The possibility of ecosystem boundary changes in northern Brazilian Amazonia during the Holocene period was investigated using soil organic carbon isotope ratios. Determination of past and present fluctuations of the forest-savanna boundary involved the measurement of natural C isotope abundance, expressed as δC, in soil organic matter (SOM). SOM C analyses and radiocarbon dating of charcoal fragments were carried out on samples derived from soil profiles taken along transects perpendicular to the ecotonal boundary. SOM δC values in the upper soil horizons appeared to be in equilibrium with the overlying vegetation types and did not point to a movement of the boundary during the last decades. However, δC values obtained from deeper savanna and forest soil layers indicated that the vegetation type has changed in the past. In current savanna soil profiles, we observed the presence of mid-Holocene charcoals derived from forest species: fire frequency at that time was probably greater, and more extensive savanna may have resulted. Isotope data and the presence of these charcoals thus suggest that the forest-savanna boundary has shifted significantly in the recent Holocene period, forest being more extensive during the early Holocene than today. During the middle Holocene, the forest could have strongly regressed, and fires appeared, with a maximum development of the savanna vegetation. At the beginning of the late Holocene, the forest may have invaded a part of this savanna, and fires occurred again.

The Cerrado biome is Brazil's breadbasket and a major provider of ecosystem services, though these dual roles are increasingly at odds, in part because there are few mechanisms to protect remaining vegetation from large‐scale agricultural expansion. We assessed Cerrado conversion to soy using over 580,000 property boundaries, covering 77% of the biome that is eligible for commercial land use, and using microwatersheds, to cover 100% of eligible areas. Soy expansion accounted for 22% of conversion during 2003–14. Only 15% of clearing exceeded restrictions on private properties under the Forest Code (FC). However, 51% of soy farms have violated the FC, five times the rate of other farms. As a leading cause of both Cerrado conversion and FC violations, the soy sector has environmental and economic incentives to shift production to already cleared land. We used suitability maps to identify potential pathways for soy expansion across both old and new cropland frontiers.

SUMMARYConserving natural vegetation cover is of critical importance for maintaining the ecological integrity and hydrological properties of large river basins (more than 100 000 km 2 ). Recent estimates indicate that more than 700 000 km

Recent studies on relict eolian dunes in the Rio Negro basin, northern Amazon, Brazil (00°35′N, 63°14′W), indicate a drier climate regime during the Late Pleistocene–Holocene transition that is different from the present humid climate. The eolian sands form long chains of linear dunes bordering the Rio Negro River and some tributaries. Here, we present thermoluminescence (TL) ages spanning the period 32,000–8000 yr B.P. The final dune stabilization took place after 8,000 yr B.P. and now the bases of the dunes are fixed by vegetation. Clustering of the TL dates suggests that the dry climate in the Amazon Basin occurred in distinct episodes and argues against current opinions that drastic ecological changes did not affect in the Amazon during the last global glaciation.

Este trabalho apresenta os primeiros resultados do esforço conjunto de várias instituições, organizadas em torno da rede Geoma (Rede Temática de Pesquisa em Modelagem Ambiental da Amazônia) para avançar a compreensão dos novos padrões e processos de estruturação do território nas novas frentes no sul do Pará, analisando padrões de desmatamento e os processos que dão origem a esses padrões. Busca-se, aqui, produzir os subsídios necessários para o desenho de políticas públicas responsáveis, que não privilegiem um único aspecto do problema, como a abertura de estradas, por exemplo. Aponta-se, então, a partir desses primeiros resultados, que apenas uma solução integrada que procure estruturar os principais agentes e processos na cadeia produtiva seria possível para minorar os efeitos do desmatamento e nortear o desenvolvimento integrado para a região, com benefícios para a floresta e para as populações que ali vivem.
This work presents the first results achieved through an interdisciplinary and multi-institutional effort conduct by the Geoma Network, aiming to advance in the comprehension of the new frontiers in the South of the Pará State, in the Amazonian region, by examining the new patterns of deforestation and the underlying processes that are generating them. Our objective is to product information aiding to draw responsible public policies considering not only one dimension of the problem like roads infra-structure, as usual. Based on the analysis presented here we pointed out that only an integrated solution, that considers the main actors and the organization of economical processes in the productive chains over the region, would be capable to minimize the effects of deforestation and would drive an integrated development policy to the region bringing benefits to forest conservation and the local population