The problem with Heather Beetles

The Heather Beetle (Lochmaea suturalis) is a native Chrysomelid leaf beetle which feeds almost exclusively on heather (Calluna vulgaris). It is common in areas whether heather grows from the south of England to Orkney in the north (Duff 2016).

Heather beetle populations are well known to fluctuate greatly from low numbers which have little over impact on heather plants to very high numbers which can lead to the widespread defoliation of heather and can cause its death.


Heather Beetle damage on Ryders Hill March 2016

Heather beetle outbreaks have historically been problematic for grouse moor owners and the issue of heather beetle and its control has been championed by the Heather Trust who have produced a short document on the species (Heather Trust undated).

In addition the Heather Trust commissioned a literature review of the species (Rosenburgh & Marrs 2010) which summarises the ecology of the beetle, its impact as a pest and strategies for control. This work has been updated (Gillingham et al 2015a and 2015b) and published as Natural England Evidence Reviews on its ecology and its management.

These reviews state the following regarding heather beetle outbreaks:-

  • ‘Considerable damage to heather can occur with complete death in the worst cases’.
  • ‘Large scale vegetation change can follow’ (heather outcompeted by invasive grass species).
  • ‘The occurrence and severity of heather beetle attacks appears to be made worse by increased levels of nitrogen in the soil and plant tissues, which has been blamed on high nitrogen pollutant inputs from the atmosphere in recent years’.
  • ‘The high nitrogen in the leaves provides the beetles with more high quality food to consume’
  • ‘Climate change is expected to lead to increased winter survival of heather beetles’

On Exmoor heather beetle is considered a major problem, and the National Park Authority report that outbreaks are common and are spreading from the south to the north of Park. They also suggest that in areas where Purple Moor Grass (Molinia caerulea) is absent the heather plants recover fully and rapidly but where Molinia is present this quickly swamps the heather and replaces it (ENPA 2015).

I have written before about the loss of heather that had occurred on the National Trust’s land in the Upper Plym valley on Dartmoor (see here). In 1995 there was a serious outbreak of heather beetle which killed off the heather in the area known as Hen Tor Fields. At the time it was assumed that overgrazing was the cause although no increase in stocking levels had taken place for a number of years.  In this specific instance the heathland communities (H12 Calluna vulgaris-Vaccinium myrtillus) were replaced by upland grass communities (U4 Festuca ovina-Agrostis capillaris-Galium saxatile) which do not naturally contain Molinia. On the wet heaths of the Upper Plym Estate there were numerous other outbreaks on heather beetle during the 1990s and 2000s (Helen Radmore NT tenant pers comm) and in these habitats Molinia now dominates (my observations).

There has been no systematic survey of heather beetle on Dartmoor and Goodfellow et al (1997) only briefly mention it “Outbreaks of heather beetle cause local declines in heather”, however my recent observations on the moor suggest that heather beetle damage is very widespread and extensive.


Heather Beetle damage on Ryders Hill – March 2016

I would be very interested to hear from anyone with information about heather beetles on Dartmoor in recent years – it is an issue which is begging for more research.

References
Duff A.G. (2016) Beetles of Britain and Ireland. Volume 4 Cerambycidae to Curculionidae. A.G. Duff (Publishing) West Runton.
ENPA (2015) Exmoor Swaling Review 2014/15. Seminar Notes ENPA. Dulverton. http://www.exmoor-nationalpark.gov.uk/__data/assets/pdf_file/0011/583454/Exmoor-Swaling-Review-2014-15.pdf
Gillingham P., Diaz A., Stillman R. & Pinder A.C. (2015a) A desk review of the ecology of the heather beetle. Natural England Evidence Review, Number 008. http://publications.naturalengland.org.uk/publication/6386866406293504
Gillingham P., Diaz A., Stillman R. & Pinder A.C. (2015b) Desk review of burning and other management options for the control for heather beetle. Natural England Evidence Review, Number 009. http://publications.naturalengland.org.uk/publication/4817807814426624
Goodfellow S., Wolton R. & Baldock N. (1997) The Nature of Dartmoor: a biodiversity profile. English Nature / Dartmoor National Park Authority publication. http://www.dartmoor.gov.uk/__data/assets/pdf_file/0014/42701/au-natureodp2.pdf
Heather Trust (undated) Heather Beetle. Download from Heather Trust Website http://media.wix.com/ugd/fdc287_2b9ec8fa073d4ca38baf4a754d7a77f4.pdf
Rosenburgh A. & Marrs R. (2010) The Heather Beetle: a review. Report to the Heather Trust. http://media.wix.com/ugd/111722_4370d9fb976442b2af6e678aa83c3663.pdf

