Past Vegetation Changes Research Articles

Late Pleistocene and Holocene vegetation changes in the arid Andean piedmont of central Argentina inferred from sediment stable carbon isotopes and C/N ratios

Stable carbon isotopes (δ13C) and C/N ratios in bulk sediment organic matter were used as indicators of C3 and C4 vegetation functional types in a ca. 40-kyr, predominantly alluvial sequence from Arroyo La Estacada (33.5°S, 69°W), in the arid Andean piedmont of central Argentina. Although this sediment sequence has the potential to contribute to the knowledge of past vegetation dynamics through its fossil pollen content, previous palynological studies provided scant information, constrained to a few time windows, because of poor pollen preservation. Stable isotope results for the total organic carbon fraction from three lithostratigraphic sections that span the past 40 kyr show shifts in δ13C values associated with changing contributions from C3 and C4 plants, suggesting this proxy can detect changes in these photosynthetic pathways, representative of Patagonian (and/or stream-margin macrophytes) and Monte phytogeographic units, respectively. Climate and local factors, such as water availability in the basin, are inferred to be the main drivers of vegetation dynamics. The C/N ratios in a few samples show that organic matter sources are algae and/or phytoplankton, not solely C3 or C4 vascular plants. The δ13C record from Arroyo La Estacada is an example of how isotope geochemistry has overcome difficulties with pollen analysis and provided a reliable tool to investigate past vegetation changes in regions where C3 and C4 are differentially distributed. Isotope values during part of the Marine Isotope Stage 3 (MIS 3) and the middle Holocene are attributed to C3 local floodplain plants, with a little or no contribution from regional terrestrial (Patagonian) vegetation. Late Pleistocene–Holocene palaeosols have a clear C4 signal of terrestrial dominance, representative of Monte plants, thus, carbon isotope values constrain the early times of MIS 1, particularly where the Pleistocene–Holocene transition occurs. A mixture of C3 and C4 values during the last 3–4 kyr is indicative of environmental conditions that prevail in the region today.

Temporal and spatial evolution of Holocene vegetation and lake hydrological status, China

Studying past climate change has important scientific significance in exploring long-term climatic variability, assessing the nature and human’s contribution to climate warming, and predicting future climate change. Here, we presented a data synthesis of pollen records, organic geochemical proxies, as well as lake-level records, along with numerical climate classification and lake-level simulations to show temporal and spatial evolution of past vegetation and hydrologic change during the Holocene in China. Both geological data and numerical modeling indicated that the evolution of vegetation shows out-of-phase relationships with lake hydrological status in various regions. China as a whole experienced optimal vegetation cover in the mid-Holocene. However, areas dominated by the Asian monsoon and the Westerlies did not uniformly show an early Holocene hydrological optimum. For the Westerlies-controlled regions, optimal conditions prevailed during the mid-Holocene. These apparent contradictions were closely related to various driving factors in different geographical regions. Precipitation has been recognized as a major influence on lake hydrological status of arid and semi-arid in northeast China, whereas in other regions of China, the combined effect of evaporation and precipitation was more influential. Likewise, the limiting factor of vegetation conditions was asynchronous in China, for example, moisture in northwestern China, temperature in the Qinghai-Tibet Plateau, as well as moisture and temperature in the monsoon marginal zones and monsoonal regions. The results provide insights into the underlying climate-forcing mechanisms, and demonstrate a new perspective on Quaternary environment change research.

