Vegetation History Research Articles

Comparative productivity of six bioenergy cropping systems on marginal lands in the Great Lakes Region, United States

AbstractGrowing lignocellulosic crops on marginal lands is a promising solution for sustainable biofuel production. We evaluated the productivity of bioenergy cropping systems (switchgrass [Panicum virgatum L., var. Cave‐In‐Rock], miscanthus [Miscanthus × giganteus, ‘Illinois clone’], hybrid poplar [Populus nigra × P. maximowiczii A. Henry ‘NM6’], native grasses [five species], early successional vegetation, and restored prairie vs. historical vegetation [as reference control]) with and without nitrogen fertilization on low‐fertility former cropland at five sites in the Great Lakes Region, United States. We reported biomass yields for the first 7 years after establishment. Switchgrass was most consistently productive across all sites but miscanthus was more productive at three of the five sites. When averaged across sites, years, and nitrogen (N) treatments, biomass yields followed the order miscanthus > switchgrass > hybrid poplar ≈ native grasses > restored prairie > early successional vegetation ≈ historical vegetation, but varied substantially by crop and site, with a significant crop by site interaction. Yields of miscanthus and switchgrass peaked after four–five growing seasons and declined thereafter, while yields of both native grasses and restored prairie increased throughout 6 years with no sign of follow‐on decline, suggesting that polycultures may outperform monocultures over the long term. Yields of early successional vegetation—similar in composition to historical vegetation at each site—did not improve with time. Nitrogen fertilization increased the yields of all cropping systems at all sites. Our results demonstrate the viability of low‐productivity former cropland for long‐term bioenergy production and suggest there is no single crop best suited for all low fertility soils.

History of vegetation and fires in the Arctic part of the Pur-Taz interfluve in the Holocene

The global climate change and significantly increased anthropogenic pressure on the Arctic and Subarctic regions require modern ecosystem monitoring and understanding of the past environmental changes. Vegetation history is reflected by pollen spectra recorded in peat deposits, investigation of which is one of the main methods in the research of long-term climatic changes. In order to reconstruct the vegetation and fire history of today’s south tundra in the lower reaches of the Taz river, we carried out palynological exploration of peat and underlying lake sediments covering the last 11.2 cal ka BP in the Tazovsky district of the Yamalo-Nenets Autonomous Okrug (Russia). In the course of the research, we found 31 pollen taxa, 4 taxa of spore plants, 2 types of fungal spores, one species of shell amoeba and green algae. We have identified several stages in the development of the local wetland biocenosis at the study site and reconstructed the history of changes in the vegetation cover of the region, including changes in the composition of the woody vegetation. Grasslands, with groups of trees among thickets of shrubs and lake-mire complexes dominated in the study area by 11.2 cal ka BP. The grasslands were gradually supplemented by wet grass communities, which were then replaced by swamps and tundra complexes in the mid-Holocene. The time periods of the local fires have been established. The fire that had the greatest effect on the vegetation at the study site was detected in the period of 8.1 cal ka BP. We have revealed periods of the least fire activity – 7.6–5.5 cal ka BP and the highest fire activity – 12.5–8 cal ka BP.

How wide, how much? A framework for quantifying the economic and ecological outcomes of altering riparian width on agricultural land

Creating and managing riparian buffer zones (RBZs) is regarded as a global best-practice management strategy for maintaining and improving waterway health. Agricultural land often utilises RBZs as highly productive pasture, exposing waterways to increased inputs of nutrients, pollutants, and sediment, in addition to reducing carbon sequestration and habitat for native flora and fauna. This project developed a novel approach to the application of multisystem ecological and economic quantification models to the property-scale, at low cost and high speed. We developed a state-of-the-art dynamic geospatial interface to communicate these outputs when switching from pasture to revegetated riparian zone via planned restoration efforts. The tool was developed using the regional conditions of a south-east Australian catchment as a case study but is designed to be adaptable around globally using equivalent model inputs. Ecological and economic outcomes were determined using existing methods, including an agricultural land suitability analysis to quantify primary production, an estimation of carbon sequestration using historic vegetation datasets and GIS software analysis to determine spatial costings of revegetation and fencing. Economic outcomes are presented in raw values of pasture produced and carbon sequestered, and fencing and revegetation costs can be easily altered for enhanced usability and interoperability. This tool can provide property-specific data for almost 16,000 properties in a catchment area of over 130,000 km2 and 19,600 km of river length. Our results indicated that current financial incentives for revegetation rarely cover the cost of giving up pasture, but these costs may be compensated by social and ecological outcomes achieved over time. This method provides a novel way of informing alternative management approaches, such as incremental revegetation plans and the selective harvesting of timber from RBZ. The model provides an innovative framework for improved RBZ management and can be used to inform property-specific responses and guide discussion among stakeholders.