Revisting Parke as spring emerges

It must be well over a year since I was last at Parke – I used to work there as the National Trust’s General Manager for Dartmoor. I met up for a quick chat with a few of my old colleagues – good to see them.

My main purpose was to meet with Kevin Bishop, the Dartmoor National Park Authority’s Chief Executive and Ali Kohler, the DNPA’s Director of Conservation and  Communities to talk about my PhD and get some ideas and feedback from them. Very helpful.

parke
Parke – looking across the parkland to Bovey Tracey

snowdropsThe snowdrops and cultivated daffodils are in full flower

moor-otter

Great to see one of the Moor Otter sculptures in the main reception – you will, I expect, hear a lot more about these when we get to the summer – see here for more details – there are going to be 100 of them (all different) dotted around the National Park later in the year

wild-daffodilOn the way home I drove down the Teign Valley and stopped to photograph the wild daffodils that are beginning to flower in profusion – those in full sunlight were flowering – those in shade will need a couple more weeks

hazel-catkinsAlso got to see the hazel catkins in full flower – I love it when they turn yellow

 

 

The problem with bracken

Bracken (Pteridium aquilinum)  is a contentious species which is almost universally hated on Dartmoor (except in the handful of places where it harbours the nationally threatened butterfly, the High Brown Fritillary (Argynnis adippe).

Bracken was once harvested as an important crop and used for animal bedding and as a roofing material. These practices dropped out of favour as other more modern materials were used instead and as a result bracken was no longer managed and began to spread.

This spread of bracken can be damaging to the historic environment as its dense network of rhizomes can seriously interfere with any sub-surface archaeology. It is also a species which is very unpopular with hill-farmers as it spread reduces the area of palatable grazing for livestock. Likewise conservationists do not like the species as its spread can reduce areas of inherently interesting vegetation communities e.g. heather stands (Marrs and Watts 2006).

bracken

Bracken tends to grow on deep well drained soils which do not become waterlogged. As a result it is absent on Dartmoor from the blanket bog and wet heathland communities as these are too wet. These deeper better drained soils on the moor support heathland (NVC H8 Calluna vulgaris-Ulex gallii heath) and upland grassland communities (NVC U4 Festuca ovina-Agrostis capillaris-Galium saxatile grassland and U5 Nardus stricta-Galium saxatile grassland). Bracken can encroach into wet heath communities (M15b Trichophorum cespitosus, Erica tetralix wet heath and M15d Trichophorum cespitosus, Erica tetralix wet heath, Vaccinium myrtillus sub-community if these have become drier as a result of hydrological changes, over grazing or burning (Marrs and Watts 2006).

These National Vegetation Classification (NVC) communities can change depending on the management regime they receive. Averis et al (2004) suggest the following changes to National Vegetation Classification communities which can all lead to an increase in bracken communities. The communities described below follow the NVC (Rodwell 1991 & 1992).

  • If H8 Calluna vulgaris-Ulex gallii heath or H12 Calluna vulgaris-Vaccinium myrtillus heath is over grazed or over burnt it can change into M25 Molinia caerulea-Potentilla erecta or U4 Festuca ovina-Agrostis capillaris-Galium saxatile
  • If U4 Festuca ovina-Agrostis capillaris-Galium saxatile grassland or U5 Nardus stricta-Galium saxatile grassland are under grazed then can turn to H8 Calluna vulgaris-Ulex gallii heath or H12 Calluna vulgaris-Vaccinium myrtillus heath
  • However all four of the communities mentioned above (H8, H12, U4 & U5) can be invaded by bracken and turn into U20 Pteridium aquilinum-Gallium saxatile

