Incrementally Rich Seeding Treatments in Tallgrass Prairie Restoration

Abstract

Experimental plots were established in 2007 to examine relationships between seeding mixture treatments and establishment of tallgrass prairie plantings. Native grass and wildflower seed mixtures, representing four functional groups (C₄ grasses, C₃ grasses, nitrogen-fixing species, and late-flowering composites), were sown at five levels of richness—4, 8, 12, 16, and 20 species—in 900-m² plots. Annually, I measured total cover, species richness, and evenness for target and non-target species. Plots seeded with 16 and 20 species achieved 100% target cover by the second year; plots seeded with 12 species had 100% target cover by the fourth year. Plots seeded with 8 or more species had less non-target cover than 4-species plots by the second year, a pattern that persisted. Target species richness of plots increased directly with treatment seeding richness, except there was no difference between the 16- and 20-species treatments in four of the years. Non-target species richness varied among treatments in five of seven years, with non-target richness highest in 4- and 8-species treatments. There were few treatment effects on target evenness; non-target evenness differed among years. The years 2011 through 2013 were drought years. There was no evidence that non-target cover or richness increased in any treatments during the drought, however, target cover was lower in the 12- and 16-species treatments in drought years relative to pre-drought (2010). The results, that establishment of prairie-like communities can be hastened by sowing more species at the outset, can inform grassland restorations in which diversity and persistence are key goals.