The Pantanal, the world's largest tropical wetland and a globally significant centre of biodiversity, has been increasingly threatened by fire. The extreme fire season of 2019-20, which caused enormous environmental damage, was linked to drought. However, predicting the future of fire in this region is challenging because of complex interactions among topography, seasonal flooding, and diverse vegetation. Here, we investigate climatedriven changes to fire regimes across five distinctive vegetation types by integrating millennial-scale histories of fire and climate with high-resolution monitoring and remote sensing data from the last two decades. We show that the impacts of climate change on fire activity varies depending on vegetation. In savannahs, fire occurrence is highly correlated to biomass availability, while seasonally dry tropical forest burns only under extreme drought conditions. The seasonally flooded vegetation mosaic is observed to be highly flammable under low rainfall and protracted dry seasons. This study highlights that new fire threats to low-lying flooded vegetation are emerging as human impact and climate change reshape fire regimes in the Pantanal.

For millennia, climate changes and Indigenous peoples have influenced Earth’s tropical and subtropical forests. Their relative importance affects our understanding of these ecosystems’ resilience to current anthropogenic changes, so is subject to intensive research and debate. South America’s Atlantic Forest, a global biodiversity hotspot, has been largely absent from this conversation. Here we focus on one of this region’s most iconic, ancient and threatened formations—southern Brazil’s highland mosaic of Araucaria Forest and Campos grasslands. Using novel integrations of palaeo-data and ecological modelling, we assess how climatic and human drivers shaped these landscapes, often through changes to fire dynamics, over the last 6,000 years. We show that climate changes made significant contributions to Araucaria Forest expansions over the last several thousand years, driven by non-linear responses of fire-forest feedback loops to minor climatic shifts. However, within Araucaria Forest areas that experienced more intense human use and occupation, Indigenous people cultivated crops, modified fire dynamics, and profoundly affected vegetation structure and composition. Our results challenge binary views of climate- versus human-driven past vegetation change. Climate, humans and fire all shaped these landscapes through space and time in complex and interacting ways, all of which must be considered to understand or effectively conserve them.

ABSTRACT This study presents the modern pollen signature and Holocene vegetation and climate history of the evergreen forest and associated ecosystems in the Bahia Coastal Forest ecoregion of Brazil's Atlantic Forest biodiversity hotspot. Artificial pollen traps provided the modern pollen signature of the evergreen forest, which is marked by Urticaceae/Moraceae, Simarouba , Crepidospermum / Protium , Sloanea , Sapotaceae and Diploon , and presence of rare forest tree pollen types. The pollen signature of the wooded mussununga , an associated ecosystem, is characterized by Byrsonima , Doliocarpus , Lundia and Araliaceae. Fossil pollen from Lagoa Canto Grande shows that the early to middle Holocene (11 154–7731 cal a bp ) vegetation was characterized by regional dominance of semi‐deciduous forest, under a less humid and cooler climate than today, as well as coastal vegetation on sandy soils ( restinga ), mangrove and patches of alluvial forests. Relative sea‐level rise during the middle Holocene caused regional changes in the distribution of alluvial forests, restingas and mangroves. A change to warmer and more humid climatic conditions during the middle to late Holocene (7731–434 cal a bp ) led to forest community changes, with the establishment of the modern evergreen forest.

The Casarabe culture (500-1400 CE), spreading over roughly 4,500 km2 of the monumental mounds region of the Llanos de Moxos, Bolivia, is one of the clearest examples of urbanism in pre-Columbian (pre-1492 CE) Amazonia. It exhibits a four-tier hierarchical settlement pattern, with hundreds of monumental mounds interconnected by canals and causeways1,2. Despite archaeological evidence indicating that maize was cultivated by this society3, it is unknown whether it was the staple crop and which type of agricultural farming system was used to support this urban-scale society. Here, we address this issue by integration of remote sensing, field survey and microbotanical analyses, which shows that the Casarabe culture invested heavily in landscape engineering, constructing a complex system of drainage canals (to drain excess water during the rainy season) and newly documented savannah farm ponds (to retain water in the dry season). Phytolith analyses of 178 samples from 18 soil profiles in drained fields, farm ponds and forested settings record the singular and ubiquitous presence of maize (Zea mays) in pre-Columbian fields and farm ponds, and an absence of evidence for agricultural practices in the forest. Collectively, our findings show how the Casarabe culture managed the savannah landscape for intensive year-round maize monoculture that probably sustained its relatively large population. Our results have implications for how we conceive agricultural systems in Amazonia, and show an example of a Neolithic-like, grain-based agrarian economy in the Amazon.

