by Lauren de la Parra, Creative Climate Solutions
Pollinators play a vital role in human health and well-being, and we rely on them for the essential ecosystem services they provide. Pollinators – a category of wildlife that includes some species of birds, bats, butterflies and moths, flies, beetles, and of course, bees – are defined by their indispensable role in the reproductive processes of between 75-95% of all flowering plants. They are also keystone species in many ecosystems, providing critical support for the natural processes that maintain ecosystem health and species biodiversity.
The economic importance of these unsung heroes therefore also comes as no surprise – In Massachusetts, over 45% of agricultural commodities, including cranberries and many fruits and vegetables, rely on pollinators for healthy yields, with pollinators contributing an average of $1,200 per acre.
Pollinators are already in decline
It is alarming then to discover that pollinators’ numbers are dropping dramatically every year, particularly due to habitat destruction from land conversion to agriculture and development. According to the UN Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES)’ 2017 assessment report on pollinators, 16% of all vertebrate pollinators (including bats and hummingbirds) are at risk of extinction, and at least 9% of all insect pollinator species are also threatened – including 40% of bees, which are the most important pollinators in terms of global agriculture and plant reproduction. Honey bee populations in the United States have experienced unsustainably high loss rates in recent years, with commercial colony loss over winter exceeding 30% annually, up from a 10-15% historical average.
Compounding these losses are the catastrophic impacts of the parasitic mite Varroa destructor, which arrived in the US in 1987 and completely changed beekeeping on the global scale (V. destructor feed on bees’ organs, and transmit over a dozen viruses, while simultaneously suppressing bees’ immune systems; without treatment, infected colonies die within 6 months – 2 years). Combined with the still-prevalent use of harmful insecticides such as neonicotinoids, high colony loss rates begin to come into perspective. While many countries have banned neonicotinoids altogether, and their use has faced many legal challenges in the United States, they are still common today. However, there is hope for the bees here in Massachusetts: in early 2019, An Act protecting pollinators by eliminating harmful products was passed in the House of Representatives, and the Senate recently referred the bill to committee.
Enter climate change
As if these threats to survival were not enough for pollinators to contend with, climate change is exacerbating many of the impacts already being observed. As temperatures warm, some pollinator species are shifting their ranges to track migrating habitat. Combined with habitat loss and fragmentation from human activities, this climate-induced displacement can be devastating for pollinators. For instance, a 2015 study in Science found that the southern limits of the ranges of many species of bumblebee in Europe and North America have shifted north, by as much as 300km (186 miles) since 1975. Yet, the northern edges are staying the same, contracting their overall potential habitat.
Warmer long-term weather averages are also affecting the annual onset of spring, which has several important implications for pollinators. First, as spring shifts earlier, corresponding changes in the phenology, or the timing of biological events such as rate of development or date of emergence (Xerces Society), of both plants and pollinators are creating what is known as “phenological mismatch.” Flowers are blooming half a day earlier each year, corresponding to an almost month earlier blooming on average than 45 years ago. Many bees, however, are not awakening from their winter slumber at correspondingly earlier times in the year, meaning that flowers may be blooming before bees are ready to pollinate them. This can have cascading consequences, wherein plants are done flowering before they are pollinated, and when bees do awaken, there is not enough food available to sustain them. Add into the mix the fact that warmer temperatures and increasing frequency and intensity of drought can reduce the number of flowers that plants produce, as well as the amount of nectar and pollen they bear, and the potential impacts to bee livelihood become stark.
Pollinators in the city
There is good news and bad news for pollinators in urban environments. The good news is that recent studies have shown urban areas to be relatively more attractive and beneficial to pollinators than nearby farmland, pointing to the role cities can play in creating climate-resilient wildlife habitat. One recent study shows that bumble bees have higher survival and reproduction rates in cities and towns, while another found higher numbers of bee species in urbanized areas than in neighboring farmland in 12 UK cities and towns. Both teams speculate that this may be in part because of a reduced exposure to neonicotinoids and other pesticides in cities.
