Should Dartmoor be a temperate Rain Forest or a cultural landscape? Discuss ..

I gave a 20 minute talk yesterday at Butterfly Conservation’s conference on the future of the south west’s uplands where I very briefly summarised the findings of my PhD research. I’m interested in why people disagree about the way that Dartmoor is managed and grazed and I’m looking at it from the perspective of the various stakeholder narratives. Is Dartmoor overgrazed or undergrazed? Should it be richer in wildlife? Should much of it be rewilded? Should the blanket bog, valley mires and wet heath be re-wetted? What about the historical landscape – should it be re-grazed so that the monuments become visible again within the landscape? What is to be done about the Molinia (Purple Moor Grass) jungle and the Western Gorse encroachment? What about the hill-farmers’ narratives? Lots of questions, lots of viewpoints and lots of disagreement.

My talk prompted this exchange on Twitter today following an initial tweet from Farming Wilder.

Followed by a response from George Monbiot – arguing that a temperate rain forest should be re-established.

But what of the existing wildlife interest?

A comparison of Dartmoor to the Amazon ….

The case for a varied but cultural landscape….

Is this the beginning of a compromise?

Nobody is actually happy with the status quo but …

Not all Dartmoor hill-farmers will agree with this but some evidently do …

An interesting social enterprise …

With the parlous state of hill-farm economics, the spectre of Brexit, continuing climate change and atmospheric nitrogen pollution, the status quo is untenable and change and new ideas are needed. This exchange suggests a possible alternative, there are of course many others such as a 21st century return to ‘Levancy and Couchancy’ (only keeping the number of animals on the Commons that you can feed over winter from the meadows on your home farm –  growing hay and silage organically) and a new Transhumance (summering of animals on the Commons and then ‘finishing’ of them in the lowlands).

To be continued ……



Heather beetle damage on Dartmoor 2019

I have been very surprised how much Heather Beetle damage there is on Dartmoor this year. The Heather Beetle larvae hatch in June and then feed on the young leaves and shoots. As a result the affected parts of the heather plant turn orange brown.

Heather Beetle damage. It is very characteristic and eye catching.

Last week I walked from Rowtor on Okehampton Common up the military road to Observation Post 15 and then down to Ockerton Court. All the way along the track there are signs of extensive damage to the heather plants – I would estimate that over 90% of plants are affected.

Work carried out in the north of England and in Scotland suggest that the larvae are active until the end of August when they drop down into the litter and pupate into adult beetles. Despite three separate searches on Okehampton Common, the Forest of Dartmoor and Headland Warren Common I only managed to find three larvae and one adult beetle.

Here is a Heather Beetle larvae on Okehampton Common eating the few remaining green leaves of the plant.

I suspect that the absence of larvae and adults during my searches in the first week of August means that the larvae have already dropped into the litter and are beginning to pupate – as a result larvae and adults are not visible. However the very extensive areas of damaged heather indicates that they have been very active in June and July.

It is possible for the heather to recover from this attack and I will be monitoring it to see if it does. However parts or all of the heather plant can be killed. When this happens the shoots turn from orange brown to grey.

This is mature heather at Ockerton Court which has been killed by Heather Beetle

In this image the areas of dead heather (darker brown bits) are being over run by Purple Moor Grass (Molinia caerulea) – the bright green shoots of this year’s growth and the light brown leaves from last year. Molinia is unable to replace heather whilst the heather is alive but can and does do so when it is dead.

Heather Beetle is a seriously under-recorded species on Dartmoor – the National Biodiversity Network database has just one record and the is from Fingle Woods and not from the high moor!

There is clearly a need to gather more records ….

There is anecdotal evidence nationally that Heather Beetle attacks are getting worse and it has been suggested (based on research from the Netherlands) that the severity and frequency of Heather Beetle outbreaks is linked to the levels of atmospheric pollution – particularly nitrogen levels.

Dartmoor receives high levels of nitrogen deposition as a result of its high rainfall – Natural England have reported that Dartmoor receives 24kg / ha / annum of nitrogen (as NOx) which is damaging the blanket bog and mires. This high level of nitrogen deposition may also be responsible for the high levels of Heather Beetle damage.

Heather Beetles are a natural part of the moorland wildlife community and historically damage to heather was limited except in the ‘outbreak’ years. Last year when I was walking the Commons in July I also noticed extensive areas of affected heather – at this point in time heavy attacks appear to be frequent – maybe even annual.

There are implications for wildlife, conservation and hill-farming as a result of these serious Heather Beetle attacks.

  1. The heather plants themselves are either killed or remain stunted
  2. The species of wildlife which feed on heather shoots are also impacted – this includes moth species such as the Emperor Moth and the Fox Moth, whose hairy caterpillars are important prey items for one of Dartmoor’s iconic and successful birds – the cuckoo.
  3. Heather has long been a conservation indicator for the condition of Dartmoor’s Commons and historically grazing levels were reduced significantly to reduce overgrazing pressures to conserve heather.
  4. Heather is also a winter food for sheep on the Commons, if the amount of heather generally is significantly reduced as a result of Heather Beetle attacks it put pressure of the remaining plants that have survived.

