The contemporary distribution of pollen in eastern North America: A comparison with the vegetation

By mapping and summarizing 478 pollen counts from surface samples at 406 locations in eastern North America, this study documents the relationships between the distributions of pollen and vegetation on a continental scale. The most common pollen types in this region are pine, birch, oak, and spruce. Maps showing isopercentage contours or isopolls for 13 important pollen types reflect the general N-S zonation of the vegetation. The maps and tabulations of average pollen spectra for the six major vegetational regions indicate high values for the following pollen types in each region: (1) tundra-nonarboreal birch, sedge, and alder; (2) forest/tundra-spruce, nonarboreal birch and alder; (3) boreal forest-spruce, jack pine (type), and arboreal birch with fir in the southeastern part; (4) conifer/hardwood forest-white pine, arboreal birch, and hemlock with beech, maple, and oak in the southern part; (5) deciduous forest-oak, pine, hickory, and elm, with beech and maple in the northern part, and highest values of oak and hickory west of the Appalachian crest; and (6) southeastern forest-pine, oak, hickory, tupelo, and Myricaceae. In some cases, less abundant pollen types are diagnostic for the region, e.g., bald cypress in the southeast. In the conifer-hardwood region and southward, pollen of weeds associated with deforestation and agriculture is abundant. The maps also show that much of southeastern U.S. and the area just to the east of Hudson Bay are in need of additional sampling. At 51 of the sites, absolute pollen frequencies (APF; grains/ml lake sediment) were obtained. These confirm the major conclusions from the percentage data, but differences are evident, e.g., the percentages of alder pollen peak in the tundra whereas alder APFs peak in the boreal forest, and spruce percentages peak in the forest-tundra whereas spruce APFs peak in the boreal forest. Because the APF data reflect the patterns of absolute abundance of individual taxa in the vegetation as well as the overall forest densities, future counts of modern pollen should include APF determinations. The effects of sedimentation processes on APF quantities indicate that APF samples should be obtained from moderate size lakes of similar morphology and hydrology and that, in each lake, several samples from the profundal zone should be pooled to create a sample representative of that lake.     

Holocene climatic change in the northern Midwest: Pollen-derived estimates

Mapping of Holocene pollen data in the midwestern United States has revealed several broadscale vegetational changes that can be interpreted in climatic terms. These changes include (1) the early Holocene northward movement of the spruce-dominated forest and its later southward movement after 3000 yr B.P. and (2) the eastward movement of the prairie/forest border into southwestern Wisconsin by 8000 yr B.P. and its subsequent westward retreat after 6000 yr B.P. When certain basic assumptions are met, multiple regression models can be derived from modern pollen and climate data and used to transform the pollen record of these vegetational changes into quantitative estimates of temperature or precipitation. To maximize the reliability of the regression equations, we followed a sequence of procedures that minimize violations of the assumptions that underlie regression analysis. Reconstructions of precipitation during the Holocene indicated that from 9000 to 6000 yr B.P. precipitation decreased by 10 to 25% over much of the Midwest, while mean July temperature increased by 0.5° to 2.0°C. At 6000 yr B.P. precipitation was less than 80% of its modern values over parts of Wisconsin and Minnesota. After 6000 yr B.P. precipitation generally increased, while mean July temperature decreased in the north, and increased in the south. The time of the maximum temperature varies within the Midwest and is earlier in the north and later in the south.     

