A full-glacial biota from southeastern Iowa,USA

Wisconsinan full-glacial silts filling a swale exposed in Conklin Quarry, Johnson Co., Iowa, contain a large and diverse biota that includes pollen, bryophytes, vascular-plant macrofossils, small mammals, molluscs, and insects. Radiocarbon dates on wood from the top, middle and bottom of the swale fill respectively were 16710 ± 270, 17 170 ± 205, and 18090 ± 190 yr BP. The pollen diagram is dominated by Picea (spruce), Pinus (pine), and Cyperaceae (sedge), and it records low pollen accumulation rates. Plant macrofossils include a number of tundra species along with Picea and Larix (larch) needles and small pieces of wood. The insect fauna contains many species now confined to the forest-tundra transition zone of northwestern Yukon and Alaska. Small mammals include the tundra indicators Dicrostonyx (collared lemming), and probably Microtus miurus (singing vole) together with boreal forest taxa. The molluscs include extinct and relict species and show the widest range in present geographic distribution, but Rocky Mountain and especially northern elements predominate in the swale fill. All these lines of evidence lead to consistent palaeoclimato-logical interpretation and palaeoecological reconstruction. The dominant habitats represented by the biota and sedimentary environment collectively included open calcareous silty to sandy or gravelly upland sites, minerotrophic fens (wetlands), pond- or stream-side clayey to sandy shores, and shallow (possibly ephemeral), cold, clear-water ponds. Mean July temperatures were probably 11° to 13°C cooler than at present. The biota indicates that a Picea-Larix krummholz with extensive tundra openings was present in southeastern Iowa between 18090 and 16710 yr BP.     

Late Quaternary palaeoecological and palaeoclimatological reconstruction in the Gutaiului Mountains,northwest Romania

Macrofossil, pollen, lithostratigraphy, mineral magnetic measurements (SIRM and magnetic susceptibility), loss‐on‐ignition, and AMS radiocarbon dating on sediments from two former crater lakes, situated at moderate altitudes in the Gutaiului Mountains of northwest Romania, allow reconstruction of Late Quaternary climate and environment. Shrubs and herbs with steppe and montane affinities along with stands of Betula and Pinus, colonised the surroundings of the sites prior to 14 700 cal. yr BP and the inferred climatic conditions were cold and dry. The gradual transition to open Pinus–Betula forests, slightly higher lake water temperatures, and higher lake productivity, indicate more stable environmental conditions between 14 700 and 14 100 cal. yr BP. This development was interrupted by cooler and drier climatic conditions between 14 100 and 13 800 cal. yr BP, as inferred from a reduction of open forests to patches, or stands, of Pinus, Betula, Larix, Salix and Populus. The expansion of a denser boreal forest, dominated by Picea, but including Pinus, Larix, Betula, Salix, and Ulmus started at 13 800 cal. yr BP, although the forest density seems to have been reduced between 13 400 and 13 200 cal. yr BP. Air temperature and moisture availability gradually increased, but a change towards drier conditions is seen at 13 400 cal. yr BP. A distinct decrease in temperature and humidity between 12 900 and 11 500 cal. yr BP led to a return of open vegetation, with patches of Betula, Larix, Salix, Pinus and Alnus and individuals of Picea. Macrofossils and pollen of aquatic plants indicate rising lake water temperatures and increased aquatic productivity already by ca. 11 800 cal. yr BP, 300 years earlier than documented by the terrestrial plant communities. At the onset of the Holocene, 11 500 cal. yr BP, forests dominated by Betula, Pinus and Larix expanded and were followed by dense Ulmus forests with Picea, Betula and Pinus at 11 250 cal. yr BP. Larix pollen was not found, but macrofossil evidence indicates that Larix was an important forest constituent at the onset of the Holocene. Moister conditions were followed by a dry period starting about 10 600 cal. yr BP, which was more pronounced between 8600 and 8200 cal. yr BP, as inferred from aquatic macrofossils. The maximum expansion of Tilia, Quercus, Fraxinus and Acer between 10 700 and 8600 cal. yr BP may reflect a more continental climate. A drier and/or cooler climate could have been responsible for the late expansion (10 300 cal. yr BP) and late maximum (9300 cal. yr BP) of Corylus. Increased water stress, and possibly cooler conditions around 8600 cal. yr BP, may have caused a reduction of Ulmus, Tilia, Quercus and Fraxinus. After 8200 cal. yr BP moisture increased and the forests included Picea, Tilia, Quercus and Fraxinus. Copyright © 2004 John Wiley & Sons, Ltd.     

