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. http://publications.naturalengland.org.uk/publication/6140185886588928

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
µg/m3
NOx Concentration
µg/m3
SO2 Concentration
µg/m3
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 http://www.apis.ac.uk/ (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 such 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

 

Medium

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

Medium

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.

References

Aerts R., Berendse F., de Caluwe H. & Schmitz M. (1990) Competition in Heathland along an Experimental Gradient of Nutrient Availability. Oikos 57: 310-318.

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.

Bignal K., Ashmore M. & Power S. (2004) The ecological effects of diffuse air pollution from road transport. English Nature Research Reports Number 580

Bobbink R., Hicks K., Galloway J., Spranger T., Alkemade R., Ashmore M., Bustmante M., Cinderby S., Davidson E., Dentener F., Emmett B., Erisman J.-W., Fenn M., Gilliam F., Nordin A., Pardo L. & De Vries W. (2010) Global assessment of nitrogen deposition effects on terrestrial plant diversity: a synthesis. Ecological Applications 20 (1): 30-59.

Bobbink R., Hornung M. & Roelofs J.G.M. (1998) The effects of air-bourne pollutants on species diversity in natural and semi-natural European vegetation. Journal of Ecology 86: 717-738.

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., Rosenburg A. E. & Field C.D. (2015) The importance of atmospheric quality in determining upland vegetation. In Meade R. (ed) (2015)

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., Carroll J.A., Dise N.B. & Payne R.J. (2014) Impacts and indicators of nitrogen deposition in moorlands: results from a national pollution gradient study. Ecological Indicators 45: 227-234.

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.

Defra (2015) Emissions of air pollutants in the
UK, 1970-2014, Statistical Release: 17 December 2015, Defra National Statistics https://www.gov.uk/government/ uploads/system/uploads/attachment_data/ le/486085/Emissions_of_air_pollutants_statistical_ release_2015_-_Final__2_.pdf

Emmett, B.A., Rowe, E.C., Stevens, C.J., Gowing, D.J., Henrys, P.A., Maskell, L.C. & Smart, S.M. 2011. Interpretation of evidence of nitrogen impacts on vegetation in relation to UK biodiversity objectives. JNCC Report 449. http://jncc.defra.gov.uk/page-5895

Field C., Dise N., Payne R., Britton A., Emmett B., Hallowell R., Hughes S., Jones L., Lees S., Leake,J., Leith I., Phoenix G., Power S., Sheppard L., Southon G., Stevens C. and Caporn S. M. (2014). The Role of Nitrogen Deposition in Widespread Plant Community Change Across Semi-natural Habitats. Ecosystems 17(5): 864-877

Fox R., Oliver T. H., Harrower C., Parsons M. S., Thomas C. D & Roy, D. B. (2014), Long-term changes to the frequency of occurrence of British moths are consistent with opposing and synergistic effects of climate and land-use changes. Journal of Applied Ecology, 51: 949–957.

Hall J. & Smith R. (2015) Trends in critical load exceedances in the UK. CEH. http://www.cldm.ceh.ac.uk/sites/cldm.ceh.ac.uk/files/TrendsReport_June2015_WEB.pdf

Hall J., Dore T., Smith R., Evans C., Rowe E., Bealey B., Roberts E., Curtis C., Jarvis S., Henrys P., Smart S., Barrett G., Carter H., Collier R. & Hughes P. (2016). Defra Contract AQ0826: Modelling and mapping of exceedance of critical loads and critical levels for acidification and eutrophication in the UK 2013-2016 Final Report: 25 July 2016, accessed on 16 December 2016 at: https://uk-air.defra.gov.uk/ assets/documents/reports/cat13/1611011543_ AQ0826_FinalReport_25July2016.pdf

JNCC (2011) Evidence of nitrogen deposition impacts on vegetation: implications for country strategies and UK biodiversity commitments. This is a summary of JNCC reports 447 & 449. http://jncc.defra.gov.uk/pdf/Project%20summary%20v4_final.pdf

Kirkham F.W. (2001) Nitrogen uptake and nutrient limitation in six hill moorland species in relation to atmospheric nitrogen deposition in England and Wales. Journal of Ecology 89: 1041-1053.

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.

