Restoring closed trails in the Sonoran Desert: interactions of seed timing, seed source, and ripping

Ecological restoration is a promising way to improve ecological function, habitat connectivity, and esthetic values for recreation. However, effective restoration practices for arid environments remain elusive. To help fill this knowledge gap, we tested ripping soils, seed mixtures, including adding native seed bank topsoils, and seeding timing on permanently closed trails at sites in the Sonoran Desert, Arizona, U.S.A. Ripping had the desired effect of decreasing soil bulk density and increasing infiltration and water-holding capacity of closed trails. However, ripping increased non-native plant cover by 14.1% and decreased native plant cover by 2.2% by the fourth year of the study. Seed mixtures performed best when planted before the winter rains compared to before the summer monsoon, but only 3 of the 10 seeded species persisted across years. The seed bank topsoil application was most effective at increasing native species richness in the first year and yielded an average of two more plant species than unseeded plots over the 4-year experiment, but only in unripped plots. By the fourth year of the study, plots on the ripped and unripped closed trails had similar levels of plant cover and richness as the nearby native plant community, even in unseeded plots, suggesting that in small disturbed areas, the plant community has the potential to regenerate without inputs if disturbance is removed.