A survey of modern pollen and vegetation along a south–north transect in Mongolia

Aim This modern pollen‐rain study documents the spatial and quantitative relationships between modern pollen and vegetation in Mongolia, and explores the potential for using this relationship in palaeoclimatic reconstructions. Location East‐central Mongolia. Methods We collected 104 pollen surface samples along a south–north transect across five vegetation zones in Mongolia. Discriminant analysis was used to classify the modern pollen spectra into five pollen assemblages corresponding to the five vegetation zones. Hierarchical cluster analysis was used to divide the main pollen taxa into two major groups and seven subgroups representing the dry and moist vegetation types and the main vegetation communities within them. Results Each vegetation zone along the transect can be characterized by a distinctive modern pollen assemblage as follows: (1) desert zone: Chenopodiaceae–Zygophyllaceae–Nitraria–Poaceae pollen assemblage; (2) desert‐steppe zone: Poaceae–Chenopodiaceae pollen assemblage; (3) steppe zone: Artemisia–Aster‐type–Poaceae–Pinus Haploxylon‐type pollen assemblage; (4) forest‐steppe zone: Pinus Haploxylon‐type–Picea–Artemisia–Betula, montane forb/shrub and pteridophyte pollen assemblage; and (5) mountain taiga zone: Pinus Haploxylon‐type–Picea–Poaceae–Cyperaceae, montane forb/shrub and Pteridophyte pollen assemblage. Main conclusions Based on the ratio between the major pollen taxon groups and subgroups, we propose two pollen–climate indices that represent the precipitation and temperature conditions in the study region. When plotted along our south–north transect, the moisture indices (M) and temperature indices (T) mimic the regional gradients of precipitation and temperature across Mongolia very closely. These pollen–climate indices can be used for palaeoclimatic reconstruction based on fossil pollen data.     

Modern pollen–vegetation relationships along transects on the Whangapoua Estuary, Great Barrier Island, northern New Zealand

Aims To quantify pollen–vegetation relationships from saline to freshwater in an estuarine gradient from surface samples of the modern pollen rain, to allow more accurate interpretations of the stratigraphic palynological record. Location Whangapoua Estuary, Great Barrier Island, northern New Zealand. Methods Six transects were laid out along a vegetation sequence running from estuarine mud to freshwater swamp. Along these transect lines, 108 plots were sampled for vegetation and surface sediments from wet sand, mud, plant litter or moss (sand and mud sites are inundated by most tides, other sites less frequently). All sediment samples were analysed for pollen. The relationships between plant species frequency and pollen representation were examined at a community scale using twinspan and ordination analyses, and for individual species using fidelity and dispersibility indices, regression and box‐plot analyses. Results The quantitative relationships between source taxon vegetation frequency and its pollen representation varied between species due to differential pollen production and dispersal. twinspan of the surface pollen samples suggests five vegetation types: (A) mangrove (Avicennia marina); (C) Leptocarpus similis salt meadow; (D) Baumea sedges; (E) Leptospermum shrubland; and (F) Typha/Cordyline swamp forest. The (B) Juncus kraussii community is not represented palynologically owing to the destruction of its delicate pollen grains during acetolysis of samples. Detrended correspondence analysis places these communities on an estuarine‐to‐freshwater gradient. However, pollen assemblages at the seaward end of the salinity gradient are less clearly representative of the associated vegetation than those at the landward end, probably because the open vegetation at the former allows the influx of wind‐ and water‐dispersed pollen from surrounding vegetation. Main conclusions The vegetation pattern (zonation) at Whangapoua is reflected in the pollen rain. When the long‐distance and over‐represented pollen types are excluded, five out of six of the broad vegetation communities can be identified by their pollen spectra. Species with high fidelity and low‐to‐moderate dispersibility indices can be used to identify the vegetation types in the sedimentary sequences. The more open vegetation types at the ‘marine end’ of the sequence tend to be ‘overwhelmed’ by regional pollen, but the nature of the sediments and the presence of discriminatory species (e.g. A. marina, Plagianthus divaricatus, Cordyline australis), even in small amounts, will allow correct identification of the local vegetation represented in sedimentary palynological sequences. A box‐plot analysis indicates that the pollen and spore types A. marina (mangroves), Sarcocornia quinqueflora (salt meadow), P. divaricatus (sedges), Gleichenia (shrubland) and C. australis (swamp forest) are highly discriminatory in relation to vegetation type. These discriminatory palynomorphs help with the interpretation of stratigraphic pollen studies. However, salt marsh vegetation communities in the sediments must be interpreted with caution as the marine sediments are easily affected by erosion, bioturbation and tidal inundation effects.     