Multiple pre-Columbian (pre-1492 CE) archaeological sites now challenge the traditional portrayal of Amazonia as a ‘pristine wilderness’. This is especially true within the forest-savanna mosaic landscapes of lowland Bolivia, where the pre-Columbian Casarabe Culture constructed hundreds of settlement mounds, integrated with a dense causeway-canal network – one of the most complex, stratified societies yet discovered in Amazonia. Excavations at previous sites indicate that this culture sustained itself by practicing large-scale, maize-based agriculture. However, the Casarabe Culture’s mounds have also been found within the riparian forests abutting major river systems, where their inhabitants could have benefitted from greater access to forest resources and local fish species. To determine whether these differences influenced how the Casarabe Culture utilised the landscape, we conducted palaeoecological analysis on the sediments collected from Laguna Loma Suarez (LLS), an oxbow lake situated adjacent to a monumental habitation mound within these riparian forests. Our analysis reveals that, despite significant differences in natural resource availability, the Casarabe Culture continued to cultivate maize locally around LLS for over a millennium, between 280 BCE and 1130 CE, with anthropogenic fires largely restricted to the open savannas. Our record also suggests that the Casarabe Culture possibly delayed either forest recovery or natural forest encroachment until after the nearby settlement mound was abandoned. These findings, when compared with those of other sites in the region, show that maize was an important crop in pre-Columbian times, irrespective of major differences in natural resource availability across the complex forest-savanna mosaic settings of Amazonian Bolivia.

The Llanos de Moxos in the Bolivian Amazon, the second largest South American wetland, hosts many endemic species and a rich archaeological record that spans the entire Holocene. Despite its ecological and archaeological importance, very little is known about its Holocene environmental history. A growing body of evidence suggests that neotectonics played an important role in shaping its modern landscape and controlling past flooding dynamics, but the chronology and vertical displacements of past tectonic events are still largely unknown. Here, we present new data from a core taken at Lake Oceano, a large ria lake in the northern part of the Llanos de Moxos. To identify changes in the lithology and environment, we performed a battery of analyses, such as XRF scanning, mineralogy, granulometry, C/N and C and N stable isotopes, and also built an age-depth model using eighteen radiocarbon dates obtained from accelerator mass spectrometry (AMS) determinations. Based on the sedimentology and chemical analyses, we identified three major disturbances in the lake sedimentation that we interpret as positive tectonic events (i.e., tectonic uplifts). The first identified event occurred at approximately 13,400 cal yr BP and led to the formation of the lake by blocking the river course. A second uplift event took place around 10,000 cal yr BP, accompanied by a significant change in the geochemistry of the lake sediments. Furthermore, we have verified a third event at 6000 cal yr BP, previously recognized as responsible for the onset of Lake Rogaguado (aprox. 100 km NE of Lake Oceano), one of the largest lakes in South America. Overall, we show that ria lakes can provide key sedimentary archives to reconstruct the past timing and intensity of tectonic events. We discuss the interplay between tectonics and climate, highlighting the connection between tectonics and the region's flood history, with crucial implications for the interpretation of both archaeological and palaeoecological records throughout the Holocene.

Southern Brazil's highland Araucaria Forest-Campos grassland mosaic is an ancient and iconic landscape in the globally important Atlantic Forest biodiversity hotspot. Human land use has inflicted significant losses on the region's natural vegetation since the late 19th Century, but these have not been effectively quantified. This study uses land cover maps and forest survey data to assess how much of the mosaic's natural vegetation remains, the quality of this remnant vegetation, how it has changed since 1985, and the extent to which it is protected. Natural vegetation covers 13.9-37.3 % of the Araucaria Forest-Campos mosaic's core regions and 13.0-38.0 % of the whole area, depending on the dataset. Most remnant areas are degraded and remaining forests have low average integrity. In only minorities of forest plots are the landscape's characteristic Araucaria angustifolia trees still present (23.5 % in the Araucaria Forest region), moderately abundant (11.4 %), or >50 % of the canopy (0.5 %). Major expansions in cropland and forest plantations between 1985 and 2018 drove net/absolute losses of 12.7 %/24.1 % in the mosaic's natural forest and 38.1 %/43.2 % in its natural grasslands. Protected Areas and Indigenous Territories cover 4.6 % of the core mosaic and 6.5 % of the whole region. These conserve important remnant vegetation, though grasslands are under-protected. By analysing and integrating diverse and complementary data sources, we significantly improve on and add nuance to previous estimates of the quantity and quality of Araucaria Forest remnants. This study also provides the first robust, quantitative estimate of remaining highland grassland across southern Brazil.

