Brush control is one of the oldest and quickest ways to increase carrying capacity for livestock production, but the economics of this and other range improvement practices have changed. Before the energy crisis of the 1970s, it was less costly to use fossil fuels and fertilizers that are fossil fuel based in range improvement. Following the increase in fuel costs, brush control practices became more costly, as did the cost of planting seed and applying fertilizer. Beginning in the 1950s, ranchers, in collaboration with the university and several government agencies, planned and conducted burns to control brush. By the 1970s, subdivisions and single-family homes had moved into the state’s range and forestlands, creating a huge liability for burning. Prescribed burning is still economical in many instances, but the liability risk, air quality concerns, and cost has resulted in a decrease in burning. The decision to improve rangelands depends on several factors, including financial returns from the improvement, risk of failure, government subsidies, financial returns from alternative practices, effects on vegetation, including recovery following treatment, and current and projected livestock prices and ranch costs. Costs and returns to vegetation management vary with many factors. Differences in site potential and prevailing weather conditions influence the success of vegetation management. Livestock prices, growth rack as well as fuel and labor costs, are important influences that vary over time.
Availability of equipment such as special seeders can also influence costs and practice success. While costs and returns have been reported in budgets in the past, today this information is scarce and highly site-specific. Consequently, we will not attempt to generalize about costs and returns of vegetation management practices. Unlike range improvement to increase ranch profit, reducing fire hazard and restoration of native plants to rangelands are not constrained by profit goals. Consequently, restoration projects often operate under a different set of economic rules than those that guide ranchers. Fuel reduction and restoration of native plants to public and private lands are often subsidized by government programs or by funds from conservation organizations. Creating a profit is seldom an objective. Instead, managing vegetation to reduce fire hazard holds the promise of reducing fire suppression costs and economic losses to catastrophic fires. But realization of the promise will require long-term and permanent investment in vegetation management practices.Historically, oak and shrub removal has been recommended to increase forage production in oak woodlands. From the 1940s to the 1980s, mechanical and chemical tree and shrub control and prescribed burning were often used to selectively thin oak woodlands . In some cases, all trees and shrubs in chaparral and oak woodlands were controlled, resulting in a type-conversion to annual grassland .
Seeding and fertilization often accompanied tree and shrub control. On sites where oak trees are dense and canopy cover is high, forage productivity can be increased by oak tree thinning . On sites where tree density is sparse, such as the oak savannas of the central and southern Sierra Nevada foothills, forage productivity and quality are greater under the trees and oak removal may decrease forage production . In most cases the removal of blue oaks to less than 25 percent canopy cover resulted in increased forage production. In general, live oak stands with greater than 25 percent canopy cover will have less forage growth than cleared areas .Landowners, state agencies, and the University of California have a long history of collaboration on brush control, including prescribed burning . Consequently, there is an extensive literature on prescribed burning and fire effects on woody plants in California’s annual rangelands . Control of woody plants in oak woodland and chaparral ecosystems has been a major theme of ranchers and fire control agencies. Native Americans used fire as a management tool to enhance habitat and to manage food and fiber plants. McClaran and McClaran and Bartolome estimated fire return intervals of about 25 years in oak woodlands prior to European settlement. After settlement, the return interval was around 7 years, due to more frequent burning by settlers.
In the 1940s, Sampson estimated that oak woodland burning by ranchers resulted in return intervals of 8 to 15 years. Beginning in the 1940s, County Range Improvement Associations, in collaboration with the University of California and the California Department of Forestry , conducted prescribed burns to increase forage production and decrease fire hazard. From 1945 to 1975, more than 9,000 burning permits were used to burn more than 2.5 million acres of California rangeland. While prescribed burning continues today, urbanization and air quality concerns have reduced the use of fire as a management tool. Today, fire frequency is more likely to be on the order of 25 to 50 years or longer. Thus, while prescribed burning and mechanical and chemical brush control were frequently used to remove or reduce the shrub and tree layers in oak woodlands and chaparral , since the beginning of the twenty-first century they have been used less frequently. While fire was the first method of brush control, over the years mechanical and chemical methods have also been important. Often fire has been used in combination with mechanical, biological, and chemical methods. Partnering with government agencies such as Cal Fire may provide avenues for mitigating liability for controlled burning on private lands through programs such as the Vegetation Management Program . On public lands, the USDA Forest Service and the Bureau of Land Management are potential partners. These programs usually require the landowner to prepare for the fire by constructing fuel breaks, though the burn itself is conducted by the government agency .Biological control has been defined simply as the utilization of natural enemies to reduce the damage caused by noxious organisms to tolerable levels . One approach to biological control has been termed classical biological control; it involves the discovery, importation, and establishment of exotic natural enemies, with the hope that they will suppress a particular organism’s population. This approach has been most successful in situations in which an organism moves or has been transported to a new environment, usually without the natural enemies that have regulated its population and prevented major outbreaks. There are few examples of classical biological control agents for woody plants on rangelands. Tamarisk beetles have shown some effect on saltcedar along rangeland riparian areas. Biological control of Klamath weed , a non-woody plant, clone rack is discussed in a later section. Weed scientists consider the use of grazing or browsing by domestic animals to be a cultural practice rather than a classical biological control. Goat browsing has been used successfully in California’s oak woodlands and chaparral . While browsing is not an effective means of reducing well-established brush stands, it is useful in managing resprouting and reestablishment following fire and other methods of control. Targeted grazing for managing vegetation is covered in the eighth publication in this series, “Grazing Management.”Mechanical methods are often used in the control of woody plants. For example, heavy equipment such as bull dozer blades with brush rakes or heavy-duty disks can be used to remove small shrubs, and anchor chains pulled between two bull dozers can uproot larger shrubs. In past years, the ball and chain method was used to layover and uproot brush on steep slopes. Adams reviewed the use of these mechanical methods.