Late Wisconsin periglacial environments of the southern margin of the Laurentide Ice Sheet reconstructed from pollen analyses

Full‐glacial pollen assemblages from four radiocarbon‐dated interstadial deposits in southwestern Ohio and southeastern Indiana imply the presence of herbaceous vegetation (tundra or muskeg with subarctic indicator Selaginella selaginoides) on the southern margin of the Miami lobe of the Laurentide Ice Sheet ca. 20 000 ¹⁴C yr BP. Scattered Picea (spruce) and possibly Pinus (pine) may have developed regionally ca. 19 000 ¹⁴C yr BP, and ca. 18 000 ¹⁴C yr BP, respectively. Spruce stumps in growth position support a local source of pollen. Prior to the ca. 14 000 ¹⁴C yr BP glacial advance, small amounts of Quercus (oak) and other deciduous pollen suggest development of regional boreal (conifer–hardwood) forests. Copyright © 2002 John Wiley & Sons, Ltd.     

Vegetation,climate, and fire during the late-glacial–Holocene transition at Spruce Pond,Hudson Highlands,southeastern New York,USA

Pollen, plant macrofossil, and charcoal records from Spruce Pond (41°14′22″N, 74°12′15″W), southeastern New York, USA dated by AMS provide details about late-glacial–early Holocene vegetation development in the Hudson Highlands from >12410 to 9750 ¹⁴C yr BP. Prior to 12410 yr BP, vegetation was apparently open, dominated by herbs and shrubs (Cyperaceae, Gramineae, Tubuliflorae, Salix, Alnus, Betula), possibly with scattered trees (Picea and Pinus). However, Picea macrofossils are not found until 12410 yr BP. Development of a temperature deciduous–boreal-coniferous forest featuring Quercus, Fraxinus, Ostrya/Carpinus, Pinus, Picea, and Abies occurs between 12410 and 11140 yr BP. A return of predominantly boreal forest taxa between 11140 and 10230 yr BP is interpreted as an expression of the Younger Dryas cooling event. Holocene warming at 10230 yr BP is signalled by arrival of Pinus strobus, coincident with expansion of Quercus-dominated forest. Fire activity, as inferred from charcoal influx, appears to have increased as woodland developed after 12410 yr BP. Two charcoal influx peaks occur during Younger Dryas time. Early Holocene fire activity was relatively high but decreased for approximately 100 yr prior to the establishment of Tsuga canadensis in the forest at 9750 yr BP. © 1997 by John Wiley & Sons, Ltd.     

Late Wisconsinan Vegetation and Environment of the Tunica Hills Region, Louisiana/Mississippi

Pollen, plant macrofossil, and radiocarbon-dating studies of seven exposures of fluvial sediments in the Tunica Hills region of southeastern Louisiana and southwestern Mississippi provide new information on late Wisconsinan vegetation, flora, and environment of the region. The assemblages date between 25,250 and 17,530 yr B.P. Pollen and macrofossil assemblages are dominated by Picea, which comprises 40-70% of the pollen assemblages. Abies and Larix pollen and macrofossils are absent, in contrast to sites to the north in the central Mississippi Valley. Deciduous hardwoods (Quercus, Fagus, Fraxinus, Carya, Juglans nigra, Acer, Ulmus) are minor components of both pollen and macrofossil assemblages. Radiocarbon dates of Picea and Quercus wood indicate that these two genera grew contemporaneously in the region. Regional upland forests were dominated by Picea. Picea cones and cone fragments are not typical of any extant North American species, and probably represent either an extinct species or an extinct variety or subspecies of Picea glauca. Late Wisconsinan climate of the region was cooler than present, but not necessarily as cool as implied by P. glauca or other "boreal" taxa.     

