High-resolution Pollen Analysis Research Articles

Short-lived vegetational and environmental change during the Preboreal in the Biebrza Upper Basin (NE Poland)

A pollen diagram from the upper Biebrza basin (NE Poland) shows a conspicuous pollen fluctuation around 9650 BP, which is superimposed on a broader pollen fluctuation correlated with a more open vegetation phase during the Preboreal generally found in Europe. High-resolution pollen analyses indicate a duration of only a few years in which Pinus forests became more open. The resulting niches were partly occupied by Betula trees and partly by Betula shrubs, Artemisia, and Chenopodiaceae. Shortly before the increased opening of the upland vegetation, reed vegetation developed in the valley, in which Sparganium and later Typha became prominent. At the end of the short fluctuation, this reed vegetation diminished. The wetland vegetation development might be partly related to hydrological changes caused by a reduced evapotranspiration of the opened upland forest. The data presented here show that the open vegetation phase of the Preboreal was not of uniform character, but that within its short time span of ca 150 years an even shorter fluctuation of a few years to a few decades occurred. It is unknown whether this is a regionally restricted phenomenon or whether it has an extra-regional character.

Abrupt and consistent responses of aquatic and terrestrial ecosystems to the 8200 cal. yr cold event: a lacustrine record from Lake Arapisto, Finland

A 8400—7700 yr cal. BP section of the sediments of a small lake in southern Finland was studied by high-resolution pollen and cladoceran analyses to examine the response of terrestrial and aquatic ecosystems to the 8200 cal. yr BP cold event. Furthermore, a pollen-based Tann reconstruction and proportions of chydorid ephippia were used to determine changes in temperature and in the length of open-water season during the event. The pollen data, with abrupt decreases of the early-flowering Alnus, Corylus and Ulmus at c. 8350 cal. yr BP, may partly reflect vegetation dynamics but possibly also decreased pollen productivity and reproduction caused by cold winters and springs. The reconstructed Tann indicated a rapid temperature fall and a subsequent recovery. Proportions of chydorid ephippia suggested a considerable reduction in the length of open-water season at the beginning of the event, followed by periodically shorter open-water seasons. In the aquatic ecosystem only one species, the dominant planktonic cladoceran Bosmina longirostris, responded by decreasing dramatically and almost became extinct during the coldest period. However, we were unable to reconstruct the causative link between the inferred climate change and its decrease. The response of both aquatic and terrestrial proxies at c. 8350 cal. yr BP was consistent, indicating an abrupt start of the event and also an abrupt end at c. 8100 cal. yr BP.

Dynamique holocène de la végétation et occupation des Pyrénées andorranes depuis le Néolithique ancien, d’après l’analyse pollinique de la tourbière de Bosc dels Estanyons (2180 m, Vall del Madriu, Andorre)

The pollen analysis of a new sedimentary sequence performed at the Bosc dels Estanyons peat bog (2180 m a.s.l., Eastern Pyrenees, Andorra) is presented. Seven radiocarbon measurements and complementary macro-charcoal, stomata, and pollen influx analyses are employed to illustrate the dynamics of high-mountain vegetal communities since the end of the Late Glacial period. This high-resolution pollen analysis outlines the evolution of human activities since the Mesolithic–Early Neolithic transition for the first time in this area.

Climate variability in the Aral Sea basin (Central Asia) during the late Holocene based on vegetation changes

