The Holocene spread of Picea abies (L.) Karst. in Fennoscandia and adjacent areas

Aim The Holocene spread of Picea abies in Fennoscandia is well established from many sites and thus provides an opportunity for detailed study of the dynamics of tree spread and population expansion. Early‐ and mid‐Holocene macrofossil evidence for presence of P. abies in Fennoscandia has questioned traditional interpretations of the timing and direction of its spread. This paper aims to determine when, from where and by which pathways P. abies spread into Fennoscandia. Understanding the character and dynamics of this spread may give insight into the general understanding of Holocene tree spread. Location The north‐western distribution of P. abies in Europe, including Norway, Sweden, Finland, Estonia, Latvia, Lithuania, north‐western Russia, parts of Byelorussia and Poland. Methods Holocene pollen diagrams with independent dating control were collected from this region. The timing of the onset of the continuous curve, the timing of the rise of the curve, the first appearance of frequencies of 1%, 3%, 5%, and 10%, as well as timing and the maximum amount of P. abies pollen, was obtained from these pollen diagrams. A GIS analysis was used to display the data and interpolate ages over the area under investigation. Results Maps are presented showing a clear ESE to WNW trend in the spread of P. abies for all characters interpolated. The timing of the rise of the curve was difficult to use as sites east of the Baltic have slowly rising P. abies frequencies while the western sites often show a rapid rise. Main conclusions The spread of P. abies in Fennoscandia and adjacent areas can be separated into two phases: (i) A rapid early Holocene spread out of Byelorussia and northern Russia at low population density giving rise to small outpost populations, possibly as far west as the Scandes Mountains. (ii) A mid‐ to late Holocene front‐like spread at high population densities moving from east to west into the Baltic Republics and Finland, into northern Scandinavia and then moving south and west towards its present‐day distributional limits.     

Scattered late‐glacial and early Holocene tree populations as dispersal nuclei for forest development in north‐eastern European Russia

Aim Concepts about patterns and rates of post‐glacial tree population migration are changing as a result of the increasing amount of palaeobotanical information being provided by macroscopic plant remains. Here we combine macrofossil, pollen and stomata records from five sites in north‐eastern European Russia and summarize the results for the late‐glacial–early Holocene transition. The late‐glacial–early Holocene transition encompasses the first indications of trees (tree‐type Betula, Picea abies, Abies sibirica and Larix sibirica) and subsequent forest development. Considerable time‐lags between the first macrobotanical and/or stomata finds of spruce (Picea abies) and the establishment of a closed forest are reconsidered. Location Pechora basin, north‐eastern European Russia. Methods We used plant macrofossil, stomata, pollen and radiocarbon analyses to reconstruct late‐glacial and early Holocene tree establishment and forest development. The data were derived from lake sediment and peat archives. Results Palaeobotanical data reveal an early Holocene presence (11,500–10,000 cal. yr bp ) of arboreal taxa at all five sites. One site presently located in the northernmost taiga zone, shows the presence of spruce and reproducing tree birch during the late‐glacial. Given the current view of post‐glacial population dynamics and migration rates, it seems likely that the source area of these early tree populations in north‐eastern European Russia was not located in southern Europe but that these populations had local origins. Results thus support the emerging view that the first post‐glacial population expansions in non‐glaciated regions at high latitudes do not reflect migration from the south but were a result of an increase in the size and density of small persisting outlying tree populations. Main conclusions Results suggest that the area east of the margin of the Scandinavian ice sheet to the Ural Mountains had isolated patches of trees during the late‐glacial and early Holocene and that these small populations acted as initial nuclei for population expansion and forest development in the early Holocene.     

