Role of man in the history of vegetation of the Ellero valley (maritime Alps, Italy)

The pollen analysis of a sediment core from a peat bog (Rifugio Mondovi) at the mountain belt (1760 m) in the Ellero Valley (Italian Maritime Alps) shows the postglacial vegetation history. The sequence starts at 12,000 BP during a peak of pine pollen; this first phase shows a low representation of birch and the presence of Tilia. Younger Dryas is characterised by increasing percentages of Artemisia, showing the presence of deciduous Quercus, fir and beech. Elm appears at the beginning of the Holocene during the second pine peak (9800 BP). A 3000-year hiatus is present. Sedimentation resumes at 6000 BP in a Rhododendron fir-wood. The present timberline at 1500 m, at the limit of the beech wood, is a result of the decline of the fir-wood at 2600 BP, which allowed an expansion of beech. During this period, there was a continual increase in Gramineae and deciduous oak and the first occurrences of evergreen oak are observed. The development of larch occurs at 1800 BP, together with walnut, chestnut, cereals and vine.     

Variable expression of pathogenesis-related protein allergen in mountain cedar (Juniperus ashei) pollen

Allergic diseases have been increasing in industrialized countries. The environment is thought to have both direct and indirect modulatory effects on disease pathogenesis, including alterating on the allergenicity of pollens. Certain plant proteins known as pathogenesis-related proteins appear to be up-regulated by certain environmental conditions, including pollutants, and some have emerged as important allergens. Thus, the prospect of environmentally regulated expression of plant-derived allergens becomes yet another potential environmental influence on allergic disease. We have identified a novel pathogenesis-related protein allergen, Jun a 3, from mountain cedar (Juniperus ashei) pollen. The serum IgE from patients with hypersensitivity to either mountain cedar or Japanese cedar were shown to bind to native and recombinant Jun a 3 in Western blot analysis and ELISA. Jun a 3 is homologous to members of the thaumatin-like pathogenesis-related (PR-5) plant protein family. The amounts of Jun a 3 extracted from mountain cedar pollen varied up to 5-fold in lots of pollen collected from the same region in different years and between different regions during the same year. Thus, Jun a 3 may contribute not only to the overall allergenicity of mountain cedar pollen, but variable levels of Jun a 3 may alter the allergenic potency of pollens produced under different environmental conditions.     

Evidence of long-distance transport of mountain cedar pollen into Tulsa, Oklahoma

 Previous study of Cupressaceae pollen in the Tulsa atmosphere during December and January suggested that the source of this pollen is the Juniperus ashei (mountain cedar) populations that occur mainly in southern Oklahoma and central Texas. The present investigation examined the evidence of long-distance transport of pollen from these populations during the 1996/1997 season at three sites in Oklahoma using Burkard traps. Two of the pollen-monitoring stations were operated in conjunction with Mesonet meteorological stations. It was found that the December and January Cupressaceae pollen occurs outside of the local season at Tulsa. Pollen concentrations are intermittent and correspond to days of peak concentrations at sites nearer the mountain cedar populations. Peak concentrations are associated with winds coming from the south over the mountain cedar areas. Diurnal rhythms show night-time peaks with a delay in timing at the northern-most site. These results are all consistent with the hypothesis that pollen is being transported over long distances from the mountain cedar populations to Tulsa, Oklahoma. These findings are important as they represent one of the few incidences of long-distance transport of pollen in significant concentrations to an area where the source vegetation is not present. Pollen-monitoring sites located in conjunction with Mesonet meteorological stations provide a unique opportunity to further examine atmospheric conditions during long-distance transport events. This will aid future studies of the spatial modeling of long-distance dispersal of pollen. Received: 20 October 1997 / Revised: 24 June 1998 / Accepted: 26 June 1998     

Altitudinal variation in the reproductive performance of the Mediterranean shrub Rhamnus lycioides L.

