Vegetation density is the main driver of insect species richness and diversity in small private urban front gardens

Urbanisation changes natural ecosystems and vegetation to urban green spaces, and causes insect communities to experience novel challenges for survival. New evidence suggests that urban green spaces, no matter how small, can provide meaningful habitats for insects. Information on design and management of small gardens (<6 m 2 ) in dense urban areas is still scarce. In particular, it is hardly known which garden designs provide most benefits to insects. We surveyed 65 small urban façade gardens (μ=1.7m 2 ) in Amsterdam and The Hague in The Netherlands and measured various garden attributes that are expected to be relevant for general, flower-visiting and herbivorous insect species richness and diversity. Plant coverage and richness were the strongest predictors of insect biodiversity and species richness. We found no support for associations with native plants or garden size. To strengthen insect biodiversity in the urban environment, we recommend future design of urban green spaces to focus on maximising coverage and richness of vegetation. Although there are advantages to using native species, we acknowledge that garden owners often prefer exotic species. Some of these can also affect insect diversity and abundances positively. Shown are either plus or minus signs indicating a positive or negative trends from the models that predict species richness and Shannon biodiversity of insects, pollinators or herbivores by the design of small urban gardens. * indicates a statistically significant trend at p-value < 0.05. A plus or minus sign without * means a visible statistically non-significant trend. A greyed out square indicates exclusion of the term in the model. A white square indicates non-significant and non-visible trend. • Small urban gardens hold large potential for supporting urban insect communities. • Total vegetation cover was the strongest predictor for insect diversity and richness. • Plant richness was the second strongest predictor, but not for herbivorous insects. • Garden size had no effect on insect diversity or richness. • Native plant species did not impact insect diversity or richness.