The late Holocene palaeoecological sequence of Serranía de las Villuercas (southern Meseta,western Spain)

New pollen results and radiocarbon dating from a valley mire in south-western Spain are presented. This is a region where few palaeoecological records have been preserved and the sequence yields important new palaeobotanical evidence for the late Holocene. The landscape is shown as having been largely open woodland, but more wooded than at present. The vegetation history of the last four millennia in these montane territories of south-western Iberia is discussed in the light of anthropogenic indicators, archaeological and documentary archives; fire incidence and climate change. Alnus is the predominant pollen type, although a decline is noted during the last couple of centuries. Its presence is connected with local topography behaving as a phreatophyte, that is, a plant which obtains a significant amount of water from the zone of saturated soil. A framework is also provided for the age and ecological dynamics of some major woodland taxa—Betula, Corylus, Ilex, evergreen and deciduous oaks, Ericaceae and Pinus. In addition, the natural status of several pollen taxa and local trends in biodiversity are discussed. We consider that the results of our work will have important implications for the understanding of the vegetation history in a floristically very rich area, with a noticeable diversity of woody taxa, and a relatively well preserved ecosystem structure.     

Woodland history of northern Greece from the mid Holocene to recent time based on evidence from peat pollen profiles

The woodland history of the northern mountainous parts of Greece is considered in the context of pollen profiles from bogs in Rhodopes, Lailias-Vrontou, Paiko, Voras and Pieria. In the time period covered by these diagrams (only those from Voras and Lailias extend back to the 7th millennium B.P.) the overall trends in the woodland history at the particular sites are comparable but there are also substantial differences that are attributed to the effects of human influence which varied in time, intensify and extent. The earlier phase, which corresponds to the Atlantic period of Firbas, is characterized by mixed deciduous woodlands with Quercus or Tilia the main components. This is followed by the phase (Subboreal) in which coniferous woodlands, which consisted of Abies and Pinus, dominated. In this time, Fagus gradually expanded. In the final phase (Subatlantic), Abies becomes more or less extinct and Fagus has a dominant role. These developments broadly correspond with those recorded in pollen profiles from Central Europe.     

Mid to late Holocene vegetation and land use history in the Weald of south-eastern England: multiple pollen profiles from the Rye area

The High Weald is an unusually well-wooded area in southern England. A high proportion of this woodland is ancient, being formerly exploited as seasonal pasture and coppice. Multiple pollen profiles from the Rye area have been used to elucidate the origins of this cultural landscape. By combining sites with small and large pollen source areas, both local and regional patterns of vegetation change have been determined. The mid-Holocene Tilia-dominated woodlands were subjected to temporary clearance as early as the Neolithic. This woodland was more extensively exploited over a ca. 700 year period from the beginning of the Bronze Age. The main elements of the modern landscape (woodland, pasture and limited cultivation) can be traced back to a more intensive phase of human activity, which commenced in the late Bronze Age. A regional increase in Fagus sylvatica pollen ca. 750 B.C. probably reflects the use of the Wealden woods for pasturage. There is no palynological evidence that the fuel demands of the Roman iron industry resulted in widespread woodland destruction. The early Anglo-Saxon period appears to have been one of land-use continuity, with a second increase in Fagus pollen at ca. A.D. 700 corresponding to historical evidence for the presence of wood-pastures in the Weald.     

Postglacial vegetation history in Luxembourg: new charcoal data from the cave of la Karelslé (Waldbillig, eastern Gutland)

The archaeological site of La Karelslé (Waldbillig, Luxembourg) provides the first important charcoal sequence in Luxembourg for the development of Holocene plant cover. During the Pre-boreal, the results show open woodland vegetation dominated by Pinus sylvestris type in association with Betula sp. and Rosaceae. After an important gap covering the Boreal and the early Atlantic, the data reveal the dominance of a deciduous Quercus woodland with Tilia sp., Fraxinus excelsior and Corylus avellana. Finally during the sub-Boreal, the assemblages indicate a cooler and wetter climate and Quercus woods with Fagus sylvatica and Taxus baccata. There is no clear evidence for human impact. Received June 5, 2001 / Accepted December 3, 2001     