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. http://publications.naturalengland.org.uk/ publication/6140185886588928

Payne R. J. (2014) The exposure of British Peatlands to nitrogen deposition 1900-2030. Mires and Peat volume 14, Article 04 pp1-9.

Payne R. J., Dise N.B., Stevens C. J. Gowing D. J. & BEGIN partners (2013) Impact of nitrogen deposition at the species level.  PNAS 110: 984-987.

Plantlife (2017) We need to talk about nitrogen. The impact of atmospheric nitrogen deposition on the UK’s wild flora and fungi. http://www.plantlife.org.uk/application/files/3514/8935/6858/We_need_to_talk_about_Nitrogen_FINAL_webpdf.pdf

Rodwell J. S. (ed) (1991) British Plant Communities. Volume 2. Mires and heaths. Cambridge University Press. Cambridge.

RoTAP (2012). Review of Transboundary Air Pollution: Acidification, eutrophication, ground level ozone
and heavy metals in the UK. Centre for Ecology and Hydrology, Edinburgh. Available from: http://www. rotap.ceh.ac.uk/

Stevens C., Jones, L., Rowe E., Dale S., Hall J., Payne R., Evans C., Caporn S., Sheppard L., Menichino N. & Emmett B. (2013) Review of the effectiveness of on-site habitat management to reduce atmospheric nitrogen deposition impacts on terrestrial habitats. Countryside Council for Wales. (CCW Science Report no: 1037 (A), CEH Project no. C04949)

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

Stevens C.J., Dise N.B., Mountford J.O. & Gowing D.J. (2004) Impact of nitrogen deposition on the species richness of grasslands. Science 303: 1876-1879.

Stevens C.J., Dupre C., Dorland E., Gaudnik C., Gowing D.J.G., Bleeker A., Diekmann M., Alard D. Bobbink R., Fowler D., Corcket E., Mountford J.O., Vandvik V., Aarrestad P.A., Muller S. & Dise N.B. (2010) Nitrogen deposition threatens species richness of grasslands across Europe. Environmental Pollution 158: 2940-2945.

Ockinger E., Hammarstedt O., Nilsson S.G. & Smith H.G. (2006) The relationship between local extinctions of grassland butterflies and increased soil nitrogen levels. Biological Conservation 128: 564-573.

Stevens C.J., Dupre C., Dorland E., Gaudnik C., Gowing D.J.G., Bleeker A., Diekmann M., Alard D. Bobbink R., Fowler D., Corcket E., Mountford J.O., Vandvik V., Aarrestad P.A., Muller S. & Dise N.B. (2011) The impact of nitrogen deposition on acid grasslands in the Atlantic region of Europe. Environmental Pollution 159: 2243-2250.

Stevens C.J., Payne R.J., Kimberley A. & Smart S.M. (2016) How will the semi-natural vegetation of the UK have changed by 2030 given the likely changes in nitrogen deposition? Environmental Pollution 208: 879-889.

Stevens, C.J., Smart, S.M., Henrys, P.A., Maskell, L.C., Walker, K.J., Preston, C.D., Crowe, A., Rowe, E.C., Gowing, D.J. & Emmett, B.A. 2011. Collation of evidence of nitrogen impacts on vegetation in relation to UK biodiversity objectives. JNCC Report 447. http://jncc.defra.gov.uk/page-5894

Terry A.C., Ashmore M.R., Power S.A., Allchin E.A. & Heil G.W. (2004) Modelling the impacts of atmospheric deposition on Calluna-dominated ecosystems in the UK. Journal of Applied Ecology 41: 897-909.

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.

van den Berg L.J.L., Jones L., Sheppard L.J., Smart S.M., Bobbink R., Dise N.B. & Ashmore M.R. (2016) Evidence of the differential effects of reduced and oxidised nitrogen deposition on vegetation independent of nitrogen load. Environmental Pollution 208:890-897.

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).

[1] http://publications.naturalengland.org.uk/publication/4508672642252800

Atmospheric pollution from Ozone – an elephant in the Uplands?

Low level ozone (O3) is produced following the reaction in warm sunlight of nitrates (NOx) and Volatile Organic Compounds (VOCs) both of which derive from vehicle and shipping emissions (Caporn & Emmet 2009). Unlike the atmospheric pollutants of nitrogen and sulphur, atmospheric levels of O3 are increasing by around 0.2 ppb per annum or by 4ppb in the last 20 years (RoTAP 2012).

