Regional Vegetation Development Research Articles

Response of ecosystem services and environmental dynamics in large open-pit coal mines: A case study in semi-arid areas

Surface coal mining in semi-arid regions has detrimental impacts on the structure and function of surface ecosystems, thereby impeding the attainment of regional sustainable development goals. Moreover, the impact of climate change on ecological restoration in semi-arid mining areas is an inevitable consideration. To elucidate the response of ecosystem services in mining areas to regional climate change, topography, soil, vegetation and socioeconomic development, this study selected six large-scale surface coal mines located in semi-arid regions of China as research objects. In this study, we aimed to assess the main ecosystem services (carbon sequestration, soil conservation, and flow regulation) provided by these mines. In addition, we analysed the spatial and temporal evolution and interrelationships of these ecosystem services. Furthermore, we explored the underlying mechanisms between ecosystem services and environmental factors. The results showed the following: (1) Geospatially, there was a gradual decrease in carbon sequestration and flow regulation from northeast to southwest in the mining areas. However, the soil conservation exhibited an upward trend. Throughout the research period, the carbon sequestration change rate in the six mining areas displayed an initial downward and subsequent upward trend, the rate of soil conservation exhibited a gradual upward trend, and the flow regulation decline rate followed a downward trend. (2) Change rate of carbon sequestration and soil conservation in the six mining areas showed a significant positive correlation (r = 0.51, p < 0.001), with the strongest correlation observed in the Shengli Mining Area (r = 0.64, p < 0.001). (3) Ecosystem service changes in the mining areas were primarily driven by initial conditions (95.0%), followed by meteorological factors (4.2%). Three ecological restoration models were proposed for the different regions based on driver analyses. The findings of this study offer scientific evidence that can be used to inform ecological management, enhance ecological security, and promote regional sustainable development in mining areas.

Irrigation expansion has kept pace with the CO2 fertilization effect on vegetation growth in a typical arid region

Dynamics of vegetation in arid areas have drawn worldwide attention. The expansion of irrigated cropland (ICE) in arid regions contributes to increased food security and impacts on the extent and development of regional vegetation. However, the quantitative attribution of vegetation growth variation from ICE and biogeochemical factors (e.g., atmospheric CO2 concentration, climatic factors) is still lacking. Here, we assessed key drivers of vegetation growth in the inland arid region of Northwest China (IANC) from 1982 to 2018, including ICE, increased nitrogen rates, elevated atmospheric CO2 concentration (eCO2) and climate drivers, using normalized difference vegetation index (NDVI) and ecosystem gross primary productivity (GPP) as measures. These variables were quantified through trend decomposition, machine learning algorithms, and a satellite-based model. The results show that vegetation growth was increased in IANC mainly due to eCO2 and ICE. After 1995, as the regional climatic aridity intensified, the CO2 fertilization effect on vegetation growth decreased, as the atmospheric CO2 concentration continued to increase. Meanwhile, irrigated cropland area increased sharply, and ICE-driven GPP variation exceeded that driven by eCO2 in the whole region, while the ICE-driven NDVI variation exceeded that due to eCO2 when the ICE reached 6.38%. The ICE effect on regional vegetation growth rather than the CO2 fertilization effect has mitigated the slowdown of the rate of vegetation growth caused by climate changes. Although the ICE is conducive to food security and continuous greening of arid areas, further reclamation will exacerbate water scarcity. Our results provide research base for identifying the scale of sustainable agricultural development.