Holocene vegetation and climate change from near Lake Pedder, south-west Tasmania, Australia

Aim To use surface pollen and vegetation relationships to aid the interpretation of a Holocene pollen record. Location South‐west Tasmania, Australia. Methods A survey was undertaken of surface‐pollen samples from the major regional vegetation types: alpine, rain forest and moorland. Relationships between vegetation type and surface‐pollen representation were analysed using twinspan classification and ordination. A core was retrieved from moorland vegetation, and interpretation of the fossil pollen sequence was aided using relationships detected in our surface‐pollen analysis. Results Regional vegetation types are reflected in the pollen rain of south‐west Tasmania, despite the over‐representation of important rain forest tree species in samples from non‐forest sites. twinspan classification of the surface‐pollen samples identified the following indicator pollen taxa for each vegetation type: Astelia alpina (alpine); Lagarostrobos franklinii (rain forest); Leptospermum and Melaleuca (moorland). Detrended correspondence analysis of the surface‐pollen samples clearly separates samples from each vegetation type. Correlation of the ordination axes with environmental data identified a dominant temperature/altitudinal gradient in the surface‐pollen data (R = 0.852/0.844). Application of the results of the surface‐pollen analysis to the fossil sequence revealed that fire‐promoted moorland has dominated the local environment around the core site for the entire Holocene. Changes in fossil pollen composition also suggest that temperatures increased through the Late Glacial to peak in the mid‐Holocene and declined thereafter, a trend consistent with other sites in the region. Main conclusions Pollen spectra can successfully be used to predict local vegetation in south‐west Tasmania. At least this part of inland south‐west Tasmania has remained forest‐free throughout the Holocene, conflicting with the dominant palaeoecological paradigm of a mid‐Holocene dominated by rain forest. A comparison with pollen records from moorland vegetation across the region suggests that fire‐promoted moorland has dominated the landscape since the Late Glacial. We suggest that burning by people through the Late Glacial (if not earlier) facilitated the spread of moorland throughout the region, greatly restricting the expansion of rain forest. The continued influence of fire throughout the Holocene in this perennially wet landscape argues for a revision of the dominant human‐occupation model that depicts an abandonment of the interior of south‐west Tasmania in the Late Glacial in response to the expansion of rain forest.     

The significance of the oil palm (Elaeis guineensis Jacq.) in the late Holocene environments of west and west central Africa: A further consideration

Abundant archaeological evidence of the occurrence of the endocarp of the oil palm,Elaeis guineensis, in the rain forest and woodland savanna zones of west and central Africa from about 5000 B.P. has shown the tree to be an important element in the subsistence economy of the region; its pollen also has been recorded in most of the regional terrestrial sediments studied so far. The distinct and consistently sudden and more marked increases in this pollen during the late Holocene when compared with the late Tertiary and late Pleistocene frequencies strongly indicate that the late Holocene upsurges were due to both natural and human factors favourable for the expansion of this heliophytic tree. Reasons are given for suggesting that upsurges in oil palm pollen during the late Holocene period in this region can be used as indices of plant cultivation. While the oil palm is known from early Tertiary deposits in west Africa, its earliest palynological record from terrestrial sediments in the west central part dates back only to the early Holocene. More palynological studies of Tertiary and Quaternary terrestrial cores are required to establish with more certainty the antiquity ofE. guineensis in west central Africa.     

A new Late-glacial and Holocene record of vegetation and fire history from Lago del Greppo, northern Apennines, Italy

Detailed Late-glacial and Holocene palaeoenvironmental records from the northern Apennines with a robust chronology are still rare, though the region has been regarded as a main area of potential refugia of important trees such as Picea abies and Abies alba. We present a new high-resolution pollen and stomata record from Lago del Greppo (1,442 m a.s.l., Pistoia, northern Apennines) that has been dated relying on 12 terrestrial plant macrofossils. Late-glacial woodlands became established before 13000 cal b.p. and were dominated by Pinus and Betula, although more thermophilous taxa such as Quercus, Tilia and Ulmus were already present in the Greppo area, probably at lower altitudes. Abies and Picea expanded locally at the onset of the Holocene at ca. 11500 cal b.p. Fagus sylvatica was the last important tree to expand at ca. 6500 cal b.p., following the decline of Abies. Human impact was generally low throughout the Holocene, and the local woods remained rather closed until the most recent time, ca. a.d. 1700–1800. The vegetational history of Lago del Greppo appears consistent with that of previous investigations in the study region. Late-glacial and Holocene vegetation dynamics in the northern Apennines are very similar to those in the Insubrian southern Alps bordering Switzerland and Italy, across the Po Plain. Similarities between the two areas include the Late-glacial presence of Abies alba, its strong dominance during the Holocene across different vegetation belts from the lowlands to high elevations, as well as its final fire and human-triggered reduction during the mid Holocene. Our new data suggest that isolated and minor Picea abies populations survived the Late-glacial in the foothills of the northern Apennines and that at the onset of the Holocene they moved upwards, reaching the site of Lago del Greppo. Today stands of Picea abies occur only in two small areas in the highest part of the northern Apennines, and they have become extinct elsewhere. Given the forecast global warming, these relict Picea abies stands of the northern Apennines, which have a history of at least 13,000 years, appear severely endangered.     

