Search

European vegetation during representative “warm” and “cold” intervals of stage-3 was inferred from pollen analytical data. The inferred vegetation differs in character and spatial pattern from that of both fully glacial and fully interglacial conditions and exhibits contrasts between warm and cold intervals, consistent with other evidence for stage-3 palaeoenvironmental fluctuations. European vegetation thus appears to have been an integral component of millennial environmental fluctuations during stage-3; vegetation responded to this scale of environmental change and through feedback mechanisms may have had effects upon the environment. The pollen-inferred vegetation was compared with vegetation simulated using the BIOME 3.5 vegetation model for climatic conditions simulated using a regional climate model (RegCM2) nested within a coupled global climate and vegetation model (GENESIS-BIOME). Despite some discrepancies in detail, both approaches capture the principal features of the present vegetation of Europe. The simulated vegetation for stage-3 differs markedly from that inferred from pollen analytical data, implying substantial discrepancy between the simulated climate and that actually prevailing. Sensitivity analyses indicate that the simulated climate is too warm and probably has too short a winter season. These discrepancies may reflect incorrect specification of sea surface temperature or sea-ice conditions and may be exacerbated by vegetation–climate feedback in the coupled global model. [Copyright &y& Elsevier]

Pollen records from archaeological sites provide a direct reflection of the vegetation in the immediate vicinity, enabling an accurate depiction of anthropogenic impacts on vegetation. In this study, we applied the biomization technique to fossil pollen data to reconstruct human impact on the biome at the Chengzishan archaeological site in western Liaoning, China, and hence to explore the response of temperate forest vegetation to human activities. The results indicate that the original vegetation at Chengzishan was warm temperate coniferous and broadleaved mixed forest (TEDE). The findings suggest a shift in biome dominance over time, with cool temperate steppe (STEP) replacing TEDE as the dominant biome in response to human activities. Combined with archaeobotanical records, we conclude that the observed vegetation changes in the pollen record were closely linked to deforestation, fire use, and agricultural activities. [ABSTRACT FROM AUTHOR]

• Uncertainties in paleo-habitat definition limit adequate vegetation reconstruction. • Plant functional indicators are of limited value for paleovegetation reconstruction. • Biome scale analyses of functional types rarely apply to plant communities. • Underlying basis for whole-plant modal PFT construction and use is described. • Modal PFTs are more functionally informative than individual traits. Plant functional traits are widely applied in models that simulate the effects of climate change on biodiversity and resource management. Here the aim is to examine the potential role of specific plant functional traits and their whole-plant syndromes (Plant Functional Types or PFTs as specific 'modal' trait assemblages) as indicators of vegetation response to climate change, past, present and future. Because plant functional characteristics have evolved through time, it is widely argued that models of vegetation performance under future climates should benefit from a study of plant response under previous climates. This paper presents an overview first, of developmental concepts underlying the current use of PFTs as indicators of plant response to environmental change, second, implications arising from species acclimation and third, process-based models used in reconstruction of vegetation under mainly Holocene environments but also with respect to present and future climates. In this regard the role of individual functional traits in 'biomization' procedures in vegetation response models is briefly discussed. It is concluded that, while PFTs possess limited indicator value at biome scale, uncertainties in the delimitation of local paleohabitats greatly restrict their use as indicators for paleovegetation reconstruction at community level. Emerging hypotheses are: 1) A whole-plant system of modal PFTs based on a novel set of functional traits can provide an improved alternative to PFTs and traits used in models of vegetation response to climate change, 2) Modal PFTs are potentially more efficient indicators of vegetation response to climate change than individual traits, 3) Improved plant functional selection criteria can lead to more efficient parameterization of Earth System and Dynamic Global Vegetation Models. [ABSTRACT FROM AUTHOR]

