Attracting indigenous pollinators to urban greenspaces

Abstract

Urban greening actions across the world are being carried out to support resident, rare and locally extinct insect pollinators. In parallel, an array of best-practise resources have been designed to support build-environment practitioners and professionals seeking to or tasked with implementing greening actions for pollinators. Three main themes permeate these resources: (1) small greenspaces can provide large ecological benefits; (2) high-quality pollinator habitat should include a large share of indigenous plant species; and (3) considering stakeholders aspirations, motivations, experience, and concerns is critical for designing effective actions. Despite high interest in implementing these actions, few projects have evaluated their ecological benefits or demonstrated achievement of specific objectives. Even fewer have been specifically co-designed by practitioners and researchers to bridge the science-practice gap. Here, we demonstrate the success of a co-designed greening action in attracting indigenous pollinators to an urban greenspace. We compiled a plant-pollinator interactions dataset in a public park, within a densely urbanised municipality, that was purposefully greened with indigenous plant species to support existing and attract new indigenous pollinators. We then assessed: (1) how pollinator species richness and species-specific occupancy varied amongst plant species, and how these metrics compared between the existing greenspace plant species and the new added indigenous ones; (2) the effect of flower cover of the added indigenous plant species on the probabilities of occurrence of indigenous and introduced pollinators; and (3) the effect of the added indigenous plant species on the structure of the greenspace plant-pollinator ecological network. An addition of only six indigenous plant species resulted in a 2.5-fold increase in the number of indigenous pollinator species and other flower-visiting insects observed in the park. The added indigenous plants established interactions with all the indigenous pollinators and remarkably almost half of these were found interacting exclusively with the added indigenous plants. Additionally, the number of indigenous pollinators associated with a given plant species was on average 3.5 times higher for the added indigenous plants than for the baseline ones and the probabilities of occurrence of indigenous pollinators were on average invariable higher in the added indigenous than in the baseline plant species. The plant and insect community changes sparked by the greening action resulted in concomitant changes to the structure of the sites plant-pollinator network. We found an average 4.2-fold increase in the number of interactions linking the greened compared to the baseline network, with almost half of these interactions comprising those between the added indigenous plants and indigenous pollinators. By showing that replacing lawn with indigenous plants leads to positive ecological outcomes for indigenous pollinators and other flower-visiting insects - including increasing the overall greenspace biodiversity by attracting new indigenous insect species to the site - our findings contribute to the evidence base underpinning best-practise resources and provide encouragement to build-environment practitioners and professionals responsible for or endeavouring to support existing or bringing insect pollinators back into our cities. Our study establishes a pathway and acts as a catalyst for researchers and government officials seeking to collaboratively demonstrate that greening is a valuable and sound investment for achieving goals from local, regional and global biodiversity and sustainability plans and policies.