Disentangling the response of vegetation dynamics to natural and anthropogenic drivers over the Qinghai-Tibet Plateau using dimensionality reduction and structural equation model

The Qinghai-Tibet Plateau (QTP), also referred to as the “roof of the world”, is a distinct alpine ecosystem located at an average elevation of more than 4000 m. Climate variation and anthropogenic activity have affected vegetation development on the QTP during the past few decades, but it is still debatable how significant a role any of these causes has played. According to land surface air temperature data around the world, during the past 50 years, temperatures on the QTP have risen twice as rapidly as the average global level. Previous studies have employed the residual method to examine the impacts of anthropogenic activities on vegetation development, with a lack of actual data validation and less attention to explaining the complex interactions and pathways between vegetation growth, natural factors (climate change and topography), and anthropogenic drivers. Furthermore, although the relationships between vegetation dynamics and terrain have been addressed, the interactions in which meteorological factors influence vegetation growth in accordance with topographical variations remain inadequately elucidated. The raster datasets employed in this study include MODIS NDVI, meteorology, topography, as well as anthropogenic activity from 2000 to 2018. A suite of methods including partial correlation coefficient (PCC), principal component analysis (PCA), and partial least squares structural equation model (PLS-SEM) were applied to explore the interrelationships between various influencing factors and regional vegetation development over the past two decades. The results suggested that: (1) an elevation-specific temperature threshold existed, indicating that temperature could promote or inhibit vegetation growth depending on whether it is below or above this threshold, respectively, which was controlled by a trendline equation; (2) the PLS-SEM and PCA results showed that vegetation development was dominantly promoted by temperature and was most sensitive to precipitation; (3) topography, especially elevation, affected vegetation growth indirectly by influencing climatic change, while anthropogenic drivers had positively contributed to vegetation dynamics on the QTP under the influence of implementing ecological management such as the nature reserves establishment.

Spatiotemporal Variation in and Responses of the NDVI to Climate in Western Ordos and Eastern Alxa

Vegetation is an important component of the terrestrial ecosystem, and studying the rules of vegetation change and its driving factors is helpful to strengthen the ecological protection and sustainable development of regional vegetation. This study analyzes the changes in Normalized Difference Vegetation Index (NDVI) and its response to climate factors in the five regions of western Ordos and eastern Alxa in China between 2000 and 2020. The MODIS NDVI and meteorological data from 2000 to 2020 was used and the ordinary least squares, trend analysis, and correlation analysis methods were analyzed. The NDVI in this region shows spatial differentiation and is high in the east and low in the west. The overall NDVI has shown a significant increasing trend (p &lt; 0.01), and the slope value of the rate of change also shows that the NDVI in 98.17% of the area is increasing. On a temporal scale, NDVI had a significant positive correlation with precipitation (p &lt; 0.01), but no significant correlation with temperature changes. On a spatial scale, NDVI was positively correlated with precipitation, which accounted for 95.57% of spatial changes, of which a significant positive correlation accounted for 34.99% (p &lt; 0.05). Meanwhile, the temperature and NDVI were negatively correlated but not significantly. A positive correlation accounted for 45.95% of the change, but the insignificant negative correlation accounted for 54.05%. Therefore, comprehensive analysis showed that precipitation played a leading role in the NDVI in the study area. The results are helpful to study the driving mechanism of vegetation growth and provide reference for vegetation protection in regions of western Ordos and eastern Alxa of Inner Mongolia, China.

Eemian to Early Weichselian regional and local vegetation development and sedimentary and geomorphological controls, Amersfoort Basin, The Netherlands

