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

Abstract

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.

Disturbance is more important than seeding or grazing in determining soil microbial communities in a semiarid grassland

“…Construction included the excavation and refilling of a central pipeline trench (1-3 m deep) using heavy equipment. Restoration of the site occurred in September of 2014 immediately after construction and included redistributing the topsoil and drill-seeding into 19-mm deep furrows at a rate of 4.01 kg/ha pure live seed comprised of 18 species of woody shrubs, perennial grasses, perennial forbs, and annual forbs native to Arizona (USDA 2019) (Farrell & Fehmi 2018).…”

“…The left map shows the location of the experimental site along the buried pipeline corridor that runs through the Sonoran Desert of southern Arizona, U.S.A., to the border of Mexico. The right map displays the experimental design showing the seeded, unseeded, and control treatment plots of the pipeline construction zone.Figure adaptedfromFarrell and Fehmi (2018).…”

Seedling recruitment in mountain grassland restoration: Effects of soil preparation and grazing

“…Grazing animals negatively affect seedling recruitment by trampling and later on by biomass removal. Trampling by livestock does not only damage seedlings but also strongly affects the soil by erosion (Farrell & Fehmi, 2018) or destabilization (Tasser et al, 2003), particularly on mountain grassland slopes. On the other hand, trampling may have a positive effect on seedling recruitment of transferred species, since pre-existing vegetation is damaged by bruising, crushing, plant displacement or burial in mud (Bilotta et al, 2007), limiting competition with non-target species.…”

Best served deep: The seedbank from salvaged topsoil underscores the role of the dispersal filter in restoration practice

“…While size may limit the regeneration of deeply buried propagules, it is likely that in our study the disadvantage of deep burial was counteracted by the greater number of seeds contained in the greater thickness of soil. It is also likely that the soil‐stored seeds had a lower exposure to transfer‐related deterioration (e.g., friction) when topsoil was spread at the greater thickness and resulted in a better quality seeding mix overcoming the dispersal limitation filter (Long et al ., 2015; Farrell & Fehmi, 2018).…”

“…It is also likely that the soil-stored seeds had a lower exposure to transfer-related deterioration (e.g., friction) when topsoil was spread at the greater thickness and resulted in a better quality seeding mix overcoming the dispersal limitation filter (Long et al, 2015;Farrell & Fehmi, 2018).…”