Concentrations of O3 are often higher in rural areas than urban ones. In the spring and summer night time levels in the uplands of the UK can remain high whilst in the lowlands they follow a cyclical pattern reducing to very low night time levels. As a result during sunny spells upland areas can be exposed to very high levels of continuous O3 exposure for many days. Over the past 20 years, peak concentrations of O3 have decreased but annual mean concentrations have increased (RoTAP 2012).


These maps show the O3 concentrations in the UK between March to May and May to July. It is clear that upland areas (amongst others) receive high levels of O3 during these months. O3 concentrations on Dartmoor are amongst the highest in the country (RoTAP 2012).

O3 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).

Mills et al (2007) published data on individual species responses to O3, they reported that 80.4% of species in raised and blanket bog, 60% in valley and transition mires and 51.7% in temperate shrub heathland were O3 sensitive.

Franzaring et al (2000) in an experiment in the Netherlands found that after 28 days exposure to increase O3 concentration Purple Moor Grass (Molinia caerulea) showed significantly increased shoot weights and increased root to shoot ratios.

Hayes et al (2006) studied the response of various upland plant species grown in solardomes with varying concentrations of O3. They found that the sedge Star Sedge (Carex echinata) suffered leaf injury symptoms, the grass Red Fescue (Festuca rubra) also showed signs of leaf injury and premature senescence, the grass Yorkshire Fog (Holcus lanatus) and the sedge Common Yellow-sedge (Carex demissa) were unaffected and the forb Heath Bedstraw (Galium saxatile) whilst the grass Mat Grass (Nardus stricta) showed signs of biomass loss the following spring.

As reported above the peak concentrations of O3 have decreased but the means have increased. Hayes et al (2010) found that in a simulated situation upland species still responded detrimentally when the peak concentrations were lowered and the means increased.

Wedlich et al (2012) showed than in upland meadows in the Pennines increased O3 concentrations did not affect grasses but did significantly reduce the forb community, thus favouring the grass species.

In another experiment the effects of increased O3 concentrations on Heather (Calluna vulgaris) were tested (Foot et al 1996). They reported that Heather can be adversely affected by prolonged O3 episodes particularly if these are followed by or co-incide with frosting temperatures.

JNCC published a review of the impacts of O3 on nature conservation (Morrissey et al 2007) and concluded that ‘Ozone is, and is likely to remain, a significant threat to many BAP Priority Habitats. However, the knowledge base on which to assess these specific risks is extremely small, and a targeted programme of research to address these gaps is urgently needed.

The environmental impacts of O3 are complex, in addition to the impacts described above O3 is also a greenhouse gas in its own right along with carbon dioxide and methane (Caporn and Emmett 2009) and additionally Wyness et al (2011) reported that enhanced nitrogen deposition exacerbates the negative effect of increasing background O3 in the grass Cocksfoot (Dactylis glomerata) but not in the forb Meadow Buttercup (Ranunculus acris).

Mills et al (2013) reviewed the impact of rising O3 levels in the atmosphere on ecosystem services and found that O3 had the potential to detrimentally effect all of the services. For example, high O3 concentrations have the potential to reduce carbon sequestration and speed up global warming, increase methane emissions, reduce crop productivity, reduce biodiversity and worsen air quality.

Natural England is beginning to acknowledge the implications of increased O3 and published the following (NE 2015)

Ground level ozone is a toxic atmospheric pollutant of growing concern, with potentially harmful effects on plant communities (Morrissey et al. 2007). It is formed in the lower atmosphere in the presence of sunlight by complex photochemical reactions between pollutants from a range of sources including traffic. Critical levels for ozone effects on vegetation are already widely exceeded and background emissions of precursors in the northern hemisphere are increasing (Natural England 2008; RoTAP 2012).

The implications for biodiversity of increasing background levels of ground-level ozone. Background ozone levels have now increased to a level where exposure to ozone may cause adverse effects in semi-natural vegetation, especially in the spring months in upland Britain.

However unlike for nitrogen deposition (see here) no specific measures for action have been set out yet.

