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