Fossil pollen from Los Toldos locality: A record of the Late-glacial transition in the Extra-Andean Patagonia

Paleoenvironmental changes during the Late-glacial transition are interpreted from a pollen record from two caves at Los Toldos (47°22′S; 68°58′W) in Extra-Andean Patagonia in Argentina. The paleoenvironmental interpretation is based on changes in the ratio between shrub and grass steppe taxa and on comparison with other pollen records from the region. Between 12,600 and 8750 yr BP two vegetational changes occurred thought to reflect the establishment of Holocene-type atmospheric circulation patterns. The first change is at ca. 11,000 yr BP expressed by replacement of shrub steppe with Ephedra by a grass steppe. The second change occurred ca. 10,000 yr BP when the grass steppe was replaced by a shrub steppe dominated by Asteraceae. Before ca. 11,000 yr BP the environmental conditions were extremely arid with precipitation lower than 200 mm. Between ca. 11,000 and ca. 10,000 yr BP effective moisture increased, probably related to an increase in precipitation to about 200 mm under cold conditions. A grass steppe extended through Patagonia and Tierra del Fuego, at least as far north as 47°S. It is difficult to find modern analogues for pollen associations south of 47°S older than 10,000 yr BP. Possibly at that time climate patterns were markedly different from today. At about this time of environmental changes Level 11 industry associated with extinct grazing herbivores developed. Starting at ca. 10,000 yr BP, with expansion of the shrub steppe of Asteraceae east of the Andes at 47° to 52°S and forest at 51°–54°S west of the Andes, temperature increased while water availability decreased. Precipitation probably was similar to the present, which suggests that the modern climate patterns were established at the beginning of the Holocene. The Toldense Industry, which is associated with remains of modern fauna as well as with the last remains of the Pleistocene fauna, developed in this period. The beginning of this development coincides with the extinction of Pleistocene fauna.     

Late-glacial vegetation associated with caribou and mastodon in central Indiana

The Christensen Mastodon Site, located in central Indiana, contains a rich assemblage of vertebrates (including mastodon, caribou, and giant beaver), invertebrates, and plant macrofossils in situ in lake and bog sediments of late-glacial age. Studies of pollen and plant macrofossils suggest the existence of open, white spruce-dominated boreal forests from >; 14,000 yr B.P. to ca. 13,000 yr B.P. The regional decline of spruce, local occurrence of black spruce, white spruce, and larch, immigration of many hardwood taxa (e.g., ash, oak, elm), and the initiation of bog development are recorded beginning about 13,000 yr B.P. Recent reconstructions of late-glacial and early postglacial vegetational changes provide a context for understanding the disappearance of mastodons. The dramatic and rapid restriction of boreal forests along the retreating ice margin from 11,000 to 9000 yr B.P. may have caused a substantial reduction of mastodon populations. A diminished population would be more susceptible to small-scale, stochastic events such as short-term extremes of weather, outbreaks of disease, or predation pressure from paleoindian hunters.     

Late-Quaternary vegetation history at White Pond on the inner Coastal Plain of South Carolina

At White Pond near Columbia, South Carolina, a pollen assemblage of Pinus banksiana (jack pine), Picea (spruce), and herbs is dated between 19,100 and 12,800 ¹⁴C yr B.P. Plants of sandhill habitats are more prominent than at other sites of similar age, and pollen of deciduous trees is infrequent. The vegetation was probably a mosaic of pine and spruce stands with prairies and sand-dune vegetation. The climate may have been like that of the eastern boreal forest today. ¹⁴C dates of 12,800 and 9500 yr B.P. bracket a time when Quercus (oak), Carya (hickory), Fagus (beech), and Ostrya-Carpinus (ironwood) dominated the vegetation. It is estimated that beech and hickory made up at least 25% of the forest trees. Conifers were rare or absent. The environment is interpreted as hickory-rich mesic deciduous forest with a climate similar to but slightly warmer than that of the northern hardwoods region of western New York State. After 9500 yr B.P. oak and pine forest dominated the landscape, with pine becoming the most important tree genus in the later Holocene.     