Postglacial establishment and expansion of marginal populations of sugar maple in western Québec, Canada: Palynological detection and interactions with fire, climate and successional processes

An isolated sugar maple ( Acer saccharum Marsh.) stand is located in the boreal forest of Abitibi, about 75 km beyond its present northern range limit. When did this relatively thermophilous tree species establish after ice retreat? Were its populations more abundant than now sometimes in the past? If so, when and how did they expand then retracted? How did the species persist in boreal forest over time? What could have been the role of fire on this stand? To answer those questions, we reconstructed the postglacial fire and vegetation history from three lacustrine sediment sequences distributed along a c. 180 km latitudinal transect from southern boreal forests to the northern portion of deciduous forests. From north to south, those are lakes Labelle, Chasseur and Fur. We explored a procedure based on pollen accumulation rates in order to detect the probable presence of sugar maple within the lakes’ watershed. The procedure successfully indicates a sugar maple establishment c. 7800–5100 cal. BP at Fur, 5500–4400 cal. BP at Chasseur and c. 4000–2700 cal. BP at Labelle, in the north. At Fur, the subsequent sugar maple expansion happened 1 to 2 thousand years after establishment, during colder and moister climatic conditions favoring Pinus strobus L. replacement by Betula spp. c. 6000–5000 cal. BP. Sugar maple establishment, persistence or expansion is apparently not linked to a change in fire activity at Fur and Chasseur, but at Labelle, the species was more abundant during periods of shorter fire return intervals from 2000 to 500 years ago. Our study suggests that northern (Chasseur and Labelle) sugar maple establishment and possible expansion was probably more controlled by a complex interaction of inhibition and facilitation dynamics than by climate alone, a process reliant on the dominant vegetation’s composition and structure.

Vegetation History and the Exploitation and Use of Plant Resources in Aceramic Neolithic Cyprus: an Assessment of Recent Archaeobotanical Research

Vegetation History and the Exploitation and Use of Plant Resources in Aceramic Neolithic Cyprus: an Assessment of Recent Archaeobotanical Research

Control of hydrologic conditions and vegetation composition on carbon dynamics characterized by 13C enrichment in a dune-meadow cascade ecosystem in a semi-arid region

The variation of 13C enrichment (Δ13C and Δδ13C) is an effective indicator of the spatiotemporal dynamics of carbon stock. However, based on 13C enrichment, the effects of global climate change, land use types and historical vegetation succession on carbon dynamics have been found to be equivocal. Taking semi-mobile dune (SD) and meadow wetland (MW) ecosystems in the Horqin Sandy Land as examples, this study examined the stable carbon isotope ratios (δ13C) during the growing seasons in 2019 and 2020, and determined the factors controlling the continuum δ13C. The results revealed that throughout the carbon migration process, under different physiological mechanisms of carbon assimilation, distribution, and respiration, the seasonal variation of carbon isotope patterns exhibited significant differences in the air-plant-soil continuum of dune and meadow ecosystems. The MW with long-term stable vegetation coverage had higher soil carbon turnover than that in SD. In SD, both long-term and short-term restoration-accelerated soil carbon turnover. The effect of soil moisture (Ms) on Δδ13C (the surface soil δ13C minus leaf δ13C) will exceed that of air temperature in SD and MW. In MW, field capacity (FC) was the decisive indicator of various sources of Ms (rainfall, groundwater) affecting 13C enrichment variation. Δ13C (the discrimination of leaf carbon isotope) exerted a positive effect on Δδ13C only when Ms at 0–20 cm < FC, indicating the variable effect of photosynthesis on soil respiration throughout the growing seasons. Moreover, vegetation composition can also affect the extent to which soil respiration responds to photosynthesis.

