Range (by James E. Preston, Range Specialist, Soil Conservation Service)
Napa County contains 311,195 acres of rangeland, which is 64 percent of the county. Land ownership is primarily non-Federal. Being part of the northern coast ranges, Napa County is dominated by irregular, knobby, landslide topography of the Franciscan Formation. Elevation ranges mainly from 50 to 3,500 feet. Occasional ridges are above 4,000 feet. Precipitation is controlled by moisture-bearing winds from the Pacific Ocean. Precipitation increases sharply from the coast inland and then rapidly diminishes. There is also an increase from south to north.
A range site is a distinctive kind of rangeland that differs from other kinds of rangeland in its potential to produce native plants (15). It is an interpretation of the soil, and it is a product of all environmental factors. A range site is an ecological subdivision of the landscape for study, evaluation, and management. Range sites are the basis for mapping the landscape and inventorying the range.
The essence of a range resource inventory is comparison of the site's potential with the site's present condition for analysis for planning or other purposes.
Under grazing or browsing, plant species increase or decrease in proportion to the whole plant community. The response of a species to grazing depends on the season of the year that the plant is being used, on the type of animal using the plant, and on the intensity of use. Range trend is a determination of whether range condition is improving or deteriorating. The more important characteristics of vegetation and soil that indicate trend in range condition include plant vigor, abundance of seedlings, changes in composition, presence of plant residue, and stability of the soil.
For example, the natural potential vegetation for a certain range site may be grass, oak, and scattered brush. However, due to some disturbance or mismanagement, the site converts to pure brush. Similarly, the potential may be a mixture of soft chess, wild oats, and forbs, but due to mismanagement it reverts to foxtail fescue and vinegarweed. For some soils, potential is thick stands of brush.
The natural potential vegetation may not be the most productive vegetation for forage for livestock or big game. Natural potential vegetation is not a realistic management objective for sites in which the vegetation consists of annuals. The potential vegetation for some sites is brush or timber. Wild oats and ripgut brome dominate the potential vegetation for other sites. Range conditions below the potential permit higher percentages of soft chess, clover, and filaree, which make better wildlife and livestock forage.
A range site can be in poor ecological condition and at the same time be in good hydrologic condition. This often happens in Calif ornia-Mediterranean-type climates. Good hydrologic condition should always be a goal of sound range management.
Proper grazing use includes leaving adequate litter residue (10). Proper grazing use is essential on all sites for runoff and erosion control and for enhancement of wildlife habitat and recreation value.
Soils in Napa County have been grouped into nine range sites. These are described on the following pages. Production is expressed as a current year's growth in air-dry weight per acre.
This site consists of well drained clays of the Diablo series. Depth to soft consolidated sandstone and shale is 40 to 60 or more inches. Slope is 5 to 50 percent. Elevation ranges from 50 to 1,500 feet. Annual precipitation is 25 to 30 inches. Permeability is slow. Available water capacity is 6 to 10 inches. There is a hazard of erosion if a good plant cover is not maintained.
The potential plant community is approximately 70 percent grasses and 30 percent forbs. The grasses include 25 percent soft chess, 15 percent wild oats, 10 percent ryegrass, 5 percent ripgut brome, 5 percent wild barley, 5 percent annual fescue, 5 percent red brome, and a trace of perennial grasses such as needlegrass, wildrye, bluegrass, and melic. The forbs include
10 percent burclover, 10 percent filaree, 5 percent annual clover, 3 percent wild carrot, and 2 percent annual lupine. There are usually no trees on this site.
The total annual production, air-dry weight, is 4,000 pounds per acre in favorable years and 2,000 pounds per acre in less favorable years.
Heavy grazing by livestock causes desirable forage plants such as soft chess and wild oats to decrease and less desirable species such as wild barley, annual fescue, red brome, wild carrot, nitgrass, medusahead, dogtailgrass, tarweed, fiddleneck, popcornflower, vinegarweed, turkey mullein, thistle, and mustard to increase.
