Productivity of Loessal Grasslands in the Kluane Lake Region, Yukon Territory, and the Beringian "Production Paradox"

Abstract

ABSTRACT. The Beringian "Production Paradox" is posed by abundant evidence that large ungulates populated unglaciated portions of northwestern North America and adjacent northeast Asia during the late Pleistocene, while botanical data from the same period suggest a poorly productive tundra environment. It is not clear how the large animals sustained themselves, but portions of Beringia, locally in receipt of loess, may have harbored sufficient forage-producing plants to nourish these animals. Loessal soils in the region today are warm and dry in summer, and are often used as rangelands. The loessal hypothesis was examined on grasslands in the Kluane Lake area, southwest Yukon Territory, at sites which have recently received loess blown from the Slims River delta. The biomass and species diversity of grasslands around the lake increase with the quantity of silt in the soil. Likewise, soil fertility indices, including total nitrogen, available nitrogen (NH 4 ), and total carbon, increase with silt content, particularly at sites where the soil surface has been stable for some time, and a "humified" loess (Ahk) horizon has developed. These results support the hypothesis that sites in receipt of loess may have played a significant role in the vegetative productivity of the Beringian ecosystem.Key words: Beringia, production paradox, cryosols, loess, Kluane Lake, Yukon Territory RÉSUMÉ. Le paradoxe de production Béringien signale que de nombreux indices témoignent de la présence de larges ongulés dans des régions non-glaciées du nord-ouest de l'Amérique du Nord et du nord-est de l'Asie adjacente durant le Pléistocène supérieur, alors que des données botaniques datant de la même époque suggèrent l'existence d'une toundra peu productive. Comment d'aussi larges animaux ont pu subvenir à leurs besoins n'est pas absolument clair mais certaines portions de la Béringie recevant des apports en loess ont pu récéler suffisamment de plantes fourragères pour les nourrir. Aujourd'hui, les sols loessiques de la région sont chauds et secs durant l'été et sont souvent utilisés comme pâturages. L'hypothèse loessique est examinée pour les prairies des environs du lac Kluane, en particulier dans les sites où des loess provenant du delta de la rivière Slims se sont récemment accumulés. La biomasse et la diversité des espèces dans les prairies avoisinant le lac accroissent avec la quantité de silt contenue dans le sol. De même, les indices de fertilité du sol, incluant l'azote total, l'azote libre (NH 4 ) et le carbone total accroissent avec le contenu en silt, particulièrement dans les sites où la surface est demeurée stable durant un certain temps et où un horizon loessique humifié (Ahk) s'est developpé. Ces résultats confirment l'hypothèse que les sites ayant eu des apports en loess ont pu jouer un rôle significatif dans la productivité végétale de l'écosystème Béringien.

Topographically controlled grassland soils in the Boreal Cordillera ecozone, northwestern Canada

“…(3) Along the southeastern shore of Kluane Lake, calcareous loess derived from the delta of the glacier-fed Slims River occurs as a silty veneer draped over a hummocky landscape of coarse glaciofluvial deposits. Loess deposition accelerated during the late Holocene in response to glacier expansion and increased sediment delivery by the Slims River (Laxton et al 1996). Dust storms occur frequently in the lower Slims River valley during low water conditions and can be observed blowing across Kluane Lake.…”

“…In steeply sloping grasslands, much of the tephra veneer has been modified by organic matter accumulation to form Ah horizons that are generally less than 10 cm thick and overlie buried profiles classified as Melanic Brunisols (Strickland et al 2005). In grasslands at Kluane Lake, southwestern Yukon, A horizons of Melanic and Eutric Brunisols exhibit effervescence and alkaline soil reactions, reflecting their calcareous loess parent material (Laxton et al 1996).…”

Biogeographical Evidence for the Grass (Poaceae) Species of Pleistocene Beringian Lowlands

“…1990). Similarly, grasses may have been favored over other plants in the Pleistocene by ungulate grazing and trampling (Zimov et al, 1995) and loess deposition (Laxton et al, 1996). Impressive natural stands of A. latifolia grow on silty tundra in northern Sakha (Yakutia, Fig.…”

The Pleistocene Peopling of the North: Paleolithic Milestones and Thresholds Horizons in Northern Eurasia

“…The debated concept (Stanley, 1980) of an extinct distinct Pleistocene biome developed progressively (Hibbert, 1982). Controversies arose from reconciling actualist extrapolations to the Pleistocene and across latitudes of living vegetation formations (Hammen, Wijmstra, Zagwijn, 1971) with ecological incompatibilities between pollen and fossil mammal evidence (Colinvaux, 1980;Colinvaux, West, 1984;Laxton, Burn, Smith, 1996). Palynological arguments to the effect that glacial maxima, high-latitude, periglacial continental zones became sparse "desolate" tundras or polar deserts were refuted by comprehensive reviews, fossil and mummi ed mammal evidence (including stomach contents), pollen, plant/ animal ecology, insects, and dated sites (Nowak et al, 1930;Vereshchagin, 1971;Bader, 1968;Vereshchagin, Baryshnikov, 1982;Kislev, Nazarov, 1985;Guthrie, 1985Guthrie, , 1989Guthrie, , 2001Auguste, 1996;Laxton, Burn, Smith, 1996;Kahlke, 1999;Orlova, Kuzmin, Zolnikov, 2000;Orlova, Kuzmin, Dementiev, 2000;2007;Harington, Cinq-Mars, 2008): most Pleistocene cycles supported distinct habitats with few modern biota analogs of complex oral and faunal mosaics (Yurstev, 1982), "Pleistocene plaids versus Holocene stripes" (Guthrie, 1989); the Biome formed an extinct biotic zone unit encompassing a sympatric amalgam of different plant and animal communities and sub-communities throughout northern Eurasia and Beringida (Guthrie, 1985;Markova, Puzachenko, Kolfschoten, 2010).…”