Contingency of Grassland Restoration on Year, Site, and Competition From Introduced Grasses

Abstract

Semiarid ecosystems such as grasslands are characterized by high temporal variability in abiotic factors, which has led to suggestions that management actions may be more effective in some years than others. Here we examine this hypothesis in the context of grassland restoration, which faces two major obstacles: the contingency of native grass establishment on unpredictable precipitation, and competition from introduced species. We established replicated restoration experiments over three years at two sites in the northern Great Plains in order to examine the extent to which the success of several restoration strategies varied between sites and among years. We worked in 50‐yr‐old stands of crested wheatgrass (Agropyron cristatum), an introduced perennial grass that has been planted on >10 × 106 ha in western North America. Establishment of native grasses was highly contingent on local conditions, varying fourfold among years and threefold between sites. Survivorship also varied greatly and increased significantly with summer precipitation. No consistent differences were found between drilling and broadcasting in their effects on establishment, but survivorship was nearly threefold higher in broadcast plots. Plots without seed added, or with native hay added, had almost no seedlings of native grasses. In contrast, broadcasting the residue remaining after cleaning seeds from native hay produced the highest seedling densities of any treatment. Competition from A. cristatum was significantly and consistently reduced through annual application of a generalist herbicide (glyphosate), which increased native grass establishment and survivorship and the richness and total cover of native species. Herbicide decreased standing crop and increased soil moisture and available nitrogen. A. cristatum was controlled without suppressing native vegetation, both by spraying in early spring, which selectively killed the cool‐season A. cristatum, and by application with a wick, which selectively killed the taller A. cristatum. A. cristatum persisted over four years, however, in spite of annual herbicide application. A. cristatum cover in control plots increased significantly with summer precipitation. In summary, broadcasting and drilling differed little in their effects on establishment, but broadcasting increased survivorship and will allow the emergence of plant‐induced heterogeneity. Competition from introduced species can be reduced but not eliminated by continuing herbicide application. Lastly, the positive relationships between precipitation and both A. cristatum and native seedling survivorship suggest that management should focus on controlling A. cristatum during dry years and on introducing native species during wet years. Corresponding Editor: I. C. Burke.

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

“…Heterogeneous recovery of arid and semiarid v www.esajournals.org landscapes from fire and responsiveness to rehabilitation efforts is common (Robichaud et al 2000, Bakker et al 2003, James and Svejcar 2010. 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.…”

“…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. But, post-fire soil disturbance increases risk of accelerated erosion and further loss of existing vegetation unless additional erosion-control measures are implemented to mitigate the destabilizing effects of surface disturbance (Pierson et al 2007, Miller et al 2012.…”

“…Post-rehabilitation precipitation is one of the primary factors controlling seeding success in arid and semi-arid ecosystems (Bakker et al 2003, Bernstein et al 2014. Climate conditions during the first year after the MFF rehabilitation efforts were clearly unfavorable for seedling germination and establishment ( Fig.…”

Changes in botanical diversity of sown grasslands due to naturalization and extensive management

“…Grassland succession and restoration problems have been the concern of scientists from different countries of the world (Muller et al, 1998;Jones & Hayes, 1999;Pywell et al, 2002;Bakker et al, 2003;HellströM, 2004;wilson & Pärtel, 2003;lindBorg & eriksson, 2004;wilson et al, 2004;walker et al, 2004;HedBerg & kotowski, 2010;lencová & PracH, 2011;török et al, 2010Jírová, 2012, etc.). Because of the abandonment of traditional small-scale farming at the end of the 20 th century, the number of semi-natural grasslands has declined in many European countries (craMer et al, 2008).…”

Restoring Crested Wheatgrass Stands to Big Sagebrush for Improved Sage-grouse Habitat: A Literature Review

“…Herbicide application at the correct phenological stage (8 to 15 cm height) is crucial for determining treatment effectiveness. Applications in the early spring when crested wheatgrass is beginning growth and before desired native species initiate growth, appears to be the most effective , Bakker, Christian, Wilson & Waddington 1997, Bakker et al 2003, Peat & Bowes 1995, Romo, Grilz & Delanoy 1994. Glyphosate applications should not be relied upon to completely eliminate crested wheatgrass (Table 4).…”