Aims Rhamnus lycioides L. subsp. Oleoides (Rhamnaceae) is a perennial shrub native to the Mediterranean Basin distributed along an altitudinal gradient, from sea level up to 1?000 m a.s.l. The specific goals of our study were (i) to compare plant morphology between two contrasting populations, (ii) to determine the reproductive system of R. lycioides, quantifying the relative importance of insects and wind as pollen vectors, (iii) to test if pollen limitation differs between populations, (iv) to study the main factors influencing fruit set and (v) to compare plant reproductive performance (mass allocation to flowers, fruits and seeds) between the two habitats.Methods In the present study, we examined plant morphology and the reproductive performance of R. lycioides L. in contrasting environments in two populations located at the extremes of its altitudinal range in the island of Mallorca (Balearic Islands, Western Mediterranean Basin) along a 3-year period. Plant morphology, the relative importance of insects and wind as pollen vectors, the pollen limitation to seed production and the plant reproductive performance (mass allocation to flowers, fruits and seeds) were determined.Important findings Rhamnus lycioides individuals showed a higher plant surface/plant height ratio at the mountain than at the coast. This species appeared to be ambophilous despite its inconspicuous flowers, although the relative importance of wind as a pollination vector was higher at the mountain than at the coastal site. Fruit set was much higher at the mountain, where pollen appeared to be a limiting factor. By contrast, fruit set was not limited by pollen availability at the coastal population, where resource (water and nutrients) limitation seemed to be more determining. Flower size was greater at the coast, in contrast to fresh fruit weight that was higher at the mountain. Despite the relatively few differences between sites in precipitation patterns along the study period, water availability appeared to be the key factor explaining not only fruit set but also the reproductive performance of this species in the study populations.     

Do moss samples,pollen traps and modern lake sediments all collect pollen in the same way? A comparison from the forest limit area of northernmost Europe

Moss polsters, pollen traps and lake surface sediment samples are commonly used as climate calibration data or as modern analogues for reconstructing vegetation from fossil profiles, but the differences in pollen content between these media have received little attention. This study aims to analyse how the three media differ in reflecting individual vegetation types and spatial differences in vegetation. 119 modern samples (64 moss polsters, 37 lake surface sediment samples and 18 pollen traps from which a collection was made annually) were taken from northern Fennoscandia and the Kola Peninsula as a broad transect crossing the northernmost forest limits of Betula pubescens ssp. czerepanovii (mountain birch), Pinus sylvestris (Scots pine) and Picea abies (Norway spruce). The pollen assemblages from these samples were compared with the surrounding vegetation visually and via PCA (principle components analysis) and cluster analysis. Both comparisons allow a correct distinction between pollen assemblages of arctic/alpine heath, mountain birch dominated areas, and boreal coniferous forests. The differences between the vegetation zones are stronger than the differences between the sampling media. Nevertheless, lake sediment samples from the mountain birch woodland zone tend to overestimate pine and underestimate birch. Pollen traps are biased towards lower tree pollen percentages and higher values of shrubs, herbs and Cyperaceae. This bias is especially strong in traps that have missing years in the data. Irrespective of the vegetation zone, pollen traps tend to have lower Pinus pollen percentages than in the adjacent moss polsters.     

Pollen Dispersal in a Mountain Area

Atmospheric pollen, phenologic and meteorologic data collected during 12 intervals throughout one year in Tauber traps at different elevations allowed conclusions on vertical pollen dispersal in a mountain/valley system in the Niederhorn, Switzerland. Thus, pollen spectra at higher elevations near the timberline cannot be explained by dispersal through upslope winds but through gradient winds, i.e., winds from the general prevailing direction. The gradient wind direction lying perpendicular to the slope in consideration resulted in high elevation pollen spectra representing a regional aspect whereas the lower elevation spectra more or less faithfully recorded the local vegetation. High pollen numbers occur only during the respective local pollen production period. Secondary high pollen numbers related to precipitation maxima amount to about 10%, exceptionally 20% of the total annual pollen of the respective taxon. Thus, the washout of the pollen filtered in the vegetation seems to be of minor importance. Pollen production decreases quantitatively with increasing elevation, even for the same taxon and apparently independent from the actual growth density. This fact, combined with the regionality of the pollen dispersal at high elevation leads to a distortion of the near timberline pollen assemblages in terms of the local vegetation represented. Thus, lowland pollen dispersal mechanism cannot be used to explain pollen dispersal mechanism in mountain/valley systems.     

