COPY FOR TEST Moor House Grazing Plots

Located in North England, the Moor House Grazing Plots is 74 km₂ in size and is part of the UNESCO Biosphere Reserve and European Special Protection Area. It is heterogenous in habitat type and altitude (blanket bog and grasslands), and because the area is a Common under English Law, sheep from various farms have been grazing freely for villages in the Eden Valley.

In 1952 Moor House was designated as an NNR primarily for research purposes. At that time, it was estimated that there were 15,400 sheep (4.4 sheep ha-1). In 1972, grazing density reduced to 7000 sheep (2 sheep ha-1) due to the formalising of grazing rights under the Commons Registration Act. Later in 2000, the grazing density was further reduced to approximately 3500 (1 sheep ha-1) due to buy-out of some commoners grazing rights.

Each of the four habitats have different plots, all with different plot sizes, sheep densities, and vegetation types (see Table 1). The experimental plots were set up when the fencing was erected to keep sheep from grazing one of the paired plots, the other was left for sheep to graze. The blanket bog plots (Bog Hill and Hard Hill A-D) were set up first, which was followed by the high-level grasslands, and then the high-level blanket bog plots. Finally, the intermediate grassland plots were set up.

Each habitat is represented by at least two sites to provide some degree of replication and at each site there is a sheep grazed plot, and an ungrazed plot (where sheep grazing was stopped by fencing). The vegetation was sampled by using point quadrats which was used to calculate species richness, abundance, composition and canopy height.

Different vegetation species thrive depending whether sheep graze or not

In order to understand how sheep grazing would affect the ecosystem, Milligan et al. (2016) compared the species diversity and abundance of the vegetation between the grazed and ungrazed plots. They found that species richness decreased through time, but the vegetation changes in species biodiversity differed between the ungrazed and grazed plots.

Figure 1 shows the simplified results: On the grazed plots, vascular plants, grasses, lichen, liverworts and mosses all decreased in biodiversity. But the herbs, sedges, rushes and shrubs all increased. On the ungrazed plots, the vascular plants, grasses and liverworts all decreased at a faster rate, while the lichen decreased at a slower rate indicating negative effects. The herbs, sedges, rushes and shrubs all increased in biodiversity, as did the mosses which illustrate the positive benefits of sheep grazing.

Overall, while some vegetation does better, others do not when sheep are grazing. The shift towards sedges, herbs and shrubs indicates biotic homogenisation (where two or more spatially distributed ecosystems become increasingly similar over time). This can lead to loss of biodiversity. Even if sheep were reduced, it is unlikely that the vegetation would change over a long period and thus be restored. Any willingness to change the vegetation composition should be accompanied by other land-management measures.

Maintaining local vegetation is crucial to upland restoration after sheep grazing

It is possible that the sheep might be removed as part of a restoration scheme. This and other types of land abandonment can have negative or positive effects depending on the area. The question is how will plant communities respond. To examine this, Alday et al. (2022) looked at trends in the vegetation community between grazed and ungrazed plots. They found some differences albeit not too many between the grazed and the ungrazed plots.

In the grazed plots, species richness and abundance recovered after 2000. There were particular improvements in vascular plants, mosses and liverworts, with the first two recovering the fastest. Lichens however did not improve, and this could be because they are being influenced by the plant communities surrounding them, or competition with vascular plants as a result of increased nitrogen. The fact that each plant had its own trends over the long-term suggested that the response is dependent on the plant community.

Additionally, they found no difference in recovery rates between the ungrazed and grazed plots. The fact that vegetation in the ungrazed plots is recovering may be due to decreased pollutant levels or the temperature increasing. 

Overall, these results suggest that maintaining vegetation by increasing the seedbanks of local species is central to restoration to prevent invasion by species that may have a negative effect. Ultimately, these conclusions will contribute towards developing the right land-management practices in restoring upland habitats.

Plant biodiversity can recover if sheep grazing is removed but it can take time

The Wet Desert hypothesis proposes that because grazing would decrease plant species diversity, then if grazing is removed, that diversity will then increase. There are two assumptions inherent in this hypothesis: the species that grazers remove will select for traits that leads to biotic homogenisation, and that the species that have been reduced by grazing but recovers if grazing is removed will have better nutrition, digestibility, palatability and decomposability.

Marrs et al. (2020) tested this hypothesis. They selected seven key plant species that were present or abundant in the ungrazed plots of one experiment, but absent or had low abundance in the grazed plots. They undertook tests on the seven key one’s and others to compare the nutrition, digestibility, palatability and decomposability.

They discovered that the seven key plant species that had better nutrition, digestibility, palatability and decomposability than the other species were the ones that saw an increase in diversity in the ungrazed plots. Their ability to be more digestible than other species means that their increase in diversity would contribute towards reversing biotic homogenisation. Moreover, using the rates of recovery, Marrs et al. (2020) were able to calculate how long it would take for blanket bog and grasslands to recover (20-40 years, and 60 years respectively).

Overall, removing sheep grazing will enable plant biodiversity to recover, but it will take time. Marrs et al. (2020) provided recommendations for land-managers should they wish to speed up this recovery.

Emeritus Bulley Professor Rob Marrs

Tel: +44(0) 7957 929086

Email: Calluna@liverpool.ac.uk

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