Predick, K. I. 2002. The importance of flood regime for tree growth and shrub productivity on the Wisconsin River floodplain and uplands. MS Thesis, University of Wisconsin, Madison.

Large river floodplains are diverse systems that provide a variety of ecosystem services. Productivity in floodplains may be highly influenced by flood regime and the flood tolerance of individual species, but relatively few studies have directly tested for such effects. We studied tree growth and shrub productivity in leveed and unleveed areas of the Wisconsin River floodplain and in upland forests to address two questions:  (1) How do tree growth rates and shrub productivity in floodplain forests of the Wisconsin River vary with flood regime and compare to upland tree growth? (2) What is the relationship between flood occurrence and the growth rate of flood-tolerant and flood-intolerant tree species?  This was assessed using tree increment cores to determine annual growth rates.  Mean annual basal area increment (BAI) between 1996 and 2000 of floodplain forest stands was ~300 mm2/m2/year, and reduction of flood regime by levees did not influence tree growth rates. Furthermore, mean BAI and relative basal area increment (RBAI) did not differ between floodplain and upland forest stands, although species composition differed.  Aboveground net primary production of the dominant shrub (Zanthoxylum americanum) ranged from 2  to 117 g/ m2/year and was significantly reduced by levees. The five-year (1996-2000) average annual BAI and RBAI of individual trees differed significantly among species (1190 mm2/yr for Fraxinus pennsylvanica, 1892 mm2/yr for Betula nigra, and 2913 mm2/yr for Quercus velutina and ellipsoidalis.. These results suggest that, although species occurrence and community composition may vary with flood regime, tree growth rates are minimally influenced by location relative to the floodplain or levees. Setback levees on the Wisconsin River floodplain do not appear to be altering tree productivity.