Pollen Assemblages Research Articles

Human landscape modification and expansion of tropical woodland in southern Arabia during the mid‐Holocene from rock hyrax middens

AbstractAimDryland ecosystems, such as those in southern Arabia, are particularly vulnerable to climate and land‐use change. Aridification and human subsistence changes at the end of the Holocene Humid Period at 6–4 ka have been used as an iconic example for evaluating such impacts to resilience of arid systems. Although records of ancient environments can provide critical insight into the biotic and abiotic mechanisms that alter ecosystems, traditional archives, such as lake deposits, are not common in southern Arabia after 6 ka; thus, we must use alternative archives.LocationYemen.TaxonPlants; Rock Hyrax (Procavia capensis).MethodsWe use fossil pollen and stable isotopes (δ15N; δ13C) of rock hyrax (P. capensis) middens from Wadi Sana, Yemen, to look at changes in ecosystem structure and function across this key transition from 6 ka to the present. A total of 17 middens were radiocarbon‐dated and stable isotopes were measured. Of these, pollen was extracted from hyraceum of 14 middens and identified using a light microscope. Fossil pollen assemblages were then compared to existing modern pollen samples from throughout Arabia.ResultsDuring the mid‐Holocene from at least 6 to 4.7 ka, the pollen flora reflects a landscape with abundant tropical trees. These included foundational woody taxa, such as Terminalia and Boswellia sacra (frankincense), which had a strong positive influence on local hydrology and the economy, respectively. Increased charcoal abundances also suggest that wildfire occurred periodically.Main conclusionsConnections with archaeological evidence suggest a strong link between human management and the presence of Terminalia woodland during the mid‐Holocene. These may have promoted increased groundwater storage and ponding as regional rainfall was decreasing. The mid‐Holocene expansion of Boswellia sacra (frankincense) may have helped support resin trade that became a critical export from the region. Fires were more common than today, suggesting semi‐arid but continuous vegetation cover across what is now bare ground. Finally, after 1 ka, increased sedge abundances at the expense of grasses and trees suggest the development of desert conditions.

Climate, fire and vegetation history from subtropical North Stradbroke Island (Minjerribah), eastern Australia, during the last three interglacials

ABSTRACTRecords of Australian palaeoclimate beyond the last glacial cycle are rare, limiting detailed analysis of long‐term climate trends and associated ecosystem responses. This study analyses a discontinuous pollen and charcoal record from Fern Gully Lagoon, North Stradbroke Island (Minjerribah), subtropical Queensland, Australia, which covers much of the last ~210 ,000 years. Climate variation is inferred from changes in vegetation, while analysis of micro‐ and macrocharcoal is used to infer fire activity. Pollen assemblages consist of ~40% rainforest taxa during marine isotope stage (MIS) 7a–c and early MIS 5. These are inferred to result from high rainfall in the Australian subtropics, which was also evident in north‐east and central Australia. Human impact from 21 ,000 years ago likely supressed post‐MIS 2 rainforest expansion to some extent. However, the increased Holocene abundance of herbs and grasses and reduced representation of aquatic taxa suggest that the Holocene was relatively dry when compared with early MIS 5 and MIS 7a–c. Similar MIS 5 and early MIS 7a–c climates, in contrast to a notably drier Holocene, suggest that the progressive interglacial drying trend most strongly recorded in central Australia was not a major feature of subtropical eastern Australian climates.

