Seeding alters plant community trajectory: Impacts of seeding, grazing and trampling on semi-arid re-vegetation

Questions: How do seeding, cattle grazing, and vehicular use impact vegetation establishment and soil movement on a newly reclaimed pipeline right-of-way? Will these factors result in differing plant community trajectories?. Location: Southern Arizona (USA). Methods: Within a pipeline disturbance, we randomly selected nine plots to be seeded with an 18 species mix and nine to be left unseeded. Adjacent to the disturbance, we selected nine undisturbed unseeded control plots for a total of 27 plots (30 m × 45 m each). Within each of the 27 plots, we established a grazed–trampled, grazed–untrampled and ungrazed–untrampled subplot. One year after pipeline reclamation, we analysed the impacts of seeding, grazing and trampling on native plant cover, undesirable plant cover, herbaceous biomass, species richness, soil movement and plant community trajectories in comparison to surrounding undisturbed sites. Results: Seeding disturbed sites with a diverse seed mix resulted in greater native plant cover, higher species richness and fewer undesirable species than were found in unseeded disturbed sites. Unseeded disturbed areas were similar to the undisturbed control areas in species richness and had comparable plant community trajectories. The combined impacts of grazing and trampling reduced native plant cover and herbaceous biomass and were associated with increased soil erosion in comparison to subplots protected from grazing and trampling. Conclusions: Natural vegetation recruitment can be a viable option in semi-arid reclamation projects when the soil seed bank is preserved and there are proximal seed sources. While seeding improved quantitative vegetation metrics, using a seed mix comprised of different species than the preexisting vegetation may set the reclaimed vegetation on a different plant community trajectory. The general prescription of protecting new reclamation sites from grazing and trampling is supported.