Pollen limitation and fruit abortion in a declining rare tree,the Eurasian yew (Taxus baccata L.): A reproductive cost of ecological marginality

Populations of rare tree species such as the dioecious and anemophilous yew (Taxus baccata) are especially prone to extinction if they occupy marginal habitats. This is the case of yew populations growing in Mediterranean mountains under dry climate and a severe anthropogenic disturbance regime, which show insufficient regeneration. We examined two of the likely mechanisms driving this population decline. The study was conducted in a central Spanish yew population in 2005 and 2006. On one hand, we tested for the effect of the amount of pollen received by female flowers by means of a pollen addition experiment. On the other hand, we tested for the effect of initial fruit set on abortion and mature fruit production. Finally, we evaluated the effect of the spatial arrangement of male and female yew trees on realized fecundity. The success of fertilization and fruiting in the experimental population was pollen-limited. Female trees aborted ca. 70% of the fruit set in both years and treatments. Fruit set was significantly influenced by the females' neighbourhood, with fecundity decreasing exponentially with distance to the nearest male in both years. Overall, our results indicate that factors associated with ecological marginality have a strong influence on yew performance.     

Isolation and characterization of polymorphic nuclear microsatellite loci in <Emphasis Type="Italic">Taxus baccata</Emphasis> L.

Seven polymorphic nuclear microsatellite markers for Taxus baccata L. (English yew) were developed using an enriched-library method. An additional polymorphic SSR was obtained by testing eight primer pairs from the congeneric species Taxus sumatrana. Mendelian inheritance for the seven Taxus baccata SSRs was proved by genotyping 17 individuals and 124 megagametophytes (conifer seed haploid tissue). A total of 96 individuals from 5 different populations (10–26 samples per population) were used to estimate genetic diversity parameters. High levels of genetic diversity, with values ranging from 0.533 to 0.929 (6–28 alleles per SSR) were found. No linkage disequilibrium between pairs of loci was detected. All loci but one showed significant departures from Hardy–Weinberg equilibrium. Excess of homozygosity was probably due to high inbreeding in English yew populations, an outcome of low effective population size and/or fragmented distribution. Highly polymorphic SSRs will be used to conduct population genetic studies at different geographical scales and to monitor gene flow.     

Étude en culturein vitro de la dormance embryonnaire chezTaxus baccata L.

Mature seeds ofTaxus baccata L. andTaxus baccata L.fastigiata Loudon contain embryos which are both immature and dormant. Embryo cultures were carried out in order to test the relative effciency of gibberellins (GA₃ and GA₄), chilling and leaching. The increase of germination percentages depends on the treatment applied and the tested variety. WithTaxus baccata, the germination of which is very difficult, a double treatment either leaching and gibberellins or leaching and chilling are necessary to obtain a high percentage of germination. Our results are compared with facts already known on mature dormant embryos of other plants.     

Understanding the changing value of natural resources: an integrated palaeoecological–historical investigation into grazing–woodland interactions by Loch Awe, Western Highlands of Scotland

Aim We aim to compare fine resolution pollen data from a former seasonal pasture with historical evidence for grazing and woodland use. We discuss the complexities and benefits of integrating qualitative and quantitative information, and the implications for studies of past wood–grazing interactions and their relevance to current conservation management. Location Corries is an abandoned farm township in Scotland's Western Highlands. Methods Two sources were used: (1) pollen evidence from a former seasonal pasture, analysed at c. 20‐year intervals and dated using ¹⁴C and ²¹⁰Pb, provides a c. 1100‐year local vegetation and land‐use history; (2) written sources document resource regulation and changing socio‐economic circumstances at local to national scales over the last c. 400 years. Results Each source records woodland and livestock management at different spatial and temporal scales: written evidence provides a clearer understanding of general (estate) rather than farm‐scale changes, while small pollen basins record localized woodland–grazing dynamics, which can be difficult to extrapolate to the landscape scale. Both sources indicate a dynamic wood–grazing balance and together provide clearer evidence for incentives and drivers controlling this relationship. The first palynological phase of woodland incursion (ad c. 1210–1490) pre‐dates the surviving written records, but a second (ad c. 1680–1760) occurs during a period of increasing market value for cattle, when farmers may have increased grazing despite regulations to protect woods. The site is not representative of grazing intensification associated with the introduction of extensive sheep farming because the farmer protected the woods (ad c. 1760–1880) until they were cleared (ad c. 1880–1920) for quarrying (ad 1885–1904), which accounts for the limited palynological evidence for grazing. Main conclusions Written evidence for past stocking levels is too fragmentary and ambiguous to allow long‐term quantitative analysis, but a local historical context is important for interpreting local pollen records. Management decisions that determined grazing–woodland interactions were shaped by changing values, markets, agricultural practices and regulatory structures, which can result in nonlinear relationships between stocking levels and woodland continuity. Many woods were managed for multiple purposes in the past and promoting natural processes or pursuing pre‐anthropogenic baselines will result in the erosion of cultural features that have shaped present landscape values.     