Patterns in recent and Holocene pollen accumulation rates across Europe – the Pollen Monitoring Programme Database as a tool for vegetation reconstruction

Abstract. The collection of modern, spatially extensive pollen data is important for the interpretation of fossil pollen assemblages and the reconstruction of past vegetation communities in space and time. Modern datasets are readily available for percentage data but lacking for pollen accumulation rates (PARs). Filling this gap has been the motivation of the pollen monitoring network, whose contributors monitored pollen deposition in modified Tauber traps for several years or decades across Europe. Here we present this monitoring dataset consisting of 351 trap locations with a total of 2742 annual samples covering the period from 1981 to 2017. This dataset shows that total PAR is influenced by forest cover and climate parameters, which determine pollen productivity and correlate with latitude. Treeless vegetation produced PAR values of at least 140 grains cm−2 yr−1. Tree PAR increased by at least 400 grains cm−2 yr−1 with each 10 % increase in forest cover. Pollen traps situated beyond 200 km of the distribution of a given tree species still collect occasional pollen grains of that species. The threshold of this long-distance transport differs for individual species and is generally below 60 grains cm−2 yr−1. Comparisons between modern and fossil PAR from the same regions show similar values. For temperate taxa, modern analogues for fossil PARs are generally found downslope or southward of the fossil sites. While we do not find modern situations comparable to fossil PAR values of some taxa (e.g. Corylus), CO2 fertilization and land use may cause high modern PARs that are not documented in the fossil record. The modern data are now publicly available in the Neotoma Paleoecology Database and aid interpretations of fossil PAR data.

Significance of the Ukrainian loess-palaeosol sequences for Pleistocene climate reconstructions: rock magnetic, palaeosol and pollen proxies

Variations of rock magnetic parameters in loess-palaeosol sequences, related to climatic and environmental conditions during their formation, are a powerful tool for palaeoclimate reconstruction. Combined enviromagnetic study of loess deposits in Ukraine and its assessment for the palaeoreconstruction purposes are carried out in the framework of the National Research Foundation of Ukraine project 2020.02/0406 ‘Magnetic proxies of palaeoclimatic changes in the loess-palaeosol sequences of Ukraine’. Environmental/climatic reconstructions of the past are fulfilled using a significant number of palaeoindicators: morphology and lithological properties of palaeosols and loesses, their pollen assemblages and a wide range of magnetic characteristics. In this paper, we present a multi-proxy approach to palaeoenvironmental reconstructions, and introduce preliminary results obtained from magnetic susceptibility of loess-palaeosol sequences in the northern (at Vyazivok), central (Stari Kaydaky) and southern (Roksolany) parts of the Ukrainian loess belt. The amplitudes of palaeoclimate change established using magnetic proxies are well correlated with the lithological, palaeopedological and palynological patterns of the sites, and with the global oxygen-isotope scale (MIS). Ongoing studies of the Stari Kaydaky section confirm the correlation of the Upper Zavadivka (S3) soil unit and Lower Zavadivka (S4) soil unit with MIS 9 and MIS 11, respectively (this was proved earlier at the Vyazivok and Roksolany sites). The underlying Lubny (S5) pedocomplex likely corresponds to MIS 13, and the Martonosha (S6) pedocomplex to MIS 15. Palaeomagnetic investigations at Stari Kaydaky have not so far reached the Lower Shyrokyne unit, in which the Matuyama—Brunhes boundary has been detected at Roksolany and Vyazivok. The Upper Shyrokyne (S7S1) palaeosol unit has normal polarity and is preliminarily correlated with MIS 17.

Palynostratigraphy and palaeoenvironmental evolution of the Aptian to lower Cenomanian succession in the Serranía de Cuenca (Eastern Spain)

