Impacts and Management of Biological Invasions

Invasive species are a source of many urgent conservation problems, and our ability to manage biological invasions is severely limited by a lack of even the most basic information about most invasive species.

Our lab works on many aspects of the biology and management of invasive species, from the development and testing of conceptual and quantitative models to the practical application of ecologically-based control strategies.

SOIL LEGACIES, MUTUALISM DISRUPTION, AND DIRECT AND INDIRECT EFFECTS OF AN INVASIVE SHRUB

As a large, nitrogen-fixing shrub, Scotch broom (Cytisus scoparius (L.) Link; Fabaceae) changes soil nutrients when it invades prairies and disturbed forests in the Pacific Northwest. In addition, broom produces high concentrations of alkaloids, which may have allelopathic effects on native plants and on soil fungi. Broom's effect on soil chemistry leads to the disruption of ectomycorrhizal fungal (EMF) mutualisms. We have de that broom invasion leaves a soil “legacy effect” that persists long beyond the removal of the invader.

With our collaborators at Joint Base Lewis-McChord, we saw massive failure of reforestation efforts in invaded clearcuts. We found that soil chemical changes accompanying broom invasion influenced the growth and establishment of Douglas fir seedlings. We use greenhouse experiments, field studies, and next-generation sequencing techniques to disentangle the direct and indirect effects of broom invasion on forest regeneration.

For more details, see our Information for Practitioners,

and our publications, for example:

Grove, S, NP Saarman, GS Gilbert, B Faircloth, KA Haubensak, and IM Parker. 2019. Ectomycorrhizas and tree seedling establishment are strongly influenced by forest edge proximity but not soil inoculum. Ecological Applications 29 (3), e01867.

Grove, S, KA Haubensak, and IM Parker. 2015. Persistence of a soil legacy following removal of a nitrogen-fixing invader. Biological invasions 17 (9), 2621-2631.

INVASION, BIOTIC RESISTANCE, AND THE ROLE OF DISTURBANCE IN A NOVEL INVADER

Dittrichia graveolens (L.) Greuter (stinkwort) is an annual plant in the Asteraceae family native to the Mediterranean Basin. It was first introduced to California in 1984 in Santa Clara County, where it is found primarily along roadsides and in disturbed soils. However, this ruderal species has recently been observed spreading away from roadsides to areas that have more densely vegetated plant communities, representing a common pattern for invasive plants. We also know that disturbance plays an important role in the invasion process for many non-native species and may inadvertently facilitate the movement of invasive species into plant communities. However, some native species may provide biotic resistance and offer a pathway to bolstering restoration sites and native communities with species that can help deter invasion through species interactions. In collaboration with Blue Oak Ranch Reserve, our primary research aim is to study biotic resistance to invasion, assessed by the ability of D. graveolens to compete with established vegetation under a range of disturbance conditions and with a common native plant species with a similar life history (Hemizonia congesta subsp. luzulifolia (D.C.) Babc. & H.M. Hall; Asteraceae).

IMPACTS AND CONTROL OF AN INVASIVE UNDERSTORY GRASS

Erect veldtgrass (Ehrharta erecta Lam.; Poaceae) is an invasive grass actively spreading in California. Our work contributes to a better understanding of the ecology, impacts, and potential for control of E. erecta in order to guide management practices. We quantified the impacts of E. erecta on native plant species richness and abundance across 11 sites of forest understory on the UC Santa Cruz campus. Strikingly, we measured nearly four times greater total vegetation cover in plots invaded by E. erecta. However, native plants were not significantly less abundant in invaded plots than in reference plots. We did, however, find evidence of change in community composition in response to E. erecta abundance. Our findings demonstrate that native species can persist in the presence of E. erecta, although the long-term impacts on populations of the perennial plants that dominate the forest understory are still unknown.

We also compared the effectiveness of mechanical (hand pulling) and chemical (glyphosate) management methods. We found substantial reductions in E. erecta using both mechanical and herbicide treatments, but herbicide application also produced greater reductions in native species cover and species richness.

We conclude that effective management of E. erecta is possible using either manual or chemical removal methods; the optimal method may depend on the availability of manual labor and the sensitivity of the habitat to non-target effects on native plants.

For more details, see our Information for Practitioners,

and

Ray, C. A., Sherman, J. J., Godinho, A. L., Hanson, N., & Parker, I. M. 2018. Impacts and best management practices for Erect Veldtgrass (Ehrharta erecta). Invasive Plant Science and Management, 11(1), 40-48.

You can find publications from these projects and more at Ingrid's Google Scholar page.

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