Bracken can be controlled either by cutting, rolling or the use of herbicides (asulam). However treatments must be repeated yearly if bracken is to be controlled, complete eradication is usually not possible. All these methods are time consuming and expensive. Rolling is often not possible due to the terrain or rocks and asulam can now only be used under an Emergency Authorisation licence as its use was outlawed in 2012 [1], there are also concerns that stocks of asulam are not in short supply as it is no longer being manufactured.

bracken-bruising-003Bracken rolling on Dartmoor by the National Trust

Pakeman et al (1995) showed that bracken had increased significantly over the past few centuries in Britain but they also showed that between 1970 to 1980 there had been a 3.4% decrease on Dartmoor (by 1.9km2 of bracken being gained but 3.8km2 being lost).

Pakeman et al. (2000) ‘concluded that the current abundance of Pteridium was less than, or at worst, equivalent to maximum historical records’. It is clear therefore that the abundance of bracken has fallen and risen depending on its harvesting or clearance by humans.

Werkman et al (1996) carried out experiments where bracken and heather and a mix of the two were grown in open topped tents to mimic climate warming and where different plots were treated with additional nitrogen inputs. They found bracken growing in the tents with additional nitrogen grew more vigorously and for a longer growing season than plants not grown in tents where no nitrogen was added. The bracken under the former conditions also encroached into the heather stands.

Werkman et al (2002) in another experiment found that bracken responded positively to increased temperatures but did not respond to increased nitrogen levels. They concluded that in a warmer climate bracken will continue to replace heather. They added a caveat that if climate change led to drier summers then water could be a limiting factor in the spread of bracken.

The implication of both papers by Werkman et al (1996, 2002) is that bracken will also spread into areas of upland grassland as well as areas dominated by heather.

Hill-farmers and other land managers on Dartmoor such as the National Trust spend considerable time and money attempting to control bracken on the moor, it would appear that in the future more effort will be required if bracken is not to spread further.

So rather like Purple Moor Grass Molinia caerulea, bracken does respond to anthropogenic changes to the atmosphere. In the case of bracken to increased temperatures caused by rising CO2 levels and in the case of Molinia to increased nitrogen levels caused by pollution from vehicles and agriculture (see here).

If a future climate change scenario on Dartmoor led to rising temperatures and reduced rainfall it is not impossible that the current areas of wet heath and those areas dominated by Molinia could become dry enough to allow the encroachment of bracken into these areas too.

 References
Marrs R.H. & Watts A.S. (2006) Biological Flora of the British Isles: Pteridium aquilinum (L.) Kuhn. Journal of Ecology 94, 1272–1321
Pakeman, R.J., Le Duc, M.G. & Marrs, R.H. (2000) Bracken distribution in Great Britain: strategies for its control and the sustainable management of land. Annals of Botany, 85B, 37–46.
Pakeman, R.J., Marrs, R.H., Howard, D.C., Barr, C.J. & Fuller, R.M. (1995) The bracken problem in Great Britain; its present extent and future changes. Applied Geography, 16, 65–86.
Rodwell J.S. (ed) (1991) British Plant Communities. Volume 2. Mires and heaths. Cambridge University Press. Cambridge.
Rodwell J.S. (ed) (1992) British Plant Communities. Volume 3. Grasslands and montane communities. Cambridge University Press. Cambridge.
Werkman B.R. & Callaghan T.V. (2002) Responses of bracken and heather to increased temperature and nitrogen addition, alone and in competition. Basic and Applied Ecology 3: 267-276.
Werkman B.R., Callaghan T.V. & Welker J.M. (1996) Responses of bracken to increased temperature and nitrogen availability. Global Change Biology 2: 59-66.

[1] http://www.brackencontrol.co.uk/asulam

More on Purple Moor Grass – Molinia and water levels

In my blog yesterday I wrote about the the rise in abundance of purple moor grass (Molinia caerulea) on Dartmoor, the challenges of suppressing its dominance along with the role that aerial pollution may be playing in encouraging it – see here. Today I am looking at the performance of Molinia in situations where the water table has been deliberately raised so as to restore and rewet degraded peatlands.

