Appalachian Laboratory

Economic and Ecological Services for Turfgrass Suitability Evaluations

For our Turfgrass Assessment project, we evaluated each turfgrass species based on six economic and ecological services to determine their suitability for use as a roadside cultivar in order to maximize economic and ecological value and minimize maintenance costs and safety risks.  Following is a more detailed summary and explanation of each of those service categories:

Cost Symbol

Commericial Availability and Cost - Seed that is used for roadside turfgrass establishment needs to be commerically available and affordable.  We considered grass species and cultivars as viable candidates for roadside planting if they are currently available commercially, although promising but undeveloped species or cultivars are noted.  Ratings are based on cost per acre, which reflects not only the quantity available for purchase but also seed size and recommended seeding rate.  We received this information from Chesapeake Valley Seed.

Symbol indicating rate of establishment
Rate of establishment - Contractors will get paid only when 90-92% grass cover has been established. Thus, rapid establishment of turfgrasses is desired for pure economic reasons, as well as for reducing erosion on new cut slopes and roadside fills. We assessed rate of establishment by reviewing germination rate of grass species under laboratory, greenhouse, and field conditions. We also reviewed the literature that monitored percent cover and/or quality through time, including the establishment year.

Symbol indicating ease of maintenance
Ease of maintenance - Vertical growth rate and overall short stature are important traits in roadside vegetation owing to budget constraints that limit the frequency with which the grass is mowed. In addition, turfgrasses that require no fertilization, liming, or irrigation will decrease the need for continued maintenance past establishment therefore reducing long-term maintenance costs. We therefore determined the stature of each species through information provided by nurseries and species fact sheets, and reviewed scientific papers that focused on  the performance of species under low-maintenance conditions.

Symbol indicating erosion.
Erosion control - Turfgrasses that produce deep roots and dense sod, and that can increase infiltration capacity will stabilize soils, draw water away from road sides, and decrease run-off, providing erosion control and local nutrient retention. We determined the potential of each species to provide erosion control by reviewing papers that studied rooting depth and sod density under greenhouse and natural conditions. 

Symbol indicating ecosystem benefits
Ecosystem benefits - As living organisms, grasses contribute to the functioning of ecosystems. Benefits to ecosystems include erosion control, nutrient retention, plant and animal biodiversity, and habitat for pollinators and wildlife. However, many turfgrasses are non-native and were specifically selected for their growth habit. Thus, turfgrasses may be invasive to native habitats and be reducers of native biodiversity.  We review these potential positive and negative ecosystem effects paying particular attention to whether species are native or considered to be potentially invasive or weedy.

Symbol indicating resilience
Resilience - The roadside environment in Maryland is an extreme environment that is dry and hot in the summer and cold in the winter with soils that are compacted, low in fertility, generally acidic, and sodic due to road deicers. As highly disturbed ecosystems, roadside environments receive propagule pressure from surrounding ecosystems such that desirable species have to compete with volunteers, many of which are weedy and invasive. Thus, species require a combination of traits for optimal survival. We rate each turfgrass for 7 traits that together provide an overall resilience rating as well as information that determines which climatic zones in Maryland may be the most suitable for the species or cultivars of a species.

We identified 7 traits within the primary evaluation category of resilience that together provide an overall resilience rating:

Symbol for drought tolerance
Drought and heat toleranceHeat reflected from the pavement and the constant wind from passing vehicles results in a microclimate along roadsides that is droughty. In addition, roadsides are engineered to rapidly drain water away from the roadside into swales, storm drains or storm water retention ponds, decreasing the availability of water to roadside vegetation. Providing supplemental irrigation for roadside vegetation is cost-prohibitive such that turfgrass species selected for roadsides need to be drought tolerant to survive. Drought tolerance is conferred through a range of morphological and physiological mechanisms, the most common of which are deep root systems that allow plants to avoid drought by accessing water resources deep in the soil column; low evapotranspiration rates that conserves water within leaves; and dormancy during the hottest and driest times of the summer.

Symbol indicating tolerance to low fertility soils
Tolerance to low fertility soils - Soils after construction are generally poor, low in organic matter, microbial activity, and cation exchange capacity. It is often recommended to amend roadside soils with compost after showing that the soil amendments were able to enhance persistence as opposed to using salt and drought tolerant cultivars. Nitrogen deposition is higher along roadsides owing to vehicle exhaust, which can interact with salt to increase plant uptake of nitrogen.

Symbol indicating tolerance to cold and freezing.
Cold and freezing tolerance -  Maryland is located in the transition zone between warm climates of the southern United States that are suitable for warm season grasses with the C4 photosynthetic pathway, and cool climates in the northern U.S. that are more suitable for cool-season grasses with the C3 photosynthetic pathway. The transition zone provides opportunities for using a diversity of turfgrass species in roadside plantings but also places many species at the edge of their range. Maryland, for example, delineates the northern edge of the bermudagrass range and may be close the southern edge for red fescue. Furthermore, Maryland spans a wide elevation range from sea level to over 3000 feet (=1000 m) on the Appalachian Plateau and thus offering a range of climates. Cold temperatures and freezing soils and sod are therefore important considerations for assessing the suitability and potential for success of turfgrasses along roadsides in Maryland.

Symbol indicating salinity tolerance.
Salinity tolerance - Deicers are used in winters to keep roads free of ice. These salts leach into the soils along roadsides and leave residues on above-ground plant parts that can negatively impact germination, growth, and survival. Other research has found that salt was the primary cause of turfgrass failure along roadsides but that persistence could be significantly improved by amending soils. Both sodium and chloride are toxic to plants and can interfere with a plants’ water holding capacity, but tolerance to high salt levels vary among species and cultivars and with plant developmental stage. It has been observed that foliar exposure was most likely an important aspect of relative salinity tolerance assessments and argue that under prolonged exposure to salinity, cultivar selection is of little importance relative to species selection. 

Symbol indicating sensitivity to acidic soils
Tolerance to acid soils -  Most soils in Maryland (without addition of agricultural lime) tend to be acidic and buffered by the Al system. Thus, native soils are generally between pH of 4.0 to 5.5. Some surface horizons enriched in organic materials may have even lower pH values. Exceptions to these would be particular types of geological parent materials that are less extensive, and which are more base-rich; limestone and dolomite (for sedimentary rocks) and mafic igneous and metamorphic rocks (such as in the Baltimore gabbro complex, the Boyds diabase sill in Montgomery county, and various diabase dikes associated with the triassic rocks of the piedmont.) These exceptional cases could have subsoil pH values that range into the mid-6s, although surface horizons may be more weathered, organic rich, and thus, have lower pHs than the subsoils. The soils along highways are challenging, because the earth has been disturbed during construction. Thus, it is often unclear what soil horizons might be exposed at the surface and therefore hard to predict what soil pH would be. Topsoils that are tested along MD roadsides immediately after road construction can have high pH but it is unclear how long this condition lasts. We rated species more highly if they could tolerate a wide range of pH’s, including acid soils and high aluminum tolerance.

Symbol indicating wear tolerance
Wear tolerance - Roadside environments need to be mowed regularly to maintain aesthetic appeal, provide sight distance, and minimize fire hazards. Roadsides also see some traffic from cars that pull over during emergencies. Thus, turfgrasses planted along roadsides have to be able to withstand traffic from vehicles.


Symbol indicating species' tolerance to competition
Tolerance to competition - To survive in a community with other plant species, a grass species needs be competitive enough to withstand competition pressure for light, nutrients, and water from other species. This includes resisting the invasion of weeds, which are successful when resident species do not provide adequate ground cover and hence offer niche opportunities for new colonizers.