A survey of modern pollen and vegetation along an altitudinal transect in southern Georgia, Caucasus region

This paper describes the pollen representation of vegetation patterns along an altitudinal transect in the South Caucasus region. Surface sediments from eight small- to medium-sized lakes and wetlands were analysed for modern pollen, and the results analysed numerically using detrended correspondence analysis (DCA) and dichotomised ordination (TWINSPAN). Pollen spectra from the semidesert region have a clear palynological signal characterised by an abundance of Chenopodiaceae. Differentiation of oak forest, upper tree-line and subalpine communities is more difficult: all are dominated by arboreal pollen (AP) types. The authors propose a number of indicator pollen types and pollen threshold values that may assist in detecting tree-line variations and deforestation events in Holocene pollen diagrams.     

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 application of multiple discriminant analysis to the reconstruction of the vegetation history of Fynbos,southern Africa

The fynbos biome of southern Africa is floristically diverse and explanations of this diversity have frequently invoked historical processes, in particular environmental change. Few sites exist within the region which facilitate palaeoecological reconstructions, but a relatively deep sequence of organic sediments in the Cederberg mountains in the south-western Cape Province of South Africa has been analysed for fossil pollen content. Conventional zonation of the resultant absolute pollen diagram reveals an apparent absence of marked vegetation change during the last 14500 years. Pollen analysis has its limitations under circumstances where the high plant diversity and incompleteness of reference material entails that pollen identifications may usually be made only down to family level. In order to assess whether the presumed stability of vegetation communities during the late Pleistocene and Holocene is an artefact of these taxonomic limitations, a comprehensive contemporary pollen sampling programme was conducted. Multiple discriminant analysis was applied to the contemporary data and suggests that contemporary pollen spectra are accurate reflections of the surrounding vegetation. Discriminant analysis is further able to identify analogue communities prevailing at various times during the sedimentation period. Rather than being truly stable, the vegetation of these mountains is shown to have been dynamic in response to changes in precipitation inputs, fire regime and human activity. Nevertheless, the vegetation history is characterised by relatively subtle changes in plant community patterns, a fact which may have played an important role in the evolution of prolific species diversity. It is concluded that contemporary pollen rain studies, combined with multiple discriminant analysis, may be especially valuable interpretive tools in situations of high plant species richness.     

Biodiversity and pollen analysis: modern pollen studies and the recent history of a floodplain woodland in S. W. Ireland

One of the problems with biodiversity for palynologists is that their samples come from an unbounded area and source area varies with both pollen/spore type and vegetation type. There have been two broad approaches to the problem of inferring diversity from pollen/spore samples; firstly the use of pollen type richness as a proxy for species richness, and secondly the ‘identification’ of past vegetation communities aided by ecological inference and historical or modern data concerning species affinities and typical diversity. The estimation of biodiversity from pollen analysis depends upon the pollen count, taxonomic precision, source strength for individual types and dispersal/transport of pollen from source areas to the site. A transect of surface pollen samples is used here to test the effect of a vegetation boundary on pollen/spore diversity and compare the pollen/spore diversity with the species richness of the woodland. Palynological richness (at a constant count sum) does, to some extent, reflect changing local vegetation along the transect. Type count curves also reflect the changes in vegetation type along the transect due to the partial influence of species richness on pollen/spore richness. This study suggests that depending upon the woodland composition, the woodland may not entirely drown-out the pollen signal of the surrounding vegetation, and that a small woodland may be more representative (as a sampling site) of the valley floor diversity than a raised mire. The surface transect is also used in the interpretation of Medieval pollen levels from The Gearagh.     

