Rob Marrs is analysing data on vegetation change in long-term manipulative experiments in the British uplands
It is a fact of life that the species that occur within a landscape change through time. This change can be brought about by a range of factors, including climate change, pollution, land-management and random events. But, such change can be very slow, for example in the British uplands where the climate is harsh. If we wish to conserve our upland landscapes, therefore, we need to know how they change, the speed at which they change and the factors that drive these changes. Accordingly in my project I will measure the speed and direction of change in two case-studies where change has been partly enforced by management – rewilding and bracken control. I will do this using data collected from long-term manipulative experiments, where the effects of management can be compared against a business-as-usual, no-treatment control.
Rewilding, the effects of no-sheep
Removal of sheep has been suggested as part of an attempt to make upland landscapes ‘more wild’. I hypothesise that overgrazing by sheep has reduced the conservation value of the landscape, and hence if it is removed, the vegetation should recover. I will test this by comparing the vegetation change in ten separate experiments set up between 1954 and 1967 in the north Pennines; each experiment has paired sheep-grazed and ungrazed plots. I will measure change in three ways, considering (1) individual plant species, (2) plant communities, and (3) using use a trait-based approach to tease out effects of pollutant loads.
Bracken is one of the world’s most intractable weeds, causing considerable problems in Britain. Over the last 40 years, we have developed good techniques to control this Triffid, but we do not know how resilient it is – i.e. how quickly and how strongly it ‘bounces-back’ from even quite successful treatment. I have maintained two large-scale experiments on bracken control for 25 years, and both were very successful in more or less eradicating it. However, I deliberately stopped applying control treatments in 2012 to assess the bounce-back effect, and since then have been measuring both bracken recovery, and as important, the impact of recovering bracken recovery on the underlying plant species. This time for recovery will be of critical importance for the deployment of large-scale bracken control schemes.
Both case-studies will impact on our theoretical knowledge of ecological processes in upland ecosystems and the quantification of rates of change will have great relevance for land managers.