Vegetation stability characterized the central Tibetan Plateau over the last two millennia but has recently begun to change

The vegetation history of the central Tibetan Plateau over the last two millennia provides an important baseline for exploring future vegetation evolution. In this paper, we analyze high-resolution records of pollen, grain-size, total organic carbon (TOC) and total nitrogen (TN) for a 66.5 cm deep sediment core collected from Beilei Co on the central Tibetan Plateau. Between ca. 210 CE and 1988 CE, pollen spectra together with other proxies show that the Beilei Co region was covered by alpine steppe and experienced a relatively stable environment, with only slight changes in vegetation composition and minor climatic variations. However, since 1988 CE, abundances of Artemisia and Cyperaceae have begun to increase, while those of Chenopodiaceae (current accepted Latin name is Amaranthaceae) and Asteraceae have decreased sharply. Both the pollen assemblages and other proxies show that the study area is currently undergoing a major change and that the period of vegetation stability that has characterized the past two millenia has now ended. We argue that the recent changes in the vegetation may be caused by increasing precipitation and/or thawing permafrost due to global warming. In the future, the alpine steppe around Beilei Co may be replaced by alpine meadow.

Low sensitivity of net primary productivity to climatic factors in three karst provinces in southwest China from 1981 to 2019

Karst areas are sensitive to environmental changes due to their fragile ecological environments. It is imperative to explore the temporal and spatial variations in the characteristics of vegetation net primary productivity (NPP) and evaluate the influence of different driving factors on NPP. Taking three karst provinces in southwest China as the study area, where the historical vegetation changes and the mechanisms influencing these changes remain unclear; therefore, the present study used vegetation NPP data from 1981 to 2019 to analyze the temporal and spatial variations in the characteristics of vegetation NPP using slope trend analyses and the sequential Mann-Kendall test. The influence of each driving factor on vegetation NPP and the interaction between each driving factor were investigated using the optimal parameters-based geographic detector (OPGD) model. The results were as follows: (1) The annual variation of the total NPP in the study area from 1981 to 2019 showed a fluctuating growth trend, with a slow growth rate before 2005 followed by a rapid increase. (2) The annual fluctuations in the seasonal NPP in the study area were generally upward, and the total NPP of vegetation in summer was the highest, but the growth rate of NPP in autumn was the fastest, and the area with the largest increase in NPP in autumn was the largest. (3) NPP was related to natural factors, with slope being the primary influencing factor at the annual scale. However, at the seasonal scale, there were differences in the explanatory power of the influencing factors on vegetation NPP. The highest explanatory power was observed for surface soil moisture in spring, air temperature in summer, and precipitation in autumn and winter. (4) The spatiotemporal evolution of NPP characteristics was affected by the interaction among various natural factors. At the annual and seasonal scales, the interaction between each climatic factor and slope greatly enhanced the explanatory power of individual climatic factors. Taken together, the interaction between slope and precipitation contributes the most to NPP.

Mid- to Late-Holocene coastal morphological evolution, vegetation history and land-use changes of the Porto Gulf UNESCO World Heritage site and its surroundings (NW Corsica Island, Western Mediterranean)