High-resolution pollen analyses (∼ 50 yr) from sediment cores retrieved at Chernyshov Bay in the NW Large Aral Sea record shifts in vegetational development from subdesertic to steppe vegetation in the Aral Sea basin during the late Holocene. Using pollen data to quantify climatic parameters, we reconstruct and date for the first time significant changes in moisture conditions in Central Asia during the past 2000 yr. Cold and arid conditions prevailed between ca. AD 0 and 400, AD 900 and 1150, and AD 1500 and 1650 with the extension of xeric vegetation dominated by steppe elements. These intervals are characterized by low winter and summer mean temperatures and low mean annual precipitation ( P mm < 250 mm/yr). Conversely, the most suitable climate conditions occurred between ca. AD 400 and 900, and AD 1150 and 1450, when steppe vegetation was enriched by plants requiring moister conditions ( P mm ∼ 250–500 mm/yr) and some trees developed. Our results are fairly consistent with other late Holocene records from the eastern Mediterranean region and the Middle East, showing that regional rainfall in Central Asia is predominantly controlled by the eastern Mediterranean cyclonic system when the North Atlantic Oscillation (NAO) is in a negative phase.

Early Pliocene vegetation changes forced by eccentricity-precession. Example from Southwestern Romania

Repetitive changes in Early Pliocene marine and continental sediments were forced by astronomical cycles (eccentricity, precession) and related to low amplitude climatic fluctuations as demonstrated at Capo Rossello and Monte San Nicola (Sicily). This work aims to establish if such climatic fluctuations have also controlled changes in the vegetation during the warm Early Pliocene. High-resolution pollen analysis of the Lupoaia section (SW Romania) provides evidence of a clear response owing to its location within a delta system which constitutes a reliable area for pollen deposition near the Carpathians (i.e. capable of registering all the vegetation ecosystems from edaphic coastal associations up to the highest altitudinal belts), and owing to its Southeastern European longitude probably where warm–humid air masses arrived regularly, making the region a highly favourable refuge for thermophilous plants. Eccentricity appears to have controlled fluctuations in temperature (development of thermophilous elements during eccentricity minima, and descent of altitudinal trees during eccentricity maxima) while precession appears to have forced changes in humidity (expansion of cypress swamps related to precession maxima, and spread of herbaceous marshes requiring more humidity related to precession minima) with respect to increased precipitation and run-off.

Fluctuations in the East Asian monsoon over the last 144 ka in the northwest Pacific based on a high-resolution pollen analysis of IMAGES core MD01-2421

A high-resolution pollen analysis of IMAGES core MD01-2421 (45.83 m) from the northwest Pacific off central Japan was used to clarify the vegetation history of central Japan over the past 144 ka. An age model was constructed using the oxygen isotope stratigraphy of benthic foraminifera, 12 accelerator mass spectrometry (AMS) 14C datings, and two tephra layers with known eruption ages. The pollen temperature index T p [ = 1 0 0 × T w / ( T c + T w ) , where T w is the sum of temperate taxa and T c the sum of subalpine taxa] values were high during 129–119, 115–100, 82–76, 53–49, and 15–0 ka. Cool-temperate broad-leaved forests developed during the high- T p periods and subalpine conifer forests grew during the low- T p periods. The T p fluctuated synchronously with summer insolation at 36°N, where the core was collected. During periods with abundant Cryptomeria or Sciadopitys (120–118, 115–89, 78–70, and 4–0.3 ka), the East Asian summer monsoon was stronger and the annual precipitation was greater in central Japan than at present (>2000 vs. 1500 mm). Fluctuations in the sea-surface temperature (SST) calculated from the oxygen isotopes of foraminifera in core MD01-2421 and changes in the strength of the summer monsoon were synchronous. The SST was determined by the currents passing over the core site, rather than by the strength of summer insolation. Northward movement (high SST) of the Kuroshio Current, which is under the influence of the summer Okhotsk high pressure, was strong near the summer insolation minima when precipitation was high, particularly around 116, 94, and 71 ka. Thus, the strengths of both summer insolation and the East Asian summer monsoon have determined the vegetation history of central Japan for the last 144 ka.

Mid- to late-Holocene El Nino-Southern Oscillation dynamics reflected in the subtropical terrestrial realm.

