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RESUMO -(O conceito de bioma). O termo fitofisionomia foi proposto praticamente ao mesmo tempo que o termo formação. O termo bioma, proposto mais tarde, apenas adicionou a fauna à uniformidade fitofisionômica e climática, características desta unidade biológica. Várias modificações conceituais foram apresentadas por diversos autores, ao longo do tempo, acrescentando outros fatores ambientais ao conceito original, como o solo, por exemplo. Walter propôs um conceito essencialmente ecológico, considerando bioma como uma área de ambiente uniforme, pertencente a um zonobioma, o qual é definido de acordo com a zona climática em que se encontra. Este conceito considera ainda outros fatores ambientais ecologicamente importantes, como altitude e solo, distinguindo, então, orobiomas e pedobiomas. Um outro fator a ser considerado seria o fogo natural (pirobiomas). Bioma e domínio morfoclimático e fitogeográfico não são sinônimos, uma vez que este último não apresenta necessariamente um ambiente uniforme. O bioma de savana tropical é constituído por um complexo de fitofisionomias, um complexo de formações, representando um gradiente de biomas ecologicamente relacionados, razão suficiente para considerar este complexo como uma unidade biológica.Palavras-chave: formação, bioma, zonobioma, domínio, savana ABSTRACT -(The biome concept). The terms phytophysiognomy and formation were proposed practically at the same time. The term biome, proposed later, only added the element fauna to the phytophysiognomic and climatic uniformity of the formation concept. Several conceptual modifications have been presented by a number of authors along time, adding other environmental factors to the original concept of biome, as soil for example. Walter proposed an essentially ecological concept, considering biome as an area of uniform environment, belonging to a zonobiome, which is defined by the climatic zone where it is found. This concept takes into consideration other important ecological factors, as altitude and soil, which then constitute orobiomes and pedobiomes. Another factor to be considered is natural fire (pyrobiomes). Biome and morphoclimatic and phytogeographical domain are not synonyms, since the latter does not necessarily have a uniform environment. The tropical savanna biome is a complex of phytophysiognomies, a complex of formations, which represents a gradient of ecologically related biomes, reason enough to consider this complex as a biological unit.Key words: formation, biome, zonobiome, domain, savanna IntroduçãoCom o agravamento dos problemas ambientais em nível global, como as queimadas de florestas na Amazônia, o aumento de gás carbônico na atmosfera e seu conseqüente efeito no aquecimento do Planeta, o crescimento do buraco de ozônio sobre o pólo sul, o avanço das fronteiras agrícolas, em detrimento das áreas naturais e etc., tem aumentado muito o interesse dos pesquisadores e de toda a mídia em denunciar tais fatos e procurar soluções. Hoekstra et al. (2005) ressaltaram que, além de uma "crise de extinção", ao nível...

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This paper presents the quantities of macro-nutrients (N, P, K, Ca, Mg and S) released from the ground layer vegetation to the atmosphere during six experimental burnings, in a Brazilian open savanna, named ‘campo-cerrado’. The values were obtained by comparing the amounts of nutrients in the fuel and in the ash resulting after the burn, in three different seasons. On average, 20.6 kg of N, 1.6kg of P, 7.1 kg of K, 12.1kg of Ca, 3.0 kg of Mg, and 3.2kg of S ha−1 were transferred from the plant biomass to the atmosphere, representing mean percentages of 95% for N, 51% for P, 44% for K, 52% for Ca, 42% for Mg, and 59% for S. The burn season showed no significant influence on the amounts of nutrients transferred to the atmosphere. Some relationships involving the quantities of macro-nutrients released, fuel moisture, the combustion efficiency during the burns, and the initial standing biomass in the area were also tested. Comparing the average output of macro-nutrients to the atmosphere obtained in this study with their inputs via rainfall, in the same area, it was estimated that three years would be an adequate interval between prescribed burnings for this campo-cerrado, to speed up nutrient recycling without impoverishing the system.

This paper presents a reconstruction of the Holocene palaeoenvironmental evolution in the central São Paulo State (Brazil) based on anthracological analyses, in association with soil isotopic composition (δ13C) and radiocarbon dating from four sites. Anatomical identification of charcoal particles allows the reconstitution of past plant associations, and consequently of the vegetation and climate history. Rather precise interpretations may be achieved when associating anthracology and soil δ13C analysis. In the early Holocene, climate was dry and an open cerrado vegetation (savanna) covered most of this area. A cerradão (forested savanna) or a semideciduous forest existed in the more humid localities. After 3500/3000 14C yr BP the climate was more humid, similar to the present, leading to the establishment of forested vegetation in all the studied sites. Com parison of these results with various palaeoenvironmental studies carried out in the Brazilian phytogeographical zone of cerrado and semideciduous forest suggests that at least its greater part presented a similar trend in the climatic evolution during the Holocene. This phytogeographical zone presented a dry climate during the early Holocene, then a more humid climate during the late Holocene. Climatic conditions similar to the present appeared from 5000 to 1000 yr BP, depending on the site.

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O presente trabalho procura analisar comparativamente os efeitos das queimadas e das saúvas na ciclagem dos nutrientes minerais em ecossistemas de cerrado. Sugere-se uma possível relação antagônica entre eles, tanto do ponto de vista temporal quanto espacial.