Time lags and disturbance legacies: Community transitions over 150 years in an Indiana wetland

Background/Question/Methods

Paleoecological data demonstrate that a 3,000 year old wetland in Indiana had remarkably stable
community composition from its formation until the mid-1800s. A large shift in community
composition is coincident with the arrival of European settlers, who altered wetland configuration
and sedimentation rates via railroad construction, industrial development, and harvesting of
upland pines. We used paleoecological techniques to investigate the patterns of community
turnover post-settlement. We analyzed macrofossil abundance and taxa composition for the past
150 years at 5-10 year intervals in multiple sediment cores from a large (6 ha) wetland fragment.

Results/Conclusions

Macrofossil analyses demonstrate that two community transitions occurred in this wetland
over the past 150 years. The pre-disturbance community, co-dominated by diverse sedge
meadows and open water taxa (e.g. Brasenia schreberi, Najas flexilis), disappeared with
European settlement. Post disturbance a transitional community formed, indicated by a marked
increase in Sparganium sp. and Schoenoplectus acutus and a concurrent loss in open water taxa.
The transitional community lasted until about fifty years ago when the modern Cephalanthus-
Typha matrix formed. These results indicate that it may take centuries for community changes to
play out, and even long-term ecological data spanning multiple decades may not be sufficient to
understand community responses to disturbances.