1 markRhododendron ponticum (pictured below) is a fast-growing, non-native, invasive species currently threatening biodiversity in the UK.
Rhododendron ponticum
Originally introduced from Spain as a decorative plant for gardens, R. ponticum forms large thickets and outcompetes native plants such as bryophytes, other woody plants and wildflowers. Particularly severely affected are Atlantic oak woodland areas of coastal land in the western United Kingdom. Clearance programmes to remove R. ponticum have been in place for approximately 30 years in that region. Data was gathered on how the removal of R. ponitcum allows for affected sites to recover and for native species to be restored.
A quadrat study was carried out at three sites:
- An area of dense Rhododendron ponticum thickets
- An area of intermediate ponticum coverage
- An area of uninvaded land as a control
In each study, the number of species in each area's understorey was counted, as well as the % vegetation cover. This data is shown on the graphs below, which have been plotted with a line of best fit.
Calculate the range of species found at a R. ponticum density of 2 log arbitrary units.
1 markState how the % vegetation cover can exceed 100% in a given area.
1 markSuggest why a log scale is used to show the density of R. ponticum in the graphs.
1 markExplain the decline in the number of species found as the density of R. ponticum increases, as found in this study.
2 marksSuggest two ways in which R. ponticum could affect competition.
1 markIn an extension of this study, the spread of epiphytes (plants that grow on other plants, but not parasitically) was examined as a function of the time elapsed since the human clearance of R. ponticum from an area of ancient woodland. Typical taxa of epiphytes include mosses and liverworts. This was done to estimate how well a woodland habitat could recover from an invasion by R. ponticum. One theory is that R. ponticum can affect successive species long after all its biomass has been cleared away from a site. The results are shown in the diagram below.
Estimate the number of years before the number of species found on cleared land first exceeded the number of species found in uninvaded woodland.
3 marks(i) Discuss whether the clearance of a R. ponticum invasion has an impact on the recovery of the woodland habitat.
(ii) Suggest a reason for any impact observed.
3 marksIn a further study, a series of measured soil core samples were taken from thirty sites within the Atlantic woodland
- 10 sites uninvaded by R. ponticum
- 10 sites cleared of R. ponticum more than 10 years previously
- 10 sites of dense R. ponticum coverage
Identify the species that was sampled on the fewest sites when the R. ponticum growth was densest.
1 markUsing the data in part (h), identify, with a reason, the species that benefited most from the clearance of R. ponticum from Atlantic coastal woodland.
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