Owners’ perception does not match actual ground-dwelling invertebrate diversity in their garden

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Brigitte Braschler, Valerie Zwahlen, José D. Gilgado, Hans-Peter Rusterholz and Bruno Baur, Department of Environmental Sciences, University of Basel, Basel, Switzerland

Background/Question/Methods
Urban domestic gardens are important for human well-being, biodiversity and other ecosystem functions. These gardens constitute a large area of heterogeneous habitat potentially providing habitat for many species. Biodiversity-promoting initiatives would benefit from their owners being aware of the state of biodiversity in their gardens. We examined whether garden owners’ perceptions match actual biodiversity in their gardens and whether perceptions are influenced by the owners’ ecological knowledge and the main function assigned to their garden. We used a structured interview to assess the motivations and biodiversity knowledge of owners of 33 domestic gardens in the city of Basel and its surroundings (Switzerland) and related them to a survey of native plants and several groups of ground-dwelling invertebrates in their gardens. The groups of ground-dwelling invertebrates examined are considered as biodiversity indicators but are typically not directly promoted by garden owners.
Results/Conclusions
Owners showed different priorities with habitat promotion for biodiversity receiving on average higher scores than cultivation, recreation and garden designing. Owners prioritizing biodiversity promotion had gardens with high habitat type richness, while owners with a high priority for garden designing had gardens with low habitat type richness. The garden owners’ perceptions of both native plant and overall invertebrate diversity were not correlated with actual diversity data for native plants and ground-dwelling invertebrates. The garden owners’ knowledge on different taxonomical groups varied widely. However, the perceptions of the abundance of invertebrate groups by garden owners with good biodiversity knowledge were not more accurate than those from owners with less knowledge. Despite their willingness, many owners do not know all opportunities to promote biodiversity. Asked about potential improvements for biodiversity promotion in their gardens, most owners (68%) suggested creating new habitat types such as extensively managed meadows with flowers, piles of stones, and ponds. However, 21% of owners stated that no further improvement for native biodiversity is possible in their garden, even though many of these gardens had invasive non-native plant species, which could be replaced by native species. Our study showed that many owners are motivated to promote native biodiversity in their garden. However, most owners are limited by gaps in their ecological knowledge. Initiatives to further biodiversity-friendly gardening should thus transfer knowledge.