The Role of Native and Domestic Grasses in Erosion Control

Craig W. Edminster

INTRODUCTION

Conservation of soil resources, reduction of sediment loss to streams, and conservation of water resources remain important national, regional and local environmental priorities. The use of domesticated turfgrass and forage grasses in pastures and crop rotations, reduced tillage systems, construction sites, highway right-of-way, stabilization of mine spoils, and agricultural buffer strips have mitigated serious erosion and sediment loss in both rural and urban environments (Stewart et al 1975, 1976). There is increasing interest in the use of indigenous native grasses for reclamation, watershed protection, and rangeland planting in the Pacific Northwest. Several species, which could provide an alternative to commonly used introduced grasses, have been investigated by NRCS/USDA and the Corvallis Plant Materials Center (Darris and Lambert, 1990). Little empirical data is available on the interaction of native grass seeding management (wildlife, livestock, wildfire, riparian, forested, erosion control) and cultural practices to enhance their establishment in the Pacific Northwest. Literature is abundant on the establishment of domesticated species and is, as a result, utilized around the world. Domestic and native grasses and their role in soil conservation and erosion control in the Pacific Northwest will be reviewed.

SEDIMENT AND RUNOFF CONTROL

Vegetation is probably the most important factor in the hydrologic cycle and the variable most affected by human activity. Dense canopies of vegetation protect the soil from erosion and increase water infiltration (Balogh, et al. 1990). Amount of sediment lost from disturbed construction sites depends primarily on (1) the duration and extent of the disturbance, (2) the volume and rate of surface runoff, (3) the configuration and topography of the exposed site, and (4) the use of mitigated soil conservation practices (Daniel et. al. 1979). During construction, temporary erosion control devices will mitigate off site transport of eroded sediment. These practices include (i) construction of temporary silt fences to stop particle transport; (ii) construction of small check dams or weirs to flatten upstream slopes and decrease the velocity of runoff; and (iii) use of temporary mulches, matting, or blankets to reduce erosive forces until vegetation or long-term measures are in place. Long-term erosion and runoff control techniques should be used on sites with highly erosive soils, steep banks, or design elements conductive to rapid runoff and sediment transport. A wide range of techniques including (a) planting of native vegetation with soil stabilization canopies and root system; (b) placement of short silt fences; (c) use of wattling; (d) construction of terraces on steep slopes with drainage swales that collect and divert runoff water; (e) Construct detention ponds within drainage channels which reduce runoff velocity and provides temporary storage for eroded sediment.

GRASSLAND IMPROVEMENT

Grassland improvement in an agricultural context entails the use of management to increase primary and secondary production. Common improvement strategies involve the introduction or encouragement of plant genotypes of high nutritional quality, high yield, and long stand life and the use of animals genotypes with efficient feed conversion. Inputs are commonly used to alleviate limitations to growth, such as soil fertility, and to control undesirable competitors, predators and parasites. Finally, grassland improvement includes measures that support environmental improvement such as species diversity, preservation of natural conditions, and recreation. More drastic or expensive improvement measures are often used to revitalize grasslands in poor conditions. Milton et al. (1994) proposed a five-step model of changes in status of arid and semi-arid grassland vegetation beginning with optimum secondary production and ending in denudation. As a grassland ecosystem condition decreases toward denudation, the expense of improvement practices generally increases and the likelihood of restoring secondary production to economically useful levels diminishes. The planting of vegetative material on disturbed sites therefore, requires modest to high levels of inputs for long term primary as well as secondary production. "Sculpture seeding" has been recognized as an effective method of establishing introduced grasses and legumes on disturbed sites, pastures and roadside. The approach is to seed a range of late to early serial (series) species with different, but compatible traits. This may include a range in seedling vigor, plant height and persistence, reproductive maturity, tolerance to abiotic and biotic stress, forage quality and other attributes. A similar approach can be used for native seed plantings. Proper species selection among and within introduced and native grass material will be a key to the rapid establishment and long term persistence of wetland, riparian and upland sites. However, site preparation, management and cultural practices post and pre establishment of a new grassland system will be the most important component in properly restoring a disturbed site.

