Late Holocene Vegetation Changes Research Articles

Late Glacial and Holocene vegetation and lake changes in SW Yakutia, Siberia, inferred from sedaDNA, pollen, and XRF data

Only a few palaeo-records extend beyond the Holocene in Yakutia, eastern Siberia, since most of the lakes in the region are of Holocene thermokarst origin. Thus, we have a poor understanding of the long-term interactions between terrestrial and aquatic ecosystems and their response to climate change. The Lake Khamra region in southwestern Yakutia is of particular interest because it is in the transition zones from discontinuous to sporadic permafrost and from summergreen to evergreen boreal forests. Our multiproxy study of Lake Khamra sediments reaching back to the Last Glacial Maximum 21 cal ka BP, includes analyses of organic carbon, nitrogen, XRF-derived elements, sedimentary ancient DNA amplicon sequencing of aquatic and terrestrial plants and diatoms, as well as classical counting of pollen and non-pollen palynomorphs (NPP). The palaeogenetic approach revealed 45 diatom, 191 terrestrial plant, and 65 aquatic macrophyte taxa. Pollen analyses identified 34 pollen taxa and 28 NPP taxa. The inferred terrestrial ecosystem of the Last Glacial comprises tundra vegetation dominated by forbs and grasses, likely inhabited by megaherbivores. By 18.4 cal ka BP a lake had developed with a high abundance of macrophytes and dominant fragilarioid diatoms, while shrubs expanded around the lake. In the Bølling-Allerød at 14.7 cal ka BP both the terrestrial and aquatic systems reflect climate amelioration, alongside lake water-level rise and woodland establishment, which was curbed by the Younger Dryas cooling. In the Early Holocene warmer and wetter climate led to taiga development and lake water-level rise, reflected by diatom composition turnover from only epiphytic to planktonic diatoms. In the Mid-Holocene the lake water level decreased at ca. 8.2 cal ka BP and increased again at ca. 6.5 cal ka BP. At the same time mixed evergreen-summergreen forest expanded. In the Late Holocene, at ca. 4 cal ka BP, vegetation cover similar to modern conditions established. This study reveals the long-term shifts in aquatic and terrestrial ecosystems and a comprehensive understanding of lake development and catchment history of the Lake Khamra region.

Mid-to late Holocene vegetation and environmental change at local and regional scales based on a multi-proxy analysis of the upper Danube Delta, Romania

The Danube Delta is Europe's largest wetland system and of unique biogeographical character. Whilst its geomorphological evolution is relatively well-known its ecological history is poorly understood, including the history of human impact, as a result of the dynamic nature of deltaic systems, and the scarcity of reliably dated successions. In this paper, we report a multi-proxy record of palynology, sediment texture, geochemistry, and ostracods from the upper reaches of the Danube Delta. We use these data to reconstruct a mid-to-late Holocene history of vegetation and environmental changes at local and regional scales, which serve as a model for understanding baseline conditions in delta apex regions. From 7500 to 6200 ​cal ​yr BP, the study site was part of an inter-distributary channel-levee system connected to coastal lagoons and sensitive to sea-level fluctuations but transitioned to a partially-disconnected lacustrine environment after 5700 ​cal ​yr BP. These geomorphologically-driven landscape changes strongly influenced the pollen source area making it complex to interpret palynoassemblages. Prior to 5700 ​cal ​yr BP, palynoassemblages were predominantly river-transported, reflecting widespread hinterlands, and providing information for the regional reconstruction of the vegetation history in the northern Dobrogea region. These data reveal the early presence of Carpinus and Fagus in southeastern Romania, prior to their spread through the Carpathian Basin. After 5700 ​cal ​yr BP, initiated by a slowdown in the relative rate of rise of the Black Sea, peat accumulation commenced within the shallow lake depocentre and airborne pollen became the dominant source. These pollen data record an expansion of herbaceous taxa and highly diverse marsh and aquatic taxa. Tree cover became dominated by Quercus, with low percentages of Carpinus, Betula, Ulmus, and Tilia. The earliest pollen evidence indicative of human impact commences c. 6500 ​cal ​yr BP) and, after 3200 ​cal ​yr BP, the decline in Quercus and a synchronous rise in archaeological artifacts, points to an opening of the landscape by forest clearance and an enlargement of arable areas. In particular, clearance and agriculture during the development of the Hallstattian Babadag culture (c. 3200-2800 ​yr BP) reflects an increase in population and settlement density during that late interval. Our paper comprises the first mid-to-late Holocene palynological record for the Danube Delta and highlights how human activity has profoundly altered the dryland region, creating landscapes comparable to today from around 3200 years BP, while the local deltaic landscape retained its character over the last six millennia.