High resolution pollen analysis of mid- to late-Holocene peat deposits from southwest Florida reveals a stepwise increase in wetland vegetation that points to an increased precipitation-driven fresh water flow during the past 5,000 years. The tight coupling between winter precipitation patterns in Florida and the strength of the El Niño-Southern Oscillation (ENSO) strongly suggests that the paleo-hydrology record reflects changes in ENSO intensity. A terrestrial subtropical record outside the Indo Pacific Warm Pool both documents ecosystem response to the known onset of modern-day ENSO periodicities, between approximately 7,000 and 5,000 years B.P., and subsequent ENSO intensification after 3,500 years B.P. The observed increases in "wetness" are sustained by a gradual rise in relative sea level that prevents a return to drier vegetation through natural succession.

A Middle Wisconsin interstadial in the northern Andes

This article reports the occurrence of a Middle Wisconsin interstadial, Pedregal, in the northern Venezuelan Andes, as demonstrated by high-resolution pollen analysis of a previously dated peat layer. Paleoclimatic trends are deduced mainly from changes in the abundance of tree pollen from the uppermost Andean forests. Previous calibration of this pollen with modern analogs has enabled reconstructions of prior altitudinal displacements of montane ecological belts and temperature changes. Paleotemperatures were deduced from the current lapse rate (−0.6 °C/100 m). After a glacier advance, represented by an underlying till, average temperatures increased to 3 °C lower than modern temperatures during the Pedregal interstadial and then dropped again to approximately 7 °C lower than modern. It is the oldest Quaternary paleoclimatic event reported thus far in the area.

Present-Day Rhythmic Deposition in the Grand Rhone Prodelta (NW Mediterranean) According to High-Resolution Pollen Analyses

Abstract A high-resolution pollen study (136 samples) has been performed on the KTR05 core (738 cm long) located in the modern Grand Rhone prodelta. The objectives were (1) to evaluate the palynological and sedimentological record quality of a prodelta in comparison with fluvial inputs (2) and to quantify lost sediment (resuspensions) in this area. The core covers more than the last thirty years. By comparison with the modern pollen rain both in the Rhone delta and in the mid-drainage basin (Lyon), a seasonal forcing in pollen deposition has been demonstrated. Monthly pollen successions can be evidenced in a well preserved sequence, providing an estimate of the true sedimentation rate (60 cm.yr−1). Importance of disturbed or incomplete sequences suggests that most of the sediment first deposited in the prodelta (around ⅔) has been resuspended. Sedimentological and palynological data record not only seasonal but fluvial impact. The progressive shift of the prodelta has been evidenced firstly with sedimento...

Environmental variability and human adaptation during the Lateglacial/Holocene transition in Japan with reference to pollen analysis of the SG4 core from Lake Suigetsu

High-resolution pollen analysis of annually laminated sediments from Lake Suigetsu in Japan revealed that climate amelioration at 16,500 varve years before present (vy BP) triggered the expansion of cool temperate deciduous broad-leaved forest. The oldest pottery appearance in Japan coincided with this climate amelioration. Significant vegetation change occurred from 15,000 to 14,500 vy BP. The period during 15,000–14,500 vy BP was a time of ecological transition from a Glacial-type ecosystem, eventually destroyed by global warming, to a new Postglacial-type ecosystem represented by that in Lake Suigetsu. It is believed that the completion of this ecological transition actually took nearly 500–800 years. This drastic change in the ecosystem had forced people to create a new strategy of adaptation. The Japanese Neolithic Jomon culture, mainly sustained by gathering nuts and fishing, was widely established at this time. On the other hand, the cold period which correlates with the Younger Dryas in Europe had no significant ecological influence on the Japanese ecosystem and human culture.