Ironically it is thought that the severity and frequency of Heather Beetle attacks has increased because the nitrogen has made the young shoots and leaves more nutritious, it is also reported that sheep preferentially graze the new shoots too for the same reason.

There is a dearth of information on Heather Beetle issues on Dartmoor but from my own observations this year and last it is a potentially serious and widespread problem. However it would also appear that the problem is not universal across the moor. I searched for it in the heather stands around the Warren House Inn  and found Heather Beetle attacks to be minor – perhaps this level of damage is the natural level – whereas the levels seen on Okehampton Common, the north part of the Forest and on Headland Warren Common are the outbreak levels.

It seems to me that there is a clear need to better understand the Heather Beetle situation on Dartmoor, this would be in the interests of Natural England, the Dartmoor National Park Authority and the Dartmoor Commoners Council. The time to survey for the impacts of Heather Beetle is July and August. Maybe a bit of ‘Citizen Science’ could come to the rescue?

I would also be interested to hear from people who have found the characteristic orange brown stands of heather this year on Dartmoor.

I’ve written before about Heather Beetles and this link takes you to my blog which contains further information and some references you can download.

Soil compaction on Dartmoor

I’ve now seen first hand some compacted soils on the moor. We spent some time looking at some soils which should have good drainage qualities opposed to the peat water logged soils higher up.

Richard Smith (Environment Agency), Sue Everett (Sustainable Soils Alliance), Mark July (former Natural England) and Tim Harrod (former Soil Survey of England and Wales) inspecting a compacted soil on Peter Tavy Common

The compaction means that the water cannot flow into the profile as there is a layer of compressed (gleyed) soil which is impermeable – as a result this soil has a perched water table. When it rains hard the water flows across the surface and down the hill side. The Environment Agency are interested in ameliorating this so that flooding incidents in Peter Tavy can be reduced.

Here is a soil from the Moor Gate series which is not compacted – the soil is friable to the touch and shows no signs of compression or gleying. Heavy rain on this soil will flow down through the profile and not across the surface.

The general theory is that the compaction at say, Peter Tavy Common happened between 1960-1990 and main suspects were cattle and ponies.

The question now is do these soils have the capacity to repair themselves or are they permanently damaged? These compacted soils are often very acidic and as a result possess very poor soil faunas which could potentially undo the damage.

I would be interested to know whether the last 60 years of atmospheric nitrogen pollution has lowered the pH of these soils and as a result reduced the soil fauna’s ability to repair the soil structure.

Unfortunately I cannot find anything in the literature to evidence a progressive lowering of pH in upland soils over the past 60 years – does anyone know of any evidence for this?

Soils are now very high on Defra’s agenda and it seems that answering questions like this and finding a remedy for such upland soil compaction is a high priority.

However there is a problem. The organisation that could have answered this question The Soil Survey of England and Wales has been disbanded (1987) and today soil science is a low profile academic discipline meaning that there are very few qualified professionals around to carry out such studies.

This has mean that the publication of ‘Soils in Devon IX Soil Survey Record No. 117 by Dr Tim Harrod has been undertaken pro bono by a retired soil scientist from the former Soil Survey of England and Wales. It is a majestic piece of scholarship which should have been funded by the State and not by crowd funding!


Defra undoubtedly needs to invest in soil science and soil scientists as otherwise solutions to problems will all too often be based on speculation (as above and here) and not science.

Air pollution – a health issue and cars to blame right?

Four House of Commons Select Committees (The Environment Food and Rural Affairs, Environmental Audit, Health, and Transport Committees) have published their joint report on ‘Improving Air Quality’ – you can download it here.

The report concludes that ‘Air pollution cuts short an estimated 40,000 lives across the country each year, costing the UK an annual £20 billion.’ Amongst its many recommendations it states that Government must

  • Introduce a Clean Air Act to improve existing legislation and enshrine the right to clean air in UK law.
  • Bring forward the date by which manufacturers must end the sale of conventional petrol and diesel cars, in line with more ambitious commitments from around the world. Manufacturers of private, public and commercial vehicles should also take steps to reduce emissions from tyres and braking mechanisms, known as the ‘Oslo e ect’, which is also a signi cant contributor to poor air quality.
  • Require the automobile industry to contribute to a new clean air fund, following the ‘polluter pays’ principle, on a scale that adequately compensates for the health costs of diesel pollution.

Despite the terms of reference for the report investigating ‘how effectively do Government policies take into account the health and environmental impacts of poor air quality?’, the final report has been framed as exclusively a health issue with the wider environmental impacts being completely ignored.