Biome changes and their inferred climatic drivers in northern and eastern continental Asia at selected times since 40 cal ka bp

Recent global warming is pronounced in high-latitude regions (e.g. northern Asia), and will cause the vegetation to change. Future vegetation trends (e.g. the “arctic greening”) will feed back into atmospheric circulation and the global climate system. Understanding the nature and causes of past vegetation changes is important for predicting the composition and distribution of future vegetation communities. Fossil pollen records from 468 sites in northern and eastern Asia were biomised at selected times between 40 cal ka bp and today. Biomes were also simulated using a climate-driven biome model and results from the two approaches compared in order to help understand the mechanisms behind the observed vegetation changes. The consistent biome results inferred by both approaches reveal that long-term and broad-scale vegetation patterns reflect global- to hemispheric-scale climate changes. Forest biomes increase around the beginning of the late deglaciation, become more widespread during the early and middle Holocene, and decrease in the late Holocene in fringe areas of the Asian Summer Monsoon. At the southern and southwestern margins of the taiga, forest increases in the early Holocene and shows notable species succession, which may have been caused by winter warming at ca. 7 cal ka bp. At the northeastern taiga margin (central Yakutia and northeastern Siberia), shrub expansion during the last deglaciation appears to prevent the permafrost from thawing and hinders the northward expansion of evergreen needle-leaved species until ca. 7 cal ka bp. The vegetation-climate disequilibrium during the early Holocene in the taiga-tundra transition zone suggests that projected climate warming will not cause a northward expansion of evergreen needle-leaved species.

Soil phytoliths as indicators of initial human impact on San Cristóbal Island, Galápagos

I analyzed phytoliths from soil profiles on San Cristóbal Island in the Galápagos Islands to determine whether historical human impact and recent vegetation dynamics are visible in the phytolith record. I extracted phytoliths from soil samples taken from four test pits located at the village, an abandoned field, a forest, and an active agricultural field - all located within the former El Progreso plantation (AD 1860–1920). Changes in the ratio of tree to grass phytoliths with depth in all four samples suggest changes in vegetation composition from forest to open vegetation dominated by grasses, which reflects the removal of forest with colonization and the first permanent human occupation of the archipelago in the middle 19th century. This paper shows that the changes in vegetation brought about by colonization and land clearing for plantations are documented in the soil phytoliths record, and suggests that phytoliths can be used as an indicator of past vegetation change in future work on the historical ecology of the Galápagos archipelago.

Seasonal and canopy height variation in n-alkanes and their carbon isotopes in a temperate forest

The stable carbon isotopic composition (δ13C) of terrestrial leaf wax components, such as n-alkanes (δ13Calk), is used extensively to address questions about past changes in vegetation, climate and the carbon cycle. To interpret sedimentary δ13Calk values, characterization of the environmental and biological controls on carbon isotopic fractionation during plant metabolism is required, especially for fractionation that occurs during photosynthesis (ɛleaf-CO2 or Δleaf) and n-alkane biosynthesis (εalk-leaf). Although much is understood about controls on ɛleaf-CO2, little is known about seasonal or within canopy variation in n-alkane composition and εalk-leaf. To address the gap, we sampled 5 common tree species (Acer rubrum, Acer saccharum, Juniperus virginiana, Sassafras albidum and Ulmus americana) from buds to senescing leaves from within a single temperate forest in southwestern Ohio, USA. We measured n-alkane concentration, δ13Calk, leaf biomass δ13C (δ13Cleaf), δ13C of atmospheric CO2 within the canopy, luminous flux and specific leaf area (SLA). In angiosperms, δ13Calk values were low in the buds, increased substantially (4–6‰) to the highest values in young leaves and then decreased (1–3‰) in mature leaves. Seasonal variation in δ13Calk values generally tracked changes in δ13Cleaf, but the fractionation between leaf and n-alkanes (εalk-leaf) was variable, with lower values in buds (−6.7 ± 1.1‰) than in young leaves (−4.9 ± 2.3‰). Later in the growing season, εalk-leaf values stabilized and ranged between −2.5 and −6.5‰, with a mean of −4.3 ± 1.4‰ in angiosperms. Stabilization of δ13Calk values coincided with settling of SLA and increase in average chain length (ACL). For the conifer, temporal variation in δ13Calk values was smaller (ca. 2‰) compared with the angiosperms, and εalk-leaf values slightly increased when n-alkane production increased. Average εalk-leaf value in the conifer at the end of the growing season was −5.0 ± 0.7‰. We speculate that εalk-leaf variation in both angiosperms and the conifer reflects changes in the source of carbon for plant metabolism, as well as the timing of wax synthesis. We also tested canopy effects on n-alkane concentration and carbon isotopic fractionation at different heights and extent of canopy closure. n-Alkane concentrations were higher at the top of the canopy by 2–8 times than in the lower canopy. The εleaf-CO2 values were more negative at the lower two thirds of the canopy than the upper one third of the canopy by 2–4‰ in two species with closed canopies. The εalk-leaf values did not vary with height and extent of canopy closure. To further explore the link between canopy leaves and leaf litter, we compared δ13Calk values of mature canopy leaves with those in leaf litter collected during senescence, and the offsets were within ca. 1‰. The results confirm indications that leaf litter δ13Calk values reflect those of the upper canopy leaves due to not only high leaf biomass in the upper canopy but also to high n-alkane production.