Ecosystem response to Lateglacial and early Holocene climate oscillations in the Great Lakes region of North America

Fossil pollen, plant macrofossils, gastropods, and elemental and stable-isotope geochemistry in a sediment core from Twiss Marl Pond, southern Ontario, Canada, were used to document climate oscillations during the Last Glacial–Interglacial transition (13,000–8500 ¹⁴C BP) and understand their ecological effects. Chronology was provided by AMS ¹⁴C dating and regional pollen correlation. Oxygen isotope (δ¹⁸O) results from mollusc shells, Chara-encrustations and bulk carbonates show a classic climate sequence of a warm Bølling–Allerød (BOA) at 12,500–10,920 ¹⁴C BP, a cold Younger Dryas (YD) at 10,920–10,000 ¹⁴C BP, the Holocene warming at 10,000 ¹⁴C BP, a brief Preboreal Oscillation (PB) at 9650 ¹⁴C BP, and a possible Gerzensee/Killarney (G/K) cooling shortly before 11,000 ¹⁴C BP.Clay sediments at the base of the core contain high herb and shrub pollen and abundant arctic/alpine plant macrofossils, indicating a treeless tundra with severe soil erosion in watershed. During the BOA warm period, authigenic marl began to be deposited, and Picea woodland became established. The establishment of Picea woodland after peaks of δ¹⁸O and of carbonate accumulation suggests a lagged response of upland vegetation to BOA warming. In contrast, the occurrence of warmth-loving aquatics Najas flexilis and Typha latifolia at that time indicates sensitive responses of aquatic plants. The YD cooling is indicated by a 1.5‰ negative excursion in δ¹⁸O, an increase in minerogenic matter and higher concentrations of erosion-derived elements (Al, Na, K, Ti and V). Pollen data show no forest transformation in response to YD cooling, which is attributed to the insensitive nonecotonal vegetation at that time. However, more openings in the forests and increased erosion in the watershed are indicated by a slight increase of herb pollen, high concentrations of erosion elements and a Pediastrum peak. The onset of the Holocene was marked by an abrupt increase of 2‰ in δ¹⁸O and the replacement of Picea woodland by Pinus-dominated forest. The Picea recurrence at 9650 ¹⁴C BP demonstrates sensitive response of ecotonal vegetation to the PB climate oscillation, which is also indicated by 0.4‰ negative excursion of δ¹⁸O. These new results suggest the importance of multiproxy records for reliable paleoclimate reconstruction.Reevaluation and revised chronologies of previously published sites (Gage Street, and Nichols Brook) in the eastern Great Lakes region show their major δ¹⁸O shifts correlative to the YD and PB oscillations as documented from Twiss Marl Pond and nearby Crawford Lake. The sequence and magnitude of climatic oscillations from these sites match in detail with records from the Atlantic Seaboard, suggesting that these oscillations are an expression of broad-scale, probably global, climate change rather than local meltwater-induced climate cooling.     

The importance of plant macrofossils in the reconstruction of Lateglacial vegetation and climate: examples from Scotland,western Norway,and Minnesota,USA

Lateglacial and early Holocene (ca 14–9000 ¹⁴C yr BP; 15–10,000 cal yr BP) pollen records are used to make vegetation and climate reconstructions that are the basis for inferring mechanisms of past climate change and for validating palaeoclimate model simulations. Therefore, it is important that reconstructions from pollen data are realistic and reliable. Two examples of the need for independent validation of pollen interpretations are considered here. First, Lateglacial-interstadial Betula pollen records in northern Scotland and western Norway have been interpreted frequently as reflecting the presence of tree-birch that has strongly influenced the resulting climate reconstructions. However, no associated tree-birch macrofossils have been found so far, and the local dwarf-shrub or open vegetation reconstructed from macrofossil evidence indicates climates too cold for tree-birch establishment. The low local pollen production resulted in the misleadingly high percentage representation of long-distance tree-birch pollen. Second, in the Minnesotan Lateglacial Picea zone, low pollen percentages from thermophilous deciduous trees could derive either from local occurrences of the tree taxa in the Picea/Larix forest or from long-distance dispersal from areas further south. The regionally consistent occurrence of low pollen percentages, even in sites with local tundra vegetation, and the lack of any corresponding macrofossil records support the hypothesis that the trees were not locally present. Macrofossils in the Picea zone represent tundra vegetation or Picea/Larix forest associated with typically boreal taxa, suggesting it was too cold for most thermophilous deciduous trees to grow. Any long-distance tree pollen is not masked by the low pollen production of tundra and Picea and Larix and therefore it is registered relatively strongly in the percentage pollen spectra.Many Lateglacial pollen assemblages have no recognisable modern analogues and contain high representations of well-dispersed ‘indicator’ taxa such as Betula or Artemisia. The spectra could have been derived from vegetation types that do not occur today, perhaps responding to the different climate that resulted from the different balance of climate forcing functions then. However, the available contemporaneous plant-macrofossil assemblages can be readily interpreted in terms of modern vegetation communities, suggesting that the pollen assemblages could have been influenced by mixing of locally produced pollen with long-distance pollen from remote vegetation types that are then over-represented in situations with low local pollen production. In such situations, it is important to validate the climate reconstructions made from the pollen data with a macrofossil record.     