Tree species dynamics and disturbance in three Swedish boreal forest stands during the last two thousand years

Abstract. Data from three forest stands for the past 2000 yr show how the shade-intolerant species Pinus sylvestris and Betula pubescens maintain significant populations in the Swedish boreal landscape. Age structure data from a northern stand close to the range limits of Picea abies and Pinus complement a local pollen diagram, and reveal cyclic population fluctuations which can be related to periods of climatic stress and fire. Pollen data from two southern stands show that high fire frequencies in the past prevented the expansion of Picea populations. Reduction of the fire frequency during the last 200 yr has favoured Picea. A long time perspective reveals the population dynamics of long-lived species and indicates the controlling factors. Such knowledge permits assessment of the current status and likely future of forest stands.     

Holocene timber-line dynamics at Bachalpsee, a lake at 2265 m a.s.l. in the northern Swiss Alps

Palaeobotanical analysis and radiocarbon dating of lake sediments from Bachalpsee (2265 m a.s.l.), a small lake above the present-day timber-line in the northern Swiss Alps reveals that the region was already deglaciated during the Younger Dryas. The sediment record is dominated by long-distance transported pollen that originates from lowland vegetation but the plant macrofossils give evidence of the local vegetation development. Comparison with palaeobotanical results from three sites along an altitudinal transect permits the reconstruction of the regional timber-line history. Throughout the entire Holocene the catchment of Bachalpsee consisted of a mosaic of open meadows and dwarf shrubs (Salix, Vaccinium, Rhododendron). Chironomid and cladoceran assemblages suggest that the early to mid-Holocene was the warmest interval at Bachalpsee. Comparison of the palaeobotanical results with those from the mire “Feld” (2130 m a.s.l.) in the vicinity of Bachalpsee showed that during the mid-Holocene the timber-line was formed by Pinus cembra and Picea abies with some scattered Abies alba trees and was situated close to Bachalpsee but never reached its catchment. The maximum timber-line in the Northern Alps was reached between 6000 and 3000 cal b.p. which is several millennia later than in the Central Alps. The species composition of the tree-line (Abies alba, Pinus cembra and the absence of Larix decidua) points to less continental and moister climatic conditions compared with the central Alps during the early to mid-Holocene. From 3000 cal b.p. onwards the timber-line was lowered by human deforestation with the most intense pulses of human impact occurring since the Middle Ages. The catchment of Bachalpsee has been used as alpine pasture since the Bronze Age.     

Influence of human impact and bedrock differences on the vegetational history of the Insubrian Southern Alps

Vegetation history for the study region is reconstructed on the basis of pollen, charcoal and AMS¹⁴C investigations of lake sediments from Lago del Segrino (calcareous bedrock) and Lago di Muzzano (siliceous bedrock). Late-glacial forests were characterised byBetula andPinus sylvestris. At the beginning of the Holocene they were replaced by temperate continental forest and shrub communities. A special type of temperate lowland forest, withAbies alba as the most important tree, was present in the period 8300 to 4500 B.P. Subsequently,Fagus, Quercus andAlnus glutinosa were the main forest components andA. alba ceased to be of importance.Castanea sativa andJuglans regia were probably introduced after forest clearance by fire during the first century A.D. On soils derived from siliceous bedrock,C. sativa was already dominant at ca. A.D. 200 (A.D. dates are in calendar years). In limestone areas, however,C. sativa failed to achieve a dominant role. After the introduction ofC. sativa, the main trees were initially oak (Quercus spp.) and later the walnut (Juglans regia). Ostrya carpinifolia became the dominant tree around Lago del Segrino only in the last 100–200 years though it had spread into the area at ca. 5000 cal. B.C. This recent expansion ofOstrya is confirmed at other sites and appears to be controlled by human disturbances involving especially clearance. It is argued that these forests should not be regarded as climax communities. It is suggested that under undisturbed succession they would develop into mixed deciduous forests consisting ofFraxinus excelsior, Tilia, Ulmus, Quercus andAcer.     

