Despite the importance of urbanization as a major driver of land-use change across the world, there have been surprisingly few attempts explicitly to quantify the provision of ecosystem services at a city-wide scale.
The study provides evidence that the current assumption that urban land in the UK has a zero carbon density is incorrect. More work is needed to quantify ecosystem services at the citywide scale. The results do raise important issues regarding how trees are handled in cities. Carbon stored in trees will eventually be released when the tree dies. To maintain the carbon store, plants must continually be replaced. Ideally the authors state, cities site trees where they will be able to fully mature, thus providing a long term carbon sink. Additionally landscape and tree maintenance practices can be carbon intensive. The authors write, “If 10% of the present council grassland (equating to 1,005,744 m2) was planted and maintained with trees, an extra 28,402 tones of carbon could be added to the current pool (a net figure accounting for the loss of herbaceous cover and gain of tree cover). This corresponds to a 12% increase in the existing vegetation carbon stock for the city.” (2011) A BBC News Science and Environment report.
The full article, published in the Journal of Applied Ecology is here: