Biodiversity Outcomes Measured in Italian Community Garden Projects

Urban gardens in Italy have become subjects of ecological monitoring as researchers attempt to quantify what biodiversity benefit, if any, these scattered green patches provide in built environments where natural habitat is otherwise absent. The findings from studies in Bologna, Turin, Milan, and across a six-city transect challenge earlier assumptions that urban gardens primarily serve human food production, and establish their role as measurable habitat for insects, particularly pollinators.

The Bologna Urban Farm Study: Before and After

One of the most methodologically rigorous Italian datasets on urban garden biodiversity comes from a four-year study conducted at a Bologna urban farm site (two years pre-establishment, two years post-establishment). Researchers from the University of Bologna tracked populations of wild bees and hoverflies (syrphid flies) through the transition from a vacant urban lot to an active community growing space with complex vegetation.

The study documented clear increases in pollinator abundance following garden establishment, linked specifically to the introduction of diverse flowering herbaceous species alongside vegetable crops. The researchers noted that hoverflies — often overlooked in pollinator assessments that focus on bees — emerged as the dominant pollinators on the Bologna site, a finding with implications for how garden managers select companion planting species.

Why Syrphid Flies Matter

The prominence of syrphid flies (family Syrphidae) in the Bologna data reflects a wider pattern in European urban ecology studies. Where wild bee populations have declined due to pesticide exposure or habitat fragmentation, hoverfly species have in some cases maintained or increased their presence in urban green spaces. This partially compensates for pollination service gaps, but the substitution is not complete: some plant species are pollinated exclusively or preferentially by specific bee genera.

Garden management practices affect which pollinators are present. Bare soil patches, important for ground-nesting solitary bees, are frequently absent from intensively managed urban plots where weed suppression covers all exposed ground. The Bologna research team identified this as a straightforward intervention: leaving 10–15% of non-cropped garden area uncovered dramatically increases habitat availability for ground-nesting bee species.

Multi-City Monitoring: Six Italian Urban Areas

A 2023 research programme coordinated through the University of Milano-Bicocca deployed standardised monitoring protocols across six Italian cities to assess urban pollinator diversity and abundance. Over 6,000 samples of wild bees and hoverflies were collected across the study period, covering sites in Milan, Turin, Bologna, and three additional urban centres.

The study's primary output is a set of plant-pollinator interaction networks for each city, mapping which plant species attract which pollinator groups. These networks are intended to inform municipal planting specifications for urban green spaces — not only gardens, but street tree selection, park design, and green infrastructure along transport corridors.

Local Garden Features vs. Landscape Context

A separate research thread, published in Landscape Ecology (2025), addressed a contested question in urban biodiversity science: does local garden management (what is planted, how soil is managed, what structure the garden has) matter more than the surrounding urban landscape for determining which pollinators are present?

The analysis — drawing on data from multiple European urban garden networks including Italian sites — concluded that local-scale features are the dominant drivers of pollinator community composition. Specifically:

• Vegetation height diversity positively predicted pollinator species richness
• Floral richness (number of flowering plant species in bloom simultaneously) was the strongest single predictor of bee abundance
• Woody plant diversity (shrubs, small trees) supported distinct pollinator assemblages absent from purely herbaceous sites
• Bare soil cover was positively associated with ground-nesting bee species
• Landscape context (the type of urban matrix surrounding the garden) had weaker and less consistent effects than local features

This finding has direct management implications: garden coordinators can increase biodiversity outcomes without changing the surrounding city, by modifying internal vegetation structure and reducing the intensity of ground cover management.

Turin: Pollinators at Orti Generali

Documentation from Orti Generali's Mirafiori Sud site notes that the Mirafiori district gardens have contributed to greater biodiversity for pollinators, a claim referenced in the project's submission to the Council of Europe Landscape Award and in the European Forum on Urban Agriculture (EFUA) project profile.

The project integrates non-crop flowering species at field margins and in a dedicated pollinator strip, a design approach that has become standard in Italian agri-environment schemes at larger scales but remains less common in municipal urban garden programs, where productive space is typically maximised over habitat provision.

Plant Species Composition and Its Effects

Beyond pollinators, Italian urban gardens support measurable plant species diversity — including volunteer (spontaneous) species that colonise disturbed edges and uncultivated strips. Studies in Bologna-area gardens have recorded 60–80 spontaneous plant species per site, with legumes and composites particularly well-represented. While some of these are considered garden weeds, several are significant resources for specialist bee species that cannot use the generalised flowers of vegetable crops.

The tension between maximising food production and preserving biodiversity habitat is documented in Italian urban garden literature. Programs that explicitly reserve space for non-crop vegetation — Orti Generali being the most-cited example — record higher pollinator diversity than programs where every available sq m is in vegetable production.

Measurement Methods Used in Italian Studies

Italian urban garden biodiversity studies have used three primary sampling approaches:

• Pan traps: Shallow bowls filled with soapy water, placed at ground level and canopy level; collect foraging insects over standardised periods. Fast to deploy; does not require specialist field identification at capture stage.
• Transect walks: Timed observer-walks along fixed routes, recording all flower-visiting insects within a defined observation width. Captures active foraging behaviour and plant-pollinator interactions.
• Nesting habitat surveys: Assessment of potential nesting resources (bare soil area, dead wood, hollow stems) to estimate habitat suitability beyond foraging.

The six-city Milan-coordinated study used all three methods in combination, allowing comparison of abundance data (pan traps), interaction data (transect observations), and habitat data (nesting surveys) across urban garden types.