Because no single method of control is effective in all situations, biological, cultural, mechanical, and chemical methods are often used in combinations to achieve the best control. Use of prescribed fire is often preceded by mechanical or chemical treatments that allow the brush to dry for several months. Herbicides may be used to kill brush before application of fire or mechanical methods. Chemicals may be applied to clean up after large-scale application of fire or mechanical control. Chemicals or goats can be used following fire to suppress reemerging vegetation. Often seeding of desired species follows control of brush and other weeds to stabilize soil, improve forage production and quality, reduce fire hazard, and improve habitat.In the 1980s, concern about poor oak regeneration, combined with firewood harvesting and permanent conversion to other uses, led to a University of California and state agency cooperative program to improve oak regeneration. Regeneration of blue oaks was of particular concern because they are weak resprouters on some dry sites and because of a number of factors that limit seed germination, seedling establishment, and survival to the tree stage . In the past 30 years, researchers in the University of California Division of Agriculture and Natural Resources developed successful restoration methods of planting acorns and transplanting seedlings and protecting naturally produced seedlings and saplings . They developed site/habitat-specific practices to improve oak regeneration ; identified grazing practices that could protect oaks ; studied oak woodland habitat values ; documented and classified oaks and oak woodlands ; and investigated landowner attitudes about oaks and oak woodlands . Before it was recognized that blue oaks and other oak species were not regenerating on some sites, it was a common practice to remove live oaks, and in some places blue oaks, to increase forage production. Following oak removal, increased light, moisture, heat, and soil nutrients contributed to increased forage production compared to that of natural grassland patches that occur in a mosaic pattern with oak woodlands. But three reports have shown that about 15 years after oak removal, forage production where oaks had been removed was similar to forage production in the natural grassland patches. They attribute this to gradual depletion of the nutrients that had accumulated under the oak canopy. On blue oak sites where regeneration was poor, firewood cutting and removal of oaks have decreased. Raguse et al. developed guidelines for oak woodland range improvement. They recommended leaving woody vegetation along riparian zones and other drainage ways to reduce erosion and also on rocky outcrops and shallow soils where opportunities for increased forage production are low. They also recommended leaving trees on slopes exceeding 30 to 40 percent and leaving scattered groups or corridors of trees of different age classes for wildlife habitat and to maintain an aesthetic view scape. They suggested that seeding of improved forage species only in cleared areas could be used to fill gaps in the ranch’s forage sources.Annual rangeland grazing or carrying capacity is severely reduced by weed infestations. While the annual rangelands are largely populated by introduced annual plants, some are the target of weed control efforts to improve forage quantity and quality and to improve native grass and forb restoration. Yellow starthistle , medusahead , and barb goatgrass are the focus of most rangeland weed control programs, but control of various other thistles, perennial pepper weed , and certain poisonous plants remains locally important. Fire has proven useful for managing many of these weeds, but concerns about liability and air pollution limit the use of prescribed burning. DiTomaso reviewed the impact and management of invasive weeds on rangelands and called for integrated approaches to rangeland weed management. He concluded that successful management of noxious weeds on rangelands will require the development of a long-term strategic plan incorporating prevention programs, education materials and activities, and economical and sustainable multiyear, integrated approaches that improve degraded rangeland communities, enhance the utility of the ecosystem, and prevent reinvasion or encroachment by other noxious weed species. Here, we will review three rangeland weeds that currently receive the most attention and one weed that was successfully controlled using biological methods.DiTomaso et al. published a management guide for yellow starthistle that addresses the introduction and spread of yellow starthistle as well as its biology, ecology, and control methods, including strategic planning of control programs. Tillage, mowing, and hand removal are among the mechanical methods reviewed in this guide.Prescribed burning and targeted grazing can be valuable tools in an integrated management program. Herbicides, both pre-emergent and postemergent, can also successfully control yellow starthistle. In particular, clopyralid, aminopyralid, and aminocyclopyrachlor provide excellent control at low rates. All three of these compounds have both pre- and postemergence activity. A combination of a spring burn followed by a pre-emergent herbicide application in the following growing season has been found to be one of the most successful strategies for yellow starthistle control. The burn suppresses current plants and acts to stimulate germination of much of the remaining seed bank the next fall, which the herbicide then controls.