川北若尔盖高原玛曲-红原一带表土中孢粉组合的特征

通过对四川若尔盖高原玛曲—红原一带20个表土孢粉样的分析,研究了该区域表土孢粉组合与现代植被的关系。结果显示,玛曲—红原一带表土的孢粉组合基本反映了现代植被的整体特征,与现代植被在植被类型、植被带的空间排列、主要建群种属和优势种属等方面基本一致。依据孢粉的百分含量,可以划分为亚高山灌丛植被区,亚高山灌丛、亚高山草甸植被区和高寒草甸、草原植被区3个植被带。表土花粉的代表性因种属的不同而各有差异,松属和菊科花粉具超代表性,云杉属花粉的代表性较好,禾本科和莎草科具低代表性,而桦木属则不具有超代表性,可能与桦木属花粉不易搬运有关。3个植被区中的表土孢粉的种类、比例与现代植被均存在一定的差别,这可能与植被退化有关。     

Late Glacial and Holocene vegetation history in the southern part of Transylvania (Romania): pollen analysis of two sequences from Avrig

We present here the results of pollen analysis of two sequences of about 8.06 m and 11.90 m length, originating from two adjacent peat bogs in the southern part of Transylvania province, Romania (155 and 122 pollen spectra). The vegetation record, which is supported by 17 ¹⁴C dates, begins in the Late Glacial interstadial when forest recolonisation began with the development of Pinus, without a pioneer Betula phase. Picea began to expand from regional refuges. After a well‐defined Younger Dryas, the Holocene opens with the expansion of Betula, Ulmus and Picea, followed, at about 10 400 cal. yr BP, by Fraxinus, Quercus and Tilia. The Corylus optimum is correlated with the Atlantic chronozone (after 8600 cal. yr BP). The local establishment of Carpinus occurred at about 6500 cal. yr BP, with a maximum at about 5700 cal. yr BP. Fagus pollen is regularly recorded after 8200 cal. yr BP. This taxon became dominant at about 3700 cal. yr BP. The first indications of human activities appear at around 7200 cal. yr BP. Copyright © 2005 John Wiley & Sons, Ltd.     

A record of Lateglacial and early Holocene environmental and ecological change from southwestern Connecticut,USA

Analyses of a sediment core from Highstead Swamp in southwestern Connecticut, USA, reveal Lateglacial and early Holocene ecological and hydrological changes. Lateglacial pollen assemblages are dominated by Picea and Pinus subg. Pinus, and the onset of the Younger Dryas (YD) cold interval is evidenced by higher abundance of Abies and Alnus viridis subsp. crispa. As climate warmed at the end of the YD, Picea and Abies declined and Pinus strobus became the dominant upland tree species. A shift from lacustrine sediment to organic peat at the YD–Holocene boundary suggests that the lake that existed in the basin during the Lateglacial interval developed into a swamp in response to reduced effective moisture. A change in wetland vegetation from Myrica gale to Alnus incana subsp. rugosa and Sphagnum is consistent with this interpretation of environmental changes at the beginning of the Holocene. Copyright © 2009 John Wiley & Sons, Ltd.     

Pre-glacial and interglacial pollen records over the last 3 Ma from northwest Canada: Why do Holocene forests differ from those of previous interglaciations?