Evolutionary implications of nucleotide sequence relatedness between Alnus nepalensis and Alnus glutinosa and also between corresponding Frankia microsymbionts

Frankia DNAs were isolated directly from root nodules of Alnus nepalensis and Alnus nitida collected from various natural sites in India. For comparison, a nodule sample from Alnus glutinosa was also collected from Tuebingen, Germany. Nucleotide sequence analyses of amplified 16S–23S ITS region revealed that one of the microsymbionts from Alnus nepalensis was closely related to the microsymbiont from Alnus glutinosa. A similar exercise on the host was also carried out. It was found that one sample of Alnus nepalensis was closely related to Alnus glutinosa sequence from Europe. Since both Frankia and the host sequences studied revealed proximity between Alnus glutinosa and Alnus nepalensis, it is hypothesised that the common progenitor of all the alders first entered into an association with Frankia, and the symbiotic association has evolved since.     

The vegetational history of the northern Apennines, Italy: information from three new sequences and a review of Regional vegetational change

Abstract. The results of pollen analysis and radiocarbon dating are presented from three northern Apennine sequences; Lago Padule in northern Tuscany and Lago Pratignano and Ospitale in the Emilia-Romagnan Apennines. This is the first detailed pollen stratigraphic information from sites in Emilia-Romagna and north Tuscany and extends eastwards the area from which information on vegetational history is available. The sequence from Lago Padule is one of the most complete Holocene records known from the northern Apennine region. Lago Pratignano has the deepest sequence of organic sediments (1544 cm) and the fastest rates of sediment accumulation (up to 28 cm per 100 years) providing the highest resolution record for the mid to late Holocene periods in the region. High rates of sedimentation have also occurred at Ospitale where organic sediments are 780 cm deep and began to form at approximately 5500 bp. The record from Lago Padule is compared with Holocene records from two nearby sites and a series of Regional Pollen Assemblage Zones is defined for the eastern area of the northern Apennines. The main features of vegetational change identified are: (i) a‘pioneer’phase of rapid forest development during the early Holocene followed by the establishment of an upper forest belt dominated by Abies, and a belt of mixed deciduous forest at lower altitudes; (ii) the appearance and rapid expansion of Fagus between approximately 5200 bp and 2900 bp forming a mixed Abies-Fagus association in the upper forest belt; and (iii) the overall reduction of forest cover, and dominance of Fagus in the arboreal vegetation from around 2900 bp. The scheme of Regional PAZs for the eastern area is used as a framework for the review of pollen stratigraphic information and radiocarbon dates from other sites in the northern Apennine region. Characteristics of pollen records which can be identified in sequences from across the region are identified and the chronology of similar changes in pollen stratigraphy is examined. The scheme of four regional PAZs for the Holocene period is shown to be valid for the entire northern Apennine region. The examination of a series of pollen records shows that Fagus appeared earlier in the western than the eastern part of the region during the mid Holocene and became dominant in the northern Apennine forests post 3000 bp. The impact of anthropogenic activity and climatic change on the spread and development of Fagus are discussed. The palynological evidence which is now available from the northern Apennines is compared with information for the region shown in the‘European pollen maps’of Huntley & Birks (1983). This study provides an updated review of the representation of different tree taxa in Holocene pollen records from the northern Apennines and illustrates the role of the northern Apennines as a refugium for trees during the Wurmian Lateglacial.     

