Urban Landscapes: Turfgrass Benefits

Abstract

Recently, turfgrass has received scrutiny from the public in many parts of the United States due to the misconception that it has limited benefits and has negative impacts on the environment. These negative impacts are often associated with water and chemical usage during turfgrass maintenance. Even with these ill-advised concerns, turfgrass remains an important component of urban landscapes. Contrary to public opinion, turfgrass has numerous environmental, ecological, economical, social, and societal benefits. This review paper summarizes and highlights the benefits of turfgrass systems.

1. Introduction

Turfgrass is an important component of urban landscapes, where its uses include but are not limited to home lawns, golf courses, athletic fields, roadsides, commercial buildings, schools, and parks. However, there is a misconception that turfgrass systems have limited benefits and can have negative impacts on the environment due to their inappropriate management [1,2]. Additionally, their economic, social, and societal benefits are often overlooked. Several authors have summarized and presented the environmental, ecological, economical, social, and societal benefits of turfgrass [3,4,5,6,7]. This review paper highlights the benefits and builds upon these previous summaries with recent findings.

2. Turfgrass Benefits

2.1. Environmental and Ecological

Typically, turfgrass is established and grown on disturbed urban soils [8]. This is especially true in urban areas, where development removes existing vegetation, strips the topsoil, and compacts the subsoil, leading to urban soils generally having a loss of soil organic matter and soil structure, increased bulk density, and reduced permeability [9,10]. Turfgrass is effective for soil stabilization and erosion control due to it having a high shoot and root density, which helps to physically stabilize the soil, induces resistance to overland water flow, and allows more time for infiltration while decreasing runoff and erosion [3,6,11]. Due to the ability of turfgrass to stabilize the soil, limit soil erosion, and provide dust control, it is utilized in urban areas including closed landfills and abandoned properties [3,4,7,12].

Turfgrass roots also create a diversity of channels in the soil that increase the water infiltration within the turfgrass rootzone [6]. When turfgrass was compared to a mixed-species stand (i.e., ornamental ground covers, woody shrubs, and trees), there were no differences in the surface runoff [13]. Turfgrass also increases the time to runoff and decreases the runoff (with a mean runoff volume < 1% of the total precipitation) relative to that in impervious surfaces with or without trees and porous pavement [14,15]. Moreover, in non-frozen soil conditions, turfgrass decreased the runoff by 54% and reduced the total phosphorus (P) loading in the runoff by 50% compared to prairie vegetation [16,17]. Turfgrass stands also have greater water infiltration and retention and less runoff than artificial lawns and xeriscaping [18,19]. The ability of turfgrass to reduce surface water runoff and increase infiltration results in groundwater recharge [3,5]. Turfgrass (37%) provides a similar average groundwater recharge compared to that of woodchip mulch (47%) and a greater groundwater recharge compared to that of a pollinator landscape (i.e., flowering forbs; 26%) [20]. Furthermore, turfgrass provides similar groundwater protection and recharge abilities to those of prairie vegetation [21].

Properly maintained and actively growing turfgrass results in little nutrient loss from leaching and runoff and has minimal sediment runoff [7,11,13,22,23,24]. This is attributed to turfgrass having a high root and shoot density, resulting in increased infiltration and reduced runoff [25]. When fertilizer was applied within the regional recommended ranges to healthy turfgrass, it resulted in negligible nutrient leaching in the various turfgrasses [26,27,28,29,30,31]. Additionally, following the best management practices in terms of fertilizer and irrigation, the nutrient losses from turfgrass can be similar to those in unmanaged, natural systems, and the nitrogen (N) levels in the groundwater are not related to the amount of N applied to the turfgrass [32,33]. Turfgrass also resulted in 92%, 39%, and 47% lower N, P, and potassium (K) leaching compared to a mixed-species stand (i.e., ornamental ground cover, woody shrubs, and trees), respectively [13,22]. Furthermore, turfgrass reduced the N leaching by 92% and 57% relative to that in woodchip mulch and a pollinator landscape (i.e., flowering forbs), respectively [20]. However, N leaching is more likely to occur if fertilizer is applied when the turfgrass is growing slowly or is inactive [7]. Additionally, over-irrigation is also a potential factor influencing N leaching from turfgrass [24].