Modern pollen and vegetation relationships in the mountains of southern California,USA

The relationship between modern pollen assemblages and modern vegetation along two elevational transects within the Transverse and Peninsular Ranges of southern California, USA, is demonstrated using cluster analysis of the pollen data. Cluster analysis separates the Sonora Desert vegetation, Valley grassland/agricultural land and chaparral vegetation types on the San Jacinto Mountains transect. Chaparral is not easily separated on the San Bernardino Mountains transect, probably due to the presence of Quercus dumosa (scrub oak) there. The lower montane Quercus – Pinus (oak – pine) community is distinct from other forest types, and can be subdivided palynologically based upon relative importance of Quercus, Pinus and Cupressaceae [primarily Calocedrus decurrens (incense cedar)] pollen. Subdivisions include Quercus – Pinus – Cupressaceae, Quercus – Cupressaceae – Pinus and Quercus – Pinus assemblages. Higher elevation Pinus – Abies (pine – fir) and Pinus-dominated communities are also differentiated from one another, although the subalpine vegetation type only occurs on the San Bernardino Mountains transect. Though the study area presently straddles a transition between winter-wet and summer-wet climatic regimes, differences between the pollen assemblages in the two mountain ranges are minimal. Pollen assemblages from lower elevations document the effects of human activities, primarily agriculture, on the modern pollen rain of the region, with the occurrence of introduced citrus (Citrus sp.) and shade (Eucalyptus sp.) trees and weedy disturbance indicators (e.g., Brassicaceae).     

Modern pollen representation of source vegetation in the Qaidam Basin and surrounding mountains, north-eastern Tibetan Plateau

We use a data set of 35 surface pollen samples from lake sediments, moss polsters and top soils on the north-eastern Tibetan Plateau to explore the relationship between modern pollen assemblages and contemporary vegetation patterns. The surface pollen transect spanned four vegetation zones––alpine meadow, steppe, steppe desert and desert––under different climatic/elevational conditions. Relative representation (R _rel) values and Principal Components Analysis (PCA) were used to determine the relationships between modern pollen and vegetation and regional climate gradients. The results show that the main vegetation zones along the regional and elevational transects can be distinguished by their modern pollen spectra. Relative to Poaceae, a high representation of Artemisia, Nitraria and Chenopodiaceae was found, while Cyperaceae and Gentiana showed values in the middle range, and Ranunculaceae, Asteraceae, Ephedra and Fabaceae had low relative representation values. PCA results indicate a high correlation between the biogeoclimatic zones and annual precipitation and annual temperature and July temperature. The Artemisia/Chenopodiaceae ratio and the Artemisia/Cyperaceae ratio are useful tools for qualitative and semi-quantitative palaeoenvironmental reconstruction on the north-eastern Tibetan Plateau. Surface lake sediments are found to have different palynomorph spectra from moss cushion and soil samples, reflecting the larger pollen source area in the contemporary vegetation for lakes.     

Interpretation of the last‐glacial vegetation of eastern‐central Europe using modern analogues from southern Siberia

Aim Interpretation of fossil pollen assemblages may benefit greatly from comparisons with modern palynological and vegetation analogues. To interpret the full‐ and late‐glacial vegetation in eastern‐central Europe we compared fossil pollen assemblages from this region with modern pollen assemblages from various vegetation types in southern Siberia, which presumably include the closest modern analogues of the last‐glacial vegetation of central Europe. Location Czech and Slovak Republics (fossil pollen assemblages); Western Sayan Mountains, southern Siberia (modern pollen assemblages). Methods Eighty‐eight modern pollen spectra were sampled in 14 vegetation types of Siberian forest, tundra and steppe, and compared with the last‐glacial pollen spectra from seven central European localities using principal components analysis. Results Both full‐ and late‐glacial pollen spectra from the valleys of the Western Carpathians (altitudes 350–610 m) are similar to modern pollen spectra from southern Siberian taiga, hemiboreal forest and dwarf‐birch tundra. The full‐glacial and early late‐glacial pollen spectra from lowland river valleys in the Bohemian Massif (altitudes 185–190 m) also indicate the presence of patches of hemiboreal forest or taiga. Other late‐glacial pollen spectra from the Bohemian Massif suggest an open landscape with steppe or tundra or a mosaic of both, possibly with small patches of hemiboreal forest. Main conclusions Our results are consistent with the hypothesis that during the full glacial and late glacial, the mountain valleys of the north‐western Carpathians supported taiga or hemiboreal forest dominated by Larix, Pinus cembra, Pinus sylvestris and Picea, along with some steppic or tundra formations. Forests tended to be increasingly open or patchy towards the west (Moravian lowlands), gradually passing into the generally treeless landscape of Bohemia, with possible woodland patches in locally favourable sites.     

