Backyard Biodiversity ConservationGreen space Urban planning ABSTRACTThe human population is increasingly disconnected from nature due to urbanisation. To counteract this phenomenon, the UK government has been actively promoting wildlife gardening. However, the extent to which such activities are conducted and the level of resource provision for biodiversity (e.g., food and nesting sites) within domestic gardens remains poorly documented. Here we generate estimates for a selection of key resources provided within gardens at a national scale, using 12 survey datasets gathered across the UK. We estimate that 22.7 million households (87% of homes) have access to a garden. Average garden size is 190 m 2 , extrapolating to a total area of 432,924 ha. Although substantial, this coverage is still an order of magnitude less than that of statutory protected areas.Approximately 12.6 million (48%) households provide supplementary food for birds, 7.4 million of which specifically use bird feeders. Similarly, there are a minimum of 4.7 million nest boxes within gardens. These figures equate to one bird feeder for every nine potentially feeder-using birds in the UK, and at least one nest box for every six breeding pairs of cavity nesting birds. Gardens also contain 2.5-3.5 million ponds and 28.7 million trees, which is just under a quarter of all trees occurring outside woodlands. Ongoing urbanisation, characterised by increased housing densities, is inevitable throughout the UK and elsewhere. The important contribution domestic gardens make to the green space infrastructure in residential areas must be acknowledged, as their reduction will impact biodiversity conservation, ecosystem services, and the well-being of the human population.

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Question: What floras are typically associated with domestic gardens in cities? Location: The urban areas of the cities of Belfast, Cardiff, Edinburgh, Leicester and Oxford, UK. Methods: The composition and diversity of plant species in 267 urban domestic gardens in the five cities was recorded by complete census and quadrat sampling. Results: The entire garden flora consisted of 1056 species, of which 30% were native and 70% alien. 34% of the 50 most frequently recorded species in gardens were native, a number of them being weeds. Although plant species richness in individual gardens varied with garden area, the above breakdowns held true when the cities were considered individually. The only exception was Belfast where, overall, plant species richness was slightly lower than in any of the other cities. Comparing quadrat samples, species richness was found to be greater in the garden habitats of each of the cities than in a number of other habitats, with species accumulation curves showing no sign of reaching saturation at 120 quadrats. This is due to the high proportion of alien species found in gardens, and in particular those surviving at low densities as a result of human intervention. Conclusion: There was surprisingly little difference in plant species richness, diversity or composition between the cities, despite the variation in geographical and climatic factors. This suggests that human factors such as plant availability, garden management and social/economic status of individual householders had an overriding influence.

Domestic gardens make substantial contributions to the provision of green space in urban areas. However, the ecological functions provided by such gardens depend critically on their configuration and composition. Here, we present the first detailed analysis of variation in the composition of urban gardens, in relation to housing characteristics and the nature of the surrounding landscape, across different cities in the United Kingdom. In all five cities studied (Belfast, Cardiff, Edinburgh, Leicester, and Oxford), garden size had an overwhelming influence on garden composition. Larger gardens supported more of the land-use types recorded, in greater extents, and were more likely to contain particular features, including tall trees and mature shrubs, areas of unmown grass and uncultivated land, vegetable patches, ponds, and composting sites. The proportional contribution of non-vegetated land-uses decreased as garden area increased. House age was less significant in determining the land-use within gardens, although older houses, which were more likely to be found further from the urban edge of the city, contained fewer hedges and greater areas of vegetation canopy >2 m in height. Current UK government planning recommendations will ultimately reduce the area of individual gardens and are thus predicted to result in fewer tall trees and, in particular, less vegetation canopy >2 m. This might be detrimental from ecological, aesthetic, social, and economic stand points.