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Spatial pattern formation in semi-arid shrubland: a priori predicted versus observed pattern characteristics

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Abstract

Ecologists increasingly use spatial statistics to study vegetation patterns. Mostly, however, these techniques are applied in a purely descriptive fashion without a priori statements on the pattern characteristics expected. We formulated such a priori predictions in a study of spatial pattern in a semi-arid Karoo shrubland, South Africa. Both seed dispersal and root competition have been discussed as processes shaping the spatial structure of this community. If either of the two processes dominates pattern formation, patterns within and between shrub functional groups are expected to show distinct deviations from null models. We predicted the type and scale of these deviations and compared predicted to observed pattern characteristics. As predicted by the seed dispersal hypothesis, small-scale co-occurrence within and between groups of colonisers and successors was increased as compared to complete spatially random arrangement of shrubs. The root competition predictions, however, were not met as shrubs of similar rooting depth co-occurred more frequently than expected under random shrub arrangement. Since the distribution of rooting groups to the given shrub locations also failed to match the root competition predictions, there was little evidence for dominance of root competition in pattern formation. Although other processes may contribute to small-scale plant co-occurrence, the sufficient and most parsimonious explanation for the observed pattern is that its formation was dominated by seed dispersal. To characterise point patterns we applied both cumulative (uni- and bivariate K-function) and local (pair- and mark-correlation function) techniques. Based on our results we recommend that future studies of vegetation patterns include local characteristics as they independently describe a pattern at different scales and can be easily related to processes changing with interplant distance in a predictable fashion.

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Author notes

  1. Frank M. Schurr

    Present address: Department of Ecological Modelling, Permoserstr. 15, 04318 Leipzig, Germany

Authors and Affiliations

  1. Institute of Ecology, University of Jena, Dornburger Str. 159, 07743, Jena, Germany

    Frank M. Schurr, Oliver Bossdorf & Jens Schumacher

  2. Department of Community Ecology, UFZ Centre for Environmental Research Leipzig-Halle, Theodor-Lieser-Str. 4, 06120, Halle, Germany

    Oliver Bossdorf

  3. Department of Conservation Ecology, University of Stellenbosch, Private Bag X1, 7602, Matieland, South Africa

    Suzanne J. Milton

  4. Max-Planck Institute for Biogeochemistry, Carl-Zeiss-Promenade 10, 07745, Jena, Germany

    Jens Schumacher

Authors
  1. Frank M. Schurr
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  2. Oliver Bossdorf
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  3. Suzanne J. Milton
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  4. Jens Schumacher
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Correspondence to Frank M. Schurr.

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Schurr, F.M., Bossdorf, O., Milton, S.J. et al. Spatial pattern formation in semi-arid shrubland: a priori predicted versus observed pattern characteristics. Plant Ecology 173, 271–282 (2004). https://doi.org/10.1023/B:VEGE.0000029335.13948.87

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