Gorse seed weevil,Apion ulicis Forst, was released into New Zealand in 1931 to help control gorse, Ulex europaeus L. This study examines the effect of the weevil in reducing annual seed production of gorse at three sites over 3 years. Weevils oviposited only during spring, and infested up to 90% of immature pods during that period. However, the many pods produced both earlier and later than this escaped attack. Lack of synchrony between weevil reproductive activity and gorse pod production limits the impact of the weevil on the annual gorse seed crop. Better adapted populations of Apion ulicis may exist in southern Europe and these could be introduced to increase predation on seed.

Extensive areas in the upper Midwest have been invaded by spotted knapweed, and effective management strategies are required to reestablish native plant communities. We examined effects of mowing, mowing plus clopyralid, or mowing plus glyphosate in factorial combination with hand pulling and burning on knapweed abundances on a knapweed-infested site in western Michigan. We applied mowing and herbicide treatments in summer 2008, and seeded all plots with native grasses and forbs in spring 2009. We conducted the knapweed pulling treatment from 2009 to 2012 in July. The prescribed burn was conducted in April 2012. By 2012, hand pulling reduced adult knapweed densities to 0.57 ± 0.12 m−2 (0.053 ± 0.011 ft−2) (mean ± SE), which was 5.8% of nonpulled treatments, juvenile densities to 0.29 ± 0.07 m−2 (2.1% of nonpulled treatments), and seedling densities to 0.07 ± 0.06 m−2 (2.6% of nonpulled treatments). After 3 yr, hand pulling reduced seed bank densities to 68 ± 26 m−2 as compared to 524 ± 254 m−2 in nonpulled treatments and 369 ± 66 m−2 in adjacent untreated areas of the study site. Without hand pulling, effects of mowing or mowing plus glyphosate were short-lived and allowed knapweed to rapidly resurge. In comparison, although a single mowing plus clopyralid treatment maintained significantly reduced densities of knapweed for 4 yr, by 2012 knapweed biomass in the nonpulled clopyralid treatment was approximately 60% of that in the other nonpulled treatments. Burning had minimal impacts on knapweed densities regardless of treatment combination, probably as a result of low fire intensity. Results demonstrated that persistent hand pulling used as a follow-up to single mowing or mowing plus herbicide treatments can be an effective practice for treating isolated spotted knapweed infestations or for removing small numbers of knapweed that survive herbicide applications.

Invasive species frequently need to be controlled as part of efforts to reestablish native species on degraded sites. While the effectiveness of differing control methods are often reported, the impacts these methods have on the establishment of a native plant community are often unknown. To determine methods that effectively reduce spotted knapweed (Centaurea stoebe) while enhancing native species establishment, we tested 12 treatment combinations consisting of an initial site preparation (mowing, mowing + clopyralid, or mowing + glyphosate), in factorial combination with annual adult knapweed hand pulling and/or burning. We established 48 plots and applied site preparation treatments during summer 2008, seeded 23 native forbs and grasses during spring 2009, pulled adult knapweed annually from 2009-2012, and burned in the early spring 2012. During July of 2011 and 2012, percent cover of all species was visually estimated. By 2011, seeded species had established in all treatment plots, including plots that retained greater than 50% knapweed cover, indicating that native species successfully established despite knapweed dominance. Mowing alone had no longterm impacts on community development. Clopyralid favored non-native grass establishment, while glyphosate encouraged non-native forbs. Clopyralid had minimal impacts on native forb establishment, but did effectively control knapweed. Pulling reduced knapweed cover, increased non-native grass cover and enhanced native species establishment. Burning had little impact, possibly due to low intensity and unseasonable weather. On the heavily invaded site we studied, combining the use of clopyralid with hand pulling effectively controlled knapweed and favored the establishment of seeded native grasses and forbs.

Questions:Restoring native-dominated plant communities often requires controlling invasive species, reintroducing native species, and implementing continued management practices. Can single herbicide applications to control Centaurea stoebe L. encourage establishment of seeded native species more effectively than a single mowing? Can annual hand pulling to control C. stoebe favor the persistence of seeded native species?Can mid-spring burning reduce C. stoebe and increase native forbs and grasses? After eight years, will the restored plant communities differ from those in untreated areas?Location: Bass River Recreation Area, Ottawa County, MI, USA. Methods:We studied the effects of site preparation (mowing, clopyralid, glyphosate), hand pulling of C. stoebe, and burning on restoring native plant communities on a C. stoebe-infested site. Over eight years, we quantified the development of the plant communities on plots seeded with native grasses and forbs, and report on the second four years here.Results: Native-dominated plant communities developed using both herbicides, but while clopyralid provided longer control of C. stoebe, clopyralid-treated plots had fewer native species than glyphosate-treated plots. Native-dominated plant communities also developed on plots that were only mowed once before seeding, achieving similar native species richness as the glyphosate treatment. Hand pulling controlled C. stoebe, burning increased relative cover of native graminoids and decreased that of non-native grasses, and hand pulling and burning in combination increased relative cover of native forbs. After eight years, the restored plant communities had greater native species cover and richness and higher mean Coefficient of Conservatism, Floristic Quality Index, and Shannon's Diversity Index values than untreated areas. Conclusions: Site preparation, seeding, hand pulling of C. stoebe, and annual burning facilitated restoration of native-dominated plant communities on a C. stoebe-infested site. Effects accumulated over a period of eight years, illustrating the importance of continued management and monitoring as part of similar restoration efforts. Additional supporting information may be found online in the Supporting Information section at the end of the article. Appendix S1. Aerial view of the study site, showing the four experimental blocks of 12 5-m × 5-m plots each. Appendix S2. Frequency of occurrence and mean relative percent cover of common and seeded species. Appendix S3. Plant cover, diversity, and floristic quality data. Appendix S4. Knapweed lifestage density data.