Modelling the spread of Fagus sylvatica and Picea abies in southern Scandinavia during the late Holocene

Aim To test the hypothesis that dispersal characteristics alone can explain the past migration patterns of Fagus sylvatica and Picea abies observed in southern Scandinavia. Location Scandinavia, Europe. Methods The spreading dynamics of both species were analysed using a quantitative data–model comparison approach. Pollen data recording the arrival of the two species at 24 small forest‐hollow sites distributed across the study area were compared with simulated arrival times. The simulations were based on diffusive spread combined with long‐distance dispersal events. By systematically applying different parameter combinations yielding the desired colonization speeds we could identify values for the long‐distance dispersal component that minimized deviations from the observed arrival times. Results According to the minimization process, the optimal spreading rates were 100 m year^?1 for F. sylvatica and 250 m year^?1 for P. abies. Simulated dispersal alone could adequately explain the wave‐like spread of P. abies but failed to explain the scattered establishment pattern observed for F. sylvatica in Scandinavia. At the fine scale of stand establishment, local microclimatic conditions or site disturbance might be more important. The estimated spreading rates are high because the species colonized Scandinavia from different geographic directions and the rates slowed when their ranges overlapped. We present new estimates for the distance and frequency of long‐distance dispersal events for our modelled species. Main conclusions Our analyses suggest that the late Holocene spread of P. abies in Scandinavia was fairly rapid and was limited only by biological processes of dispersal, while that of F. sylvatica was limited by other factors probably controlled by site properties. Picea abies has maintained a rapid and constant rate of spread throughout at least the last 4000 years, despite significant changes in climate. There is uncertainty about the precise relationship between P. abies and climate in Scandinavia, so future distributions are not easy to forecast. For F. sylvatica in Scandinavia, site quality appears to have been a limiting factor, so future land use is likely to dictate its future distribution dynamics in combination with climatic factors.     

Pollen and macroscopic analyses of sediments from two lakes in the High Tatra mountains, Slovakia

The paper presents the results of investigations concerning the accumulation processes, sediment composition, pollen and macroscopic analyses of sediments from the lakes Popradské pleso (1513 m) and Štrbské pleso (1345 m) in the High Tatra mountains, western Carpathians, Slovakia. While Popradské pleso is undoubtedly of glacial origin with silts in the Lateglacial layers and algal gyttja in the Holocene layers, Štrbské pleso or its greater part originated recently between the 16th and the beginning of the 18th centuries when the previous bog of Atlantic or early Subboreal age was flooded with water after the dispersed outflow from the bog depression was blocked. Our pollen and macrofossil analyses indicate mountain tundra in the Lateglacial and a continuous presence of coniferous forest with Picea abies with admixture of Pinus cembra, Larix decidua, Juniperus communis and Pinus cf. mugo in the uppermost elevations at the alpine forest limit since the very beginning of the Holocene. No noticeable oscillation of the forest line can be interpreted from our pollen analyses. It seems probable that its position was controlled by geomorphological and edaphic conditions rather than by the Holocene climatic changes. Spruce forests dominated at elevations between ca. 1000–1400 m during the whole Holocene.     

Middle to Late Holocene vegetation history of the Upper Engadine (Swiss Alps): the role of man and fire

To reconstruct the vegetation and fire history of the Upper Engadine, two continuous sediment cores from Lej da Champfèr and Lej da San Murezzan (Upper Engadine Valley, southeastern Switzerland) were analysed for pollen, plant macrofossils, charcoal and kerogen. The chronologies of the cores are based on 38 radiocarbon dates. Pollen and macrofossil data suggest a rapid afforestation with Betula, Pinus sylvestris, Pinus cembra, and Larix decidua after the retreat of the glaciers from the lake catchments 11,000 cal years ago. This vegetation type persisted until ca. 7300 cal b.p. (5350 b.c.) when Picea replaced Pinus cembra. Pollen indicative of human impact suggests that in this high-mountain region of the central Alps strong anthropogenic activities began during the Early Bronze Age (3900 cal b.p., 1950 b.c.). Local human settlements led to vegetational changes, promoting the expansion of Larix decidua and Alnus viridis. In the case of Larix, continuing land use and especially grazing after fire led to the formation of Larix meadows. The expansion of Alnus viridis was directly induced by fire, as evidenced by time-series analysis. Subsequently, the process of forest conversion into open landscapes continued for millennia and reached its maximum at the end of the Middle Ages at around 500 cal b.p. (a.d. 1450).     

