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Quaternary environments and N. hemisphere temperate forests Distribution Holocene dynamics The interglacial cycle “Long core” records Last Glacial Maximum refuges Migrations (rates and agents) Genetic divergence Quaternary extinctions
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Global distribution of temperate forests Temperate forest 30°N 45°N 60°N 45°S 60°S 30°S 15°S 15°N Eq.
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Pollen sites, eastern North America
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Pollen diagram, Kirchner Marsh, Minnesota. from: Webb (1980) J. Interdisciplinary History, 10, 749-772.
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Reconstructing post-glacial climate change (Kirchner Marsh, MINN)
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Reconstructing post- glacial vegetation change at a site
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The post-glacial (Blytt-Sernander) sequence
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Interglacial cycle of vegetation and soils (based on Iversen, 1948)
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Interglacial vegetation succession, Japan Climate PhaseDominants TemperatureMoisture Upper Cryptomeria, Sciadopitys TemperateWet Middle Cyclobalanopsis,WarmWet Castanopsis LowerFagus, LepidobalanusCoolWet from: Miyoshi et al., (1999) Rev. Palaeobot. Palynol, 104, 267-283.
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Is there a repetitive interglacial cycle? e.g. vegetation succession in mid to late Quaternary interglacials in Britain
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Does an increase in Pinus signal the end of an interglacial? Kirchner Marsh, MINN.
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> 50 ka >100 ka Long cores from temperate forest areas 30°N 45°N 60°N 45°S 60°S 30°S 15°S 15°N Eq.
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from: PAGES website Pollen record, Lago di Monticchio (Italy)
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Pollen record, Grande Pile (France) From: Guiot (1998) Nature 388, 25-27.
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Pollen record, Lake Biwa (Japan) Pinus = cool indicator; Cryptomeria = warm Indicator; Artemisia -grass-herb (not shown) “steppe/tundra” in full-glacial phases
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Pollen record, Carp Lake, WA. from: Whitlock and Bartlein (1997) Nature, 388, 57-61.
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from: Whitlock and Grigg, in: Webb et al., (1999) Mechanisms of Global Change at Millenial Time Scales, AGU Monograph, p 227-241.
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Heinrich events recorded at Lake Tulane, FLA.
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Present (potential) vegetation of North America Biome maps from: www.esd.ornl.gov/projects/qen
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LGM vegetation (18 ka 14 C yrs BP): North America
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Present (potential) vegetation of Europe
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LGM vegetation (22-14 ka 14 C yrs BP): Europe
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LGM (a) and present (b) pollen and vegetation (c,d) patterns in East Asia from: Harrison et al. (2001) Nature 413, 129-130. NB continental shelf extent
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Reconstructing LGM refuges and post- glacial migrations: isopoll data from: Davis and Shaw (2001) Science 292, 673-679.
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LGM refuges (R) and post-glacial isochrons in eastern North America. Where there separate Atlantic and Gulf refuges? R? White pine E. hemlock Oaks Elms
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How quickly did trees migrate in eastern North America in the post-glacial? 0 100 200 300 400 500 Jack/Red pine White pine Spruce Larch Elm Hemlock Balsam fir Maple Beech Oak Hickory Chestnut m / yr Data: Davis; in West et al. (1980) “Forest Succession: Concepts and Applications”. Springer-Verlag p. 153; and Delcourt and Delcourt (1987) “Quaternary Ecology” (after Webb, 1986)
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(=a x b) (a) (b) (c) (=a x c)
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Was the rate of post-glacial migration controlled by rates of climatic change or seed size? m / year Data: see previous slide and USDA (1974) “Seeds of Woody Plants in the United States” Agric. Handbook No. 450. 500 400 300 200 100 0 seed wt. (mg) 1 10 100 1 000 10 000 oaks white pine spruce larch elm hemlock hickory maple fir beech chestnut jack pine red pine
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Are seed-caching birds the main agents of dispersal in post-glacial time for ‘nut trees’? Fagus grandiflora Quercus macrocarpa blue jay passenger pigeon see: Webb (1986) Quat. Res. 26, 367-375 for discussion
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Postglacial fossil finds: passenger pigeon (dots) and blue jay (triangles ) from: Delcourt and Delcourt (1987) “Quaternary Ecology”
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Were some endochorous temperate trees marooned? (i.e. refugial relicts?) e.g. Maclura pomifera (osage orange) fruit weighs up to 1 kg Source: USDA Handbook - Silvics of Forest Trees Range
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Was this a product of the extinction of potential megafaunal vectors? e.g. Megalonyx jeffersoni (Jefferson’s ground-sloth) extinct by 10ka BP
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Did post-glacial migration result in reduced genetic diversity in northern populations? Allelic diversity low high from: Cwynar and MacDonald (1988) Amer. Nat. 129, 463-469. Colonization date in ka BP from pollen data
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Which refugial populations supply the migrants? e.g.Fagus crenata (a montane species during interglacials) recolonized northern Honshu and Hokkaido from northern coastal refuges after LGM LGM coastal refuges from: Davis and Shaw (2001) Science 292, 673-679.
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Hypothetical refugia and migration paths of Alnus rubra since the LGM based on genetic variation from: Hamann et al., (1998) Can. J. Forest Res., 28, 1557-1565.
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Post-glacial colonization routes of tree species based on DNA variation Fagus sylvatica Quercus sp. Taberlet et al., (1998) Molecular Ecology 7, 453-464
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Post-glacial colonization routes of tree species based on DNA variation Taberlet et al., (1998) Mol. Ecol. 7, 453-464; Scottii et al. (2000) Mol. Ecol. 9, 699-708. Abies alba Picea abies
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Post-glacial colonization routes of animals based on DNA variation from: Hewitt (2000) Nature, 405, 907-913.
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Post-glacial colonization routes of animals and subsequent hybrid contact zones from: Hewitt (2000) Nature, 405, 907-913.
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From: Jackson and Weng (1999) Proc. Nat. Acad. Sci. US, 96, 13847-13852. Extinction: Picea critchfeldii was a dominant tree in eastern North America in LGM; it died out about 15 000 cal. yrs BP Above: cross- sections of needles (E-G are P. critchfeldii). Left: cones of P. critchfeldii
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Why is the European forest depauperate? Quercus (oak) Acer (maple) Fagus (beech) Castanea (chestnut) Carya (hickory) Ulmus (elm) Tilia (basswood) Juglans (walnut) Liquidambar (sweet gum) Nyssa (sour gum) E N AmEuropeE Asia XXX XFX XXX XFX X = extant; F = fossil
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Quaternary extinctions of trees in the Netherlands loss of sub-tropical genera
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Causes of Quaternary plant extinctions 1. Abrupt climate change? 2. Barriers to migration (e.g. E-W mountain ranges)? 3. Loss of seed dispersal agents?
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