Climatic history of the northeastern United States during the past 3000 years

Abstract. Many ecosystem processes that influence Earth system feedbacks – vegetation growth, water and nutrient cycling, disturbance regimes – are strongly influenced by multidecadal- to millennial-scale climate variations that cannot be directly observed. Paleoclimate records provide information about these variations, forming the basis of our understanding and modeling of them. Fossil pollen records are abundant in the NE US, but cannot simultaneously provide information about paleoclimate and past vegetation in a modeling context because this leads to circular logic. If pollen data are used to constrain past vegetation changes, then the remaining paleoclimate archives in the northeastern US (NE US) are quite limited. Nonetheless, a growing number of diverse reconstructions have been developed but have not yet been examined together. Here we conduct a systematic review, assessment, and comparison of paleotemperature and paleohydrological proxies from the NE US for the last 3000 years. Regional temperature reconstructions (primarily summer) show a long-term cooling trend (1000 BCE–1700 CE) consistent with hemispheric-scale reconstructions, while hydroclimate data show gradually wetter conditions through the present day. Multiple proxies suggest that a prolonged, widespread drought occurred between 550 and 750 CE. Dry conditions are also evident during the Medieval Climate Anomaly, which was warmer and drier than the Little Ice Age and drier than today. There is some evidence for an acceleration of the longer-term wetting trend in the NE US during the past century; coupled with an abrupt shift from decreasing to increasing temperatures in the past century, these changes could have wide-ranging implications for species distributions, ecosystem dynamics, and extreme weather events. More work is needed to gather paleoclimate data in the NE US to make inter-proxy comparisons and to improve estimates of uncertainty in reconstructions.

