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Implications of Plant Density on the Resulting Community Structure of Mine Site Land


  • Lara V. Jefferson

    Corresponding author
    1.  Institute for Plant Conservation, Chicago Botanic Garden, 1000 Lake Cook Road, Glencoe, IL 60022, U.S.A.
    2.  Department of Environmental Biology, Curtin University of Technology, G.P.O. Box U1987, Perth 6845, Western Australia
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The relative abundances of Chenopodiaceae shrubs are different from the seed composition in the original seed mix when sown on mine waste material in semiarid regions of Western Australia. Experiments were therefore undertaken to determine what species interactions are responsible for shifts in relative abundance after seeding. The growth parameters of five members of the Chenopodiaceae were used to determine intra- and interspecific density-dependent interactions. Dominant and subordinant species were paired and grown in pots at differing densities. The growth parameters measured were height, root, and shoot biomass. Of the five species chosen for this study, Maireana georgei (golden bluebush) and Enchylaena tomentosa (ruby saltbush) do not establish well on mine site areas. These were sensitive to density in monoculture, as well as in the presence of both Atriplex bunburyana (silver saltbush) and Atriplex codonocarpa (flat-topped saltbush). Although Maireana brevifolia (small leaf bluebush) does establish successfully on mine sites when sown, it showed the same negative reaction when grown in monoculture and in a two-species mixture. Atriplex bunburyana and A. codonocarpa, in contrast, are dominant species and reacted differently when grown with increasing numbers of the target species (M. georgei, M. brevifolia, and E. tomentosa). Atriplex bunburyana did not exhibit any decreases in growth when grown in competition with up to four plants of the target species. However, A. codonocarpa did react adversely to the presence of the target species. It is thought that the resulting plant community organization reflects the original seed mixture, which is usually sown at a high density. Yet, this study has shown that the differing intra- and interspecific density responses of these chenopod species provide an indication of the resulting community organization. To maximize diversity and to prevent dominance by highly competitive species, such as A. bunburyana, it is important to take density-dependent effects into account during the restoration planning stage.