Past vegetation dynamics of Vltavský luh, upper Vltava river valley in the Šumava mountains. Czech Republic

Six pollen diagrams from peat bogs in the Vltavsky luh (upper Vltava river valley) provide new information about vegetation reconstruction, woodland dynamics, and local development of mires during the Late-glacial and Holocene. Vegetation development began in the Oldest Dryas/B?ling with open park plant cover. In the Aller?d, woodland with Pinus and Betula developed, and in the Younger Dryas there was a steppe tundra with plants of open habitats. In the Pre-boreal, woodland tundra grew. In the Boreal, Corylus spread, and a major expansion of Picea began in the early Boreal. Picea spread during the Atlantic probably by two different migration routes. Fagus immigrated earlier than in the Bayerischer Wald and Oberpf?lzer Wald in the adjoining parts of Germany, and had its major expansion in the early Atlantic. Abies expanded in the late Atlantic. The great abundance of Abies in this area is remarkable, forming Abies or Abies-Fagus woods in less extreme habitats. Human occupation started in the Sub-boreal, as shown by both archaeology and palynology. However, human impact is recognized from anthropogenic indicators which appear in the early Atlantic. At the end of the later Sub-atlantic the development of natural woodland was interrupted by plantation of Picea according to historical and palynological evidence. Received November 13, 2000 / Accepted July 7, 2001     

Understorey foraging and habitat selection by sheep in mixed Atlantic woodland

Abstract. The main objectives of this study were to investigate sheep foraging behaviour in mixed Atlantic woodland and to assess its impact on the forest understorey. We established 89 plots along four forest types: Fagus woodland, Quercus woodland, riparian gallery forest and conifer plantations. The presence of plant species in the forest understorey and their foraging damage was surveyed bimonthly from July 1996 to June 1997. In addition, we estimated the selection of woodland types by sheep through the pellet‐group count technique. The intensity of foraging by sheep was negligible for most of the plant species, however several species showed substantial damage in some woodland types. Among the species that were abundant and widespread in the entire study area, Rubus ulmifolius, graminoids and Ilex aquifolium were consumed most. Sheep selected only larch plantations, where grasses and Rubus were very abundant. This grazing behaviour reduced browsing damage of the understorey of woodland stands with higher conservation value, such as Quercus and Fagus woodlands.     

Effects of browsing in relation to vegetation cover on common yew (<Emphasis Type="Italic">Taxus baccata</Emphasis> L.) recruitment in Mediterranean environments