Late Holocene vegetation and climate change in the northern Tibetan Plateau region based on a palynological analysis from Lake Ayakum

In this paper, we undertake a high-resolution palynological analysis of a sediment core covering the last 1500 years obtained from Lake Ayakum in the northern Tibetan Plateau, to improve the understanding of regional climate fluctuations and their driving mechanisms. The pollen spectra are dominated by herbaceous species such as Artemisia, Chenopodiaceae, Cyperaceae and Poaceae, which grew in various alpine desert settings. Four pollen assemblage zones are identified using stratigraphically constrained cluster analysis, representing climate history at different stages. The Artemisia/Chenopodiaceae (A/C) ratio and axis score of the first principal component are used to infer regional moisture conditions and reveal a temporal pattern that is consistent with various records from central Asia. The source of Cyperaceae pollen is mainly from marsh wetlands distributed around the lake, which responded sensitively to the lake level fluctuations. In contrast, arboreal pollen is mainly a long-distance transported component, reflecting changes in regional vegetation. Our findings show that the northern Tibetan Plateau experienced relatively wet conditions during the Dark Age Cold Period and the Little Ice Age, while relatively dry conditions occurred during the Medieval Warm Period and the last two centuries. Fluctuations in moisture levels are broadly consistent with moisture records elsewhere in western China, and show a good correlation with phase changes of the North Atlantic Oscillation. The climate changes in the northern Tibetan Plateau are supposed to be primarily triggered by the NAO phases through south-north migrations of the mid-latitude westerlies during the late Holocene.

Late Holocene Vegetation and Environmental Changes of Coastal Lowlands in Northern Iran: Possible Role of Climate, Human Impact and Caspian Sea Level Fluctuations

Coastal forests and wetlands play an important role in supporting biodiversity, protecting the hinterlands and shorelines from erosion and also contributing to carbon sequestration and freshwater storage. To reconstruct late Holocene vegetation and environmental dynamics in the coastal lowlands of northern Iran and to detect the possible role of climate, human and Caspian Sea level fluctuation on coastal ecosystems, multi-proxy analysis was applied on the sediment cores from the inland Eynak (EYK) lagoon and near coast Bibi Heybat (BBH) alder swamp. Results shows that in the last 170 years, strong reduction of alder forest occurred around Eynak lagoon, while an expansion occurred in the coastal area in the last 100 years. This indicates that human impact shifted from the near coast to elevated inland, which might be due to the raised water level from the Caspian Sea and the coastal area of BBH region was flooded by brackish water from the Caspian Sea, and was not so suitable for agriculture anymore. This study indicate that alder swamp extent is different between coastal and inland sites, suggesting that further studies of multiple records across the region are needed. Moreover, this study helps to distangle human impacts from wetland processes and thus will be an important contribution to effective climate mitigation and conservation strategies. This multi-proxy study presents important palynological records, which helps to understand past and future impacts of various drivers, such as climate, human impact and sea level changes on wetland ecosystems both regionally and globally.

Late Glacial and Holocene vegetational and climate changes and their impact on material cultures in the Crimean Mountains (founded on pollen data from cave deposits)