Vegetation,fire, and climate history of the northwestern Great Basin during the last 14,000 years

The northwestern Great Basin lies in the transition zone between the mesic Pacific Northwest and xeric intermountain West. The paleoenvironmental history based on pollen, macroscopic charcoal, and plant macrofossils from three sites in the northwestern Great Basin was examined to understand the relationships among the modern vegetation, fire disturbance and climate. The vegetation history suggests that steppe and open forest communities were present at high elevations from ca 11,000 to 7000 cal yr BP, and were replaced by forests composed of white fir, western white pine, and whitebark pine in the late Holocene. Over the last 11,000 years, fires were more frequent in mid-elevation forests (10–25 fire episodes/1000 years) and rare in high-elevation forests (2–5 fire episodes/1000 years). Applying modern pollen–climate relationships to the fossil pollen spectra provided a means to interpret past climate changes in this region. In the past 9000 years summer temperatures decreased from 1 to 4 °C, and annual precipitation has increased 7–15%. These results indicate that the millennial-scale climate forcing driving vegetation changes can be quantified within the intermountain West in general and northwestern Great Basin in particular. In addition, fire can be considered an important component of these ecosystems, but it does not appear to be a forcing mechanism for vegetation change at the resolution of these records.     

Late Quaternary vegetational changes on the east side of Yellowstone park,Wyoming

A bog pond 4 km east of Yellowstone Lake has a pollen record starting with an Artemisia spruce assemblage, implying alpine vegetation. A layer of volcanic ash, dated as 14,360 ± 400 BP (probably Glacier Peak or Mt. St. Helens J), occurs within the zone, which terminates at 11,630 ± 180 BP. The rest of the pollen sequence is dominated by lodgepole pine, with reappearance of spruce pollen in modest quantities about 4500 BP, according to dating provided by a layer of Mt. Mazama ash (6600 BP). The present vegetation of the area is marked by forests of lodgepole pine with some stands of spruce and fir. The pollen sequence suggests that the upper treeline before 11,600 y. a. was perhaps 500 m lower than today. The climate then became warmer and/or drier than today (Altithermal interval). About 4500 y. a., a slight climatic reversal took place, roughly contemporaneous with the regrowth of glaciers in the western mountains (neoglaciation).     

Multi-proxy record of postglacial environmental change, south-central Melville Island, Northwest Territories, Canada

A sediment core from Lake BC01 (75°10.945′N, 111°55.181′W, 225 m asl) on south-central Melville Island, NWT, Canada, provides the first continuous postglacial environmental record for the region. Fossil pollen results indicate that the postglacial landscape was dominated by Poaceae and Salix, typical of a High Arctic plant community, whereas the Arctic herb Oxyria underwent a gradual increase during the late Holocene. Pollen-based climate reconstructions suggests the presence of a cold and dry period ~12,000 cal yr BP, possibly representing the Younger Dryas, followed by warmer and wetter conditions from 11,000 to 5000 cal yr BP, likely reflective of the Holocene Thermal Maximum. The climate then underwent a gradual cooling and drying from 5000 cal yr BP to the present, suggesting a late Holocene neoglacial cooling. Diatom preservation was poor prior to 5000 cal yr BP, when conditions were warmest, suggesting that diatom dissolution may in part be climatically controlled. Diatom concentrations were highest ~4500 cal yr BP but then decreased substantially by 3500 cal yr BP and remained low before recovering slightly in the 20th century. An abrupt warming occurred during the past 70 yr at the site, although the magnitude of this warming did not exceed that of the early Holocene.     

Holocene history and environmental reconstruction of a Hercynian mire and surrounding mountain landscape based on multiple proxies

We discovered the first peat section covering the entire Holocene in the Hrubý Jeseník Mountains, representing an island of unique alpine vegetation whose history may display transitional features between the Hercynian and Carpathian regions. We analysed pollen, plant macrofossils (more abundant in bottom layers), testate amoebae (more abundant in upper layers), peat stratigraphy and chemistry. We found that the landscape development indeed differed from other Hercynian mountains located westward. This is represented by Pinus cembra and Larix during the Pleistocene/Holocene transition, the early expansion of spruce around 10,450 cal yr BP, and survival of Larix during the climatic optimum. The early Holocene climatic fluctuations are traced in our profile by species compositions of both the mire and surrounding forests. The mire started to develop as a calcium-rich percolation fen with some species recently considered to be postglacial relicts (Meesia triquetra, Betula nana), shifted into ombrotrophy around 7450 cal yr BP by autogenic succession and changed into a pauperised, nutrient-enriched spruce woodland due to modern forestry activities. We therefore concluded that its recent vegetation is not a product of natural processes. From a methodological viewpoint we demonstrated how using multiple biotic proxies and extensive training sets in transfer functions may overcome taphonomic problems.     

