Roads are a ubiquitous part of our landscape, yet they often cause habitat fragmentation and may provide dispersal corridors for non-native species. To minimize negative effects of roads, vegetation managers increasingly plant native species and manage for wildlife on roadsides. However, native plant establishment may be limited by competition from non-native species. Additionally, competitive interactions may shift under different disturbance frequencies. Our objective was to investigate the influence of disturbance frequency (mowing) and reduced competition (pre-planting herbicide) on the establishment of two native wildflower species (Gaillardia pulchella, Coreopsis lanceolata) in the context of Paspalum notatum-dominated roadsides. Paspalum notatum (bahiagrass) is an introduced rhizomatous grass commonly planted on roadsides and pastures in the southeastern United States. Paspalum notam pastures in two Florida locations were treated with herbicide (glyphosate, imazapic, and an untreated control), sown with G. pulchella or C. lanceolata seed, and mowed two or six times per year. We counted wildflower density each fall and spring and estimated percent cover of wildflowers, other forbs, graminoids, bare ground, and litter in fall, spring, and summer for two years after wildflower planting. We conducting a seed bank study (following the seedling emergence method) with soil cores randomly sampled one year after planting.
Results/Conclusions
The glyphosate treatment provided the greatest establishment for G. pulchella and C. lanceolata by reducing the extant vegetation cover (primarily P. notatum). Results from this study indicated some species-specific responses to establishment treatments. The imazapic treatment improved establishment of C. lanceolata but not G. pulchella compared to the control. Seeding wildflowers into P. notatum without disturbing the extant vegetation (a commonly implemented establishment method) resulted in moderate cover of C. lanceolata and marginal establishment for G. pulchella. Coreopsis lanceolata cover and density increased during initial establishment and remained high (e.g., 40-80% in the glyphosate treatment) throughout the study, with few seasonal fluctuations. However, cover of G. pulchella remained below 25% throughout the study (all treatments), decreasing during winter but increasing to original establishment levels during spring and summer. Mowing frequency (timed to allow for wildflower persistence and seeding in this study) did not affect cover or seed bank density for either species. Since roadside mowing in Florida is typically timed to control height of the dominant grass species rather than to facilitate wildflower persistence, it is unclear whether the mowing frequencies in this study would have the same effect on roadside wildflower populations if differently timed.