Pollen data has been obtained from archaeological horizons in cave and rock shelter deposits, on the high plateaux (the Yaila) and the slopes of the Crimean Mountains. This data, supported by geochronometry and lithology, indicate multiple environmental oscillations during the Late Glacial and Holocene. These had a significant impact on changes in the Final Palaeolithic, Mesolithic and Neolithic. Pollen assemblages from Late Glacial deposits indicate the existence during the last glacial of refugia of a broad-leaved flora on the lower mountain slopes. During the Late Glacial interstadials, the tribes of the Shan-Koba culture hunted forest game indicative of a temperate climate. From the Younger Dryas into the Greenlandian (11,500–10,300 cal BP) the Swiderian hunters were visitors to the treeless Crimean yailas from the northern Ukraine. During the Greenlandian, two warm and humid phases, when the forests extended, alternated with cool and arid phases when the woodland shrank and xeric herbs became important in the yailas. The Shpan culture that existed later during the Greenlandian (between c. 10,600 and 9100 cal BP) was influenced by migrations of steppe hunters from the Crimean plain area, and they hunted game that included more animals of open ecotopes. During the end of Greenlandian and the beginning of Northgrippian (9000–7500 cal BP), broad-leaved woodlands appeared at the yaila edges, with such warmth-loving species as Rhus coronaria, Cornus mas and Hedera taurica, and mesophytic steppe occupied the yailas. The tribes of the Late Mesolithic Murzak-Koba culture and the Neolithic Tash-Air culture were hunters of the game living in the broad-leaved forests, particularly wild pig. Nevertheless, the Tash-Air tribes continue to exist during a cool and arid phase after 7500 cal BP. The second half of the Meghalayan (since 2600 BP) had a humid climate: they were times showing a larger extension than before of pine and juniper onto the yaila, though an arid phase occurred at 2900-2600 cal BP. After 1000 BP, broad-leaved trees almost completely disappeared near the yaila and ferns spread enormously (due to the impact of cold winters in the Little Ice Age or to forest clearance). The role of arboreal vegetation and broad-leaves trees, as well as xeric herbs, changed cyclically during different phases of the Late Glacial and Holocene on the yailas, but mesophytic steppe always remained the dominating vegetation type there.

Late Holocene land use evolution and vegetation response to climate change in the watershed of Xingyun Lake, SW China

Knowledge of the past interactions between climate and human land use is essential for understanding the possible future relationships between global change and human societies. In this study, we used pollen and other multi-proxy analyses of the sediments from Xingyun Lake in central Yunnan Plateau to reconstruct the history of land use and ecosystem dynamics during the last 3,200 years. The pollen results indicate that the vegetation became more open gradually and many secondary forests began to grow during the last 100 years. During the Medieval Climatic Anomaly (MCA), the vegetation is dominated by broad-leaved trees, while during the Little Ice Age (LIA) the broad-leaved trees declined but Picea/Abies expanded. Human land use has impacted on the regional vegetation and landscape since 50 CE; large-scale human land use occurred after 750 CE. The sediment accumulation rate (SAR), pollen record, and 14C age offsets reveal that soil erosion is well correlated with human activity and changes in vegetation cover. Before 750 CE, soil erosion was probably limited, but after 750 CE it increased drastically as a result of human activity, and then decreased during the last 100 years. According to the results of the redundancy analysis (RDA), we conclude that climate had an important impact on the regional vegetation, and the late Holocene vegetation changes of Xingyun Lake catchment were mainly influenced by temperature.

Compound-specific stable carbon and hydrogen isotope analyses of late-Holocene vegetation and precipitation change at Laguna Los Mangos, Costa Rica

New compound-specific isotope analyses of a sediment core from Laguna Los Mangos in southern Pacific Costa Rica improves understanding of late-Holocene precipitation change in a region with limited paleoprecipitation records that is vulnerable to future climate change. We established paleoprecipitation and paleovegetation records from compound-specific stable hydrogen and carbon isotopic compositions of terrestrially-derived n-alkanes (δ2Halkane and δ13Calkane) to assess paleohydrologic variability and potential linkages to paleoecological change and human activity as revealed by prior analyses of the Los Mangos core. The δ2Halkane values were corrected for isotopic fractionation using pollen counts from the same core. The Los Mangos record extends to 4200 cal yr BP and small increases in δ13C values of C29, +0.6‰, and C31 alkanes, +0.3‰, (δ13CC29, 31) indicate a slight increase in C4 vegetation after initial introduction of maize agriculture to the watershed at ca. 3360 cal yr BP. This slight increase in C4 vegetation is followed by the largest positive carbon isotope excursions in the record, as compared to record averages (δ13CC29 = +3.2‰, δ13CC31 = +5.0‰). Paleohydrologic variability likely influenced vegetation and human activity at Los Mangos. Lake desiccation during the late-Terminal Classic Drought (TCD) resulted in a sedimentary hiatus in the Los Mangos record from ca. 950 to 450 cal yr BP. Positive excursions in comparison to record averages occur for both δ2HC29 and δ2HC31 proxies (δ2HC29 = +25.3 to +13.4‰ and δ2HC31 = +6.5‰) during the middle Little Ice Age (LIA) and indicate drier than average conditions, but there is no evidence of desiccation during this period. Thus, drought conditions during the LIA were apparently not as severe at Los Mangos as during the TCD, possibly because of differing forcing mechanisms for LIA climate that originated, or were more clearly expressed, in the Atlantic basin.