Humans have been modifying ecosystems since before the Holocene began ca. 12,000 years ago, even in Neotropical regions. The Amazon was once thought to be ‘pristine’ and only lightly impacted by Indigenous people before European colonization in the Americas (e.g., pre-Columbian); however, multiple lines of evidence have shown that Indigenous human activities over the past millennia have left ecological legacies on modern ecosystems. We review the various lines of evidence used to reconstruct pre-Columbian Indigenous human activity in Amazonia, and assess the spatial and temporal resolution and limits of each one of them. We suggest that a multi-proxy approach is always preferred, and that lines of evidence that cover overlapping yet discrete spatial and temporal scales can provide a robust and comprehensive assessment of the nuances of pre-Columbian Indigenous human activities in Amazonia, and how they affect modern ecosystems.

The Amazon Rainforest Ecotone (the ARF- Ecotone ) of the southwestern Amazon Basin is a transitional landscape from tropical evergreen rainforests and seasonally flooded savannahs to savannah woodlands and semi-deciduous dry forests. While fire activity plays an integral role in ARF- Ecotones , recent interactions between human activity and increased temperatures and prolonged droughts driven by anthropogenic climate change threaten to accelerate habitat transformation through positive feedbacks, increasing future fire susceptibility, fuel loads, and fire intensity. The long-term factors driving fire in the ARF- Ecotone remain poorly understood because of the challenge of disentangling the effects of prolonged climatic variability since the Last Glacial Maximum (LGM; ~24,000 to 11,000 cal BP) and over 10,500 years of human occupation in the region. To investigate this issue, we implement an interdisciplinary framework incorporating multiple lake sediment cores, with varying basin characteristics with existing regional palaeoclimatological and archaeological data. These data indicate expansive C 4 grasslands coupled with low fire activity during the LGM, higher sensitivity of small basins to detecting local-scale fire activity, and increased spatial diversity of fire during the Holocene (~10,500 cal year BP to the limit of our records ~4,000 cal year BP), despite a similar regional climate. This may be attributed to increased human-driven fire. These data raise the intriguing possibility that the composition of modern flora at NKMNP developed as part of a co-evolutionary process between people and plants that started at the beginning of the ARE occupation.

Phytolith analysis is a well-established archaeobotanical tool, having provided important insights into pre-Columbian crop cultivation and domestication across Amazonia through the Holocene. Yet, its use as a palaeoecological tool is in its infancy in Amazonia and its effectiveness for reconstructing pre-Columbian land-use beyond archaeological sites (i.e., ‘off-site’) has so far received little critical attention. This paper examines both new and previously published soil phytolith data from SW Amazonia to assess the robustness of this proxy for reconstructing pre-Columbian land-use. We conducted the study via off-site soil pits radiating 7.5 km beyond a geoglyph in Acre state, Brazil, and 50 km beyond a ring-ditch in northern Bolivia, spanning the expected gradients in historical land-use intensity. We found that the spatio-temporal patterns in palm phytolith data across our soil-pit transects support the hypothesis that pre-Columbian peoples enriched their forests with palms over several millennia, although phytoliths are limited in their ability to capture small-scale crop cultivation and deforestation. Despite these drawbacks, we conclude that off-site soil phytolith analysis can provide novel insights into pre-Columbian land use, provided it is effectively integrated with other land-use (e.g., charcoal) and archaeological data.