This is therefore a partial narrative and a missed opportunity. I have previously reviewed the literature concerning the atmospheric nitrogen pollution in the uplands (see here and here) and have termed it the ‘elephant in the uplands’. Additionally I have also looked at the impact of low level ozone (which is formed in warm weather as a result of a reaction between NO2 and volatile organic compounds) – see here. The evidence that atmospheric pollution has detrimentally impacted on the vegetation of the uplands is compelling. This narrative explains the rise in extent and vigour of purple moor grass at the expense of heather especially in the light that heather beetle outbreaks have been and are widespread and destructive. Additionally, even in an era of reduced sheep numbers, heather shoots are vulnerable to selective grazing by sheep as nitrogen deposition has enhanced their nutritional value. I conclude that atmospheric pollution is a driver of change and not just an inconvenience.

Ozone is a well-known phytol-toxic gas and Ashmore (2005) provides a comprehensive overview of its significant adverse effects on human health, crop yields, forest growth and species composition and damage in semi-natural vegetation. For example, 1.2 million tonnes of lost wheat production in 2000 (which accounted for 7% of the total) was reported in the UK (RoTAP 2012 – see here).

The wider impacts of nitrogen deposition on nature conservation in the UK have been reviewed here and here and the wider impacts of ozone on nature conservation in the UK have been reviewed here.

Figure 1 on page 16 of the report is portrayed without the necessary accompanying warning.

With the exception of ammonia this graph shows that all emissions including nitrogen oxides are in sharp decline. However, despite the large falls in nitrogen emissions, the deposition of all nitrogen compounds has hardly fallen at all. This unexpected situation has arisen as the atmospheric chemistry over Britain has been altered leading to more rapid oxidisation of nitrogen. This rapidly oxidised nitrogen is deposited in the UK when previously it would have been exported to Continental Europe (RoTAP 2012 – see here). Low level ozone concentrations continue to rise.

Most interestingly a paper has just been published in Science Advances which concludes that agriculture is a major source of NOx pollution in California. The abstract of the paper (see here) concludes ‘

These approaches point to a large, overlooked NOx source from cropland soil, which is estimated to increase the NOx budget by 20 to 51%. These estimates are consistent with previous studies of point-scale measurements of NOx emissions from the soil. Our results highlight opportunities to limit NOx emissions from agriculture by investing in management practices that will bring co-benefits to the economy, ecosystems, and human health in rural areas of California.

I wonder if this research and the discovery of this overlooked sourced of NOx might explain why deposition levels in the UK are not dropping when emissions are. We could really do with some research on this matter in the UK.

The Select Committees report is good and if the recommendations are enacted progress will be made but it is a partial narrative and so only a partial solution. A range of measures are needed to ensure air quality improvements in rural areas too.

Ashmore M.R. (2005) Assessing the future global impacts of ozone on vegetation. Plant, Cell and Environment 28: 949-964.


Atmospheric pollution, grazing numbers and soil compaction

Three things have happened to me during the last week which have really got me thinking.

Firstly, last week I gave a talk at the Fingle Bridge Inn – ‘The Elephant in the Uplands and a tale of two narratives’ – a story about the impact of atmospheric pollution on Dartmoor – see here. During the Q & A session after the talk we were discussing purple moor grass (Molinia caerulea) and I suggested that Molinia needed hard summer grazing from cattle to reduce its abundance. A member of the audience who was from an agricultural background then asked whether it would be a good idea therefore to lime the Commons ….. (i.e. the addition of calcium rich minerals to the soil to reduce the acidity).

To be honest I was a bit stumped. I thought that such an intervention on a Site of Special Scientific Interest would be a ‘potentially damaging operation’ and as a result Natural England would not permit it. More to follow later on ….

Secondly, my Twitter feed is full of discussions around soil compaction on Dartmoor.








Thirdly, I received an email from Kevin Cox, owner of part of Holne Moor Common which discussed the previous two issues. Kevin, like myself has heard Commoners recently advocating the use of lime, a practice that was common in the past even on the Commons of Dartmoor. He also sent me a paper (McCallum et al 2016) which suggested that the liming of upland pastures could be justified from a conservation perspective as it raised the pH which led to a significant increase in the earthworm population and thus provided an enhanced food supply for breeding lapwings.

Might the issues of atmospheric pollution, liming and soil compaction actually all be part of the same story?

The atmospheric pollution narrative
‘The Elephant in the Uplands and a tale of two narratives’ argues that the evidence that atmospheric pollution has detrimentally impacted on the vegetation of the uplands is compelling. This narrative explains the rise in extent and vigour of purple moor grass at the expense of heather especially in the light that heather beetle outbreaks have been and are widespread and destructive. Additionally, even in an era of reduced sheep numbers, heather shoots are vulnerable to selective grazing by sheep as nitrogen deposition has enhanced their nutritional value. I conclude that atmospheric pollution is a driver of change and not just an inconvenience.