Late-Holocene vegetation change reveals the environment of ancient people and the origin of Huashan cliff paintings in Guangxi, southwestern China

Human activities in the historical period were determined by the natural environment and social characteristics. The Zuojiang Huashan Rock Art Cultural Landscape in Guangxi is the most important World Heritage for prehistorical culture in southwestern China. However, knowledge about the natural environment and associated historic human–climate interactions during the period of cliff painting creation remains scarce, which has been an obstacle to understanding the process of regional civilization. Here, we report a pollen record from the core distributing region of Huashan cliff paintings to interpret the natural environment and climate changes, and further to discuss how and why ancient people create these giant cliff paintings based on the relationships of human–climate interactions. Pollen results imply an existence of a mixed broad-leaf and conifer forest in the woodland landscape at Huashan region before 1860 cal. yr BP, after which pine forests were more prevalent. During the cliff painting period from 2370 to 2115 cal. yr BP, broad-leaf and conifer trees dominated the tree layer and provided the key source materials for painting. It can be reasonably assumed that people used stake or ladder to climb the cliffs and created the cliff paintings during a humid climate condition from 2560 to 2000 cal. yr BP. Furthermore, the humid climate during 2700 and 2400 cal. yr BP had been interrupted by short-term drought episodes. These turbulent climate episodes probably played the role of disasters and impacted on the human activities, leading to the social–political tensions and the out-break of war. During the Qin and Han Dynasties, social–political changes relieved the pressure from natural climate changes and led to a more stable society, in which the creating of cliff paintings was gradually fading. Our results manifest the necessity to analyze the natural environment and social–political background in combination in this study on ancient human activities.

Late Glacial-early holocene vegetation and environmental changes in the western Iberian Central System inferred from a key site: The Navamuño record, Béjar range (Spain)

A new record from a long sediment core (S3) in Navamuño (1505 m asl, western Iberian Central System) provides the reconstruction of the vegetation history and environmental changes in the region between 15.6 and 10.6 ka cal BP, namely during the Late Glacial and the early Holocene, using a multiproxy analysis (pollen-based vegetation and climate reconstruction, sedimentary macrocharcoals, loss-on-ignition, magnetic susceptibility and X-ray fluorescence (XRF) measurements). The results are then compared with other sequences from the Iberian Central System and the whole Iberian Peninsula in order to better understand the past dynamics of the main forest constituents. The pollen record shows a shift from open pine forests ∼15.6–14.7 ka cal BP (Oldest Dryas) to mixed open pine-birch woodlands ∼14.7–14.0 ka cal BP (Bølling). Woodlands were succeeded by a steppe-like landscape until ∼13.4 ka cal BP (Older Dryas), which was replaced again by high-mountain pine forests and riparian woodlands ∼13.4–12.6 ka cal BP (Allerød). A great development of cold steppe grasslands linked to the decline of birch woodlands is documented ∼12.6–11.7 ka cal BP (Younger Dryas). The early Holocene (11.7–10.6 ka cal BP) was characterized by a progressive reforestation of the study area by pine and birch forests in the highlands and oak woods in the lowlands. Temperate tree taxa (Carpinus betulus, Castanea sativa, Corylus avellana, Fraxinus, Juglans, Tilia, and Ulmus) were also common but likely at lower elevations. Pollen of Fagus sylvatica was already recorded during the Late Glacial and the early Holocene. The marked increasing local fire activity during the warmer and wetter Allerød oscillation could be related to a rise in tree cover, supporting the climatically driven character of these fires. Nevertheless, the strong increase in fire activity during the Younger Dryas would probably be related to growing tree and shrub mortality, as well as to the wet/dry biphasic structure of this stadial. The standard “Modern Analogue Technique” has been also applied to the Navamuño sequence to provide quantitative climate estimations for the Late Glacial and the early Holocene periods. This record is one of the few continental archives that show the climatic trend between the Late Glacial and the early Holocene in central Iberia, agreeing with many other regional records from the Western Mediterranean.