Stratigraphy,paleontology, and age of Lake Algonquin sediments in southwestern Ontario,Canada

Molluscs, ostracodes, diatoms, pollen, plant macrofossils, peat, and wood have been found in glacial Lake Algonquin sediments, and estuarine-alluvial sediments of the same age, in southern Ontario. Molluscs and ostracodes are particularly abundant and widespread. Pollen analysis of Lake Algonquin sediments, bogs on the Algonquin terrace, and upland bogs above the Algonquin terrace, indicate that Lake Algonquin was still in existence at the time of the spruce-pine pollen transition, previously dated at an average of 10,600 yr BP at a number of sites in Michigan, Ohio, and southern Ontario. Wood in estuarine-alluvial sediments graded to the Algonquin level is of similar radiocarbon age. Evidence from several sites in the eastern Great Lakes area suggests the presence of a preceding low-water stage (Kirkfield outlet stage); drowned and alluviated valleys and fining-upward sediment sequences have been identified in this study as further supporting evidence. Lake Algonquin drained from the southern sites by isostatic tilting and eventual opening of the “North Bay outlet” some time shortly after 10,400 yr BP.Our radiocarbon dates suggest the low-water stage has an age of about 11,000 yr BP, and that Lake Algonquin drained 10,000–15,000 y. a. Dates previously published for the Lake Michigan basin are generally too young in comparison with ours, and dates on the Champlain Sea are generally too old. More critical evaluation of all dating results is desirable.From fossil remains we suggest a rapidly expanding fauna in the waters of Lake Algonquin. The spruce pollen period was a time of rapid faunal and floral migration, when the ice front was retreating from Kirkfield to North Bay, Ontario. Diversity of some species and fossil numbers increased substantially at the transition from spruce to pine just before Lake Algonquin drained.     

Changes of treelines and alpine vegetation in relation to post‐glacial climate dynamics in northern Fennoscandia based on pollen and chironomid records

Palaeoclimatic records derived from a variety of independent proxies provide evidence of post‐glacial changes of temperature and soil moisture in northern Fennoscandia. We use pollen percentage, pollen influx, stomatal and chironomid records from Toskaljavri, a high‐altitude lake in northern Finland, to assess how treelines and alpine vegetation there have responded to these climate changes. The evidence suggests that the cool, moist climate of the early Holocene supported birch forest in the area 9600 cal. yr BP onwards and that a rise of temperature triggered the immigration of pine at 8300 cal. yr BP. At 6100–4000 cal. yr BP altitudinal treeline in the area was formed by pine, in contrast to the modern situation where mountain birch reaches a higher elevation. Alpine vegetation also demonstrates clear changes. Plant communities typical of dry, oligotrophic heaths of northern Fennoscandia expanded during the dry climatic period at 7000–4000 cal. yr BP and decreased in response to cooler and moister conditions after 4000 cal. yr BP. Alpine plant communities favouring moist sites show an inverse pattern, expanding after a change towards moister climate after 4000 cal. yr BP. In a redundancy analysis (RDA), a statistically significant proportion of the variability in the total chironomid assemblages was captured by changes in the pollen types reflecting alpine vegetation typical of moist sites. Although chironomid community changes appeared to follow the major patterns in the alpine vegetation succession, the present study does not support a direct link between the changing treeline position and chironomid stratigraphy. Rather, the data indicate that the terrestrial and aquatic environments have each responded directly to the same ultimate cause, namely changing Holocene climate. Copyright © 2002 John Wiley & Sons, Ltd.     