However, although I referred to it on my extended blog on atmospheric nitrogen pollution (here), I had failed to make the link to one of the other impacts of nitrogen deposition – it also acidifies the soil.

The role of lime?
I was keen to understand better what my lime questioner had meant by his query, so I emailed him (Fairfax Luxmore). He replied that he had heard from a farmer in the Peak District that liming had increased the grazing output ten-fold and that liming also releases phosphate if the pH is low. He also stated that on Dartmoor where liming had traditionally occurred in the past it had encouraged the growth of ‘sweet grasses’ (which need phosphate) which the stock favoured. My previous literature review had identified that atmospheric nitrogen pollution on Dartmoor had changed the environment from being nitrogen limited to a phosphate limited one and that this change had favoured the growth of Molinia at the expense of heather.

The McCallum lime, earthworms and lapwing paper referred to above also outlines that lime sales for agricultural purposes peaked in the 1960s and has subsequently tailed off dramatically. So, at the very time that the deposition of atmospheric nitrogen pollution was sill increasing (and causing soil acidification), the application of lime which counter-acted it was decreasing. I have no data for the soil fauna and earthworms on Dartmoor but it is perhaps not unreasonable to suggest that the acidification of Dartmoor’s peaty soils would also have led to a decrease in earthworms and other soil fauna biomass.

Soil compaction on Dartmoor
It is uncontestable that the patter of cloven and uncloven hooves over the decades has led to the compaction of soils on the Commons of Dartmoor, especially as Kevin Cox explained in his email to me that the ungrazed soils on the other side of the Common fence were ‘friable and free-draining’.

Richard Smith & David Hogan

Compacted soil

Fence line on Buckfastleigh Moor edge

Free draining soil from over fence line

The question for me though is, has this compaction occurred as a result of grazing pressures post World War Two or is it the result of grazing pressures from the 12th century onwards? I ask this question as there appears to have been eras in the past when the Commons were grazed as heavily if not more heavily than the post war era without detrimental impact.

I have written before about Charles Vancouver and his claims that there were 14,000 sheep and the ‘usual proportion of cattle’ on Widecombe and Buckland in the Moor Commons in 1807, that the grass was knee high in May and barely half consumed in the beginning of November (see here). If Vancouver’s figures are correct I have calculated that the grazing pressure in 1807 was six times the figure considered acceptable today if the moorland vegetation is not to be damaged from overgrazing. Vancouver’s sheep figures are perplexing and many are sceptical about their validity, but perhaps there is an explanation.

A speculative synthesis
Atmospheric pollution levels in Britain rose following the beginning of the Industrial Revolution (a transitional process which started in 1760 and was in full swing by 1840), atmospheric nitrogen emissions peaked in the late 1980s but deposition levels have remained high especially in upland and urban areas. These compounds of nitrogen are driving vegetational change and have reduced the acidity of the soil in the uplands.

As a result, plant communities have become phosphate limited and nitrogen rich which has favoured grasses such as Molinia and the peaty soils have a much reduced soil fauna. The loss of the soil fauna (especially earthworms) has meant that soils are unable to recover from animal trampling and have become compacted.

In 1807, when Vancouver visited Dartmoor, the Industrial Revolution had barely started and atmospheric nitrogen pollution was very low. Phosphate was not a limiting factor and as a result ‘sweet grasses’ flourished and the soil was healthy and not acidified, earthworms and other soil fauna were abundant and were able to counter the compaction of the trampling of herbivores.

The evidence suggests that the impact of atmospheric nitrogen pollution is considerable, both to vegetation and the soil. It is also clear that levels of atmospheric nitrogen pollution will remain high for decades to come (Stevens 2016).

So, what of liming? There is some evidence to suggest that the liming of acid grassland does not reduce species richness in plant communities as long as manures or fertilisers are not also added (Kirkham et al 2008). However even if it were considered desirable (I think more work would be needed if SSSIs / SACs were to be limed) it is difficult to see how it would be practical across the 35,882 ha of Dartmoor’s Commons.

Photos courtesy of Kevin Cox.

Kirkmam F.W., Tallowin J.R.B., Sanderson R.A., Bhogal A., Chambers B.J. & Stevens D.P. (2008). The impact of organic and inorganic fertilizers and lime on the species richness and plant functional characteristics of hay meadow communities. Biological Conservation 141: 1411-1427.

McCallum H.M., Wilson J.D., Beaumont D., Sheldon R., O’Brien M.G. & Park K.J. (2016) A role for liming as a conservation intervention? Earthworm abundance is associated with higher soil pH and foraging activity of a threatened shorebird in upland grasslands. Agriculture, Ecosystems and Environment 223:182-189.

