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Lay Summary for paper 'A systems approach reveals urban pollinator hotspots and conservation opportunities'

15 January 2019

We have prepared a lay summary of our paper recently published in Nature Ecology and Evolution, which outlines the key points of the study.

'A systems approach reveals urban pollinator hotspots and conservation opportunities' by Katherine C. R. Baldock, Mark A. Goddard, Damien M. Hicks, William E. Kunin, Nadine Mitschunas, Helen Morse, Lynne M. Osgathorpe, Simon G. Potts, Kirsty M. Robertson, Anna V. Scott, Phillip P. A. Staniczenko, Graham N. Stone, Ian P. Vaughan, Jane Memmott in Nature Ecology and Evolution

 

RATIONALE

In this study we set out to identify important land uses for pollinators in urban areas in the United Kingdom. We used our data to identify key forage plants for urban pollinators and to propose strategies to improve pollinator conservation in towns and cities.  This was the first systematic survey of all insect pollinator groups across all urban land uses, comparing plant-pollinator communities from 360 sites located in four UK cities (Bristol, Reading, Leeds and Edinburgh). We mapped all land uses in each city and sampled the following nine land uses: allotments (equivalent to community gardens), residential gardens, cemeteries & churchyards, urban nature reserves, parks, road verges, other urban greenspace, manmade surfaces, and pavements. Each land use was sampled in ten sites in each city, leading to 40 replicates per land use.  We sampled the insects visiting flowers, and recorded the plant species they visited, along a 100 m transect at each site, sampling each site three times over two years and walking more than 2000 transects.  We used the data to address the following questions: (1) Which land uses have higher pollinator abundance and species richness? (2) Which land uses have higher flower abundance and species richness? (3) Is pollinator abundance in residential gardens linked to higher household income? (4) Which plant species are visited more often by pollinators? (5) How do flower and pollinator abundance compare between land uses when considering the data at the level of entire cities? (6) How can the robustness of pollinator communities to species loss be improved at a city scale?

 

SUMMARY OF RESULTS

1. Which land uses have higher pollinator abundance and species richness?

Approximately 5000 flower-visiting insects were sampled, the majority (90%) were identified to species by experts. Analyses showed that numbers of bees were higher in allotments and gardens compared to the majority of other land uses. Numbers of hoverflies were similar in allotments, gardens, cemeteries, nature reserves and parks, with statistically higher abundances in allotments and gardens compared to other greenspaces, verges and pavements.  Non-syrphid Diptera were statistically less abundant on pavements and manmade surfaces than in any other land use, and statistically more abundant in allotments and cemeteries than on road verges.  There were no differences in bee or hoverfly species richness among land uses, species richness for non-syrphid Diptera was statistically lower for pavements than most other land uses.

2. Which land uses have higher floral abundance and species richness?

Floral abundance was statistically higher in allotments and gardens than in all other land uses.  This pattern was driven by the higher flower abundance of non-native plant taxa in allotments and gardens; native flower abundance did not differ among most land uses.  Similarly, the richness of flowering plants was statistically higher in allotments and gardens than in all other land uses, a pattern caused by the higher richness of non-native taxa in allotments and gardens than in all other land uses.

3. Is pollinator abundance in residential gardens linked to higher household income?

We found that numbers of pollinator visits to flowers were statistically higher in gardens located in neighbourhoods with higher household incomes which suggests that socio-economic factors can influence the quality of floral resources available for pollinators in urban gardens.

4. Which plant species are visited more often by pollinators?

Insects were recorded visiting a wide range of native and non-native plant taxa.  We used models to show that 14 plant species (nine native and five non-native species), were visited significantly more often than expected in three or more cities, which suggests that they may be particularly important for pollinators in urban areas.  Four native species (creeping thistle, hogweed, creeping buttercup and dandelion) and one non-native species (borage) were visited significantly more often than expected in all four cities.

5. How does pollinator abundance compare between land uses when considering the area of each land use in each city?

We combined our data on pollinator abundance with the total areas of each land use to estimate the numbers of pollinators per land use in each of the four cities. Although our data show that allotments received high numbers of pollinators per unit area, they contained relatively few pollinators at a city scale (1-3%) as allotments comprise less than 1% of the area of cities.  Gardens comprise large areas (24-36% of cities) and also have high numbers of pollinators, thus when the data were scaled up to city level, gardens hosted an estimated 54-83% of pollinators in the four cities.  In comparison, urban greenspace areas (parks, roads and other greenspace combined) comprise 27-35% of the study cities but have far fewer pollinators at a city scale compared to gardens.  Managing public greenspaces to benefit pollinators thus provides a clear opportunity for city-level improvement of urban areas for pollinators.

6. Which land uses are important in terms of the community robustness at a city scale?

A modelling approach was used to test the effect of increasing the area of each land use in turn to the four cities, measuring how the additional area of each land use affected plant-pollinator community robustness at a city scale.  Robustness is a measure of how a community responds to species loss; robust communities can withstand some extinction whereas species loss in fragile communities leads to a cascade of other extinctions.  The model predicted that increasing the area of allotments resulted in the greatest increase in the plant-pollinator community robustness at a city level.

This approach was also used to predict the effect of increasing the flower abundance of three common native plant species (dandelion, daisy and white clover) in parks, road verges and other greenspaces, showing that this led to increased plant-pollinator community robustness at a city scale.  As the abundance of all three plant species is likely to be increased by reducing mowing, this suggests that reducing mowing frequencies is likely to benefit pollinator communities.

 

CONCLUSIONS

Based on our findings, we make three recommendations for improving urban areas for pollinators:

1. City planners and local councils should look at ways to increase the area of allotments in towns and cities.  Allotments are good for pollinators as well as people and increasing their area by even a small amount could have a big effect on the robustness of plant-pollinator communities at a city scale.

2. Ensure gardens are maintained in new developments and that existing gardens are managed with pollinators in mind.  Gardens make up a large proportion of urban areas and better garden management could have a significant effect on pollinator conservation.

3. Improvement of public greenspace management for pollinators, e.g. through mowing less often and adding flowering plants, bushes and trees.