By Larry Branham, Range Specialist, Natural Resources Conservation Service

There are approximately 325,000 acres of rangeland in Colusa County. The majority of rangeland is located in the western part of the county and is situated between the irrigated cropland on the valley floor and the brush and forestland of the mountains. Elevation ranges from about 200 to 7000 feet.

The typical livestock enterprise is a cow-calf operation although stocker operations do occur. The 1996 Colusa County Agricultural Commissioner summary reported there were 24,000 cattle and calves valued at over seven million dollars. In addition some range areas are used in a long rotation with dryland cereal grain production.

The weather has a significant influence on the growth of range vegetation. The occurrence of the first effective rainfall and distribution of subsequent rainfall as well as temperature greatly affects seasonal growth and total forage production. Typically, soil moisture conditions are favorable when temperatures are too low (December through February) for good plant growth and soil moisture can be limiting when temperatures are optimum for plant growth (April and May). Soil moisture conditions in the spring greatly affects total production and species composition.

In addition to climate, the factors of soils, topography and aspect influence forage production and species composition.

Soil factors which affect forage production are effective rooting depth, water holding capacity, texture, organic matter, fertility and parent material. These factors in varying combinations determine the forage production potential of the soil. In general, the deeper fine textured soils have a high forage production potential while the shallow, coarser textured soils tend to have a lower production potential.

Grazing on soils when they are wet can lead to severe soil compaction. Fine textured soils such as clay and clay loams are especially prone to compaction. Compaction increases the bulk density and strength of the soil while reducing the infiltration rate and porosity. These conditions lead to increased runoff, slow seedling growth and restricted root development. Compaction and its effects can be lessened by maintaining adequate ground cover and by allowing the soil to rest and recover through prescribed grazing management.

Soil parent material affects the type and amount of nutrients available for plant growth. In some cases, the proportion of nutrients may limit plant growth. Soils derived from serpentintic parent materials, such as those found in Bear Valley may exhibit reduced production because of the high magnesium to calcium ratio.

Topography affects the moisture regime that influences forage production. Steep slopes tend to have high runoff that reduces the opportunity for infiltration of rainfall as well as having high potential for erosion. Moderate to gentle slopes have reduced runoff and more opportunity for infiltration with a lower potential for erosion. Flat and bottom areas collect and hold runoff that can create saturated soil conditions.

Aspect affects forage production primarily through increased temperatures and solar radiation. South and west slopes tend to dry faster and mature earlier in the spring. North slopes tend to be colder in the winter and mature later in the spring.

Range vegetation in the area is dominated by annual cool season grasses and forbs, the majority being introduced from Europe. Cool season annuals begin each year from seed, requiring favorable moisture and temperature conditions for germination.

These introduced species include both desirable forage species such as soft chess, wild oats, burr clover and filaree, as well as less desirable species such as medusahead, star thistle and red brome.

Warm season summer growing species do occur, but, they are usually of little forage value. These species include tar weed, vinegar weed and turkey mullein. These species grow and survive on residual soil moisture not utilized by the cool season species.

Native plant species, particularly the perennial grasses, do occur throughout the rangeland area of the county. Their contribution to overall forage production is limited, but where they do occur they provide significant forage both early and late in the growing season. Cool season native perennial grasses include the needle grasses, wild ryes, onion grasses and pine bluegrass. Additional native species include woody plants such as blue oak, foothill pine, California juniper, buckbrush, manzanita, chamise and native forbs such as lupines, brodiaeas, lilies and poppies.

Proper management is essential to maintain or improve the sustained productivity of rangeland for livestock, wildlife and related resources. Proper management must address the needs of the animal as well as the needs of the plant.

Following are management concerns and range improvement practices that should be considered for the proper use of rangeland.

Prescribed grazing is the controlled harvest of range forage at a level and intensity that optimizes forage production while at the same time addressing the needs of the associated resources; plants, animals, soil and water. Guidelines for developing a grazing management plan may include key forage species, season of use, seasonal plant growth, forage utilization, animal nutrition, livestock distribution, and proper grazing use.

The key forage species may be a single or select group of species such as native perennial grasses or a desirable plant community. In either case it is important to know the growth and reproductive requirements of the chosen species and develop management guidelines to address these needs.