Stevens C.J., (2016). How long do ecosystems take to recover from atmospheric nitrogen deposition? Biological Conservation, Vol. 200: 160-167

Fingle Bridge Inn

I was at the Fingle Bridge Inn near Drewsteignton a couple of nights ago to give my talk on ‘The Elephant in the Uplands and a tale of two narratives’ – based on this paper – see here. If you want any more details on the atmospheric pollution issue and the science behind it see my various blogs on the topic here.

I also took this photo of the Inn which I rather like!

The 25 year Environment Plan – the wait is over

After months of waiting the Plan has finally been published and launched by the Prime Minister. So ….. has the wait been worth it? Of course this is just a plan BUT if it is delivered an awful lot to do with the environment will change for the better. There will of course be those who say it doesn’t go far enough here and opportunities have been missed there – they will probably be right too. BUT, my goodness who would have thought a plan such as this would have been published during the Paterson or Leadsom eras? I’m not going to systematically review the document I’m just going to pull out a few bits and pieces that caught my attention and made me smile.

You can download and the the 25 year plan here and I recommend you do 

To start with I wonder whether the cover of the report contains a Defra joke? This is Mam Tor in the Peak District with the sun rising in the background (at least I assume it is rising). It is owned by the National Trust who are developing plans to encourage hen harriers and peregrines back into the area. A new dawn is breaking …. hang on …. that was somebody else.

Back to Gove, he repeats in his introduction this –

We will support farmers to turn over fields to meadows rich in herbs and wildflowers, plant more trees, restore habitats for endangered species, recover soil fertility and attract wildlife back. We will ensure broader landscapes are transformed by connecting habitats into larger corridors for wildlife, as recommended by Sir John Lawton in his official review.

In the main report we are told again that subsidies are on the way out.

£3.2bn is spent in the UK under the CAP. £2.59bn of this is spent under ‘Pillar 1’ – the ‘basic payment scheme’ (BPS). This pays farmers according to the amount of land they own, rather than the outcomes they achieve. It concentrates money in the hands of those who already have significant private wealth, without improving environmental outcomes.

And that the ‘greening’ measures have failed and that only a fraction of the money has been spent on things that make a difference.

There have been efforts to improve this by ‘greening’ one third of BPS payments – but scholars have recently found these to be largely ineffective. Just £0.64bn – 20% of the total – is spent on environmental stewardship programmes under ‘Pillar 2’.

The principle public good ….. that is progress!!

After a period of stability to ensure a smooth transition, we will move to a system of paying farmers public money for public goods. The principal public good we want to invest in is environmental enhancement.

OK nothing specifically about uplands, hill-farmers or Commons but Gove covered them in his OFC speech last week – see here. These topics will be specially covered in the Agriculture Command paper due in the Spring and all will be well! Hill-farmers will be supported and the uplands will be restored.

Incentives ….. and ….. the ‘polluter pays’ – I never thought that I would read that regarding fertiliser and pesticide usage

We will introduce a new environmental land management system to deliver this. It will incentivise and reward land managers to restore and improve our natural capital and rural heritage. It will also provide support for farmers and land managers as we move towards a more effective application of the ‘polluter pays’ principle (whereby for costs of pollution lie with those responsible for it).

Here is the strong influence on Government that the Natural Capital Committee has had. Before the NCC ‘externalities’ were just jargon from economists but now it looks like we will all be using the word to reduce pollution.

Farming can be a powerful force for environmental enhancement but it currently generates too many externalities such as emissions from livestock and pollution from fertilisers and pesticides. Overall, farming is now the most significant source of water pollution and of ammonia emissions into the atmosphere in the UK. It accounts for 25% phosphate, 50% nitrate and 75% sediment loadings in the water environment, which harms ecosystems.

Finally a clear and not tacit admission that atmospheric pollution harms soils and alters vegetation.

By ensuring fertilisers are used efficiently, we can cut the air and water pollution that harms public health and the environment, and reduce greenhouse gas emissions. Poor storage of manure and slurry can lead to the release of harmful chemicals and gases such as ammonia (in 2015, more than four-fifths of ammonia emissions in the UK stemmed from agriculture). This can cause acid rain, combine with pollution from traffic and industry to form smog, and harm soils and vegetation.

A clear indication that peat bogs will be conserved and managed better in the future.

Our peat bogs and fens are important habitats that provide food and shelter for wildlife, help with flood management, improve water quality and play a part in climate regulation. Most peat soils support ecosystems that are sensitive to human activities including drainage, grazing, liming and afforestation. This makes them susceptible to degradation if poorly managed.

If I were still working at Wicken Fen on the National Trust’s Vision or the Wildlife Trust’s Great Fen project I would be very excited about this – opportunities, opportunities, opportunities.

Over the last 200 years, we have lost 84% of our fertile peat topsoil in East Anglia. The fens there could lose the remainder in just 30-60 years given current land management practices and a changing climate. In view of this, we intend to create and deliver a new ambitious framework for peat restoration in England.