Molinia ‘is most abundant and grows most vigorously on sites where there is ground water movement, good soil aeration and an enriched nutrient supply’ according to Taylor et al (2001). One might suspect therefore that on sites where the water table is high – reaching the surface, and constant Molinia might be at a competitive disadvantage to other wet loving species.

Peat

Over the centuries many peatlands in the UK have been drained either for agricultural purposes or for peat cutting. Today conservation organisations are attempting to restore many of the remaining drained fragments of these original peatlands. Thomas (2015) described such an approach in the Manchester Mosses Special Area of Conservation (SAC). It should be noted that the Manchester Mosses are lowland raised bogs and not upland blanket bogs such as we get on Dartmoor. Nevertheless these remaining fragments of peat had been drained and were dominated by Molinia. The restoration work carried out  on a variety of reserves within the Manchester Mosses SAC was carried out by the Cheshire Wildlife Trust, the Lancashire Wildlife Trust and Warrington Borough Council. At all three sites it  became impossible to maintain raised water levels as the adjacent land had been fully drained and all the sites had ditch networks which further facilitated drainage. The restoration work at these sites involved blocking ditches and installing plastic piles around the perimeter to stop the water from escaping. The three sites combined totalled 193ha and therefore such an approach although expensive was feasible. Once the water levels had been raised it had a dramatic impact on the Molinia dominated swards – in all cases the Molinia declined and was replaced by such plant species as Sphagnum mosses and cottongrass.

Anderson (2015) describes work carried out on the North Yorkshire Moors and the Peak District. Both these areas have been severely impacted by sulphur dioxide pollution (from heavy industry since the Industrial Revolution), this has led to acidified soils which ended up killing many of the sensitive plant species e.g. Sphagnum mosses. In addition these areas attract huge numbers of visitors and as a result these Moors have suffered from a large number of accidental and deliberate wild fires. These two factors combined with heavy sheep grazing led to erosion and gulley formation (which drained the otherwise wet peat) on these moors on a very large scale. Restoration work has been going on for several decades now in the North Yorks Moors and the Peak District to try to undo the damage caused by pollution, overgrazing and wild fires. This has involved blocking gulleys with thousands of small wooden dams and in many cases the aerial re-seeding of the Moors with heather. Prior to the commencement of this restoration many of these areas had become dominated by Molinia.  The dams in many places have resulted in the raising of the water table which in turn has seen the Molinia decline and wetland species such as Sphagnum return.

Examples from the uplands and lowlands showing that where water tables can be raised sufficiently the rise and expansion of Molinia can be halted so that sites of conservation importance can start their journeys back to favourable condition.

The Exmoor Mires Project aims to deliver multiple ecosystem service outcomes by restoring peatland areas of Exmoor previously drained as part of historic conversion to agriculture or during peat cutting activities. Since 2006 the Project has restored around 2000ha of peatlands at over a dozen sites. Smith et al (2014) describe the results of their vegetation monitoring of the Project. On sites where water levels were successfully raised they have clear evidence which shows that the original Molinia dominated communities have been replaced more species rich wetland ones. At several sites the Molinia swards prevailed after the restoration work had been carried out but the authors blame failures in the ditch blocking and bunding works i.e. the water levels were not raised sufficiently to remove the Molinia.

screen-shot-2017-01-12-at-15-53-06

More recently on Dartmoor via The Dartmoor Mires Project,  a series of pilot projects have been carried out to rewet small areas where erosion had been taking place. The situation on Dartmoor regarding moorland erosion is very different from the situation described earlier in the Peak District and the North Yorkshire Moors. Dartmoor did not receive very high levels of sulphur dioxide from the Industrial Revolution on account of its south westerly location and the direction of the prevailing winds. Unlike Exmoor, the Commons of Dartmoor did not see the level and extent of agricultural drainage in the second half of the 20th century.

