Novel Treatments for Native Forb Restoration in The Great Basin

The restoration of native forbs in the Great Basin remains challenging and problematic. Variable soil water and the presence of soil pathogens are thought to contribute to unsuccessful restoration. Novel treatments that increase soil water or reduce mortality from soil pathogens are needed for increasing restoration success of native forbs. We compared the efficacy of two treatments for enhancing native forb restoration: snow fences and N-sulate fabric. Treatments were selected based on their potential to improve soil water availability. We also examined whether different fungicide and hydrophobic seed coatings could reduce mortality from soil pathogens. We replicated treatments plus a no-treatment control at three sites in the Great Basin in a randomized complete block design over two years. Basalt milkvetch (Astragalus filipes Torr. ex A. Gray) and western prairie clover (Dalea ornata Douglas ex Hook.), forb species native to the Great Basin, were seeded inside each treatment. Sites spanned a latitudinal gradient to encompass different precipitation and temperature regimes. To evaluate the efficacy of our restoration treatments, we measured germination, seedling emergence, establishment, and second-year survival. Basalt milkvetch was the only species that was influenced by our treatments while western prairie clover had near-zero germination and subsequent seedlings. The effects of snow fences and N-sulate fabric varied by life stage and site with snow fences increasing establishment at the most southerly site, and N-sulate fabric 23 increasing seedling emergence at one of the two northerly sites. Seed coatings increased seedling emergence at all sites but did not affect establishment or survival. None of our restoration treatments affected second-year survival, and survival was low overall. Our study indicates that our treatments are most effective during the first year of restoration and that additional management actions are needed in subsequent years to improve restoration success. Introduction Seeding is a key management practice to counter land degradation and disturbance in semiarid ecosystems (Knutson et al., 2014). While grasses and shrubs typically comprise the core of restoration and revegetation seedings, other functional groups, especially native forbs, are under-represented due to limited availability and high seed costs (Richards et al., 1998; Walker and Shaw, 2005). Furthermore, many forb seedings have limited success or fail entirely (Rawlins et al., 2009). Abiotic and biotic factors can significantly limit the successful restoration of forb species (Parkinson et al., 2013; Jones et al., 2016). In particular, unsuccessful native forb restoration is often the result of highly variable environmental conditions such as limited soil water and the presence of soil fungal pathogens (James et al., 2011; Hardegree et al., 2017). In semiarid ecosystems, precipitation and soil water availability vary sharply within and between years, resulting in short time frames in which soil water is adequate for plant establishment and survival (Chambers et al., 2007). This variability can lead to low rates of seed germination and can negatively affect newly emerged seedlings (Pyke, 1990; Chambers, 2000). In addition, biotic factors, such as soil pathogens, have also been 24 shown to inhibit seed germination and seedling emergence (Crist and Friese, 1993; Gornish et al., 2015). In sagebrush-steppe ecosystems, soil pathogens can cause a significant amount of seed loss and mortality (Chambers and MacMahon, 1994) and can kill vulnerable seedlings through seedling blight and root rot (Madsen et al., 2016). Due to the importance of both abiotic and biotic conditions in restoring native forbs, restoration often focuses on manipulating these conditions to increase establishment. Multiple restoration methods for altering soil water availability in semiarid ecosystems have been examined (Pilliod et al., 2017). These include mulching, which decreases evaporation and may increase infiltration (Banerjee et al., 2006); chiseling, which increases infiltration and percolation (Winkel et al., 1991); imprinting, which consists of creating small depressions or microsites in the soil to facilitate moisture accumulation and retention (Montalvo et al., 2002); and irrigation (Roundy et al., 2001). Similarly, other studies have examined how fungicides (Cox et al., 2011) or other soil amendments such as biochar (Lehmann et al., 2011) and activated carbon (Kulmatiski, 2011) can affect restoration outcomes by altering soil pathogen loads. We examined two novel techniques that have the potential to directly affect abiotic site conditions – snow fences and plant protection fabric. Additionally, we also used seed coatings to alter how seeds interact with soil pathogens and soil water. In the Great Basin Region of the U.S., where much of the annual precipitation falls in the form of snow (Bailey, 1995), snow fences have the potential to serve as a restoration tool. Snow fences can alter site conditions by capturing wind-blown snow into dense snow drifts, which depending on depth, duration of snow pack, and timing of snow melt, can 25 lead to significant increases in soil water availability throughout the spring and summer (David, 2013; Loik et al., 2013). Snow fences have been shown to improve restoration outcomes by increasing soil water availability during periods of seed germination and seedling emergence, leading to an increase in seedling emergence and establishment of Wyoming big sagebrush (Artemisia tridentata Nutt. subsp. wyomingensis [Beetle and A. Young]) and other native species in sagebrush-steppe restoration (David, 2013). Their use for restoration of native forbs, however, has been limited (but see, David, 2013). Plant protection fabric, while less commonly used in dryland restoration, can also alter abiotic conditions by reducing evaporation and thus enhancing soil water availability (Geyer, 2001). Although plant protection fabric has been shown to have positive effects on establishment in temperate ecosystems (Tilley et al., 2009), the use of this fabric to alter abiotic conditions for restoration within semiarid ecosystems has remained relatively unexplored (but see, Schmal et al., 2007). Managers can also potentially increase native forb restoration success by manipulating seeds rather than the surrounding abiotic conditions. Seeds of many Great Basin species are physiologically and/or physically dormant and require a dormancybreaking treatment to germinate (Monsen and Stevens, 2004). Seeds that are physically dormant are often scarified with acid or mechanical treatments, while seeds that are physiologically dormant require a period of cold and moist or warm and moist stratification to increase germination (Baskin and Baskin, 2001). Seed coating allows for the direct application of various materials to a seed that can influence seed germination and seedling emergence. With this technology, fungicides can be directly applied to a 26 seed coat, creating a protective barrier that reduces seed and seedling mortality from soil fungal pathogens (Madsen et al., 2016). Alternatively, hydrophobic materials and polymers can also be applied to a seed coat, which can help mitigate highly variable abiotic conditions by preventing seed imbibition and germination until more optimal soil water and temperature conditions in the spring (Madsen et al., 2016). In this study, we examined how snow fences, plant protection fabric, and seed coatings affected native forb restoration. To accomplish this, we conducted a field experiment at three sites in the Great Basin that spanned a latitudinal gradient. At each site, we quantified germination, seedling emergence, seedling establishment, and secondyear survival of two native forbs. As such, we were able to determine which treatments led to the greatest success at each life stage and whether treatments had similar effects regardless of site conditions along a latitudinal gradient.