Detecting human impact in the pollen record using data-model comparison

Palaeoecological data are compared with output from climate-driven forest simulation models to separate human influence as a driver of vegetation dynamics from other drivers such as climatic change. The transition from Tilia cordata to Fagus sylvatica dominance in a small forest hollow in Denmark was not predicted by a climate-driven forest simulation model and could be ascribed to anthropogenic impact. This transition can be upscaled to a large region of north-west Europe and contributes to a data-model mismatch for the European distribution of Fagus 6,000 years ago. A data-model mismatch for Picea abies during the last few centuries in southern Scandinavia can also be attributed to anthropogenic impact. Combining pollen data and vegetation models can help with the important task of upscaling from the scale of the forest stand, where anthropogenic impact is readily detectable, to regions and continents, where it is more challenging to distinguish anthropogenic impact from the impacts of climatic change.     

A mid-Holocene vegetational and anthropogenic record in the Guanabara Bay region,Rio de Janeiro State,SE Brazil,assessed by palynological and charcoal data

Palynological and charcoal fragment analyses of Guanabara Bay sediments, as well as radiocarbon dating, were carried out on one 220 cm long sedimentary core collected from the northeast sector of the bay, near the São Gonçalo coast. This study aims at recognising and explaining the environmental history of this region during the mid-Holocene, and to identify the anthropogenic influences on it. The palynological data indicate the predominance of ombrophilous forest vegetation in the Guanabara Bay Hydrographic Basin at c. 6500 calendar years bp. During this period (pollen zone 1), the concentrations of pollen grains and spores may still have been controlled by the Holocene Maximum Transgressive Event. After a phase of low concentrations of palynomorphs, there was a considerable increase in the accumulation patterns of pollen and spore grains (pollen zone 2). This increase can probably be related to the retreat of the sea level event after the Holocene Maximum Transgressive Event. The 75 cm of the core top (pollen zone 3) provide clear evidence of human influence in the area, which is inferred from the significant reduction in ombrophilous forest pollen grains, the significant increase in herbaceous pollen grains, the presence of exotic pollen types (Eucalyptus and Pinus), and high concentration of carbonaceous particles.     

Earliest Holocene vegetation history and island biogeography of the Isle of Man, British Isles

Aim To present radiocarbon dated early Holocene pollen analytical data from two sites on the northern plain of the Isle of Man and to discuss the implications of the vegetation history in relation to severance of the island from the British Isles and to identify further evidence for divergent biogeographical development previously exemplified by the survival and apparent dwarfism of late glacial Megaloceros giganteus (Giant Deer). Location The Isle of Man, British Isles. Methods Pollen analysis and AMS radiocarbon dating of late glacial to early Holocene lake sequences at Pollies and Curragh‐y‐Cowle on the northern plain of the Isle of Man. Results The pollen data indicate a prolonged period of pre‐woodland vegetation after the late Glacial/Holocene transition, which lasted for most of the first post‐glacial millennium. This persistence of pre‐forest environments meant that the expansion of Betula woodland occurred later in this part of the Isle of Man than in adjacent areas of Britain and Ireland. Conclusions The Isle of Man, in the northern Irish Sea, was isolated from Britain during the late Glacial period perhaps explaining the delayed arrival of tree species. Delayed rise of the Holocene forest compared with surrounding regions probably reflects severance of the land‐bridge with Cumbria, but also could be a function of climate changes during the early Holocene and local environmental conditions. Late survival and the dwarfism of the Megaloceros giganteus (Giant Deer) fauna is another example of biogeographical divergence during the early Holocene/late Glacial of the Isle of Man. The delayed afforestation and absence of human hunters in the Manx early Holocene offers a permissive environmental context for the as yet unproven survival of Megaloceros into the early Holocene.     

