Concurrent management of an exotic species and initial restoration efforts in forests

Published source details Murphy S.D. (2005) Concurrent management of an exotic species and initial restoration efforts in forests. Restoration Ecology, 13, 584-593.
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Summary

Garlic mustard Alliaria petiolata, native to Europe, is an invasive herbaceous plant in woodlands of eastern North America. It poses a severe threat to native forest ground flora in the region by monopolization of light, moisture, nutrients, soil and space. Forest fragmentation and resultant microenvironment changes appears to facilitate invasion. Garlic mustard impedes restoration efforts as it tends to outcompete much of the native understory plant community. An experiment was conducted to determine if bloodroot Sanguinaria canadensis (a native woodland herbaceous perennial) could outcompete garlic mustard and suppress its spread.

Study site: The study area was a degraded woodlot (31,916 m²) located on a farm 16 km northwest of Waterloo, Ontario, Canada. The choice of experimental locations within the site was based on the criteria that they had large populations of garlic mustard Alliaria petiolata but few or no individuals of bloodroot Sanguinaria canadensis were present.

Species choice: Anecdotal observations of the impact of garlic mustard and which native species seemed less vulnerable or appeared to recover after invasion led to the choice of bloodroot, which seemed to fit these requirements. It is a native woodland herbaceous perennial reaching 50 cm in height at flowering with palmate leaves up to 30 cm in width. It spreads via rhizomes and seeds, the latter are dispersed by ants.

Transplanting: Arbitrarily chosen bloodroot rhizomes growing near the experimental plots (25–75 m away) were tagged in spring and summer 1997. In autumn, the rhizomes were dug up inside a soil clod, removed briefly to measure length and biomass, and transplanted within the same soil clod. The transplants were assessed in April 1998 - all leafed in spring having survived the transplanting.

Bloodroot was transplanted at densities of 0, 1, 2, 3, 5, 7, 9, 11, 15 and 20 ramets/m² in 1997 in areas with initial garlic mustard densities of 128 seedlings and 31 rosettes/m².

Garlic mustard suppression: As of 2000, data analyses indicated that initial bloodroot densities of as few as five ramets/m² suppressed garlic mustard. Initial relatively high bloodroot densities of nine and 11 ramets/m² resulted in the lowest numbers of garlic mustard late-spring seedlings, numbers and sizes of year 1 and 2 rosettes, numbers and area of stem leaves, numbers of flowering individuals, number of flowers, number of fruits. Bloodroot also reduced garlic mustard height at flowering.

Conclusions: This experiment within a degraded woodlot indicates that transplanting bloodroot was effective at mitigating the spread of garlic mustard. Whether this process of suppression of garlic mustard will continue in the longer term and if ²reestablishment of bloodroot will assist in restoration of native forest ground flora is however unknown.

(See also Case 247: Control of an invasive plant, garlic mustard Alliaria petiolata, using a glyphosate herbicide, Hueston Woods State Park, Ohio, USA)

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