Ecological responses of insect pollinators and flower-visitors to indigenous plant additions in urban greenspaces

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Ecological responses of insect pollinators and flower-visitors to indigenous plant additions in urban greenspaces

Luis Mata^1,*, Estibaliz Palma², Sally Dawe^3,4, Maree Keenan^3,5, Phoenix Wolfe^3,6 and Amy K. Hahs¹

¹ School of Agriculture, Food and Ecosystem Sciences, University of Melbourne, Parkville 3010, Australia.

² Lookfar Research, Black Rock 3193, Australia.

³ Centre of Excellence for Biosecurity Risk Analysis, University of Melbourne, Parkville 3010, Australia.

⁴ Greater Dandenong City Council, Dandenong 3175, Australia.

⁵ Yarra Ranges Council, Lilydale 3140, Australia.

⁶ North East Catchment Management Authority, Wodonga 3690, Australia.

⁷ Trust for Nature, Melbourne 3000, Australia. 

* Corresponding author: lmata@unimelb.edu.au

Abstract

1. Urban greening actions are being carried out globally to support insect pollinators and other flower-visitors, with best-practise resources developed for planning and implementation. Despite high interest, few projects have evaluated ecological benefits, demonstrated achievement of specific objectives, or been co-designed by practitioners and researchers to bridge the science-practice gap.

2. We show how a targeted greening action led to positive ecological changes in the species richness, flower visitation and network structure of a greenspace’s community of insect pollinators and flower-visitors. We compiled a plant-insect interactions dataset in a public park within a densely urbanised municipality, where newly added indigenous plants partially replaced lawn among pre-existing vegetation to support indigenous pollinators and flower-visitors. We assessed: (1) species richness and visitation of pollinators and flower-visitors across pre-existing and newly added plant species; (2) the effect of flower cover on indigenous and introduced pollinator and flower-visitor probabilities of visitation; and (3) the effect of the added indigenous plants on the structure of the greenspace’s plant-insect ecological network.

3. Adding 150 m² of garden beds planted with six indigenous plant species resulted in a 2.5-fold increase in indigenous pollinator and flower-visitor species in the park. On average, the number of pollinator and flower-visitor species per plant was 3.5 times higher for the added indigenous plants, and the visitation probabilities of indigenous pollinators and flower-visitors were on average consistently higher in the added than pre-existing plants.

4. We found an average 4.2-fold increase in the number of interactions linking the greened compared to the pre-existing network, with almost half of these comprising those between the added indigenous plants and indigenous pollinators and flower-visitors.

Practical implication: By shedding light on the fact that it is possible to spark positive ecological outcomes for indigenous insect pollinators and flower-visitors by replacing lawned areas with indigenous plant species, our findings make a key contribution to the evidence base underpinning best-practise greening resources, and offer guidance and support to a wide-ranging group of built-environment practitioners and professionals, seeking to support existing insect pollinators and other flower-visitors or to bring them back into our urban environments.

Keywords: Bees, Butterflies, Co-design, Ecological networks, Evidence base, Hoverflies, Nature in cities, Urban ecology, Urban greening