The Aptian to lower Cenomanian succession from the Serranía de Cuenca region (Eastern Iberia, Spain) comprises a time-span largely understudied regarding palynology and biostratigraphy. This research studies the deposits of three stratigraphic units that crop out in this region (the Contreras Formation, the El Burgal Member and the Utrillas Group), allowing identification, study and sampling of the palynofloras from the Aptian–?early Cenomanian time-interval. The studied sections are grouped into three sectors based on the palynostratigraphic ages obtained: the MPB, TU, and CT sectors, respectively. The palynoflora is dominated by gymnosperm pollen grains and diversified spores of ferns and allies. The palynofloral evidence and regional geology indicate that the sampled levels in the MPB sector are Aptian in age, whereas those levels sampled at the TU and CT sectors are dated as middle Albian–?early Cenomanian. The Aptian palynofloras of this sector differ from other contemporaneous sites of Europe and North America in the possible occurrence of tricolpate angiosperm pollen. In general, angiosperm pollen does not present high percentages; however, it becomes more diversified from the middle Albian in the TU and CT sectors, where more than 20 taxa were recorded on average. The studied pollen assemblages conform with the characteristics of the early Cenophytic palynofloras. Likewise, an increase in dinocysts towards the upper levels of the sedimentary succession in the TU and CT sectors is consistent with the transgressive nature of the deposits, documenting the progressive landward expansion of Western Tethys in Iberia during Albian to ?early Cenomanian times.

Palynological evidence indicates the paleoclimate evolution in southeast China since late marine isotope stage 5

Four coastal cores collected from Fujian province in southeast China revealed new palynological evidence of vegetation, sea level, and climate changes since the late marine isotope stage (MIS) 5. A comparison between modern and fossil pollen assemblages, using scanning electron microscopy and 45 dating samples ensured an accurate interpretation of pollen data. The evergreen Quercus-dominated pollen assemblage indicated that a relatively warm subtropical climate prevailed during the last glaciation, whereas large amounts of Tsuga pollen indicated distinct cooling during early MIS2. Marine dinocysts revealed three transgressional intervals in the Holocene, early MIS3, and late MIS5, which corresponded to a globally sea-level rising. Richer pollen from tropical and subtropical broad-leaved trees and higher sand content in grain-size components confirmed a warm climate during the early MIS1 and early MIS3, and strong river flow associated with heavy precipitation during late MIS5, reflecting the sensitive response of the land climate to high summer insolation. During the early MIS3 period, the reconstructed optimum climate was consistent with the sea surface temperature records in the west Pacific and northern South China Sea and summer monsoon signal from terrestrial records, implying that high summer insolation strongly affected the climate of East Asia.

Modern Pollen Assemblages in Typical Agro-Pastoral Ecotone in the Eastern Tibetan Plateau and Its Implications for Anthropogenic Activities

Long-term evolution of human-environment interaction in the Qinghai-Tibetan Plateau (QTP) has been discussed intensively in recent years. The identification of human-related pollen types may help explore the coupled process of climate change, ecological response and anthropogenic activities on the QTP. The aim of this study is to evaluate the impact of anthropogenic activities on surface pollen assemblages and identify pollen indicators associated with grazing and cultivation in typical agro-pastoral ecotone of the eastern QTP. Totally 84 surface samples were analyzed from five vegetational communities in the eastern QTP, which are identifiable based on surface pollen assemblages. Principal component analysis of 29 pollen types and two supplementary variables of human influences were used to assess the impact of anthropogenic activities on surface pollen assemblages in eastern QTP. Severe grazing led to increase of Rosaceae, Ranunculaceae, Fabaceae, Taraxacum-Type, Aster-type and Saussurea-Type in pollen assemblages. Highland agricultural cultivation can be identified by the content and morphological characteristic of Brassicaceae and Cerealia Poaceae pollen. The aerial dispersed distances of Brassicaceae and Cerealia Poaceae pollen are very short, and domesticated herbivores are important factors, which disperse the Cerealia Poaceae pollen into pastures in agro-pastoral ecotone of the QTP. Modern pollen indicators of cultivation and grazing activity will provide precise references for fossil pollen study of prehistoric human activities in the QTP.

Relationships between climate and phylogenetic community structure of fossil pollen assemblages are not constant during the last deglaciation.

