Late Pleistocene shrub expansion preceded megafauna turnover and extinctions in eastern Beringia

The collapse of the steppe-tundra biome (mammoth steppe) at the end of the Pleistocene is used as an important example of top-down ecosystem cascades, where human hunting of keystone species led to profound changes in vegetation across high latitudes in the Northern Hemisphere. Alternatively, it is argued that this biome transformation occurred through a bottom-up process, where climate-driven expansion of shrub tundra (Betula, Salix spp.) replaced the steppe-tundra vegetation that grazing megafauna taxa relied on. In eastern Beringia, these differing hypotheses remain largely untested, in part because the precise timing and spatial pattern of Late Pleistocene shrub expansion remains poorly resolved. This uncertainty is caused by chronological ambiguity in many lake sediment records, which typically rely on radiocarbon (14C) dates from bulk sediment or aquatic macrofossils—materials that are known to overestimate the age of sediment layers. Here, we reexamine Late Pleistocene pollen records for which 14C dating of terrestrial macrofossils is available and augment these data with 14C dates from arctic ground-squirrel middens and plant macrofossils. Comparing these paleovegetation data with a database of published 14C dates from megafauna remains, we find the postglacial expansion of shrub tundra preceded the regional extinctions of horse (Equus spp.) and mammoth (Mammuthus primigenius) and began during a period when the frequency of 14C dates indicates large grazers were abundant. These results are not consistent with a model of top-down ecosystem cascades and support the hypothesis that climate-driven habitat loss preceded and contributed to turnover in mammal communities.

Last interglacial environment of the Baikal Region (Southern Siberia, Russia) based on analysis of fossil invertebrates and plants

New data on fossil insects, soil and freshwater invertebrates, plant macrofossils, pollen and spores were obtained from a problematic lower unit of the reference section Bely Yar-II (Tunka Rift, Baikal Region, Russia). The invertebrates show a natural succession from a small lake to a wetland; plant macrofossils confirm the early stages of succession. Pollen and spore data reflect a wide range of environments and vegetation from moderate climate supporting regional forests to relatively cold, dry parkland. New Uranium-Thorium data (99 ± 20 ka and 101 ± 13 ka), along with environmental reconstructions, indicate that the lower unit was probably formed during one of the cold sub-stages towards the end the last inter-glaciation (MIS5).

Historia de la vegetación del sitio Huapilacuy II durante el Holoceno Medio a partir del análisis polínico y de macrofósiles vegetales, Isla Grande de Chiloé, Chile

This study examines the new fossiliferous site Huapilacuy II of Mid-Holocene age (7,344±51-6,865±58 cal years BP.) located in the northwestern coast of the Isla Grande de Chiloé. This area was not affected by the successive Pleistocene glaciations, and therefore it presents a biogeographic relevance as a potential area of refugia and stability for the vegetation. The presence of plant macrofossils contained in a sedimentary sequence of ca. 300 cm thick, confers a special interest to the site, due to the scarce information available on this type of indicator in paleoenvironmental studies of southern Chile. Additionally, several pollen-based reconstructions from the southern Lake District of Chile (40-44˚ S), document the Holocene sequence of recolonization by the different temperate rainforests types that today occupy this region, although there are non-Holocene records for the Pacific coast of the region. The aim of this study is to reconstruct the local environmental conditions and paleoecology based on the stratigraphic context and the analysis of plant macrofossils at the site Huapilacuy II. In addition, based on the pollen analysis of the deposit, we provide new information to reconstruct the regional characteristics of the vegetation during the Middle-Holocene. In particular, the plant macrofossil record of marsh species contained in the sediments of the lower section of the studied sedimentary sequence, together with the pollen analysis of the same sequence, document a first phase of plant colonization at 7,344±51 cal yrs. BP, with predominance of Poaceae, ferns, and trees with regeneration capacity in open areas, such as Embothrium coccineum and Drimys winteri. The analysis of leaf macrofossils and palynomorphs recovered from several intercalated layers, from the middle section of the sedimentary sequence, show the local and regional development of dense and very humid forests dominated by Aextoxicon punctatum, associated with several species of Myrtaceae. The presence of soil moisture indicator species, such as Luma chequen, Myrceugenia sp. and Myrtaceae Blepharocalyx-type is consistent with the sedimentary environment and the local development of swamp or riverine forests. This hygrophile forest environment is also consistent with the assemblage of fossil mosses, dominated by species that grow today in dense closed-canopy forests, such as Weymouthia, Ptychomnium, Rigodium, Porothamnium and Eucamptodon. The regional correlation of the pollen spectra from Huapilacuy II and other records from the Lake District allows us to establish latitudinal and longitudinal differences of tree composition in the temperate-rainforests that expanded during the Early to Mid-Holocene. In particular, this study established for the northwestern coast of the Isla Grande de Chiloé the presence of the coastal association of the valdivian forest (As. Lapagerio-Aextoxiconetum), currently distributed along the Chilean coastline between 30˚- 43˚S. In contrast, the Valdivian associations recorded in other areas of the region exhibit the dominance of Eucryphia cordifolia, Caldcluvia paniculata, Weinmannia trichosperma and different species of Nothofagus. Despite the differences in tree composition, the fossil bryophyte species recorded in several of the sites compared are common with those reported for Huapilacuy II, thus showing the wide ecological range of Chilean bryophytes associated with closed-canopy temperate-rainforests.