Stability and instability on Maya Lowlands tropical hillslope soils

Substantial lake core and other evidence shows accelerated soil erosion occurred in the Maya Lowlands of Central America over ancient Maya history from 3000 to 1000years ago. But we have little evidence of the wider network of the sources and sinks of that eroded sediment cascade. This study begins to solve the mystery of missing soil with new research and a synthesis of existing studies of tropical forest soils along slopes in NW Belize. The research aim is to understand soil formation, long-term human impacts on slopes, and slope stability over time, and explore ecological implications. We studied soils on seven slopes in tropical forest areas that have experienced intensive ancient human impacts and those with little ancient impacts. All of our soil catenas, except for one deforested from old growth two years before, contain evidence for about 1000years of stable, tropical forest cover since Maya abandonment. We characterized the physical, chemical, and taxonomic characteristics of soils at crest-shoulder, backslopes, footslopes, and depression locations, analyzing typical soil parameters, chemical elements, and carbon isotopes (δ13C) in dated and undated sequences. Four footslopes or depressions in areas of high ancient occupation preserved evidence of buried, clay-textured soils covered by coarser sediment dating from the Maya Classic period. Three footslopes from areas with scant evidence of ancient occupation had little discernable deposition. These findings add to a growing corpus of soil toposequences with similar facies changes in footslopes and depressions that date to the Maya period. Using major elemental concentrations across a range of catenas, we derived a measure (Ca+Mg)/(Al+Fe+Mn) of the relative contributions of autochthonous and allochthonous materials and the relative age of soil catenas. We found very low ratios in clearly older, buried soils in footslopes and depressions and on slopes that had not undergone ancient Maya erosion. We found high (Ca+Mg)/(Al+Fe+Mn) values on slopes with several lines of evidence that suggest relative youth, soils possibly formed since Maya abandonment. Carbon isotopes (δ13C) also provide some evidence of past vegetation change on slopes. We found strong evidence for maize or other alien C4 species in an ancient terrace soil and additional evidence in buried footslopes but only evidence for C3 species (like tropical trees) on the backslopes and other crest-shoulders. The fact that steep slopes preserved no evidence of C4 species inputs may mean that the ancient Maya maintained forests here. Alternatively, ancient Maya land uses eroded slopes, with the δ13C signatures detected today being the result of more recent soil development under forest over the last millennium. Additional evidence that these soils are recent in age includes elevated (Ca+Mg)/(Al+Fe+Mn) values, skeletal soil profiles, and low soil magnetic susceptibility. Besides the evidence for truncating backslopes and aggrading footslopes, the ancient Maya built agricultural terraces that accumulated soils and altered drainage. All these ancient Maya slope alterations would have influenced modern tree distributions, because many tree species in the modern forest show strong preferences for different soil types and topographic situations that the ancient Maya changed.

Vegetation dynamics during last 35,000 years at a cold desert locale: preferential loss of forbs with increased aridity

AbstractPaleoecological records are an important source of data to better understand ecological responses to climate. To help understand vegetation–climate relationships in the Great Basin cold desert of North America, we analyzed 154 plant taxa from 52 fossil woodrat middens that spanned both an 800‐m elevation gradient and the last 35,000 yr (35 ka) within a single study area. Vegetation was analyzed by community assemblage (CA), by plant functional type, and by individual species. Concordant with a predominant trend of increased aridity since glacial maximum, CA change was largely unidirectional despite centennial‐scale cycles of climate variation. Richness of forb and other herbaceous plant functional types peaked from 15 to 26 ka during glacial maximum and then gradually decreased from ~15 ka to present. Analysis of individual taxa indicates that once a herbaceous species was lost from the study area, that species did not re‐occur. In contrast, woody (shrubs and trees) species richness peaked from 8 to 15 ka during and following the Bolling‐Allerod rapid warming. However, most tree taxa that established during this period of warming were subsequently lost as climate became more arid after the beginning of Mid‐Holocene Temperature Maximum warming ~8 ka. These shifts in plant functional types decreased relative richness of forbs compared to shrubs (i.e., decreased forb/shrub ratio), and these shifts continue to the present despite intervening cycles of climate cooling and warming. We conclude that the relative importance of herbaceous species in current CAs of the Great Basin cold desert has been decreasing for the last 15 ka. We also speculate that decreased richness of herbaceous species has, in part, provided opportunities for exotic species to establish and proliferate in the Great Basin during the last 100 yr. Thus, observations of past vegetation change suggest that increased aridity with future climate warming will continue to favor woody vegetation over herbaceous species at our cold desert locale, at least until invasive species displace native shrub species.