Late Quaternary Araucaria forest, grassland (Campos), fire and climate dynamics, studied by high-resolution pollen, charcoal and multivariate analysis of the Cambará do Sul core in southern Brazil

Late Quaternary vegetation, fire and climate dynamics have been studied based on high-resolution dated pollen and charcoal samples and multivariate data analysis. The samples were taken from a 212-cm-long sediment core of a bog in the Cambará do Sul region on the highlands of northeastern Rio Grande do Sul State, Brazil. The records, including seven AMS radiocarbon dates, span 42 840 14C years, for the first time extending the reconstruction of past environmental changes on the southern Brazilian highlands back to the Last Glacial Maximum (LGM) and pre-LGM times. The last 1100 years provide a decadal resolution. Initially the site was a permanent shallow lake which became seasonally dry after 26 900 14C yr BP. Seasonal climate with a long annual dry period prevailed until the late Holocene. The climate was somewhat wetter from 42 840 to 41 470 14C yr BP and from 41 470 to 26 900 14C yr BP than during the LGM and the late-Glacial period. Natural fires were rare, but became very frequent after 7400 cal BP, suggesting human occupation of the southernmost Brazilian highlands since that time. The records suggest that a species-rich Campos (grassland) vegetation existed in the area under a relatively dry and cold climate during glacial times under possibly as low as −10°C. The record also suggests that small populations of Araucaria were probably only present in refugia of deep and protected valleys and/or on wetter coastal slopes. Campos vegetation existed through the early and mid-Holocene until 4320 cal yr BP, after which Araucaria forest expanded into the network of gallery forests along the streams. By 1100 cal yr BP the Araucaria forest replaced the Campos vegetation reflecting the onset of the wettest period with no marked annual dry season. The marked expansion of the Araucaria forest coincided with the reduction in fire. Between AD 1520 and 1770 Weinmannia became a common taxa in the Araucaria forest, suggesting a shift to warmer climatic conditions on the highlands. This interval was synchronous with a cool phase within the Little Ice Age known from North Atlantic land records. After about AD 1780 human activities changed the original forest composition, first by introducing cattle into the forest and than by selective logging of Araucaria trees. Multivariate analysis of the pollen data shows compositional changes that follow a trajectory alternating undirectional, random phases and phases with directional, sometimes fast transitions. The results also show that compositional changes in the vegetation are slower during cool periods (LGM compared to pre-LGM) and faster in warm periods (Holocene).

Rapid vegetation change during the early Holocene in the Faroe Islands detected in terrestrial and aquatic ecosystems

AbstractHigh‐resolution pollen, plant macrofossil and sedimentary analyses from early Holocene lacustrine sediments on the Faroe Islands have detected a significant vegetation perturbation suggesting a rapid change in climate between ca. 10 380 cal. yr BP and the Saksunarvatn ash (10 240±60 cal. yr BP). This episode may be synchronous with the decline in δ18O values in the Greenland ice‐cores. It also correlates with a short, cold event detected in marine cores from the North Atlantic that has been ascribed to a weakening of thermohaline circulation associated with the sudden drainage of Lake Agassiz into the northwest Atlantic, or, alternatively, a period with distinctly decreased solar forcing.The vegetation sequence begins at ca. 10 500 cal. yr BP with a succession from tundra to shrub‐tundra and increasing lake productivity. Rapid population increases of aquatic plants suggest high summer temperatures between 10 450 and 10 380 cal. yr BP. High pollen percentages, concentrations and influx of Betula, Juniperus and Salix together with macrofossil leaves indicate shrub growth around the site during the initial phases of vegetation colonisation. Unstable conditions followed ca. 10 380 cal. yr BP that changed both the upland vegetation and the aquatic plant communities. A decrease in percentage values of shrub pollen is recorded, with replacement of both aquatics and herbaceous plants by pioneer plant communities. An increase in total pollen accumulation rates not seen in the concentration data suggests increased sediment delivery. The catchment changes are consistent with less seasonal, moister conditions. Subsequent climatic amelioration reinitiated a warmth‐driven succession and catchment stabilisation, but retained high precipitation levels influencing the composition of the post‐event communities. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Laminated sediments, human impact, and a multivariate approach: a case study in linking palynology and archaeology (Steisslingen, Southwest Germany)