Late Holocene vegetation and climate changes in the Great Hinggan Mountains, northeast China

High-latitude region is sensitive to global climate change, and pollen record in sediments could reflect vegetation variation which responded to climate change. The Great Hinggan Mountains are main distribution areas of peatlands in high-latitude region in China and located at East Asian summer monsoonal margin, however, the variation of vegetation and climate in this region is still unclear. Based on the AMS 14C dating, we analyzed the pollen assemblages to reconstruct vegetation history in Tuqiang (TQ) peatland, and we also used the principal component analysis to reconstruct the temperature and effective moisture and compared with other palaeoclimate records. Pollen assemblage denoted a coniferous and broad-leaved mixed forest on the surrounding mountains, and peatland vegetation gradually evolved from herb community (Cyperaceae) to bush community (Ericaceae). The climate of north part in the Great Hinggan Mountains was mainly controlled by the East Asian Summer Monsoon which related to ocean-atmosphere interactions in the tropical Pacific. During the period from 3300 to 1150 cal yr BP, the dominant plant was Cyperaceae, with coniferous and broad-leaved mixed forests bordered the peatland, which pointed to a relatively warm and wet climate. Between 1150 and 600 cal yr BP, the expansion of pine forests indicated a cool climate. The interval of 600–300 cal yr BP, the climate became cold and dry which related to the Little Ice Age. Since the 300 cal yr BP, Betula and Ericaceae dominated, the climate became warmer and drier. The obvious increase of secondary birch forests at the expense of pine forests may be the results of human disturbance, anthropogenic activities strengthened gradually and the variation of peatland vegetation was influenced mainly by anthropogenic activities rather than by climate since approximately 600 cal yr BP.

Late Holocene transformations of lower montane forest in the Beskid Wyspowy Mountains (Western Carpathians, Central Europe): a case study from Mount Mogielica

This article presents a reconstruction of Late Holocene vegetation changes within the lower montane forest zone in the Beskid Wyspowy Mountains (Western Carpathians, Central Europe). Pollen, non-pollen palynomorphs, loss on ignition, and microscopic charcoal analyses were applied to a profile collected from the deposits of the rich fen which developed in the landslide depression. The results reveal that during the period between ca. 4800 ± 70 and 4160 ± 60 cal. BP, Picea abies dominated in the local forests. Between ca. 4800 ± 70 and 4660 ± 60 cal. BP, Acer was an important component in local woodlands, which distinguishes the study site from others in the Western Carpathians. At ca. 4100 ± 60 cal. BP, forests dominated by Abies alba and Fagus sylvatica expanded. Nowadays, this type of vegetation is characteristic of the lower montane zone in the Polish Western Carpathians. This expansion was probably a consequence of environmental disturbances related to the cold and wet ‘4.2 ka BP’ event. The spread of these forests was preceded by a short episode of expansion of Tilia (Tilia cordata and/or Tilia platyphyllos) which was a very local event. The area of the Beskid Wyspowy Mountains provided suitable habitats for the occurrence of T. baccata, which has not been recorded in pollen data spanning the Middle and beginning of the Late Holocene from this mountain range. A significant increase in the percentages of Kretzschmaria deusta, a parasitic fungus, reveals that A. alba–F. sylvatica forests provided an optimal habitat for such species during the period from 4070 ± 60 to 47 cal. BP. Since ca. 2640 ± 110 cal. BP, pollen of pioneer trees, such as Pinus sylvestris and Betula, as well as human activity indicators (Cerealia type and Plantago lanceolata) have become more frequent. Nonetheless, it is highly probable that this section of deposits also includes the presence of one or more sedimentary gaps.

