Brush Management: Past, Present, Future

2. Mechanical Practices prior to 1975

2 Mechanical Practices prior to 1975 A variety of mechanical tools and procedures were developed to combat brush problems throughout the eradication and control eras. Extensive mechanized brush control has a history beginning in the early 1930s that has developed through concurrent and distinct phases involving the use of plows, saws, steel cables, heavy chains, large rolling choppers, large rootplows , and other equipment. This chapter reviews the early efforts at mechanical brush manipulation until 1975, the beginning of the brush management era. Factors Influencing Mechanical Brush Management Methods In the years from the first efforts at serious mechanical control of brush until about the mid-1970s, several things emerged about woody plant physiology and morphology that were important in the design of practices. One of the most significant of these was the aggressive resprouting ability following top removal of several important woody species, including honey mesquite (Prosopis glandulosa var.glandulosa) and huisache (Acacia smallii), as well as a host of associated shrub species. Top removal, or even top growth damage, stimulated buds at the base of stems on subterranean root crowns or on roots of some species, such as lotebush (Zizyphus obtusifolia) and Macartney rose (Rosa bracteata). Therefore, mechanical practices, fire, or even biological control by grazing animals that resulted in top removal provided only short-term relief from resprouting woody plants. The aggressiveness of this regrowth was observed by many and documented by Powell et al. (1972) who showed that huisache cut near ground line on April 1 elongated approximately 4 feet of new growth by October 1 of the same year. Seedling survival after top growth removal is also significant. Scifres et al. (1971) reported that 60% of seedlings survived after being cut above the cotyledonary axil 7 days after emergence and 95% survived after 7 weeks. Seedlings that were cut 1 month after emergence resprouted within 5 days. Once a seedling is established, it is virtually impossible to cause mortality with mechanical equipment that provides only top removal. Although the Wayne T. Hamilton and C. Wayne Hanselka 17 seedlings will suffer mortality if cut below the cotyledonary axil, this area of the plant is too close to ground level for effective clipping with equipment on range landscapes. It became obvious that mechanical brush control practices were often followed by an unwanted spread of pricklypear (Opuntia spp.) Pricklypear density increased by a factor of 2 to 3 times on rootplowed, rootplowed and raked, and on chained areas compared to adjacent untreated areas (Dodd 1968). Thousands of acres of South Texas that had moderate to sparse stands of pricklypear before chaining or rootplowing were converted to solid pricklypear patches by these practices (Meadors et al. 1973). Grubbing of mesquite in the Texas Rolling Plains had similar, although less dramatic , results where pricklypear was associated with mesquite and was spread by mechanical grubbing equipment. By the mid-1970s, the cost of broadcast mechanical practices was high enough to make a single treatment, such as chaining or even rootplowing, only marginally economical in most cases within their effective treatment lives. This brought recognition of the need for a more strategic, long-term approach and planning for low-cost, follow-up practices to stretch benefits of initial high-cost treatments (Scifres et al. 1985). Hundreds of thousands of acres were chained in the 1950s and 1960s with no maintenance treatments . Similarly, areas were rootplowed, or rootplowed, raked, and seeded to introduced grass species with no long-term maintenance of woody plant reinvasion. As cost of initial treatments escalated it became more difficult to show acceptable returns on investment without maintaining the maximum benefits from these treatments for 10 to 20 years. It also became obvious that there were significant differences in the potential of different ecological sites (range sites) to pay for investments in woody plant management (Allison and Rechenthin 1956). This led to more discriminating locations of treatments on the landscape. The first recognition of site differentials was based on soil depth, inherent fertility, and productivity potential with relation to forage for livestock. Near the end of the period in the late 1960s and early 1970s, wildlife habitat became a consideration in the design of mechanical treatments, with vegetation types and their physical structure and nutritional utility gaining in importance. Shallow ridge sites where species such as guajillo (Acacia berlandieri) were present or riparian areas with mesic environments (including large trees, dense shade, and mast) were not usually treated. However, this was still primarily...