Urban green spaces can act as refuge for bees. Bees appear to thrive better in cities compared to surrounding agricultural land. But are urban green spaces enough for conserving bees?
Declining bee numbers and diversity of other insects, some of whom are also pollinators, has led to the emergence of a growing concern regarding the natural biodiversity of the planet and the future of food security. It is clearly evident that anthropogenic stress is the main driver of the ongoing loss in biodiversity worldwide.
Cities occupy only 2-3% of the global land area but supports more than 55% of the world’s total population. To sustain this 3% of land surface and all that is in it, 44% of the world’s habitable land is already put under cultivation and the share is projected to grow massively as the world human population grows. And this is just half the picture as we haven’t yet taken our oceans into consideration.
The land area is not the only thing to account for. It is all that lives on it that concerns us. All the food we eat comes from plants. All the meat and other animal products we consume comes from animals that sustain on plants. And 75% of all the plants we cultivate depends on pollinators. We have already lost a large percentage of wild bees and other insects to the ongoing extinction event which is often termed the sixth mass extinction or Anthropocene Mass Extinction due to its human-driven nature.
Cities are not a habitable place for living things other than humans. So are our agricultural lands because we do not tolerate ‘trespassers’ – both human and animal, and plants (we call them weeds!). We take legal actions against the first, spray pesticides or create physical and chemical barriers against the second and apply weedicides or simply pull out the third from our farmlands. Our cultivated lands are chemical laden, mechanical and lifeless monoculture farms that thrive on factory made chemicals we call nutrients, gallons of water and lots of fossil fuels.
Intelligent as we are, we still do not realise the simple fact that the whole planet is a network of different entities, each connected to the other and each dependent on the rest, we humans being an integral part of it. If one small unit collapses, the whole structure caves in. Sitting at the top of the pyramid we ignore the small creaking sounds underneath as fibre by fibre the monument erodes.
For the urban human it is a different story altogether. He is disconnected from his very source itself – nature. Attempts at reconnecting the city dweller with nature have led to proposals about scaling up the number and size of urban green spaces like parks, botanical gardens, community gardens, green avenues, home gardens, rooftop gardens, urban vacant lots and more of the type. Many countries have already passed legislation that require every person to be within some minimal distance to greenery and easy access to nature for all. Connection with nature is essential for both our physical and mental well-being. We shall talk about the health benefits of greenery elsewhere.
With more than half the human population living in cities there is a lot that can be done to conserve bees and biodiversity. A large portion of our food production can be brought within the premises of our cities if proper planning be done and strong initiatives from both the people and the government be undertaken. Let’s take a look at how urban green spaces can help conserve bee numbers and biodiversity in our cities.
Concrete surfaces impact bees negatively but there is a solution
The proportion of impervious surface is often used as an indicator of the degree of urbanization of a site. Many studies have shown that increasing area of impervious surface have negative impacts on bee population and diversity. They show a sharp fall on these two parameters when compared to surrounding rural landscapes. Including floral patches that provide food resources and favourable habitat for bees in urban settings can offset some of the negative impacts of concrete ground covers.
Cavity nesting bees thrive while ground nesting bees decline in urban green spaces
Bees (Hymenoptera: Anthophila) are said to fare pretty well in urban settings compared to other insect taxa like Lepidoptera, Diptera and Coleoptera. A particular category of bees thrives better in urban environments. It is the cavity-nesting bees. Due to the presence of buildings and many constructed structures, cavity-nesting bees have adapted to exploit the urban environment to their advantage. Their abundance thus appears to be disproportionately more to other bee taxa in urban samples when compared to samples taken from nearby rural or semi-urban areas.
Arranging bee hotels on green roofs, domestic gardens, parks and allotments have significantly increased the number of cavity nesting bees in urban areas.
However, ground nesting bees decline with increased area of impervious surfaces, a measure of urbanization.
Making room for ground nesting bees in cities
Decreasing the area of impervious ground covers and replacing them with soil can help alleviate the problem of declining populations of ground-nesting bees. Urban green spaces like parks, gardens, old golf courses with native trees and shrubs and low intensity land management have shown positive effects on ground-nesting bee populations.
Even home gardens and urban parks that follow a no-till, no-mowing and no-pruning policy or a low frequency land management regime, help provide favourable habitat to ground-nesting bees and a variety of other insects, small mammals and birds.
Man-made structures like soil squares, which are concrete tubs or indentations on the ground filled with soil, has shown ground-nesting bees successfully using such provisions for nest construction.
Moreover, increasing the area of permeable surfaces and plant cover in cities can reduce the urban heat island effect and better management of stormwater that prevents urban flooding and also recharges ground water levels.
Creating green corridors with urban green spaces could help to connect the bee community
Urban green spaces can connect natural wild pollinator populations to urban populations by creating a network of natural and semi-natural habitats that serve as corridors for movement of wild bees. Urban green spaces act as steppingstone habitats for allowing free movement of pollinators to suitable environments.
But connecting wild native bee populations to reared ones which are generally exotic poses another threat – the spread of new diseases. So, instead of rearing more honeybees for pollination services we must work towards increasing this ecosystem service from wild bees. And that can be only done by creating favourable resource rich habitats for them.