Abstract Two new records from the Amersfoort glacial basin are investigated by means of pollen analysis. The cores are situated in the deeper part, close to the original Eemian stratotype Amersfoort 1 (Zagwijn, 1961) and at the margin of the basin. The aim is to reconstruct the Eemian and Early Weichselian vegetation development and to explore the impact of accommodation space, influx of allochthonous pollen and geomorphology on the vegetation composition. The results of the Amersfoort Basin are compared to the current Eemian stratotype in the Amsterdam Basin and other Eemian sites in the Netherlands. An almost complete Eemian to Early Weichselian sequence (E2-EWII) was retrieved from the deeper part of the Amersfoort basin. The late Saalian (LS) to early Eemian transition is not recorded in the Amersfoort basin, in contrast to the deeper Amsterdam Basin. The basin marginal core Den Treek reveals a condensed late Eemian (E5-6) and Early Weichselian (EW I-II) succession showing the importance of accommodation space. The first impact of the Eemian transgression is registered at the E3 to E4a boundary in the Amersfoort and Amsterdam basins, and highest sea level is proposed at the end of pollen zone E5. Upstream in the Eemian delta, in the palaeo-Vecht valley and IJssel Basin, the transgression is recorded later. The influx of reworked (allochthonous) pollen in clastic sediment units hampers vegetation and climatic reconstructions during the LS and Eemian. The early appearance of Picea in zone E4 and Abies in zone E5 in clastic sediment intervals can be related to long-distance transport by the river Rhine and redistribution in the Eemian delta. Local vegetation development can complicate regional biostratigraphic correlations. Alnus, considered characteristic for the late Eemian (E5-6), shows large differences over short distances in the Amersfoort Basin, related to local alder growth since Eemian E3. Carpinus, diagnostic for pollen zone E5, shows high values in the basins adjacent to higher, well-drained ice-pushed ridges, but low values in low-relief environments. Salt- to brackish-water marshes were present during high sea level in zone E5 in the Amsterdam and Amersfoort basins, while further upstream in the Rhine delta brackish to fresh-water tidal conditions dominated. In line with Zagwijn (1961), the E6 to EWI boundary is defined at the first opening of the vegetation cover with Calluna, Poaceae and Artemisia increase, often coinciding with a lithological change from organic to clastic deposition, reflecting increased landscape instability. The cores from the Amersfoort basin reveal a complete Eemian to Early Weichselian record. It is suggested to define the boundary stratotype for the base of the Weichselian Stage in the Amersfoort Basin. The current stratotype Amsterdam-Terminal reveals a fully developed LS to Eemian transition and contains the boundary stratotype for the base of the Eemian Stage.

Prolonged interglacial warmth during the Last Glacial in northern Europe

Few fossil‐based environmental and climate records in northern Europe are dated to Marine Isotope Stage (MIS) 5a around 80 ka BP. We here present multiple environmental and climate proxies obtained from a lake sequence of MIS 5a age in the Sokli basin (northern Finland). Pollen/spores, plant macrofossils, NPPs (e.g. green algae), bryozoa, diatoms and chironomids allowed an exceptionally detailed reconstruction of aquatic and telmatic ecosystem successions related to the development of the Sokli Ice Lake and subsequent infilling of a relatively small and shallow lake confined to the Sokli basin. A regional vegetation development typical for the early half of an interglacial is recorded by the pollen, stomata and plant macrofossil data. Reconstructions of July temperatures based on pollen assemblages suffer from a large contribution of local pollen from the lake's littoral zone. Summer temperatures reaching present‐day values, inferred for the upper part of the lake sequence, however, agree with the establishment of pine‐dominated boreal forest indicated by the plant fossil data. Habitat preferences also influence the climate record based on chironomids. Nevertheless, the climate optima of the predominant intermediate‐ to warm‐water chironomid taxa suggest July temperatures exceeding present‐day values by up to several degrees, in line with climate inferences from a variety of aquatic and wetland plant indicator species. The disequilibrium between regional vegetation development and warm, insolation‐forced summers is also reported for Early Holocene records from northern Fennoscandia. The MIS 5a sequence is the last remaining fossil‐bearing deposit in the late Quaternary basin infill at Sokli to be studied using multi‐proxy evidence. A unique detailed climate record for MIS 5 is now available for formerly glaciated northern Europe. Our studies indicate that interglacial conditions persisted into MIS 5a, in agreement with data for large parts of the European mainland, shortening the Last Glacial by some 50 ka to MIS 4‐2.

