Long-term effects of seeding after wildfire on vegetation in Great Basin shrubland ecosystems

1. Invasive annual grasses alter fire regimes in shrubland ecosystems of the western USA, threatening ecosystem function and fragmenting habitats necessary for shrub-obligate species such as greater sage-grouse. Post-fire stabilization and rehabilitation treatments have been administered to stabilize soils, reduce invasive species spread and restore or establish sustainable ecosystems in which native species are well represented. Long-term effectiveness of these treatments has rarely been evaluated. 2. We studied vegetation at 88 sites where aerial or drill seeding was implemented following fires between 1990 and 2003 in Great Basin (USA) shrublands. We examined sites on loamy soils that burned only once since 1970 to eliminate confounding effects of recurrent fire and to assess soils most conducive to establishment of seeded species. We evaluated whether seeding provided greater cover of perennial seeded species than burned-unseeded and unburned-unseeded sites, while also accounting for environmental variation. 3. Post-fire seeding of native perennial grasses generally did not increase cover relative to burned-unseeded areas. Native perennial grass cover did, however, increase after drill seeding when competitive non-natives were not included in mixes. Seeding non-native perennial grasses and the shrub Bassia prostrata resulted in more vegetative cover in aerial and drill seeding, with non-native perennial grass cover increasing with annual precipitation. Seeding native shrubs, particularly Artemisia tridentata, did not increase shrub cover or density in burned areas. Cover of undesirable, non-native annual grasses was lower in drill seeded relative to unseeded areas, but only at higher elevations. 4. Synthesis and applications. Management objectives are more likely to be met in high-elevation or precipitation locations where establishment of perennial grasses occurred. On lower and drier sites, management objectives are unlikely to be met with seeding alone. Intensive restoration methods such as invasive plant control and/or repeated sowings after establishment failures due to weather may be required in subsequent years. Managers might consider using native-only seed mixtures when establishment of native perennial grasses is the goal. Post-fire rehabilitation provides a land treatment example where long-term monitoring can inform adaptive management decisions to meet future objectives, particularly in arid landscapes where recovery is slow.