RESEARCH ARTICLE Supplementing Seed Banks to Rehabilitate Disturbed Mojave Desert Shrublands: Where Do All the Seeds Go? Lesley A. DeFalco, 1,2 Todd C. Esque, 1 Melissa B. Nicklas, 1,3 and Jeffrey M. Kane 1,4 Abstract Revegetation of degraded arid lands often involves sup- plementing impoverished seed banks and improving the seedbed, yet these approaches frequently fail. To under- stand these failures, we tracked the fates of seeds for six shrub species that were broadcast across two contrasting surface disturbances common to the Mojave Desert—sites compacted by concentrated vehicle use and trenched sites where topsoil and subsurface soils were mixed. We eval- uated seedbed treatments that enhance soil-seed contact (tackiﬁer) and create surface roughness while reducing soil bulk density (harrowing). We also explored whether seed harvesting by granivores and seedling suppression by non-native annuals inﬂuence the success of broadcast seed- ing in revegetating degraded shrublands. Ten weeks after treatments, seeds readily moved off of experimental plots in untreated compacted sites, but seed movements were reduced 32% by tackiﬁer and 55% through harrowing. Harrowing promoted seedling emergence in compacted sites, particularly for the early-colonizing species Encelia farinosa, but tackiﬁer was largely ineffective. The inherent surface roughness of trenched sites retained three times the number of seeds than compacted sites, but soil mix- ing during trench development likely altered the suitability of the seedbed thus resulting in poor seedling emergence. Non-native annuals had little inﬂuence on seed fates dur- ing our study. In contrast, the prevalence of harvester ants increased seed removal on compacted sites, whereas rodent activity inﬂuenced removal on trenched sites. Future suc- cess of broadcast seeding in arid lands depends on eval- uating disturbance characteristics prior to seeding and selecting appropriate species and seasons for application. Key words: arid land restoration, germination require- ments, harvester ants, Messor pergandei, plant competi- tion, rodents. Introduction Vascular plants in arid- and semiarid environments spend a portion of their life cycle as seeds in the soil seed bank where they are vulnerable to surface disturbances such as wildﬁre (Esque 2004), grazing by domestic and feral animals (Zhao et al. 2001; Kinloch & Friedel 2005; Eldridge et al. 2006; Kassahun et al. 2009), trampling, and vehicle impacts (Sternberg et al. 2004; DeFalco et al. 2009). Removal of disturbances does not always ensure the recovery of seed numbers or species composition in the short term (Kassahun et al. 2009). Natural replenishment of the seed bank depends on seeds drifting from nearby intact areas assisted by wind or surface ﬂow during rainfall events. In addition, for shrubs and 1 US Geological Survey, Western Ecological Research Center, Las Vegas Field Station, 160 N. Stephanie Street, Henderson, NV 89074, U.S.A. 2 Address correspondence to L. A. DeFalco, email ldefalco@usgs.gov 3 Permanent address: 244 South Pitkin Road, Craftsbury Common, VT 05827, U.S.A. 4 Present address: Northern Arizona University, School of Forestry, Flagstaff, AZ 86001, U.S.A.  2010 Society for Ecological Restoration International doi: 10.1111/j.1526-100X.2010.00739.x perennial grasses with large seeds that do not easily disperse, granivores can move seeds to favorable sites for germination but also consume and store large quantities of seeds, thereby removing them from the soil-seed bank (Brown et al. 1979; Barber´ a et al. 2006; Vander Wall et al. 2006). In general, disturbances left to naturally recover often lack persistent seed banks or late successional species in the ﬂora, thus requiring replenishment by other means (Bakker et al. 1996; DeFalco et al. 2009). Natural recovery of surface disturbances in the Mojave Desert is typically slow (Webb 2002), and active revegetation efforts in recent decades have sought to restore low-elevation Larrea tridentata and Ambrosia dumosa and mid-elevation Yucca brevifolia and Coleogyne ramossisima communities to their pre-disturbance conditions. Restoration of broad dis- turbed areas has included replenishing depleted desert seed banks through broadcast seeding in combination with prepar- ing the seedbed (Kay & Graves 1983). Broadcast seeding may be a more viable option for revegetating large disturbances in arid environments compared to more intensive treatments such as transplanting greenhouse-raised seedlings, but the costs and beneﬁts of seeding and other treatments are rarely assessed JANUARY 2012 Restoration Ecology Vol. 20, No. 1, pp. 85–94 85