Which Is More Sustainable, Single Species Stand or Mixed?.

Recent interest in productivity of plant mixes as compared to monocultures prompted us to mine the extensive databases of native plant mixes (the ecological site productivity data) and the crop productivity data of USDA-NRCS for high yielding forage crops on several soil types in many counties in the U.S.  We  compared native plant community productivity with alfalfa (in Nebraska, Kansas, and Oklahoma) or with coastal bermudagrass (in Texas), with specific interest in seeing how low the monoculture productivity had to be in order for the diverse native system to have similar productivity to the monoculture.  In 70 to 75% of the sites, alfalfa was more productive than the native communities.  Our regressions showed that alfalfa annual productivity had to drop to 3.2 Mg ha^-1 in order for the native communiy to be comparable in Nebraska, and to 3.0 for native communities to be comparable in Oklahoma, and failed to ever be less than native communities in Kansas.  In Texas, native communities were comparable to coastal bermudagrass when the latter had productivity of 4.6 Mg ha^-1.    Forty-two percent of the Texas sites had higher productivity for the native communiy.  When we extended this work to switchgrass, the regressions showed that in no case was native communiy productivity comparable to switchgrass productivity in the range of reported yields.   However, buffelgrass results for southern Texas showed native communities had higher annual productivity at all sites where buffelgrass was less than 4.4 Mg ha^-1.