The dynamic nature of Holocene vegetation : A problem in paleoclimatology, biogeography, and stratigraphic nomenclature

For more than a century it has been postulated that the Holocene vegetation of western Europe has changed in significant ways. A half-century ago a lively debate revolved on whether there were one or two dry intervals causing bogs to dry out and become forested, or whether instead the climate warmed to a maximum and then cooled. Today none of these climatic schemes is accepted without reservation, because two nonclimatic factors are recognized as significant: the differential immigration rates of dominant tree types (e.g., spruce in the north and beech in the south) brought unexpected changes in forest composition, and Neolithic man cleared the forest for agriculture and thereby disrupted the natural plant associations.In North America some of the same problems exist. In the hardwood forests of the Northeast, which are richer than but otherwise not unlike those of western Europe, the successive spread of white pine, hemlock, beech, hickory, and chestnut into oakdominated forests provides a pollen sequence that may yield no climatic message. On the other hand, on the ecotone between these hardwood forests and the conifer forests of the Great Lakes-St. Lawrence area, the southward expansion of spruce, fir, and tamarack in the late Holocene implies a climatic cooling of regional importance, although the progressive conversion of lakes to wetlands favored the expansion of wetland forms of these genera.In the southeastern states the late-Holocene expansion of southern pines has uncertain climatic significance. About all that can be said about the distribution and ecology of the 10 or so species is that some of them favor sandy soils and are adapted to frequent fires. In coastal areas the expansion of pines was accompanied by development of great swamps like Okefenokee and the Everglades—perhaps related to the stabilization of the water table after the early Holocene rise of sea level. The vegetation replaced by the pines in Florida consisted of oak scrub with prairie-like openings, indicating dry early Holocene conditions, which in fact had also prevailed during the time of Wisconsin glaciation.In the Midwest the vegetation history provides a clearer record of Holocene climatic change, at least along the prairie border in Minnesota. With the withdrawal of the boreal spruce forest soon after ice retreat, pine forest and hardwood forest succeeded rapidly, as in the eastern states. But prairie was not far behind. By 7000 years ago the prairie had advanced into east-central Minnesota, 75 miles east of its present limit. It then withdrew to the west, as hardwoods expanded again, followed by conifers from the north. The sequence easily fits the paleoclimatic concept of gradual warming and drying to a maximum, followed by cooling to the present day. It is supported by independent fossil evidence from lake sediments, showing that lakes were shallow or even intermittently dry during mid-Holocene time.Here we have a paleoclimatic pattern that is consistent with the record from glaciers in the western mountains—a record that involves a late-Holocene Neoglaciation after a mid-Holocene interval of distant glacial recession. Just as the Neoglaciation is time-transgressive, according to the review of its evidence by Porter and Denton, so also is the mid-Holocene episode of maximum warmth, and they are thus both geologicclimate units. The warm episode is commonly termed the Hypsithermal, which, however, was defined by Deevey and Flint as a time-stratigraphic unit that is supposed to have time-parallel rather than time-transgressive boundaries. It was defined on the basis of pollen-zone boundaries in western Europe and the northeastern United States that have a sound biogeographic but questionable paleoclimatic basis. Perhaps it should be redefined as Porter and Denton suggest, as a geologic-climate unit with recognizable time-transgressive boundaries that match the gradual geographic shifts in the general circulation of the atmosphere and the resulting location of storm tracks and weather patterns. Holocene glacial and vegetational progressions provide a good record of climatic change, if one can work out the lag effects related to the glacial economy and the geographic factors controlling tree migration. The terminology for the Holocene, where so much time control is available, should indicate the dynamic character not only of the climate but also of the geologic and biogeographic processes controlled by climate.     