Studies in New Zealand Oligocene and Miocene Plant Macrofossils

<p>Assemblages of fossil leaves ranging in age from Upper Oligocene to Upper Miocene or Lower Pliocene have been examined from localities in Southland, Central Otago, the Dunedin area, the Buller region and Great Barrier Island. Nearly 200 form taxa have been recognized so far; of these 52 are figured and described and the remainder are included in an illustrated catalogue. Conifers, Casuarinaceae and Nothofagus spp. are discussed in detail. Thirteen new species are named and described: Gleichenia southlandica, Hypolepis maruiensis, Blechnum maruiense, Dacrydium (Lagarostrobos) franklinoides, Microcachrys imbricata, Phyllocladus strictus, Libocedrus compressa, Nothofagus southlandica, Gymnostoma stellata, Gymnostoma crassa, Casuarina avenacea, Metrosideros diffusoides and ? Eucalyptus roxburghiensis. Six new species are described but not named as more detailed study is still proceeding. A further ten new form taxa are identified to genus level only. The fossil flora from the Kaikorai Valley, Dunedin, originally described by Oliver (1936) is revised and Blechnum proceroides, Nothofagus pinnata, N. australis, N. kaikoraiensis and Ripogonum latipetiolatum are new names arising from this revision. The fossil assemblages from Southland and Central Otago are derived from heath, swamp and forest communities developed on an early to mid Tertiary peneplain. In contrast the fossil floras of the Buller region reflect predominantly forest vegetation developed on young soils of a prograding coastal floodplain backed by rapidly rising fault block ranges, while the fossil floras of Dunedin and Great Barrier Island reflect vegetation periodically affected by volcanic activity. Late Oligocene and Miocene climates throughout New Zealand appear to have been humid and at least as warn as Auckland today, although conditions on the east coast of the South Island may have been cooler and drier than on the west. The sediment containing the Landslip Hill fossil flora is interpreted as a silcrete and resembles similar deposits in Australia. The uncompressed state of the fossils and the preservation of turgid cell structures indicates early silica cementation in a surface or near-surface environment, probably as a result of direct precipitation of silica from ground water. The present-day New Zealand flora appears to be derived in part from the late Cretaceous flora of coastal eastern Gondwanaland. Other south-west Pacific floras may stare a similar origin, and may also have contributed to the New Zealand flora following fragmentation of the continental margin. The distribution of New Zealand Tertiary plants, as far as it is known, is consistent with my inferred paleogeography.</p>