Disentangling the influence of environmental drivers on community assembly is important to understand how multiple processes influence biodiversity patterns and can inform understanding of ecological responses to climate change. Phylogenetic Community Structure (PCS) is increasingly used in community assembly studies to incorporate evolutionary perspectives and as a proxy for trait (dis)similarity within communities. Studies often assume a stationary relationship between PCS and climate, though few studies have tested this assumption over long time periods with concurrent community data. We estimated two PCS metrics-Nearest Taxon Index (NTI) and Net Relatedness index (NRI)-of fossil pollen assemblages of Angiosperms in eastern North America over the last 21 ka BP at 1 ka intervals. We analyzed spatiotemporal relationships between PCS and seven climate variables, evaluated the potential impact of deglaciation on PCS, and tested for the stability of climate-PCS relationships through time. The broad scale geographic patterns of PCS remained largely stable across time, with overdispersion tending to be most prominent in the central and southern portion of the study area and clustering dominating at the longitudinal extremes. Most importantly, we found that significant relationships between climate variables and PCS (slope) were not constant as climate changed during the last deglaciation and new ice-free regions were colonized. We also found weak, but significant relationships between both PCS metrics (i.e., NTI and NRI) and climate and time-since-deglaciation that also varied through time. Overall, our results suggest that (1) PCS of fossil Angiosperm assemblages during the last 21ka BP have had largely constant spatial patterns, but (2) temporal variability in the relationships between PCS and climate brings into question their usefulness in predictive modeling of community assembly.

Identifying floristic diversity from the pollen record in open environments; considerations and limitations

Pollen analysis provides a key technique for the reconstruction of post-glacial vegetation. Modern observation of the plant-pollen relationship, through the use of surface pollen studies, is an instrumental process for informing these reconstructions. However, results from surface pollen studies suggest that the diversity of pollen assemblages is rarely a faithful representation of the diversity of the local vegetation. Pollen diversity at high altitude is determined by both the composition and density of the local vegetation and long-distance pollen.This paper examines the relationship between floristic and palynological diversity using surface samples collected from alpine communities found on three glacier forelands (Austerdalsbreen, Storbreen and Grjøtbreen) in the Jostedalsbreen-Jotunheimen region of Norway. Several diversity indices indicate the complexity of the relationship between palynological and floristic diversity. This is accentuated in open, high altitude, sparsely-vegetated sites, where palynological diversity is a measure of the diversity of the long-distance pollen assemblage rather than the diversity of the local vegetation. Even at sites on older moraines at Storbreen and Austerdalsbreen, where the vegetation is denser and more diverse, the relationship is not simple but depends on pollen production of the taxa that dominate the local vegetation. On Storbreen foreland, for example, the diversity of small, insect-pollinated plants growing locally is poorly represented in the pollen assemblage which is dominated by long-distance arboreal pollen. The surface pollen results were compared with fossil pollen data from a palaeosol at Memurubreen in Eastern Jotunheimen. DCA ordination indicates that the fossil pollen spectra are distinct from the modern samples, due to differences in the pollen assemblages, probably related to lower treelines in the past associated with climatic cooling or human impact. The palaeosol samples are most similar to modern samples from heath and snowbed communities, found on older terrain at Grjøtbreen and Storbreen, and the diversity indices also show strong similarities with these communities. The potential for improvements in methodology to increase resolution is considered.

Early Pennsylvanian to early Permian (Bashkirian-Asselian) miospore and pollen assemblages of the Czech part of the Intra-Sudetic Basin

Early Pennsylvanian to early Permian (Bashkirian-Asselian) miospore and pollen assemblages of the Czech part of the Intra-Sudetic Basin

The palynology of the Lower-Middle Jurassic transition of the North Caucasus (southwest Russian Federation), calibrated with index ammonites

