Managing Purple Moor Grass

According to Ian Mercer (in his Dartmoor New Naturalist book pp118-120) around 35% of Dartmoor’s Commons are now dominated by Purple Moor Grass (Molinia caerulea) – now often just referred to as Molinia. It is considered to be a major problem for the Commoners as it shades out the more nutritious grasses and a major problem for conservationists as it dominates habitats and reduces the dwarf shrub communities such as heather.

The reasons behind the increase in Molinia are contested and unclear. Overgrazing and over burning have been blamed as has the increase in sheep grazing as opposed to summer cattle grazing. The conservation agenda as articulated and prescribed by Natural England has been to promote increased spring grazing by cattle and reduced burning (swaling). Mercer telling says the following ‘the system that allows a hill-farmer to maintain a good enough herd of the hardy stock and of the right number all year round to be profitable and to follow current nature conservation thinking about a regime for blanket bog vegetation management has yet to be devised.’

This conundrum is at the heart of the debate on Dartmoor about favourable condition and the extent / decline of heather on the moor.

Last September the National Trust team based at Marsden Moor in Yorkshire organised a three day conference on this very topic (it is a major issue for all upland areas in the UK not just Dartmoor). I unfortunately was unable to attend the conference but fortunately the proceeding have now been published.

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You can download this 200+ page document here.

If you are interested in the quality of our habitats in the uplands then this document is essential reading. The report consists of a number of scientific presentations from the country’s leading experts along with a series of case studies describing the actions and outcomes of a number of site managers.

This is a major contribution to understanding the management of our uplands and it shows how complex the problem is.

For example, Rob Marr and his team from Liverpool University replay their research from the early 2000s which told us that grazing and burning regimes in isolation will not solve the problem, they only got reductions in Molinia when they also used herbicides.

Simon Caporn’s team explain the role played by atmospheric pollution and tell us that whilst sulphur dioxide pollution is now a thing of the past, nitrogen deposition is definitely on the increase and that this along with rising carbon dioxide levels (as a result of climate change) and ozone may very well be promoting the growth and spread of Molinia.

These presentations (and all the others) are well worth reading and mulling over as they explain why the quest for ‘favourable condition’ in the uplands is currently so elusive.

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