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

Abstract

Summary1. 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 unburnedunseeded 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 highelevation 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.

Evaluating rehabilitation efforts following the Milford Flat Fire: successes, failures, and controlling factors

“…Soils and landscape attributes that govern resilience are often implicated , Knutson et al 2014, and in our analyses we did observe significant effects of soil type on plant cover and composition every measurement year (Table 2, Fig. 5; Appendix: Table A4).…”

“…No action could leave burned areas in an undesired ecological condition for years (Newhall et al 2004, Steers and Allen 2010, Knutson et al 2014. Applying seed without any attempt to increase soil-seed contact (either using rangeland drill or roughening approaches) can result in very low germination rates (Winkel et al 1991, Bakker et al 2003.…”

“…In a review of post-fire seedings, Robichaud et al (2000) found rangeland seedings increased total plant cover less than half of the time. Furthermore, the studies compiled by Robichaud et al (2000) are from generally more mesic environments than the Milford Flat study area, suggesting that probability of success for areas as dry as Milford are likely even lower (e.g., Knutson et al 2014).…”

“…Though these soil-disturbing approaches potentially increase establishment of desired species and/or limit establishment of undesired species (exotics and/or invasives), such approaches also can involve significant uncertainty and risk (USGAO 2006, Knutson et al 2014. First, disturbance by heavy equipment during rehabilitation can negatively impact any desired species that survived the wildfire.…”

Human Land-Use and Soil Change

“…Furthermore, negative feedbacks between broad-scale soil destabilization and wind-driven saltating sands further hampered establishment of desired species in these aridic soils (Duniway et al 2015). Indeed, direct manipulations of rangeland plant communities are more likely to be successful in more mesic soil systems than aridic (Knutson et al 2014), suggesting desirable impacts on soil change and dynamic soil properties are much more likely in mesic than aridic soil systems.…”