Benefits of trees in the Krasiński Gardens, Warsaw

Krasiński Garden in Warsaw

Abstract

Trees can improve air quality by absorbing pollutants and particulate matter, making them an important resource in urban environments, where pollution levels are high. The impact of trees on air quality in the Krasiński Gardens in Warsaw was investigated, and the different species, size, and quality of trees were considered.

Intervention overview

Urban areas are at particular risk of poor air quality due to large population sizes, industrial activities, and fossil fuel-based transportation. The WHO estimates that, worldwide, 4.2 million people died prematurely from exposure to outdoor air pollution in 2016 (Ambient Air Pollution, 2021), with the Health and Environment Alliance estimating 45,000 annual deaths due to air pollution in Poland alone.

Well-managed trees are a vital resource in urban areas as they provide multiple ecosystem services, including removing harmful air pollutants (McPherson, 2017). One such pollutant is tropospheric ozone (O3), which is considered the 3rd most significant GHG after carbon dioxide (CO2) and methane (CH4) (Ehhalt & Prather, IPCC Chap 4, 2001) and also has negative health implications. Additionally, trees remove pollutants PM2.5, NO2, and SO2, exposure to which can cause mortality and morbidity from cardiovascular and respiratory disease and lung cancer, among other health issues (Hassan Bhat et al., 2021).

Warsaw, the capital and largest city of Poland, has a population of almost 1.8 million in 2022 (Population Stat, 2022) (just over 1.7 million at the time of the study in 2014), making it susceptible to poor air quality and other challenges related to urbanisation. This study evaluates the health benefits associated with air quality ecosystem services of urban trees, focusing on the Krasiński Gardens in Warsaw, which had 932 trees from 43 different species at the time of the study (2016).

The i-Tree Eco software was used to determine the air pollution removal by species, by processing their main parameters: 1) field data inventory of urban forest structure - species, condition, height and diameter; 2) air pollution concentrations of O3, NO2, SO2 and PM2.5, obtained from a nearby monitoring station; and 3) meteorological data which was air temperature and solar radiation data for Warsaw. The economic value was determined by estimating the impact of each pollutant on adverse health in terms of mortality and morbidity, this value increased with population density.

Outcomes

Annually, the trees removed 149.9 kg of ozone. The amount removed between species was most strongly correlated with the crown diameter: each small, medium, and large-crown diameter mature tree removed 34.5 g, 104.9 g, and 428.1 g ozone/year, respectively. The trees removed 94.4kg NO2, 119kg SO2, and 10.9 kg PM2.5 per year. This varied most according to crown diameter: the total amount of air pollutants (including ozone) removed for small-, medium-, and large-diameter crown trees was 61g, 190g, and 750g, respectively, with an average of 287 g/year.

The total health value of air pollution removal in monetary terms was estimated as US$363,167.55 per tonne, with 96.6% of these benefits coming from PM2.5. This is the cost of mortality and morbidity avoided and does not consider total health costs of all potential benefits provided by trees, such as mental health benefits. The removal of PM2.5 had the greatest impact at US$3964.93/year, accounting for 69% of the total economic gain despite accounting for only 4.1% of total pollutants removed. Removal of ozone, NO2, and SO2 had economic values of US$1570.05, US$176.43, and US$5.29/year, respectively (using 2022 exchange rates between PLN and USD).

Feasibility and potential impact of scale up

Warsaw has fewer urban green spaces than the average European capital city, indicating potential for scale-up; more trees can be planted in Warsaw (EAA Green Infrastructure, 2022).

Pollution removal of sites in other cities showed some differences to Krasiński Gardens: average pollution removal per tree in Calgary, Canada was 25 g/year, while Udine, Italy saw 494 g/year. Average values in New York and Minneapolis in the USA, however, saw similar values to those in the Krasiński Gardens, with 292 g and 283 g/year, respectively. These differences, or similarities, are mostly due to leaf area, and so policy makers should favour the planting of large trees. The most beneficial trees found in the study in terms of all air pollutant removal were Horse chestnut, Silver maple, Ash, English oak, Norway maple and Little leaf linden. However, the importance of pollutant-tolerant and resilient tree species is noted, as these will mitigate the risks of relying on a few tree types.

Although this study is a good example of economic valuation of health benefits associated with ecosystem services, it did not consider all potential health benefits (both monetary and non-monetary) provided by the trees, such as mental health benefits of recreational use of the park. Potential health disbenefits may arise from emissions of harmful pollutants such as BVOCS or the potential increase in pests, pathogens and diseases which put the trees at risk. This will increase maintenance costs and risk of tree death, creating preventable economic strain and loss of the important pollution removal services provided. Furthermore, existing literature on urban green space suggests increased vegetation is associated with increased tick bites which have public health implications (Hansford et al., 2017). A thorough assessment of both benefits and trade-offs can offer meaningful information to guide the sustainable management of urban trees.

References

Academic profile / relevant organisation’s page

  • Szkop, Z. (2016). An evaluation of the ecosystem services provided by urban trees: The role of Krasiński Gardens in air quality and human health in Warsaw (Poland). Environmental & Socio-Economic Studies, 4(4), 41–50. https://doi.org/doi:10.1515/environ-2016-0023

Supplementary information

  • Ambient (outdoor) air pollution. (2021). Retrieved 11 August 2022, from https://www.who.int/news-room/fact-sheets/detail/ambient-(outdoor)-air-…
  • Population Stat. (2022). Warsaw, Poland Population. https://populationstat.com/poland/warsaw
  • Percentage of total green infrastructure, urban green space, and urban tree cover in the area of EEA-38 capital cities (excluding Liechtenstein). (2022, February 21). [Data Visualization]. European Environment Agency. https://www.eea.europa.eu/data-and-maps/daviz/percentage-of-total-green…
  • McPherson, E. G., Xiao, Q., van Doorn, N. S., de Goede, J., Bjorkman, J., Hollander, A., Boynton, R. M., Quinn, J. F., & Thorne, J. H. (2017). The structure, function and value of urban forests in California communities. Urban Forestry & Urban Greening, 28, 43–53. https://doi.org/10.1016/j.ufug.2017.09.013
  • Hansford, K. M., Fonville, M., Gillingham, E. L., Coipan, E. C., Pietzsch, M. E., Krawczyk, A. I., Vaux, A. G. C., Cull, B., Sprong, H., & Medlock, J. M. (2017). Ticks and Borrelia in urban and peri-urban green space habitats in a city in southern England. Ticks and Tick-Borne Diseases, 8(3), 353–361. https://doi.org/10.1016/j.ttbdis.2016.12.009
  • Hassan Bhat, T., Jiawen, G., & Farzaneh, H. (2021). Air pollution health risk assessment (AP-HRA), principles and applications. International Journal of Environmental Research and Public Health, 18(4), 1935.

Contact

Image attribution

  • Krasiński Garden in Warsaw. Author: Robert Wielgórski. CC BY 3.0. Image details

Related Content