Habitat creation on a grand scale …

Through changes in the way we manage our land, we will develop a Nature Recovery Network providing 500,000 hectares of additional wildlife habitat, more effectively linking existing protected sites and landscapes, as well as urban green and blue infrastructure.

Five years ago commissioning a review into National Parks would have been a recipe for their further emasculation – this can only mean they are going to be strengthened and properly funded! Who to chair the review? Dame Fiona Reynolds would be a good choice in my view.

The UK’s first National Parks were created by an Act of Parliament in 1949 following the government’s 1947 Hobhouse Report, which remains the basis for most protected landscape designation in England today.

Now, 70 years on, the Government will commission a review for the 21st Century. This will consider coverage of designations, how designated areas deliver their responsibilities, how designated areas are financed, and whether there is scope for expansion. It will also consider opportunities to enhance the environment in existing designations, and expand on the existing eight-point plan for National Parks to connect more people with the natural environment.

To my eyes much of this plan looks excellent, of course it will only be effective if things happen – that is the next stage.

This tweet which I posted earlier sums up my feelings

There is also an annex which was published alongside the main report – this is also very good – it is full of useful data with url links to the sources. You can download the annex here.

I can’t see the Defra joke though in this image – can you?

ECOS Student Article Competition – I’m a winner!

I’m delighted to say that my article entitled ‘The elephant in the uplands and the tale of two narratives’ has won BANC’s ECOS Student Article competition.

You can read the paper here – it’s open access and you can read the other winner and commended papers here. Of the nine winners, highly commended and commended papers four of the students are from Exeter University. Well done to everyone and thank you  BANC – an organisation I have been a member of for over 35 years!  BANC is the British Association of Nature Conservationists and it publishes the journal ECOS – see here for more details.

Air pollution and climate change from aviation and shipping

I have recently been writing about atmospheric pollution from nitrogen and ozone (see here and here). According to a report from Natural England (NE 2015 p10) around a third of the nitrogen pollution on Dartmoor comes from long range nitrogen sources. This means the nitrogen comes from international sources and includes pollution from aviation and shipping.
Easyjet over Exeter

Currently carbon dioxide emissions from aviation account for around 2% of global emissions but these are set to rise by up to 400% according to the UN. As well as emitting carbon dioxide jet engines also emit nitrogen oxides, sulphur oxides, soot and water vapour.

Globalisation and our one-liberal economic model means shipping is also a group area

Shipping accounts for 2% of total global emissions and this could rise by between 230-350% by 2050. As well as emitting carbon dioxide shipping engines also emit nitrogen oxides, sulphur oxides and soot.

Neither aviation or shipping are explicitly covered by the Paris Agreement on Climate Change but their continued growth will pose a serious threat to Dartmoor and elsewhere as a result of carbon dioxide, ozone and nitrogen pollution.

Natural England (2015) Atmospheric Nitrogen Theme Plan. Developing a strategic approach for England’s Natura 2000 sites. Improvement Programme for England’s Natura 200 Sites – Planning for the future.

Atmospheric Nitrogen Pollution and its impact on Dartmoor – the other elephant in the countryside

Since the Industrial Revolution humans have altered the natural biogeochemical cycles by increasing the availability of biologically reactive forms of natural elements such as nitrogen (Caporn & Emmett 2009).

In the UK, there are two distinct forms of nitrogen pollution – nitrogen oxides (NOx) and ammonia (NH3). Emissions from vehicles, power stations and factories are largely responsible for NOx, whilst emissions from agriculture (livestock manures and fertilisers) account for the majority of NH3.

NOx compounds (known as oxidised nitrogen) can be deposited ‘wet’ i.e. in rain as nitrate (NO3) or ‘dry’ i.e. as a gas as nitrogen oxide (NO2). NH3 compounds (known as reduced nitrogen) can be deposited wet as ammonium (NH4) or dry as ammonia gas (NH3). NOx and NH3 compounds cause acidification (lowering the pH) and eutrophication (increasing nutrient levels).

NOx emissions peaked around 1990 and by 2015 had fallen 69% compared to the 1970 level. Ammonia levels have by comparison fallen just 9.9% between 1980 and 2015 (Defra 2015).

However, despite the large falls in nitrogen emissions, the deposition of all nitrogen compounds has hardly fallen at all. This unexpected situation has arisen as the atmospheric chemistry over Britain has been altered leading to more rapid oxidisation of nitrogen. This rapidly oxidised nitrogen is deposited in the UK when previously it would have been exported to Continental Europe (RoTAP 2012).

As a result, many parts of the UK have been receiving high levels of nitrogen deposition for decades.

This map shows nitrogen deposition between 2011-2013

This map shows ammonia concentrations

This map shows acidity
(Source: Centre for Ecology and Hydrology).

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 most affected Natural Area in England.

