Urban gardens provide a reliable food supply for pollinators

Urban gardens are an important part of the cityscape and they add to the ecological, environmental and aesthetic value of a city. A recent study by the scientists at the University of Bristol discovered that urban gardens provide a steady supply of energy-rich nectar from March to October.

Pollinators are guaranteed a steady food supply if they visit numerous gardens, despite variations in both the quantity and timing of nectar production from one site to another. This is in contrast to earlier research on agriculture, where pollinators are subjected to periodic nectar production cycles with apparent seasonal gaps.

“In this study, we investigate for the first time how the nectar supply of residential gardens varies in space and time and use our results to develop evidence-based management recommendations for pollinator conservation in urban areas,” wrote the study authors.

“Nectar sugar is the main energy source for adult pollinators, particularly important for powering their flight muscles, but nectar resources have declined in rural areas due to land-use change.”

The researchers noted that the findings of their study can be used to establish evidence-based management suggestions for pollinator conservation in urban locations.

“We knew that gardens were important habitats for UK pollinators, providing 85 percent of nectar sugar in urban landscapes and a great diversity of flowering plants,” said Nick Tew, a PhD student in Bristol’s School of Biological Sciences. 

“However, we did not know how nectar production varied between individual gardens or through the months of the year. It is particularly important to understand garden-to-garden variation to advise how best to collectively manage our gardens for pollinators.”

The researchers surveyed 59 home gardens in Bristol, UK, at monthly intervals from March to October. The researchers coupled floral abundances with nectar sugar data for each of the 472 data samples to measure each garden’s nectar output, examining the size, temporal stability, variety, and composition of garden nectar supplies.

The results revealed that there is a huge variance in the nectar output of the surveyed gardens ranging from 2 grams to 1.7 kilograms for a year, and this was dictated not by the size of the garden, but by how people decided to maintain their gardens.

As a result of the efforts of several independent gardeners located throughout a city, a stable and diverse supply of food for city pollinators has emerged.

“We measured the amount of nectar produced by flowers in 59 residential gardens in Bristol. We found that individual gardens vary in both how much food they provide and when they provide it during the year. However, because flying pollinators like bees can visit many different gardens, they are likely to be able to find food in residential neighborhoods whenever they need it.” said Nick.

“This means that everyone has the potential to help pollinators in a meaningful way, even with a small garden, and there is a lot of room for improvement, with some gardens providing hundreds of times less food than others, depending on what people choose to plant, weed, prune or mow.” explained Nick further.

The findings of the study can be applied by gardeners to aid the pollinators and thereby contribute to the biodiversity of the city. 

Gardeners can help by planting open flowers that bloom later in the year, because tubular blooms are only accessible to long-tongued insects like bumblebees provide 79 percent of nectar in late summer and autumn. Shrubs are also a good way to squeeze a lot of flowers into a small space, and they are responsible for 58 percent of all nectar in gardens.

The research is published in the Journal of Applied Ecology.

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By Ashikha Raoof, Earth.com Staff Writer