The pilot Dartmoor Mires Project has however successfully demonstrated at least at some of the sites that raising water levels via small scale dams in localised areas of erosion can lead to a  reduction in the area of bare peat (at Blackabrook Head, Blackabrook Down and South Tavy Head ) and that the process of paludification re-commences, i.e. new peat is formed, along with an increase in ‘beneficial mire species’ (at Blackabrook Head, Blackabrook Down and Winney’s Down Area 1). However to date there has not been a decrease in the abundance and distribution of Molinia. In the control site (where no rewetting was carried out) however the abundance of Molinia did increase (Lunt 2015). It is however fair to say that the Dartmoor project has not been running for very long and when the sites are re-surveyed in the future it could be expected that Molinia will start to decline as has happened on the other sites discussed.

At the moment work on the Dartmoor Mires Project has been halted whilst an evaluation of the results to date is carried out. It will be interesting to see whether following the pilot scheme, work will recommence on a large scale which may then have a bigger impact on parts of the Molinia dominated moor.

References
Anderson P. (2015) Molinia – the importance of controlling water and other management techniques. In Meade (2015) pp39-54.
Lunt P. (2015) Dartmoor Mires Project Vegetation Analysis 2015. Download here.
Meade R. (ed) (2015) Managing Molinia. Proceedings of a 3-day conference 14-16 September 2015, Huddersfield, West Yorkshire, UK. National Trust. https://www.nationaltrust.org.uk/marsden-moor-estate/documents/managing-molinia.pdf
Smith D.M.,  Barrowclough C., Glendinning A.D.  &  Hand A. (2014) Exmoor Mires Project: Initial analyses of post restoration vegetation monitoring data. In the Bog Conference September 2014. Download  here.
Taylor K., Rowland A.P. & Jones H.E. (2001) The Biological Flora of the British Isles: Molinia caerulea. Journal of Ecology 89: 126-144.
Thomas P. (2015) Problems with Molinea caerulea in the restoration of lowland peat bogs – Manchester Mosses Special Area of Conservation (SAC). In Meade (2015) pp127-133.

The problem with Purple Moor Grass…. Molinia

Purple Moor Grass (Molinia caerulea) – here after called Molinia – has increased rather dramatically in recent times on Dartmoor and elsewhere in the British uplands. This blog attempts to answer why this has happened.

Looking at Dartmoor (and indeed all the UK’s Uplands) today it is easy to forget that the rise to dominance of Molinia on the mires and blanket bogs is a recent phenomenon. Wolton et al (1994) in their report on heather condition on Dartmoor based on fieldwork carried out in 1989/90 concluded that ‘Purple Moor Grass’ consisted of less than 1% of Dartmoor’s Commons i.e. less than 2,800 ha.

screen-shot-2017-01-09-at-16-08-38

Figure 1a p18 from Wolton et al (1994)

Although comparative figures are not available for Dartmoor today it is widely agreed that this figure has increased dramatically but an increase of 20x does not seem inappropriate in my view.

Chambers et al (1999) showed from paleoecological research that the rise of Molinia is a recent phenomenon, this work also showed that the rise of Molinia was at the expense of heather communities.

The spread of Molinia concerns farmers as this grass is relatively unpalatable to stock and it is of concern to conservationists as the ‘rafia’ fields of the grass produce monotonous species-poor landscapes which suppress other moorland species such as heather.

molinia

The spread of Molinia was originally thought to be caused as a result of overgrazing and excessive burning. Averis et al (2004) suggest the following changes to National Vegetation Classification communities which can all lead to an increase in Molinia communities. The communities described below e.g. M25 Molinia caerulea-Potentilla erecta mire follow the NVC (Rodwell 1991).

  • If blanket bog (M17 Trichophorum cepitosus-Eriophorum vaginatum blanket mire) is overgrazed or burnt it changes into poor quality wet heath (M15 Trichophorum cespitosus, Erica tetralix wet heath) and then Molinia grassland (M25 Molinia caerulea-Potentilla erecta mire)
  • If wet heath (M15) is overgrazed or burnt it changes into Molinia grassland (M25)
  • If heathland (H12 Calluna vulgaris-Vaccinium myrtillus heath / H8 Calluna vulgaris-Ulex gallii heath) is overgrazed or burnt it changes into poor quality wet heath (M15) or  Molinia grassland (M25)

The original restoration management prescriptions from English Nature and Nature England focused on reducing the grazing pressure and reducing burning on the mires and forbidding it on the blanket bog.  Whilst such prescriptions aided the blanket bog it was very much less successful at reducing the incidence of Molinia on the mires.