A late Wisconsin and Holocene vegetation history from the central brooks range: Implications for Alaskan palaeoecology

Five pollen diagrams reveal late Wisconsin and Holocene vegetation changes in the Walker Lake/Alatna Valley region of the central Brooks Range, approximately 100 km west of the area studied by D. A. Livingstone (1955, Ecology36, 587–600). New insights into the vegetation history of this region are provided by calculations of pollen influx and by the use of linear discriminant analysis to separate Picea glauca and P. mariana pollen. Three major pollen zones are identified: (1) a basal herb zone, characterized by high percentages of Cyperaceae, Gramineae, Salix, and Artemisia, and low total pollen influx; (2) a shrub Betula zone with increased total pollen influx and very high percentages of Betula pollen, predominantly in the size range of B. nana and B. glandulosa; and (3) and Alnus zone dominated by Alnus pollen. Lakes currently within the boreal forest or near tree line show relatively high percentages of Picea pollen in the Alnus zone. Several striking vegetation changes occurred between ca. 10,000 and 7000 yr B.P. Between ca. 11,000 and 10,000 yr B.P., Populus balsamifera pollen percentages as great as 30% indicate that this species was present at low-elevation sites near Walker Lake. These populations declined abruptly ca. 10,000 yr ago and have never regained prominence. About 8500 yr B.P., Picea glauca pollen reached 10–15%, indicating the arrival of P. glauca in or near the study area. P. glauca populations evidently decreased ca. 8000 yr ago, when Picea pollen percentages and influx fell to low values. About 7000 yr B.P., Alnus pollen percentages and influx rose sharply as alder shrubs became established widely. Picea once more expanded ca. 5000 yr ago, but these populations were dominated by P. mariana rather than P. glauca, which increased slowly at this time and may still be advancing northward. Some vegetation changes have been remarkably synchronous over wide areas of interior Alaska, and probably reflect responses of in situ vegetation to environmental changes, but others may reflect the lagged responses of species migrating into new areas.     

Postglacial forest patterns associated with till and outwash in northcentral Upper Michigan

Pollen analysis of lake sediments reveals that small areas of till and outwash in northcentral Upper Michigan have influenced plant distributions throughout postglacial time. Each substrate has different textural characteristics. Modern forest communities form a mosaic, with jack pine woodlands occupying the medium sands of the Yellow Dog Plains outwash and white pine-hardwood communities on both till and outwash soils in the Michigamme Highlands to the south.The analysis of modern pollen samples from 21 lakes within the area indicates that pollen can be used to study the distribution of local vegetation in relation to substrate type. Fossil pollen from three of the lakes documents the character of ancient forest on Yellow Dog outwash, Michigamme outwash, and Michigamme till.Unique boreal communities occupied each area immediately after deglaciation. Between 8000 and 7000 y.a., white pine and maples migrated into the study area and replaced jack pine in forests on the Highlands, but not on the Plains. Jack pine has continued to occupy the Plains since early postglacial time. White pine reached highest densities on Michigamme outwash, and deciduous trees increased primarily on till during the presumably dry climates which existed 8000-5000 yr BP. As the climate became more mesic, forests on the Highlands changed, so that by 3000 yr BP the communities on Michigamme outwash and till were indistinguishable on the basis of pollen. Present-day forest patterns of the area became established at that time.Pollen influx rates, measured at each lake, generally support interpretations based on pollen percentages and were similar to values reported elsewhere. Variations in influx values are within the range expected for the method.     