Mid- to late Holocene vegetation change recorded at a Neolithic site in the Yangtze coastal plain, East China

There has been an ongoing debate about human impacts on the evolution of the vegetation cover on the Yangtze delta plain dating back to the Neolithic period. In this study, we carried out pollen identification and grain size analysis on two sediment profiles obtained from the Neolithic Guangfulin site in the Yangtze delta. Together with published results of radiocarbon ages, organic elemental chemistry and archaeological findings, we reconstructed the palaeoecological evolution and human activities at the site during the mid- to late Holocene and distinguished between the impacts on vegetation induced by human and hydrological processes. The results show three events of significant reduction in the abundance of arboreal pollen, which occurred at c. 4635, 2000, and 800 cal yr BP, respectively. The first two events were accompanied by an obvious increase in Poaceae pollen, whereas the last one occurred with a sharp increase in the abundance of Brassicaceae pollen. These findings suggest that the reductions in arboreal pollen resulted from deforestation for the expansion of rice cultivation at c. 4635 and 2000 cal yr BP, and expansion of Brassicaceous oil crops c. 800 years ago. The change in cultivation pattern c. 800 years ago was consistent with the increase in population migration from northern China caused by war at that time. The pollen of aquatic plants increased sharply at c. 4500 cal yr BP, which reflected the change in hydrological environment related to sea-level rise at the Yangtze River mouth.

Late Pleistocene and Holocene vegetation changes and anthropogenic impacts in the Cauvery delta plains, southern India

A 5 m long core from Uttarangudi in the distal plain of Cauvery delta in South India provides evidences of vegetation, climate and anthropogenic activities during the late Pleistocene and Holocene. The pollen catchment area for this region is the localised sources, including the adjoining Tertiary upland plateau. The recorded variation in pollen assemblages and sediments indicates that the environmental conditions have changed over time from aerial oxidising to lacustrine or ponded environment. The lack of pollen records from 17,802 cal BP until 11,535 cal BP suggests severe drier conditions and an extremely patchy, species-poor Tropical Dry Evergreen Forest (TDEF) vegetation community associated with an arid climate. Between 11,535 and 8487 cal BP, partial climatic amelioration appears to have occurred, and the trend become humid until 7034 cal BP characterised by the expansion of the TDEF vegetation and strengthening of the monsoon precipitation. The period from 7034–3553 cal yr BP recorded a regressive transition of the forest taxa influenced by a weakened monsoon precipitation and enhanced anthropogenic activity. The subsequent increase of disturbance signals post 3553 cal yr BP is in agreement with independent archaeological evidences obtained from this region.

Uncoupling human and climate drivers of late Holocene vegetation change in southern Brazil

In the highlands of southern Brazil an anthropogenitcally driven expansion of forest occurred at the expense of grasslands between 1410 and 900 cal BP, coincident with a period of demographic and cultural change in the region. Previous studies have debated the relative contributions of increasing wetter and warmer climate conditions and human landscape modifications to forest expansion, but generally lacked high resoltiuon proxies to measure these effects, or have relied on single proxies to reconstruct both climate and vegetation. Here, we develop and test a model of natural ecosystem distribution against vegetation histories, paleoclimate proxies, and the archaeological record to distinguish human from temperature and precipitation impacts on the distribution and expansion of Araucaria forests during the late Holocene. Carbon isotopes from soil profiles confirm that in spite of climatic fluctuations, vegetation was stable and forests were spatially limited to south-facing slopes in the absence of human inputs. In contrast, forest management strategies for the past 1400 years expanded this economically important forest beyond its natural geographic boundaries in areas of dense pre-Columbian occupation, suggesting that landscape modifications were linked to demographic changes, the effects of which are still visible today.

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.

Late Holocene vegetation and climate change on the southeastern Tibetan Plateau: Implications for the Indian Summer Monsoon and links to the Indian Ocean Dipole

