Use of Small-scale Disturbances to Establish Native Plants in an Abandoned Agricultural Field

Small-scale disturbances in plant communities create open patches that may allow new species to invade or suppressed species to become more abundant. We evaluated whether small-scale disturbances in an abandoned agricultural field dominated by exotic grasses could be used to increase abundance and diversity of native plants. Coverboards made of plywood (2 X 122 X 81cm) were laid out on a 15 meter by 15 meter grid in the South Hayfield at the Field Station in 2008 for a study of the Butler’s garter snake. The boards were kept in place until March 2010, creating many small-scale disturbances after removal of the boards. One of four treatments was applied to each of these experimental plots: 1) no seeding, or seeded with a mix of, 2) native forbs, 3) native grasses, or 4) both forbs and grasses. The plots were seeded in July 2010, and vegetation was sampled August - September 2011. Percent cover of each plant species was estimated in each disturbance plot. A paired undisturbed plot was sampled to describe the background vegetation of the field. Species richness and diversity were higher in disturbed plots than in the undisturbed community for both seeded and unseeded plots. Seeded plots had much greater abundance and diversity of native species than unseeded disturbances, particularly for plots seeded with forbs. The forb-only seed mix provided the highest establishment of seeded species after one full growing season, and suppressed exotic species more than the grass-only seed mix. However, only Black-eyed Susan (Rudbeckia hirta), Wild bergamot (Monarda fistulosa), and Whorled milkweed (Asclepias verticillata) established in more than half the plots in which they were seeded. Grasses established poorly compared to the most successful forb species. However, the grasses were very small plants after a single growing season; their frequency may have been underestimated and their cover may increase in subsequent seasons