We synthesize pollen spectra from eleven dated stratigraphic sections from central and northern Yukon. Palaeomagnetic and tephra dating indicates the earliest assemblages, representing closed canopy Pinus and Picea forest, are middle-late Pliocene age. More open forest conditions, indicated by increased Poaceae and with evidence of permafrost, are dated at ca 3 Ma. While Pinus pollen is abundant at 3 Ma, it is reduced in records after 2.6 Ma, and subsequent Pleistocene interglacial forest records are repeatedly dominated by Picea, along with Alnus and small but significant amounts of Abies. Surface sample comparisons indicate that Abies was more widespread and abundant in past interglaciations than at present and that Middle-Pleistocene Picea–Abies forest grew in the northern Yukon Porcupine Basin, 500 km beyond modern Abies limits. In contrast, Pinus, which occurs today in southern and central Yukon, was not a significant component of these Pleistocene interglacial forests. Late-Holocene pollen assemblages with rare Abies and high Pinus are the most distinct in the past 2.6 Ma. Possible factors driving Holocene difference are paleoclimate, paludification, changes in megafaunal herbivory and an unusual fire regime. Anthropogenic burning is a factor unique to the Holocene, and if it is shown to be important in this case, it would challenge our notion of what constitutes boreal wilderness.     

Late Pleistocene vegetation of Kings Canyon,Sierra Nevada,California

Seven packrat midden samples make possible a comparison between the modern and late Pleistocene vegetation in Kings Canyon on the western side of the southern Sierra Nevada. One modern sample contains macrofossils and pollen derived from the present-day oak-chaparral vegetation. Macrofossils from the six late Pleistocene samples record a mixed coniferous forest dominated by the xerophytic conifers Juniperus occidentalis, Pinus cf. ponderosa, and P. monophylla. The pollen spectra of these Pleistocene middens are dominated by Pinus sp., Taxodiaceae-Cupressaceae-Taxaceae (TCT), and Artemisia sp. Mesophytic conifers are represented by low macrofossil concentrations. Sequoiadendron giganteum is represented by a few pollen grains in the full glacial. Edaphic control and snow dispersal are the most likely causes of these mixed assemblages.The dominant macrofossils record a more xeric plant community than those that now occur on similar substrates at higher elevations or latitudes in the Sierra Nevada. These assemblages suggest that late Wisconsin climates were cold with mean annual precipitation not necessarily greater than modern values. This conclusion supports a model of low summer ablation allowing for the persistence of the glaciers at higher elevations during the late Wisconsin. The records in these middens also suggest that S. giganteum grew at lower elevations along the western side of the range and that P. monophylla was more widely distributed in cismontane California during the Pleistocene.     

The Holocene vegetation history of the Khibiny Mountains: implications for the post‐glacial expansion of spruce and alder on the Kola Peninsula,northwestern Russia

Pollen and peat botanical investigations of the Lutnermayok peat bog, Kola Peninsula, northwestern Russia, were carried out, and 21 surface pollen samples were studied. Combined with previous studies our data form the basis for the vegetation history over the last 7000 yr of the Khibiny Mountains. Pinus sylvestris was the dominant species between 7000 and 5000 yr BP and Picea obovata penetrated to the Khibiny Mountains ca. 5500/5300 yr BP. Since 4500 yr BP, Picea replaced Pinus in major parts of the area and dominated the forest cover. Picea immigrated to the Kola Peninsula after 7000 yr BP. There were two paths of spruce migration: from the southeast and the southwest. Grey alder, Alnusincana, immigrated to the Kola Peninsula from the southwest and northwest about ca. 8000 yr BP. Grey alder has been restricted to its modern range since 4000 yr BP. The range of vertical movement of the treeline in Khibiny Mountains during the last 700 yr was 240–260 m, which corresponds to an amplitude of summer temperature change of 2°C. Copyright © 1999 John Wiley & Sons, Ltd.     