Climatic control on vegetation and sedimentary dynamics during the Miocene (Burdigalian to Langhian) in northeastern Tunisia

Palynological and sedimentological analyses were performed on Miocene sediments of North-East Tunisia in order to detect the changes in depositional environments, including those linked to eustasy, along with changes in vegetation and climate. The specific integration of palynological (pollen and dinocysts) and sedimentological (including facies analysis) data indicate that shallow marine settings persisted until the early Burdigalian–Langhian, and that open marine environments developed progressively in the late Langhian. Since the early Serravallian, deltaic environments developed under a fluctuating, but predominantly warm climate. The palynological data support a subtropical climate during the Burdigalian, with tropical conditions prevailing at the Langhian–Serravallian transition. The observed high frequency values of megathermic and mega-mesothermic pollen taxa represent the vegetation response to the Miocene climatic optimum (MCO).     

Mountain cedar pollen induces IgE-independent mast cell degranulation, IL-4 production, and intracellular reactive oxygen species generation

Cedar pollens cause severe allergic disease throughout the world. We have previously characterized allergenic pollen glycoproteins from mountain cedar (Juniperus ashei) that bind to allergen-specific immunoglobulin E (IgE). In the present report, we investigated an alternative pathway of mast cell activation by mountain cedar pollen extract through IgE-independent mechanisms. We show that mountain cedar pollen directly induces mast cell serotonin and IL-4 release and enhances release induced by IgE cross-linking. Concomitant with mediator release, high levels of intracellular reactive oxygen species (ROS) were generated, and both ROS and serotonin release were inhibited by anti-oxidants. These findings suggest that alternative mechanisms exist whereby pollen exposure enhances allergic inflammatory mediator release through mechanisms that involve ROS. These mechanisms have the potential for enhancing the allergenic potency of pollens.     

Vegetation development at a mountain settlement site in the Swedish Scandes during the late Holocene: palaeoecological evidence of human-induced deforestation

A palaeoecological study was conducted close to the forest limit in the northern Scandinavian mountain range. The aim was to elucidate the degree to which human impact has affected the vegetation at Hiednikvalta, a Stállo settlement site. Stállo settlements consist of round hut foundations that have a hearth in the middle and are surrounded by a low turf wall. They were probably established by Sámi people using the mountain areas for hunting and/or reindeer herding. In order to separate the effects of humans and climate on the vegetation, a reference area approach was adopted, i.e. the vegetation development at the Stállo settlement site Hiednikvalta was compared with the vegetation development in a forested reference area Avvuhatjåhkkå, at the same altitude as Hiednikvalta but with no archaeological remains of settlements. Peat stratigraphies were retrieved at the two sites and pollen analysis, loss-on-ignition (LOI), pollen accumulation rates (PAR), macrofossil analysis and Betula pollen size statistics were all examined. The results indicate that Hiednikvalta was forested with Betula trees prior to the Stállo settlement period, which occurred between the eighth and thirteenth centuries. Human activities resulted in a decrease in tree cover at the site, as found in a previous study at Adamvalta, another Stállo settlement site in the region. However, the magnitude of vegetation change, and the post-Stállo vegetation development differed between the two areas, suggesting that site-specific factors are important. The use of reference areas in palynological studies is also discussed.     