Common yew (Taxus baccata L.) stands are recognized as prioritary habitats for biodiversity conservation within the European Union. The effects of browsing on the regeneration capacity and spatial dispersal of T. baccata recruits at the European southern limit of the species in the Mediterranean Basin have been herein studied. The efficacy of T. baccata recruitment has been evaluated at six localities in the Northern Sardinia mountains, which have similar altitude, climate, soil, and vegetation but have different types of uses (three were grazed by livestock and three were not). At each site, five habitats have been identified for T. baccata seed dispersal: reproductive female T. baccata canopy, reproductive female Ilex aquifolium canopy, non-fleshy-fruited tree canopy, fleshy-fruited shrubs, and open areas. The density of seedlings was found to be greater under fleshy-fruited trees (reproductive female T. baccata and I. aquifolium) than under shrubs, whereas the sapling density was higher in shrubby habitats, especially at grazed sites due to the mechanical protection afforded by the spiny shrubs against herbivores. Land use (LU) has been found to be the most important factor in determining the spatial distribution of seedlings and saplings in relation to forest habitats. Although browsers had an ephemeral but positive effect on seed germination through their trampling and the resultant scarification, this process eventually became ineffective as was shown by the occurrence of the lowest density of saplings in those habitats where the density of seedlings was the highest. The ultimate and most important effect of browsing was the sharp decrease in the density of saplings, and their almost complete extinction, in non-shrubby habitats. This study highlights the result that, in Mediterranean ecosystems, browsing constitutes the main negative factor on T. baccata seedling-sapling transition and furthermore confirms the necessity to preserve shrubby patches in the vicinity of reproductive female T. baccata and I. aquifolium to permit the regeneration of T. baccata in the presence of livestock. Moreover, at ungrazed sites, T. baccata is able to colonize non-shrubby shady habitats. The application of different management strategies to ungrazed and grazed sites should therefore be the main direction in the management and preservation of T. baccata stands in the Mediterranean region.     

WIND POLLINATION OF TAXUS CUSPIDATA

The air disturbance patterns created by and around the ovules of Taxus cuspidata are quantified for various orientations to the direction of ambient airflow, and are shown to largely dictate the motion (vectoral trajectories) and mode of deposition of windborne pollen on ovule surfaces. Perpendicular orientation to the direction of airflow results in two regions characterized by high densities of adhering pollen — one on the windward surface of the ovule, resulting from direct inertial collision, and another on the leeward surface resulting from non-inertial sedimentation. Parallel and inclined orientations of the ovule to the direction of airflow produce quantitative and qualitative variations in the pattern of adhering pollen resulting from inertial and non-inertial deposition. Direct collision of windborne pollen grains with the micropylar ends of ovules occurs for all orientations to wind direction. The aerodynamics of the ovulate shoot complex of Taxus cuspidata is related to that previously described for conifer ovulate cones, cycad megastrobili, and simulated wind tunnel analyses of archaic Paleozoic ovules based on scale models. Water transport of pollen (adhering to integument and bract surfaces) to micropyles quantitatively alters the distribution of adhering pollen grains on ovule surfaces. Although there is no evidence that pollen grains of this species are osmotically ruptured, observations do not preclude the possibility that water transport of pollen may reduce the number of viable pollen grains reaching the micropyle.     

Production of taxanes by Taxus baccata plant cells

In callus cultures of Taxus baccata grown on agar media according to Murashige and Skoog supplemented with different growth hormones 8 taxol analogues were identified.     

Changes in intracellular localization of peroxidase during Microsporogenesis in Gymnosperms

Cytochemical investigations on peroxidase localization during microsporogenesis inLarix europaea D.C.,Taxus baccata L. andPinus sylvestris L. have revealed striking differences in the localization and activity level of this enzyme linked with the developmental stage. The localization and level of activity of peroxidase, typical of each stage, changed in the course of microsporogenesis in a strictly orderly way, giving a characteristic and stable pattern. The pattern of intracellular peroxidase localization proved to be the same for microsporogenesis of all the gymnosperms in question. It is suggested that the identity of that pattern in plants so phylogenetically distant asTaxus baccata L. andPinus sylvestris L. indicates that peroxidase activity in gymnosperms’ microsporogenesis is connected with the fundamental and genetically well stabilized processes of meiotic cytodifferentiation. Moreover, enhanced peroxidase activity has been found in the sites of callose walls synthesis of dyads and tetrads, which suggests the participation of this enzyme in callose synthesis.     

A pollen-analytical investigation at Threepwood Moss

Summary

Absolute and relative pollen analyses from Threepwood Moss in south-east Scotland are presented. Three local pollen assemblage zones with sub-divisions, together with stratigraphic evidence, indicate the mire succession from minerotrophy to ombrotrophy and the vegetational history of the area during the mid-Flandrian period to present-day. The landscape was initially shrub dominated, chiefly by Corylus, with a subsequent inspread of Betula which retained its importance in the tree cover and was never displaced by Alnus while mixed oakwood taxa are poorly represented. Consequent on deforestation due to anthropogenic activities, open habitat communities replaced the woodland.