Studies in New Zealand Oligocene and Miocene Plant Macrofossils

<p>Assemblages of fossil leaves ranging in age from Upper Oligocene to Upper Miocene or Lower Pliocene have been examined from localities in Southland, Central Otago, the Dunedin area, the Buller region and Great Barrier Island. Nearly 200 form taxa have been recognized so far; of these 52 are figured and described and the remainder are included in an illustrated catalogue. Conifers, Casuarinaceae and Nothofagus spp. are discussed in detail. Thirteen new species are named and described: Gleichenia southlandica, Hypolepis maruiensis, Blechnum maruiense, Dacrydium (Lagarostrobos) franklinoides, Microcachrys imbricata, Phyllocladus strictus, Libocedrus compressa, Nothofagus southlandica, Gymnostoma stellata, Gymnostoma crassa, Casuarina avenacea, Metrosideros diffusoides and ? Eucalyptus roxburghiensis. Six new species are described but not named as more detailed study is still proceeding. A further ten new form taxa are identified to genus level only. The fossil flora from the Kaikorai Valley, Dunedin, originally described by Oliver (1936) is revised and Blechnum proceroides, Nothofagus pinnata, N. australis, N. kaikoraiensis and Ripogonum latipetiolatum are new names arising from this revision. The fossil assemblages from Southland and Central Otago are derived from heath, swamp and forest communities developed on an early to mid Tertiary peneplain. In contrast the fossil floras of the Buller region reflect predominantly forest vegetation developed on young soils of a prograding coastal floodplain backed by rapidly rising fault block ranges, while the fossil floras of Dunedin and Great Barrier Island reflect vegetation periodically affected by volcanic activity. Late Oligocene and Miocene climates throughout New Zealand appear to have been humid and at least as warn as Auckland today, although conditions on the east coast of the South Island may have been cooler and drier than on the west. The sediment containing the Landslip Hill fossil flora is interpreted as a silcrete and resembles similar deposits in Australia. The uncompressed state of the fossils and the preservation of turgid cell structures indicates early silica cementation in a surface or near-surface environment, probably as a result of direct precipitation of silica from ground water. The present-day New Zealand flora appears to be derived in part from the late Cretaceous flora of coastal eastern Gondwanaland. Other south-west Pacific floras may stare a similar origin, and may also have contributed to the New Zealand flora following fragmentation of the continental margin. The distribution of New Zealand Tertiary plants, as far as it is known, is consistent with my inferred paleogeography.</p>

Forest Steppe-Like Vegetation Near Cherskiy (West Beringia) During the Early Pleistocene Olyorian Period Reconstructed Using Plant Macrofossils

The lower Kolyma region is known for rich Early Olyorian large mammal assemblages including plesiomorphic musk ox, reindeer, horse, broad-fronted moose, steppe mammoth and cave bear. Data on the vegetation in zonal habitats from the Olyorian period are, in contrast, scarce. Earlier palynological results from classical Olyorian sites indicated predominant grassland vegetation with scattered larch occurrences but are, due to limited taxonomical resolution, uncertain. Plant macrofossil data were, so far, only available from azonal, aquatic habitats. Here, we describe Olyorian palaeo-vegetation from an exposure near Cherskiy, Nizhnekolymsky District, Sakha Republic, Russia. The macrofossil-based reconstruction of palaeo-vegetation revealed the existence of an open forest steppe comprising a mosaic of sparse larch groves in a dry grassland composed of tundra steppes, degraded meadow steppes and saline meadows. In the larch groves, light demanding shrubs and dwarf shrubs such as shrub birch (Betula cf. fruticosa, B. nana ssp. exilis), raspberry (Rubus idaeus), cowberry (Vaccinium vitis-idaea), and crowberry (Empetrum nigrum) formed the understory. Ruderal pioneer plants point to open ground as result of disturbances, possibly due to the activity of large herbivores. The nitrophytic ruderal species Urtica dioica, in particular, suggests locally increased nutrient supply from animal excretions. Also, the abundant remains of Chenopodium cf. prostratum might be explained by disturbances and nutrient enrichment, but Chenopodium is also characteristic of salt accumulation in the soil owing to high evaporation under arid conditions, which are also indicated by alkali grass (Puccinellia sp.). The presence of trees and shrubs indicates interglacial-like temperature conditions but the dominance of dry grassland species and the occurrence of facultatively halophytic plants (Chenopodium prostratum, Puccinellia sp.) suggests aridity, which is more typical of cold stages. During the early Pleistocene, i.e., prior to the Early-Middle Pleistocene transition (EMPT) culminating around 900 ka ago, the duration of climate cycles was shorter and the amplitude of climate fluctuations was smaller. Ice-rich permafrost formed only after the EMPT during increasingly extreme cold stages, and, during warm stages, its thawing resulted in paludification of the active layer. Prior to the EMPT, the climate in West Beringia was constantly relatively dry, more or less moderate and more stable than thereafter. In contrast to modern tundra and northern taiga in the study region, dry habitats apparently prevailed during the time of deposition of the plant macro-remains.