Carpobrotus edulis (L.) N.E. Br.

Rounded Global Status Rank: GNR - Not Yet Ranked

Management Requirements: Manual control methods are not recommended for C. edulis because they are unlikely to kill the plant due to its ability to resprout from stem pieces. Also, manual control can be more labor intensive and more disruptive to habitat than chemical control methods. The herbicide glyphosate (e.g., Roundup) has been demonstrated to be effective in controlling this species (Mulroy et al. 1992).

Prescribed burning also has been recommended as a possible control for C. edulis. Conditions for prescribed burning should be controlled to maximize the likelihood of high (i.e., over 100 celsius) soil temperatures during fire, thereby reducing viability of the Carpobrotus seedbank. Also, because brush rabbits are effective at reducing seedling establishment and they tend to forage less than 30 m from cover, it may be possible to enhance herbivore use of burns by keeping the burned areas small (D'Antonio et al. 1993).

Management Programs: An experiment in Vandenberg Air Force Base, California, tested the minimum effective concentration of the herbicide glyphosate (this experiment used Roundup) for control of C. edulis. Sixteen herbicide test plots were established using 4 different concentrations of Roundup (2.0 percent, 1.5 percent, 1.0 percent, and 0.5 percent) on 4 different densities of C. edulis (sparse, moderate, dense, and solid). All concentrations resulted in damage and some mortality of C. edulis. The higher concentrations produced more rapid and more complete kills than lower concentrations. The speed of kill is considered important because damaged or dying C. edulis may send out adventitious roots and be revived by seasonal rainfall. The researchers found very little incidental damage to native plants in the herbicide test plots (Mulroy et al. 1992).

Following the dose experiment, a large-scale C. edulis treatment was attempted in Vandenberg Air Force Base using 2 percent Roundup. The chemical treatment was carried out on 350 acres known to be infested with C. edulis. To minimize indirect effects on native plants, application of Roundup was not used around aquatic or wetland habitats or at windspeeds of over 5mph. At least initially, this experiment plans to leave dead C. edulis plants in place to decompose, which is believed to continue to stabilize soil while allowing native species to gradually take over (Mulroy et al. 1992).

Monitoring Programs: On Vandenberg Air Force Base, a monitoring program has been set up to determine the results of a large-scale C. edulis control experiment. Monitoring will specifically identify the effectiveness of the chemical control (e.g., percent of plants killed and areas that need retreatment), reestablishment of C. edulis from seedbank, and recolonization of treated areas by other weeds versus native species (Mulroy et al. 1992).

Management Research Programs: Current management research programs on Vandenberg Air Force Base include a revegetation experiment within a large-scale treatment area for C. edulis. A number of factors potentially affecting revegetation in the treatment areas will be investigated. The following factors will be tested: removal of treated C. edulis versus leaving it to decompose; reseeding with native species versus reliance on natural dispersal and seedbanks; and neutralizing acidified soil with lime versus no lime. In addition, experiments are being set up to determine the possibility of developing methods of C. edulis treatment and on-site disposal of dead plants while promoting revegetation of native species (Mulroy et al. 1992).

Comments: Carpobrotus edulis is a hardy perennial that survives most winters in coastal areas and is extensively planted as a sandbinder (Heywood 1993).

Stewardship Overview: Control of C. edulis is complicated by its ability to resprout from stem pieces, alter soil chemistry, and build up huge biomass in areas it infests. Preliminary results from management studies on Vandenberg Air Force Base show that C. edulis can be controlled with the herbicide glyphosate (e.g., Roundup). Carefully applied chemical treatments resulted in very little damage to nearby native species. Further experiments should help to provide more information on restoring dune scrub communities after infestation of C. edulis (Mulroy et al. 1992).

Species Impact: In areas where it has been introduced, Carpobrotus edulis can readily overgrow native species and its invasion into burned chaparral habitat in California can severely impact vegetative recovery. In California, C. edulis invasion threatens many of the endemic and declining plant taxa found in maritime chaparral habitat (D'Antonio et al. 1993).

The mat-forming habit that is characteristic of C. edulis can smother and kill native vegetation. The mechanism by which "smothering" occurs is unknown but may include one or many of the following: uptake of water or nutrients, shading, or alteration of soil chemistry. C. edulis acidifies the soil, which may impede recolonization by native species into areas that were once infested by C. edulis (Mulroy et al. 1992).