Holocene Vegetation and Plant Diversity Changes in the North-Eastern Siberian Treeline Region From Pollen and Sedimentary Ancient DNA

Although sedimentary ancient DNA (sedaDNA) has been increasingly used to study paleoecological dynamics (Schulte et al., 2020), the approach has rarely been compared with the traditional method of pollen analysis for investigating past changes in the vegetation composition and diversity of Arctic treeline areas. Here, we provide a history of latitudinal floristic composition and species diversity based on a comparison of sedaDNA and pollen data archived in three Siberian lake sediment cores spanning the mid-Holocene to the present (7.6–0 cal ka BP), from northern typical tundra to southern open larch forest in the Omoloy region. Our results show that the sedaDNA approach identifies more plant taxa found in the local vegetation communities, while the corresponding pollen analysis mainly captures the regional vegetation development and has its limitations for plant diversity reconstruction. Measures of alpha diversity were calculated based on sedaDNA data recovered from along a tundra to forest tundra to open larch forest gradient. Across all sites, sedaDNA archives provide a complementary record of the vegetation transition within each lake’s catchment, tracking a distinct latitudinal vegetation type range from larch tree/alder shrub (open larch forest site) to dwarf shrub-steppe (forest tundra) to wet sedge tundra (typical tundra site). By contrast, the pollen data reveal an open landscape, which cannot distinguish the temporal changes in compositional vegetation for the open larch forest site and forest-tundra site. Increasing Larix pollen percentages were recorded in the forest-tundra site in the last millenium although no Larix DNA was detected, suggesting that the sedaDNA approach performs better for tracking the local establishment of Larix. Highest species richness and diversity are found in the mid-Holocene (before 4.4 ka) at the typical tundra site with a diverse range of vegetational habitats, while lowest species richness is recorded for the forest tundra where dwarf-willow habitats dominated the lake’s catchment. During the late Holocene, strong declines in species richness and diversity are found at the typical tundra site with the vegetation changing to relatively simple communities. Nevertheless, plant species richness is mostly higher than at the forest-tundra site, which shows a slightly decreasing trend. Plant species richness at the open larch forest site fluctuates through time and is higher than the other sites since around 2.5 ka. Taken together, there is no evidence to suggest that the latitudinal gradients in species diversity changes are present at a millennial scale. Additionally, a weak correlation between the principal component analysis (PCA) site scores of sedaDNA and species richness suggests that climate may not be a direct driver of species turnover within a lake’s catchment. Our data suggest that sedaDNA and pollen have different but complementary abilities for reconstructing past vegetation and species diversity along a latitude.

Vegetation dynamics during the last 7500 years on the extreme southern Brazilian coastal plain

For the first time in the extreme southern Brazilian coastal plain, we analyzed palynomorphs in a continuous sequence, using an outcrop profile of relict muds in Hermenegildo Beach (33°42′12″S, 53°18′57″W), Santa Vitória do Palmar, Rio Grande do Sul state. Five radiocarbon dates were obtained. The results revealed the plant succession in an ancient water reservoir near the coastal line. 7500–4000 BP: Marine organisms and freshwater taxa, with herbaceous marsh at the margins. Marine taxa were markedly present from 6000 to 5000 BP, the time of the maximum transgression. Regionally, the vegetation was dominated by grasslands and forest groupings. 4000–2000 BP: Regressive marine phase, with an increased record of freshwater organisms due to increased rainfall. A large increase in herbaceous marsh components resulted in a gradual filling-in of the water reservoir and the development of regional vegetation. 2000–1760 BP: With the end of the marine regression, progressive desalinization promoted the local herbaceous marsh development. Regionally, grassland and forest also developed, indicative of climate amelioration. Local plant succession ceased during this phase of herbaceous marsh ca. 1760 BP, when beach sands covered the sedimentary sequence. This study reveals the phases of a hydrosere in a coastal water reservoir, influenced by marine oscillations, with gradual desalinization and filling-in that culminated in an herbaceous marsh deposit. These results provide a basis for understanding many other similar relict muds spread throughout the coastal plain in the extreme south of Brazil.

