THE PLEISTOCENE "TUNDRA-STEPPE" AND THE PRODUCTIVITY PARADOX: THE LANDSCAPE APPROACH

Abstract

“Tundra-steppe” means either a certain type of plant community with codominance of both steppe and tundra species (including prostrate shrubs), or a type of landscape, codominated by both steppe and tundra (Yurtsev, Relic Steppe Complexes of Northeastern Asia. Nauka Press, Novosibirsk (in Russian) 1981; In: Hopkins, Matthews Jr., Schweger, Young, (Eds.), Paleoecology of Beringia. Academic Press, New York, 1982, pp. 157–177). A discrepancy between Pleistocene glacial climates that were much colder and drier than present in Beringia and the highly diverse herbivorous fossil fauna (the “productivity paradox”) is explained in terms of much greater diversity of herbaceous vegetation (grasses, sedges and forbs) in the mosaic of Beringian ‘tundra-steppe’ landscapes. Analysis of the relic distribution of some predominantly herbaceous plant communities throughout Beringia (Yurtsev, 1981, 1982, Komarovskiye chteniya (Vladivostok) 33 (1986) 3–53 (in Russian); Protection of Gene- and Coenotic Pool of the Herbaceous Biogeocoenoses, Sverdlovsk, 1988, pp. 128–129 (in Russian); Bridges of Science Between North America and the Russian Far East, 45th Arctic Science Conference, Abstracts, Vol. 1. Dalnauka Press, Vladivostok, 1994, p. 268; Paleontological Journal, 6 (1996)) provides the phytogeographic and landscape — ecological grounds for the reconstruction of plant cover of these landscapes. Dry watersheds and slopes had cryophytic (cold-adapted) steppes, cryoxerophytic (cold and dry-adapted) herbaceous and prostrate shrub-herbaceous communities, dry herb-prostrate shrub tundras, and tundra-steppe communities proper. All sorts of depressions on interfluves and in valleys along with concave pediments were occupied by dry steppe-meadows and brackish-water moist meadows. In some specific habitats sparse groupings of continental halophytes (plants growing in saline soils) of “arctic takkyrs”, zoochoric (plants with seeds dispersed by animals) groupings of annual-biennial “ruderals” and, finally, sparse xeric-psammophytic (plants adapted to dry, sandy soils) vegetation of “sand seas” occurred. Meadows in valleys and on slope pediments were the most productive as pastures for ungulates due to the redistribution of moisture and nutrients within landscapes. The lowest parts of the exposed shelf in the Bering Strait vicinities were the “bottle-neck” for the dispersal of steppe plants and animals.