Monday, August 6, 2007

PS 7-89: Examining the creation of alternate stable states in herbaceous community structure on ancient agricultural fields

Hoski Schaafsma and John Briggs. Arizona State University

This presentation summarizes the results of two studies of anthropogenic legacies in herbaceous communities documented on separate prehistoric agricultural systems that have been abandoned for between 650 and 750 years. Prehistoric agricultural practices at both study sites showed different degree of soil manipulation from simply clearing surface stones to significant alterations of soils through direct additions of new soil and amendments. The differing degrees of manipulation provide a gradient on which to evaluate the ‘strength of the legacy’ or amount of change that each agricultural technique has created in the modern landscapes. At both locations these patches are manifest as different plant communities and altered soil properties within the agricultural features when compared to control areas showing no signs of ancient cultivation. We have found that the differing degrees of prehistoric agricultural soil manipulations have left varying ‘strengths of legacy’ in the herbaceous communities and in the soils. These anthropogenic manipulations have increased the heterogeneity of the original landscapes, altered plant community structures, and the distribution of local populations resulting in long-term anthropogenic changes on a landscape scale. The persistence of these legacy patches provides a natural experiment with which to examine the genesis and longevity of alternate stable states of the extant plant community structures.

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