The Indian Summer Monsoon (ISM) is one of the most important climate systems, whose variability and driving mechanisms are of broad interest for academic and societal communities. Here, we present a well-dated high-resolution pollen analysis from a 4.82-m long sediment core taken from Basomtso, in the southeastern Tibetan Plateau (TP), which depicts the regional climate changes of the past millennium. Our results show that subalpine coniferous forest was dominant around Basomtso from ca. 867 to ca. 750 cal. yr BP, indicating a warm and semi-humid climate. The timberline in the study area significantly decreased from ca. 750 to ca. 100 cal. yr BP, and a cold climate, corresponding to the Little Ice Age (LIA) prevailed. Since ca. 100 cal. yr BP, the vegetation type changed to forest-meadow with rising temperatures and moisture. Ordination analysis reveals that the migration of vegetation was dominated by regional temperatures and then by moisture. Further comparisons between the Basomtso pollen record and the regional temperature reconstructions underscore the relevance of the Basomtso record from the southeastern TP for regional and global climatologies. Our pollen based moisture reconstruction demonstrates the strong multicentennial-scale link to ISM variability, providing solid evidence for the increase of monsoonal strengths over the past four centuries. Spectral analysis indicates the potential influence of solar forcing. However, a closer relationship has been observed between multicentennial ISM variations and Indian Ocean sea surface temperature anomalies (SSTs), suggesting that the variations in monsoonal precipitation over the southeastern TP are probably driven by the Indian Ocean Dipole on the multicentennial scale.

Vegetational and agricultural dynamics at Burgäschisee (Swiss Plateau) recorded for 18,700 years by multi-proxy evidence from partly varved sediments

Little is known about the timing and the vegetation dynamics shortly after the Last Glacial Maximum (LGM) on the Swiss Plateau 19,000–15,000 cal bp. Subsequent Late Glacial and Holocene vegetation changes are better known; however, it is unclear if the few available palynological and macrofossil records are able to capture the entire vegetation variability of the region. A new palaeoecological multi-proxy study using pollen, spores, charcoal and X-ray fluorescence (XRF) from Burgaschisee (Swiss Plateau, 465 m a.s.l.) is applied to reconstruct vegetation, fire and land use for the past 19,000 cal years. Steppe tundra vegetation established at c. 18,700 cal bp only c. 300 years after the end of the LGM and deglaciation. A shift from steppe tundra (Artemisia, Helianthemum) to shrub tundra (Betula nana, Salix, Juniperus) with sporadic tree Betula stands occurred around 16,000 cal bp, most likely in response to climate warming after the end of Heinrich event 1. Abundant spores of coprophilous fungi (Sporormiella, Cercophora) may reflect the presence of Pleistocene large herbivores (e.g. Mammuthus primigenius, Bison bonasus, Rangifer tarandus). Afforestation started more than 2,000 years later with Juniperus and tree Betula around 14,500 cal bp. Mixed Betula and Pinus sylvestris forests persisted until 10,800 cal bp, when mixed elm forests expanded into the region in response to climate warming. Around 8,200 cal bp, mesophilous Fagus sylvatica and Abies alba partly replaced more heliophilous species in the forests, when climate became less continental and more moist. Pollen of Cerealia, Plantago lanceolata and other crops and weeds suggest that agricultural activities became significant during the Neolithic around 6,500 cal bp (4550 cal bc). Archaeological findings from Neolithic pile dwellings around 5,950 cal bp (4000 cal bc) indicate local settlements around the lake. The lake sediments are laminated for most of the last c. 6,800 years. With two independent proxies (XRF and pollen), we can demonstrate that these laminations are annual, suggesting short-term mixing of the lake water due to a more open landscape in response to land use. Our study shows that the annually laminated (varved) sediments from Burgaschisee have a great potential for high-resolution multi-proxy analyses covering the past c. 6,800 years. They can provide accurate ages of cultural phases that might be compared with dendrochronologically dated evidence from lake dwellings.

Climatic and anthropogenic forcing of prehistorical vegetation succession and fire dynamics in the Lago di Como area (N-Italy, Insubria)

Combined pollen, charcoal and modeling evidence from the Insubria Region suggests that fire was a major driver of late Holocene vegetation change. However, the extent and timing of fire response dynamics are not clear yet. We use lacustrine sediments from Lago di Como (N-Italy, S-Alps) to assess if the reconstructed vegetation and fire dynamics were relevant at large scales and if they coincided in time with those observed at smaller sites. The lake, due to its size (142 km2) and economic potential, was very attractive for early land use and human presence in this area is well documented since ca. 10,000 yrs ago (Mesolithic). We used pollen, plant macrofossils and charcoal to reconstruct the vegetation composition and fire activity. During the Younger Dryas and the Early Holocene until ca. 8000 cal BP natural dynamics prevailed. Subsequently, land use and slash-and-burn activities increased at the Mesolithic-Neolithic transition and became widespread around ca. 6500 cal BP. Microscopic charcoal and numerical analyses demonstrate that anthropogenic fires had a determinant influence on long-term vegetation dynamics at regional scales in Insubria. Microscopic charcoal and pollen and spores indicative of land use show that human pressure intensified after ca. 5300 cal yr BP and even more since ca. 4300 cal yr BP. Our results suggest that important species which disappeared or were strongly reduced by land use and fire (e.g. Abies alba, Tilia, Ulmus) will potentially reestablish in the Lago di Como area and elsewhere in Insubria, if land abandonment initiated in the 1950s will continue.