Holocene environments of central Iturup Island, southern Kuril archipelago, Russian Far East

AbstractTwo lake records document Holocene changes in sea level, vegetation, and climate on the Okhotsk and Pacific sides of central Iturup Island, southern Kuril Islands. The sediment cores originated within tidal flats that subsequently developed into a marine strait which crosscut the island as sea levels rose during the early Holocene. Brackish lagoons and eventually freshwater lakes formed by ~7100 cal yr BP associated with warmer than present conditions. Past vegetation changes indicate a clear Holocene thermal maximum recorded on the Pacific coast but a less distinct optimum on the western shores (~7200–6100 cal yr BP). A gradual cooling toward modern levels occurred ~6100–3500 cal yr BP. Four prominent layers of coarse sediment found in mid- to late Holocene lake deposits may correspond to intervals of climate cooling/dune formation previously documented in coastal sections. Although chronological limitations question the synchronicity of these events across the south Russian Far East, it seems probable that they have a regional signature. However, the mechanisms responsible for Holocene climatic changes are likely the result of complex interactions of hemispheric-scale atmospheric patterns, marine characteristics, and regional feedbacks rather than simply fluctuations in sea levels as suggested in the current interpretative model.

Neolithic woodland management and land-use in south-eastern Europe: The anthracological evidence from Northern Greece and Bulgaria

Wood charcoal (anthracological) remains accumulated in archaeological deposits provide a valuable tool for reconstruction of past local vegetation and its use. They can offer evidence complementary to pollen analysis or be the main source on past vegetation change in areas where no pollen preservation is available. The current study assembles the anthracological evidence from 18 Neolithic sites situated in the zone spanning between the Lower Danube plain and the Aegean coast. This evidence is presented within the broader archaeological and paleoecological context of the region and in cal. years BC and/or BP. The data is interpreted in terms of land-use related to woodland management and exploitation of woodland resources during three chronological phases which could be distinguished within the Neolithic of south-eastern Europe: a) 6500-5800 cal. BC, b) 5800-5500 cal. BC, and c) 5500-4900 cal BC). The main vegetation type targeted by the Neolithic population were the thermophilous, mixed deciduous oak communities, which contained a rich and diverse undergrowth of light-demanding and fruit/nut bearing trees, shrubs and herbs. Those plant communities were the major source of fuel wood, forest pasture, fodder, gathered fruits, etc. The analyses indicate stability and sustainability of the firewood procurement and woodland management practices for the whole considered period and further suggest that the Neolithic land-use strategies favoured the rich and often fruit-bearing undergrowth of the oak forests and woodland.

Exploring the Ecological History of a Tropical Agroforestry Landscape Using Fossil Pollen and Charcoal Analysis from Four Sites in Western Ghats, India

Contrary to expectations, some human-modified landscapes are considered to sustain both human activities and biodiversity over the long-term. Agroforestry systems are among these landscapes where crops are planted under native shade trees. In this context, ancient agroforestry systems can provide insight into how farmers managed the landscape over time. Such insight can help to quantify the extent to which tropical forests (especially habitat-specialist trees) are responding to local and landscape-level management. Here, we extracted fossil pollen (indicator of past vegetation changes) and macroscopic charcoal (indicator of biomass burning) from four forest hollows’ sedimentary sequences in an ancient agroforestry system in Western Ghats, India. We used a mixed-modelling approach and a principal components analysis (PCA) to determine past trajectories of forest change and species composition dynamics for the last 900 years. In addition, we reconstructed the long-term forest canopy dynamics and examined the persistence of habitat-specialist trees over time. Our results show that the four sites diverged to a surprising degree in both taxa composition and dynamics. However, despite these differences, forest has persisted over 900 years under agricultural activities within agroforestry systems. This long-term analysis highlights the importance of different land-use legacies as a framework to increase the effectiveness of management across tropical agricultural lands.