The soils are well suited to seeding with perlagrass if an adequate seedbed can be prepared. They are also suited to seeding with improved annual grasses and legumes where seeding is needed. Forage plants on these soils respond well to nitrogen and sulfur fertilizer. Little brush has invaded this site. Where brush has invaded, clearing is feasible.
Deer graze grass and forbs heavily on this site from December to April where this site is adjacent to cover. Drinking water is needed during dry seasons.
This site consists of well drained clay loams, silty clay loams, silt loams, gravelly loams, and loams of the Fagan, Bressa, Dibble, and Contra Costa series. The subsoil is silty clay loam or clay. Depth to standstone and shale is 20 to 60 inches. Slope is 5 to 75 percent. Elevation ranges from 200 to 2,000 feet. Annual precipitation is 20 to 35 inches. Permeability is slow or moderately slow. Available water capacity is 4 to 10 inches. These soils are subject to landslipping if good plant cover is not maintained.
The natural plant community consists of approximately 60 percent grasses, 30 percent forbs, and scattered blue and live oak. The grasses include 20 percent soft chess, 10 percent wild oats, 5 percent stipa, 5 percent California brome, 5 percent blue wildrye, 5 percent ripgut brome, 5 percent red brome, 3 percent wild barley, and 2 percent squirreltail. The forbs include 15 percent burclover, 5 percent filaree, 3 percent annual clover, 2 percent annual lupine, 2 percent American vetch, and 3 percent brodiaea.
The total annual production, air-dry weight, is 3,200 pounds per acre in favorable years and 1,600 pounds per acre in less favorable years.
Heavy grazing by livestock causes desirable forage plants such as soft chess and wild oats to decrease and less desirable forage plants such as wild barley, annual fescue, red brome, wild carrot, nitgrass, medusahead, dogtailgrass, tarweed, fiddleneck, popcornflower, vinegarweed, turkey mullein, and mustard to increase.
Most of the soils in this site that have slopes of less than 50 percent can be seeded to adaptable grasses and legumes. Forage plants respond well to fertilizer that contains nitrogen, phosphorus, and sulfur. Proper grazing and proper planning are important.
Deer graze grass and forbs from December to April. The wild oats and oak trees make this site very suitable for turkey. This site is also suitable habitat for wild pig because of the presence of broadiaea and other bulb-producing plants and oak mast. Drink-Ing water is needed during dry seasons.
Shallow Coarse Loamy range site
This site consists of well drained and somewhat excessively drained loams and gravelly loams of the Maymen, Millsholm, and Lodo series. Depth to sandstone and shale is 6 to 20 inches. Slope is 15 to 75 percent. Elevation ranges from 400 to 2,500 feet. Annual precipitation is 25 to 40 inches. Permeability is moderate or moderately slow. Available water capacity is 1 to 4 inches.
The potential plant community is about half shrubs and trees, about half grasses and forbs, and some remnant perennial plants. The shrubs and trees include 10 percent interior live oak, 5 percent digger pine, 5 percent scrub oak, 10 percent chamise, 7 percent whiteleaf manzanita, 3 percent toyon, 2 percent redberry, 3 percent mountainmahogany, and 5 percent buckbrush. The grasses and forbs include 10 percent soft chess, 5 percent wild oats, 5 percent ripgut brome, 5 percent filaree, 10 percent burclover, 5 percent annual clover, 5 percent Spanish clover, 2 percent annual lupine, 2 percent wild carrot, and 1 percent yarrow.
The total annual production of grasses and forbs is 2,400 pounds per acre in favorable years and 1,200 pounds per acre in less favorable years. The total annual production of shrubs is 2,000 pounds per acre in favorable years and 1,500 pounds per acre in less favorable years. The total amount of vegetation above ground, for consideration of fuel management and cover values, is estimated at 10 tons per acre.
Heavy grazing of the grasses and forbs by livestock causes such plants as soft chess, wild oats, and burclover to decrease and such plants as wild barley, annual fescue, red brome, wild carrot, nitgrass, dogtailgrass, tarweed, fiddleneck, popcornflower, and vinegarweed to increase.
The soils on this site are not suitable for seeding and fertilizing because of the shallow depth and low available water capacity. Proper grazing and proper planning are the most important considerations.
