Arboreal Pollen Research Articles

Fire history and fire ecology of Northern Kruger (KNP) and Limpopo National Park (PNL), southern Africa

This paper explores the general correlations between fire and grass/tree relationships, as represented by fossil charcoal and pollen, from different vegetation types in the savanna ecosystems of the neighbouring Kruger (KNP) and Limpopo (PNL) national parks. Our analysis suggests that the basic presumption that fire is a main driver of vegetation dynamics in the savanna ecosystem by suppressing tree seedlings and encouraging grasses needs to be re-examined. An improved approach is to understand how fire may act both as a negative and positive feedback in different vegetational phases and both as a driver and responder in transitions between phases. The correlation between arboreal pollen (AP) percentages and charcoal influx suggests that in the grassland phase (< 5% AP), fire acts as a driver of woody recruitment and as a positive feedback, i.e. potentially driving the system to shift into a savanna phase. In the savanna phase (5—10% AP) fire limits woody recruitment and acts as a negative feedback in maintaining the savanna. Thus, in the savanna phase other factors than fire alone drive the transition from savanna to woodland-forest. In the riparian phase, where evidence of farming is present particularly from AD 1600 onwards, fire appears to facilitate tree recruitment where AP ranges between c. 10 and 20% AP. Though a decline in AP abundance can be seen contemporaneously with charcoal peaks, our analysis suggests that overall, human-induced fires do not seem to have a negative impact on woody cover. Our results have implications for fire management as riparian-dominated phases and savannas with a sufficient woody cover are less sensitive to changes in fire policies than open grasslands that may, with a change in fire frequency, change into another state.

Climate changes inferred from integrated multi-site pollen data in northern Taiwan

In this study, we synthesized the fossil pollen data from 10 lake sediments and 2 land cores to integrate the alteration of forest covered areas in northern Taiwan with changes in humidity and temperature over the last 2000 years. The abundance of arboreal pollen, fern spores and Tsuga pollen in the pollen and spore assemblages were used as indicators. Our results suggested that the climate in northern Taiwan was stably cool and dry during 2000–1000 cal. yr BP, but changed to wet and warm during 1000–500 cal. yr BP, which corresponded to the Medieval Warm Period (MWP). In addition, an increased density and dispersal of Tsuga pollen corresponding to 500–200 cal. yr BP was observed, which corresponded to the Little Ice Age (LIA). In recent years, a decline in Tsuga pollen density and increased fern spore density has been observed, which indicates an increase in temperature associated with elevated rainfall. Based on the synthesized data set, we conducted GIS mapping of such changes in the north of Taiwan over time. The results revealed that the temporal and spatial climate changes could be inferred from the palynological GIS mapping method, and that the fluctuations in temperature over time matched well with the global climate events, including MWP, LIA and recent warming.

Airborne pollen flora of a deciduous mesic forest in Turkey

Airborne pollen composition of a deciduous mesic forest in northwestern Turkey is compared with the flora of the forest and a wider area. The airborne assemblage is constituted by 641.553 pollen belonging to 32 orders, 54 families and 96 genera. Of these, 380.000 (59.2%) belong to native and 257.180 (40.1%) to non-native plants. Among the native taxa arboreal pollen (AP) is represented by 55.7% and non-arboreal (NAP) by 44.3%. All of the arboreal elements of the forest are Quercus, Castanea, Carpinus, Ulmus, Alnus, Populus, Salix, Fagus, Tilia, Acer, Corylus, Prunus, Rubus, Ligustrum, Phillyrea which represented in the airborne assemblage. Incorporation of NAP to airborne composition is less than AP and they more likely provide an indication of the composition of local plant communities and hence represent vegetation of immediate vicinity. The most common NAP taxa are Poaceae, Plantaginaceae, Asteraceae, Urticaceae, Apiaceae, Cannabaceae, Polygonaceae and Cyperaceae. Pollen of climbers are less represented than AP but more than NAP taxa. Platanus orientalis (30.7%) and Pinus and Cupressus (20.2%) constitute half of the non-native flora; the rest is the pollen of exotic, alien and horticultural taxa from numerous parks and gardens in İstanbul.