Patterns and dynamics of European vegetation change over the last 15,000 years

AbstractAimPalaeoecological reconstructions document past vegetation change, with estimates of fast shifts in species distributions. The resulting rates of plant spread are often not matched by model simulations of climate‐driven vegetation dynamics. Genetic surveys of extant plant populations document directions of the post‐glacial spread of trees, challenging traditional interpretations. Our aim is to examine an updated continental pollen data set from Europe in the light of the new ideas about vegetation dynamics emerging from genetic research and vegetation modelling studies.LocationEurope.MethodsWe use pollen data from the European Pollen Database (EPD) to construct interpolated maps of pollen percentages documenting changes in the distribution and abundance of major plant genera and the grass family in Europe over the last 15,000 years.ResultsOur analyses confirm high rates of post‐glacial spread with at least 1000 m year−1 for Corylus, Ulmus and Alnus and average rates of 400 m year−1 for Tilia, Quercus, Fagus and Carpinus. The late Holocene expansions of Picea and Fagus populations in many European regions cannot be explained by migrational lag. Both taxa shift their population centres towards the Atlantic coast suggesting that climate may have played a role in the timing of their expansions. The slowest rates of spread were reconstructed for Abies.Main conclusionsThe calculated rates of post‐glacial plant spread are higher in Europe than those from North America, which may be due to more rapid shifts in climate mediated by the Gulf Stream and westerly winds. Late Holocene anthropogenic land use practices in Europe had major effects on individual taxa, which in combination with climate change contributed to shifts in areas of abundance and dominance. The high rates of spread calculated from the European pollen data are consistent with rapid tracking of early Holocene climate change by common tree species, documenting that plants can spread fast tracing their climate space, regardless of their dispersal strategy.

Analysis of MODIS albedo changes over steady woody covers in France during the period of 2001–2013

Using MODIS satellite data, this study examines the presence and causes of albedo trends in vegetation in France during the last decade. Special attention is paid to steady woody areas. During the last decade, 0.31% of the land surface of France has been identified as being affected by a sudden albedo shift due to land cover changes (LCC). Excluding these sudden changes in land cover, we show a significant (decreasing) albedo trends over 3.5% of France (p-value<0.01). In most cases (84%), trends were identified in non-vegetated and non-steady vegetated covers; however, gradual albedo trends were observed in steady woody covers in over 0.1% of the surface area of France. The majority (59.9%) of these woody covers were broadleaved tree covers; the remainder was divided between needle-leaved and mixed tree covers and shrub cover. On average, in the steady woody covers affected by gradual albedo trends, the visible albedo shift was −0.0088 between 2001 and 2013, i.e., a loss of 20.1–29.8% depending on the woody cover type. This decrease in albedo was supported by a significant gradual increase (p-value<0.05) in the normalized difference vegetation index (NDVI). This increase in greenness appears to be linked to the under-use of woody areas in France, leading to denser forests. The impact of these gradual albedo trends on the radiative forcing (RF) was estimated and compared to the impact of LCCs. During the 21st century in France, the impact on the radiative forcing of steady woody covers could reach +0.2W.m−2. This value is 2.5 times larger than IPCC estimates based on past vegetation changes.

Past tree cover of the Congo Basin recovered by phytoliths and δ13C along soil profiles

Abstract The tropical moist forests (TMF) of the Congo Basin are extremely diverse in terms of structure and functional diversity. Previous paleoecological work suggests that these forests have experienced dramatic changes over the last millennia, related to climate or humans. These disturbances still influence today's repartition of forests and savannas as well as species distributions. The objective of this study is to explore the sensitivity of phytolith assemblages, compared to the δ 13 C of soil organic carbon (SOC), to reconstruct past tree cover of the present TMF. Large transects across different geological substrata and forest communities were explored. In total, 18 soil profiles were investigated for pedogenic features, and 53 radiocarbon dates from SOC and charcoals were obtained. Phytolith extractions from modern soils and along four soil profiles were performed. The δ 13 C of SOC and phytolith assemblages were interpreted in terms of tree cover changes. One of the most interesting results highlighted by this study was the strong match between phytolith tree cover and the δ 13 C signal; as it not only aids the interpretation of δ 13 C soil signals, but also puts into question the transport behavior of phytoliths in soil by processes that are still poorly understood. The δ 13 C SOC method has been successfully used to study major vegetation changes in Africa, but has never been previously constrained with another proxy of tree cover. This study confirms the value of a multi-proxy approach to investigate past vegetation changes in African tropical moist forests, and shows that SOC δ 13 C and phytolith signatures in soil profiles display the same dynamics and are complementary. They suggest that the majority of the present forested sites never experienced a true savanna phase.

