1!(Dis)Assembly of the Great Lakes Forests!Photo credit: Rob Alderink!• Pleistocene placement of the forests - where did they hang out!• Holocene migrations - how and when did they assemble into the Great Lakes!• Recent past, present, and future changes – the dis-assembly?!The Questions!• Vegetation refers to the physical appearance (physiognomy) of the forest type - ecology driven!• Flora refers to the species (genus, family) composition of any given forest - history driven!Vegetation vs. Flora!Northern hardwood forests in WI and MI have sugar maple, but beech co-dominates mainly in MI!• The vegetation and flora as we see it now (Holocene) was dramatically affected by Pleistocene events!Pleistocene - the Ice Ages!2!• In the Tertiary, earth experienced intensification towards climatic cooling!• Culminated with a series of glacial-interglacial cycles in Pleistocene!• North American flora and vegetation profoundly influenced by these “ice-age” events!Pleistocene - the Ice Ages!Break-up of the great Northern Hemisphere Arcto-Tertiary forests!Pleistocene - the Ice Ages!• Wisconsin glaciation (last epoch) most important - maximum at 18,000 ya!• Assembly of flora and vegetation of most Great Lakes was during the late Pleistocene and Holocene - (14,000 ya to present)!Pleistocene - the Ice Ages!Pleistocene - the Ice Ages!• North America south of glaciers!• Beringia, much of Alaska, Siberia!• Coastal plains, steep coastlines of Pacific northwest!• Wisconsin Driftless Area - never completely surrounded by ice!Ice-free Areas!3!Pleistocene - the Ice Ages!What was happening south of the glacial maxima?!?!Pleistocene - the Ice Ages!• Paleobotanists aided by the pollen record (especially trees) in lakes and bogs to understand Pleistocene vegetation and flora!Pleistocene - the Ice Ages!Yearly deposits accumulate in lake bottoms to be covered by silt in layers, or in bog peat strata!Pleistocene - the Ice Ages!• Pollen record of White Pond, South Carolina (33o N)!• Note boreal elements (spruce) early in the record!4!Pleistocene - the Ice Ages!• Pollen record of Wood Lake, WI (45o N)!• Note boreal elements (spruce) early in the record!Pleistocene - the Ice Ages!18,000 ya! 28 - 25,000 ya!• Extensive boreal (taiga) forest zone to 33°S!• Mixed deciduous forest zone near Gulf!• 18,000 ya harshest conditions; zones were further north earlier!Pleistocene - the Ice Ages!Illinois 16K years ago!White spruce - Picea glauca!!Most widespread tree in North America!• Much of eastern North America would have looked like this boreal scene!Pleistocene - the Ice Ages!13,000 ya!• 14,000 ya ice begins retreat!• Vegetation units move north!11,000 ya!• Proglacial lakes form!• St. Lawrence Seaway exposed!Lake Agassiz!5!Holocene - the Recent Times!8,000 ya!Present!Prairie peninsula!extends east!• Ice retreats continues into Holocene (10,000 ya)!• Warmest time of Holocene is Hypsithermal - 8,500 to 6,000 ya!• Pleistocene placement of the forests - where did they hang out!• Holocene migrations - how and when did they assemble into the Great Lakes!• Recent past, present, and future changes – the dis-assembly?!The Questions!18,000 ya!Present!How and when did this assembly in the Great Lakes happen? !Assembly of Flora & Vegetation!• Pollen record shows waves of species over time!• Boreal elements (spruce) early in the Holocene, followed by pines, and then oaks, maples and lastly beech!spruce!pine!oak!beech!maple!Assembly of Flora & Vegetation!6!Shifts of vegetation belts starting at about 13,000 ya with tundra, spruce, pine, northern hardwood, pine-oak, and then oak-hickory!tundra!boreal!spruce-pine!pine-spruce-hardwood!mixed hardwood!oak-hickory!Assembly of Flora & Vegetation!Coniferous species migrated into the Great Lakes region in waves (flora):!Boreal species like spruce, tamarack, and balsam fir arrived first!Assembly of Flora & Vegetation!Assembly of Flora & Vegetation!Coniferous species migrated into the Great Lakes region in waves (flora):!Boreal species like spruce, tamarack, and balsam fir arrived first!Assembly of Flora & Vegetation!Coniferous species migrated into the Great Lakes region in waves (flora):!Boreal species like spruce, tamarack, and balsam fir arrived first!7!Assembly of Flora & Vegetation!Coniferous species migrated into the Great Lakes region in waves (flora):!Xeric pine species like jack pine and red pine arrived next!Assembly of Flora & Vegetation!Coniferous species migrated into the Great Lakes region in waves (flora):!. . . followed by more mesic loving white pine!Assembly of Flora & Vegetation!Coniferous species migrated into the Great Lakes region in waves (flora):!Hemlock, characteristic of mesic Northern Hardwood forests, arrived last!Assembly of Flora & Vegetation!Angiosperm hardwoods migrated into the Great Lakes region in waves towards the end of conifer migration:!Oaks arrived first from the south - 11,000 ya!8!Assembly of Flora & Vegetation!Angiosperm hardwoods migrated into the Great Lakes region in waves towards the end of conifer migration:!Elms arrived at about the same time from the southeast - 11,000 ya!Assembly of Flora & Vegetation!Angiosperm hardwoods migrated into the Great Lakes region in waves towards the end of conifer migration:!Hickories arrived shortly thereafter from the southwest - 10,500 ya!Assembly of Flora & Vegetation!Angiosperm hardwoods migrated into the Great Lakes region in waves towards the end of conifer migration:!Followed by mesic-loving maples . . .!Assembly of Flora & Vegetation!Angiosperm hardwoods migrated into the Great Lakes region in waves towards the end of conifer migration:!. . . and finally American beech last!9!Rate of species migration (shown in the chart below as miles per year) is dependent on a number of factors: !• location during Pleistocene!• ecological climate envelope of each species!• type of seed/fruit dispersers!• seed dispersal rate (seed/fruit weight given in mg) !Assembly of Flora & Vegetation!Red pine!vs.!American beech!Rate of species migration (shown in the chart below as miles per year) is dependent on a number of factors: !• location during Pleistocene!• ecological climate envelope of each species!• type of seed/fruit dispersers!• seed dispersal rate (seed/fruit weight given in mg) !8.7 mg!250