The paleoclimate of the Eastern Mediterranean during the transition from early to mid Pleistocene (900 to 700 ka) based on marine and non-marine records: An integrated overview

Climate change is frequently considered an important driver of hominin evolution and dispersal patterns. The role of climate change in the last phase (900–700 ka) of the Middle Pleistocene Transition (MPT) in the Levant and northeast Africa was examined, using marine and non-marine records. During the MPT the global climate system shifted from a linear 41 k.yr. into a highly non-linear 100 k.yr. system, considerably changing its global modulation. Northeast Africa aridity further intensified around 950 ka, as indicated by a sharp increase in dust flux, and a jump to overall higher levels thereafter, coinciding with a lack of sapropels in the deep eastern Mediterranean (930–690 ka). The increased dust flux centering at ∼800 ka corresponds to the minima in 400 k.yr. eccentricity, a minima in 65 °N solar forcing and in the weakest African monsoon precession periodicity. This resulted in expansion of hyper-arid conditions across North Africa, the lowest lake levels in eastern Africa and the lowest rainfall in the Nile River headwaters. In the eastern Mediterranean an increasing continental signature is seen in glacial stages 22 (∼880 ka) and 20 (∼800 ka). Lower arboreal pollen values also indicate arid conditions during these glacial stages. The southern and eastern parts of the Negev Desert, unlike its northern part, were hyper-arid during the MPT, making them highly unsustainable. The fluctuations in the stands of Lake Amora follow global climate variability but were more moderate than those of its last glacial Lake Lisan successor. In the northern Jordan-Valley Hula Lake, frequent fluctuations in lake level coincide with both global climate changes and minor changes in water salinity varying from fresh to oligohaline. It appears therefore that the most pronounced and widespread deterioration in climate occurred in northeast Africa from 900 to 700 ka, whereas in the Levant the corresponding climatic changes were more moderate.

Early to middle Holocene pollen record from the Laptev Sea (Arctic Siberia)

On the basis of pollen and spore assemblages in sediment core from the eastern Laptev Sea shelf, climatic fluctuations and related changes in vegetation on the adjacent land can be recognized for the time from 11.3 cal. ka BP to 5.3 cal. ka BP. Around 11.3 cal. ka BP, climate was warmer than now and southern shrubby tundra was widely distributed on the coast. Until 10.3 cal. ka BP, shrub tundra dominated and climate was milder than today. The time interval 10.3–9.0 cal. ka BP was marked by increased abundance of arboreal plants; climate became more humid and warmer. In the interval of 9.3–8.0 cal. ka BP, climate was increasingly humid and warm, and forest-tundra vegetation occupied more favorable locations in the region. The increased abundance of arboreal pollen in the shelf zone can be interpreted as a response to the northward displacement of the treeline after 9.0 cal. ka BP. From approximately 7.6 to nearly 5.3 cal. ka BP, southern shrub tundra was renewed and climatic conditions were warmer than now.

Climate-driven environmental change in the Zhada basin, southwestern Tibetan Plateau

The Zhada basin is a large Neogene extensional sag basin in the Tethyan Himalaya of southwestern Tibet. In this paper we examine environmental changes in the Zhada basin using sequence stratigraphy, isotope stratigraphy, and lithostratigraphy. Sequence stratigraphy reveals a long-term tectonic signal in the formation and filling of the Zhada basin, as well as higher-frequency cycles, which we attribute to Milankovitch forcing. The record of Milankovitch cycles in the Zhada basin implies that global climate drove lake and wetland expansion and contraction in the southern Tibetan Plateau from the Late Miocene to the Pleistocene. Sequence stratigraphy shows that the Zhada basin evolved from an overfilled to underfilled basin, but continued evolution was truncated by an abrupt return to fluvial conditions. Isotope stratigraphy shows distinct drying cycles, particularly during times when the basin was underfilled. A long-term environmental change observed in the Zhada basin involves a decrease in abundance of arboreal pollen in favor of nonarboreal pollen. The similarity between the long-term environmental changes in the Zhada basin and those observed elsewhere on and around the Tibetan Plateau suggests that those changes are due to global or regional climate change rather than solely the result of uplift of the Tibetan Plateau.