Two coastal areas located on the North-Western side of Corsica Island have been investigated to reconstruct their Mid- to Late-Holocene landscape evolution together with the history of human occupation. Particular attention has been paid to the study of shoreline migration and vegetation history alongside land-use. Three boreholes were drilled to a maximum depth of 4.20 m and laboratory work comprised the identification of molluscs and pollen/NPPs as well as sedimentological analyses. Chronostratigraphy is based on a series of 18 radiocarbon datings and enabled to reconstruct the environments in the Fangu Estuary to the north of the World Heritage site over the last six millennia, and over the last four millennia on the Girolata coastal plain to the south. Palaeogeographic reconstruction of shoreline mobility is established for each site based on borehole chronostratigraphy analysis. In addition, two original pollen and NPPs diagrams have been established for the Girolata and Fangu sites. These reveal that anthropogenic activities began to significantly impact local vegetation cover ca. 2500 years BP at Girolata, and ca. 2000 years BP at Fangu. Of particular interest, our work records the first complete pollen sequence in Corsica for Roman times at Girolata: first, the exploitation of cereals, grapevines and the development of husbandry is observed during the Roman Republic (500 BCE–0), followed by the almost exclusive cultivation of Olea sp. during the Roman Empire (0–500 CE). Following this, and using other regional pollen studies obtained for NW Corsica, we propose a regional evolution of the complex human-environment interactions for the last six millennia. Our results reveal a peak of regional forest decline (the most intense event recorded for the Late-Holocene) from the 11th to the 16th centuries CE which can be attributed to the exploitation of wood resources during the Pisan and Genoese dominations of the island.

Vegetation dynamics in arid central Asia over the past two millennia linked to NAO variability and solar forcing

The role of NAO modes and solar activity, together with their potential relationship, in driving hydroclimatic variability in arid central Asia over the past two millennia remain controversial—partly due to the limitations of the resolution or time span of existing paleoclimatic records. Vegetation ecosystems at high altitudes are very sensitive to hydroclimate variations. Here, we present a vegetation history for the past two millennia based on a pollen record with an average time resolution of four years from Lake Dalongchi in the Tianshan Mountains. Our results show a millennial-scale drying trend during the past 2000 years, with the vegetation changing from forest-steppe and forest to steppe as the intensity of mid-latitude westerlies gradually decreased. We suggest that the dynamic link between the NAO and moisture variability in arid central Asia depends on the NAO phase in the context of changes in westerlies intensity. The moisture variability in arid central Asia shows a positive relationship with NAO phases when the precipitation delivered by the mid-latitude westerlies exceeded a threshold level in the period of 0–1100 CE. However, over the last millennium, the role of the NAO mode was weakened by solar forcing when the regional moisture gradually decreased below this threshold. The decline of the ancient Silk Road was possibly related to this humid-to-try climate shift at∼1100 CE.

Postglacial Fire and Vegetation History from Doheney Lake in the Sinlahekin Wildlife Area, Okanogan County, Washington

In recent decades, dry ponderosa pine (Pinus ponderosa)-dominated forests of the eastern Cascades have experienced a dramatic increase in large, high-severity wildfires resulting in significant damage to natural resources. However, relatively little is known about long-term trends in postglacial fire activity in these forests. The purpose of this study was to reconstruct the fire and vegetation history of the Doheney Lake watershed, located in north-central Washington, using macroscopic charcoal and pollen analysis of a ca. 12,330-year-long lake sediment record. The results illustrate that regional climatic change, as well as climatically-controlled vegetation shifts, were the primary drivers of fire activity during much of the postglacial period. In particular, the establishment of the modern forest between ca. 7500 and 6000 cal yr BP due to cooler and moister conditions led to greater amounts of burnable biomass and generally higher levels of fire activity. The study results also suggest that greater interannual climate variability linked to drought may have played a role in the highly variable fire activity during much of the past 6,000 years. Additionally, it is likely that Indigenous cultural burning contributed to the fire activity at the site prior to Euro-American settlement, in particular during the past 4,000 years. Since ca. 125 cal yr BP (1825 CE), an almost complete absence of fire has allowed for the encroachment of shade-tolerant trees and has resulted in the potential for catastrophic wildfire, like that experienced at the site in 2015.