INTRODUCED SPECIES FOR EROSION CONTROL MIXTURES

  1. RYEGRASS has been used extensively as a short-lived component in erosion control mixtures. Their key attribute in erosion control is rapid seedling establishment, tolerance to slightly acidic soils and excellent spring and fall forage growth when rainfall is abundant in the Pacific Northwest. In addition they serve as an excellent nurse crop in low input plantings. Ryegrass is intolerant of droughty, nutrient deficient soils and therefore may senescence and die during the early establishment period, which provides an excellent growing environment for long lived, grass species. Lolium perenne (Perennial ryegrass) tetraploid and diploid sources are commonly used in erosion control plantings. The diploid being more tolerant of grazing pressure (mowing) and more persistent than the larger leafed, more robust and less cold tolerant tetraploid. The use of very late maturing diploid perennials such as Elka and Essence® has been recommended to reduce reseeding potential and enhance long lived species establishment. Lolium multiflorum (Annual ryegrass) Annual ryegrass is the most commonly used cool-season grass in conservation and erosion control in the Pacific Northwest. Annual ryegrass has the best seedling vigor and lowest cost per pound of all the cool season grass species. At low planting rates it can provide good to fair nurse or companion crop attributes. At extremely high seeding rates it can provide living mulch attributes. Annual ryegrass has excellent reseeding capability and seed can remain dormant in soil for up to five years. Therefore, its use is often discouraged where mixed species longevity is desired. Westerwold ryegrass and genetic mixtures containing high percentages of Westerwold germplasm are readily available in the Pacific Northwest (cv Gulf, Oregon Common). Westerwold ryegrass require a very short floral induction period for plant vernalization and results in reseeding potential (Gardner and Loomis, 1953). Under these circumstances annual ryegrass can become a weedy grass in erosion control mixtures. True Italian ryegrass cultivars (cv Sultan, Total) developed in Europe that require significantly more floral induction to induce seed production should be considered as an alternative if annual ryegrass is used.
  2. FINE FESCUE - There are six species of fine fescue recognized for their use in turf and forage production systems in the Pacific Northwest. They include, but are not limited to, chewings fescue F. rubra L. subsp. commutata, hard fescue F. longifolia, and sheeps or blue fescue F. ovina; and the rhizomatous type: slender creeping red fescue F. rubra L. subsp. tricholphylla and strong creeping red fescue Festuca rubra L. subsp. rubra. Strong creeping red fescue has been used extensively in conservation and erosion control mixtures primarily because of excellent seedling vigor, tolerance to acidic soils, good shade tolerance (understory) and rhizomatous growth habit. Strong creeping red fescue requires very little supplemental fertilization once established and grows well on shallow and rocky cut bank riparian and upland sites. Strong creeping red fescue is a moderately tall plant species and is highly compatible with many other tall and short serial species of introduced grass.
  3. Phleum pratense (Timothy) has been used as a minor component in mixtures for wetland, bottomland and stream bank restoration where imperfect soil drainage may be a limiting factor. It is poorly adapted for erosion control mixtures because of its lack of seedling vigor. Therefore, mixtures containing rapid establishing species as a nurse crop are advised. Timothy is also intolerant of drought soils so its establishment on well drained sloped areas in riparian and upland sites is not recommended.