Critical load is defined as the amount of acid or nitrogen deposition below which significant harmful effects do not occur to sensitive habitats. ‘Exceedance’ is the amount of excess acid or nitrogen deposition above this critical load (Hall & Smith 2015).

Table showing the actual atmospheric pollution levels or the Blanket Bogs, Atlantic Wet Heaths with Erica tetralix and European Dry Heaths along with the exceedance loadings
Nitrogen Deposition

kg N/ha/yr

Acid Deposition

Nitrogen | Sulphur keq/ha/yr

Ammonia Concentration


NOx Concentration


SO2 Concentration


Maximum: 30.38

Minimum: 14.28

Average: 21.65

Maximum: 2.17 | 0.5

Minimum: 1.02 | 0.21

Average: 1.55 | 0.35

Maximum: 1.63

Minimum: 0.51

Average: 0.75

Maximum: 8.09

Minimum: 4.05

Average: 4.9

Maximum: 0.75

Minimum: 0.43

Average: 0.5

Empirical Critical Load kg N/ha/yr Acidity Critical Loads (keq) Critical Level

(µg NH3/m3 annual mean)

Critical Level

(µg NOx/m3 annual mean)

Critical Level

(µg SO2/m3 annual mean)

Blanket bog  5-10

Wet heath    10-20

Dry heath     10-20

MinCLMaxN: 0.830 MaxCLMaxN: 1.363 1 30 75
Habitats with Critical Load Exceedances on Dartmoor
Blanket bog

Atlantic Wet heath

European Dry Heath

Blanket bog Blanket bog

Atlantic Wet heath

European Dry Heath

(maximums but not averages)

No exceedance No exceedance

Source: Air Pollution Information Service (accessed 24/3/17)

There is an extensive academic literature on the implications of atmospheric nitrogen pollution for semi-natural habitats. Bobbink et al (1998) in an Essay Review highlight the three main impacts:

  • Accumulation of nitrogenous compounds resulting in enhanced availability of nitrate and ammonium
  • Soil mediated effects of acidification
  • Increased susceptibility to secondary stress factors

Stevens et al (2004) reported that long-term chronic nitrogen deposition had significantly reduced plant species richness. Their study (which included a Dartmoor site) found that for every 2.5kg N ha-1 of nitrogen deposition one species per 4m2 quadrat was lost. At the time of their study they suggested that with an average nitrogen deposition rate of 17 kg N ha-1 yr -1 there was a 23% reduction in species richness compared to sites receiving the lowest levels of atmospheric nitrogen.

Similar results were found in additional surveys on this topic (Stevens et al 2010 and Stevens et al 2011).  van den Berg et al (2016) analysed the British Countryside Survey data and also found clear evidence for nitrogen deposition effects on plant species richness. Their research also suggested that mires and heaths were more sensitive to ammonia deposition than nitrate deposition.

Field et al (2014) found that whilst the diversity of mosses, lichens, forbs and graminoids decline, the cover of graminoids increases.

Kirkham (2001) conducted a study on 8 eight moorland sites including one on Dartmoor and found that the accumulation of nitrogen had changed a substantial proportion of the Heather (Calluna vulgaris) dominated uplands from nitrogen limited ecosystems into phosphorus limited ones. He suggested that this favoured Purple Moor Grass (Molinia caerulea) as it was a species that was better adapted to phosphorus limitation.

However, Bobbink et al (2010) describes a more complex relationship between nitrogen, Molinia and Calluna. They suggest from studies in the Netherlands that nitrogen deposition increases the productivity of the dwarf shrubs such as Calluna and that if the dwarf shrub canopy remains closed then the dwarf shrubs remain the stronger competitor against grasses such as Molinia and Tufted Hair Grass (Deschampsia flexuosa). However if the dwarf shrubs canopy is opened up by disturbance then the grasses can become dominant.

Bobbink et al (2010) also state that disturbance to the dwarf shrub canopy by either Heather Beetle (Lochmaea suturalis) attack, winter frost injury or drought are increased in likelihood by enhanced nitrogen deposition. Kirkham (2001) also found that nitrogen deposition led to increased concentrations of nitrogen in the growing shoots of Calluna and he cites an unpublished report by S.E Hartley which suggested that this made the Calluna plants more susceptible to increased grazing pressure by sheep. He then concluded that increased nitrogen content in the shoots of Calluna resulting from atmospheric pollution may therefore be playing a part in the deterioration of Calluna moorland caused by overgrazing.

Payne et al (2013) found that approximately 60% of all plant species studied react adversely to nitrogen deposition at levels below the published critical load exceedances.

The effects of nitrogen deposition are not related only to plant communities. Fox et al (2014) in a study of the long-term changes in British moth communities found that moth species associated with low nitrogen, based on their larval host plant characteristics, declined most strongly. In a study from Sweden Ockinger et al (2006) reported that butterfly species which relied on nutrient poor conditions tended to decrease whilst those reliant on nutrient rich conditions tended to increase. They suggested that this indicated a negative effect of increased nitrogen in the soil resulting from the active fertilizing of pastures and / or atmospheric nitrogen deposition.

