Restoration efforts in sites invaded by exotic grasses: Improved by native soil amendment

Background/Question/Methods Old World Bluestems (OWB; Bothriochloa bladhii; B. ischaemum) are non-native, perennial, warm-season grasses that have been planted extensively throughout the Great Plains through the USDA-NRCS Conservation Reserve Program.  In addition, state Departments of Transportation have seeded OWB along roadsides for soil erosion control. These species are known to occur in Texas, Oklahoma, Kansas, Colorado, New Mexico, Ohio, Louisiana, and Florida are now common in roadsides and pastures, and are invading into adjacent native grasslands. In monocultures, OWBs reduce biodiversity and habitat for small mammal, bird, and arthropod communities relative to native prairie.  To examine the conversion of OWB monocultures to native prairie grass and forb species, we established field sites at the Marvin Klemme Range Research Station in western Oklahoma. A combination of herbicide applications and prescribed burning were implemented in 2007 to eradicate OWB, followed by seeding of native grass and forb species. Single, multiple, and combined treatments of glyphosate and burning were applied throughout the growing season in 10x10m plots. In March 2008 each 10x10m plot was split into two subplots, with either a high diversity seed mix (34 native plant species) or a NRCS recommended seed mix (8 native plant species) no-till seeded into each subplot.  August 2008, percent cover of all seedling and adult plants was visually estimated.

Results/Conclusions Limited germination was observed in all plots, with <20% of any species of either seed mix exhibiting germination.  In a complementary greenhouse study, seeds of each species from the high diversity seed mix (34 total species) were seeded into freshly collected field soil from each OWB eradication treatment (single, multiple, and combined treatments of glyphosate and burning) and percent germination was assessed 1,2,3,4, and 7 weeks following seeding. Soil from OWB monocultures sites significantly reduced germination of all native species tested. Soil collected from OWB eradication sites (receiving glyphosate and burning) were generally characterized by increased germination of native seeds, as compared to OWB monoculture sites. However, amending the field soils with native prairie soil improved germination of all treatment soils, with a 10-fold increase in germination observed for many of the native species.  This study indicates that successful remediation of OWB monocultures to native plant communities may be improved with amendments of native prairie soils, thereby restoring soil biotic communities and function.