ABSTRACT Uncertainty remains over local‐scale responses of ecotonal Amazonian forests to middle Holocene drying due to the scarcity, and coarse spatial resolution, of lacustrine pollen records. This paper examines the palaeoecological potential of soil phytoliths, stable carbon isotopes and charcoal for capturing local‐scale ecotonal responses of different types of Bolivian Amazonian forest to middle Holocene climate change. Soil pits 1 m deep were dug at ecotones between rainforest, dry forest, Chaco woodland and savannah, and sampled at 5–10 cm resolution. Both phytolith and stable carbon isotope records indicate stability of dry forest–savannah ecotones over the last ca. 6000 years, despite middle Holocene drought, revealing the dominance of edaphic factors over climate in controlling this type of ecotone. In contrast, δ 13 C data reveal that rainforest–savannah ecotones were more responsive to climate change, with rainforest likely replaced by drought‐tolerant dry forest or savannah vegetation during the mid‐Holocene, consistent with regional‐scale lacustrine pollen records. However, such shifts are not apparent in most of our phytolith records due to insufficient taxonomic resolution in differentiating rainforest from dry forest. Charcoal data show that ecotonal dry forests experienced greater fire activity than rainforests and that recent high fire activity at all forest sites is unprecedented since at least the middle Holocene.

There is a major concern for the fate of Amazonia over the coming century in the face of anthropogenic climate change. A key area of uncertainty is the scale of rainforest dieback to be expected under a future, drier climate. In this study, we use the middle Holocene (ca. 6000 years before present) as an approximate analogue for a drier future, given that palaeoclimate data show much of Amazonia was significantly drier than present at this time. Here, we use an ensemble of climate and vegetation models to explore the sensitivity of Amazonian biomes to mid-Holocene climate change. For this, we employ three dynamic vegetation models (JULES, IBIS, and SDGVM) forced by the bias-corrected mid-Holocene climate simulations from seven models that participated in the Palaeoclimate Modelling Intercomparison Project 3 (PMIP3). These model outputs are compared with a multi-proxy palaeoecological dataset to gain a better understanding of where in Amazonia we have most confidence in the mid-Holocene vegetation simulations. A robust feature of all simulations and palaeodata is that the central Amazonian rainforest biome is unaffected by mid-Holocene drought. Greater divergence in mid-Holocene simulations exists in ecotonal eastern and southern Amazonia. Vegetation models driven with climate models that simulate a drier mid-Holocene (100-150 mm per year decrease) better capture the observed (palaeodata) tropical forest dieback in these areas. Based on the relationship between simulated rainfall decrease and vegetation change, we find indications that in southern Amazonia the rate of tropical forest dieback was similar to 125,000 km(2) per 100 mm rainfall decrease in the mid-Holocene. This provides a baseline sensitivity of tropical forests to drought for this region (without human-driven changes to greenhouse gases, fire, and deforestation). We highlight the need for more palaeoecological and palaeoclimate data across lowland Amazonia to constrain model responses.

First described over 120 years ago in Brazil, Amazonian Dark Earths (ADEs) are expanses of dark soil that are exceptionally fertile and contain large quantities of archaeological artefacts.The elevated fertility of the dark and often deep A horizon of ADEs is widely regarded as an outcome of pre-Columbian human influence 1 .Archaeological research provides clear evidence that their widespread formation in lowland South America was concentrated in the Late Holocene, an outcome of sharp human population growth that peaked towards 1000 BP 2-4 .In their recent paper Silva et al. 5 argue that the higher fertility of ADEs is principally a result of fluvial deposition and, as a corollary, that pre-Columbian peoples just made use of these locales, contributing little to their enhanced nutrient status.Soil formation is inherently complex and often difficult to interpret, requiring a combination of geochemical data, stratigraphy, and dating.Although Silva et al. use this combination of methods to make their case 5 , their hypothesis, based on the analysis of a single ADE site and its immediate surroundings