Reproductive variability and pollen limitation in three Betula taxa in northern Sweden

This 3-yr study documents large variation in pollination and seed quality in birches (Betula) in northern Sweden between taxa, high and low altitude populations, and among years Seed quality was positively correlated with pollination degree and improved by pollen supplementation in B pubescens ssp pubescens in the mountain area, indicating pollen limitation Betula pendula showed the same tendency, but less pronounced Reduced sexual reproduction of B pendula in the mountain area might more often be due to limited resources for seed maturation and defense of the seeds against predispersal seed predation In contrast, coastal populations of both species display relatively high pollination rates and supplemental pollination had no effect on seed quality, suggesting that pollen limitation is rare or absent here The mountain birch Betula pubescens ssp tortuosa showed generally lower pollination and seed quality compared with B pubescens ssp pubescens , but not compared with mountain populations of B pendula It is concluded that pollen limitation may occur in Betula , but to what extent varies with taxon, altitude and year The seed quality is also strongly affected by other factors such as infections of gall midges (Semudobia spp, Diptera Cecidomyndae) and incomplete seed maturation     

Pine needles and pollen grains of Pinus mugo Turra – A biomonitoring tool in high mountain habitats identifying environmental contamination

Pinus mugo Turra is a typical pine tree from mountain habitats. It is ideal as a bioindicator for air quality monitoring, but, to the best of our knowledge, has never been implemented to determine organic compound concentrations. This study presents the initial methodology for the use of pine needles to measure contamination levels and evaluate genotoxicity potentials caused by long-range transport of pollutants at sites in the Slovak mountains in comparison to an industrial urban area. Pinus mugo needles have many positive attributes, particularly the five-year lifetime of needles compared with other species of pine. The presence of epicuticular wax on the surface of needles allows accumulation of lipophilic organic compounds. Pine needles were analyzed for POP compounds (PCBs, OCPs, PBDEs), PAHs, PFCs and lead. A pollen grain abortion assay with Pinus mugo species was also tested as a method to identify contamination of high mountain habitats. The concentration of organic compounds increased proportionally with needle age. Concentrations along the mountain transect were heavily influenced by atmospheric transport and proximity to potential sources of contamination from industry and residential areas from north and south of the mountain. The slope exposure direction had a large impact on concentrations of PBDEs (mainly for BDE 209). High concentrations of PFCs were discovered near a ski resort, where the use of these substances is high due to fluorinated ski waxes and personal outdoor clothing. A positive correlation between pollen grain abortivity and elevation was observed, with the strongest effect on pollutants at the top of the mountains. The results showed the highest genotoxicity at the site near a pulp mill (Zilina), where the frequency of abortive pollen grains was 3.1 times higher than at the control site. Lead content increased gradually with needle age, and a correlation was found between Pb levels in needles and pollen abortivity. It can be concluded that Pinus mugo is a suitable bioindicator species for assessment of long-term trends of atmospheric contamination in high mountain habitats.     

Investigating a flower-insect forager network in a mountain grassland community using pollen DNA barcoding

Faced with the decline of pollinators, it is relevant to strengthen our understanding of the whole plant-pollinator web in semi-natural grasslands that serve as refuges for pollinator populations. The aim of this study was to explore the diversity of flower-foraging insects involved in pollen transfer in mountain semi-natural grasslands. Insects actively collecting pollen and/or nectar were caught in spring in six mountain semi-natural grasslands displaying a floristic richness gradient. Individual determinations of insects were made at the finest possible taxonomic scale and pollen loads were removed from the insect body. Using next-generation DNA sequencing, pollens were identified through the ribosomal DNA cistron using the ITS2 database and the ITS plant rDNA cistron sequences from Genbank. A total of 236 flower-foraging insects were collected. Diptera represented 82% of the total catches distantly followed by Hymenoptera (15%) and Apoidea (bees) (11%). Visual observations revealed that Diptera foraged on 16 of the 21 flower species visited by insects. DNA metabarcoding showed that 82% (191) of all of the collected insects were carrying pollen and 44% (104) were carrying two genera of plants or more. Our results demonstrate that Diptera are potential key-pollinators in mountain semi-natural grasslands that cannot be overlooked by the scientific community. However difficulties of taxonomic determination due to severe shortage of experts for Diptera have to be urgently overcome. Further studies on the link between pollen transfer and actual pollination in a global change context are also required. Moreover, our results support the idea that DNA metabarcoding provides accurate information about the plants-insects networks but it also pointed out sensitive issues, especially the necessity to build reliable national barcode databases.     

