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Carbon dioxide (CO2) has been increasing in atmospheric concentration since the Industrial Revolution. A decreasing number of stomata on leaves of land plants still provides the only morphological evidence that this man-made increase has already affected the biosphere. The current rate of CO2 responsiveness in individual long-lived species cannot be accurately determined from field studies or by controlledenvironment experiments. However, the required long-term data sets can be obtained from continuous records of buried leaves from living trees in wetland ecosystems. Fine-resolution analysis of the lifetime leaf record of an individual birch (Betula pendula) indicates a gradual reduction of stomatal frequency as a phenotypic acclimation to CO2 increase. During the past four decades, CO2 increments of 1 part per million by volume resulted in a stomatal density decline of -0.6%. It may be hypothesized that this plastic stomatal frequency response of deciduous tree species has evolved in conjunction with the overall Cenozoic reduction of atmospheric CO2 concentrations.

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Mapping of two low‐centred ice‐wedge polygons in the Yakutian tundra (NE Siberia) along a regular grid with 1‐m spacing revealed large spatial variability in thaw depths and strong correlation with relief, water and vegetation. Average thaw depths in polygon ridges (23 cm and 31 cm) were smaller than in depressions (33 cm and 40 cm, respectively). The greatest thaw depths, however, were also found in the ridges and probably result from thermal erosion by water flow. Copyright © 2009 John Wiley & Sons, Ltd.

Aim To identify and interpret spatial patterns of vegetation and sedimentation during the Weichselian Late-glacial.Location North-eastern Germany and the adjacent fringe of north-western Poland.Methods An inspection and comparison of palynological data from c. 150 sites.Results Open Vegetation phase I (Oldest Dryas = earlier part of the Meiendorf, 12,900-12,450 14 C bp) and the Hippophaë phase (Bølling = later part of the Meiendorf; 12,450-12,000 bp) were rather homogeneous palynologically in the study area. Open Vegetation phase II (Older Dryas; 12,000-11,900 bp) is strongly recorded in the northern part of the study area with relatively thick sediments (suggesting severe soil erosion), but it can hardly be traced 200 km further to the south. This is attributed to sea buckthorn (Hippophaë) shrubs persisting longer in the south due to higher temperatures, to Betula forests expanding earlier under the influence of a more humid climate or to a generally denser vegetation independent of the behaviour of Hippophaë and Betula. During the late-glacial Betula/Pinus forest phase (Allerød; 11,900-11,000 bp), pine (Pinus) forests dominated in the southern regions, whereas birch (Betula) forests prevailed in the north. Open Vegetation phase III (Younger Dryas; 11,000-10,000 bp) was characterized by heathlands in the northern regions with scattered birches and with sedimentation dominated by in-washed silicates. In the south, pine parklands occurred with sedimentation dominated by local primary production which had markedly decreased after the previous warmer vegetation phase.Main conclusions The differences in vegetation and sedimentation during the open vegetation phases are attributed to a colder climate in the north than in the south, probably related to a climatic gradient between the ice-free continental central Europe and the decaying Scandinavian ice sheet. The vegetation patterns during the late-glacial Betula/Pinus forest phase are attributed to edaphic differences between the predominantly till plains in the northern part of the study area and the prevailing sandy outwash plains and Urstromtäler of the southern regions.

The tephrostratigraphy of lake sediments in the Endinger Bruch provides the first robust age model for

Ice-wedge polygon mires feature a micro-relief of dry ridges, shallow wet depressions, deeper wet troughs and transitional sites, resulting in a local mosaic of vegetation. The correct recognition of these landscape elements in palaeoecological studies of peat sections requires insight about the suitability of proxies and their potential for palaeoecological reconstruction in order to reconstruct vegetation and wetness patterns as well as dynamics. This paper analyses a 105.5 cm long peat section with a base dating to about 4000 cal yr BP from an ice-wedge polygon mire near Kytalyk (NE Siberia). Pollen, macrofossils, testate amoebae, geochemistry and sediment properties were analysed in order to compare the suitability of these proxies to reconstruct past surface wetness. The proxies show similar wetness trends. Pollen and geochemistry data did not always permit wetness reconstruction, the former because many pollen types do not allow the identification of taxa at a low taxonomic resolution, the latter because later taphonomic processes modify chemical variables in deeper peat layers. Macrofossils provided the most detailed wetness reconstruction, because they could be identified to genera or species, for which the moisture requirements are accurately known from their present-day distribution in ice-wedge polygons. All proxies, except geochemistry, show an obvious change from wet to dry conditions at around 20 cm depth. However, as the proxies sometimes show contradictory results, a multi-proxy approach is preferable over a single proxy interpretation as it allows the reconstruction of environmental development in a broader palaeoecological context. Figure 2 Location of ice-wedge polygon Lhc11 near the Kytalyk research station along the Berelekh River: (A, B) the study area, indicated are the most important landforms; (C) satellite image of the study area (GeoEye image from 2010, 0.5 m resolution, by courtesy of K. van Huissteden, Vrije Universiteit, Faculty of Earth and Life Sciences, Amsterdam); and (D) ice-wedge polygon Lhc11. This figure is available in colour online at wileyonlinelibrary.com/journal/ppp 78 A. Teltewskoi et al.