Palynomorphs from the Toarcian and Aalenian Djigiat Formation of Karachay-Cherkessia in the Kuban River Basin (North Caucasus, southwest Russian Federation) are reported for the first time. Five samples carefully selected for their biostratigraphical content were studied to document the palynological assemblages. Four samples (1, 2, 3, 4) were collected from pieces of rock with key index ammonite specimens, and sample 5 comprises fragments of ammonite shells from a sideritic concretion. Three of these samples (4, 2 and 1) yielded relatively abundant and diverse aquatic microplankton (acritarchs, dinoflagellate cysts, prasinophytes and zygnematalean algae) and terrestrial palynomorphs (pollen and spores); the remaining two samples (3 and 5) were less productive and contained fewer than 50 palynomorph specimens. The study of the dinoflagellate assemblages provided characteristic and key information. These are the uppermost Toarcian Nannoceratopsis Assemblage and the uppermost Toarcian to lowermost Aalenian Parvocysta Suite Assemblage. The former is overwhelmingly dominated by Nannoceratopsis with sparse numbers of the Parvocysta suite, and the latter yielded more diverse and common specimens of Parvocysta and its relatives. This is consistent with the hypothesis that the Parvocysta suite migrated from the Boreal Realm further south into Laurasia during the Toarcian. Certain dinoflagellate cysts such as Mancodinium semitabulatum and Scriniocassis spp., which are typical of Europe and much of Greater Laurasia are absent. Composition of the pollen and spores proved relatively out to be monotonous, and cannot be subdivided. However, in general, the composition of the assemblages of spores and pollen is consistent with the Toarcian–Aalenian transition.

Palaeobotanical record of the Eemian Interglacial succession at the Jagodne site (Garwolin Plain, central Poland)

Our high-resolution data of pollen and macrofossils from 2 cores taken from the Jagodne site (Garwolin Plain) reveals a pollen succession covering the final part of the Late Saalian (Marine Isotope Stage MIS 6) and embracing the Eemian (MIS 5e). The results correspond to Regional Pollen Assemblage Zones (RPAZ). The hornbeam phase (E5 RPAZ) has been subdivided into subzones and compared to the corresponding division of the key profile of the Garwolin Plain, Kozłów K2-19. The comparison revealed a considerable sedimentary hiatus in the E5 RPAZ at Jagodne. This is attributed to significant palaeohydrological changes occurring widely in this zone, and also seen at other Eemian sites in Poland. Another specific feature of the Jagodne site is the early, rapid terrestrialisation of the palaeolake and its transformation into a raised bog, which occurred already at the end of the hornbeam phase. The Sphagnum dominated peatbog developed for a long time as evidenced by a thick peat layer covering also the Early Vistulian. Both pollen and plant macrofossil data correspond well to observed lithological boundaries, providing a consistent record of palaeoenvironmental and palaeoclimate changes. The results obtained contribute to knowledge of palaeoenvironmental changes and palaeoclimate interpretation of that area.

Basin-specific records of lake oligotrophication during the middle-to-late Holocene in boreal northeast Ontario, Canada

Descriptions of regional climate expression require data from multiple lakes, yet little is known of how variation in records within morphometrically complex lakes may affect interpretations. In northeast Ontario (Canada), this issue was addressed using records of pollen, pigments, and diatoms in three sediment cores from two small boreal lakes spanning the last ~6000 years. Pollen analysis suggested warm conditions between ~6000 and ~4000 cal yr BP, coherent with previous assessments from boreal eastern Ontario and western Quebec. Analysis of phototrophic communities from fossil pigments and diatom valves suggested relatively eutrophic conditions with lower lake-levels during this interval. Generalized additive model trends identified significant regional changes in pollen assemblages and declines in pigment concentrations after ~4000 cal yr BP consistent with cooler and wetter climate conditions that resulted in regional lake oligotrophication and increased lake levels during the late-Holocene. Despite contemporaneous changes in pollen and pigment biomarkers across lakes, cores collected from adjacent basins of the same lake (Green Lake) did not show similar trends in fossil pigments likely reflecting preferential deposition of clay-rich allochthonous material in the deeper central basin and suggesting that regional signals in climate may be complicated by lake- or basin-specific catchment processes.

