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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.