Leaf waxes in litter and topsoils along a European transect

Abstract. Lipid biomarkers are increasingly used to reconstruct past environmental and climate conditions. Leaf-wax-derived long-chain n-alkanes and n-alkanoic acids may have great potential for reconstructing past changes in vegetation, but the factors that affect the leaf wax distribution in fresh plant material, as well as in soils and sediments, are not yet fully understood and need further research. We systematically investigated the influence of vegetation and soil depth on leaf waxes in litter and topsoils along a European transect. The deciduous forest sites are often dominated by the n-C27 alkane and n-C28 alkanoic acid. Conifers produce few n-alkanes but show high abundances of the C24 n-alkanoic acid. Grasslands are characterized by relatively high amounts of C31 and C33 n-alkanes and C32 and C34 n-alkanoic acids. Chain length ratios thus may allow for distinguishing between different vegetation types, but caution must be exercised given the large species-specific variability in chain length patterns. An updated endmember model with the new n-alkane ratio (n-C31 + n-C33) / (n-C27 + n-C31 + n-C33) is provided to illustrate, and tentatively account for, degradation effects on n-alkanes.

Atlas of pollen and spores and their parent taxa of Mt Kilimanjaro and tropical East Africa

Abstract The accurate and consistent identification of fossil pollen is essential to allow robust inferences to be drawn with regard to past vegetation and climate change. Identifications are best achieved through the direct inspection of reference material. Most substantial reference collections are located at research institutions in Europe or North America, which restricts access for researchers trying to advance palynology in less developed countries. Due to the development of digital imaging and fast internet access it is now possible to produce high quality images from pollen and spore reference collections and make them globally available. In this pollen and spore atlas we contribute to this growing body of work by presenting images of 240 pollen types (in 202 genera and ∼79 families) and 30 spore types (in 25 genera and ∼17 families) from a wide range of different vegetation types originating from the Kilimanjaro area and tropical East Africa. We provide an overview on the range of pollen and spore types commonly found in Last Glacial and Holocene sedimentary archives in studies from the Kilimanjaro area and tropical East Africa. Besides a pollen key, detailed information is given on pollination, habitus and habitat which all support the interpretation and environmental reconstructions from pollen records. The atlas will serve as useful guide for palynological investigations, aiming at detailed and comprehensive reconstruction of past vegetation, environmental and climate change in tropical East Africa.

Fossil fruits of Koelreuteria (Sapindaceae) from the Miocene of northeastern Tibetan Plateau and their palaeoenvironmental, phytogeographic and phylogenetic implications

Fruits of Koelreuteria are well known in the Tertiary deposits of western United States, eastern Asia and Central-East Europe, yet unequivocal reproductive organs of this genus from other areas remain rare in the fossil record. Here, a new species Koelreuteria quasipaniculata Xiangchuan Li, Liang Xiao et Wenlong He sp. nov. is recognized from the Early to Middle Miocene Garang Formation of Zeku in northeastern Tibetan Plateau, Central Asia. This new species is characterized by dehiscent, membranous capsules with an asymmetrical, narrowly ovate shape, and reticulate venation including subparallel, straight lateral veins and one to two ovoid or ellipsoidal seeds each valve. Its capsular valves closely resemble those members of the K. paniculata-type group in gross form, i.e. the extant K. paniculata Laxmann distributed in eastern Asia and the Oligocene-Pliocene K. macroptera (Kováts) Wilfred Norman Edwards from Central-East Europe. The newly discovered fossil materials corroborate the occurrence of Koelreuteria in the Tibetan Plateau during the Early to Middle Miocene, and add to the diversity of Koelreuteria in Central-East Asia during the Miocene, which has been well represented from the Cenozoic deposits of the northern hemisphere. This fossil record together with other co-occurring arborescent plants (e.g. Acer, Ulmus and Fraxinus) contributes to our understanding of past vegetation change in the northeastern Tibetan Plateau. Furthermore, the historical distribution range of Koelreuteria is significantly expanded by the present record into Central Asia formerly known as a geographic region lacking extant and fossil records.

