Abstract

Palynologic analyses of four short cores collected along shallow- to deep-water transects in Second and Gignac lakes indicate two periods of forest clearance for farming. The first deforestation was by Huron Indians between A.D. 1450 and 1650, when a maple (Acer), beech (Fagus), and oak (Quercus) forest was cleared and corn (Zea) planted. This disturbance is identified by decreased tree pollen and increased Pteridium, Artemisia, and other herbs and is confirmed by Zea pollen in Gignac Lake. From 1650 to 1875 there was a forest succession to oak, birch (Betula), and pine (Pinus). Following this recovery European loggers and farmers cleared this forest and attempted farming. Besides a reduction in tree pollen, a product of this deforestation includes the pollen of weedy Ambrosia, Gramineae, and introduced European Rumex and Plantago. During the last 25 years an increase in tree pollen indicates local forest recovery consistent with present land use.By relating upland vegetation successions to lacustrine algal assemblage changes, probable ecological controls on algae during the last 600 years are identified. Peridinium willei Huitfeldt-Kaas and Pediastrum respond to changes induced by forest clearance and agriculture. Aquadulcum awendae n. sp. and Peridinium wisconsinense Eddy prefer less alkaline water.Variations in palynomorph influx are related to basin morphology and water circulation. Gignac Lake, a steep sided and relatively deep lake, directs palynomorphs from shallow marginal banks to the deeper basin, whereas Second Lake, with a gently sloping shallow lake bottom, preferentially accumulates palynomorphs close to shore.

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