Semiarid Old‐field Restoration: Is Neighbor Control Needed?

Abstract

Restoration practice suggests that neighbor control is essential in semiarid grasslands, but ecological theory predicts that neighbor effects are relatively small in young fields. We investigated the effectiveness of neighbor control (mowing and herbicide) for establishing native grasses in a recently abandoned field in southwestern Saskatchewan, Canada. We also examined its interactions with common restoration techniques, such as mulching (straw and sawdust) and contrasting sowing methods (drilling, and broadcasting cleaned seeds, cleaning remainders, and native hay). The experiment was repeated over three years to examine the effect of weather. Neighbor control had no effect on establishment and rarely any effect on first‐year survival. This contrasted with significant effects of neighbor control on community and ecosystem‐level variables (species richness, water, N). The lack of neighbor effects is concordant with theory which predicts low competition intensity from ruderal annuals. Establishment in seeded plots varied two‐fold among years in drilled plots and 50‐fold in broadcast plots, and it was lowest during a cool, dry summer. Thus, variables beyond human control are a major factor determining restoration success. Overall, broadcasting was as effective as drilling. The highest long‐term establishment of native species was produced by broadcasting cleaning remainders. Almost no seedlings emerged from plots supplied with native hay. Straw mulch increased soil moisture and available N, and sawdust decreased N, but neither had any long‐term effect on native grasses. Our results suggest that restorations of semiarid old fields should focus less on neighbor control and more on strategies for exploiting suitable years for germination, either by monitoring soil moisture or through repeated seeding.

The roles of exotic grasses and forbs when restoring native species to highly invaded southern California annual grassland

“…These year-to-year differences in cover of native forbs reinforce the importance of yearly variation in structuring these communities (Wilson et al 2004;Cox and Allen 2008). Seeded species were also affected by yearly variation, and some, especially the perennials, may not have established during the short timespan (2 years) of the study due to the relatively late seeding and yearly variations in timing and amounts of precipitation.…”

Efficacy of Exotic Control Strategies for Restoring Coastal Prairie Grasses

“…Treatment effects on native grasses declined although native cover remained lower in the control, soil removal, and herbicide plots that were unmulched. Other studies have suggested that interannual climatic variation, which is beyond the control of practitioners, may be more important than the restoration method used (Cox and Allen 2011;Wilson et al 2004), so that investing resources in multiple years of seeding or planting may enhance restoration success more than expensive efforts to control exotic competition. What is clear is that long-term monitoring is needed to evaluate the efficacy of different restoration treatments, a call that has been made repeatedly in the academic literature (Matthews and Spyreas 2010;Rinella et al 2012), but is less commonly implemented (Kettenring and Adams 2011).…”

The ecology of restoration: historical links, emerging issues and unexplored realms

“…Historical and stochastic effects create patterns not fully explicable with simple deterministic models. Several types of contingency are critical drivers of community structure in ecological systems, and are not only theoretically interesting, but also have strong implications for ecological restoration (Bakker et al 2003;Wilson et al 2004). For example, the presence or absence of herbivores can have profound effects on community development and structure (see Howe & Lane 2004).…”