This work aims to understand mangrove resilience to changes in a wave-influenced delta in southeastern Brazil during the late Holocene using an integrated analysis of palynology, sedimentology, and geochemistry (813C, 815N, C:N and C:S ratio), and radiocarbon dating on two sediment cores. The data indicated three mangrove succession phases: 1) an estuarine point bar/tidal flat occupied by a mixture of mangrove species (-2660 - 2050 cal yr BP); 2) a tidal flat dominated by Laguncularia mangroves (-2050 - - 900 cal yr BP); and 3) tidal flats with Laguncularia mangroves upstream and establishment of Rhizophora/Avicennia mangrove at the river mouth (-900 cal yr BP until present). The geochemical results suggest a dominance of C3 terrestrial plants with a mixture of C4 plants and organic matter of marine/estuarine origin throughout the late Holocene. Laguncularia and Rhizophora trees were established since - 2660 cal yr BP as pioneers, followed thereafter by Avicennia. Currently, tidal flats upstream are occupied by mangroves mainly represented by Laguncularia. Rhizophora/ Avicennia mangroves occur at the mouth of the river. The relative sea-level fall during the late Holocene, as well as the channel dynamics, caused the development of tidal flats and mangrove succession inland. The succession of Rhizophora, Laguncularia, and Avicennia, followed by the permanence of only Laguncularia, is likely related to the resilience of each mangrove genus to habitat disturbance (e.g., salinity and sediment grain size fractions) caused by sea-level changes and channel dynamics. Our results show that mangroves may be resilient to the effects of Atlantic sea-level fluctuations, but the floristic structure in the past is different from that of today.

AbstractIn contrast to temperate regions, relationships between basin characteristics (e.g., type/size) and fossil pollen archives have received little attention in Amazonia. Here, we compare fossil pollen records of a small palm swamp (Cuatro Vientos; CV) and a nearby large lake (Laguna Chaplin, LCH) in Bolivian Amazonia, demonstrating that palm swamps can yield Quaternary pollen archives recording the history of terrestrial vegetation beyond the basin margin, rather than merely a history of localized swamp vegetation dynamics. The pollen assemblages from these two contrasting basins display remarkable agreement throughout their late Quaternary history, indicating past drier climates supported savanna landscape during the last glacial maximum (LGM; 24,000–18,000 cal yr BP) and savanna/semideciduous forest mosaic during the middle Holocene (7000-4750 cal yr BP) at both regional (inferred from LCH) and local (inferred from CV) spatial scales. Additionally, the local-scale catchment of CV and the basin's proximity to the riverine forests of the Río Paraguá enables exploration of the extent of gallery/riverine forests during the LGM and middle Holocene. We show that, between 24,000–4000 cal yr BP, riverine/gallery rainforests were substantially reduced compared with present, challenging the hypothesis that gallery rainforests were important refugia for rainforest species during the drier LGM and middle Holocene.

Brazil's Atlantic Forest biome is one of the world's biodiversity hotspots, whose heterogeneous ecosystems are threatened by habitat loss and climate change. Palaeoecological research can provide essential context for the impacts of anthropogenic climate change in the 21st Century and beyond, but existing studies have notable limitations in the insights they can provide: vegetation proxy data are spatially and temporally skewed with inconsistent taxonomic resolution; existing modelling studies typically overlook individualistic species-level responses, are limited in temporal coverage, and lack close integration with empirical palaeoecological data. Here, we investigate the impact of major climate changes upon the species-level floristic composition of southern Brazil's Atlantic Forest, from the Last Glacial Maximum (LGM) to the late 21st Century, by modelling the distributions of 30 key species at seven time slices since the LGM and comparing the assemblages they form with an unprecedented dataset of palaeoecological proxy data. We find notable compositional changes through time across our study area, especially during the early Holocene, which was characterised by extensive no-analogue plant communities. Aspects of these modelled floristic changes are captured in proxy records but many occur in data-sparse regions, highlighting geographic foci for future palaeoecological investigation to test these model predictions. Our findings highlight the individualistic responses of Atlantic Forest plant species to climate change and help resolve long-standing palaeoecological questions - explaining the dominance of highland grasslands at the Last Glacial Maximum (likely due to low atmospheric CO2 concentrations), clarifying the LGM extent of coastal tropical forest (probably in a grassland matrix on exposed continental shelf), and explaining the origins of Araucaria angustifolia's western populations (from climatic (micro-)refugia rather than human-mediated dispersal). Our results also set the 21st Century's impending climate and vegetation changes in a 21,000-year temporal context, revealing that, under a high emissions scenario, more than 100,000 km(2) of the southern Atlantic Forest will experience more climate-driven floristic change in the coming decades than it has in the last 21 millennia. (C) 2021 Elsevier Ltd. All rights reserved.