This range site is one of the most important deer habitats in the county because of the diversity of food and cover plants. From October to May deer use shrubs, trees, grasses, and forbs. This site is also suitable habitat for turkey if drinking water is available. This site is very suitable for wild pig because brodiaea and other bulb-producing plants and oak mast provide adequate food and cover. Because of the diversity of cover, this site is very suitable for quail.
This site can be improved for wildlife habitat by releasing understory vegetation and making forage shrubs more accessible. Growth of nutritious shrub sprouts should be encouraged, and drinking water is needed during dry seasons.
This site consists of well drained very stony loams and loams of the Hambright and Kidd series. Depth to bedrock ranges from 10 to 20 inches. Rock outcrops are common. Slope ranges from 2 to 75 percent. Elevation ranges from 400 to 4,300 feet. Annual precipitation is 23 to 60 inches. Permeability is moderate. Available water capacity is 1 to 3 inches.
The natural potential plant community is approximately 75 percent shrubs and trees and 25 percent grasses and forbs. The trees and shrubs include 20 percent whiteleaf manzanita, 10 percent chamise, 10 percent wavyleaf ceanothus, 5 percent Sonoma ceanothus, 15 percent toyon, 2 percent yerba-santa, 10 percent scrub oak, and 3 percent California laurel. Blue oak, digger pine, and live oak form a 20 percent crown cover. The grasses and forbs include 10 percent soft chess, 5 percent filaree, 6 percent annual clover, 2 percent annual lupine, and 2 percent wild carrot.
The total annual production of grass and forbs, air-dry weight, is 1,600 pounds per acre in favorable years and 600 pounds per acre in less favorable years. The total annual production of shrubs and trees, airdry weight, is 5,000 pounds per acre in favorable years and 3,500 pounds per acre in less favorable years. The total amount of vegetation above ground, for consideration of fuel management and cover values, is estimated at 20 or more tons per acre.
If brush is chained, shredded, burned, or manipulated in some way to prevent the excessive accumulation of old growth, browse forage can become unavailable to livestock and wildlife. Many thousand acres of this range site is inaccessible for grazing.
Brush management, proper grazing, and proper planning are important. The soils on this site are not suitable for seeding and fertilizing because of the shallow depth and low available water capacity.
This site is only fair habitat for deer because of the small amount of open area. From October to May, deer use shrubs, trees, grasses, and forbs. This site is poor habitat for turkey because of the lack of open areas. This site is very suitable for wild pig because brodiaea and other bulb-producing plants and oak mast provide adequate food and cover. This site is very good habitat for quail and fair habitat for band-tailed pigeon.
Establishing browseways or lanes from clearings improves access to and use by wildlife. Small clearings are less likely to cause excessive erosion than large clearings, and deer are better able to use the increased food produced. In large cleared areas, deer population generally does not grow rapidly enough to make full use of the new food supply. Drinking water is needed during dry seasons.
This site consists of well drained loams of the Sobrante, Guenoc, and Los Gatos series. Depth to sandstone and basic igneous bedrock ranges from 22 to 40 inches. Slope ranges from 5 to 75 percent. Elevation ranges from 400 to 3,000 feet. Annual precipitation is 25 to 40 inches. Permeability is moderate or moderately slow. Available water capacity is 3 to 8 inches.
The natural potential plant community is approximately 75 percent grasses and forbs and as much as 25 percent shrubs and trees. The grasses and forbs include 15 percent soft chess, 5 percent wild oats, 5 percent stipa, 5 percent California brome, 5 percent blue wildrye, 10 percent burclover, 10 percent filaree, 5 percent annual clover, 5 percent Spanish clover, 2 percent annual lupine, 2 percent buttercups, 2 percent primrose, 2 percent blue-eyed-grass, and 1 percent brodiaea. The shrubs and trees include manzanita, ceanothus, toyon, California laurel, and black oak.
The total annual production of grasses and forbs, air-dry weight, is 2,000 pounds per acre in favorable years and 800 pounds per acre in less favorable years. The total annual production of shrubs and trees, airdry weight, is 800 pounds per acre in favorable years and 600 pounds per acre in less favorable years.