Quaternary palynology of the Pacific slope of Washington

Quaternary deposits on the Pacific slope of Washington range in age from the earliest known interglaciation, the Alderton, through the Holocene. Pollen stratigraphy of these deposits is represented by 12 major pollen zones and is ostensibly continuous through Zone 8 over more than 47,000 radiocarbon yr. Before this, the stratigraphy is discontinuous and the chronology less certain. Environments over the time span of the deposits are reconstructed by the comparison of fossil and modern pollen assemblages and the use of relevant meteorological data. The Alderton Interglaciation is characterized by forests of Douglas fir (Pseudotsuga menziesii), alder (Alnus), and fir (Abies). During the next younger interglaciation, the Puyallup, forests were mostly of pine, apparently lodgepole (Pinus contorta), except midway in the interval when fir, western hemlock (Tsuga heterophylla), and Douglas fir temporarily replaced much of the pine. Vegetation outside the limits of Salmon Springs ice (>47,00034,000 yr BP) varied chiefly between park tundra and forests of western hemlock, spruce (Picea), and pine. The Salmon Springs nonglacial interval at the type locality records early park tundra followed by forests of pine and of fir. During the Olympia Interglaciation (34,00028,000 yr BP), pine invaded the Puget Lowland, whereas western hemlock and spruce became manifest on the Olympic Peninsula. Park tundra was widespread during the Fraser Glaciation (28,00010,000 yr BP) with pine becoming more important from about 15,000 to 10,000 yr BP. Holocene vegetation consisted first of open communities of Douglas fir and alder; later, closed forests succeeded, formed principally of western hemlock on the Olympic Peninsula and of western hemlock and Douglas fir in the Puget Lowland. Over the length of the reconstructed environmental record, climate shifted between cool and humid or relatively warm, semihumid forest types and cold, relatively dry tundra or park tundra types. During times of glaciation, average July temperatures are estimated to have been at least 7°C lower than today. Only during the Alderton Interglaciation and during the Holocene were temperatures higher for protracted periods that at present.     

The biogeographical role of Pinus forest on the Northern Spanish Meseta: a new Holocene sequence

The aim of this paper is to reconstruct the variation in the vegetation during the Holocene on the Northern Meseta through pollen analysis in order to determine the roles played by Pinus and Quercus in the vegetation dynamics. A new pollen sequence, Camporredondo, in the centre of the Duero River basin, Northern Meseta, Spain, is presented. It covers the period from ca 11,250 to 1630 cal yr BP. The Camporredondo sequence suggests that a forested landscape existed from the start of the Holocene with values of approximately 90% of arboreal pollen mainly derived from pine forests in the surroundings. Shortly after 8600 cal yr BP pine forests continued to dominate but the landscape became more open while stands of deciduous and evergreen Quercus developed. Around 4500 years ago, coinciding with the start of a period of less rainfall, the lacustrine areas in these territories began to silt up, favouring hydrophytic taxa such as Salix or Cyperaceae. A comparison with other Holocene pollen sequences from the central-eastern part of the Northern Meseta confirms the presence of pine forests in the whole region since the early Holocene. We discuss the variations of the general vegetation pattern in terms of the local or regional conditions at each site. Throughout the Holocene, Pinus forests dominated at least in the eastern half of the Duero River basin. The typical Holocene substitution of conifers by broadleaf species as recorded in other parts of the Iberian Peninsula and Europe, never takes place in the study area. The results of the present study suggest that the current view of the potential vegetation in the Spanish Northern Meseta should be reviewed.     

First Reconstruction of the Habitat of Hunter-Gatherers in the Mamakan Archaeological Area in the Middle Holocene,Patom Highlands

The first radiocarbon-dated pollen record from the Mamakan section is presented. This record has become the basis for the reconstruction of the vegetation and climate of the Middle Holocene in the Mamakan archaeological area, where a number of well-known Siberian archaeological sites of the Late Mesolithic–Middle Bronze period are located. Reconstructions suggest that sparse spruce and larch stands dominated in the area between 6450 and 6150 cal BP. Later, from 6150 to 4700 cal BP, Scots pine began to spread in a warmer climate than before, following the general trend of its expansion in the southern part of Eastern Siberia. A cooler climate than previously with increased soil and air humidity occurred in the Mamakan region from 4700 to 3840 cal BP, causing the regional expansion of Siberian pine. The time interval from 3840 to 3600 cal BP was characterized by the significant development of pine, spruce, and larch forests. On the basis of the age model, we assume that, in the lower reaches of the Vitim River and, probably, in other mountain regions north of Lake Baikal, Scots pine spread about 600 years later than in the Cis-Baikal region and east of the lake. This transition from dark coniferous-taiga to light coniferous-taiga with a predomination of Scots pine signifies the most fundamental change in vegetation of the Baikal region in the Holocene. This is often discussed as one of the possible causes of the Middle Neolithic cultural hiatus (6660–6060 cal BP), which has been documented in the archaeological records from different parts of this vast region. Reconstruction of vegetation in the Mamakan region suggests that the territory of the Nizhnii Vitim River has been favorable for humans during most of the hiatus recorded in the Cis-Baikal area and may have been considered as a refuge for populations of hunter-gatherers in the Middle Neolithic.

