Evaluating seed and microsite limitation to the establishment of a native forb in a non-native pasture grass

Restoration of degraded lands often requires introducing new species to increase richness. However, suitable microsites must also be present for plant establishment to occur. We tested effects of seed and microsite limitation on establishment of Coreopsis lanceolata, a native forb, in a remnant pasture dominated by Paspalum notatum, a non-native pasture grass widely planted in Florida. Experimental plots (25 m²) were seeded in north-central Florida, USA, in November 2006. Microsites were created by disturbing the extant plant community (scraping topsoil to 13 cm, applying glyphosate, or control) and irrigating (5 cm one day before seeding, 5 cm/week for six weeks following seeding, or no irrigation). Seed limitation was tested by seeding with 100, 600, or 1100 pure live seeds m^-2. When measured 2.5 months after seeding, density and cover of C. lanceolata were greater in plots with the full irrigation treatment and high seeding rate than all other treatment combinations. In plots with before-seeding irrigation and no irrigation, C. lanceolata cover was less than 10% and did not differ among seeding rates or disturbance treatments. At the high seeding rate, glyphosate (intermediate disturbance) resulted in greater C. lanceolata cover than the control (no disturbance) or scraped plots (highest disturbance). At the low seeding rate, C. lanceolata density and cover did not differ among disturbance or irrigation treatments, suggesting that an initial density must be present before microsite limitation effects become evident. Disturbance had a greater effect on C. lanceolata cover than density, indicating that conditions for growth are more limiting than those for emergence. Results signify that seed and microsite limitations, as well as their interactions, contribute to lack of establishment in this system.