Позднеголоценовая динамика растительного покрова и увлажнённости климата юго-восточного сектора Западно-Сибирской равнины по данным палинологического и ризоподного исследований торфяных отложений

Позднеголоценовая динамика растительного покрова и увлажнённости климата юго-восточного сектора Западно-Сибирской равнины по данным палинологического и ризоподного исследований торфяных отложений

Differential response of vegetation in Hulun Lake region at the northern margin of Asian summer monsoon to extreme cold events of the last deglaciation

The response of vegetation to extreme cold events during the last deglaciation is important for assessing the impact of possible extreme climatic events on terrestrial ecosystems under future global warming scenarios. Here, we present a detailed record of the development of regional vegetation in the northern margin of Asian summer monsoon during the last deglaciation (16,500–11,000 cal yr BP) based on a radiocarbon-dated high-resolution pollen record from Hulun Lake, northeast China. The results show that the regional vegetation changed from subalpine meadow-desert steppe to mixed coniferous and deciduous forest-typical steppe during the last deglaciation. However, its responses to the Heinrich event 1 (H1) and the Younger Dryas event (YD) were significantly different: during the H1 event, scattered sparse forest was present in the surrounding mountains, while within the lake catchment the vegetation cover was poor and was dominated by desert steppe. In contrast, during the YD event, deciduous forest developed and the proportion of coniferous forest increased in the mountains, the lake catchment was occupied by typical steppe. We suggest that changes in Northern Hemisphere summer insolation and land surface conditions (ice sheets and sea level) caused temperature and monsoonal precipitation variations that contributed to the contrasting vegetation response during the two cold events. We conclude that under future global warming scenarios, extreme climatic events may cause a deterioration of the ecological environment of the Hulun Lake region, resulting in increased coniferous forest and decreased total forest cover in the surrounding mountains, and a reduction in typical steppe in the lake catchment.

Effects of late Holocene climate variability and anthropogenic stressors on the vegetation of the Maya highlands

Climate variability and human activities have shaped the vegetation communities of the Maya region of southern Mexico and Central America on centennial to millennial timescales. Most research efforts in the region have focused on the lowlands, with relatively little known about the environmental history of the regional highlands. Here we present data from two sediment sequences collected from lakes in the highlands of Chiapas, Mexico. Our aim was to disentangle the relative contributions of climate and human activities in the development of regional vegetation during the late Holocene. The records reveal a long-term trend towards drier conditions with superimposed centennial-scale droughts. A declining moisture trend from 3400 to 1500 cal yr BP is consistent with previously reported southward displacement of the Intertropical Convergence Zone, whereas periodic droughts were probably a consequence of drivers such as El Niño. These conditions, together with dense human occupation, converted the vegetation from forest to more open systems. According to the paleoecological records, cultural abandonment of the area occurred ca. 1500 cal yr BP, favoring forest recovery that was somewhat limited by low moisture availability. About 600 cal yr BP, wetter conditions promoted the establishment of modern montane cloud forests, which consist of a diverse mixture of temperate and tropical elements. The vegetation types that occupied the study area during the last few millennia have remained within the envelope defined by the modern vegetation mosaic. This finding highlights the importance of microhabitats in the maintenance biodiversity through time, even under scenarios of high climate variability and anthropogenic pressure.

Tundra vegetation stability versus lake-basin variability on the Yukon Coastal Plain (NW Canada) during the past three centuries

Palaeoclimatic reconstructions of the northern Yukon show cooler conditions before AD 1850 followed by gradual warming, and 20th-century temperature measurements indicate decadal-scale temperature fluctuations. The impact of climate on regional vegetation and lake systems has seldom been observed on this scale, however. With this study, we provide a sub-decadal reconstruction of regional vegetation and lake-basin development for the past 300 years, covering the ‘Little Ice Age’ and the period of recent warming, in low Arctic tundra. We analysed a short lake sediment core from the Yukon Coastal Plain. The age–depth relationship of the core is based on 210Pb/137Cs validated by AMS radiocarbon dating. We analysed terrestrial pollen abundances as proxies for regional vegetation development, and we used grain size and biogeochemical analyses (TOC, TN, TOC/TN, δ13C) and the analysis of semiaquatic pollen to describe the lake development. Stable abundances of regional pollen taxa between AD 1730 and AD 2012 accompanied by climatic warming indicated that the regional vegetation was not sensitive to climate change. Based on changes in TOC/TN, δ13C and pollen of shallow-water taxa, we reconstructed an increase in lake water depth after AD 1910 that likely followed climatic warming. We attributed this development to climate-driven thaw subsidence in the lake basin. The impact of widespread permafrost thaw on regional vegetation needs to be better constrained in order to predict the limits of vegetation stability and drivers of lake changes in the region.

