Turf lawns are estimated to cover roughly 2% of the continental United States (Milesi et al., 2005), mostly in highly urban areas. Although management of lawns varies by function and individual manager, it is typically characterized by three primary cultural practices: mowing, fertilizing, and irrigation (Turgeon, 1999). These practices are intended to favor turf species and, when applied in tandem with proper establishment techniques, result in stands of uniform turf. Despite lawns being currently managed as uniform monocultures, they are often host to flowering plants that provide foraging resources for bees and other pollinators. A recent insect survey of park lawns hosting dandelion (Taraxacum officinale F.H. Wigg.) and white clover (Trifolium repens L.) conducted in Lexington, Kentucky (Larson et al., 2014), found 37 associated bee species. These plant species are typically considered weeds in the United States and are sometimes eliminated through the use of broadleaf herbicides. However, lawns managed intentionally for forb abundance and richness would likely have a beneficial impact to local foraging bee communities. Previous research has suggested a strong positive relationship between forb community richness and pollinator community richness that likely extends to lawn communities as well (Ebeling et al., 2008; Potts et al., 2003). Such management goals would necessitate the reduction of other lawn inputs and would further the goal of increased sustainability. Mowing often correlates negatively with plant species richness in lawns (Bertoncini et al., 2012; Garbuzov et al., 2014; Lerman et al., 2018; Shwartz et al., 2013; Smith and Fellowes, 2015), and managing floral lawns could lead to less-intensive mowing regimes. The inclusion of legumes such as white clover has shown to enhance turf nitrogen uptake through nitrogen fixation (McCurdy et al., 2014; Sincik and Acikgoz, 2007), and would potentially reduce fertilizer inputs into lawns.
At the other extreme of flowering lawns, researchers as the University of Reading in the United Kingdom have abandoned the use of turfgrasses altogether, and have been developing species lists and management practice guidelines for purely floral lawns (Smith and Fellowes, 2015) that have been found to have benefits to flower-visiting insects (Smith et al., 2014). These lawns may provide benefits to flower-visiting insects, but they are not meant to be areas of high human traffic and recreation. Human traffic on monocultures of white clover was found to reduce green cover up to 14 times faster when compared with hybrid bermudagrass [Cynodon transvaalensis Burtt- Davy 3 C. dactylon (L.) Pers.], suggesting the importance in turfgrasses for maintaining long-term cover in variable traffic conditions (Brosnan et al., 2014). Another potential challenge of these nonturfgrass plantings is the reliance on precultivation and installation, which can be costly on a large scale, and the potential need for more specialized care. In addition, there is still a strong cultural connection with turf lawns (Harris et al., 2013), and an intermediate flowering lawn that combines turfgrass and floral species may have broader and more practical appeal, especially for recreational use. For these reasons, grass–forb mixes established from seed are an important area of focus for future research. This type of floral-enhanced lawn should provide quick groundcover, reduce lawn maintenance, save money, and provide typical lawn functions such as recreation.
Although floral lawns hold great promise in improving biodiversity in urban areas, guidelines for establishing usable forbs in a lawn are needed to encourage adoption. The main objective of this study was to identify a turfgrass species that would allow for better success in the introduction of flowers not typically thought of as turf weeds. An ideal turfgrass species would maintain groundcover, but also allow for establishment and bloom of its forb companions. Some effort has been made into developing seeding strategies for white clover into established lawns to benefit pollinators and soil nitrogen (McCurdy et al., 2013; Sparks et al., 2015). White clover is an established agronomic crop that is widely associated with pasture agriculture, and is well adapted to the grazing systems under which it evolved (Leffel and Gibson, 1973). Pasture systems and lawns are similar in many ways, (e.g., compaction and cutting by animals or humans) and it is no surprise that white clover does well in both environments. So although white clover is a viable option for improving lawn floral abundance, more forb options are needed to improve the diversity and conservation value of turfgrass lawns.
To understand more fully how turfgrass species influence other forbs, we selected four common turfgrass species used in home lawns in the northern United States to mix with a species of clover: Kura clover (Trifolium ambiguum M. Bieb.). Kura clover is a rhizomatous perennial plant originating from eastern Europe/western Asia and has been investigated as a cold-tolerant forage plant for pasture cattle in the United States. Kura clover is not commonly cultivated across the United States, but it can be found growing infrequently in seminatural areas. Kura clover is known for its slow establishment period and sensitivity to grass competition (Hill and Mulcahy, 1995; Seguin et al., 1999) when used under pasture conditions. Kura clover’s agronomic properties, such as high seed germination rates and grazing tolerance, combined with its sensitivity to competition make it an ideal model species for isolating how competitive pressure from different turf species might affect the establishment and bloom of flowering plants not typically associated with turfgrass lawns.
We predicted that slow-establishing and nonrhizomatous turf species would favor Kura clover establishment and bloom, whereas fast-establishing and rhizomatous species would disfavor Kura establishment and bloom. Our primary goal was to identify turfgrass species that can be seeded at their recommended rates while minimizing turfgrass species-specific competitive effects. Identifying turfgrass species more amenable to forb species additions is important to subsequent studies aimed at identifying other limiting factors in forb establishment, such as germination and mowing tolerance. This is the first of a series of studies that aims to provide foraging resources for pollinating insects in turf lawns.
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