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Soil Moisture Enhancement Techniques Aid Shrub Transplant Success in an Arid Shrubland Restoration

Abstract In arid and semi-arid environments, where low and unpredictable rainfall is typical, establishment of perennial vegetation can be enhanced with modest increases in soil moisture. We evaluated methods for promoting shrub transplant establishment. We transplanted approximately 1 000 3-mo-old seedlings in April 2004, 2005, and 2006, using a full-factorial design with combinations of three treatments: addition of mycorrhizae spores to the root zone, addition of a hydrogel to the root zone, and placement of a wood obstruction south of the plant. We planted three shrubs: big sagebrush (Artemisia tridentata Nutt. ssp. tridentate), four wing saltbush (Atriplex canescens [Pursh] Nutt.), and rubber rabbitbrush (Ericameria nauseosa [Pall. ex Pursh] G.L. Nesom & Baird ssp. nauseosa) in a 1.2-ha area. The summer months of 2004 and 2006 were dry, leading to low survivorship (< 1%). With higher rainfall in summer 2005, transplant survivorship was ∼18%. For the 2005 transplants, A. tridentata had the highest survivorship after one growing season (31.0%), followed by A. canescens (20.6%) and E. nauseosa (6.9%). Placing a wood obstruction near the plant was significant in the statistical model to describe short-term overall transplant survival and survival of A. tridentata. Placing hydrogel in the root zone also explained short-term overall transplant survival, as well as survival of E. nauseosa. However, by 4.5 yr after transplanting, there was no significant treatment effect on survival. Thus, for transplanting shrub seedlings on arid or semi-arid sites, we recommend some form of resource enhancement technique to increase short-term survival. In this experiment, both the obstruction and hydrogel treatments were effective. We recommend the obstruction treatment since slash is often readily available onsite, has low labor requirements and cost, and it increased transplant survival of A. tridentata, a species of conservation concern; however, other treatments may be appropriate for individual species.