Payne (2014) writing about the exposure of British peatlands to nitrogen deposition concluded that ‘nitrogen deposition is a serious threat to British peatlands and is likely to remain so for some time to come’.

In a study looking at the likely impacts of nitrogen deposition up to 2030 Stevens et al (2016) state that for heaths and bogs ‘we project overall reductions in species richness with decreased occurrence of tricolours lichens and some bryophytes, reduced cover of dwarf shrubs and a small increase in grasses’.

Addressing the question of how long do ecosystems take to recover from atmospheric nitrogen deposition Stevens (2016) concluded ‘There are a number of barriers to recovery such as continued critical load exceedance and lack of seed bank or local seed source, and there is potential for vegetation communities to reach an alternative stable state where species lost as a consequence of changes due to nitrogen deposition may not be able to recolonise.’

Whilst the conservation agencies and N.G.O.s were quick to respond to the threat posed by sulphur dioxide pollution and ‘acid rain’ in the 1970s and 1980s they have been much slower to respond to the threat posed by nitrogen pollution. English Nature published a report in 2004 (Bignall et al 2004) on the ecological effects of diffuse pollution from road traffic but that was as much a response to the requirement to provide planning authorities advise on new roads schemes – the report looked at localised impacts rather than diffuse ones.

In 2011, the Joint Nature Conservation Committee published a series of reports it had commissioned on the evidence of nitrogen deposition impacts on vegetation (Stevens et al 2011, Emmett et al 2011 and JNCC 2011). This work provided a new analysis of eight national scale datasets which showed significant responses in cover and presence of 91 plant and lichen species in relation to nitrogen deposition. The summary report concluded that ‘nitrogen deposition is compromising our ability to deliver current conservation commitments such as the objective to achieve Favourable Condition Status under the Habitats Directive.’ This report also contained various recommendations for the country agencies.

Natural England (2015) published a document entitled ‘Atmospheric nitrogen theme plan – developing a strategic approach for England’s Natura 2000 sites. The plan reported that in England 80% of sensitive Special Areas of Conservation (SAC) and 70% of sensitive Special Protection Areas (SPA) are estimated to exceed the critical load for one or more of their protected features.

Exceedance of nitrogen site relevant critical loads for SACs (left) and SPAs (right)

As can be seen from the left hand map both of Dartmoor’s moorland SACs exceed the critical load levels.

The document also contains a table setting out the threats from nitrogen for each of England’s SACs. The Dartmoor relevant section is set out in the following table.

SAC Name Sensitivity code Level of CL exceedance Likelihood of N impact Relevance of local agricultural NH3 sources Potential significance of local NH3 measures
Dartmoor Very sensitive

CL 5-10 kg N/ha/yr

Very high

CL exceedance > 28kg N/ha/yr

Very likely

Sensitive and high level of CL exceedance



Agricultural deposition 20-40%, NH3 dry deposition > 10-20 kg N /ha/yr

NH3 emissions within 2-3km of site 6-10 kg N /ha/yr


The theme plan then proposes a trial of ‘Site Nitrogen Action Plans’ (SNAP) which would document:

  • The current status of the site in terms of nitrogen deposition and attribution of this nitrogen to identify the most significant sources,
  • The expected future decline in background deposition at the site as a result of existing national and international measures,
  • Coordinated locally targeted measures to reduce the contribution of local sources where feasible and appropriate,
  • Habitat restoration and management measures that mitigate the impact of atmospheric nitrogen.
  • Five trial sites have been selected in England, the nearest one to Dartmoor is the Culm Grasslands SAC and the most similar one to Dartmoor in habitat type and size is the South Pennines SAC.

At this point it is not clear what progress has been made on the trial SNAPs. However Natural England’s published Site Improvement Plan (SIP) for Dartmoor [1] has listed ‘Air pollution: impact of nitrogen deposition’ as its third priority area (behind ‘Hydrological Changes’ and ‘Wildfire / Arson’) although at this point no budget has been allocated and no ‘delivery partners’ have been identified.

The impact of atmospheric nitrogen pollution has recently received more profile and publicity with the publication of a report by Plantlife (2017) ‘We need to talk about nitrogen – the impact of atmospheric nitrogen deposition on the UK’s wild flora and fungi’. It would appear that the problems of atmospheric nitrogen pollution are becoming more widely known but there are still many conservation managers who are still unaware of the issue.

Unfortunately raising the profile of the issue is likely to prove easier than solving the problem – the measure suggested in the Dartmoor SIP is ‘control, reduce and ameliorate atmospheric nitrogen impacts’, which as this review shows will be easier said than done.


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