More of urban green spaces with perennial plant gardens and no-mow grass lawns
Numerous studies have shown a decline in bee numbers and diversity with increased mowing frequency.
Native plants are lost, nests and larvae destroyed when lawns and gardens are mown. Soil tillage is another reason for declining populations of ground-nesting bees in both agricultural and urban gardens.
Planting perennial native plants have recorded 50 times more visits by bumble bees over control plots.
Undisturbed meadows with perennial flowering varieties provide more nectar and suitable habitats for bees and other pollinators.
Converting grass lawns to flower gardens can increase bee populations across the city and provide more pollination services to urban farms.
A big fat YES to organic gardens!
Pesticides are the prime cause of insect death in agricultural environments. Bees are affected equally. Neonicotinoids have already caused a ruckus, killing off bees in and around fields where the pesticide has been used.
A growing consciousness among urban gardeners about the harmful effects of pesticides on human health and declining pollinator numbers have led to shifting favour towards organically grown food. Organic gardens are favourite spots for bees and plants benefit from the increased pollination service received from higher bee visits.
Green roofs to support pollinators and combat heat islands
Many cities are shifting towards utilizing rooftops for increasing area of total green cover. Green roofs not only provide resource rich steppingstone habitats for bees but also lower temperatures of buildings that heat up due to the urban heat island effect.
Studies have shown green roofs role in supporting urban biodiversity. Quite a large variety of bees have been recorded foraging on green roofs but only buildings with less height were successful at attracting them. However, the proportion of cavity nesting bees and generalist bees recorded from green roofs were still higher. Surrounding habitat including proximity to natural spaces had a strong influence on the diversity and frequency of bee visits on roof top gardens.
Beekeeping can be cool but too much of one thing is not good
Knowledge about declining bee numbers and concern for the environment has led to a hype in urban beekeeping. As genuine as the concern may be, many urban beekeepers do not know yet that they may be causing more harm than benefit to the bee community.
Bees kept for honey comprise just two or three species at most – Apis mellifera, Apis cerana and some stingless bee species. They are all generalist foragers by nature.
Increasing bee population with just a few domesticated bee species without providing enough resources for them to feed on creates competition with other wild bees. Due to their larger numbers and generalist nature, honeybees out-compete native wild bees. Creating habitats for wild bees by planting resource rich native plants and trees have shown to benefit native bees and specialists.
More woody trees along avenues and parking lots
Large flowering woody trees provide an abundance of high-quality pollen and nectar for feeding bees and other pollinators when compared to the same area of small plant gardens. They also provide habitat for birds and small mammals. Many bees prefer nesting on high branches of woody trees and thus are benefited. A study done in the US have listed many woody trees that host numerous species of bees and can boost urban bee diversity if plantings are amplified by both area and density.
Large woody trees in urban green spaces also provide shade and can lower high temperatures common in cities. Placing them along avenues and parking lots made of impervious asphalt can absorb large amounts of heat, cooling the ground surface in return.
YES, to non-native but NO to invasive and hybrid ornamental plants in urban green spaces
Invasive plants are a clear no but non-native and some ornamental varieties have proven themselves attractive to a number of bee species. Most urban bee species are polylectic and will include flowers with high quality pollen and nectar readily into their diet.
Many research papers that studied for attractiveness of native plants over non-native plants have found no significant differences in bee visitation rates between native and non-native flowering plants. In fact, non-native flowering plants tend to maintain the phenology of their native climate, and this helps in providing yearlong pollen and nectar rich resources for bees when planted in urban green spaces. Non-native plants are also more resistant to invasive pests that may have originated in their native land (often the case for tropical plants).
But some hybrid ornamental varieties that have been selected for showy flowers are not favoured by bees because they do not conform to nature’s fit and so must not be planted amply.
Native flowering plants, woody trees and wildflowers are favourites for native bees and specialist bees so native flowering plants and trees always takes the top spots when it comes to planting bee friendly gardens.
Conclusion
Research done till date suggests that urban green spaces can help support bee populations in cities. But more research is needed to understand the ecological dynamics of urban bees and future manifestations of practices currently deemed favourable. There have been many instances in biodiversity conservation projects where endeavours aimed at proliferating the beneficial effect of selected practices have generated unknown and unwanted outcomes. Such things generally happen when conclusions are reached without proper or incomplete understanding of ecological phenomenon. One practice that have yielded good results in one location may not generate the same outcome in another region. So, steps should be taken carefully and tailor-made to the need and characteristics of the particular region under observation.
More initiatives from governments and non-governmental organisations are needed to combat and reverse the ongoing pollinator collapse.
At an individual level many small steps can be taken towards bee conservation in urban areas. It may be as simple as maintaining a small backyard garden or a few flowering plants on your balcony and not spray chemical pesticides on them.
Just keep an eye out for bees and pollinators in your own garden or your neighbour’s or at the flowering plants growing in the local park while you take your stroll. Notice which flowers the pollinators like. Learn if the plant is native or exotic or even invasive. Then decide accordingly if that plant should be promoted to attract more pollinators. Such small initiatives can help save the global pollinator population from extinction.