Phytosociological and palynological studies of alpine steppe communities on the northern Tibetan Plateau,Qinghai Province,China

The dry cold climate in the highland of the eastern Kunlun Mountains in Qinghai Province, north‐western part of China supports the establishment of alpine grassland, consisting of Poaceae and Cyperaceae species and dwarf shrub communities dominated by Potentilla and Krascheninnikovia shrubs. The phytosociological vegetation studies carried out around Lake Heihai (36°00′N/93°26′E, 4446 m a.s.l.) reveals a complex pattern of high mountainous vegetation, including three major vegetation communities. A Polygonum sibiricum community occupies wet and slightly saline sites close to the Heihai lake shoreline and Kobresia robusta and Poa pachyantha communities are characteristic for the drier slopes. These communities differ in ecological conditions, exposure and several characteristic species that form local subunits. Main ecological factors influencing plant growth are moisture coming from glacial melt water and the composition and texture of the surface sediments. The atmospheric circulation (i.e. monsoonal wind system) and the different amount of insolation of the southern and northern slopes are of minor importance for the establishment of the different communities. The reflection of the vegetation composition in the modern pollen rain is generally poor, since the pollen spectrum is highly influenced by the local appearance of taxa. Though the vegetation unit of a alpine steppe can be detected. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Pollen assemblages of tauber traps and surface soil samples in steppe areas of China and their relationships with vegetation and climate

We use 86 pollen trap and surface soil pollen samples in steppe areas of China to explore the relationships between modern pollen, vegetation, and climate. The modern pollen spectra from both sources have comparable compositions with regard to the major pollen taxa. However, the number of taxa in the traps was higher than in the surface soil samples. Both pollen accumulation rates and pollen concentrations are higher in the typical steppe areas than in the desert steppe areas. Discriminant analysis indicates that pollen spectra from trap and surface soil samples roughly reflect the vegetation zones of desert steppe and typical steppe, especially in the case of the trap samples. Detrended canonical correspondence analysis suggests that pollen assemblages have a significant relationship with the temperature of the coldest month and the mean annual precipitation.     

Numerical analysis of modern and fossil pollen spectra as a tool for elucidating the nature of fine-scale human activities in boreal areas

Modern pollen assemblages from the major vegetation units (both natural and anthropogenic) on the island of Hailuoto, Finland are studied from 29 surface moss samples. A total of 59 pollen and spore taxa are recorded. The pollen data-set is related by redundancy analysis (RDA) to six external synthetic variables that characterize in general terms the different major ecological situations relevant to the land-use on the island (sand, humus, forest, field, deforested, treeless). Weighted average (WA) optima are calculated to identify which pollen taxa are most indicative of four of these external variables. Two fossil pollen diagrams from Hailuoto are re-interpreted by positioning their samples on the RDA plot of the modern data-set and by classifying the modern and fossil spectra together in a minimum-variance cluster analysis. The RDA plot shows that the strongest features in the modern pollen assemblages are the contrast between spectra from dry sandy soils and those from damper soils with more organic content, and between assemblages from forested and unforested areas. For anthropogenic situations the numerical analyses detect a distinction in the pollen assemblages characterizing fields from those representing farms and trackways but is less successful in separating the latter two. The WA optima indicate that most pollen taxa considered as indicator types primarily represent a mixed field/farm category of land-use. The RDA and minimum-variance cluster analysis confirm that the two fossil sites have had different vegetational histories. In neither is there any phase equivalent to the modern farm situation on Hailuoto. The initial phase in each diagram represents shore meadows and fields but because Poaceae pollen is identifiable only to family level it is not possible to separate these two habitat types.     