Comparisons are drawn between Threepwood Moss and other sites in Britain to establish chronozones and to illustrate the vegetational variation due to latitude and altitude.     

Microsporogenesis in Taxus baccata L.: The Development of the archaesporium

An ultrastructural and cytochemical investigation of the developmentof the mierosporangium of Taxus baccata reveals many resemblancesto comparable events in other land plants, but also severaldistinctive features. During early development the archaesporiumcontains groups of degenerate cells which ultimately disappear,presumably by resorption. Scattered elsewhere in the cells ofthe archaesporium are highly ordered bodies, possibly crystal-likeformations of tubulin. The tapetum differentiates from the outerlayer of the archaesporium. Mitoses coincidentally cease tobe detectable within the sporangium and the sporogenous cellsbecome recognizable about three weeks before their nuclei entermeiosis. Although, as in other gymnosperms investigated, theearly development of the archaesporial cells is not synchronized,there is a tendency for synchrony to be acquired by the sporogenouscells and diad formation takes place more or less simultaneouslythroughout the sporangium. Measurements by microfluorometry of RNA levels during developmentof the archaesporium show a progressive rise in the RNA contentof the cells up to the beginning of meiosis. Microsporogenesis, Taxus baccata, archesporium     

Production of taxanes by Taxus baccata plant cells

Summary In callus cultures of Taxus baccata grown on agar media according to Murashige and Skoog supplemented with different growth hormones 8 taxol analogues were identified.     

The effects of the Taupo Tephra eruption of c. 1718 bp on the vegetation of Mt Hauhungatahi, central North Island, New Zealand

Abstract. An altitudinal series of eleven fine resolution pollen diagrams were used to examine the role of volcanism in forest dynamics on Mt Hauhungatahi. Partial pollen diagrams from four of these sites, chosen to illustrate the major effects of the 1718 bp Taupo eruption, are presented. Following the eruption Libocedrus bidwillii expanded in all sites. Open sites created by the eruption may have facilitated an expansion already underway as a result of more variable climatic conditions since c. 3000 bp . Weinmannia racemosa invaded upper montane forest c. 650 bp . The current altitudinal sequence of forest types, with Libocedrus dominating the subalpine and Weinmannia the upper montane forests, has thus been synthesized only within the last 1800 years. This is interpreted as a consequence of individualistic species' responses to major disturbance by the eruption. The results support nonequilibrium theories of community composition.     

<Emphasis Type="Italic">Taxus baccata</Emphasis> in the Azores: a relict form at risk of imminent extinction

Taxus baccata L., a Tertiary relict formerly widespread in the Azores Archipelago, was recently classified as “probably extinct”. This paper documents the persistence of the species in the Azores and provides its first characterization by means of morphometric and genetic analyses. Only five individuals were found, growing on Pico Island. Although the population size is critically small it retains some highly significant characteristics for the assessment of the genetic diversity of the species and its phylogeography. The leaves of the Azorean provenance were smaller than those of all other Taxus baccata described in literature; moreover, they have a higher stomata density and more numerous stomata rows. These features are all “primitive”, according to suggested morphological evolutionary trends. We assume that sequence analysis of the chloroplast trnS–trnQ intergenic spacer demonstrates that the Azorean population represents a different evolutionary line within Taxus. This suggests a more direct derivation from ancestors than provenances from Mediterranean and European regions. These individuals may be the last survivors of an ancient lineage, preserved in the Azores as part of the Macaronesian flora. Immediate conservation action focusing on site protection and ex situ reproduction strategies is recommended to save this lineage from imminent extinction.     

Factors affecting the in vitro rapid germination of Taxus embryos and the evaluation of taxol content in the plantlets

A simple and efficient in vitro method for breaking the dormancy of Taxus baccata L. cv. Stricta seeds was investigated. The highest rate of germination (100%) of embryos isolated from seeds, which had been washed with running tap water for 7 days, was obtained after 7 days of culture on modified Murashige and Skoog or Heller media. The taxol equivalent content in 2-month-old Taxus plantlets was investigated using anti-taxol polyclonal antibodies. The results showed that the taxol equivalent content varied, depending on Taxus species and on the individuals in the same taxon.