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UW-Madison BOTANY 422 - The Holocene

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Assembly of the Great LakesFlora and Vegetation. . . the Holocene . . .Assembly of Great Lakes Flora18,000 yaPresentHow did the assembly of flora and vegetation in the Great Lakes happen? ?• Pollen record shows waves of vegetation over time• Boreal elements (spruce) early in the Holocene, followed by pinecommunities, and then oak, maple, and other hardwoodssprucepineoakbeechmapleAssembly of Great Lakes FloraShifts of vegetation beltsstarting at about 13,000 ya withtundra, spruce, pine, northernhardwood, pine-oak, and thenoak-hickorytundraborealspruce-pinepine-spruce-hardwoodmixedhardwoodoak-hickoryAssembly of Great Lakes FloraConiferous species migrated into theGreat Lakes region in waves:Boreal species like spruce, tamarack,and balsam fir arrived firstAssembly of Great Lakes FloraAssembly of Great Lakes FloraConiferous species migrated into theGreat Lakes region in waves:Boreal species like spruce, tamarack,and balsam fir arrived firstAssembly of Great Lakes FloraConiferous species migrated into theGreat Lakes region in waves:Boreal species like spruce, tamarack,and balsam fir arrived firstAssembly of Great Lakes FloraConiferous species migrated into theGreat Lakes region in waves:Xeric pine species like jack pine andred pine arrived nextAssembly of Great Lakes FloraConiferous species migrated into theGreat Lakes region in waves:. . . followed by more mesic whitepineAssembly of Great Lakes FloraConiferous species migrated into theGreat Lakes region in waves:Hemlock, characteristic of mesicNorthern Hardwood forests, arrivedlastAngiosperm trees migrated into theGreat Lakes region in waves towardsthe end of conifer migration:Oaks, hickories and elms arrivedfirst - 11,000 ybpAssembly of Great Lakes FloraAssembly of Great Lakes FloraAngiosperm trees migrated into theGreat Lakes region in waves towardsthe end of conifer migration:Followed by mesic-loving maplesAssembly of Great Lakes FloraAngiosperm trees migrated into theGreat Lakes region in waves towardsthe end of conifer migration:And finally American beech lastRate of species migration (shown in the chart below as miles per year)is dependent on a number of factors:• location duringPleistocene• ecological climateenvelope of eachspecies• type of seed/fruitdispersers• seed dispersal rate(seed/fruit weightgiven in milligrams)Assembly of Great Lakes FloraImportantly, the different species of trees (and herbs) entering the GreatLakes region after the glaciers retreated entered via different routes - thatis, they came from different refugia or surviviaAssembly of Great Lakes FloraWhite pine from the Alleghenianrefugium and present distributionOaks from either the Alleghenian (white oak) or Ozarkian(bur oak) refugia and present overlapping distributionsAssembly of Great Lakes FloraImportantly, the different species of trees (and herbs) entering the GreatLakes region after the glaciers retreated entered via different routes - thatis, they came from different refugia or surviviaAlleghenian Ozarkian• Examine idea of Pleistocenerefugia or survivia moregenerally for NorthernHemisphere• Centers of endemism• Differential extinctionAssembly of Great Lakes FloraImportantly, the different species of trees (and herbs) entering the GreatLakes region after the glaciers retreated entered via different routes - thatis, they came from different refugia or surviviaAlleghenian OzarkianHigh frequency of endemic species in central Alaska was used by EricHulten (1937) to argue for a major unglaciated Beringian refugiumduring PleistoceneEndemic species percontour intervalPleistocene Refugia ?Based on similar levels ofnarrow endemism, Hultenproposed a central eastAsian refugiumPleistocene Refugia ?The assembly of Holocene flora in northern Europe, especially GreatBritain, shows a similar pattern to that in eastern North Americaelm alderfast migrationbeechslow migrationPleistocene Refugia ?Presence of survivia or refugia of these plants and animals south of theice has been a major contention in Europe — are these centers ofgenetic diversity actually refugia during the Pleistocene?Pleistocene Refugia ?Presence of survivia or refugia of these plants and animals south of theice has been a major contention in Europe — are these centers ofgenetic diversity actually refugia during the Pleistocene?Pleistocene Refugia ?Presence of survivia or refugia of these plants and animals south of theice has been a major contention in Europe — are these centers ofgenetic diversity actually refugia during the Pleistocene?Levels of species endemism in the North Atlantic -black pie sections indicate proportion of endemismLack of endemism in putativeglacial “refugia” in North Atlantic,but high endemism in “refugia”south of glaciated regionsPleistocene Refugia ?Also contentious is whether the east-west running mountains incentral Europe were a barrier to deciduous forest southward retreatduring glacialsNorthSouthPleistocene Refugia ?Are the Pleistocene glaciers to blame for the lower European treediversity relative to eastern North America and eastern Asia?Europe 106 tree spp.Eastern NorthAmerica156 tree spp.Eastern Asia 876 tree spp.Pleistocene Refugia ?Tsuga — hemlockEuropeEastern NorthAmericaEastern AsiaTsuga found in all three areas as fossilsPresent in all three areas at presentThree examples illustrating the depauperate nature of European flora now:Pleistocene Refugia ?EuropeEastern NorthAmericaEastern AsiaLiriodendron found in all three areas as fossilsPresent in only two areas at presentLiriodendron tulipfera — tulip tree Liriodendron chinenseThree examples illustrating the depauperate nature of European flora now:Pleistocene Refugia ?Pterocarya - wingnutIcelandIdahoEuropeEastern NorthAmericaEastern AsiaPterocarya found in all three areas as fossilsPresent in only one area at presentThree examples illustrating the depauperate nature of European flora now:Pleistocene Refugia ?Closely related species (such asoaks) can often be part of differentfloristic elements.This is due to both differentecological preferences (such ashydric vs. mesic vs. xeric) and togeographical origin.Quercus - the oaksAssembly of Great Lakes FloraThe flora of the Great Lakes can be divided into a number of elements,each of which shares a common geographical origin.1. Alleghenian: group of species with ranges centered fromCumberland and Great Smoky mountains; dominant in deciduousforests; e.g. white pine, hemlock and basswood; ancient elementextending back to the


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UW-Madison BOTANY 422 - The Holocene

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