Modern pollen samples from alpine vegetation on the Tibetan Plateau

• 1 A set of 316 modern surface pollen samples, sampling all the alpine vegetation types that occur on the Tibetan Plateau, has been compiled and analysed. Between 82 and 92% of the pollen present in these samples is derived from only 28 major taxa. These 28 taxa include examples of both tree (AP) and herb (NAP) pollen types.
• 2 Most of the modern surface pollen samples accurately reflect the composition of the modern vegetation in the sampling region. However, airborne dust‐trap pollen samples do not provide a reliable assessment of the modern vegetation. Dust‐trap samples contain much higher percentages of tree pollen than non‐dust‐trap samples, and many of the taxa present are exotic. In the extremely windy environments of the Tibetan Plateau, contamination of dust‐trap samples by long‐distance transport of exotic pollen is a serious problem.
• 3 The most characteristic vegetation types present on the Tibetan Plateau are alpine meadows, steppe and desert. Non‐arboreal pollen (NAP) therefore dominates the pollen samples in most regions. Percentages of arboreal pollen (AP) are high in samples from the southern and eastern Tibetan Plateau, where alpine forests are an important component of the vegetation. The relative importance of forest and non‐forest vegetation across the Plateau clearly follows climatic gradients: forests occur on the southern and eastern margins of the Plateau, supported by the penetration of moisture‐bearing airmasses associated with the Indian and Pacific summer monsoons; open, treeless vegetation is dominant in the interior and northern margins of the Plateau, far from these moisture sources.
• 4 The different types of non‐forest vegetation are characterized by different modern pollen assemblages. Thus, alpine deserts are characterized by high percentages of Chenopodiaceae and Artemisia, with Ephedra and Nitraria. Alpine meadows are characterized by high percentages of Cyperaceae and Artemisia, with Ranunculaceae and Polygonaceae. Alpine steppe is characterized by high abundances of Artemisia, with Compositae, Cruciferae and Chenopodiaceae. Although Artemisia is a common component of all non‐forest vegetation types on the Tibetan Plateau, the presence of other taxa makes it possible to discriminate between the different vegetation types.
• 5 The good agreement between modern vegetation and modern surface pollen samples across the Tibetan Plateau provides a measure of the reliability of using pollen data to reconstruct past vegetation patterns in non‐forested areas.

     

Modern pollen and stomate deposition in lake surface sediments from across the treeline on the Kola Peninsula, Russia

We sampled and analyzed surface sediments from 31 lakes along a latitudinal transect crossing the coniferous treeline on the Kola Peninsula, Russia. The major vegetation zones along the transect were tundra, birch-forest tundra, pine-forest tundra, and forest. The results indicate that the major vegetation types in our study area have distinct pollen spectra. Sum-of-squares cluster analysis and principal components analysis (PCA) groupings of pollen sites correspond to the major vegetation zones. PCA ordination of taxa indicates that the first axis separates taxa typical of the forest zone (Pinus, Picea) from taxa typical of tundra and forest-tundra zones (Polypodiaceae, Ericaceae, and Betula). The current position of the coniferous treeline, defined in our region by Pinus sylvestris, occurs roughly where Pinus pollen values reach 35% or greater. Arboreal pollen (AP)/non-arboreal pollen (NAP) ratios were calculated for each site and plotted against geographic distance along the transect. AP/NAP ratios of 7 or greater are found within pine-forest tundra and forest vegetation zones. Pinus stomates (dispersed stomatal guard cells) are absent from sites north of the coniferous treeline and all but two samples from the forested sites contain stomates. Stomate concentrations among the samples are highly variable and range from 10 to 458 per ml and positively correlate with the changing Pinus pollen values.     

Pollen-rain-vegetation relationships along a forest-savanna transect in southeastern Cameroon

Modern soil and litter samples from southeastern Cameroon, collected along a continuous forest–savanna transect were analysed for pollen content to define modern pollen–vegetation relationships. The pollen results, completed and compared with botanical inventories, leaf area index and basal area measurements performed in the same area, clearly registered the physiognomy, the main floristic composition and floral richness of the two sampled ecosystems. Distortions were observed between sampled vegetations and their pollen rain, related to important differences in pollen production and dispersal of plant species: this is a general feature in many tropical regions. The pollen data in the area studied reflected well the recent transgression of forest versus savanna. This permitted us to define inside the forest ecosystem more successional vegetation communities than the botanical surveys allowed.     