A Pleistocene succession from beneath Chelford Sands at Oakwood Quarry,Chelford, Cheshire

A thin sequence of in situ fossiliferous gravels and silts overlain by a glacigenic bed is described from a temporary exposure in a working silica sand quarry. The sequence directly overlies unweathered Mercia Mudstone. Locally the bedrock surface forms a shallow palaeovalley some 15 m deep and almost 1 km wide. The sequence in question lies close to the valley axis. The silts, pollen, plant macrofossils, Mollusca, Coleoptera, and Ostracoda assemblages each suggest a similar environment of sedimentation: a shallow pool within a treeless open landscape. Much of the bedrock within the working quarry appears to be draped by the Oakwood till and this unit is co-extensive with the glacigenic sediments over the silts and gravels. In parts at least, the till has been subject to redeposition and its upper surface has scattered ventifacts. Above this wind-deflation horizon lies the Chelford Sands Formation, in the middle of which is the Chelford Interstadial stratotype, the Farm Wood member. The biota preserved in the gravels and silts suggest a stadial prior to the Early Devensian Chelford Interstadial. This is the first unambiguous stratigraphic evidence from Cheshire of a glacial event antedating the Chelford Interstadial.     

Holocene environmental changes in the alpine zone,northern San Juan Mountains,Colorado: Evidence from bog stratigraphy and palynology

Cores from five high alpine basins in the northern San Juan Mountains show several fluctuations in lithology. Typically, peats are interbedded with coarser clastic sediments or else woody peats alternate with fibrous peat. Twenty ¹⁴C dates provide radiometric control. Sediment rates averaged about 2.5 cm/100 yr but varied at the different sites between 1.19 and 50 cm/100 yr. Rates were lower during the middle of the Holocene. Basal radiocarbon dates indicate that these high (ca. 3600 m a.s.l.) northeasterly facing cirques were icefree by 9000 BP. There is some evidence in the cores for a short climatic reversal sometime between 8000 and 7000 BP. A major change occurred in the high basins very close to 5000 BP and thereafter there are several intervals of increased clastic sedimentation which may be related to Neoglacial climatic fluctuations. Analysis of a 2.15 m core near Hurricane Basin indicates significant fluctuation of pollen and macrofossils occurred during the 9000 ± year record. The Picea/Pinus ratios are used to delimit changes in the apparent elevation of the site: the ratios indicate that a short drop of “treeline” occurred about 8000 BP and then remained near present level until about ≥1800 BP when the apparent elevation of the site rose. Macrofossils indicate that spruce was present in the Hurricane Basin (and others) at specific periods and confirms the general results of the Picea/Pinus ratios. The San Juan Mountains do not possess a glacial Neoglacial record but the stratigraphy of these high cirque basins can be used to define glacial stades (cf. Jardine, 1972). The interpreted climatic response record on vegetation and sediment flux has both similarities and differences from other records in the western mountains of North America.     

Plant and insect remains from the Wisconsinan interstadial/stadial transition at Wedron, north-central Illinois

Organic material exposed within a small swale fill in Pit 6 of the Wedron Silica Sand Co. near Wedron in LaSalle County, Illinois, includes well-preserved pollen, plant macrofossils, and insect remains. This material occurs in slackwater sediment in the lower part of the Peddicord Formation, which was deposited as existing valleys were dammed by fluvial aggradation during the initial late Wisconsinan advance of Laurentide ice into the Wedron area. Wood from the organic horizon has a radiocarbon age of 21,460 ± 470 yr B.P. (ISGS-1486). The pollen spectrum is dominated by Picea, Pinus, and Cyperaceae. Plant macrofossils comprise a mix of boreal-forest taxa, including Picea, Larix laricina, and the moss Campylium stellatum; subarctic species including Betula glandulosa, Empetrum nigrum, and Selaginella selaginoides; along with the predominantly arctic Vaccinium uliginosum var. alpinum, Dryas integrifolia, and Rhododendron lapponicum. The insect fauna contains the western montane ground beetle Opisthius richardsoni; several arctic-subarctic ground beetles including Diacheila polita, Helophorus sibiricus, and Pterostichus (Cryobius) caribou; and a diverse assemblage of insects that today inhabit the boreal forest. We interpret the biotic record to record a phase in the transition from closed boreal forest to open tundra as climatic conditions deteriorated in advance of continental glaciation.     