34. Carwitzer See (north-eastern Germany): regional vegetation development during the past 7000 years

The Carwitzer See (53° 18ʹ N, 13° 28ʹ E; 83.7 m above sea level [a.s.l.]; 3.95 km2) is a lake situated in the Feldberg Lake District in south-eastern Mecklenburg-Vorpommern. The landscape contains ...

Development of Rich Fen on the SE Baltic Coast, Latvia, during the Last 7500 Years, Using Paleoecological Proxies: Implications for Plant Community Development and Paleoclimatic Research

We present the paleoecological development of a rich fen located in the dune area on the SE Baltic coast, during the last 7500 years. The Apsuciems Mire hosts rare and endangered plant communities in Europe, such as Schoenus ferrugineus and Cladium mariscus. Analysis at high-resolution of plant macroremains in two peat cores was carried out to reconstruct local vegetation succession and fluctuations in moisture availability on the peatland, while a pollen record was developed to reconstruct plant succession, moisture variability and human activity at the regional scale. Based on the presence or the absence of macroremains of plants that occur in wet habitat e.g. Cladium mariscus, Schoenoplectus tabernaemontani, Alisma plantago-aquatica and Botrycoccocus we distinguished four wet periods ca. 6000, 2000, 1750–1550, 1200–150 cal yr. BP and four dry periods (ca. 7000, 4600–4200, 1800–1750, 1550–1200 cal yr. BP) in the peatland’s development. A water level increase at 1200 cal yr. BP triggered the development of plant communities containing Chara sp., Schoenoplectus tabernaemontani, then Cladium mariscus. Our study shows a link between climate change at the regional scale and vegetation development in Apsuciems Mire. We showed that changes in vegetation structure during last 150 years was caused by drainage and human activity.

Origin of a boreal birch bog woodland and landscape development on a warm low mountain summit at the Carpathian–Pannonian interface

Hilly regions along the Western Carpathian–Pannonian border are phytogeographically important, but their vegetation history remains largely unknown. We analysed two peat cores of Late Glacial origin from a bog woodland in the Malé Karpaty Mts (SW Slovakia) using plant macrofossil, pollen, peat chemistry and charcoal analyses to trace local successional patterns, regional vegetation development and occurrence of rare species. The small distance between the two profiles situated within homogeneous vegetation enabled us to explore small-scale differences in local vegetation history. The sediment started to accumulate at the end of the Allerød (ca. 12950 cal. yr BP), when a shallow oligotrophic/mesotrophic lake with macrophytes developed. Open pine-birch forests dominated in the landscape. During the early Holocene, the lake was infilled, mire vegetation appeared and broad-leaved forests spread in the surroundings. Two fire events indicated by increases in number of macroscopic charcoal particles were recorded. The first one, which occurred at the end of the Late Glacial, was found only in one of the profiles, while the second one affected entire mire and probably caused a hiatus spanning the middle and late Holocene. Fagus started to spread no later than 5800 cal. yr BP. Open mire vegetation reappeared after the fire (ca. 400 cal. yr BP). During the 19th century, the mire was overgrown by a birch bog woodland. The two profiles showed basically the same successional patterns, but some local events and occurrences of rare species ( Potamogeton alpinus, Potamogeton praelongus, Scorpidium scorpioides and Pleurospermum austriacum) were traced only in one of them.

