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.

(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:
Natural England (2015) Natural England Access to Evidence Information Note EIN009 Summary of evidence: Land use.
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.
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.

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.
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.
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.
Goodfellow S., Wolton R. & Baldock N. (1997) The Nature of Dartmoor: a biodiversity profile. English Nature / Dartmoor National Park Authority publication.
Heather Trust (undated) Heather Beetle. Download from Heather Trust Website
Rosenburgh A. & Marrs R. (2010) The Heather Beetle: a review. Report to the Heather Trust.

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.