In the 12,000 years preceding the Industrial Revolution, human activities led to significant changes in land cover, plant and animal distributions, surface hydrology, and biochemical cycles. Earth system models suggest that this anthropogenic land cover change influenced regional and global climate. However, the representation of past land use in earth system models is currently oversimplified. As a result, there are large uncertainties in the current understanding of the past and current state of the earth system. In order to improve representation of the variety and scale of impacts that past land use had on the earth system, a global effort is underway to aggregate and synthesize archaeological and historical evidence of land use systems. Here we present a simple, hierarchical classification of land use systems designed to be used with archaeological and historical data at a global scale and a schema of codes that identify land use practices common to a range of systems, both implemented in a geospatial database. The classification scheme and database resulted from an extensive process of consultation with researchers worldwide. Our scheme is designed to deliver consistent, empirically robust data for the improvement of land use models, while simultaneously allowing for a comparative, detailed mapping of land use relevant to the needs of historical scholars. To illustrate the benefits of the classification scheme and methods for mapping historical land use, we apply it to Mesopotamia and Arabia at 6 kya (c. 4000 BCE). The scheme will be used to describe land use by the Past Global Changes (PAGES) LandCover6k working group, an international project comprised of archaeologists, historians, geographers, paleoecologists, and modelers. Beyond this, the scheme has a wide utility for creating a common language between research and policy communities, linking archaeologists with climate modelers, biodiversity conservation workers and initiatives.

Archaeological research provides clear evidence that the widespread formation of Amazonian Dark Earths (ADEs) in tropical lowland South America was concentrated in the Late Holocene, an outcome of sharp demographic growth that peaked towards 1000 BP. In their recent paper, however, Silva et al. propose that the high fertility of ADE is not of anthropic origin but instead the result of alluvial deposition starting in the Middle Holocene (8200-4200 cal BP). In order to support this argument, they marshal data and observations from a single expanse of ADE, the archaeological site of Caldeirão, and disregard or misread other studies of ADEs in the Central Amazon region. Silva et al.'s claim, an epilogue to ‘geogenic’ models laid to rest over 40 years ago, also dismisses research showing how long-term anthropic soil enrichment occurs as a result of daily practices at contemporary indigenous settlements. Here we critically review Silva et al.’s analysis and affirm that, like most ADEs, Caldeirão has anthropic soil horizons formed by burning, deposition, and reworking of refuse associated with indigenous settlement activities between 2500 and 500 BP.

First described over 120 years ago in Brazil, Amazonian Dark Earths (ADEs) are expanses of dark soil that are exceptionally fertile and contain large quantities of archaeological artefacts. The elevated fertility of the dark and often deep A horizon of ADEs is widely regarded as an outcome of pre-Columbian human influence. Controversially, in their recent paper Silva et al.2argue that the higher fertility of ADEs is principally a result of fluvial deposition and pre-Columbian peoples just made use of these locales rather than contributing to their enhancement. Soil formation is inherently complex and often difficult to interpret, requiring a combination of geochemical data, stratigraphy, and dating. Although Silva et al. use this combination of methods to make their case, their study, based on the analysis of a single ADE site and its immediate surroundings, is too limited to distinguish among the possible mechanisms for ADE formation. Silva et al.’s conclusions contradict decades of research by archaeologists, soil scientists, geographers and anthropologists, who agree that ADEs are anthropic soils formed on land surfaces enriched by inputs resulting from pre-Columbian sedentary settlement. To be accepted, and be pertinent at a regional level, Silva et al.’s hypothesis would need to be supported by extremely solid evidence, which we demonstrate is lacking.

An estimated 90 to 95% of Indigenous people in Amazonia died after European contact. This population collapse is postulated to have caused decreases in atmospheric carbon dioxide concentrations at around 1610 CE, as a result of a wave of land abandonment in the wake of disease, slavery, and warfare, whereby the attendant reversion to forest substantially increased terrestrial carbon sequestration. On the basis of 39 Amazonian fossil pollen records, we show that there was no synchronous reforestation event associated with such an atmospheric carbon dioxide response after European arrival in Amazonia. Instead, we find that, at most sites, land abandonment and forest regrowth began about 300 to 600 years before European arrival. Pre-European pandemics, social strife, or environmental change may have contributed to these early site abandonments and ecological shifts.