Modern pollen rain in mangroves from San Andres Island, Colombian Caribbean

The precise characterisation of present-day mangrove ecosystems from modern pollen rain facilitates the accurate use of fossil pollen data for late Quaternary sea level and environmental reconstructions. Here, we investigate whether the analysis of pollen rain data corroborates existing floristic and structural characterisation of different mangrove types at the Caribbean island of San Andrés, Colombia. At 82 plots along 20 transects of four distinct mangrove types, samples were obtained of (i) surface sediments for pollen analysis, and (ii) a range of environmental parameters (including inundation levels, salinity and pH). This information was compared to previously sampled mangrove composition and tree basal area. In surface sediment samples 82 pollen taxa were found, from which 19 were present in the vegetation plots. However, because pollen may be transported by wind and/or watercourses, the overall floristic composition of the different forest types may not necessarily be reflected by the pollen spectra. Local vegetation (i.e. mangroves and beach) represented > 90% of the pollen spectra, while the regional one (i.e. hinterland forests) represented < 5% of it. Unlike the four mangrove types that were previously described in the vegetation, the analysis of pollen samples suggested only three distinct types of forest.The groups were characterised based on (i) the dominance of at least one of the true mangrove species from pollen data ordination and the presence of associated species, and (ii) their relationship with environmental parameters. Rhizophora was present in all plot samples, but did not contribute to forest type separation. In fact, just three true mangrove species proved reliable indicators of (i) high salinity and fringe mangroves (i.e. Avicennia), (ii) high pH levels and landward mangroves (i.e. Conocarpus), and (iii) natural or anthropogenic caused disturbance of forest stands (Laguncularia and associated Acrostichum fern). Hence our study confirms that mangrove pollen spectra can be accurately used to describe different mangrove environments for fossil based palaeoecological reconstructions.     

Modern pollen rain in savanna and forest ecosystems of Gabon and Cameroon,Central Atlantic Africa

Eighty modern soil surface and litter samples from southern Cameroon and Gabon, Central Atlantic Africa (5°N–4°S, 10°–15°W), were analysed for pollen content. The samples are distributed among two main vegetation types: savanna (8 samples) and forest (71 samples). The aim of this study is to provide new data on the modern pollen rain in the Guineo-Congolian phytogeographical region, mainly in forest communities (secondary and mature forests on well drained soils, and hygrophilous forests) and to interpret these data using diagrams of pollen percentages and numerical analyses. The savannas are well identified by high frequencies of non-arboreal pollen with as pollen marker the Poaceae, and the forests by high frequencies of arboreal pollen with as important families the Burseraceae, Caesalpiniaceae, Mimosaceae, Euphorbiaceae and Sapindaceae. Within the forest ecosystem, secondary and mature forests on well drained soils can be differentiated on the basis of distinct assemblages of tree pollen taxa such as Zanthoxylum, Phyllanthus, Tetrorchidium, Margaritaria discoidea in secondary forest spectra and abundance of Burseraceae, Caesalpiniaceae, Sapindaceae in mature forest ones. In addition, hygrophilous forests are well identified by the presence of high pollen contributors such as Uapaca, Nauclea, Macaranga and Raphia. This work shows that the major vegetation communities occurring today in Cameroon and Gabon can be well differentiated by their pollen assemblages.     

Successional processes induced by fires on the northern offshore islands of New Zealand

