A Paleoecological Test of a Classical Hydrosere in the Lake Michigan Dunes

Abstract

Aquatic vegetation varies along a chronosequence of dune ponds at Miller Woods, Indiana Dunes National Lakeshore. Submersed and floating-leaved macrophytes dominate the vegetation of the youngest ponds. Older ponds contain mixed assemblages of submersed, floating-leaved, and emergent plant taxa. The oldest ponds are dominated by emergent plants, especially Typha angustifolia. We conducted paleoecological studies at one of the oldest ponds to test the hypothesis that the modern vegetational array along the pond chronosequence represents a hydrarch successional sequence. Macrofossil stratigraphy of the 3000-yr-old pond indicates no significant changes in pond vegetation following early colonization until < 150 BP. Pond vegetation before 150 BP consisted of a diverse assemblage of submersed, floating-leaved, and emergent macrophyte taxa. Pollen and macrofossil data indicate a major, rapid vegetational change at < 150 BP, evidently in response to local human disturbance. Pollen data reveal that the extensive Typha stands in the older ponds have developed recently, following postsettlement disturbance. Modern vegetational differences along the chronosequence reflect differential effects of disturbance rather than autogenic hydrarch succession. This study illustrates a major pitfall in inferring successional trends from spatial sequences of vegetation.