Situated in the Alpine Foreland, Lake Steisslingen provides sediments covering the last 16,000 sidereal years. The exceptional value as an environmental archive is due to large laminated sections, found in several long cores. Counting of organic varves allowed the establishment of a detailed varve-based age model. A high-resolution pollen analysis for the period 5457 BC to 813 AD was carried out and compared with an archaeological mapping of a 5 km radius around Lake Steisslingen. The combined interpretation of the palynological and archaeological evidence facilitates a reconstruction of the settlement history and the evolution of the landscape over the last eight millenia. Several important aspects of vegetational and settlement history are illuminated: The mathematical ordination method of correspondence analysis is used to extract the main dimension of explanation from the pollen data. A single curve is generated and thought to reflect human impact. The validity of this assumed proxy is tested against the vegetational and archaeological evidence of the micro-scale area since Neolithic times. From the Steisslingen example, we conclude that human impact is the most important and, in a mathematical sense, continuous factor in vegetational development of those landscapes, which are settled since prehistoric times.

Revealing climatic variability of the last three millennia in northwestern Iberia using pollen influx data

Climatic variability of the last 3 millennia in NW Iberia has been documented using high-resolution pollen analysis of Vir-18 core, retrieved from the Rı́a de Vigo (42°14.07′N, 8°47.37′W). The depth–age model is based on two accelerator mass spectrometry 14C dates and three historically dated botanical events in Galicia: the expansion of Juglans and Pinus, as well as the introduction of Eucalyptus. During the last 3000 years, the relative pollen record demonstrates the occurrence of an open deciduous oak forest, indicating a humid and temperate climate in northwestern Iberia. Two-step forest reduction since 975 cal BC suggests climate as the main cause rather than major socio-economic changes documented in historical archives. Absolute pollen influx has been compared with instrumental summer and winter temperatures and tentatively used as a proxy of short (decadal-scale) and low-amplitude (∼1°C) temperature variations. This new approach allows us to detect for the first time in NW Iberia the millennial-scale climatic cyclicity suggested by North Atlantic records, challenging the apparent climatic stability reflected by the relative pollen record. The Little Ice Age is recorded as low pollen influx values between 1400 and 1860 cal AD, with a cold maximum at 1700 cal AD (Maunder Minimum). The Roman and Medieval Warm Periods are detected through high pollen influx values at 250 cal BC–450 cal AD and 950–1400 cal AD, respectively.

Palynological records of environmental changes in the middle part of Inner Mongolia, China

A 2.4-m-long core was extracted from Diaojiao Lake (41° 18′’ N, 112° 2l′’ E) at the foot of the northern part of Daqingshan Mts. High-resolution pollen analysis results of two sites showed 10 arboreal genera, including Pinus, Betula, Picea, Abies, Carpinus, Quercus, Ulmus and more than 20 non-arboreal genera, mainly of Artemisia, Labiatae, Nitraria, Polygonaceae, Ranunculus, Thalictrum, Umbelliferae, Caryophyllaceae and Cyperaceae dominating the record. Fern spores, aquatic pollen and algae were also observed in some sections of the cores. The sequence was divided stratigraphically into six pollen assemblage zones by a stratigraphically-constrained cluster analysis using an facremental sum of squares method. The vegetation underwent the following stage changes: steppe with sparse trees, steppe, forest, and steppe. During the middle Holocene, a mixed forest of Pinus, Betula and Quercus occurred on the mountainous areas, and Pinus forest dominated the frontal plains. Six climatic stages were inferred from total pollen flux and pollen percentage from the two sites using a transfer function: humid-cool (10000—7800 aBP), arid-cold (9200—7800 aBP), arid-warm (7800—7100 aBP), humid-warm (7100—4400 aBP), arid-warm (4400—3000 aBP), arid-cold (3000—2100 aBP) phases were identified.

