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    Author(s): J. W. Van Sambeek; Jane M. Kobe; James S. Fralish
    Date: 1997
    Source: In: Pallardy, Stephen G.; Cecich, Robert A.; Garrett, H. Gene; Johnson, Paul S., eds. Proceedings of the 11th Central Hardwood Forest Conference; Gen. Tech. Rep. NC-188. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station: 294-303
    Publication Series: General Technical Report (GTR)
    Station: North Central Research Station
    PDF: View PDF  (1.42 MB)

    Description

    This study examined the potential role of hardwood leachates in the reduction of understory forbs in oak-hickory stands following invasion by sugar maple and dense-canopy shrubs. We conducted a shaded greenhouse experiment during two summers using stonemint dittany (Cunila origanoides (L.) Britton) as an indicator species. We used a modified stair-step bioassay with donor pots producing two levels of recycled leachates from hardwood seedlings root exudates, foliage washes, and decaying leaves. At the lower density, each donor pot had three hardwood seedlings and three applications 300 cm? of mature leaves of the same species to the litter layer (LAI = 1.5). At the higher density, we doubled the number of seedlings and surface area of mature leaves in the litter layer (LAI=3.0). Donor species tested for 1 or 2 years included sand-only, sugar maple, white oak, flowering dogwood, pawpaw, and black walnut. Dittany stem height ranged from 38 cm when exposed to leachates from white oak seedlings to 49 cm when exposed to leachates from sand-only donor pots. Dittany stem dry weights showed no differences in either year in response to leachates produced by different hardwood seedlings or at the two donor densities. Most dittany stems produced nearly 2,000 flowers during a 10 week period which began with completion of axillary shoot elongation. No differences in date of flower initiation or cumulative flower production were found in response to any of the hardwood leachates. We conclude that allelopathic interference of dittany by hardwoods, if it occurs at all, may require more stressful conditions than were created in this study and that the absence of dittany in oak-hickory stands after the invasion by sugar maple or pawpaw results primarily from competition for light and other resources.

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    Citation

    Van Sambeek, J. W.; Kobe, Jane M.; Fralish, James S. 1997. Interference with shoot growth and flowering of dittany (Cunila origanoides (L.) Britton) by hardwood leachates. In: Pallardy, Stephen G.; Cecich, Robert A.; Garrett, H. Gene; Johnson, Paul S., eds. Proceedings of the 11th Central Hardwood Forest Conference; Gen. Tech. Rep. NC-188. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station: 294-303

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