Postglacial range expansion and population growth of Picea mariana, Picea glauca and Pinus banksiana in the western interior of Canada

The fossil pollen records from the sediments of thirteen lakes are used to reconstruct the postglacial spread and population expansions of Picea mariana (Mill.) B.S.P., Picea glauca (Moench) Voss and Pinus banksiana Lamb. across the western interior of Canada. The objective of this study was to examine temporal and spatial patterns in the growth of the populations and to determine if intraspecific and interspecific variations exist across a range of latitudes and elevations. Pollen accumulation rates (PARs) are estimated from pollen grain counts and sedimentation rates throughout the early to mid-Holocene and are used to represent the population level at the time of pollen deposition. Exponential equations are used to calculate population growth rates. Three-dimensional diagrams (time, space, abundance) are constructed to illustrate range expansion and population growth.The rates of population growth varied from south to north for all three species. Pinus banksiana , on average, had slower population growth rates, and its expansion across the region began over 4000 years later and lasted approximately 1000 years longer than the two Picea species. All three tree taxa experienced reduced rates of population growth at northern high elevation sites. These variations are examined in light of the physical and biological environmental conditions which existed during postglacial range expansion and population growth.     

Detection of the impact of early Holocene hunter-gatherers on vegetation in the Czech Republic, using multivariate analysis of pollen data

Pollen data from the Czech Republic was used to detect the early Holocene impact of hunter-gatherers on vegetation based on a selection of 19 early Holocene pollen profiles, complemented with archaeological information regarding the intensity of local and regional Mesolithic human habitation. Archaeological evidence was assigned to simple categories reflecting the intensity of habitation and distance from pollen sites. Multivariate methods (PCA and RDA) were used to determine relationships between sites and possible anthropogenic pollen indicators and to test how these indicators relate to the archaeological evidence. In several profiles the pollen signal was influenced by local Mesolithic settlement. Specific pollen types (e.g. Calluna vulgaris, Plantago lanceolata, Solanum and Pteridium aquilinum) were found to be significantly correlated with human activity. The role of settlement proximity to the investigation site, the statistical significance of pollen indicators of human activity, as well as the early occurrence of Corylus avellana and its possible anthropogenic dispersal, are discussed.     

Identification of Frankia strains in nodules by hybridization of polymerase chain reaction products with strain-specific oligonucleotide probes

A set of oligonucleotides has been developed to study the competitivity of two Frankia strains in the nodulation of the roots of two host plant species: Alnus glutinosa and Alnus incana. Two 20 mer-oligonucleotides, complementary to highly conserved sequences inside the nifH gene, were used as primers for the polymerase chain reaction (PCR) system in order to amplify microsymbiont DNA extracted from actinorhizae. PCR products were analyzed using two strain-specific 15-mer oligonucleotides identified in the amplified region. Hybridization data indicate that strain ACoN24d is more competitive than train ArI3 in the nodulation of both hosts.     

A comparison of symbiotic nitrogen fixation in Scotland inAlnus glutinosa andAlnus rubra

Summary Alnus glutinosa andAlnus rubra growing in the field in Scotland show specific nitrogenase activities of the same order of magnitude. The period of maximum potential nitrogenase activity coincides with that of maximum growth in late Spring and Summer. It is suggested that the retention of nitrogenase activity into the Autumn when growth has virtually ceased may be important as a contribution to the nitrogenous reserves of the tree.Bioassay of different Scottish soils, all collected from the locality of natural stands ofAlnus glutinosa, showed wide variation in the nodulation of seedlings, although generally a soil poor for nodulation ofAlnus glutinosa generally gave poor nodulation ofAlnus rubra. Soils of pH 4.5 to 6.5, best suited for growth and nitrogen fixation of the two species, often gave nodules showing highest specific nitrogen fixing activity. Young (2 to 3 year old) plants in glasshouse or controlled environment cabinet, inoculated withAlnus glutinosa endophyte, differed from mature field grown plants, however, sinceAlnus rubra required a much larger (up to 2.5 times) mass of root nodules to fix a unit quantity of N. Microscopic comparison of the nodules of glasshouse plants showed that the proportion of cells containing the vesicular (nitrogen fixing) form of the endophyte was only slightly lower inAlnus rubra than inAlnus glutinosa and it is suggested that the differences in specific nitrogen fixing activity between the two species may reflect some incompatibility of function of theAlnus glutinosa endophyte when in symbiosis withAlnus rubra.