Wild insect pollinators are critical to the formation of seeds and fruit in around 90 percent of flowering plant species, and 75 percent of crop species. Although bees are the best-documented of the insect pollinators, there are many other groups of insects that are also involved. These include flies, beetles, moths, butterflies, wasps and ants. The populations of these crucial organisms are in decline worldwide, mostly due to the activities of humans.
In response to this situation, the Swedish Society for Nature Conservation launched a campaign to encourage the public to create more favorable conditions for pollinators in their private gardens. The project, known as “Operation: Rädda bina” (“Operation: Save the bees”), ran between 2018 and 2021, and around 11,000 Swedes responded initially to the appeal. Researchers from Lund University have now evaluated the success of the measures undertaken by the citizen scientists in their own gardens.
People who responded to the campaign were asked to register pollinator-friendly interventions that they had carried out in their gardens and other green spaces. The campaign encouraged three different interventions: (i) establishing a flowering “garden meadow,” (ii) planting bee-friendly flowers in a garden, and (iii) setting up bee hotels. Those who registered an intervention then completed online questionnaires about their intervention and their perception of any changes in pollinator populations in their garden.
“We wanted to investigate measures that the public themselves chose to implement in their garden, and how these can be the most efficient,” said study co-author Anna Persson.
Of the initial respondents, just over 3,200 completed the project. Of these, 809 established flowering meadows, 1,232 planted bee-friendly flowers in their gardens, and 1,210 established a bee hotel. Approximately 19 percent of meadows, 23 percent of plantings, and 20 percent of the bee hotels were situated in the 10 most populated cities/municipalities in Sweden.
When the citizen scientists had to assess the prevalence of pollinators in their gardens, after establishing their intervention, they were asked whether they saw “many,” “few,”,or “no” insects. Because this was rather a simple and subjective metric, the researchers also asked the respondents to count the exact number of pollinators they saw in the garden in a 10-minute period on a sunny day in July. This data was used to confirm the accuracy of the simpler abundance categories, namely many, few or none.
The results, published in the journal Frontiers in Sustainable Cities, indicate that pollinators benefited most where flowering meadows were allowed to grow. This could be where a person decided not to mow a patch of grassland and let it rather grow tall with wild flowers, or where a meadow stood unused and untouched for several years. In both instances, the benefit was greater if the meadow was older and if there was a diversity of flowering species present.
People who planted bee-friendly flowers in their garden found the benefit for pollinators was greatest when the flowering plants were older and covered a large area. This is important, because people who initially record no benefit from their newly-planted flowers should not give up, but should continue with the knowledge that older, more established flower beds will bring the pollinators in time.
Bee hotels, in turn, tended to attract more inhabitants if they were located in flower-rich gardens, if they were older, and if the nest holes were no larger than one centimeter in diameter.
Anna Persson believes the results of the study are helpful when giving guidance to those who want to make their gardens attractive for pollinators.
“For example, we can show that it will pay off to create large and species-rich meadows and flower plantings, and that it is important not to give up after a few years, because the measures improve over time. This should be emphasized in future campaigns.”
Persson also hopes that the results can inspire more people to adapt their own green space so that it becomes more favorable for insects. Gardens often cover about 30 percent of the land area in cities and towns, so garden owners, as a group, have the potential to contribute considerably to urban biodiversity.
The accuracy of citizen scientist accounts can sometimes be questioned, because the participants may have certain expectations about the results they will see.
“Our study could be affected by so-called ‘expectation bias,'” said Persson. “This means that people who have taken measures and created more species-rich gardens also expect to see more insects, and thus risk reporting too high a number.”
However, the researchers found that the actual counts of insects correlated well with what participants categorized as “many” or “few” insects. A total of 350 participants counted the insects they saw in their garden in a 10-minute period, and their responses helped to verify the accuracy of the dataset.
This study is particularly relevant since a third of Sweden’s bee species are currently considered to be endangered. The results show that steps taken by individual homeowners to make conditions in the garden more favorable to pollinators really do make a difference. This is encouraging, as pollinators are critical for functioning ecosystems and need all the help they can get at this stage.
“The situation for bees and other pollinators shows that measures to help them are important,” said Karin Lexén, Secretary General of the Swedish Society for Nature Conservation. “It’s great that the campaign has attracted so much attention, and that citizen science can continue to contribute to new knowledge.”
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