Seed limitation, not soil legacy effects, prevents native understory from establishing in oak woodlands in Scotland after removal of Rhododendron ponticum

Janet E. MacLean, Ruth J. Mitchell, David Burslem, David Genney, Jeanette Hall, Robin J. Pakeman

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Following removal of the invasive species Rhododendron ponticum the native understorey plant community typically fails to re-establish itself. Potential explanations for this failure include 1) lack of an appropriate native seed source, 2) inability of seed to penetrate a dense bryophyte layer and 3) persistence of chemical ‘legacy effects’ in the soil. We established an experiment to test these competing hypotheses in an Atlantic oak woodland where R. ponticum had been removed. The following experimental treatments were applied singly and in combination: 1) addition of a native seed mix to test for seed limitation; 2) removal of the established ground vegetation at the start of the experiment (which principally consisted of bryophytes) to test for the impact of a barrier layer; 3) addition of activated carbon to test for chemical legacy effects in the soil and 4) fertilisation as an additional measure to promote the establishment of native vascular plants. Application of the native seed mix was revealed to be an effective way to increase the cover of native vascular plants, and was particularly effective when applied after the removal of the bryophyte layer. The application of activated carbon and/or fertiliser, however, had no effect on the cover of native vegetation. We conclude that reports of R. ponticum exerting chemical legacy effects long after its removal may have been overstated and that seed limitation and inability to successfully establish in a dense bryophyte layer provided the strongest barriers to natural recolonisation by the native plant community following R. ponticum removal.
Original languageEnglish
Pages (from-to)865-872
Number of pages8
JournalRestoration Ecology
Issue number5
Early online date4 Jan 2018
Publication statusPublished - Sept 2018

Bibliographical note

We thank Scottish Natural Heritage for funding this work via a PhD studentship to JM. The National Trust for Scotland provided the field site and fenced the experiment. In particular we thank Kate Sampson and Lindsay Mackinlay at NTS staff for their assistance in establishing this experiment. RJM and RJP were funded through the 2011-2016 and 2016-2021 Strategic Research Programmes of the Scottish Government.


  • bryophytes
  • legacy effects
  • oak woodland
  • reconolisation
  • restoration
  • Rhododendron ponticum


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