Research was therefore conducted from the late 1990s onwards to determine how Molinia could be controlled. The seminal paper on this work is Marrs et al (2004) which concluded if Molinia was to be controlled in situations where it had become dominant (the so called ‘white moors’) then a combination of herbicide application, raking off the litter, soil disturbance and re-seeding with heather was required. This experimental approach was carried out in the Peak District and the Yorkshire Dales.

Attempts have been made to mimic these experimental restoration prescriptions on moorlands in the north of England but they are expensive and have been carried out on a relatively small scale by conservation bodies using their own resources (Meade 2015). Such trials have yet to take place on Dartmoor.

On Dartmoor the approach to managing Molinia has involved local swaling techniques which if followed up by intensive spring / summer cattle grazing can reduce the dominant of Molinia. However, if the burning is followed up by sheep grazing opposed to cattle grazing the Molinia tends to increase. Molinia is a fire adapted species which benefits from burning unless the initial spring growth is reduced via cattle grazing. Such a prescription has been hard to deliver on Dartmoor as there are either insufficient numbers of cattle available or they graze in areas which haven’t been burnt and ignore the new burnt areas.

The role of aerial pollutants are also known to have impacts on vegetation in the uplands. The deleterious effect of sulphur dioxide emissions has been known for a long time in places such as the Peak District as a result of smokestack emissions which began with the Industrial Revolution. Action has been taken to reduce sulphur dioxide emissions and these have dropped dramatically since the 1970s (Caporn & Emmett 2009).

More recently attention has been turned to the role that nitrogen and its compounds might have on upland plant communities.

Brown & Farmer (1996) showed that between 1989-92 total (oxidised and reduced) nitrogen deposition exceeded critical loads on Dartmoor in 841km2 out of a total of 901.77 km2 i.e. 93.3% of the total – making it the second worst performing Natural Area in England.

Payne (2014) states that nitrogen pollution from industry and intensive agriculture is one of the greatest threats to peatland ecosystems. Whilst nitrogen deposition to peatlands is currently falling and is projected to continue to fall until 2030, the accumulation of nitrogen will continue to increase and is a ‘serious threat to British peatlands and is likely to remain so for some time.’

Caporn and Field (2015) report  on research from the Netherlands where high levels of nitrogen were linked  to the increasing cover of the competitive grasses Molinia and Deschampsia at the expense of heather Calluna vulgaris and Sphagnum species. They conclude their review by stating that ‘if nitrogen deposition has been a major factor  in the spread of Molinia, this will be difficult to reverse since the deposited nitrogen accumulates in the soil-plant system’.

Heal (2002) states that increased nitrogen deposition has led to heather growth being less vigorous and competitive when compared to grasses such as Molinia which tend to flourish better.

Worryingly Des Thompson one of the UK most respected upland ecologists said ‘Some of us are beginning to form the view that some of the grass-dominated vegetation types of the southern uplands may be the product of nitrogen deposition and heavy grazing pressures. Hence, a reduction in grazing pressures alone may not necessarily result in an improvement in habitats’ (Thompson 2002).

These problems may not just be associated with nitrogen levels. Caporn and Field (2015) state that whilst the evidence of increased nitrogen deposition supports the recent rise to dominance of Molinia both carbon dioxide (CO2) and ozone concentrations in the atmosphere are continuing to rise. CO2 levels have risen from around 320 ppm in 1960 to over 400 ppm in 2016 and show no signs of slowing down. Such an increase would be consistent ‘an immediate and significant stimulation of photosynthesis. There is very little knowledge to how Molinia responds to CO2 , but it is reasonable to speculate that the long term growth response will be increased when nitrogen availability is enhanced’.