Plant Diversity and Species Composition in Relation to Soil Enzymatic Activity in the Novel Ecosystems of Urban–Industrial Landscapes

The primary producers and processes of matter and energy flow, reflected by the soil enzyme activity, are the basics of all ecosystem functioning processes. This paper reviews the relationships between the plant diversity, the physicochemical substrate parameters, and the soil enzymatic activity in novel ecosystems of the urban–industrial landscape, where the factors driving soil enzyme activity are not fully understood and still need to be studied. The relationship between the biotic and abiotic factors in the development of novel ecosystems on de novo established habitats, e.g., sites of post-mineral excavation, are shaped in ways unknown from the natural and the semi-natural habitats. The main criteria of de novo established ecosystems are the vegetation patches of the non-analogous species composition created as a result of human impact. The non-analogous species assemblages are associated with different microorganism communities because the biomass and the biochemistry of soil organic matter influence the enzyme activity of soil substrates. Moreover, the soil enzyme activity is an indicator that can dynamically reflect the changes in the microbial community structure dependent on the best-adapted plant species, thanks to the particular traits and individual adaptive adjustments of all the plant species present. This way, soil enzyme activity reflects the sum and the interactions of the elements of the ecosystem structure, irrespective of the vegetation history and the habitat origin.

Late Holocene Environmental History and Norse Settlement in Outer Fjords from South Greenland: A Case Study at Lake Qallimiut

To complement discussions about vegetation history and climate variations in south Greenland, especially during the Norse settlement, we developed a sedimentological multiproxy approach to study a 4300-year-old lacustrine core comprising pollen analysis, NPPs analysis, physical measurements (magnetic susceptibility, density, and grain size), and geochemical analyses (X-ray fluorescence, X-ray diffraction, and elemental analyses). Sediment archives were retrieved from a river-fed lake, Lake Qallimiut, located in the outer fjords of the Vatnahverfi area. The pollen analysis indicated a transition from juniper and willow cover to a dwarf birch forest. Non-pollen palynomorphs (NPPs) suggested grazing pressure and the presence of wild herbivores between 2300 and 1800 cal. BC. From ca. 1000 cal. AD, the presence of Norse farmers was evidenced in this area by archaeological surveys, and pollen analyses confirm the presence of human activities from the 11th century to the end of the 13th century. However, human impact progressively vanished between the 12th and 13th centuries, much earlier than at the other Vatnahverfi sites.

Determination of Paleoenvironmental Changes by Using δ13C, 14C Dating and Rb/Sr Ratio in Critical Karst Area of Yunnan-Guizhou Plateau, Southwestern China

Paleosols preserve archives of vegetation history, environmental changes, and sedimentary systems. The changes in vegetation history and environmental conditions in karst areas of the Yunnan–Guizhou plateau of southwestern China since the late Pleistocene were analyzed using δ13C, 14C and the Rb/Sr ratio. Our δ13C results reveal the coexistence of C3 and C4 plants (−10.91 to −30.45‰) in soil organic matter, something that is consistent with the present field vegetation assessment. The large vertical difference in the δ13C value (&gt;4‰) is related to the cultivation of agricultural crops and to changes in environmental conditions. Furthermore, the variation in δ13C values was influenced by the summer monsoon climate of the Indian Ocean and east Asia. We found that total organic carbon (TOC) concentration decreased exponentially with soil depth, indicating high carbon loss. In addition, 14C apparent age of the soil profiles ranged from modern times to 20,605 (±63) years before the present (yrs. BP) and is positively correlated with soil depth. The combined results indicate that, since the late Pleistocene era, environmental conditions in the study area have changed intermittently on a scale of millennia from hot-humid to cold-dry conditions. We speculate that there may have been extreme climate events in the study area 14,750 years BP, which are marked by a drastic change in δ13C and in the Rb/Sr ratio.