Its ability to utilize and tolerate reclaimed water and low-quality water is another benefit of turfgrass [34,35]. Furthermore, turfgrass irrigated with reclaimed water can achieve the same turf quality as turfgrass irrigated with well water [36]. The nutrients in reclaimed water can be assimilated into the plant tissue and can aid in turfgrass growth while also removing up to 647 kg N ha⁻¹ yr⁻¹ from the wastewater [34,37]. Even though turfgrass irrigated with reclaimed tailored water has been shown to minimize nitrate leaching once it is established, concerns about N leaching during its establishment from seed still exist [38]. The nitrate leaching from warm-season turfgrass species irrigated with reclaimed water was higher compared to that when using potable water irrigation up to 30 days after seeding, when neither roots nor aboveground turfgrass tissue was present. Moreover, grass with a more extensive root architecture may have an increased capacity to filter leached nitrogen compared to grasses with scarcer roots [39].

Another ecosystem service of turfgrass is sequestering carbon (C) [40,41,42,43,44]. Turfgrass has an average gross C sequestration rate of 0.9–5.4 Mg C ha⁻¹ yr⁻¹, a soil organic C accumulation rate of 0.22 Mg C ha⁻¹ yr⁻¹, and a potential soil organic C sink capacity of 20.8–96.3 Mg C ha⁻¹ [40,42,43,45,46]. Management intensities alter the rate of C sequestration; however, even when factoring in hidden C costs (mowing, irrigation, fertilizer, etc.), turfgrass is an efficient assimilator of atmospheric C and is a net C sink, with an average net C sequestration or accumulation rate of 0.4–2.5 Mg C ha⁻¹ yr⁻¹ [40,43,45,46]. Managed turfgrass has greater C sequestration compared to grasslands, cropland converted into grassland, cover crop adoption, no-till agriculture, and many agricultural crop systems [45,47,48]. Additionally, following the best management practices for turfgrass fertilization and irrigation may even reduce the net global warming potential compared to that of non-fertilized turfgrass through encouraging C sequestration since fertilized and irrigated turfgrass produces more biomass [49]. Turfgrass, particularly in urban environments, is an important contributor to global C sequestration efforts [38].

Problems with urban soil contamination include the organic, inorganic, and heavy metal pollutants created from the byproducts of combustion or industrial processes and anthropogenic sources (e.g., traffic emissions, municipal waste disposal, the corrosion of construction and building materials, etc.) [50]. Remediation of contaminated soils can be achieved through turfgrass phytoremediation and the associated plant–microbe interactions [4,7,51,52,53,54]. The dense turfgrass root system and associated rhizosphere provide a greater surface area for reactions, which may enhance phytoremediation, compared to that in tap-rooted plant systems [7,55,56]. Furthermore, turfgrasses allow for the phytoremediation of many different contaminants by assimilating them into both the aboveground and belowground plant tissue [57]. Turfgrass resulted in the greatest emergence rate and biomass in polluted soils compared to trees, shrubs, and sedges, which portrays its greater potential for the rehabilitation of contaminated soils [52]. It was also determined that turfgrass can be utilized for the bioremediation of certain herbicides and nitrate-N [53]. Turfgrass also has the potential to reduce pharmaceutical contaminant loading in the environment [58]. Turfgrass phytoremediation may be a more cost-effective method of remediating contaminated soils compared to the traditional methods [59,60].

In addition to the reclamation of contaminated soils, turfgrass also absorbs atmospheric pollutants and greenhouse gases and reduces fine particulate matter pollution, all of which are exacerbated by anthropogenic activities [4,7,61,62]. Coinciding with decreasing pollution, turfgrass produces oxygen, which improves air quality [6]. Turfgrass also improves water quality by reducing the total N by 64–90%, the total P by 44–94%, the total K by 33–73%, and suspended solids by >90% in water [63,64,65]. Additionally, turfgrass can reduce hormone pollutants by 98% in runoff [66]. Turfgrass has also been utilized in agricultural production to reduce nonpoint source pollution [64].

Turfgrass moderates temperature and reduces heat island effects through evapotranspiration [6]. Turfgrass offered an approximately 25 °C surface cooling effect relative to bare soil and decreased the maximum daytime temperature from 45.7 °C to 43.3 °C [67,68]. Furthermore, green, growing turfgrass decreases the temperature peaks in urban areas by an average of 1.9 °C and lowers maximum daily canopy temperature by 21–56% compared to dormant turf, synthetic turf, and bare soil [3,69]. Turfgrass also has a significant cooling potential that can surpass tree shade cooling at small temporal scales and at nighttime [70,71]. Irrigated turfgrass was shown to decrease the cumulative average heat fluxes in stucco-covered wood frame walls when compared to the non-irrigated-xeriscape, which were responsible for urban temperature increases, creating an urban heat island effect [72]. Temperature moderation via turfgrass evapotranspiration also saves energy and money and improves outdoor thermal comfort [3,68,73].

