Despite the human population growing in nine out of 13 of England's largest cities (b), accompanied by a substantial rise in the number of dwellings (a), the extent of greenspace in all but one of these urban areas increased between 1991 and 2006 (a). However, when changes in greenspace coverage within this 15 year period were examined corresponding to shifts in UK government planning policy in 2000, we observe opposing trends in nine of the urban cores; a rise 1991–2001, followed by a decline 2001–2006 (a).
Prior to 2000, the increase in greenspace could potentially be attributed to the large areas of industrial land that were abandoned in many English cities through the 1980s and 1990s (e.g. much of the lower Don Valley in Sheffield lay vacant by the late 1980s owing to a rapid fall in industrial output [14
]). Unfortunately, however, reliable data do not exist to corroborate this assertion (electronic supplementary material, appendix S5).
In order to limit urban expansion, policy guidelines released in 2000 [15
] recommended that brownfield sites (which include urban greenspaces such as parks, recreation grounds, allotments and domestic gardens, as well as former industrial sites) should be favoured for new residential development, and that dwelling densities should increase to at least 30 units ha−1
. The new policy target, which sought to ensure that 60 per cent of all new dwellings occupied brownfield sites, was met by 2004 and dwelling densities rose rapidly, soon exceeding 40 ha−1
(electronic supplementary material, figure S3a
). Indeed, all of the cities have become more dense through time (b
), with the number of dwellings expanding faster than the extent of the built-up area. The general trend in EVIdiff supports this conclusion, indicating that urban ‘greenness’ has decreased as a result of such infill development from 2000 to 2008 (). Population growth and urban densification have generally been greatest in the southern cities, where the proportion of greenspace coverage is smallest (in common with Europe as a whole [16
], greenspace provision increased with latitude: Spearman's rank correlation rs
= 0.626, n
= 13, p
= 0.025; electronic supplementary material, table S2).
In 2010, further changes to government planning policy were announced. Despite the emphasis on the re-use of brownfield sites remaining (though domestic gardens are no longer included in the definition), the minimum new-build density of 30 dwellings ha−1
has been retracted [17
]. As highlighted by the results of this paper, land-use change in cities is dynamic and policy-responsive. Predicting the impact of such policy alterations on the extent of greenspace is therefore difficult, especially given the complexities and contrasting forces at work in urban planning and development. However, one possible consequence of the removal of gardens from the brownfield land category is increased development pressure on land in the wider countryside, outside current urban boundaries.
As the continent of Europe gets ever more crowded, the conflict between urban densification and greenspace provision within cities is set to continue, and a careful balance between the two opposing pressures must be sought to ensure an equitable quality of life for all urban residents. Previous research has demonstrated that, even within neighbourhoods of similar urban form, the delivery of ecosystem services can vary considerably [9
]. A detailed investigation of the trade-offs associated with different mechanisms of urban densification is thus urgently required in order to account for, protect and maximize all the potential benefits associated with greenspaces in the long term.