Holocene vegetation characteristics of the southern Loess Plateau in the Weihe River valley in China

The Loess Plateau has a varied topography that creates a mosaic of hydrological and soil microclimatic conditions, and the study of its vegetation characteristics has been controversial. Two loess–palaeosol sequences of Xindian and Beizhuangcun were selected at different topographic units in the Weihe River valley to reconstruct the vegetation history for the Holocene period using high-resolution pollen analysis. Herb plants typically dominated the Xindian region during the Holocene, and sparse-wood grasslands became prominent around 8200–7700 years BP and 5500–4700 years BP. Forest-grassland covered the area between 7700 and 5500 years BP. Sparse-wood grassland dominated the Beizhuangcun region for most of the Holocene. This region contained mixed coniferous and broad-leaved forest dominated by Pinus between 6800 and 5300 years BP. Around 40% of the arboreal pollen indicates that the forest was relatively open with some grasses and shrubs. Therefore, the sparse-wood grasslands and grasslands were the dominant vegetation types in the Weihe River valley, which has the best hydrothermal conditions on the southern margin of the Loess Plateau. The forest in the Weihe valley only became extensively developed in the Holocene Optimum. Topographic units, terrain composition and loess thickness are the important factors controlling the development of this arboreal vegetation, along with temperature and precipitation.

A late–Middle Pleistocene (Marine Isotope Stage 6) vegetated surface buried by Old Crow tephra at the Palisades, interior Alaska

A 40 cm thick primary bed of Old Crow tephra (131 ± 11 ka), an important stratigraphic marker in eastern Beringia, directly overlies a vegetated surface at Palisades West, on the Yukon River in central Alaska. Analyses of insect, bryophyte, and vascular plant macrofossils from the buried surface and underlying organic-rich silt suggest the local presence of an aquatic environment and mesic shrub-tundra at the time of tephra deposition. Autochthonous plant and insect macrofossils from peat directly overlying Old Crow tephra suggest similar aquatic habitats and hydric to mesic tundra environments, though pollen counts indicate a substantial herbaceous component to the regional tundra vegetation. Trace amounts of arboreal pollen in sediments associated with the tephra probably reflect reworking from older deposits, rather than the local presence of trees. The revised glass fission-track age for Old Crow tephra places its deposition closer to the time of the last interglaciation than earlier age determinations, but stratigraphy and paleoecology of sites with Old Crow tephra indicate a late Marine Isotope Stage 6 age. Regional permafrost degradation and associated thaw slumping are responsible for the close stratigraphic and paleoecological relations between Old Crow tephra and last interglacial deposits at some sites in eastern Beringia.

Evidence disputing deforestation as the cause for the collapse of the ancient Maya polity of Copan, Honduras

Archaeologists have proposed diverse hypotheses to explain the collapse of the southern Maya lowland cities between the 8th and 10th centuries A.D. Although it generally is believed that no single factor was responsible, a commonly accepted cause is environmental degradation as a product of large-scale deforestation. To date, the most compelling scientific evidence used to support this hypothesis comes from the archaeological site of Copan, Honduras, where the analysis of a sediment core suggested a dramatic increase in forest clearance in the Late Classic period (A.D. 600-900). By contrast, in the work presented here, the authors' analysis of a longer sediment core demonstrates that forest cover increased from A.D. 400 to A.D. 900, with arboreal pollen accounting for 59.8-71.0% of the pollen assemblage by approximately A.D. 780-980. The highest levels of deforestation are found about 900 B.C. when, at its peak, herb pollen made up 89.8% of the assemblage. A second, although less pronounced, period of elevated deforestation peaked at approximately A.D. 400 when herb pollen reached 65.3% of the assemblage. The first deforestation event likely coincided with the widespread adoption of agriculture, a pattern found elsewhere in Mesoamerica. The second period of forest clearance probably was associated with the incursion of Maya speakers into the Copan Valley and their subsequent construction of the earliest levels of the Copan Acropolis. These results refute the former hypothesis that the ancient Maya responded to their increasingly large urban population by exhausting, rather than conserving, natural resources.

Microscopic Past of Poutwater Pond

Poutwater Pond Bog is a National Natural Landmark located in Holden, MA. As present-day species inhabiting this bog have been described, this study presents an insight into earlier inhabitants of the area during the mid- to late Holocene. A 5-m coring of peat was collected 10 m from the pond edge. Radiocarbon analysis of 10 sections of the core shows a nearly linear accumulation rate of peatland from 8500 years ago to the present. The presence of mineral matter at the base of the core suggests paulidification as the mechanism for formation of the bog. Microfossils were isolated from sections of the peat core by density-buoyant centrifugation, and examined using a scanning electron microscope. High-resolution images of pollen, sponge remains, and algae are presented. Circumneutral and acidobiontic diatoms were found at different depths of the core, indicating a changing water environment over time. Arboreal pollen grains were documented spanning 8500 years of vegetative history, permitting insight into the biodiversity that once existed.

Cambios en la vegetación durante el Holoceno en la región Norte del Iberá, Corrientes, Argentina

Vegetation changes during the Holocene in the North Iberá, Corrientes, Argentina. Wetlands are very important sites for palynological studies, since they represent one of the most suitable environments for fossil pollen preservation. The aim of this work was to determine, by palynological analysis of lacustrine sediments, the vegetal communities and the predominant environment during the Holocene in NW of Iberá. Two lagoons were studied: San Sebastián and San Juan Poriahú. Sediment samples were obtained with witness using a "Levingstone square-rod sampler", processed with Faegri e Iversen techniques and dated with C14. The palynological graphs were divided in zones using the Tilia program. The palynological analysis allowed visualizing diverse changes in the vegetation: from 6 140 +/- 50 to 5 170 +/- 100 a. C., the NW of Iberá was characterized by marsh-herbaceous vegetation and arboreal vegetation typical of dry vegetation. From 5 170 +/- 100 to 3 460 +/- 60 a. C., a decrease in the species frequency, typical of wet environments, is produced, and the clogging of the waterbody, from 3460 +/- 60 a. C. onwards, while continuing the dominance of herbaceous vegetation typical of these environments, the arboreal pollen, indicates the beginning of a hygrophilous forest development.

Assessment between pollen seasons in areas with different urbanization level related to local vegetation sources and differences in allergen exposure

Pollen data recorded by a single sampler in any given city often fail to reflect particular events occurring in surrounding areas. This is frequently overlooked when interpreting aerobiological results, and therefore pollen data obtained in urban areas may not necessarily be representative of the situation in more rural areas of the same city. Our purpose is to assess differences between allergenic pollen concentrations recorded in an urban area (Eskulap) and a rural/suburban (Morasko) of the same city from 2005 to 2007. Anova-Manova Scheffe, Spearman correlation and Mixed-design ANOVA whitin-subjects effects tests were applied. The results obtained have showed longer pollen seasons, earlier starts of flowering and later conclusion in the urban area. The participation of arboreal pollen in the pollen fall of both sites had enough significative similarities to determine that is linked to regional conditions, while differences in the atmospheric pollen content of herbaceous plants between sites should be due to local conditions.

Holocene vegetation history of the Kotihi lagoon (northwest Peloponnesus, Greece)

Pollen diagrams are presented from two sediment cores from the area of Kotihi lagoon in the northwestern Peloponnesus, Greece. Radiocarbon dates indicate that the analyzed sediments accumulated during the last 7000 years. Six pollen assemblage zones are recognized. The oldest zone, middle Neolithic in age, is characterized by dominance of herbaceous types (NAP). The second zone, dated to the late and final Neolithic, shows a considerable increase in the abundance of arboreal types (AP) and a decrease in herbaceous taxa. The third zone, from the Bronze Age, did not register any substantial change in the vegetation, but the various communities changed considerably. In the fourth zone, from the Iron Age to Roman period, the abundance of arboreal types varied. In the fifth zone, Medieval in age, and in the sixth zone, corresponding to the Ottoman period, arboreal pollen abundances continued to prevail. During the last 3000 years, human activity was the main factor influencing the vegetation in the study area.

Environmental changes over the past c. 29,000 years in the Middle Atlas (Morocco): A record from Lake Ifrah

A borehole core from Lake Ifrah (Middle Atlas, Morocco) provided a unique, continuous record of environmental change spanning the past c. 29,000 years cal BP (29 ka). A study of its organic matter, carbonates and magnetic susceptibility allowed us to reconstruct past climate changes and their impact on the lake's catchment area. The geochemical and pollen data show that the prevailing climate in the Middle Atlas from c. 29 ka to c. 12 ka was cold with a succession of dry and more humid periods. Prior to 24 ka the area surrounding Lake Ifrah enjoyed a relatively wet climate that allowed the survival of rare tree vegetation despite the overall cold conditions. After 12 ka, an increase in primary productivity and arboreal pollen is documented indicating the development of forest vegetation.

From forest to open pastures and fields: cultural landscape development in western Norway inferred from two pollen records representing different spatial scales of vegetation

The cultural landscape development of a farming community in western Norway was investigated through pollen analyses from a lake and a peat/soil profile. The pollen record from the lake indicates that there was a decrease in arboreal pollen (AP) by the end of the Mesolithic period (ca. 4200 cal b.c.), and that a substantial forest clearance occurred during the Bronze Age (ca. 1500 cal b.c.). The latter, together with grazing indicators and cereals, suggests a widespread establishment of farming. At the beginning of the Roman Iron Age there is an increase in heath communities. The pollen diagram from the peat/soil profile shows the forest clearance in the Bronze Age more clearly than the lake profile. This local pollen diagram is compared with modern pollen samples from mown and grazed localities in western Norway. Both analogue matching and ordination (PCA) indicate that the site was characterised by pastures and cereal fields from the Late Bronze Age to the Late Iron Age. An expansion of cereal cultivation took place during the Pre-Roman Iron Age, and an arable field was established at the site after ca. a.d. 800. This investigation illustrates the potential of selecting pollen sites reflecting different spatial scales, and complements the cultural history of the area as inferred from archaeological and historical records.

Pollen assemblages from different agricultural units and their spatial distribution in Anyang area

Pollen analysis is one of the best and possible approaches for the quantitative reconstruction of paleobotany and paleoclimate, and discrimination of human activities. In this paper, we reveal the characteristics of pollen assemblages in different agricultural units and their spatial distribution of major pollen taxa in the Anyang area where the human influences are serious, so as to get more information about climate change and human activities from pollen records. The pollen assemblages of total 122 surface soil samples from different agricultural units (farm lands, vegetable plots, wastelands, cape-lands, woodlands, etc.) indicate that herbaceous pollen dominates the pollen assemblages with an average of 73%, mainly from Poaceae, Artemisia, Chenopodiaceae and Cruciferae; arboreal pollen percentages reach 18%, mainly from Pinus and Ulmus; shrub pollen and fern spores have very low percentages. In general, pollen assemblages are consistent with vegetation composition, though some differences also exist in different agricultural units. In farmlands and vegetable lands, Poaceae pollen has the highest percentages (averaging 27%) compared to other agricultural units with dominant corn or wheat pollen, while in wastelands and woodlands, arboreal and Artemisia pollen percentages have higher values (averaging 20% and 19% respectively). Cruciferae has the highest pollen percentages (70%) in rape-lands. Both pollen assemblages and PCoA can generally identify the vegetable plots, farmlands, woodlands, wastelands, and rape-lands. Pinus and Artemisia pollens mainly appear in the western part of Anyang, which is consistent with the parent plants; Poaceae pollen mainly exist in the eastern part with more farmlands; Chenopodiaceae pollen mainly appear in the urban areas and near major roads where human influences are stronger, Cruciferae pollen can mainly be found in the urban area and in the northwest part of Anyang where more vegetables are planted.

An evaluation of the airborne pollen–precipitation relationship with the superposed epoch method

A statistical analysis was performed on a sample of 4 days sequences in which rainfall occurred during the second day, in order to establish airborne pollen–precipitation relationships. Drizzle (precipitation ≤ 1 mm) and rain (precipitation > 1 mm) events were considered as well as arboreal or non-arboreal pollen. Results showed that arboreal pollen decreases synchronically with the occurrence of a drizzle, registering the minimum value the following day of the precipitation occurrence. The high frequencies of fog and wet soil associated with the following day of drizzle occurrence support the hypothesis that besides the wash out, airborne pollen concentration could decrease by nucleation and impaction processes. As well, diurnal variation suggests that high humidity conditions could also affect pollen emission as already demonstrated by other authors.