Enrichment of airborne Japanese cedar (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis>) pollen in mountain ranges when passing through a front accompanying temperate low pressure

Values obtained by the real-time pollen monitors set up at 14 measuring points in the Tohoku region indicate that a large amount of Japanese cedar pollen was dispersed along the western region and northern flank of the Ou Mountain Range when a front accompanying the temperate low pressures passed through the west sea of northern Hokkaido. We are sure that this phenomenon is related to pollen enrichment by mountain ranges. The time at which highest concentrations of pollen grains were observed shifted from the western to the eastern side, in accordance with the path of the front. No pollen was seen after the passage of the cold front.     

Occurrence of Lewis a epitope in N-glycans of a glycoallergen, Jun a 1, from mountain cedar (Juniperus ashei) pollen

We have determined the structures of N-glycans linked to major allergens in the mountain cedar (Juniperus ashei) pollen, Jun a 1. First, two kinds of the pollen glycoallergen (Jun a 1-A and Jun a 1-B) were purified from partially purified Jun a 1 by cation exchange chromatography. The N-glycans were liberated by hydrazinolysis from the two glycoallergens and the resulting sugar chains were N-acetylated and then coupled with 2-aminopyridine. Three pyridylaminated sugar chains were purified by reversed-phase HPLC and size-fractionation HPLC from Jun a 1-A and Jun a 1-B respectively. The structures were determined by a combination of exo- and endo-glycosidase digestions, two dimensional sugar chain mapping, and electrospray ionization mass spectrometry (ESI-MS) analysis. Structural analysis indicated that Lewis a epitope (Galbeta1-3(Fucalpha1-4)GlcNAcbeta1-) occurs in the N-glycans of the pollen allergens.     

The start of the birch pollen season in Finnish Lapland: separating non‐local from local birch pollen and the implication for allergy sufferers

Determining the start of the birch pollen season requires the reliable separation of non‐local from locally produced birch pollen. The research was undertaken close to the latitudinal birch tree line at the Kevo Subarctic Research Institute (69°45′N 27°01′E) in northern Finland. By comparing phenological and aerobiological observations, the proportion of birch pollen present in the air before local anthesis commences can be delimited. We coupled this with data of pollen deposition monitored by means of a modified Tauber trap. The dominant birch species at Kevo is the mountain birch Betula pubescens ssp. czerepanovii, whereas B. pubescens ssp. pubescens is very rare, hence we consider the proportion of the southerly B. pubescens‐type pollen deposited in the pollen trap to be non‐local in origin.

We did not observe any trend towards an earlier start of the phenologically observed mountain birch anthesis at Kevo as predicted from work elsewhere. Moreover, the fixed 2.5% threshold method for determining the birch pollen season proved not to be applicable since in many years this threshold was reached before the end of continuous snow cover. The results indicate that in some years non‐local birch pollen contributes considerably to the allergen load in Lapland with up to 57% of the total birch pollen sum being recorded before the day on which local anthesis commenced, and up to 70% of the annual birch pollen deposited being of the southerly birch type.     