  4. Dactylis glomerata - Orchardgrass is a bunchgrass that has been used extensively in erosion control mixtures in West Coast Mountain Region. It has good seedling vigor, early spring forage growth, but requires well drained soil sites to persist. It is tolerant of mild soil acidity, and moderately shade tolerant, but requires supplemental fertilizer for proper growth. Orchardgrass cultivars are segregated into different maturity group; early, medium and late for their relative feed value when used in legume based forage production systems. Early maturing short statured varieties such as Paiute, Palestine are often recommended because they enter dormancy during the summer when soil moisture is depleted in the Pacific Northwest. Upon dehydration in the fall they regrow and persist.
  5. Festuca arundinacea - Tall fescue has been used on occasions in conservation and erosion control with mixed results. Tall fescue has poor seedling vigor, but exhibits good shade tolerance. Once established is a very dominate forage producer and may require aggressive management to constrain growth (mowing, burning). Tall fescue is tolerant of acidic, poorly drained, shallow soil sites, but prefers well drained sandy loam soil sites. In contrast to other cool-season grasses tall fescue may not enter into summer induced dormancy or rest period. Its deep extensive root system facilitates deep soil profile water uptake during the summer and tall fescue can dominate a riparian, upland or wetland site.
  6. Poa pratensis - Kentucky bluegrass has been used to a limited extent in the Pacific Northwest. Its most redeeming characteristic is the presence of rhizomes, which provides good soil and plant interface to reduce soil erosion potential. Its most limiting factors are that it has the poorest seedling vigor of all cool-season grasses and is intolerant of slightly acidic to acidic soils. To persist it must be established in soils with excellent internal drainage. It also requires moderate to high soil nutrition and does best in a diurnal environment where summers are hot and winters cold.
  7. Agrostis palustris - Creeping bentgrass "the golf course greens grass" has been used to a very limited extent for erosion control in the Pacific Northwest. Bentgrass is very tolerant of acidic, poorly drained soils and exhibits fair to poor seedling vigor. If hydrated throughout the season, it can dominate a planting site because of its short, aggressive stoloniferous growth habit. It is therefore incompatible in grass seed mixtures. Established stands of creeping bentgrass will require burning or very short mowing to enhance persistence.
  8. Agrostis castellana - Highland bentgrass is very tolerant of acidic, poorly drained, or shallow soil sites and exhibits good to fair seedling vigor. It also exhibits better summer drought tolerance than creeping bentgrass. Highland bentgrass has larger more robust stolons than creeping bentgrass and provides more forage for grazing animals and wildlife. Similar to creeping bentgrass it can dominate a planting site because of its aggressive stoloniferous growth habit and is therefore considered incompatible in grass seed mixtures.
  9. Agrostis tenuis - Little colonial bentgrass has been used in conservation and erosion control projects in the Pacific Northwest. This is more the result of short seed supplies than a lack of its adaptation in conservation program. Colonial bentgrass is the only Agrostis species that is compatible in mixture with other cool-season grass species. This short, acid tolerant, fine leaved species has short prolific stolons that grow more upright than prostate. It exhibits excellent drought tolerance, requires only modest soil fertility and has good to fair seedling germination.

