Human land-use changes that result in the loss or degradation of natural habitat are a leading contributor to the decline of wild bee populations and of Apis mellifera health (Winfree et al. 2009; Potts et al. 2010; Otto et al. 2016). Urbanization, the conversion of lands for urban needs, is one of the leading forms of land conversion in the United States. As of 2005, nearly 80% of the United States population lived in or near urban areas, with developed land accounting for over 100 million acres of land (McKinney 2005; USDA 2012). Urban lands are becoming more prominent, as an average of 1.5 million acres of natural and semi-natural lands, like forests and pastures, were converted to developed land annually between 2002 and 2007 (USDA 2012). There is a clear need to consider pollinator conservation within these greatly expanding land areas.
Urban bees are important pollinators of gardens, parks, urban cultivated lands, remnants of natural areas, and various other green spaces (Frankie et al. 2005; McFrederick and LeBuhn 2006; Fetridge et al. 2008; Matteson et al. 2008; Tonietto et al. 2011; Larson et al. 2014). To support bees in urban landscapes, there must be available sources of forage for pollen and nectar, as well as suitable nesting sites (Westrich 1996; Wojcik and McBride 2012). Bees can naturally occur in unmanaged urban greenspaces (Gardiner et al. 2013; Sivakoff et al. 2018) but increasing efforts have been made to redesign aspects of urban development to create habitat and forage for pollinators.
Poorly managed and high-input lawns can be associated with environmental issues including water consumption, pollution, pesticide application and exposure, and fossil fuel use (McPherson et al. 1989; Davis and Truett 2004). Furthermore, lawns under traditional management protocols in urban areas provide limited habitat for wildlife, including pollinators (Stier et al. 2013). When turfgrass landscapes are managed sustainably, they can provide ecosystem and cultural benefits, including controlling water runoff, carbon sequestration, benefits to mental health, and reduction of noise pollution, among others (Krenitsky et al. 1998; Qian and Follett 2002; Stier et al. 2013; Beard and Green 1994). Current efforts in turfgrass science seek to improve the sustainability of the turf lawn, primarily through reduction of inputs. Research on turfgrass species selection has indicated that low-input grass species, specifically the fine fescue grasses (Festuca spp.) can perform well in a lawn setting when irrigation, fertilizer, and mowing inputs are greatly reduced (Dernoeden et al. 1994; Watkins et al. 2011; Braun et al. 2020). While great strides have been made to improve the sustainability of turf lawns by reducing inputs, managing lawns to intentionally benefit pollinators is a more novel concept.
Creating an effective pollinator-friendly lawn requires balancing potentially competing aims of growing pollinator forage while maintaining aesthetically-pleasing spaces that allow for recreation. In order to balance these aims, we used flowering species that are both able to compete with turfgrass for resources and can bloom at 6.5 cm or lower, a height that is amenable with standard mowing practices. This height restriction greatly limits the plant palette that may be utilized within a lawn setting. The species utilized in our bee lawn seed mix followed recommendations by Lane et al. (2019), who found that Trifolium repens, Prunella vulgaris ssp. lanceolata, and Thymus serpyllum were able to establish with turfgrass under typical mowing conditions. Further work on flowering species suggests and that Symphyotrichum lateriflorum and Coreopsis lanceolata were able to bloom under mowing pressure, and thus potentially able to establish within turfgrass depending on environmental conditions (Lane, unpublished data).
Human perceptions of lawns are often dictated by cultural and neighborhood norms for landscape appearance, as lawns that strongly differ from what is commonplace are not well received by the public. Traditionally, flowering plants within the lawn were viewed as a nuisance, with consumers spending $450 million on lawn herbicides and plant growth regulators in 2012 (Atwood and Paisley-Jones 2017). There is evidence to suggest that public perceptions of lawn flowers may be changing (Nassauer et al. 2009). For example, while a survey of lawn preferences in April, 2010 suggested that Minnesota homeowners preferred lawns that were free of weed infestation (Hugie et al. 2012), a more recent survey of park visitors in Minneapolis, Minnesota revealed that 95.4% of respondents supported the planting of flowering bee lawns within community parks; consumers felt these lawns were aesthetically pleasing and beneficial to bees (Ramer et al. 2019).
With a growing body of literature suggesting that lawn flowers may support diverse communities of pollinators, it is essential to provide effective ways to support pollinators within turf lawns. While studies have demonstrated the value that naturally-occurring flowers may hold for pollinators (Shwartz et al. 2013; Larson et al. 2014; Lerman and Milam 2016), and have suggested strategies to enhance the number of flowers observed in a turf lawn (McCurdy et al. 2013; Sparks et al. 2015; Lane et al. 2016), none have implemented and studied the impact of a seed-mix designed specifically to provide forage for pollinators. In this study, we aimed to compare bee communities on florally-enhanced (seed-mix treatment) lawns to bee communities on lawns with naturally-occurring populations of Trifolium repens (Dutch white clover). First, we documented the bee community visiting naturally occurring populations of T. repens in lawns at sixteen public parks within Minneapolis, MN to establish the bee community present prior to floral enhancement; eight parks of these parks were then selected for further sampling, with four receiving the seed-mix. Next, we measured the establishment and persistence of the seeded forage plants included in our seed-mix. Finally, we tested whether florally-enhanced lawns increased bee diversity and supported different bee communities than lawns with only T. repens. We hypothesized that florally-enhanced lawns would support more diverse communities of bees compared to naturally-occurring clover-only lawns. The quantification of the bee communities that forage in florally-enhanced turfgrass lawns highlights the ecological value of a land management strategy that is easy to implement and maintain.