Ozone concentrations are normally higher in rural areas when compared to nearby urban areas. Wedlich et al (2012) showed than in upland meadows in the Pennines increased ozone concentrations did not affect grasses but did significantly reduce the flower (forb) community, thus favouring the grass species.

The rise in the dominance of Molinia has had profound impacts on the biological diversity of Dartmoor,  it also has a detrimental impact on the historic environment.

Whilst the impact of aerial pollution has been well researched and whilst there is a good deal of circumstantial evidence to its role in promoting grasses such as Molinia to the detriment of heather, it would appear that basic moorland management prescriptions  and the quest for ‘favourable condition’ (Natural England’s measure of success for the management of Sites of Special Scientific Interest)  appear unmodified despite the increasing evidence to suggest that upland ecosystems may have been irreversibly modified.

With almost any given topic there is a call for more research to clarify the complexities of a situation, in this instance the role of nitrogen deposition has been known for over a decade without an appropriate policy / management response.

There is a great deal of evidence now available to suggest that a tipping point has been passed. The current management prescriptions involving reduced grazing pressures on the Commons to improve and encourage the condition for species such as heather may no longer be effective as a result of the increased levels of nitrogen, CO2 and ozone  Is a fundamental new approach is needed and is ‘favourable condition’ any longer achievable? Unless this topic is tackled farmers and conservationists are likely to fail to improve the conditions of the Commons which both groups are so desperately trying to achieve.

References
Averis A., Averis B., Birks J., Horsefield D., Thompson D. & Yeo M
. (2004) An Illustrated Guide to British Upland Vegetation. Joint Nature Conservation Committee. Peterborough.
Bonn A., Allott T., Hubacek K. & Stewart J. (2009) Drivers of Environmental Change in Uplands. Routledge. London.
Brown M. & Farmer A. (1996) Excess sulphur and nitrogen deposition in England’s Natural Areas. English Nature Research Reports No. 201.
Burt T.P., Thompson D.B.A. & Warburton J. (2002) The British Uplands: Dynamics of Change. Joint Nature Conservation Committee Report No. 319.
Caporn S.J.M. & Emmett B.A. (2009) Threats from air pollution and climate change to upland systems. In Bonn et al (2009) pp34-58
Caporn S. J. M., Rosenburg A. E. & Field C.D. (2015) The importance of atmospheric quality in determining upland vegetation. In Meade R. (ed) (2015) Managing Molinia. Proceedings of a 3-day conference 14-16 September 2015, Huddersfield, West Yorkshire, UK. National Trust. https://www.nationaltrust.org.uk/marsden-moor-estate/documents/managing-molinia.pdf
Chambers F.M. Mauquoy D. & Todd P. (1999) Recent rise to dominance of Molinia caerulea in environmentally sensitive areas: new perspectives from paleo ecological data. Journal of Applied Ecology 36: 719-733.
Marrs R.H., Phillips J.D.P., Todd P.A., Ghorbani J. & Le Duc M.G. (2004) Control of Molinia caerulea on upland moors. Journal of Applied Ecology 41:398-411.
Meade R. (ed) (2015) Managing Molinia. Proceedings of a 3-day conference 14-16 September 2015, Huddersfield, West Yorkshire, UK. National Trust. https://www.nationaltrust.org.uk/marsden-moor-estate/documents/managing-molinia.pdf
Payne R. J. (2014) The exposure of British Peatlands to nitrogen deposition 1900-2030. Mires and Peat volume 14, Article 04 pp1-9.
Rodwell J.S. (ed) (1991) British Plant Communities. Volume 2. Mires and heaths. Cambridge University Press. Cambridge.
Thompson D.B.A. (2002) The importance of nature conservation in the British uplands: nature conservation and land-use changes. In Burt et al (2002) p37.
Wedlich K.V., Rintoul N., Peacock S. Cape J.N., Coyle M. Toet S, Barnes J. & Ashmore M. (2012) Effects of ozone on species composition in an upland grassland. Oecologia 168: 1137-1146
Wolton R.J., Edge S., Keddle R.M., Kendall S. & Archer R. (1994) Vegetation and Heather Condition Maps for the Commons of Dartmoor. A practical aid to their sensitive management. English Nature Report (unpublished).