Ecological anachronisms in the recruitment of temperate light-demanding tree species in wooded pastures

Authors

  • E. S. BAKKER,

    Corresponding author
    1. Nature Conservation and Plant Ecology Group, Wageningen University, Bornsesteeg 69, 6708 PD Wageningen, The Netherlands;
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  • H. OLFF,

    1. Tropical Nature Conservation and Vertebrate Ecology Group, Wageningen University, Bornsesteeg 69, 6708 PD Wageningen, The Netherlands;
    2. Community and Conservation Ecology Group, Centre for Ecological and Evolutionary Studies, University of Groningen, PO Box 14, 9750 AA Haren, The Netherlands;
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  • C. VANDENBERGHE,

    1. Nature Conservation and Plant Ecology Group, Wageningen University, Bornsesteeg 69, 6708 PD Wageningen, The Netherlands;
    2. Department of Biology, Research Group Terrestrial Plant and Vegetation Ecology, Ghent University, Krijgslaan 291 S8, 9000 Ghent, Belgium; and
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    • **

      Present address: Swiss Federal Research Institute WSL, Antenne romande c/o EPFL, Case postale 96, 1015 Lausanne, Suisse.

  • K. DE MAEYER,

    1. Nature Conservation and Plant Ecology Group, Wageningen University, Bornsesteeg 69, 6708 PD Wageningen, The Netherlands;
    2. Department of Biology, Research Group Terrestrial Plant and Vegetation Ecology, Ghent University, Krijgslaan 291 S8, 9000 Ghent, Belgium; and
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  • R. SMIT,

    1. Nature Conservation and Plant Ecology Group, Wageningen University, Bornsesteeg 69, 6708 PD Wageningen, The Netherlands;
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  • J. M. GLEICHMAN,

    1. Nature Conservation and Plant Ecology Group, Wageningen University, Bornsesteeg 69, 6708 PD Wageningen, The Netherlands;
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  • F. W. M. VERA

    1. National Forest Service, PO Box 1300, 3970 BH Driebergen, The Netherlands
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*Present address and correspondence: Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E9 (e-mail esbakker@andros.demon.nl).

Summary

  • 1Light-demanding trees and thorny shrubs in temperate plant communities may reflect adaptations to now-extinct large grazers, such as aurochs and tarpans, rendering these adaptations ecological anachronisms.
  • 2We explored the ecological functions of plant traits of Quercus robur and Prunus spinosa in areas grazed by cattle and horses, the domesticated descendants of aurochs and tarpans. Specifically, we tested the hypothesis that grazing induces a shifting mosaic of grassland, shrub thickets and woodlands through the key process of associational resistance: the protection of palatable young trees by thorny shrubs.
  • 3An exclosure experiment with transplanted Q. robur seedlings revealed that Q. robur grew best in grassland exclosures and on the edge of thorny shrub thickets, which may be viewed as an optimal balance between sufficient protection from large herbivores and sufficient light availability.
  • 4A cross-site comparison of four floodplain woodlands in north-western Europe showed that Q. robur can regenerate in the presence of large herbivores through spatial association with P. spinosa. However, we found that expansion of P. spinosa shrubs and Q. robur coincided with periods of low rabbit abundance and not with livestock density. From this, it appears that the process of associational resistance does not work with rabbits.
  • 5Synthesis and applications. With extensive grazing by large (domesticated) grazers in temperate floodplains, a shifting mosaic of grassland, shrubs and trees may develop that has high conservation value. Palatable, light-demanding Q. robur seedlings can successfully regenerate in spiny P. spinosa shrubs through associational resistance. This process does not offer protection from abundant small herbivores, such as rabbits, that can inhibit the recruitment of shrubs and trees in this mosaic vegetation. In floodplain meadows frequent flooding may be an efficient way to reduce rabbit populations, with dry conditions in summer and wet in winter. When floodplain meadows are combined with adjacent higher grounds, large herbivores can escape the floods through migration.

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