Lateglacial and Holocene changes in vegetation and human subsistence around Lake Zhizhitskoye, East European midlatitudes, derived from radiocarbon-dated pollen and archaeological records

The numerous lake and peat sedimentary archives of Central European Russia are ideal for studying the Lateglacial–Holocene climate and vegetation history of the region. However, robustly dated palaeoenvironmental records have only become available in the last decade and are still few and far between. Together with the continuously growing archaeological record and increasing focus on absolute dating of cultural assemblages, such records, where available, offer an excellent opportunity to study human-environment interactions in the region. For this study we selected one of the most detailed regional pollen records, from a 4.5-m-long sediment section from Zmeinoe Mire (56°16′53″ N, 31°15′36″ E) at Zhizhitskoye Lake (165 m a.s.l.). We performed quantitative pollen-based biome reconstruction and constructed a Bayesian age-depth model to ensure maximum chronological control of the sediment succession. To link the reconstructed vegetation changes to human activities, we gathered and summarized available archaeological data from the study area. Our results show that humid conditions and taiga-like patchy forests (spruce, pine, birch) dominated the study region during the Lateglacial. The Early Holocene (ca. 11,650–8000 cal yr BP) was marked by a warming and drying trend indicated by the spread of cool-temperate summergreen broad-leaved trees and shrubs (elm, lime, hazel) and the retreat of spruce. Warmest conditions, expressed by the maximum contribution of temperate deciduous woody taxa to the pollen assemblages, were recorded during the Middle Holocene (ca. 8000–4000 cal yr BP) when Mesolithic and Neolithic hunter-fisher-gatherer groups flourished in the region. The pollen record suggests that the regional climate became cooler and wetter after 4000 cal yr BP, which may explain the decline of the Neolithic pile dwelling settlement Naumovo at Zhizhitskoye Lake around 3800 cal yr BP. Evidence for human impact on natural forest vegetation becomes visible from 5000 cal yr BP, although it remains at modest levels until the end of the Neolithic (3500–3000 cal yr BP). Decline in arboreal pollen percentages intensified after ca. 2800 cal yr BP, indicating the onset of increased deforestation for pasture, farmland, construction material and fuel by Iron Age populations. This is in line with the foundation of the fortified Iron Age Anashkino settlement north of Zhizhitskoye Lake dated to around 2750 cal yr BP. Forest clearance further increased during the second half of the Iron Age (5th century BCE–5th century CE) and again from ca. 1200 cal yr BP after the onset of the Middle Ages.

Constraints on the paleoelevation history of the Eastern Cordillera of Colombia from its palynological record

Abstract We attempted to make an objective assessment of whether fossil pollen assemblages from the Sabana de Bogotá require surface uplift of ~2000 m since 6–3 Ma, as has been argued. We relied on recently published elevation ranges of plants for which fossil pollen has been found in sites 2000–2500 m high in the Sabana de Bogotá. The elevation ranges of fossil plants do not overlap, suggesting that those ranges may be too narrow. By weighting these elevation ranges by percentages of corresponding fossil pollen and summing them, we estimated probability density functions for past elevations. These probability distributions of past elevations overlap present-day elevations and therefore do not require surface uplift since deposition of the pollen. Fossil pollen assemblages include pollen from some plant taxa for which we do not know present-day elevation ranges, and therefore, with a more complete knowledge of elevation distributions, tighter constraints on elevations should be obtainable. The elevation of the oldest assemblage, from Tequendama, which lies at the southern edge of the Sabana de Bogotá and is thought to date from 16 to 6 Ma, is least well constrained. Although our analysis permits no change in elevation since the pollen was deposited, we consider 1000–2000 m of elevation gain since 15 Ma to be likely and consistent with an outward growth of the Eastern Cordillera.