Season of use is the period when the range is being grazed. This period typically starts in November or December and runs through April or May. Within the grazing period there are three growth phases. These phases relate to the rate of growth and quality and quantity of available forage.

The first phase begins with the fall rains and germination of the winter annual species and continues through the winter slow growth period. Available green forage is limited and livestock primarily utilize residual dry matter from the previous growing season. Forage quality is low and supplementation is usually required to meet the nutritional requirements of the livestock.

The second growth phase begins in late winter. During this period, the rate of forage growth increases and quality and quantity are adequate for livestock nutritional requirements.

The third phase begins in early spring and continues to plant maturity. During this period, forage growth exceeds the nutritional requirements of the livestock and there is a surplus of forage. It is during this period that grazing can be adjusted to leave the proper amount of residual dry matter on the soil.

Balancing livestock numbers to the different growth phases will allow for the efficient utilization of available forage, encourage the growth of desirable forage species and reduce soil trampling during the winter.

Range improvement practices such as livestock water developments, fencing and access trails are used to achieve better livestock distribution and uniform forage utilization. These practices should be part of an overall grazing management plan.

Practices such as range seeding, fertilization and brush management are used to restore or improve forage productivity. A grazing management plan must be used to insure that the conditions that required these practices do not continue to occur.

Riparian areas, although small size in total area are very important components of rangeland ecosystems. They provide essential habitat for many wildlife species, carry runoff from the rangeland and provide water and forage for livestock. Consideration should be given to managing these areas as separate units to maintain and enhance the many benefits derived from them.

In areas that have similar climate and topography, differences in the kind and amount of vegetation produced on rangeland are closely related to the kind of soil. Effective management is based on the relationship between the soils and vegetation and water.

Table 11 shows, for each soil that supports rangeland vegetation suitable for grazing, the ecological site; the total annual production of vegetation in favorable, normal, and unfavorable years; the characteristic vegetation; and the average percentage of each species. An explanation of the column headings in the table follows.

A range site or ecological site is a distinctive kind of rangeland that produces a characteristic natural plant community that differs from natural plant communities on other range sites in kind, amount, and proportion of range plants. The relationship between soils and vegetation was ascertained during this survey; thus, range sites generally can be determined directly from the soil map. Soil properties that affect moisture supply and plant nutrients have the greatest influence on the productivity of range plants. Soil reaction (pH), salt content, and a seasonal high water table are also important.

Total production is the amount of vegetation that can be expected to grow annually on well-managed rangeland that is supporting the potential natural plant community. It includes all vegetation, whether or not it is palatable to grazing animals. It includes the current year’s growth of leaves, twigs, and fruits of woody plants. It does not include the increase in stem diameter of trees and shrubs. It is expressed in pounds per acre of air-dry vegetation for favorable, normal, and unfavorable years. In a favorable year, the amount and distribution of precipitation and the temperature make growing conditions substantially better than average. In a normal year, growing conditions are about average. In an unfavorable year, growing conditions are well below average, generally because of low available soil moisture.

Dry weight is the total annual yield per acre of air-dry vegetation. Yields are adjusted to a common percent of air-dry moisture content. The relationship of green weight to air-dry weight varies according to such factors as exposure, amount of shade, recent rains, and unseasonable dry periods.

Characteristic vegetation—the grasses, forbs, and shrubs that make up most of the potential natural plant community on each soil—is listed by common name. Under composition, the expected percentage of the total annual production is given for each species making up the characteristic vegetation. The amount that can be used as forage depends on the kinds of grazing animals and on the grazing season.

Range management requires a knowledge of the kinds of soil and of the potential natural plant community. It also requires an evaluation of the present range condition. Range condition is determined by comparing the present plant community with the potential natural plant community on a particular range site. The more closely the existing community resembles the potential community, the better the range condition. Range condition is an ecological rating only.

The objective in range management is to control grazing so that the plants growing on a site are about the same in kind and amount as the potential natural plant community for that site. Such management generally results in the optimum production of vegetation, control of undesirable brush species, conservation of water, and control of erosion. Sometimes, however, a range condition somewhat below the potential meets grazing needs, provides wildlife habitat, and protects soil and water resources.

Technical assistance in rangeland management can be obtained from the local Natural Resources Conservation Service (NRCS) or the Cooperative Extension Service.