Trees and other ‘green infrastructure’ have been researched over the years with a focus on the urban environment and human health impacts from pollutants such as nitrogen oxides (NOx) and particulates (ref). Ammonia is a highly soluble and reactive gas containing nitrogen (N) which can readily deposit (called N deposition) from the atmosphere to vegetation and the soil. N deposition to sensitive habitats damage plant communities that have evolved on nutrient-poor soils (e.g. bogs, heathlands and some woodlands). There is a combined effect (Figure 1) of treebelts on ammonia concentrations through:
- capture of the plume by the canopy by deposition to the leaf surface and uptake through the stomata and
- increased mixing and dilution of the plume though the creation of eddies and turbulence from the treebelt.
The fraction of ammonia recaptured varies depending on the source strength, meteorological and surface conditions. Studies by Fowler et al. (1998), showed that between 3% and 8% of NH3 emissions from a livestock building were deposited in woodland within 300m of the source. Further work by Bealey et al. (2014), focussed on a range of planting strategies showed that woodlands designed to recapture NH3 from a range of livestock sources (at around 10-20 metres) could recapture a substantially greater fraction of NH3 emissions, up to 20%. In addition rough landscape features such as treebelts can also help disperse ammonia, reducing concentrations near sources and therefore decreasing the most extreme impacts on nearby sensitive receptor ecosystems.
The aim of the Ammonia Reduction from Trees project was to provide new scientific evidence on tree planting for reducing the impact of ammonia emissions from farming in order to inform better advice and support to farmers on ammonia mitigation and guidance. The work was organised into three work packages which were:
- WP1: collate and analyse emission and wind statistical datasets to provide a targeted approach to planting treebelts to protect sensitive habitats in the UK;
- WP2: to measure and test the effectiveness of treebelts in mitigating ammonia concentrations across a treebelt at 5 case study farms;
- WP3: to gather information and undertake farmer surveys to provide feedback on the practicalities and limitations of tree planting to mitigate ammonia emissions.
- 14 January 2022 13.30 – 15.00 Webinar: Overview of the Ammonia Reduction by Trees project. This webinar introduced the project in the context of air quality and tree planting on farms and provided a summary of key findings of the Ammonia Reduction by Trees (ART) project.
- 14 January 2022 15.10 –16.30 Workshop: What motivates farmers to plant trees? This workshop reported on farmers views on tree planting on their farms, gathered from farmer interviews and surveys as part of the Ammonia Reduction by Trees (ART) project. The attendees had a chance to discuss the findings and future approaches to tree planting incentives for farm business and environmental benefits.
- 28 January 2022 13.30 – 15.00 Workshop: Field work – ammonia monitoring in farms woodlands in Cumbria. In this workshop the lead researchers reported on the key findings from the ammonia monitoring on 5 farms in Cumbria, including free range poultry and dairy farms with woodland ranging areas and mature woodland, including different ammonia monitoring methods, meteorological records, tree measurements and modelling work comparing areas with and without trees around the farms. There was an opportunity to ask the researchers questions about the fieldwork, discuss the implications of the results and further research needs.
- 28 January 15.10 – 16.30 Workshop: Targeting tree planting. In this workshop UKCEH experts presented the modelling work on targeting tree planting to capture ammonia emissions from farming to protect sensitive SSSIs. There was chance to discuss the modelling approach, how to make use of the results and data sharing to improve the outcomes for air quality and biodiversity.
Bealey, W.J., Loubet, B., Braban, C.F., Famulari, D., Theobald, 7M.R., Reis, S., Reay, D.S., Sutton, M.A., 2014. Modelling agro-forestry scenarios for ammonia abatement in the landscape. Environ Res Lett. 9. 10 https://iopscience.iop.org/article/10.1088/1748-11 9326/9/12/125001/pdf.
Fowler, D., Pitcairn, C.E.R., Sutton, M.A., Flechard, C., Loubet, B., Coyle, M. and Munro, R.C. (1998) The mass budget of atmospheric ammonia in woodland within 1 km of livestock buildings, Environmental Pollution, 102(1), Supp1, 343-348, https://doi.org/10.1016/S0269-7491(98)80053-5.