Some city parks may be just as good bee habitat as protected natural areas are, according to a new study by researchers in Poland. The findings are a bit of good news for pollinators, which have been on the decline worldwide. The study also suggests how simple tweaks to the management of urban green spaces could help them support greater bee diversity.
Past studies have documented that urban landscapes as a whole tend to support fewer bees than natural areas – a not surprising result, since concrete and asphalt don’t provide much nectar. But this is among the first to compare bee communities in urban green spaces to those in natural landscapes, arguably a more apples-to-apples comparison.
“Efforts at mitigating global biodiversity loss have often focused on preserving large, intact natural habitats,” the researchers write. “However, preserving biodiversity should also be an important goal in the urban environment.”
The researchers analyzed bees collected from three different sites: Citadel Park, a large park in the center of Poznań, a city of half a million residents in Poland; a university botanical garden in the city; and a protected area, Wielkopolska National Park, located about 15 kilometers outside the city.
All three sites harbor similar bee abundance and diversity, the researchers found: They collected 2,799 bees representing 118 species from Citadel Park and 2,812 bees representing 101 species from the botanical garden. They compared these specimens to 2,861 bees of 110 species that had previously been collected from the national park using similar methodology.
“Large and diversified city parks may be a favourable habitat for a diverse and numerous group of bees, comparable to the fauna in natural habitats both in terms of the number of species and their abundance,” the researchers write.
What accounts for the thriving bee communities in the city parks? In a word, food. Lots of it, and lots of kinds of it. Citadel Park has trees, extensive plantings of cultivated shrubs and flowers, and some wilder areas besides. The botanical garden is more heavily managed, but it contains an extremely high diversity of plant species (which, after all, is its whole raison d’etre).
However, there are some differences between city bees and country bees. The urban parks have more social bee species than the protected area. Social bees tend to be highly adaptable and this may give them a greater ability to get along in human-modified environments. Meanwhile, the city parks have a relatively sparse assemblage of parasitic bees and fewer species of large bees than the protected area.
Citadel Park harbors more warmth-loving bees compared to Wielkopolska National Park. This is probably due to the urban heat island effect – that is, the tendency for cities to be warmer than surrounding rural areas – as well as the ruins of an old brick fortress and bare clay hillsides, which provide warm microclimates, found in the city park.
Citadel Park and Wielkopolska National Park have similar numbers of rare species (the botanical garden has fewer such species). However, the abundance of rare species is higher in the national park.
The urban parks also have a lower abundance of late-spring species compared compared to the national park. The researchers speculate that this could be because these species depend on flowers that grow in lawns and meadows, which are regularly mowed in the park. Limiting mowing while bee-friendly plants are flowering could help bolster bee populations, they suggest.
Source: Banaszak-Cibicka W. et al. “City parks vs. natural areas — is it possible to preserve a natural level of bee richness and abundance in a city park?” Urban Ecosystems. 2018.
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