It’s easy to talk about the benefits of plants in cities. It’s much, much harder to quantify how they positively affect the quality of life for city residents in terms of the services they provide.
What would it look like to develop a strategy to quantify ecosystems services to empower cities to look at zoning and planning in a new way? Faculty at the Institute for Environmental Studies at VU University Amsterdam, the Netherlands, identified six ecosystems services provided in cities and developed a way to map them into bundles for use (visual below).
The study describes urban green space (UGS) as: Trees (mostly street trees), Woodland (clustered trees, urban forest), Tall Shrub (2-5 m), Short Shrub (<2 m), Herbaceous, Domestic garden, Water and Other. The weight various types of green space carry in terms of ecosystems services was based on a review of prior research, with acknowledgement that the current evidence is variable.
While prior studies have characterized one or two ecosystem services such as carbon storage, no one has attempted to bundle services to gain a more holistic view. The services identified and bundled in the Rotterdam study include air purification, carbon storage, noise reduction, runoff retention, cooling and recreation.
Ecosystems services in Rotterdam are highest in the areas with more urban green space. However the components of the ecosystems services bundle varies based on the specific landscape.
- Air. Air purification quantified particulate matter (PM), which is very important near highways.
- Carbon. Carbon storage potential in urban environments is high. Vegetation type and biomass volume are the two variables. Trees are the most important above ground carbon sink, with perennials and shrubs contributing much less. Soils contain carbon, but because urban soils are highly disturbed, making quantifying urban soil carbon impractical. The authors acknowledge that land management significantly affects carbon storage: Highly maintained landscapes and fertilizer application emit carbon dioxide and various tree pruning regimes can significantly reduce carbon storage.
- Noise. Noise reduction by urban vegetation is both direct and indirect. The type of vegetation and its distance from the noise source are most important for reducing noise with focus on roads.
- Stormwater. Vegetation reduces runoff in a number of ways: Interception, by helping to infiltrate water, and through evapotranspiration. The size and type of vegetation influences runoff retention, as does the amount and speed of rainfall event. The model estimates interception and infiltration for vegetation based on a 10 mm rain event.
- Cooling. The urban heat island effect in London and Rotterdam has been measured to be 7C. Vegetation affects urban temperatures through shade, evapotranspiration and altering air movement and heat exchange. The study accounts for the cooling effect of vegetation through shading and evapotranspiration only. Trees, shrubs and woodland counts in full, while herbaceous vegetation, gardens and other green areas count at half because lawns do not have large cooling effect based on scientific literature.
- Recreation. Gardens were not weighted when accounting for recreational value. Parks were weighted the highest because of the diversity of vegetation and the open structure, features highly valued among residents.
Urban green space can be designed to provide ecosystems services, and using an approach like this could be just what cities need to account for functional landscapes.
Quantifying urban ecosystem services based on high-resolution data of urban green space: an assessment for Rotterdam, the Netherlands. Journal of Applied Ecology 2015, British Ecological Society, 52, 1020-1032. Marthe L. Derkzen, Astrid J.A. van Teeffelen and Peter H. Verburg, Faculty of Earth and Life Sciences, Institute for Environmental Studies (IVM), VU University Amsterdam, De Boelelaan 1087, 1081 HV Amsterdam, the Netherlands. http://onlinelibrary.wiley.com/doi/10.1111/1365-2664.12469/abstract