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.