espaciais ao longo dos ultimos 17,000 anos nestas tres areas de distribuicAo. Nos constatamos que as tres barreiras climaticas atuais tambem estiveram ativas no passado e provavelmente criaram as caracteristicas filogeograficas observadas atualmente. Os padroes assincronos dos movimentos florestais evidenciados entre a Mata Atlantica do norte e central estiveram relacionados com um padrAo antiphasing de precipitacAo de moncAo, enquanto que os da Mata Atlantica ao sul estiveram relacionados com a frequencia e intensidade da adveccAo polar nos subtropios. Nossos resultados indicam uma forte influencia do clima na distribuicAo das florestas entre o glacial tardio e o interglacial. Esse fato confronta a opiniAo formada de que o ultimo maximo glacial seria o maior (e algumas vezes o unico) condutor de vicariancia para florestas e padroes de diversidade genetica e sugere que os ciclos orbitais seriam os principais condutores de sucessivos intervalos de expansAo/contracAo da Mata Atlantica durante o Quaternario