Multiproxy lake sediment records at the northern and southern boundaries of the Aspen Parkland region of Manitoba, Canada

Aspen parkland in central Canada may change substantially with increased warming and aridity as prairies replace forests, fire return intervals decrease and lake levels decline. We examined the relationships among vegetation, climate, fire and lake-ecosystem properties using lake sediment cores from the current northern and southern boundaries of the aspen parkland in southwestern Manitoba. We analyzed pollen, charcoal, sediment magnetics, biogenic silica, phosphorus, grain size and LOI, and dated the cores using 210Pb and 14C (AMS, calibrated). The Jones Lake record, from the southern edge of the parkland, began considerably earlier (~11 000 cal. BP) than the Mallard Pond record at the northern edge (~8600 cal. BP). These sites were characterized as prairie communities with low fire severity and relatively low lake productivity during the warm, dry period from 9000 to 6000 cal. BP. Beginning around 6500 cal. BP at Jones Lake and 3400 cal. BP at Mallard Pond, conditions appeared to get wetter as indicated by arboreal pollen percentage increases from ~30% to 40— 60%, concurrent with a rise in charcoal and proxies for lake productivity (biogenic silica and percent organic phosphorus). Similar to previous studies along the prairie—forest border, we found that charcoal increased during warmer, wetter periods with increased forest cover and fuel loading rather than during warmer, drier periods of prairie dominance. Our results underscore the importance of regional changes in moisture, and its effects on lake levels and forest biomass, as a dominant control of the aspen parkland dynamics.

Airborne pollen patterns in Mar del Plata atmosphere (Argentina) and its relationship with meteorological conditions

This work is part of a series of aerobiological researches conducted in the city of Mar del Plata, Argentina. The annual, seasonal and daily features of the pollen cloud were analyzed over 2 years, together with the effects of the meteorological variables. Cupressaceae amounted to 75 and 54% of the annual total in each year, and it was analyzed separately due to its proven overrepresentation. Eighty-five pollen types were registered during the 2 years, bearing a similar annual pattern (more than 50% from August to November, December also being an important month). Arboreal pollen predominated between late winter and spring (61 and 49% of the annual total), while non-arboreal pollen did so from late spring to summer. The observed seasonality was significantly correlated with the monthly mean temperatures and associated with its effect on phenology. No significant differences along the day were detected between years and 50% of the daily total was recorded between 1000 and 1600 hours. The maximum concentration was registered at 1000 hours in spring and summer, but later in autumn and winter. Regarding the hourly scale, the significant correlation of total pollen with temperature and wind speed was positive, albeit negative with relative humidity. These effects are linked to airborne pollen release and transport. The role rainfall plays on airborne pollen is discussed. To interpret the results, it is important to consider the time scale at which the aerobiological phenomenon is analyzed.

Seasonal sedimentation in the Pliocene Villarroya Lake (N Spain) inferred from pollen analysis

High-resolution pollen analysis was performed on a short (8.7 cm thick) section with 94 varve couplets (made up of dark and light laminae) from a lacustrine facies of the Pliocene Villarroya Basin, Spain. The aim of the present study was (i) to verify the seasonality of the sedimentation and (ii) to determine if pollen data record the short-term climatic fluctuations related to variations in laminae thickness and colour. The samples displayed high pollen concentrations and very good taxonomic diversity. The composition of the pollen spectra indicated that the vegetation structure was closely linked to relief: (i) a regional open herbaceous vegetation, (ii) a local marshy and riparian environment, (iii) deciduous mixed forest at mid-altitudes, and (iv) coniferous mixed forest in the surrounding mountains at higher altitudes. In the 48 distinct couplets where the dark and light laminae have been separately sampled, the pollen content showed higher concentrations of early flowering trees in the dark ones, whereas late-flowering plants were more abundant in the light ones. Total pollen concentrations in the 48 couplets were higher in most of their dark layers. These results point to a seasonal layering. According to present-day flowering times, the dark laminae represent sedimentation in winter/spring and the light laminae sedimentation in late summer/autumn. The correlation between the AP (Arboreal Pollen)–NAP (Non-Arboreal Pollen) percentages and lamina thickness linked lamina thickness with the highest values of AP, indicating warmer periods. Variations in the ecological groups enabled us to differentiate eight pollen cycles related to short-term climatic fluctuations. These alternations seem to be more associated with seasonality in precipitation than with temperature oscillations and could be correlated with the NAO/ENSO-like and sunspot-like cycles.