Visible or not? Reflection of the 8.2 ka BP event and the Greenlandian–Northgrippian boundary in a new high-resolution pollen record from the varved sediments of Lake Mondsee, Austria

This paper presents a new pollen record from Lake Mondsee in the north-eastern European Alps and discusses changes in vegetation composition between 9000 and 7000 a BP in response to the 8.2 ka BP cooling event, which is clearly reflected in a stable oxygen isotope record from the same lake. Pollen and microcharcoal analyses performed at bi-decadal resolution provide detailed insights into the vegetation history and fire regime in the study area. The late Greenlandian and early Northgrippian between ca. 9000 and 8000 a BP were mainly characterised by the gradual expansion of spruce, accompanied by the retreat of hazel. Results of the pollen-based biome reconstruction show that the Greenlandian–Northgrippian boundary at ca. 8280 a BP was marked by a shift in the affinity scores of regional forest biomes, reflecting a decreasing role of temperate broadleaved trees and shrubs and a strengthening of boreal conifers in the study area. During the early Northgrippian between ca. 8000 and 7000 a BP, fir and beech spread around Lake Mondsee, which is in line with other pollen records from the northern Alpine Foreland, indicating cooler and moister conditions. This long-term trend is likely a response to decreasing summer insolation (i.e. decreasing summer temperatures) and the weakening of the Siberian High, which promoted westerly-driven moisture transport from the Atlantic region. Visual inspection of the Lake Mondsee pollen data does not reveal a clear signal of the 8.2 ka BP event. However, biomization results show a distinct minimum in the temperate deciduous biome scores and summed scores of plant functional types representing warm-loving tree and shrub taxa at ca. 8165–8135 a BP.

Three thousand years of anthropogenic impact and water management and its impact on the hydro-ecosystem of the Mérantaise river, Paris conurbation (France)

This article assesses the long-term hydro-sedimentary and ecological consequences of the urban pressure around Paris over the last 3000 years on the Mérantaise river. Using a geoarchaeological approach combining sedimentological, geochemical, palynological and geophysical investigations enabled us to identify the transformations of the hydrosystem and to discuss the consequences of the different types of pressure and to put the role of biophysical and historical legacies into perspective with respect to contemporary dynamics. Using two study sites, one a former pond (Mérancis), the other a former mill site (Ors mill), nine cores, two auger holes and four trenches dug in the valley floor and two electrical resistivity tomography (ERT) profiles, it was possible to reconstruct the geometry of the sedimentary deposits. Chronostratigraphy was based on 41 radiocarbon dates and the history of vegetation and anthropogenic activities was reconstructed from 42 pollen samples and non-pollen palynomorphs collected from the former pond site. Despite the expansion of wetlands in the valley bottom, the pollen data revealed strong agropastoral activities and cereal growing in the Iron Age and up until the end of the Middle Ages. For the first time, sedimentological data associated with pollen data revealed hemp retting activities from c. 675 CE. From the Late Middle Ages onwards, water management led to the creation of two ponds to feed water mills. Despite the persistence of wetlands, this study highlights the early onset of anthropogenic modifications and in particular, the start of organic pollution and eutrophication in the Early Middle Ages, attesting to early eutrophication of water quality and aquatic environments resulting from the transformation of agropastoral practices and hydraulic pressure around the largest European city during the last 1500 years, well before the inset of urban sprawl in the watershed.

Descriptive systematics of Upper Palaeocene–Lower Eocene pollen and spores from the northern Niger Delta, south-eastern Nigeria

Fossil pollen and spores are a vital source of information on the geological history of tropical vegetation including reconstructions of vegetation diversity and composition. However, such work relies on a sound taxonomic framework, and this is challenging to achieve because of the large number of pollen and spore morphotypes that are encountered in palynological preparations from tropical sediments. In tropical West Africa, for example, extensive taxonomic work on Cretaceous–Paleogene pollen and spores was undertaken in the later part of the twentieth century, but more recent palynological work has focussed on stratigraphy and basin evolution, and there is a need for additional taxonomic work on the pollen and spores of this region. We have undertaken a descriptive systematic study of pollen and spores (sporomorphs) from 15 sediment samples spanning the Upper Palaeocene–Lower Eocene of south-eastern Nigeria. A palynoflora consisting of 29 spores, two gymnosperm pollen grains, and 138 angiosperm pollen grains is described. Two new spore species are proposed, and one new genus and 18 new species of angiosperm pollen are proposed. The general vegetation type represented by the palynoflora consists of palm-dominated swamps, perhaps with mangroves. The richness of each sample ranges from 29 to 76 sporomorph taxa, and rarefaction analysis suggests an increase in diversity from the Palaeocene to the Eocene in this region. Samples from the Palaeocene Upper Nsukka Formation are dominated by pollen with botanical affinities to the Arecaceae (palms) and Araceae (arums), and this assemblage is very similar to the Palaeocene in the Neotropics.