The modern pollen–vegetation relationship in Jammu, India: a comparative appraisal

An understanding of the relationship between modern pollen and vegetation is a prerequisite for reconstruction of vegetation and climate change from fossil pollen records. We conducted palynological studies of thirty-five surface soil samples from the Jammu region of India, which revealed that Pinus, among the conifers (regional needle-leaved taxa), is over-represented in the pollen assemblage due to its high production and effective dispersal of pollen. Other coniferous and broadleaved (regional and/or extra-regional) taxa have comparatively lower values in the pollen assemblages, similar to the representation of subtropical deciduous forest elements (regional), as well as shrubby (regional and/or extra-regional) taxa. This inconsistency in the pollen assemblage could be due to long-distance transport of the former by wind and/or water from the higher reaches of the Himalayas, and also because the latter have an entomogamous pollination syndrome and are not high pollen producers. The recovered pollen assemblage presents a distorted picture of the extant vegetation; hence, caution should be exercised in interpreting fossil pollen records from the study area. Principal component analysis (PCA) shows variability in the distribution of pollen from different sites in the Jammu region, perhaps the result of transport (by wind and/ or water), altitude and/or edaphic factors of the Himalayan terrain. The study should improve our understanding of the modern pollen-vegetation relationship and aid further calibration and interpretation of fossil pollen records.

Reconstruction of Cultivated Land in the Northeast Margin of Qinghai–Tibetan Plateau and Anthropogenic Impacts on Palaeo-Environment During the Mid-Holocene

The study of past global change is paramount to comprehending the present and future, as well as to better understand the mechanisms and influences of human–land interactions in a given region. The northeastern margin of the Qinghai–Tibetan Plateau has complex natural environments, sensitive to global change, and renowned for its long history of human occupancy. This makes it an ideal region for the study of anthropogenic impacts on the paleo-natural environment. This paper reconstructed the prehistoric temporal and spatial distribution of cultivated lands on the northeast margin of Qinghai–Tibetan Plateau, and analyzed the Dianziping pollen assemblage to disclose the anthropogenic impacts on the paleo-environment. The results demonstrated that around 4.3–4.0 cal ka BP, the rapid development of the Majiayao culture boosted the population to approximately 39,200 people, over 460 km2 of the land area was converted to cropland, concomitantly, evidence of tree pollen decreased significantly. This marked the earliest identification of anthropogenic impacts on vegetation through agricultural activity in this region. At 4.0–3.6 cal ka BP, the population appeared to have diminished in conjunction with the cultivated land area. Nevertheless, forested areas continued to decrease, primarily due to adverse climatic conditions, but, anthropogenic activities played an undeniable role. Dianziping profile demonstrated the existence of natural forest in the Hehuang Valley during Qijia cultural Period. There was also evidence for the occurrence of regional fire events, suggesting large-scale burning of land cover in the area. This further illustrates anthropogenic impacts. At 3.6–2.6 cal ka BP, populations reached approximately 61,300 people, coinciding with the peak of cropland expansion. Consequently, more of the natural vegetation were converted to crops, and the superimposed influences of farming and grazing aggravated the process of deforestation and vegetation succession. Likewise, deforestation during the historical period can be explained, mostly by human driven causes with limited influence from climatic factors. The extensive exploitation of forest and expansion of cropland consequently resulted in extensive land deterioration, leaving the region with forest islands scattered in less populated, mountainous regions.

A Last Interglacial speleothem record from the Sieben Hengste cave system (Switzerland): Implications for alpine paleovegetation

