The post provided by Robin Pakeman
This post refers to the article A functional assessment of the impact of changing grazing management of upland grassland mosaics by Robin Pakeman and Debbie Fielding published in Applied Vegetation Science (https://doi.org/10.1111/avsc.12504)
The Glen Finglas experiment was set up in 2002 to look at how changes to the European Common Agricultural Policy, specifically decoupling of support from livestock numbers, might impact upland biodiversity. It is still relevant today as policies regarding agricultural support are always likely to be changed.
The initial team consisted of scientists from the Macaulay Land Use Research Institute, the Centre for Ecology and Hydrology and the Scottish Agricultural College. It is now run from the James Hutton Institute (which the Macaulay became part of in 2011) in collaboration with the University of Newcastle.
We wanted the experiment to make a policy contribution, so we set it up so we could study a species that policy makers could appreciate. We chose the meadow pipit, not in itself rare, but an important part of upland food webs and, importantly nesting at high enough densities so that an experiment was only financially challenging rather than impossible. The experiment is large, c. 0.75 km2, and needed 12 km of fencing, so maintaining and replacing this is a major commitment. However, the experiment has given us an unrivalled resource to understand how grazing impacts on a whole range of organisms and, in particular, how changes in management cascade through a system.
Glen Finglas sits at the southern edge of the Scottish Highlands. The experiment consists of four treatments replicated six times. The “control” treatment continued the recent stocking level of sheep, with three sheep per plot (0.9 sheep/ha). The other three treatments were a tripling of sheep numbers (2.7 sheep/ha), the partial substitution of sheep by cattle (but kept at the same level of offtake) and the complete removal of livestock. The large size of the plots meant that each covered a mosaic of upland plant communities, mainly wet heath, wet and dry grassland of varying quality and sedge mire. The mosaic nature of the vegetation in the experiment meant that heterogeneity had to be taken into account in the analysis, but this had the benefit of providing insights into the dynamics of the different vegetation types.
The responses of individual species took a minimum of 12 years and often 15 years to become apparent, with some species showing no detectable changes (Pakeman et al. 2019).
This paper focuses on how the changes in grazing impacted on the functional characteristics of the plant communities present to assess how management cascades through the system. Despite the significant changes in grazing, there were only small changes in trait means over 15 years. The most preferred communities, bent-fescue grasslands, were less sensitive to grazing removal than expected as a long history of being the focus of grazing meant that few species were still present that could take advantage of reduced grazing and so the mean trait values did not change. However, they did still respond to increased grazing with a shift towards more exploitative growth forms and, in consequence, making these communities more nutritious for livestock.
The least preferred communities, wet heath and mat-grass dominated grasslands, were more sensitive to grazing removal than expected; they still contain species capable of exploiting this. The upshot of this was a shift to a vegetation of even less preference for livestock. However, the presence of more preferred communities in each plot meant increased grazing had less than expected impact on communities of moderate and low preference; a finding only possible when working on a mosaic of communities. Cattle impacts were highest in the communities most sensitive to trampling, bracken and wet heath.
Results from other investigations have shown that decisions about grazing management have different impacts on different parts of the system. The meadow pipits nest at highest density in the plots with more sheep or with cattle and it appears that they prefer to forage in areas where grazing has broken up the vegetation allowing them access. This is despite there being more food for them in the ungrazed plots (Evans et al. 2015). However, nest and chick survival differences mean that there is little overall difference in productivity between the treatments (Malm et al. published online). Other results show that moth diversity is highest on the ungrazed plots, which also see the highest densities of voles, greater fox activity and a very slow build-up of soil carbon.
Management change in the upland margins will largely be driven by changes in policy, agricultural support payments and farm profitability. Different species will benefit under different management regimes, and big changes are possible if grazing removal results in woodland regeneration, which so far has been very slow. Animal species and assemblages react relatively quickly to changes in vegetation structure, but changes in plant composition and quality have taken many years to become detectable in these cold, wet and infertile habitats. How these changes then feedback into further changes in animal communities is still open, and the subject of current research. Our understanding of how decisions about grazing shape upland biodiversity has benefitted greatly from this large-scale long-term experiment. The large-scale has allowed us to see how grazing density impacts many different species and has allowed us to see how responses to grazing in a vegetation community are modulated by the presence of other vegetation types of different preference. This would not have been possible by looking at the responses of single vegetation types to grazing. The long-term nature of the experiment has meant that it is possible to see how the dynamics of the treatments have played out in a realistic time scale and to actually detect changes in the vegetation.
- Evans, D.M., Villar, N., Littlewood, N.A., Pakeman, R.J., Evans, S.A., Dennis, P., Skartveit, J., & Redpath, S.M. (2015). The cascading impacts of livestock grazing in upland eco-systems: a 10-year experiment. Ecosphere, 6, 1-15. https://doi.org/10.1890/ES14-00316.1
- Malm L.E., Pearce-Higgins, J.W., Littlewood, N.A., Karley, A.J., Karaszewska, E., Jaques, R., Pakeman, R.J., Redpath, S.M., & Evans, D.M. (published online). Livestock grazing impacts upon components of the breeding productivity of a common upland insectivorous passerine: results from a long-term experiment. Journal of Applied Ecology, https://doi.org/10.1111/1365-2664.13647
- Pakeman, R.J., Fielding, D.A., Everts, L., & Littlewood, N.A. (2019). Long‐term impacts of changed grazing regimes on the vegetation of heterogeneous upland grasslands. Journal of Applied Ecology, 56, 1794-1805. https://doi.org/10.1111/1365-2664.13420
Brief personal summary: Robin Pakeman is a senior researcher at the James Hutton Institute. His research interests include understanding long-term vegetation change, management impacts on ecosystem function and the conservation of biodiversity.