M. Rebecca Anderson

Effect of Removal of Garlic Mustard (Alliaria petiolata, Brassicaeae) on Arbuscular Mycorrhizal Fungi Inoculum Potential in Forest Soils

Garlic mustard (Alliaria petiolata), a biennial species, is considered to be among the most troublesome of the invasive plants in the Eastern Deciduous forest of North America. It has been shown to prevent or reduce mycorrhizal colonization of native herbaceous ground layer plants and trees in these forests. It is estimated that 70-90% or more of herbaceous native ground layer plant species form associations with arbuscular mycorrhizal fungi (AMF). Loss of the mycorrhizal association can reduce growth, reproductive success, and competitiveness of plant species. Using a corn root bioassay, we examined the effect of garlic mustard removal on the soil AMF mycorrhizal inoculum potential (MIP), in control plots and plots that had second-year garlic mustard removed annually for the past five years (2005-2009). Removal treatment plots had significantly (P = 0.0240, df = 28) greater MIP than control plots (25.72±2.26% and 18.29±2.04%, respectively). MIP was negatively correlated with cover of garlic mustard (r 2 = 0.1325, P < 0.05, df = 30), which accounted for 13.2% of the variation in MIP. Cover of native vegetation in removal treatment plots (104.50±2.6%) was greater than that of the control plots (95.14±3.66%), (P = 0.0236, df = 115). These results show that removal of garlic mustard results in an increase in soil MIP and cover of native species; however, there is not a complete loss of MIP associated with garlic mustard invasion. Following removal of garlic mustard, our data suggest that mycorrhizal plants recover more slowly than non-mycorrhizal species, apparently due to a delay in the establishment of a well-functioning mycorrhizal association. Our study is the first to demonstrate that the MIP of native soils and cover of native species increase following reduction in the cover of garlic mustard.

Berry Ripening and Harvest Season in Wild American Ginseng

Abstract American ginseng (Panax quinquefolius L.) is a rare to uncommon CITES Appendix II-listed perennial plant species that is harvested from the wild to supply the herbal trade. Harvest seasons for American ginseng are intended to coincide with berry ripening in the species. However, geographic patterns of harvest seasons among states suggest they may not be tied to ripening phenology. In this study, we experimentally established the relationship between berry color and subsequent seed germination 1.5 years later in a natural population. We then monitored berry ripening August 15, September 1, and September 15 in 31 populations across much of ginsengs natural range. We found no biological basis for state-to-state differences in harvest seasons, and clear evidence that in some states the harvest season is set too early to ensure full berry ripening. Variation among years was examined in a subset of populations: Results from that analysis do not alter the conclusion that improvement in ginseng management could be achieved by establishing biologically based harvest seasons.

Allelopathy as a factor in the success ofHelianthus mollis Lam.

A method to rapidly screen species suspected of producing allelochemics, using results from simple bioassay tests, is presented. By measuring the osmotic potential ofH. mollis extracts and using mannitol solutions of comparable osmotic potential, the influence of osmotic potential in the bioassay was eliminated. Nested analysis of variance was used to examine the separate influences of (1) extract concentration, (2) source of plants used in extract preparation (edge or center of clones) (3) osmotic potential of the extract, and (4) the differential development of radicles and shoots of species used in the bioassay tests. Bioassay tests for allelopathy showed that extracts made of wholeH. mollis plants significantly inhibited both radicle and shoot development of radish and wheat, but only the radicle of little bluestem. There was a significant increase in the inhibition of radish shoots and wheat radicles at high concentration of the extract, but the radicle of little bluestem was inhibited more at the lower concentration. Extracts prepared from plants collected from the clone center inhibited radish radicle development significantly more than extracts made of plants growing at the clone edge.

Comparison of the effect of early and late removal of second-year garlic mustard (Alliaria petiolata) on first-year plants and deciduous forest spring and summer dominant herbaceous groundlayer species in central Illinois, USA.

Garlic mustard, a biennial Eurasian species, has extensively invaded eastern North American deciduous forests. We studied effects of 3 years (2005–2007) of annual removal of second-year garlic mustard plants on first-year plants and native spring herbaceous species in upland and lowland woods. Treatments compared removal of second-year plants in mid-March (early treatment) or mid-May (late treatment) to a control. We recorded first- and second-year plants and native herbaceous species percent cover on April 19 and 20. First-year plant cover was higher on control than treatment plots; however, in the upland woods only control and late treatment plots differed significantly. First-year plant cover was less in removal than control plots, indicating reduced seed input; however, we found no difference in cover of second-year plants between late treatment and control plots. Results suggest second-year plants strongly compete with younger conspecifics, and their removal decreases first-year plant mortality. Removal of second-year garlic mustard did not significantly affect total cover of native herbaceous species. Second-year plants complete vegetative growth before late May and might impact early developing native species more than later growing species. We tested effect of removal of garlic mustard on native species in 2 phenological categories: spring- and summer-dominant species. We found no treatment effects on summer-dominant species. However, early treatment plots had significantly more cover of spring-dominant plants than late treatment and control in the upland woods. Indicator Species Analysis indicated a majority of spring (75%) and summer (50%) dominant species maximized performance in the early treatment.

White-tailed deer (Odocoileus virginianus) and fire effects on flowering diversity of tallgrass prairie forbs1

Abstract We studied the effect of white-tailed deer (Odocoileus virginianus Zimmermann) browsing and fire on diversity and number of prairie-forb flowering stems in a remnant tallgrass prairie in northern Illinois. Our study included two plots protected from deer browsing since 1992 and two unprotected plots. All plots were burned twice in late April of 1990 and 1991. Deer densities of 32–50 km−2 (1992–96) declined to 7–9 km−2 in 1998 and 1999 after controlled hunting. Similarity between protected and unprotected plots was initially 82%, declined to 49% during the period of high deer density, and increased to 68% in 2001 with managed hunting. Flowering stems for all forbs were tallied in 1998–2001. Diversity (Shannon index [H′] and effective number of stems [HO]) of flowering stems was higher on protected than on unprotected plots for all study years. Differences in composition and diversity between protected and unprotected plots were associated with interactions between fire and protection from deer browsing as measured by total number of flowering stems, which was significantly higher on protected than on unprotected plots in nonburn years (3.4–3.5-fold) but not in burn years (1.0–1.2-fold). The two leading species on protected plots (ashy sunflower [Helianthus mollis Lam.] and Culvers root [Veronicastrum virginicum (L.) Farw.]) tended to have fewer flowering stems in burn years and always had them in protected plots (54-fold and 70-fold higher in protected plots for the two species, respectively). For the second leading species on unprotected sites (wild quinine [Parthenium integrifolium L.]), the number of flowering stems was significantly higher in burn years (27-fold); however, there was no significant difference in the number of stems between protected and unprotected plots. These results show strong interactions between fire and deer-browsing disturbances in communities recovering from deer overabundance.