28
Jan
Your Garden and Town Landscapes Are the Change that Pollinators Need, Study Finds
(Beyond Pesticides, January 28, 2022) Do city dwellers, who typically have smaller-sized greenspaces on their lots, have any role to play in supporting pollinators? Absolutely, according to a recent study of Bristol, England residential gardens. The researchers find that the amount of “floral resource” — the abundance of actual blooms, which translates roughly to amount of nectar production — varies widely across gardens and yards, and that small urban gardens and greenspaces are actually some of the most pollinator-friendly resources. The study notes that that several factors influence how well these resources provide food for pollinators, most important among which are pollinator-friendly management practices. Beyond Pesticides notes that there are multiple resources in the U.S. on making gardens and greenspaces “friendly” and useful to pollinators, including its own BEE Protective guidance on garden and landscape management, and that employing organic management practices is critical.
The researchers hope to “develop evidence-based management recommendations to support pollinator conservation in towns and cities.” Their paper, published in the Journal of Applied Ecology, reports that the size of the Bristol gardens they studied actually had minimal relationship to the amount of nectar produced by the plants in them. There are factors beyond size that determine the utility of urban gardens to pollinators, including specific gardening practices, the diversity of plantings, the match between local pollinators and the morphology of blossoms, and the timing (“temporal availability”) of various species’ efflorescence (floral blooming).
The study evaluated nectar quantities and timing, species variety (636 taxa), and number of “floral units” (more than 2 million) across the 59 surveyed gardens and yards, whose sizes ranged from 31.3m2 to 407.7 m2. According to the paper, “Garden nectar production peaked in mid-summer, but individual gardens differed markedly in both the magnitude of their nectar supply and its temporal pattern.”
In evaluating which kinds of flowers are available when — in terms of both levels of nectar sugar available and flower morphology, which dictates what kinds of pollinators can access the nectar — the authors make recommendations about plants residents can install to make nectar sugar as reliably available to multiple pollinators across the season as possible. (See section 4.3 of the study paper.)
A note on that morphology point: organisms and native flowering plants in a given ecosystem have tended to co-evolve, and thus, be well adapted to their symbiotic relationship — a concept called “niche complementarity.” Introduction of non-native species can interrupt this “harmonic balance” because not all flowering plants work for all pollinators. For example, hummingbirds tend to favor the color red, and — with their long beaks and tongues — blooms that have long, narrow shapes (such as honeysuckle, penstemon, trumpet flower, and bee balm, among others). Honeybees, on the other hand, cannot see the color red, and do not have such extensive “gear” with which to retrieve nectar from those kinds of flowers. Instead, they prefer flowers of other colors (especially yellow), and those with a more-open structure that provides a bit of a “landing pad.” Coneflowers, black-eyed Susans, poppies, lilacs, and sunflowers are among their favorites.
The researchers note some limitations to their study. First, although they observed no significant difference in nectar sugar production between urban greenspaces in Bristol and in three other cities in the United Kingdom (UK), analogous data for non-UK cities are unavailable, so the validity of the study for other regions is unknown. Also, the data for the study are from 2019; whether the authors’ observations and conclusions (based on those data) are valid for any other given year is not clear.
One of the study’s authors, Nicholas Tew, remarked, “Most of the nectar produced in gardens is by a shrub in the corner or a border around the edge of the garden. There are some very flower-rich small gardens and some very flower-poor big gardens.” He also noted that the biggest nectar producers were shrubs, many of which grow fairly compactly and when in bloom, provide very dense flower clusters, and — perhaps surprisingly — that “the diversity you get in urban areas is remarkably high, much higher than most natural habitats, even nature reserves.”
This diversity can, according to the authors, support a greater level of pollinator diversity than surrounding rural areas are able to do. By way of explanation, Mr. Tew asserts that the variety of plant species across urban gardens is greater than what would be found in a natural habitat, and adds that the crazy quilt of small gardens across a city “create[s] much richer nectar resources” than would a small number of larger planted parcels. The researchers assert that, across the UK, gardens and yards provide an estimated 85% of nectar in urban areas.
The paper concludes: “Urban residential gardens differ markedly in the magnitude and temporal pattern of nectar supply, but bigger gardens are not necessarily better for feeding pollinators. Instead, the management decisions made by individuals are particularly important, with gardeners able to control habitat quality if not quantity. By visiting multiple gardens which differ independently in plant species composition, pollinators have the potential to access a diverse and continuous supply of nectar in urban landscapes.”
In the context of the pollinator (and general biodiversity) crises, this study offers encouragement to everyone, and to urbanites in particular, to do whatever is possible to provide food sources for pollinators, who are under significant duress from a variety of factors, including pesticide use, land management practices, intensity of land uses and increasing fragmentation of habitat, and to some extent, the climate crisis.
Nearly everyone can create one or more oases of food and habitat for pollinators, whether through a giant wildflower meadow or a few potted plants on a fire escape. The Pollinator Partnership lays out the benefits to pollinators of urban “patches” of plants, including weeds: “Green space within cities surrounds us and provides pollinators with the pollen and nectar they need. City parks, home gardens, planted medians, manicured municipal spaces, rooftop gardens, and even weedy remnants are pollinator habitat within urban areas.”
Help with creating such oases can be found across multiple resources, including:
- Gardening for Biodiversity, Pollinator-Friendly Seeds and Nursery Directory, and a Resources and Educational Materials webpage, all from Beyond Pesticides
- Planting for Pollinators, from The Nature Conservancy
- Enhancing Urban and Suburban Landscapes to Protect Pollinators, from Oregon State University
- Pollinator-Friendly Native Plant Lists, from the Xerces Society for Invertebrate Conservation
Additionally, see Beyond Pesticides’ BEE Protective Habitat Guide. Though an older resource, it nevertheless has great information on specific resource-rich species to support pollinators organized by bloom time.
Spring is coming, so now is a great time to make plans for whatever green space you may have available. Any gardener would concur: there is little so hopeful as planting and then watching Nature do her thing. Consider installing and caring for a few (or a whole bunch of) flowering plants that will help support stressed pollinators. Then grab some lemonade and enjoy the flower-and-pollinator show!
Sources: https://www.theguardian.com/environment/2022/jan/19/small-gardens-vital-as-big-ones- conserving-bees-bristol-university- study?utm_term=61e8ec53ac83a81938ee24ff2deb4078&utm_campaign=GuardianTodayUK&utm_source=es p&utm_medium=Email&CMP=GTUK_email and https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2664.14094
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