As urban farming and beekeeping continue to expand, awareness of the importance of pollinators among urban-dwellers is increasing, and campaigns to promote pollinator-friendly plantings have proliferated in many cities around the world. In part because so many cities tend to be located in coastal or riparian areas that support higher biodiversity, and also because surrounding landscapes are being transformed by inhospitable agricultural and renewables development, cities are becoming important refuges and migratory stopovers for many animal species, including pollinators. Combining refuge habitat in urban areas with pollinator-friendly practices in agriculture and renewables development could prove the winning combination for pollinator resilience – keep reading for more on this!
The bad news is that pollinators are known to be sensitive to increased heat, a hallmark of climate change that threatens to affect cities more severely than surrounding areas. The Urban Heat Island (UHI) effect, whereby urban areas tend to be warmer than surrounding natural areas by anywhere from 1-12˚C, results from the greater prevalence of impervious, heat-trapping surfaces and less cooling vegetation. The UHI can worsen existing impacts of climate change for pollinators, with a recent study finding that for every 1˚C increase in temperature, bee abundance in the city of Raleigh, North Carolina declined by 41%.
Hummingbirds are particularly susceptible to the impacts of heat; as temperatures rise, they are forced to find shade rather than continuing to feed on nectar, which their high metabolisms require in abundance to survive. Bats, too, experience acute effects of heat, including impacts to their ultrasonic hearing, affecting their ability to detect and catch prey. Cities cannot and should not replace wildlands in terms of habitat value, and conversion of wildlands is a crucial threat to biodiversity and resilience that must be proactively addressed and where possible prevented or reversed. However, cities have many beneficial roles to play in helping pollinators to survive and thrive.
Responding for pollinator resilience
In 2014, President Obama established a Pollinator Health Task Force to synthesize available research, conduct public education campaigns, develop pollinator habitat best management practices for all federal lands, and work with stakeholders to promote pollinator protection across the country. Since then, several states including Vermont, Maryland, and Minnesota have adopted pollinator-friendly solar development standards to encourage responsible renewables proliferation, and Massachusetts is now following suit. The Wildlife Conservation Society (WCS)’s Climate Adaptation Fund has recently supported two major pollinator-focused projects, one of which sets out to create 20 miles of climate-resilient hedgerow habitat for pollinators on farms in California’s Central Valley (Xerces Society), and the other which aims to create a network of fifty climate-resilient pollinator meadows using vacant lots throughout two neighborhoods in Philadelphia (National Wildlife Federation).
And speaking of cities, researchers and professionals alike are looking to Chicago, with its green roof ordinance promoting an ever-growing mosaic of rooftop gardens and greenery, to understand how urban green infrastructure can best support pollinator populations. Several studies have now documented increasing numbers and unique species of bees as Chicago’s rooftop landscape becomes greener, while observing that a diversity of pollinator-friendly plantings tend to enhance bee abundance in these spaces. Related work out of the Northeast Climate Adaptation Science Center is using Chicago as a case study for understanding the role of cities in monarch butterfly conservation as monarchs migrate between the Midwest and Mexico for the winter (reference).
Taking action
Creating and preserving habitat are the most important strategies we can advance for pollinator resilience in the face of climate change. More, and more interconnected, habitat can promote increased genetic diversity and access to food as pollinators become able to move more freely across landscapes, whether urban or rural. Planting pollinator-friendly vegetation in urban gardens and along rural farm fields alike can help to increase crop yields and support pollinator health, also helping to lessen the impacts of shrinking ranges that many pollinator species are experiencing under climate change. At the same time, avoiding pesticides and advocating for the elimination of harmful chemicals like neonicotinoids can have dramatic benefits for pollinators. Bee hotels, bat houses, and sugar water feeders for hummingbirds can attract these species and support healthy populations in a variety of land use settings.
If you are an urban-dweller, consider de-paving and planting trees to reduce localized impacts from the Urban Heat Island effect and provide additional urban pollinator habitat. No matter where you live, you can join the Million Pollinator Gardens Challenge, and follow it up by challenging your community to participate in Pollinator Week each June and to become a Bee City USA (or a Bee Campus USA for colleges and universities)! Each of us can play a role personally and within our networks and communities to support ecosystems adaptation for pollinator protection, advocate for the elimination of harmful products and destructive practices, and raise awareness about the critical role of pollinators in natural and agricultural systems.
Photo by Torrey Trust