A precisely dated speleothem isotope record from the Sieben Hengste cave system, Switzerland, reveals a Last Interglacial (LIG) climate optimum centred at 128.1 ± 1.2 ka. The oxygen isotope signal is consistent with a temperature-dominated record and shows a strong correlation with the modelled Greenland δ18O signal. The comparison with speleothems formed during the Last Glacial Maximum (LGM) in the same cave indicates a 4–5‰ difference in δ18O between peak LIG and peak LGM conditions, suggesting peak LIG temperatures being up to 3 °C higher than the Holocene average. Pollen extracted from the stalagmite indicates a vegetation response delayed by up to 3 ka with maximum pollen concentrations recorded at 125 ± 2.2 ka. Our results support a regional vegetation dominated by thermophile tree species including Corylus (hazel), Quercus robur-type (oak), Ulmus (elm), Tilia (lime tree) and Hedera (ivy), consistent with slightly warmer conditions than today. Despite the relatively low pollen concentration, the speleothem-based pollen spectra are consistent with regional pollen assemblage zones from paleolake sediments and provide the first direct paleovegetation evidence of thermophilization during the LIG at high altitudes in the Alps.

Testing the potential of pollen assemblages to capture composition, diversity and ecological gradients of surrounding vegetation in two biogeographical regions of southeastern Europe

Due to the complex relationship between pollen and vegetation, it is not yet clear how pollen diagrams may be interpreted with respect to changes in floristic diversity and only a few studies have hitherto investigated this problem. We compare pollen assemblages from moss samples in two southeastern European forests with the surrounding vegetation to investigate (a) their compositional similarity, (b) the association between their diversity characteristics in both terms of richness and evenness, and (c) the correspondence of the main ecological gradients that can be revealed by them. Two biogeographical regions with different vegetation characteristics, the Pieria mountains (north central Greece) and the slopes of Ciomadul volcano (eastern Romania), were chosen as divergent examples of floristic regions, vegetation structure and landscape openness. Pollen assemblages are efficient in capturing the presence or absence, rather than the abundance in distribution of plants in the surrounding area and this bias increases along with landscape openness and vegetation diversity, which is higher in the Pieria mountains. Pollen assemblages and vegetation correlate better in terms of richness, that is, low order diversity indices. Relatively high correlation, in terms of evenness, could be potentially found in homogenous and species poor ecosystems as for Ciomadul. Composition and diversity of woody, rather than herb, vegetation is better reflected in pollen assemblages of both areas, especially for Pieria where a direct comparison of the two components was feasible, although this depends on the species-specific pollen production and dispersal, the openness of landscape and the overall diversity of vegetation. Gradients revealed by pollen assemblages are highly and significantly correlated with those existing in vegetation. Pollen assemblages may represent the vegetation well in terms of composition, diversity (mainly richness) and ecological gradients, but this potential depends on land use, vegetation structure, biogeographical factors and plant life forms.

Palynological evidence from a sub-alpine marsh of enhanced Little Ice Age snowpack in the Marrakech High Atlas, North Africa

The grazing lands of the High Atlas are vulnerable to climate change and the decline of traditional management practices. However, prior to the mid-20th century, there is little information to examine historical environmental change and resilience to past climate variability. Here, we present a new pollen, non-pollen palynomorph (NPP) and microcharcoal record from a sub-alpine marsh (pozzine) at Oukaïmeden, located in the Marrakech High Atlas, Morocco. The record reveals a history of grazing impacts with diverse non-arboreal pollen assemblages dominant throughout the record as well as recurrent shifts between wetter and drier conditions. A large suite of radiocarbon dates (n = 22) constrains the deposit to the last ~ 1,000 years although multiple reversed ages preclude development of a robust age-depth model for all intervals. Between relatively dry conditions during the Medieval period and in the 20th century, intervening wet conditions are observed, which we interpret as a locally enhanced snowpack during the Little Ice Age. Hydrological fluctuations evidenced by wetland pollen and NPPs are possibly associated with centennial-scale precipitation variability evidenced in regional speleothem records. The pollen record reveals an herbaceous grassland flora resilient against climatic fluctuations through the last millennium, possibly supported by sustainable collective management practices (agdal), with grazing indicators suggesting a flourishing pastoral economy. However, during the 20th century, floristic changes and increases in charcoal accumulation point to a decline in management practices, diversification of land-use (including afforestation) and intensification of human activity.