Late-Holocene vegetation and climate change in Jeju Island, Korea and its implications for ENSO influences

Abstract Several recent studies suggest the hypothesis that the El Nino-Southern Oscillation (ENSO) is an important factor controlling the Holocene East Asian Monsoon (EAM). However, the mechanism underlying this influence remains unclear due to the lack of high-resolution paleoclimate records from the coast of East Asia. Here, we provide a new record of late Holocene climate change in coastal East Asia based on multi-proxy evidence (pollen, organic content, magnetic susceptibility, grain size) obtained from a sediment core from Jeju Island, South Korea. As Jeju Island is strongly influenced by the Kuroshio flow, our sediment proxy records contain ENSO signals from the tropical Pacific. The study area was affected by dry/cool conditions in the western tropical Pacific (WTP) between 4350 and 1920 cal yr BP when El Ninos were frequent, and by rapid warming/wetting and forestation since 1920 cal yr BP when La Ninas were more common. Jeju Island was relatively dry/cool between 2100 and 1600, 1300–1200, 1100–1000, 800–650, and 300–50 cal yr BP, as opposed to the Galapagos Islands, which were relatively wet/warm, reflecting the ENSO-related negative correlation between eastern and western margins of Pacific. Wet conditions may have prevailed during the early Little Ice Age (LIA) (620–280 cal yr BP) despite consistent cooling. This period of high precipitation may have been associated with the increased landfall of typhoons and with warmer Kuroshio currents under La Nina-like conditions. According to our results, EAM on the East Asian coastal margin was predominantly driven by ENSO activity, rather than by the precession effect. Paleoclimatic data from Jeju Island, with its insular position and closeness to warm Kuroshio currents, provide clear evidence of these ENSO influences.

The influence of Holocene vegetation changes on topography and erosion rates: a case study at Walnut Gulch Experimental Watershed, Arizona

Abstract. Quantifying how landscapes have responded and will respond to vegetation changes is an essential goal of geomorphology. The Walnut Gulch Experimental Watershed (WGEW) offers a unique opportunity to quantify the impact of vegetation changes on landscape evolution over geologic timescales. The WGEW is dominated by grasslands at high elevations and shrublands at low elevations. Paleovegetation data suggest that portions of WGEW higher than approximately 1430 m a.s.l. have been grasslands and/or woodlands throughout the late Quaternary, while elevations lower than 1430 m a.s.l. changed from a grassland/woodland to a shrubland ca. 2–4 ka. Elevations below 1430 m a.s.l. have decadal timescale erosion rates approximately 10 times higher, drainage densities approximately 3 times higher, and hillslope-scale relief approximately 3 times lower than elevations above 1430 m. We leverage the abundant geomorphic data collected at WGEW over the past several decades to calibrate a mathematical model that predicts the equilibrium drainage density in shrublands and grasslands/woodlands at WGEW. We use this model to test the hypothesis that the difference in drainage density between the shrublands and grassland/woodlands at WGEW is partly the result of a late Holocene vegetation change in the lower elevations of WGEW, using the upper elevations as a control. Model predictions for the increase in drainage density associated with the shift from grasslands/woodlands to shrublands are consistent with measured values. Using modern erosion rates and the magnitude of relief reduction associated with the transition from grasslands/woodlands to shrublands, we estimate the timing of the grassland-to-shrubland transition in the lower elevations of WGEW to be approximately 3 ka, i.e., broadly consistent with paleovegetation studies. Our results provide support for the hypothesis that common vegetation changes in semi-arid environments (e.g., from grassland to shrubland) can change erosion rates by more than an order of magnitude, with important consequences for landscape morphology.