This paper documents reconstructions of the vegetation patterns in Australia, Southeast Asia and the Pacific (SEAPAC region) in the mid-Holocene and at the last glacial maximum (LGM). Vegetation patterns were reconstructed from pollen data using an objective biomization scheme based on plant functional types. The biomization scheme was first tested using 535 modern pollen samples from 377 sites, and then applied unchanged to fossil pollen samples dating to 6000 ± 500 or 18,000 ± 1000 14C yr bp. 1. Tests using surface pollen sample sites showed that the biomization scheme is capable of reproducing the modern broad-scale patterns of vegetation distribution. The north–south gradient in temperature, reflected in transitions from cool evergreen needleleaf forest in the extreme south through temperate rain forest or wet sclerophyll forest (WSFW) and into tropical forests, is well reconstructed. The transitions from xerophytic through sclerophyll woodlands and open forests to closed-canopy forests, which reflect the gradient in plant available moisture from the continental interior towards the coast, are reconstructed with less geographical precision but nevertheless the broad-scale pattern emerges. 2. Differences between the modern and mid-Holocene vegetation patterns in mainland Australia are comparatively small and reflect changes in moisture availability rather than temperature. In south-eastern Australia some sites show a shift towards more moisture-stressed vegetation in the mid-Holocene with xerophytic woods/scrub and temperate sclerophyll woodland and shrubland at sites characterized today by WSFW or warm-temperate rain forest (WTRF). However, sites in the Snowy Mountains, on the Southern Tablelands and east of the Great Dividing Range have more moisture-demanding vegetation in the mid-Holocene than today. South-western Australia was slightly drier than today. The single site in north-western Australia also shows conditions drier than today in the mid-Holocene. Changes in the tropics are also comparatively small, but the presence of WTRF and tropical deciduous broadleaf forest and woodland in the mid-Holocene, in sites occupied today by cool-temperate rain forest, indicate warmer conditions. 3. Expansion of xerophytic vegetation in the south and tropical deciduous broadleaf forest and woodland in the north indicate drier conditions across mainland Australia at the LGM. None of these changes are informative about the degree of cooling. However the evidence from the tropics, showing lowering of the treeline and forest belts, indicates that conditions were between 1 and 9 °C (depending on elevation) colder. The encroachment of tropical deciduous broadleaf forest and woodland into lowland evergreen broadleaf forest implies greater aridity. This study provides the first continental-scale reconstruction of mid-Holocene and LGM vegetation patterns from Australia, Southeast Asia and the Pacific (SEAPAC region) using an objective biomization scheme. These data will provide a benchmark for evaluation of palaeoclimate simulations within the framework of the Palaeoclimate Modelling Intercomparison Project. [ABSTRACT FROM AUTHOR]

The Late Miocene palaeofloras of the La Cerdanya Basin represent a unique look into the Pyrenean Miocene forested areas of the Iberian Peninsula at a time when the European warm and humid climate was experiencing progressive cooling and aridification. Macrofossils (leaves, seeds, fruits and cones) and miospores from several outcrops revealed the composition and abundances of the different plant species present in the area during the Tortonian and early Messinian geological stages (ca. 11.1–5.7 Ma). These fossils were found in the sediment deposits of an ancient lake system situated in the southwestern part of the basin. Previous studies indicated the presence of highly diversified mixed mesophytic forests with broadleaved evergreen and deciduous trees and conifers. However, the spatial structure and distribution of these forest types remains unknown. In the present work, the biomization method was used to infer the different late Miocene vegetation types from the basin. The extent of these vegetation types was calculated using a methodology for mapping vegetation units from fossil and biome data. While previous attempts at mapping Miocene vegetation units had a broad geographical scale, the present work aimed to map the extent of the vegetation units at a small scale, recreating local and specific vegetation changes in an abrupt basin. Results showed similarly high scores between for four biome types, which represent the different types of vegetation that coexisted in the basin during the Tortonian and the early Messinian: warm-temperate evergreen broadleaf and mixed woodlands (WTEM biome), temperate deciduous forests (TEDE) and cool conifer forests (COMX and COEG). Their extent was depicted in two vegetation maps, which account for differences in palaeoaltitude and palaeoclimate. These forests occupied different vegetation belts, which shifted upwards and downwards with climatic variations and the progressive uplift of the Pyrenees during the late Miocene. Azonal riparian forests and wetland vegetation occupied the more humid areas in the centre of the basin. Nonetheless, dry conditions during the early Messinian and decrease in the lake area degraded the wetland environments, which were partially replaced by broadleaved evergreen mixed woodlands. [ABSTRACT FROM AUTHOR]