Editorial

Editorial

Relict soil features in cave sediments record periods of wet climate and dense vegetation over the last 100 kyr in a present-day semiarid region of northeast Brazil

The present-day semiarid region of NE Brazil experienced multiple periods of increased precipitation during the Quaternary. They were likely linked to global-scale events (e.g., Heinrich Events) and drove changes in vegetation dynamics, leading to the expansion of rainforest vegetation. Here, we hypothesize that soil features preserved in cave sediments records paleoenvironmental changes induced by global-scale events that affected NE Brazil during the Late Pleistocene - Early Holocene. To test this hypothesis, we analyzed the elemental and isotopic geochemistry composition, bulk sediment mineralogy, soil micromorphological features, and fauna fossil type and content of a well-preserved 6 m cave sediment profile spanning 103 kyr – 8 kyr in Toca de Cima do Pilão at the Serra da Capivara National Park. Our approach provides new information on the history of soil formation, vegetation, and climate of NE Brazil during the Late Pleistocene - Early Holocene. The results demonstrated that severe weathering and dense vegetation was the dominant paleoenvironmental conditions during wet periods, when latosolization was the main soil forming process. The evidence for wet and intense weathering periods was the co-existence of speleothems layers with Ferralsol features, such as runiquartz, granular microstructure, Fe nodules and gibbsite formation. Some of these features were found in layers deposited in synchrony with Heinrich Stadial and Younger Dryas periods, suggesting that past soil processes in NE Brazil were affected by those global-scale events. We propose five phases of latosolization in our study area during the last 100 kyr. The first was identified around 80 kyr, the second occurred around 29 kyr. The third coincided with Heinrich Stadial 1 (16 kyr) and the fourth likely occur during the Younger Dryas, and the fifth phase occurred during the middle Holocene.

Landscape and Climate Changes in Southeastern Amazonia from Quaternary Records of Upland Lakes

The upland lakes (ULs) in Carajás, southeastern Amazonia, have been extensively studied with respect to their high-resolution structural geology, geomorphology, stratigraphy, multielement and isotope geochemistry, palynology and limnology. These studies have generated large multiproxy datasets, which were integrated in this review to explain the formation and evolution of the ULs. These ULs evolved during the Pliocene–Pleistocene periods through several episodes of a subsidence of the lateritic crust (canga) promoted by fault reactivation. The resulting ULs were filled under wet/dry and warm/cool paleoclimatic conditions during the Pleistocene period. The multielement geochemical signature indicates that the detrital sediments of these ULs were predominantly derived from weathered canga and ferruginous soils, while the sedimentary organic matter came from autochthonous (siliceous sponge spicules, algae, macrophytes) and allochthonous (C3/C4 canga and forest plants and freshwater dissolved organic carbon) sources. Modern pollen rain suggests that even small ULs can record both the influence of canga vegetation and forest signals; thus, they can serve as reliable sites to provide a record of vegetation history. The integrated data from the sedimentary cores indicate that the active ULs have never dried up during the last 50 ka cal BP. However, subaerial exposure occurred in filled ULs, such as the Tarzan mountain range during the Last Glacial Maximum (LGM) and the Bocaína and S11 mountain ranges in the mid-Holocene period, due to the drier conditions. Considering the organic proxies, the expansion of C4 plants has been observed in the S11 and Tarzan ULs during dry events. Extensive precipitation of siderite in UL deposits during the LGM indicated drier paleoenvironmental conditions, interrupting the predominantly wet conditions. However, there is no evidence of widespread forest replacement by savanna in the Carajás plateau of southeastern Amazonia during the late Pleistocene and Holocene.