Stability of exotic annual grasses following restoration efforts in southern California coastal sage scrub

Abstract

Summary 1.Restoration of semi-arid shrub ecosystems often requires control of invasive grasses but the effects of these grass-control treatments on native and exotic forbs have not been investigated adequately to assess long-term stability. In southern California, coastal sage scrub (CSS) vegetation is one semi-arid shrub community that has been invaded extensively by both exotic grasses and exotic forbs and is a target for restoration. 2. We studied the effects of grass-specific herbicide, thatch removal plus herbicide and mowing on native and exotic species in a heavily invaded CSS community. We followed this grass-control experiment for 6 years to assess the stability of such treatments. We also added a soil disturbance experiment to investigate the potential influence of thatch removal and soil disturbance on exotic and native grasses and forbs. 3. In the grass-control experiment, treatments reduced exotic grass cover to differing degrees. Three years of mowing resulted in lower exotic grass cover, but only for 2 years. Both herbicide and herbicide plus thatch removal reduced exotic grasses more than mowing, and effects persisted for longer. However, reducing exotic grass cover increased seeded species only during the year of seeding. In addition, plots where exotic grasses were controlled by herbicides also experienced increases in exotic forb cover. 4. In the soil-disturbance experiment, treatments did not increase cover of native species, although plots in which soil was disturbed did have less exotic grass cover. In both experiments, plots observed in years with different rainfall experienced widely varied plant cover, emphasizing the influence that precipitation exerts in these systems. 5. Synthesis and applications . In restoration of semi-arid shrub ecosystems, grass control can reduce exotic grasses over the short-term. However, recovery of grasses in the longer term indicates that restoration does not form a new stable state. Restoration and management of semi-arid shrublands may therefore require continual grass control. Exotic forbs should also be considered for control, as they may increase when exotic grasses are removed. Yearly variations in precipitation confound determination of successful restoration efforts, and require long-term observations to detect the response of native species to treatments.

Efficacy of Exotic Control Strategies for Restoring Coastal Prairie Grasses

“…Our results are consistent with many previous studies showing that both herbicides and mulch are effective in reducing exotic grass competition and favoring native grasses (e.g., Cox and Allen 2008;Huddleston and Young 2005;Irvine et al 2013;Kettenring and Adams 2011;Nyamai et al 2011). Exotic control treatments had much weaker and less consistent effects on cover of exotic forbs, which likely reflects the fact that cover of exotics forbs, many of which are low-stature and/or have basal rosettes, is strongly influenced by competition with taller-stature grasses, both native and exotic (Cox and Allen 2011;Hayes and Holl 2011).…”

Dose-response curves of Lolium multiflorum biotypes resistant and susceptible to clethodim

“…Thus, herbicides that inhibit enzyme Acetyl-coenzyme A carboxylase (ACCase) are used as an alternative control. A major ACCase-inhibiting herbicide is clethodim, a cyclohexanedione herbicide used for weed control in annual and perennial liliopsida at post-emergence which causes limited damage to non-target species (Cox & Allen, 2008).…”

Experimental Planting of Native Shrubs on Santa Cruz Island from Small Nursery Stock

“…Because many restoration projects occur on postagricultural land in southern California, the majority of projects require actions in 4 main areas: (1) allowing disturbed soil to regenerate a natural soil profile by ending soil disturbance (tilling, rooting, etc. ); (2) Cox and Allen 2008, Eliason and Allen 2008, Yelenik 2008, Yelenik and Levine 2010. Addressing each of these issues (and often others) may be crucial to successful restoration.…”

“…Addressing each of these issues (and often others) may be crucial to successful restoration. A variety of restoration approaches have been used on the California mainland with widely varying success (Cox and Allen 2008). What works on one site may fail at another.…”

“…Some form of weed control is necessary for restoring native communities in annual grasslands (Cox and Allen 2008). Without weed control, annual grasses inhibit germination and establishment of na tive seedlings by outcompeting them for light (Eliason and Allen 1997) and water (Davis andMooney 1985, Eliason andAllen 1997).…”