LATE PLEISTOCENE-EARLY HOLOCENE LANDSCAPE ADJUSTMENT ON THE NORTHERN PLAINS IN ALBERTA: CONTRASTING THE PLANT AND FAUNAL RECORDS

The late Pleistocene-Holocene (LPEH) transition (spanning 12,000 – 8,000 yr BP) on the northern plains represents an interval of pronounced climate change associated with a shift from glacial to non-glacial conditions and consequent landscape adjustment. This adjustment included redistribution of volumes of unstable sediment, driven by paraglacial processes, slope failure, and river down-cutting, as well as drainage of proglacial lakes, and aeolian deposition. Such landscape changes had profound consequences for the nature and preservation of LPEH plant and vertebrate fossil remains and for the understanding of a more integrated picture of the biotic record. Faunal remains are generally fragmentary and usually consist of isolated elements, predominantly from large mammals, notably Bison, and are mostly recovered from fluvial sedimentary contexts along the major prairie rivers. Only rarely are complete specimens or trace evidence found. Archaeological sites provide a different, albeit selective, source of faunal remains; Bison also comprise the majority of specimens. In contrast, plant-based records (pollen or plant macroremains) are found in prairie upland contexts, such as short-lasting wetlands, in kettle lakes or lakes in meltwater channels. Few palaeoecological sites in this region yield continuous records across the LPEH interval; many are “snapshots”. Plant evidence documents rapid establishment of open vegetation across much of southern Alberta. Previous models involving northward migration of forest across the plains are not supported. Rather, forest appears to have been restricted to a narrow band along the margin of retreating Laurentide ice. Notwithstanding their differing taphonomic and depositional contexts, plant and faunal records consistently indicate rapid establishment of open grassland landscapes occupied by grazing mammals. The role of bison in structuring Holocene vegetation on the northern plains was thus established soon after deglaciation.