Rapid Lateglacial tree population dynamics and ecosystem changes in the eastern Baltic region

A growing body of evidence implies that the concept of 'treeless tundra' in eastern and northern Europe fails to explain the rapidity of Lateglacial and postglacial tree population dynamics of the region, yet the knowledge of the geographic locations and shifting of tree populations is fragmentary. Pollen, stomata and plant macrofossil stratigraphies from Lake Kurjanovas in the poorly studied eastern Baltic region provide improved knowledge of ranges of north‐eastern European trees during the Lateglacial and subsequent plant population responses to the abrupt climatic changes of the Lateglacial/Holocene transition. The results prove the Lateglacial presence of tree populations (Betula, Pinus and Picea) in the eastern Baltic region. Particularly relevant is the stomatal and plant macrofossil evidence showing the local presence of reproductive Picea populations during the Younger Dryas stadial at 12 900–11 700 cal. a BP, occurring along with Dryas octopetala and arctic herbs, indicating semi‐open vegetation. The spread of Pinus–Betula forest at ca. 14 400 cal. a BP, the rise of Picea at ca. 12 800 cal. a BP and the re‐establishment of Pinus–Betula forest at ca. 11 700 cal. a BP within a span of centuries further suggest strikingly rapid, climate‐driven ecosystem changes rather than gradual plant succession on a newly deglaciated land. Copyright © 2009 John Wiley & Sons, Ltd.     

A Last Glacial Maximum pollen record from Bodmin Moor showing a possible cryptic northern refugium in southwest England

A late Devensian palynological record is presented from Dozmary Pool (Bodmin Moor, southwest England), beyond the southern limit of the Last Glacial Maximum (LGM) British Ice Sheet. The pollen assemblages indicate predominantly herbaceous tundra–steppe communities but also include elevated levels (typically 10–20%) of conifer tree pollen (Picea, Pinus, Abies) and lower but persistent percentages of broadleaf tree pollen during the LGM. This record is seemingly at odds with the orthodox view of an entirely treeless tundra–steppe environment for this region and elimination of tree species from the British Isles during glacial maxima. Long‐distance pollen transport seems an unlikely explanation for the tree pollen considering distance to the nearest known refugia, except possibly for Pinus. Reworking of the tree pollen, often invoked in these circumstances, remains a possible alternative, especially given the abundance of these trees in the region during early Devensian interstadials. However, this explanation has been challenged by studies reporting plant macrofossil and faunal evidence for survival of temperate biota during glacial maxima and from climate modelling work that suggests some trees could have survived the glacial extremes in areas well beyond the recorded glacial refugia. Assuming reworking was not a major factor, the Dozmary Pool pollen record is consistent with the ‘cryptic northern refugia hypothesis’ that invokes survival of trees in small, scattered populations under locally favourable conditions during glacial maxima. Copyright © 2009 John Wiley & Sons, Ltd.     

The vegetation record of a mid-Wisconsin interstadial in northwest Georgia

At Green Pond, a small permanent sinkhole pond in Bartow County, northwest Georgia, organic silty clays are buried by up to 2 m of colluvium. Pollen from the clays shows that a Pinus-Quercus-herb (pine-oak-herb) flora was present before 29,630 radiocarbon yr ago. It is interpreted as the product of a xeric woodland with prairie-like openings. Between 29,630 and approximately 25,000 BP, pollen of Pinus and herbs was sparse; Quercus and Carya (hickory) predominated in the pollen rain. There were few other deciduous trees. Oak-hickory forest is thought to have been present. From 25,000 to 23,000 BP, more diverse forest with pines and some Picea (spruce) became established. At the same time Taxodium (swamp cypress) was locally abundant, as were shrubs characteristic of Coastal Plain swamps. Some time after 23,000 BP, the pond basin filled with colluvium and no further sedimentation took place, other than thin muck sedimented on the bottom of the present Green Pond.The sediments were first thought to be of Sangamon age because the pollen sequence has many of the characteristics of an interglacial cycle, but the radiocarbon dates correlate them firmly with the Farmdalian Interstadial. A comparison with known Farmdalian sites is made, but the important sites are in the northern United States and adjacent Canada, too far away to make a useful comparison of the details of pollen diagrams from the two areas. At another Bartow County pond site, Bob Black Pond (Watts, 1970), a flora predominantly of pine with spruce and oak was present immediately before 22,900 BP and a strikingly cold flora with jack-pine, spruce and northern herbs followed immediately after. The radiocarbon dates indicate that the sedimentary sequence at Bob Black Pond immediately follows that at Green Pond.