     

Postglacial vegetation history of Mitkof Island, Alexander Archipelago, southeastern Alaska

An AMS radiocarbon-dated pollen record from a peat deposit on Mitkof Island, southeastern Alaska provides a vegetation history spanning ∼12,900 cal yr BP to the present. Late Wisconsin glaciers covered the entire island; deglaciation occurred > 15,400 cal yr BP. The earliest known vegetation to develop on the island (∼12,900 cal yr BP) was pine woodland (Pinus contorta) with alder (Alnus), sedges (Cyperaceae) and ferns (Polypodiaceae type). By ∼12,240 cal yr BP, Sitka spruce (Picea sitchensis) began to colonize the island while pine woodland declined. By ∼11,200 cal yr BP, mountain hemlock (Tsuga mertensiana) began to spread across the island. Sitka spruce-mountain hemlock forests dominated the lowland landscapes of the island until ∼10,180 cal yr BP, when western hemlock (Tsuga heterophylla) began to colonize, and soon became the dominant tree species. Rising percentages of pine, sedge, and sphagnum after ∼7100 cal yr BP may reflect an expansion of peat bog habitats as regional climate began to shift to cooler, wetter conditions. A decline in alders at that time suggests that coastal forests had spread into the island's uplands, replacing large areas of alder thickets. Cedars (Chamaecyparis nootkatensis, Thuja plicata) appeared on Mitkof Island during the late Holocene.     

Sedimentologic and palynologic records of the last deglaciation and Holocene from Ballston Lake, New York

Continuous pollen and sediment records from two ∼8.5-m-long cores document late Pleistocene and Holocene sedimentation and vegetation change in the Ballston Lake basin, eastern New York State. Pebbles at the base of both cores and the geomorphology of the watershed reflect the presence of the Mohawk River in the basin prior to ∼12,900 ± 70 cal yr B.P. Ballston Lake formed at the onset of the Younger Dryas (YD) by an avulsion of the Mohawk River. The transition from clay to gyttja with low magnetic susceptibility (MS), low bulk density, and high organic carbon indicates rapid warming and increased lake productivity beginning 11,020 cal yr B.P. MS measurements reveal that the influx of magnetic particles, associated with pre-Holocene clastic sedimentation, ceased after ∼10,780 cal yr B.P. The pollen record is subdivided into six zones: BL1 (12,920 to 11,020 cal yr B.P.) is dominated by boreal forest pollen; BL2 (11,020 to 10,780 cal yr B.P.) by pine (Pinus) forest pollen; BL3 (10,780 to 5290 cal yr B.P.) by hemlock (Tsuga) and mixed hardwood pollen; BL4 (5290 to 2680 cal yr B.P.) by mixed hardwood pollen; BL5a (2680 cal yr B.P. to 1030 cal yr B.P.) by conifer and mixed hardwood pollen; and BL5b (1030 cal B.P. to present) by increasing ragweed (Ambrosia) pollen. A 62% decrease in spruce (Picea) pollen in <320 cal years during BL1 reflects rapid warming at the end of the YD. Holocene pollen zones record more subtle climatic shifts than occurred at the end of the YD. One of the largest changes in the Holocene pollen spectra began ∼5300 cal yr B.P., and is characterized by a marked decline in hemlock pollen. This has been noted in other pollen records from the region and may record preferential selection of hemlock by a pathogen or parasites.     

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.