Heavy grazing by livestock causes desirable forage plants such as soft chess and burclover to decrease and less desirable forage plants such as ripgut brome, red brome, annual fescue, wild barley, squirreltailgrass, dogtailgrass, nitgrass, silverhairgrass, tarweed, popcornflower, fiddleneck, turkey mullein, and thistle to increase.
The soils are well suited to seeding with improved annual forage plants if seeding is needed. The soils are also suited to seeding with perlagrass if an adequate seedbed can be prepared. Forage plants respond well to fertilizer. Clearing is feasible where brush has invaded.
This site is good habitat for deer, which use grasses and forbs heavily from December to April. Habitat for quail is excellent. Habitat for turkey is good, since wild oats and oak mast provide adequate food and cover. This site is fair habitat for band-tailed pigeon. This site is fair habitat for wild pig. Brodiaea and other bulb-producing plants and oak mast provide food for pigs. Drinking water is needed during dry seasons.
This site consists of well drained loams of the Millshohn series. Depth to sandstone ranges from 12 to 20 inches. Slope ranges from 15 to 75 percent. Elevation ranges from 500 to 2,500 feet. Annual precipitation is 25 to 35 inches. Permeability is moderate. Available water capacity is 2 to 4 inches.
The natural potential plant community is approximately 60 percent grasses and forbs and 40 percent shrubs and trees. The grasses and forbs include 20 percent soft chess, 10 percent remnant perennial grasses, 15 percent filaree, 5 percent annual clovers, 5 percent wild oats, 2 percent wild carrot, and 3 percent annual lupine. The shrubs and trees included 15 percent scattered oaks, 3 percent digger pine, 7 percent ceanothus, 3 percent toyon, 10 percent manzanita, and 2 percent California laurel.
The total annual production of grasses and forbs, air-dry weight, is 1,500 pounds per acre in favorable years and 800 pounds per acre in less favorable years. The total annual production of shrubs and trees, airdry weight, is 1,200 pounds per acre in favorable years and 600 pounds per acre in less favorable years. Much of the herbage is not readily available for grazing. The total amount of vegetation above ground, for consideration of fuel management and cover values, is 5 or more tons per acre.
Heavy grazing of the grasses and forbs by livestock causes desirable forage species such as soft chess, wild oats, and burclover to decrease and less desirable forage species such as ripgut brome, wild barley, annual fescues, red brome, nitgrass, and dogtailgrass to increase.
The soils are not well suited to seeding, because of the shallow depth and low available water capacity. Reduction of- brush is feasible where brush has invaded.
This site is one of the most important habitats for deer because of the diversity of food and cover plants. From October to May, deer use shrubs, trees, grasses, and forbs. This site is suitable for turkey. This site is very suitable for wild pig because broadiaea and other bulb-producing plants and oak mast provide adequate food and cover. This site is also very suitable for quail because of the diversity of cover plants.
This site can be improved for wildlife habitat by releasing understory vegetation and making forage shrubs more accessible. Growth of nutritious shrub sprouts should be encouraged. Drinking water is needed during dry seasons.
This site consists of excessively drained gravelly loams of the Henneke series. Depth to serpentine bedrock ranges from 10 to 20 inches. Slope ranges from 5 to 75 percent. Elevation ranges from 500 to 4,000 feet. Annual precipitation is 20 to 45 inches. Permeability is moderately slow. Available water capacity is I to 3 inches.
The natural potential plant community is 90 percent shrubs and trees, including 20 percent chamise, 5 percent buckbrush, 15 percent whiteleaf manzanita, 15 percent scrub oak, 5 percent yerba-santa, 5 percent toyon, 2 percent chaparralpea, 3 percent mountainmahogany, 10 percent MacNab cypress, 2 percent digger pine, and 8 percent live oak and blue oak. Scattered grasses such as stipa, poa, soft chess, annual bromes and fescues and filaree, annual clovers, and various other forbs are present in places.
The total annual production of shrubs and trees, air-dry weight, is 1,000 pounds per acre in favorable years and 600 pounds per acre in less favorable years. Much of the herbage is inaccessible to grazing animals. The total amount of vegetation above ground, for consideration of fuel management and cover values, is estimated at 5 tons per acre.
