Holocene Vegetation Change at Treeline North of Yellowknife, Northwest Territories, Canada

Abstract

Two radiocarbon-dated cores from small lakes located approximately 25 km north of the mapped boundary between forest-tundra and tundra provide records of postglacial vegetation change at the treeline near Yellowknife, NWT, Canada. Basal radiocarbon dates of 6180 and 7470 yr B.P. were obtained from the cores. The fossil pollen evidence suggests that the initial vegetation wasBetulatundra with a peatland component.Alnusbecame an important constituent of the pollen assemblages between 6900 and 5500 yr B.P. Both lakes record sharp increases inPiceacf.marianapollen at approximately 5000 yr B.P., suggesting the establishment of forest-tundra. By 3500 yr B.P.Picea marianaforest-tundra had withdrawn. The proportion of organic to inorganic sediment in the cores was at a maximum between 5000 and 3500 yr B.P. Tundra has dominated the region since 3500 yr B.P. In northwestern Canada, the maximum northward advance of treeline occurred between 9000 and 5000 yr B.P. The asynchrony in treeline advance in central and northwestern Canada may reflect that glacial ice persisted in the interior NWT longer than previously believed. Alternatively, the asynchronous history of the treeline may be a result of the geometric properties of the long-wave westerly disturbance that is manifest in the median summer position of the arctic front and ultimately controls the geographic location of the treeline.

Changes in Driftwood Delivery to the Canadian Arctic Archipelago: The Hypothesis of Postglacial Oscillations of the Transpolar Drift

“…For example, a tree line fluctuation of 100 km in the Mackenzie drainage would change the cumulative length of river courses traversing the boreal forest by only about 1%. In addition, although there have been changes in boreal forest limits on both continents during the Holocene (Nichols, 1976;Moser and MacDonald, 1990;MacDonald and Velichko, 1994), it is entirely unclear how these changes can be invoked to explain cogently the details of the driftwood records.…”

Holocene thermal maximum in the western Arctic (0–180°W)

“…Accurately dating sediment from lakes with a paucity of macrofossils, common at high latitudes, is particularly difficult. et al (1993) and Moser and MacDonald (1990) Studies that were based on fewer than three 14 C analyses for the Holocene were excluded. The age models for the lake-and marine-sediment records in our database are supported by an average of one 14 C date per 2500 yr.…”

“…The broad-scale pattern of Holocene climate change in this subregion has been identified through evidence from lakes (Moser and MacDonald, 1990;MacDonald and Gajewski, 1992;MacDonald et al, 1993;Szeicz et al, 1995;Edwards et al, 1996;Wolfe et al, 1996;Pienitz et al, 1999;Szeicz and MacDonald, 2001), peat (Nichols, 1975;Kay, 1979;MacDonald, 1983), and the distribution of paleopodzols (Bryson et al, 1965;Sorenson, 1977). Many of these studies infer a climate warmer than present during the mid-Holocene (ca 8-5 ka), resulting in increased vegetation density or a northward displacement of treeline, followed by cooling during the late Holocene (ca 4-2 ka).…”

Postglacial Vegetation at the Northern Limit of Lichen Woodland in Northwestern Québec

“…These changes include a northward advance of Picea in the MacKenzie Delta region in the early Holocene (10 000 yr BP), followed by a retreat after 7000 yr BP (Spear, 1983(Spear, , 1993Ritchie, 1984). A similar sequence has been found in central Canada, but it occurred later, with an advance and subsequent retreat between 5500 and 3500 yr BP (Nichols, 1975;Moser and MacDonald, 1990). In eastern Canada, Picea arrived at its present-day limit shortly after déglaciation less than 6000 yr BP.…”

“…1) but not in the lichen woodland (GB2: Gajewski et al, 1993;Bereziuk, Chism-I, Chism-ll: Richard, 1979). Although there is a suggestion of a decrease in spruce in northwestern Canada during the past 4000 yr BP (Spear, 1993), there is less change in central Canada (Moser and MacDonald, 1990). The modem climate patterns had set in between 6000 and 3000 yr BP, as the last of the Laurentide ice had melted by this time (COHMAP, 1988).…”