Reconstruction of past vegetation change is critical for better understanding the potential impact of future global change on the fragile alpine ecosystems of the Qinghai-Tibetan Plateau (QTP). In this paper, pollen assemblages comprising 58 records from the QTP, spanning the past 15 kyrs, were collected to reconstruct biome compositions using a standard approach. Six forest biomes were identified mainly on the southeastern plateau, exhibiting a pattern of gradual expansion along the eastern margin during early to mid-Holocene times. The alpine meadow biome was separately identified based on an updated scheme, and showed notable westward expansions towards lower latitudes and higher altitudes during early Holocene times. Consistent patterns of migration could also be identified for the alpine steppe biome, which moved eastward during the late Holocene after 4 ka. As the dominant biome type, temperate steppe was distributed widely over the QTP with minor migration patterns, except for a progressive expansion to lower altitudes in the late Holocene times. The desert biome was inferred mainly as covering the northwestern plateau and the Qaidam Basin, in relatively restricted areas. The spatial distribution of the reconstructed biomes represent the large-scale vegetation gradient on the QTP. Monsoonal precipitation expressed predominant controls on the development of alpine ecosystems, while the variations in desert vegetation responded to regional moisture brought by the mid-latitude Westerlies. Temperature changes played relatively minor roles in the variations of alpine vegetation, but exerted more significant impacts on the forest biomes. • Fossil pollen based biome reconstruction on the Qinghai-Tibetan Plateau since 15 ka. • Spatial/temporal patterns of biome changes on the QTP were illustrated and examined. • Forest and alpine meadow biomes experienced migrations during the mid-Holocene. • Vegetation changes responded closely to moisture changes with spatial divergence. [ABSTRACT FROM AUTHOR]

Lacustrine-peat sediments from the Oskino-09 borehole in Western Siberia, which span the last 7.5 cal ka BP, were sampled for pollen and plant macro-remains to better understand regional climatic changes and the position of the forest-steppe border. Analysis of palynological assemblages indicate that meadow-steppe landscapes occupied the largest area in the middle of the Holocene (7.5–4.7 cal ka BP) due to reduced effective moisture during a warm climate interval. A subsequent gradual decrease in temperatures and evaporation led to an increase in effective moisture and emergence of birch groves during 4.7–2.0 cal ka BP, with short interruptions at ca. 3.3 and 2.5 cal ka BP. The expansion of pine forests and the advance of taiga to the south were recorded at ca. 2.0 cal ka BP. There is little evidence for significant human impact on forest-steppe belt evolution, and specifically evidence for anthropogenic deforestation on the southern border of the taiga is lacking. Human activities did not start to impact forests until the emergence of semi-nomadic cattle breeding in the Iron Age. A methodological finding of this paper is that we show that the Landscape Reconstruction Algorithm (LRA) is not always reliable and often overestimates forested areas. • Forests area is overestimated by quantifying landscape assessment in forest-steppe. • Largest meadow-steppe areas were due to reduced effective moisture ca 7.5–4.7 ka BP. • Intensive spread of coniferous in Western Siberian forest-steppe ca 2.0 ka BP. • Human impact on the landscape of Western Siberian forest-steppe was not significant. [ABSTRACT FROM AUTHOR]

