Introduction to a special section: winter terrestrial ecology in Arctic and alpine tundra

I am very pleased to present this special section of articles on winter terrestrial ecology in Arctic and alpine tundra. This is a new and developing field of research, and has been hitherto little studied. Much is unknown about the ecology of the dark, cold period of the year, as traditionally ecologists have travelled to their field sites in summer, when the snow has melted and the plants, soils and invertebrates are more readily available to be studied. Arctic research in the summer is often challenging; Arctic research in the wintertime presents even greater obstacles. However, in tundra areas the long winter is an important determinant of the physical framework for living organisms, both during the winter itself and during the short growing season. Winter ecosystem respiration is an important contributor to the annual CO2 flux in the High Arctic, as shown in this issue in papers by Strebel et al. and Morgner et al., and values vary greatly between vegetation types. Carbon sink strength in the tundra is therefore overestimated if cold-season dynamics are not included, and estimates will be less biased at drier sites with little snow accumulation.