Revised human impact in north‐western Germany during the Neolithic: methodological limits and challenges

ABSTRACTThe present study aims to improve our understanding of the chronology of vegetation changes in north‐western Germany during the Neolithic. Therefore, four archived peat profiles from small mires that had been pollen analysed and partly conventionally radiocarbon dated during the 1990s were re‐evaluated. Based on new accelerator mass spectrometry (AMS) dates, there are considerable differences between the existing and the newly developed age–depth models. These are also caused by the exclusion of pollen events that were previously assumed to be synchronous, and results from archaeological investigations as dating horizons, hence avoiding circular reasoning in the present study. In addition to the re‐evaluation of archived material, a new profile was recovered, pollen analysed and AMS radiocarbon dated to gain insights into the regional vegetation development and to put local human impact on the landscape in a broader context. The results indicate three different phases of human‐induced vegetation changes. The local vegetation changes do not follow this general pattern, but reflect a very patchy landscape which in turn probably refers to quite small pollen source areas. The study emphasizes that vegetation changes seen in local pollen profiles should neither be regarded as general trends nor be used as dating horizons for neighbouring sites.

The origin of grasslands in the temperate forest zone of east-central Europe: long-term legacy of climate and human impact

The post-glacial fate of central European grasslands has stimulated palaeoecological debates for a century. Some argued for the continuous survival of open land, while others claimed that closed forest had developed during the Middle Holocene. The reasons behind stability or changes in the proportion of open land are also unclear. We aim to reconstruct regional vegetation openness and test the effects of climate and human impact on vegetation change throughout the Holocene. We present a newly dated pollen record from north-western fringes of the Pannonian Plain, east-central Europe, and reconstruct Holocene regional vegetation development by the REVEALS model for 27 pollen-equivalent taxa. Estimated vegetation is correlated in the same area with a human activity model based on all available archaeological information and a macrophysical climate model. The palaeovegetation record indicates the continuous presence of open land throughout the Holocene. Grasslands and open woodlands were probably maintained by local arid climatic conditions during the early Holocene delaying the spread of deciduous (oak) forests. Significantly detectable human-made landscape transformation started only after 2000 BC. Our analyses suggest that Neolithic people spread into a landscape that was already open. Humans probably contributed to the spread of oak, and influenced the dynamics of hazel and hornbeam.

Alluvial fan records from southeast Arabia reveal multiple windows for human dispersal

The dispersal of human populations out of Africa into Arabia was most likely linked to episodes of climatic amelioration, when increased monsoon rainfall led to the activation of drainage systems, improved freshwater availability, and the development of regional vegetation. Here we present the first dated terrestrial record from southeast Arabia that provides evidence for increased rainfall and the expansion of vegetation during both glacial and interglacial periods. Findings from extensive alluvial fan deposits indicate that drainage system activation occurred during Marine Isotope Stage (MIS) 6 (ca. 160–150 ka), MIS 5 (ca. 130–75 ka), and during early MIS 3 (ca. 55 ka). The development of active freshwater systems during these periods corresponds with monsoon intensity increases during insolation maxima, suggesting that humid periods in Arabia were not confined to eccentricity-paced deglaciations, and providing paleoenvironmental support for multiple windows of opportunity for dispersal out of Africa during the late Pleistocene.

Dry and humid phases in the highlands of southern Brazil during the last 34,000 years, and their influence on the paleoenvironments of the region

