The ecosystem services of unplanned green spaces in cities

Green spaces in cities can protect against flooding, reduce noise levels, filter pollutants from the air, and be home to a variety of plant and animal species. Moreover, they provide space for play, exercise and relaxation and can thus contribute to improving public health. Whilst these functions have been well documented in international studies of larger parks and recreational areas, there has been less previous focus on the “unofficial” green spaces in cities, such as vacated parcels and the temporary spaces that occur during processes of redevelopment. Such land can be quickly colonized by plants and animals and may also be taken into use by city residents, e.g. for children’s play. Our study examined the ecosystem services associated with these elements in the urban green infrastructure.
We developed and tested new methods to map and quantify non-sealed surfaces within Norwegian cities. Our maps identify potential ecosystems in urban areas, independent of official land use designations. The map-based analyses were combined with new field methods to record use of green spaces by people and to identify which plant species occur in these urban ecosystems and whether they have positive functions, for instance as food sources for migrating birds or pollinating insects.
The methods were tested in two Norwegian cities, Moss and Tromsø. Although we excluded parks and recreational areas from our analysis, we found footpaths in about a third of the green spaces we visited. Litter was found in almost half of the areas. The number of plant species present was low in the densely built city centre and increased with distance from the centre. We found a high incidence of black-listed plant species (present in over 40 % of green spaces). These are alien species that are considered to present a high risk of negative ecological consequences for native biodiversity.
The project also included a small questionnaire study focusing on people’s attitudes to urban biodiversity. Generally, people had a positive interest in urban biodiversity, and this interest did not appear to be limited to charismatic species. Another finding from the project related to the use of old map data by management authorities. At present there are no regulations about quality control of maps or about how often maps must be updated. Species occurrences are likely to change rapidly in an environment as dynamic as the urban and using outdated maps may be worse than not having maps at all if management efforts are directed to the wrong place, or misguided efforts are initiated that are not cost-efficient. In some cases, the public may be able to contribute to updating species maps, with the additional spin-off of increasing public awareness about biodiversity.
Overall our findings show that urban green spaces can have both positive and negative functions, suggesting that such areas warrant a more conscious management to maximize benefits and minimize unwanted consequences.