ИСТИНА

This report summarizes the methods and results of field studies conducted 18 July-2 August, 2011 at the Kharp study site in the southern Yamal region, northwest Siberia, Russia. Kharp is located in a forest-tundra ecotone at the southern margin of the Arctic tundra biome, in the eastern foothills of the northern Ural Mountains (66.83ºN, 65.98ºE). Comparisons of highresolution satellite imagery from 1968 and 2010 indicate widespread increases in alder (Alnus fruticosa ssp. sibirica) cover at the site. This finding is corroborated by pixel-based regression analysis of the Normalized Difference Vegetation Index (NDVI), derived from a Landsat imagery time-series spanning 1985-2011, that indicates strong, widespread increases in plant productivity (“greening”) in alder shrublands. A brief field reconnaissance to Kharp in 2009 revealed that most of the alder expansion occurred in areas of patterned ground with abundant sorted-circles, and that shrub recruitment was closely linked to mineral-dominated microsites at the circle centers. The primary goals of field studies in 2011 were to (1) identify important environmental state-factors associated with recent shrub expansion and greening; (2) determine whether alder expansion at Kharp is facilitated by cryogenic disturbance processes in patterned ground; (3) determine whether the distribution of older shrubs can be explained by shrub recruitment on sorted-circle microsites; (4) characterize changes to permafrost thermal regime that occur during shrubland development; and (5) characterize the changes in plant community composition that occur during shrubland development. Field methods used in 2011 differ from previous expeditions along the Eurasian Arctic Transect, which had different objectives (Walker et al. 2008, 2009a, 2009b, 2011). Studies at Kharp primarily occurred along transects established in alder-free tundra and in alder shrublands belonging to one of three categories of shrubland stand-age: recent colonization zones, mature shrublands (shrubs evident in 1968 imagery, and most shrubs ≥ 2 m height), and paludified shrublands (very old shrubs growing on organic-dominated soils). Data collected at each transect include (1) measurements of soil surface organic depth and mineral horizon thickness taken at uniform intervals along the transects, and at alders; (2) physical attributes of shrubs including age-class and canopy height; (3) soil descriptions at circle and inter-circle microsites; and (4) relevé data including plant species cover-abundance. At a subset of the transects, we also (1) mapped the locations of alders and patterned ground microsites; (2) measured Leaf Area Index (LAI); and (3) recorded daily time-series of near-surface soil temperature at different patterned ground microsites (with and without alder) using iButton dataloggers. Appendices to this report include: Appendix A – Names and addresses of the participants in the expedition; Appendix B – Soil descriptions for the transects; Appendix C – Relevé data; and Appendix D – Bird species list.