Repetitive changes in Early Pliocene vegetation revealed by high-resolution pollen analysis: revised cyclostratigraphy of southwestern Romania

A high-resolution pollen analysis has been carried out on the Lupoaia section (SW Romania) in order to check whether the repetitive clay–lignite alternations correspond to cyclic changes in climate. Increases in altitudinal tree pollen content appear to have been caused by drops in temperature, while developments of thermophilous elements correspond to rises in temperature, still under humid conditions. Such repeated changes in vegetation, on the whole consistent with the clay–lignite alternations, have been forced by cycles in eccentricity. On the basis of a comparison between the Lupoaia pollen record and (1) European climatostratigraphy (based on reference pollen diagrams documenting global changes), and (2) global climatic curves (eccentricity, δ 18O), the age of the section has been reconsidered. The Lupoaia section (i.e. from lignite IV to lignite XIII) starts just before the C3n.3n Chron and probably ends just before the C3n.1n Chron. The section represents a time span of about 600 kyr, i.e. from about 4.90 Ma to about 4.30 Ma.

Reconstruction of climatic and environmental changes in NW Romania during the early part of the last deglaciation (∼15,000–13,600 cal yr BP)

High resolution pollen, plant macrofossil, charcoal, mineral magnetic and sedimentary analyses, combined with AMS 14C measurements, were performed on multiple sediment sequences along a transect through the former crater lake Preluca Ţiganului in northwestern Romania in order to reconstruct the climatic and environmental changes during the early part of the Last Termination. Lake sediments started to accumulate at ∼14,700 cal yr BP. Initially the upland vegetation consisted of an open forest with mainly Betula and Salix and few Pinus sp., but from 14,500 cal yr BP onwards, Pinus mugo, P. sylvestris and Populus and later on also Larix became established around the lake. Between 14,150 and 13,950 cal yr BP, Pinus cembra seems to have replaced P. mugo and P. sylvestris. At ∼13,950 cal yr BP the tree cover increased and Picea appeared for the first time, together with Pinus cembra, P. mugo and Larix. From ∼13,750 cal yr BP onwards, a Picea forest developed around the site. Based on the combined proxy data the following climatic development may be inferred: 14,700–14,500 cal yr BP, cooler and wet/humid; 14,500–14,400 cal yr BP: gradually warmer temperatures, wet/humid with dry summers; 14,400–14,320 cal yr BP: warm and dry; 14,320–14,150 cal yr BP: cooler and wet/humid; 14,150–14,100 cal yr BP: warm and dry; 14,100–13,850 cal yr BP: warmer and wet/humid; <13,850 cal yr BP: warm and dry. The tentative correlation of this development with the North Atlantic region assumes that the period >14,700 cal yr could correspond to GS-2a, the time span between 14,700 and 14,320 to GI-1e, the phase between 14,320 and 14,150 cal yr BP to GI-1d and the time frame between 14,150 and 13,600 cal yr BP to the lower part of GI-1c.

Holocene environmental changes in the Central Amazon Basin inferred from Lago Calado (Brazil)