NATIVE SPECIES FOR EROSION CONTROL

  1. Elymus glaucus - Blue wildrye has been considered an alternative to perennial ryegrass or annual ryegrass as quick cover on dramatically disturbed sites, roadsides, woodlots, and upper banks of streams, riparian zones and timberland. (Annual rainfall range of 10-40 inches and seed count of approximately 120,000 seeds per pound) Blue wildrye is a tall, erect, loosely tufted, short-lived bunchgrass with excellent seedling vigor. It exhibits good shade tolerance but requires well drained deep soil sites for persistent growth. Blue wildrye is self fertile and largely self pollinated, is more drought tolerant than meadow barley and California brome and has excellent reseeding potential. Several cultivars and source identified populations are available from commercial seed suppliers.
  2. Festuca occidentalis - Western fescue has been considered a substitute for fine leaf fescue in range, understory woodland, and erosion control seedlings in the Pacific Northwest. (Annual rainfall range of 16-40 inch and seed count of approximately 450,000 seeds per pound) Western fescue is a medium size, short-lived, fine textured, tufted bunchgrass adapted to moist, shady and sloped environments usually associated with Douglas Fir and mid-elevation mixed conifer forests. Western fescue is difficult to grow in cultivation, therefore commercial seed supplies are limited.
  3. Hordeum brachyantherum - Meadow barley has also been considered as an alternative to perennial ryegrass or annual ryegrass as quick cover on dramatically disturbed sites, roadsides, upper banks of streams, riparian zones, meadows, bottom lands, salt marshes and grassy slopes. (Annual rainfall range of 12-36 inch and seed count of approximately 100,000 seeds per pound) Meadow barley is a medium size, short-lived bunchgrass with strong seedling vigor. It is tolerant of alkaline soil, will establish on infertile, compacted soils, but will not persist on dry sites. Several source identified populations are available from commercial seed suppliers.
  4. Bromus carinatus -California brome has also been considered as an alternative to perennial ryegrass or annual ryegrass as quick cover on dramatically disturbed sites, roadsides, woodlands, and upper banks of streams, riparian zones, and bottom lands. (Annual rainfall range of 12-40 inches and seed count of approximately 100,000 seeds per pound) California brome is a large, leafy, short-lived bunchgrass with strong seedling vigor. California brome is a very productive grass on fertile, well drained sites and provides good ground cover for wildlife, waterfowl and is competitive with herbaceous weeds. It is highly adapted to the hot and dry climates indicative of the Mediterranean environment in California and south central Oregon. Several cultivars and source identified populations are available from commercial seed suppliers.
  5. Festuca rubra - Red fescue is a medium sized, loosely tufted, fine leafed grass that spreads with slender underground rhizomes. (Annual rainfall range of >14 inches and seed count of 365,000 seeds per pound) It is adapted to well drained, shady sites where soils are thin and nutrient and moisture holding capacity is compromised. Many native selections have been made with better heat and drought tolerance than introduced strong creeping red fescue, and exhibit summer stay green attributes under low soil moisture conditions. One cultivar cv Molate and several source identified populations are available from commercial seed suppliers.
  6. Festuca ovina - Sheep fescue (or F. minutiflora, F. brachyphylla, F. saximontanta) are also potentially useful, but not available in the commercial seed trade.
  7. Deschampsia cespitosa - Tufted hairgrass has been recommended instead of meadow foxtail and timothy on bottomland, stream bank and open area upland sites in the Pacific Northwest where sunlight is not a limiting factor (Rhaman, 1976). (Annual rainfall range of 12-40 inches and seed count of 1,800,000 seeds per pound) It is found in wet meadows, seeps, bogs, and brackish water along the coastal waterways of the Pacific Northwest and California. Tufted hairgrass is a large, densely-tufted, moderately fine textured bunchgrass. For a small seeded species it exhibits excellent seeding vigor and tolerates a broad range of soil pH. Once established it grows extremely well on seasonably wet soil or well drained sites and can become the dominant grass on wet, nutrient deficient wetland or riparian sites. Several cultivars and source identified populations are available from commercial seed suppliers. Non-adapted sources of tufted hairgrass are imported into the U.S. from Canada and Northern Europe.