Preliminary study on pollen distribution in the surface soil of the Turpan region in the southern slope of Tianshan Mountains,Xinjiang, China

Aims Our main purposes were to analyze the relationship between vegetation and pollen in the surface soil of the Turpan region, which is located in the southern slope of the eastern Tianshan Mountains, and to compare different pollen assemblages between the Turpan region and the northern slope of the Tianshan Mountains.Methods We collected 36 modern pollen samples and carried out modern vegetation survey in the Turpan region along an altitudinal gradient from 2 000 m to -154 m. Detrended correspondence analysis and Redundancy analysis were applied to analyze the distribution pattern of pollen in surface soils. Important findings We divided the pollen spectra into four pollen assemblage zones (mountain desert-steppe and desert, Gobi gravel, typical desert and salt mash vegetation), corresponding to the major vegetation types in the Turpan region. When compared with the northern slope, the characteristics of pollen assemblages in the mountain desert-steppe and desert were similar to those in the forest-steppe on the northern slope of the Tianshan Mountains; the pollen assemblages in the Gobi gravel and the typical desert seemed to be more consistent with those in the typical desert on the northern slope; however, no analogue was found in the salt mash vegetation. Obviously, the vertical pollen spectra in Turpan region were incomplete, lacking typical forest and Artemisia desert pollen zones. Besides, similar pollen zones in the Turpan region were found at an elevation of about 300 m higher than those in the northern slope. It is remarkable that the typical tree pollen, such as Picea and Pinus, showed their extra representation in the Turpan region. On one hand, the valley forest on the southern slope of the Tianshan mountains played an important role in pollen dispersal. On the other hand, with the cold air on the northern slope over the Tianshan Mountains, pollen may be carried and deposited in the Turpan region. The rivers feeding into Aiding Lake in the Turpan region may also contribute to the distribution of Picea and Pinuspollen. Lots of pollen studies have shown that the ratio of Artemisia to Chenopodiaceae (A/C) can be used as a good indicator of the degree of humidity in the semi-arid and arid areas. Our study revealed that A/C can roughly reflect the characteristics of the desert zone in the study area. The results of Redundancy Analysis ordination on pollen assemblages and environmental factors (mean annual temperature (MAT), mean annual precipitation (MAP) and altitude (ALT)) revealed that MAP was the main environmental factor affecting the pollen assemblages in the surface soil in the Turpan region and had more significant effects on the distribution of Nitraria pollen than on the distribution of Artemisia and Chenopodiaceae.     

Sporo-Pollen Dissemination and Quantitative Character of Surface Sample of Manzhouli-Dayangshu Region

According to the profile of modern vegetation and pollen analysis of surface samples, the character of sporo-pollen assemblages from the steppe of Huluengbar to forest of Daxinganling mountain being investigated, indicated that, there existed a sylvosteppe zone in between the steppe and forest zones, in which the percentage of A. P. is a little more than that of N. A. P. (about 30%～70%). At the same time a nonlinear correlation was found between the percentage of pollen and the abundance of maternal plant. There were three states in the of plant/pollen system: (1)inferior position with abundance of pollen or the maternal plant both less than 30% or 20% .(2) dominant position with both over 70% and (3) mixed pisition with both between 30%～70%. In the first state, there existed a value of Po (pollen from another place) or Vo (short of pollen, or if none at all) in the second state, the linear correlation of pollen and plant became nonlinear and only in the third state, did the correction factor (value of R) approach constant.     