Aim Remote sensing coupled with direct observation allows recent changes in vegetation to be investigated but, in order to extend our understanding of land-cover change further back in time, different proxies for vegetation are required. The pseudobiomization ( PBM) approach has been developed to transform fossil pollen data into land-cover classes ( LCCs) in order to reconstruct broad-scale anthropogenic land-use change through time. The aim of this study was to test and refine the PBM approach through application to an extensive modern pollen dataset and comparison with remotely sensed CORINE land-cover maps for Europe. Location The study area comprised 2471 modern pollen sites from across Europe. Methods Pollen sites were assigned to one of eight LCCs using the pollen-based PBM method, which draws upon biomization techniques to transform pollen data into records of land-cover change. Five of the LCCs were 'pure' classes (e.g. broad-leaf forest) and three of them were mixed vegetation. Remotely sensed CORINE land-cover maps were used to assign LCCs to sites, and the results were compared with pollen-assigned LCCs. Results The results revealed a good correspondence between the proportions of different LCCs that were registered using CORINE and pollen-based PBM, when data were aggregated at a pan-European scale. However, the match between the two datasets was much less close at a site-specific level. The overall results were improved to c. 60% when the target was broadened to include similar as well as identical LCCs. The spatial correspondence was best across north-central Europe and least good in south-west Europe, the Mediterranean and northern Scandinavia. Main conclusions The ability of distinct data types to sense actual vegetation is limited by various sources of error; for example, both pollen and remote sensing vary in terms of spatial and temporal heterogeneity and taxonomic resolution. It is likely that many of the main sources of error are common to both methods, rather than being approach-specific. We conclude that pollen-based methods of intermediate complexity can be used as a proxy for broad-scale land-cover change across most of temperate Europe, but may be less reliable at a site-specific scale. [ABSTRACT FROM AUTHOR]

Aim The boreal tree line is a prominent biogeographic feature, the position of which reflects climatic conditions. Pollen is the key sensor used to reconstruct past tree line patterns. Our aims in this study were to investigate pollen-vegetation relationships at the boreal tree line and to assess the success of a modified version of the biomization method that incorporates pollen productivity and dispersal in distinguishing the tree line. Location Northern Canada (307 sites) and Alaska (316 sites). Methods The REVEALS method for estimating regional vegetation composition from pollen data was simplified to provide correction factors to account for differential production and dispersal of pollen among taxa. The REVEALS-based correction factors were used to adapt the biomization method and applied as a set of experiments to pollen data from lake sediments and moss polsters from the boreal tree line. Proportions of forest and tundra predicted from modern pollen samples along two longitudinal transects were compared with those derived from a vegetation map by: (1) a tally of 'correct' versus 'incorrect' assignments using vegetation in the relevant map pixels, and (2) a comparison of the shape and position of north-south forest-cover curves generated from all transect pixels and from pollen data. Possible causes of bias in the misclassifications were assessed. Results Correcting for pollen productivity alone gave fewest misclassifications and the closest estimate of the modern mapped tree line position (Canada, + 300 km; Alaska, + 10 km). In Canada success rates were c. 40-70% and all experiments over-predicted forest cover. Most corrections improved results over uncorrected biomization; using only lakes improved success rates to c. 80%. In Alaska success rates were 70-80% and classification errors were more evenly distributed; there was little improvement over uncorrected biomization. Main conclusions Corrected biomization should improve broad-scale reconstructions of spatial patterns in forest/non-forest vegetation mosaics and across climate-sensitive ecotones. The Canadian example shows this is particularly the case in regions affected by taxa with extremely high pollen productivity (such as Pinus). Improved representation of actual vegetation distribution is most likely if pollen data from lake sediments are used because the REVEALS algorithm is based on the pollen dynamics of lake-based systems. [ABSTRACT FROM AUTHOR]

Biomization provides an objective and robust method of assigning pollen spectra to biomes so that pollen data can be mapped and compared directly with the output of biomgeographic models. We have tested the applicability of this procedure, originally developed for Europe, to assign modern surface samples from China to biomes. The procedure successfully delineated the major vegetation types of China. When the same procedure was applied to fossil pollen samples for 6000 years ago, the reconstructions showed systematic differences from present, consistent with previous interpretations of vegetation changes since the mid-Holocene. In eastern China, the forest zones were systematically shifted northwards, such that cool mixed forests displaced taiga in northeastern China, while broad-leaved evergreen forest extendedc. 300 km and temperate deciduous forestc. 500–600 km beyond their present northern limits. In northwestern China, the area of desert and steppe vegetation was reduced compared to present. On the Tibetan Plateau, forest vegetation extended to higher elevations than today and the area of tundra was reduced. These shifts in biome distributions imply significant changes in climate since 6000 years ago that can be interpreted qualitatively as a response to orbital forcing and its secondary effects on the Asian monsoon. [ABSTRACT FROM AUTHOR]