The palynology of the last 34,000 years was determined for a sedimentary profile from a bog in São Francisco de Paula, Rio Grande do Sul Eastern Plateau, using radiocarbon dates (profile: 29°19′05″S, 50°08′18″W). This is a rare older palynological sequence studied in the Quaternary of southern Brazil. Between 34,300 and 28,000 BP, the records suggest a cold and semi-arid climate, with rarefied vegetation that was dominated by sparse grassland, the Araucaria forest probably in refuges. Between 28,000 and 23,500 BP, a cold and humid climate was clearly detected at the last glacial stage. The vegetation generally developed with a grassland dominion, and a water reservoir was in the study site. Between 23,500 and 12,000 BP, cold and semi-arid climate promoted the reduction of grassland, and the local water reservoir began to be filled by sediment. Between 12,000 and 10,000 BP, the rise in temperature and humidity resulted in the development of regional vegetation, and the Araucaria forest probably expanded a little from the refuges. Herbaceous marsh dominated the study site. Between 10,000 and 7500 BP, an elevated temperature and dry conditions promoted a general decrease in vegetation cover. Between 7500 and 3000 BP, a progressive increase in humidity permitted the development of local and regional vegetation and the arborous pioneers migrated from the refuges, with the expansion of forest taxa, such as Araucaria angustifolia (Bertol.) Kuntze. There was the beginning and expansion of the bogs from 6000 BP onward. The grassland decreased after 4000 BP probably due to the forest cover. The records indicate a high regional humidity after 3000 BP, which is favorable to Araucaria forest. However, the temperature elevation during this phase probably reduced the reproductive capacity of the Araucaria forest taxa, resulting in a lower rate of expansion on the grassland. The same factor probably reduced the regional bogs from 2000 BP onward.

Climatic trends for the last 70 ky BP in the SE Pacific: the Rano Aroi and Rano Raraku records from Easter Island

This paper discusses a complete record of vegetation history since the Bølling (GI-1e) warming (14,500 cal yr BP) up to the Holocene in Latvia. To date, this is the only complete record of such age in the eastern Baltic area and the northernmost area for which Bølling records are present. Combining pollen evidence, pollen accumulation rates (PAR) and plant macrofossil data, we assess the local and regional vegetation development, and we attempt to separate the true Lateglacial vegetation signal by removing the obviously redeposited thermophilous pollen; however, we remove not only their signal, we discuss the possibilities of separating the redeposition signal of the so-called “local Lateglacial trees”, pine and birch, by looking at their corrosion and degradation. The results show that the Bølling warming in the eastern Baltic area was a treeless tundra community consisting of the shrubs Betula nana, Dryas octopetala and Salix polaris. The Older Dryas cold spell is clearly recognised as a decline in the total concentration of plant macrofossils and PARs at between 14,200 and 13,500 cal yr BP. At 13,460 cal yr BP, the B. nana macrofossils disappear, and tree birch (Betula sect. Albae) appears, marking the start of tree birch forest. The presence of pine forest is confirmed by a variety of macrofossils, including bark, wood, needles and seeds, since 13,400 cal yr BP, at the same time at which pine stomata are found. The first identified pine stomata finds are associated with a Pinus PAR over 3000 grains cm−2 yr−1 and pine macrofossil finds with a Pinus PAR over 4000 grains cm−2 yr−1. During the warmest period of the GI-1a (Allerød) at 13,000–12,700 cal yr BP, a pine forest with deciduous trees (birch – Betula pendula and aspen – Populus tremula) developed in the study area. The Younger Dryas (GS-1) cooling strongly affected the floral composition in eastern Latvia. The PAR of the tree taxa declined abruptly from a maximum value at 12,700 to below 1000 grains cm−2 yr−1 at 12,600 cal yr BP. The response time for the pine forest to collapse was 100 years according to the PAR data. Pine macrofossils disappear simultaneously with the pollen signal at 12,600 cal yr BP, yet occasional Pinus stomata are recorded throughout the Younger Dryas (GS-1). The landscape was treeless shrub tundra again, with D. octopetala, S. polaris, B. nana and Juniperus present. Picea is introduced in the region within the cold Younger Dryas and is represented by stomata (12,400–12,200 cal yr BP), needles, seeds and wood (since 12,050 cal yr BP up to the Holocene). The Pleistocene/Holocene boundary at 11,650 cal yr BP is marked by changes both in vegetation composition and sediment type. The organic rich gyttja accumulated instead of silts and clays, and the start of the Holocene warm period permitted forest re-expansion in eastern Latvia.