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News Article

Trees as bio-indicators of air pollution


Trees could be a valuable tool in helping monitor air pollution in cities, a new report suggests

A recent study from Belgium has found evidence that the leaves of trees in urban locations change both chemically and physiologically after exposure to different levels of air pollution.  The report states that if these changes are carefully quantified, trees could provide widespread ‘bio-indicators’.

Air pollution can pose serious risks to human health and the environment.  Traditionally, expensive equipment is used to accurately monitor air pollution.  By adopting trees as bio-indicators, the physical and chemical changes in such organisms can be used to directly assess the effects of air pollution on the environment.

As part of the study, researchers chose two species of lime tree, a ‘hairy’-leaved and a smooth ‘non-hairy’-leaved lime.  Seven to eight trees were selected in two areas; one highly polluted industrial area and the other area containing urban green spaces with semi-natural habitat and lower air pollution levels.

Leaves were collected from different branches of each tree and researchers found that chlorophyll content was significantly lower in the more polluted area in both tree species.  In addition, for the hairy leaved lime, upper leaf light reflectance was significantly higher in the polluted area. The authors suggest that leaf hairs trap air pollutants, thereby increasing exposure. 

The researchers also found that both sides of the leaves were more likely to be reflective in the polluted area indicating structural changes to the leaf, resulting in a thinner leaf.  The authors advise that any bio-indicator approach would need to take into consideration the differences between specific species of tree.

The study concludes that trees and other plants (such as lichens) used as bio-indicators could offer a simple and cost-efficient way of monitoring air pollution and its environmental impact.

The Paper

Khavanin Zadeh AR, Veroustraete F, Buytaert JA, Dirckx J, Samson R. Assessing urban habitat quality using spectral characteristics of Tilia leaves.  Environmental Pollution 2013 Jul; 178:7-14. doi: 10.1016/j.envpol.2013.02.021.

Related Information

A recent study by Sawidis and colleagues (2012) examined the level of heavy metal air pollution using evergreen trees as biological indicators.  Mandiwana et al (2006) investigated the impact of a chromium smelter on pollution levels using topsoil, grass and tree bark.  The study found that bark reflected the levels of air pollution better than soil and grass.  Research by Kapoor et al (2012) found that the tree species Holoptelea integrifolia could be used as a control method for minimising concentrated pollutants to a safer level.

Further Reading

Guéguen, F.; Stille, P.; Geagea, M. L.; Boutin, R.; Atmospheric pollution in an urban environment by tree bark bio-monitoring – Part I: Trace element analysis. Chemosphere, 2012, 86, 10, pp 1013-1019

Kumar, R. S.; Thambavani, D. S.; Biological monitoring of roadside plants exposed to vehicular pollution in an urban area. Asian Journal of Research in Chemistry, 2012, 5, 10, pp 1262-1267

Sawidis, T.; Breuste, J.; Mitrovic, M.; Pavlovic, P.; Tsigaridas, K.; Trees as bioindicators of heavy metal pollution in three European cities. Environmental Pollution, 2011, 159, 12, pp 3560-3570

Sawidis, T.; Marnasidis, A.; Zachariadis, G.; Stratis, J.  A study of air pollution with heavy metals in Thessaloniki City (Greece) using trees as biological indicators. Archives of Environmental Contamination and Toxicology, 1995, 28, 1, pp 118-124.

Tomaševic´, M.; Antanasijevic´, D.; Aničic´, M.; Deljanin, I.; Peric´-Grujic´, A.; Ristic´, M.; Lead concentrations and isotope ratios in urban tree leaves. Ecological Indicators, 2013, 24, pp 504-509.

Article details

  • Author(s)
  • Stephanie Cole
  • Date
  • 30 September 2013
  • Source
  • Science for Environment Policy
  • Subject(s)
  • Environment
  • Forest trees