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Influence of Colonizing Shrubs on Species-Area Relationships in Alvar Plant Communities

Marcel Rejmánek and Ejvind Rosén
Journal of Vegetation Science
Vol. 3, No. 5 (Dec., 1992), pp. 625-630
Published by: Wiley
Stable URL: http://www.jstor.org/stable/3235829
Page Count: 6
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Influence of Colonizing Shrubs on Species-Area Relationships in Alvar Plant Communities
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Abstract

In herbaceous plant communities of Stora Alvaret (the Great Alvar), Öland, Sweden, we studied the dependence of species-area relationships on the canopy cover of the colonizing shrubs Juniperus communis and Potentilla fruticosa. A series of plots 0.25 - 256 m2 in area were sampled in communities with varying canopy cover of Juniperus or Potentilla. Species number - log (area) regressions always fitted data better than log (species number) - log (area) regressions. The number of species declines more dramatically with increasing Potentilla cover than with increasing Juniperus cover. The total species number in large Juniperus plots follows a unimodal curve with a peak at about 75 % shrub cover. The alvar (limestone grassland) species number in plots of all sizes declines monotonically with Juniperus cover following the regression equation S = 31.09 + 10.75 log A - 0.0025 P2, where A is area and P is percentage Juniperus cover. There is a monotonic decline of species number with increasing shrub cover in Potentilla plots of all sizes. The species richness in plots with Potentilla was fitted by the regression equation S = 16.48 + 14.91 log A-0.131 P-0.00104 P2 log A, where P is % Potentilla cover. A faster initial decline of species number with Potentilla colonization is apparently caused by its preferential establisment in species-rich, elevated microsites.

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