AQEG (2009) conclude that O3 levels are likely to continue to rise in rural and urban areas and are likely to pose an increased threat to human health and the environment generally. Whilst measures taken in the UK to reduce O3 precursor compounds, which are methane, non-methane volatile organic compounds (VOC), oxides of nitrogen and carbon monoxide, can be beneficial, it will take action on a northern hemisphere scale if effective control of O3 levels is to be achieved.

References
AQEG
(2009) Ozone in the United Kingdom. Air Quality Expert Group for Defra, Scottish Executive, Welsh Assemble Government and DoE NI.
Ashmore M.R. (2005) Assessing the future global impacts of ozone on vegetation. Plant, Cell and Environment 28: 949-964.
Bonn A., Allott T., Hubacek K. & Stewart J. (2009) Drivers of Environmental Change in Uplands. Routledge. London.
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
Franzaring J., Tonneijck A.E.G., Kooijman A.W.N. & Dueck Th.A. (2000) Growth responses to ozone in plants species from wetlands. Environmental and Experimental Botany 44: 39-48.
Hayes F., Jones M.L.M., Mills G. & Ashmore M. (2007) Meta-analysis of the relative sensitivity of semi-natural vegetation species to ozone. Environmental Pollution 146: 754-762.
Hayes F., Mills G., Jones L. & Ashmore M. (2010) Does a simulated upland grassland community respond to increasing background, peak or accumulated exposure of ozone? Atmospheric Environment 44: 4155-4164.
Hayes F., Mills G., Williams P., Harmens H. & Büker P. (2006) Impacts of summer ozone exposure on the growth and overwintering of UK upland vegetation Atmospheric Environment 40: 4088–409.
Mills G., Hayes F., Jones M.L.M. & Cinderby S. (2007) Identifying ozone-sensitive communities of (semi-) natural vegetation suitable for mapping exceedance of critical levels. Environmental Pollution 146: 736-743.
Mills, G., Wagg, S., Harmens, H. (2013). Ozone pollution: Impacts on ecosystem services and biodiversity. ICP Vegetation Programme Coordination Centre, Centre for Ecology and Hydrology, Bangor, UK.
Morrissey, T., Ashmore, M.R., Emberson, L.D., Cinderby, S. and Büker, P. 2007. The impacts of ozone on nature conservation: a review and recommendations to research and policy. JNCC Report No. 403.
Natural England (2008) State of the Natural Environment 2008. Natural England Reports No 85. Sheffield: Natural England. URL: http://publications.naturalengland.org.uk/publication/31043
Natural England (2015) Natural England Access to Evidence Information Note EIN009 Summary of evidence: Land use. http://publications.naturalengland.org.uk/publication/6684569048711168
RoTAP (2012). Review of Transboundary Air Pollution: Acidification, eutrophication, ground level ozone
and heavy metals in the UK. Centre for Ecology and Hydrology, Edinburgh. Available from: http://www. rotap.ceh.ac.uk/
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

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

We need to talk about nitrogen

Plantlife in association with a number of botanical and conservation organisations including the National Trust, RSPB and the Woodland Trust have today published an important report ‘We need to talk about nitrogen’. You can download it here. This is a quote from the report.

Amid the clamour about climate change and carbon emissions, another alarm bell, largely unheard, has been sounding for some time. Global pools of reactive nitrogen have been building in the atmosphere, soils and waters from the burning of fossil fuels and intensive farming. This excess of reactive nitrogen is now being deposited throughout the biosphere, significantly impacting our most precious semi-natural habitats, changing their plant communities and the very functions these ecosystems provide.

We need to talk about nitrogen deposition, to raise awareness of its causes and consequences, to agree on solutions, and to work together to integrate these solutions into policy and practice now.

It is a topic that I have written about before – see here. I have been surprised by how few people are aware of this issue. In my view nitrogen deposition especially in the uplands is one of the main factors involved with the changes in vegetation that have occurred over the past few decades. I am certain that nitrogen deposition is highly implicated in the rise of Purple Moor Grass (Molinia caerulea) in the uplands of the UK, including Dartmoor.

This map produced by the Centre for Ecology and Hydrology shows the extend of the problem in the UK. Nitrogen deposition is acidifying your soils and saturating them with fertiliser.

Some species of plant respond well to high nitrogen levels and grow vigorously e.g. Molinia, however the majority of plant species respond poorly, in some cases they die out and in others they are outcompeted.

I recommend you read the Plantlife report.