  8. Deschampsia elongata - Slender hairgrass is a biennial or short-lived perennial tufted grass adapted to shady areas in mixed conifer forests. (Annual rainfall range of 12-40 inches and seed count of 1,600,000 seeds per pound) It is found in wet meadows, seeps, bogs, and streams. Slender hairgrass is a medium to small, densely-tufted, fine textured, very short-lived perennial bunchgrass. It is seldom found in dense stands and is a poor competitor with other plants. Source identified or commercial seed supplies are limited.
  9. Nassella pulchra - Purple needlegrass is a large, long-lived bunchgrass well adapted to clay soils. (Annual rainfall range of 8-30 inches and seed count of 68,000 seeds per pound awned and 117,000 seeds per pound de-awned) Purple needlegrass is best used on disturbed cut slopes and in thin riparian or upland soils making it an excellent perennial grass component in revegetation and restoration mixes. As with many of the long-lived bunchgrasses, it has only fair to poor seedling vigor and is susceptible to herbaceous and annual weed competition. Fertilization to induce seedling establishment generally favors the weeds and suppresses good stand establishment. Purple needlegrass is tolerant of serpentine soils. Source identified populations are available from commercial seed suppliers.
  10. Nassella Lepida - Foothills needlegrass is a medium sized, long-lived bunchgrass with more petite and finer leaves and higher moisture requirement than purple needlegrass. (Annual rainfall range of 12-35 inches and seed count of 185,000 seeds per pound awned and 320,000 seeds per pound de-awned.) Foothill needlegrass is best used on disturbed cut slopes and in thin riparian or upland soils making it an excellent perennial grass component in revegetation and restoration mixes. As with many of the long-lived bunchgrasses, it has only fair to poor seedling vigor and is susceptible to herbaceous and annual weed competition. Fertilization to induce seedling establishment generally favors the weeds and suppresses good stand establishment. Source identified populations are available from commercial seed suppliers.
  11. Danthonia californica - California oatgrass is a small to medium-sized, long-lived tufted bunchgrass. (Annual rainfall range of 15-35 inches and seed count of approximately 75,000 seeds per pound) California oatgrass grows slowly and has weak seedling vigor, but is unique in that it stays green all year long. It is especially adapted to traffic pressure and trampling and is one of the more important native grasses adapted to highly developed well drained agricultural soils. California oatgrass is a poor seed producer and exhibits both embryo and seedcoat dormancy which has made commercial seed production prohibitive.
  12. Agrostis exarata (Spike bentgrass) Spike bentgrass is a small, short-lived, prostrate, slender stoloniferous grass species. Annual rainfall range of 20-40 inches and seed count of approximately 5,000,000-6,000,000 seeds per pound. Spike bentgrass grows along streams, bogs, seeps and meadows and is not overly competitive with other species over successive years. Source identified or commercial seed supplies are unavailable at this time.
  13. Beckmannia syzigachne - American sloughgrass is a medium-sized, biennial or short lived perennial bunchgrass. (Annual rainfall range of 20-40 inches and seed count of approximately 200,000 seed per pound) American sloughgrass grows along streams, bogs, seeps, lakes and meadows. American sloughgrass is used as a minor component in wetland and stream bank riparian restoration projects. Seed sources are sometimes available from the Canadian and the northern prairie states. Source identified seed or commercial seed sources are limited.