In addition to soil, water, and air quality improvements, turfgrass also reduces noise pollution, urban glare, UV-radiation reflection, and dust/mud problems [3,6,74,75,76]. Turfgrass areas decrease the numbers of noxious or nuisance pests, reduce allergy-related pollen, and limit human disease exposure, which is facilitated by certain insect vectors [3,7]. Additionally, green turfgrass lowers fire hazards and is recommended to prevent structural fire damage [3,77].

Turfgrass also has a role in supporting wildlife habitats, which include those of numerous non-pest invertebrates [3,6]. In urban environments, lawns and golf courses provide open spaces that attract predatory birds for hunting [78]. Turfgrass also supports the greatest diversity and number of natural enemy arthropods (e.g., ants, beetles, spiders, etc.) compared to urban ground covers [79,80]. However, turfgrass has lower beetle biodiversity and abundance than meadows and tall-grass prairies [81,82]. Furthermore, soil microbial biomass or populations increase with turf stand age and may be greater than those in native pine soil [83]. Managed turfgrass areas provide an opportunity to either promote or maintain biodiversity in urban environments [81,84]. Species and cultivar blends of turfgrasses are another way to create more resilient, biodiverse lawns that reduce weed pressure and increase lawn quality [85,86,87,88].

2.2. Social and Societal

Turfgrass has numerous recreational benefits along with its benefits to physical and mental health. Its recreational benefits include accessible and safe environments in which to exercise, engage in outdoor sports/activities, and socialize [4,7]. Furthermore, turfgrass provides a permeable, non-heatable, and safe playing surface for users, and overall, park visitors prefer turfgrass compared to artificial turf [6,89,90]. Turfgrass is often the best-suited area for recreational and leisure activities compared to other landscapes [7]. The list of recreation and leisure activities conducted on turfgrass is vast and includes a wide range of activities.

Turfgrass also has an impact on human physical and mental health. These physical health benefits include a reduced risk of chronic diseases and a lower body mass index due to a more physically active lifestyle [4,91,92]. Additionally, subjects’ mean systolic blood pressure decreased and their brainwave patterns increased following an interaction with turfgrass compared to artificial grass [93]. Heat stress was also reduced with the use of turfgrass versus artificial turf, and turfgrass creates a healthy outdoor thermal environment [94]. Artificial turfgrass can also lead to abrasion injuries and a higher foot and ankle injury rate compared to natural turfgrass [95,96]. Furthermore, the likelihood of a football player suffering a knee injury on artificial turf is increased relative to natural turfgrass [95]. Mental health benefits include reducing stress and depression symptoms, enhancements in the creativity, intellect, and cognitive skills of youth, and increasing relaxation or calmness and an overall sense of well-being [6,91,93,97,98,99,100]. It has also been reported that maintained turfgrass areas improve one’s sense of safety and are inversely related to the incidence of crime [4,7,101,102].

Urban lawns provide formal and informal opportunities for nature-based learning [103]. Turfgrass also provides aesthetic benefits, especially when it is combined within an integrated landscape [3]. Turfgrass is important to the aesthetics of a landscape because it is the background for all other landscape items, and it provides the framework that enhances the other landscape features [6]. Overall, turfgrass has a positive effect on people through its physical, mental, and social benefits [4].

2.3. Economical

In the United States, it is estimated that turfgrass accounts for 1.9% (163,812 km² ± 35,850 km²) of the total continental area [104]. The turfgrass industry has many sectors, which include lawncare services, lawn and garden stores, equipment manufacturing, sod farms, golf courses, and athletic fields [105]. The total economic output and value-added impacts of the turfgrass industry, not including athletic fields, were estimated at USD 62.2 billion and USD 37.65 billion in 2005, respectively, and the industry continues to grow in the United States [105]. The golf industry had an economic activity of approximately USD 84 billion in 2016, employs around 2 million people, and provides tourism benefits [4,84,106].

Beyond its economic impacts at the industry level, a maintained landscape with healthy turfgrass, trees, and ornamental plants increases individual homeowners’ and businesses’ property value and sales prices and enhances the perception of businesses or schools [4,7]. As mentioned, turfgrass also moderates temperature, which reduces energy costs [6].

3. Conclusions

Overall, turfgrass has numerous environmental, ecological, social, societal, and economical benefits in urban areas. It also is a major contributor to the urban landscape in terms of its functionality and aesthetics, positive ecosystem services (wildlife habitats, runoff reduction, soil stabilization, groundwater recharge, nutrient uptake, carbon sequestration, improved soil structure and development in urbanized soils, and increased soil microbial populations) and economic impact, and people’s overall well-being.