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Contrasting impacts of a native and an invasive exotic shrub on flood-plain succession

Bellingham, Peter J., Peltzer, Duane A., Walker, Lawrence R.
Journal of vegetation science 2005 v.16 no.1 pp. 135-142
Buddleja davidii, Coriaria, biomass, botanical composition, ecosystems, invasive species, mineral soils, nutrient content, primary succession, rivers, shrubs, stoichiometry, New Zealand
Question: How do Coriaria arborea, an N-fixing native shrub, and Buddleja davidii, a non-N-fixing exotic shrub, affect N:P stoichiometry in plants and soils during early stages of primary succession on a flood-plain?Location: Kowhai River Valley, northeast South Island, New Zealand.Methods: We measured soil and foliar nutrient concentrations, light levels, plant community composition and the above-ground biomass of Coriaria and Buddleja in four successional stages: open, young, vigorous and mature.Results: Coriaria occurred at low density but dominated above-ground biomass by the vigorous stage. Buddleja occurred at 5.3 ±± 1.0 stems/m² in the young stage and reached a maximum biomass of 520––535 g.m⁻⁻² during the young and vigorous stages. Mineral soil N increased with above-ground Coriaria biomass (r² == 0.45), but did not vary with Buddleja biomass. In contrast, soil P increased with Buddleja biomass (r² == 0.35), but not with Coriaria biomass. In early successional stages, 70––80%% of the species present were exotic, but this declined to about 15%% by the mature stage. Exotic plant species richness declined with increasing Coriaria biomass, but no other measures of diversity varied with either Coriaria or Buddleja biomass.Conclusion: These results demonstrate that Buddleja dominates early succession and accumulates P whereas Coriaria dominates later succession and accumulates N. A key ecosystem effect of the invasive exotic Buddleja is alteration of soil N:P stoichiometry.Nomenclature: Allan (1961) with amendments suggested by Connor & Edgar (1987), and Webb et al. (1988).