热带雨林的孢粉垂直分布规律——以海南岛现代孢粉雨为例

热带地区环境变化对研究全球气候变化显得越来越重要,热带地区的古环境记录,特别是孢粉记录是恢复过去气候的重要方法,东亚热带地区在冰期－间冰期的气候影响下,生态环境主要表现为山地植被带的垂直升降,因此,定量恢复热带地区第四纪植被垂直移动的幅度,以及作为古气候的替代性指标进行数量化转换是热带地区孢粉研究的关键,然而,我国热带地区现代孢粉雨和植被的关系研究程度较低,给热带第四纪孢粉古生态的恢复和对比带来困难,本研究较系统地总结了海南岛从低地平原到五指山1860m的垂直植被带表土的孢粉散布规律,为热带地区孢粉古环境的重建提供了新的基础数据。研究结果表明,孢粉组合的变化与垂直植被带紧密相关,孢粉的多样性随海拔升高而降低,其中针叶类随海拔升高而增加,蕨类孢子则相应减少,在低地和低山丘陵,孢粉组合显示出为干扰的影响,如防风雨的主要树种木麻黄（Casuarina),行道树台湾相思（Acacia richii)和人为砍伐后大面积生长的芒箕（Dicranopteris)群落等在一些孢粉谱中特别高,尽管如此,孢粉组合反映的垂直植被带变化仍然是清楚的,海南岛由下至上可划分出5个表土孢粉组合带－低地人类强烈干扰带（＜400m):Mallotus,Casuarina,Pinus,Myrica,Palmae,Poaceaae,Dicranopteris:--低地质陵地带（400－800m):Quercus,Castanopsis,Mallotus,Myrica,Platea,Meliaceae和大量孢子（包括Dicranopteris);--山地下带（800-1200m):Castanopsis,Quercus,Podocarpus,Dacrydium,Cyathea和单缝孢子;－－山地上带（1200-1600m):Dacrydium,Pinus,Altingia,Quercus,Castanopsis;－－山顶带（＞1600m):Pinus,Rhododendron,Dacrydium,Symplocos.     

The Late Pleistocene faunal assemblage from Cava Muracci (Latium,Italy): Palaeoenvironmental implications for coastal central Italy during MIS 3

Palaeoenvironmental information on Marine Isotope Stage 3 (MIS 3) coastal Latium is sparse, mainly based on studies of isolated faunal assemblages or long pollen records from lake sediments, often of insufficient resolution to aid in palaeoenvironmental reconstruction. This study describes in detail the Late Pleistocene faunal assemblage from layers SU11 and SU12 of Cava Muracci (Cisterna di Latina, central Italy), the first of which is a partially-preserved hyena den. The first multi-disciplinary palaeoenvironmental reconstruction of coastal Latium between 34–44 ka BP, a critical time span for the presence of the latest Neanderthals and the arrival of Anatomically Modern Humans (AMH), is provided combining palaeoecological inferences from a previous pollen study of hyena coprolites with the palaeontological study described here. The results indicate a temperate climate and a landscape characterised by the coexistence of at least three habitats within a short distance between the coastline and the inland mountains, suitable for a wide variety of species.     

Vegetation history and lake-level changes from the Younger Dryas to the present in Eastern Pyrenees (France): pollen, plant macrofossils and lithostratigraphy from Lake Racou (2000 m a.s.l.)

A multi-proxy palaeoecological investigation including pollen, plant macrofossil, radiocarbon and sedimentological analyses, was performed on a small mountain lake in the Eastern Pyrenees. This has allowed the reconstruction of: (1) the vegetation history of the area based on five pollen diagrams and eight AMS¹⁴C dates and (2) the past lake-level changes, based on plant macrofossil, lithological and pollen analysis of two stratigraphical transects correlated by pollen analysis. The palaeolake may have appeared before the Younger Dryas; the lake-level was low and the vegetation dominated by cold steppic grasslands. The lake-level rose to its highest level during the Holocene in the Middle Atlantic (at ca. 5060±45 b.p.). Postglacial forests (Quercetum mixtum and Abieto-Fagetum) developed progressively in the lower part of the valley, while dense Pinus uncinata forests rapidly invaded the surroundings of the mire and remained the dominant local vegetation until present. The observed lowering of the lake levels during the Late Atlantic and the Subboreal (from 5060 ± B.P. to 3590±40 b.p.) was related to the overgrowth of the mire. The first obvious indications of anthropogenic disturbances of the vegetation are recorded at the Atlantic/Subboreal boundary as a reduction in the forest component, which has accelerated during the last two millennia.