A modern pollen-vegetation data set of 46 samples is presented from subantarctic Campbell Island, 600 km south of the New Zealand mainland. The sampled vegetation includes all major community types: maritime turf and grassland, sedge flushes, dwarf forest, scrub, cushion bog, tussock grassland, and high altitude graminoid turfs and tundra. Macrophyllous forbs—characteristic plants of subantarctic islands—are common throughout. Most taxa have highly restricted pollen dispersal, largely due to the short stature of the vegetation and the high proportion of insect-pollinated species. Percentages of pollen or spores of the dominant taxa have a significant positive correlation with the percent vegetation cover of the corresponding species, the exceptions being the widespread ferns Polystichum vestitum and Blechnum spp., and the ubiquitous macrophyllous forb, Bulbinella rossii .The relationship between the vegetation cover of a given taxon and its pollen representation was usually not strong enough to give confidence in a quantitative reconstruction based on pollen frequency alone. However, the broad vegetation groupings have characteristic pollen and spore spectra clearly related to the abundance of their dominant plant species. Detrended correspondence analysis of the pollen spectra grouped most sites according to their source vegetation type and generated a pattern similar to that of vegetation data analysed in a similar fashion in previous studies of the island. This study, together with recent work on Auckland Island pollen and spore representation, has resulted in a combined modem palynological data base of more than 100 sites for the New Zealand subantarctic islands.     

Anthropogenic indicators in pollen diagrams in eastern France: a critical review

The focus of palaeoenvironmental sciences on past human activities and their impact on the environment necessitates a precise understanding of the history and functioning of past and present anthropogenic ecosystems. A process is outlined which uses palaeoenvironmental and historical documentation as well as present-day observations of vegetational changes from two different plant communities, which are characterised by a very specific anthropogenic flora: arable weeds and ruderals. This study is coupled with modern pollen deposition data to deduce a set of pollen types characteristic of the range of human activities practised in eastern France, a region rich in pollen data. First, phytogeographical analysis of the evolution of these plant communities since the Neolithic enables the comparison to be validated. By distinguishing between native plants and aliens introduced long ago (archaeophytes), or more recently (neophytes), and by refining their ecological characteristics, the method also enables identification of species that are strong indicators of human activities. Next, local pollen deposition in these vegetation types is examined with a number of statistical analyses (PCIA, Davis indices), confirming the relationships between a given vegetation community, its theoretical pollen rain and its actual pollen rain, thus distinguishing local and regional pollen indicators. Lastly, comparison of the results obtained by these two approaches leads to a critical synthesis of the traditional anthropogenic pollen indicators (Behre’s “indicator species”) in the study area and to the establishment of more specific local pollen indicators.     

Modern pollen assemblages from human-influenced vegetation in northwestern China and their relationship with vegetation and climate

Modern pollen spectra can improve the interpretation of fossil pollen records used to reconstruct past vegetation, climate and human impacts. It is important, therefore, to carefully examine the relationships between modern pollen spectra, vegetation, climate and human activity. Here, we present the results of an analysis of the pollen spectra of 143 surface pollen samples from farmland, wasteland, desert, steppe/meadow, forest and river valley along a transect from Lanzhou to Urumqi, in northwestern China. The modern pollen assemblages are mainly composed of Amaranthaceae, Artemisia, Poaceae, Asteraceae, Ephedra and Nitraria. The results indicate that in general the surface pollen assemblages of different vegetation types reliably represent the modern vegetation in terms of the composition of the main taxa and the dominant types. Farmland is dominated by cereal-type (≥?15%) and Amaranthaceae (≥?20%), while the pollen assemblages of wasteland (i.e. the vegetation immediately surrounding farmland) are mainly composed of Amaranthaceae (≥?25%), Artemisia (≥?20%), Poaceae (≥?10%), Asteraceae (≥?5%) and Cyperaceae (≥?5%). Amaranthaceae (≥?45%) and Ephedra (≥?10%) are the most important taxa in desert, and Cyperaceae (≥?35%) and Thalictrum (≥?2%) are the dominant pollen types in steppe/meadow. Forest and river valley samples are characterized by high frequencies of Picea (≥?10%) and Cyperaceae (≥?20%). Both constrained and partial canonical ordination techniques (RDA and partial RDA) of the main pollen types and environmental variables show that the modern pollen spectra are primarily controlled by mean annual precipitation (MAP). Cyperaceae, Thalictrum and Brassicaceae are positively correlated with MAP and negatively correlated with mean July temperature (T_July), while the representation of certain other types, such as Amaranthaceae, Ephedra and Nitraria, is negatively correlated with MAP and positively correlated with T_July. The Human Influence Index (HII) is significantly correlated with cereal-type pollen, and it can also differentiate human-influenced and natural vegetation. Our results provide a basis for improving the interpretation of fossil pollen records from arid northwestern China and similar regions.