Late-glacial and Holocene European pollen data

ABSTRACTThe European Pollen Database (EPD) is a community effort to archive and make available pollen sequences from across the European continent. Pollen sequences provide records that may be used to infer past vegetation and vegetation change. We present here maps based on 828 sites from the EPD giving an overview of changes in postglacial pollen assemblages in Europe over the past 15,000 years. The maps show the distribution and abundance of 54 different pollen taxa at 500 year intervals, supported by new age-depth models and associated chronological uncertainty analysis. Results show the individualistic patterns of spread of different pollen taxa, and provide a standardized dataset for further analysis, defining a spatial context for the study of past plant and vegetation changes and other aspects of environmental history in Europe.

Record of vegetation, climate change, human impact and retting of hemp in Garhwal Himalaya (India) during the past 4600 years

This study is focused on a 3.55-m-long sediment core retrieved from Badanital (i.e. the BT core) in 2008. Badanital (30°29′50″N, 78°55′26″E, 2083 m a.s.l.) is a small lake located in the upper catchment area of the Ganges in Garhwal Himalaya, northern India. The lake and the regional broad-leaved semi-evergreen forests are under the influence of the Indian Summer Monsoon (ISM) and westerly associated cyclones. Palynological investigation of the BT core revealed past vegetation changes reflecting both climate and human impact during the last 4600 years. Maximum spread of oaks occurred during c. AD 550–1100 and c. AD 1400–1630, that is, the intervals which partly overlap with the ‘Medieval Warm Period’ and the ‘Little Ice Age’, respectively. Three intervals of decreased oak pollen percentages are attributed to (1) continuously drier and cooler climatic conditions and fire activity ( c. 2600–500 BC), (2) severe reduction in oak forests followed by secondary succession of alder woods ( c. AD 1150–1270) and (3) pre-modern settlement activities since the British imperial occupation (after c. AD 1700). We argue that the high percentages (i.e. up to 28%) of Humulus/ Cannabis type and Cannabis type pollen point to intense local retting of hemp c. 500 BC–AD 1050. Based on our age model, Cannabis fibre production at Badanital is contemporaneous with archaeological records of ancient hemp products from different parts of Eurasia suggesting possible linkages to early trade and knowledge exchange routes connecting India and the Himalaya with Central and East Asia and possibly Europe.

Cooling and drying in northeast Africa across the Pliocene

Terrestrial records suggest that Northeast Africa experienced drying during the Pliocene; however, these records are often incomplete in time and space, and questions about this shift in climate remain. Here, we use marine sediments from Deep Sea Drilling Project (DSDP) Site 231 in the Gulf of Aden to generate a multi-proxy organic geochemical record of northeast African climate spanning 5.3–2 Ma. This new record provides a regional perspective on climate and serves as context for the fossil record of early hominin evolution. We measured leaf wax carbon (δ13Cwax) and hydrogen (δDwax) isotopic composition and TEX86 (tetraether index of 86 carbons) to investigate past changes in vegetation, aridity, and ocean temperature, respectively. In the earliest Pliocene, we infer warm subsurface ocean temperatures from TEX86, semi-arid conditions on land and extensive C4 grasslands based on δDwax, δ13Cwax and previously published pollen. After 5 Ma, ocean temperatures gradually cooled, and at 4.3 Ma there was a transition to arid conditions on land based on δDwax and pollen. Grasslands yielded to a mid Pliocene landscape of dry shrublands. This drying appears to be an atmospheric response to cooling ocean temperatures, which may reflect changes in tropical ocean circulation, the intensification of Indian Monsoon winds or perhaps other changes associated with Pliocene cooling.