Holocene environments have been reconstructed by sedimentological, mineralogical geochemical and high resolution pollen analysis of a 1190 cm-long core from Lago Calado near Manaus in Central Amazonia. The sediment core, dated by eight AMS-radiocarbon dates, has a basal age of 8330±50 14 C yr bp and documents the landscape development from a river valley before 8280 14C yr bp to a lake environment. This change is related to the rise of the Central Amazonian water level, controlled by the postglacial sea-level rise. Pollen analytical results show the formation of a local Mauritia palm-swamp along the river margin between 8280 and 7700 14C yr bp. At that time, highly diverse terra firme (unflooded upland) Amazon rainforest and poorly developed várzea/igapó (inundated) forests along the river characterized the vegetation. The expansion of várzea/igapó forests and a strong presence of aquatic plants started at 7700 14C yr bp, reflecting the rise of the Amazonian water level and the formation of the Lago Calado. The occurrence of abundant Poaceae and Cyperaceae pollen in the lake sediments since 7770 14C yr bp, suggest both the local colonization of unflooded mud banks around the lake margin and the formation of flooding meadows. Open exposed unflooded mud areas, periodically colonized by herbs, are related to seasonal Amazonian high and low water stands. In respect to the abundance of Poaceae pollen during the early and mid Holocene, these open areas must have been large, suggesting brief annual high and extensive annual low Amazonian water stands. After 4070 14C yr bp the proportion of várzea/igapó forest areas was larger than before. Herbs were less abundant, probably due to the smaller area of unflooded mud banks. The Amazonian water levels must have been higher and the period of the annual high water stands was probably longer than before. Since 2080 14C yr bp, the largest proportion of várzea/igapo forests is recorded, reflecting the highest Amazonian water level. Herbs were rare, suggesting that open unflooded mud areas around the lake were relatively small. This may perhaps also indicate that the seasonal period of the Amazonian high water level was the longest since 2080 14C yr bp. The increase of Cecropia, Poaceae and Alternanthera during the last 150 yr, suggests stronger human impact on the local vegetation. Changes to higher Amazonian water levels are related to the rise of the Atlantic sea-level. Relatively short annual high water levels during the early Holocene and relatively long annual high water levels since 4070 and especially since 2080 14C yr bp, can be interpreted as a climate change from a drier early Holocene (with lower annual rainfall rates and longer dry periods) until 4070 14C yr bp to a wetter late Holocene.

High-resolution Holocene vegetation history and climate from Hole 1034B, ODP leg 169S, Saanich Inlet, Canada

Abstract High-resolution pollen analysis of laminated marine sediments from ODP Hole 1034B in Saanich Inlet, British Columbia reveals changes in vegetation and inferred climate during the Holocene. Four main pollen zones are discerned using constrained cluster analysis. Although the timing of major vegetation changes at the Saanich Inlet is similar to other study sites in the Pacific Northwest, the composition of pollen assemblage zones is different from the mainland sites. Vegetation assemblages reconstructed from the pollen and spore record include a Douglas-fir (Pseudotsuga menziesii) parkland with abundant grass (Poaceae) and bracken (Pteridium) between 11,450 and 8300 BP (all ages are calibrated calendar years), oak (Quercus) savanna or parkland with high grass and bracken (8300–7040 BP), a mixed deciduous/coniferous forest with oak, western hemlock (Tsuga heterophylla) and Douglas-fir (7040–5750 BP), and the development of modern coastal temperate forest with the marked expansion of cedar (Cupressaceae), western hemlock, spruce (Picea) and Douglas-fir (5750–1050 BP). Climatic periods inferred from the cores include an early Holocene warm/dry interval (11,450–8300 BP), a warm period with mild winters (8300–7040 BP), a period of transitional mid-Holocene climate (7040–5750 BP), and the advent of a relatively cool/wet neoglacial climate after 5750 BP. Modern conifer forests and oak savannas became established by about 3800 BP. The Saanich Inlet pollen record indicates that vegetation and inferred climate change was particularly rapid between 8700 and 8300 BP when grass and bracken abruptly decrease and oak becomes a significant component of the paleovegetation. Because neoglacial conditions have prevailed from 3800 years to present in the Pacific Northwest, factors other than climate, such as anthropogenic modification of the landscape, may be responsible for the persistence of oak savannas.

Pollen and phytoliths in stone mounds at Pouerua, Northland, New Zealand: implications for the study of Polynesian farming

High-resolution pollen and phytolith analyses can provide direct evidence for farming in archaeological landscapes. This is demonstrated here in the analysis of two mounds at Pouerua, northern New Zealand, where evidence indicates both functional and temporal differences between the structures, and the presence of gourd Lagenaria siceraria provides direct, unequivocal evidence that this crop was cultivated and that the site was used as a garden.