In brushy fields, much of the forage and other vegetation is not available for food and cover.
Brush management and proper grazing use are effective on this site. The soils are not suitable for seeding, because of the slope and the narrow calcium-magnesium ratio.
The hydrologic condition on this site is generally poor.
This site is fair habitat for deer and quail and poor habitat for turkey, band-tailed pigeon, and wild pig.
This site consists of moderately well drained clay loams and loams of the Haire series. Depth to the clay subsoil ranges from 15 to 30 inches. Slope ranges from 9 to 30 percent. Elevation ranges from 20 to 300 feet. Annual precipitation is 25 to 30 inches. Permeability is very slow. Available water capacity is 3 to 6 inches.
The natural potential plant community consists mainly of grasses and forbs. There are some scattered oak. The grasses and forbs include soft chess, wild oats, ryegrass, filaree, Spanish clover, annual clovers, wild carrots, annual lupine, small amounts of burclover, and remnant perennial grasses.
The total annual production, air-dry weight, is 3,000 pounds per acre in favorable years and 1,500 pounds per acre in less favorable years.
Heavy grazing by livestock causes the natural plant community to decrease and less desirable forge plants such as ripgut brome, red brome, wild barley, annual fescue, medusahead, dogtailgrass, silverhairgrass, nitgrass, plantain, thistle, fiddleneck, tarweed, popcornflower, and wild mustard to increase.
The soils are well suited to seeding with perlagrass if an adequate seedbed can be prepared. They also are well suited to seeding with improved annual grasses and legumes where seeding is needed. Forage plants respond well to fertilizer. Proper grazing is important for reduced sedimentation, potential forage production, and a generally enhanced environment.
Deer graze grass and forbs heavily from December to April. Drinking water is needed during dry seasons.
This site consists of well drained clays and clay loams of the Maxwell and Montara series. Some of the soils are artificially drained. Depth to serpentine ranges from 10 to 15 inches or is more than 60 inches. Slope ranges from 2 to 50 percent. Elevation ranges from 200 to 2,500 feet. Annual precipitation is 25 to 45 inches. Permeability is moderately slow or very slow. Available water capacity is 2 to 12 inches.
The natural potential plant community is about half grasses and forbs and about half shrubs and trees. The grasses and forbs included 20 percent soft chess, 10 percent remnant perennial grasses, 5 percent filagree, 5 percent annual clovers, 5 percent Spanish clover, 2 percent annual lupine, 3 percent wild carrot, 2 percent owl clover, and 2 percent brodiaea. The shrubs and trees include 20 percent chamise, 5 percent buckbrush, 2 percent yerba-santa, 10 percent whiteleaf manzanita, 5 percent toyon, and 8 percent digger pine, live oak, and blue oak.
The total annual production of grasses and forbs, air-dry weight, is 1,250 pounds per acre in favorable years and 500 pounds per acre in less favorable years. The total annual production of shrubs and trees, airdry weight, is 1,250 pounds per acre in favorable years and 800 pounds per acre in less favorable years. Much of the herbage is inaccessible for grazing. The total amount of vegetation above ground, for consideration of fuel management and cover values, is estimated at 5 tons per acre.
Dense brush reduces access to forage. Heavy grazing by livestock causes the natural plant community to decrease and less desirable forage plants such as red brome, annual fescues, vinegarweed, nitgrass, and silverhairgrass to increase.
The soils are not suited to seeding because the dominant slope is 45 percent and the calcium-magnesium ratio is unfavorable.
This site is important habitat for deer because of the diversity of food and cover plants. From October to May, deer use shrubs, trees, grasses, and forbs. This site is suitable habitat for turkey. This site is very suitable f or wild pig because brodiaea and other bulbproducing plants and oak mast provide adequate food and cover. This site is very suitable for quail because of the diversity of cover plants.
This site can be improved for wildlife habitat by releasing understory vegetation and making forage shrubs more accessible. Growth of nutritious shrub sprouts should be encouraged. Drinking water is needed during dry seasons.