COMPANION OR NURSE CROPPING

Companion, nurse or cover cropping has been used successfully for many years in erosion control programs as an alternative or in addition to mulch and soil surface debris. Rapid development of the crop reduces the opportunity for weed encroachment and reduces potential soil erosion while providing a soil surface interface beneficial to the newly established grass or legume crop. Large seeded small grains such as rye, wheat, and oats have been used extensively for this purpose. Their vigorous seedlings ensure rapid establishment and dense fibrous roots systems stabilize soil. These small grains can be sown in spring or fall and are short lived which reduces long term plant competition. However, to prevent excessive competition with the establishing native or long lived vegetative ground cover, it is recommend that the companion crop be removed as forage before maturity or full canopy closure. Triticum x Agropyron or wheat x wheatgrass sterile interspecific hybrid is marketed as a cover crop for disturbed soil and controlling soil erosion. The sterile seed trait is desirable in a cover crop in that it does not continue to reseed itself such as other seed bearing annual grain crops. Sterility insures that seed from the plants is not viable and will not compete in the next generation with newly established natives or introduced perennial species.

SEED SOURCE

Seed sources are abundant in domesticated cool-season turf and forage. Broad area of adaptation has provided opportunity for large commercialization. Public and private breeding costs can be annualized over the life of a variety and provide strong justification for continued breeding effort across multiple species. Native grasses however, have taken a significantly different road. Natural population, source identified, land race, pre-varietal germplasm, eco-region, watershed type, tested, selected and other designations of native grass seed that narrow the area of use or adaptation will inherently limit commercial seed production. Institutions considering native grass utilization will have to treat natural source population much like a proprietary product. They will be responsible for seed collection, seed increase, seed quality standards, and inventories with little market usefulness outside of their watershed, habitat or region. All will be done at a premium over the cost of a more broadly adapted native of the same species.

SEED PRODUCTION

In domesticated seed production acceptable standards of seed production are recognized within the seed industry. Significant deviation for these levels result in premium cost for seed production on a per acre basis. These costs in a market economy are either prohibitive or lead to the failure of a cultivar or require a premium at the end user market. Commercial seed is available as certified which provides standard levels of mechanical and genetic quality. In many respects private industry markets seed that meets or exceeds the mechanical and genetic quality of certified. Many of the natural populations of native species in the Pacific Northwest have not been evaluated for seed production under mechanized seed production procedures. Elevation, latitude, watershed, slope, aspect, collection site and genetic attributes all contribute to potential seed production. Darris and Lambert, 1990 found that variability among source populations of blue wildrye Elymus glaucus L. for seed production across two locations were significant. Self pollination, cleistogamous pollination and other factors contribute to potential inbreeding, which has negative effect on potential genetic seed production. Several factors however, have contributed to the lack of commercialization of native grasses in what is recognized as the largest cool-season grass seed production area in the world.

  1. Buyers have abundant supplies of low cost cool-season grasses available from industry
  2. Broadly adapted source material is limited.
  3. Unfamiliar seed production practices discourage seed grower participation. There will continue to be strong barriers to successful commercial development of native grass seeds for the Pacific Northwest.

NATURAL REGIONS AND DOMINANT ECOLOGICAL COMMUNITIES IN PACIFIC NORTHWEST

The West Coast Mountain region includes the coastal mountains and the west slopes of the Cascade Mountains in Washington and Oregon, and the north coastal region of California. Many factors determine the composition of forest types, however, an elevation gradient is the most useful for describing changes in species composition. Douglas fir is the most extensive species. At higher elevations Pacific silver fir and mountain hemlock become dominant. Sitka spruce and redwood forest are the most common along the coast. Deciduous forest, scrub, and grassland communities also occur in the region. The Klamath Mountains support a complex and unique assemblage of plant communities because of their location between the mesic coastal forests and the dry interior valleys. The floodplains of the Willamette and Columbia Rivers support Riparian Forest, which are frequently dominated by deciduous trees. The interior valleys of the Umpqua, Rogue, and Willamette Rivers, which are in the rainshadow of the Coast Range, support communities such as oak woodlands, chaparral, and dry grasslands. Native or herbaceous understory grasses adapted to the upland, wetland and estuarine systems in the West Coast Mountains region include, but are not limited to, western fescue Festuca occidentalis, Harford's melicgrass Melica harfordii, California oatgrass Danthonia californica, red fescue Festuca rubra, onion grass Melica bulbosa, blue wildrye Elymus glaucus, leafy bent Agrostis dieogensis, tufted hairgrass Deschampsia cespitosa, bluebunch fescue Festuca idahoensis, Hall's bent Agrostis hallii, nootka reedgrass Calamagrostis nutkaensis, timber oatgrass Danthonia intermedia, western bottle brushgrass Elymus elymoides, prairie Koeler's grass Koeleria macrantha, Foothill needlegrass Nassella lepida, Purple needlegrass Nassella pulchra, California blue-eye-grass Sisyrinchium bellum, Nelson's needlegrass Stipa nelsonii, California spikenard Aralia californica, coastal salt grass Distichlis spicata, California cordgrass Spartina foliosa, barbgrass Hainardia cylindrica, dwarf alkaligrass Puccinella kurinlensis, slender arrow-grass Triglochin concinnam and seaside arrow-grass Triglochin maritimum.

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