Ecological Characteristics and Control of Gambel

Manipulation of Gambel oak for enhanced rangeland values must be in accord with ecological principles to ensure desired success. Failures in controlling Gambel oak have occurred because the growth patterns, morphological characteristics, and carbohydrate storage patterns of the species have not been taken into account. However, recurrent control will continue to be necessary since grass dominated systems should not be considered to be climax in Gambel oak dominated systems. Existing initial and maintenance control methods appear to offer only short-term solutions, which often result in more troublesome long-term management problems. Gambel oak (Quercus gambelii) is considered a major brush problem species on millions of acres of foothill ranges in Colorado, Utah, New Mexico, and Arizona. Creating open grasslands by removal of mature stands of Gambel oak from these ranges increases watershed values and presents several advantages to the livestock producer (Marquiss 1972). The greatest benefits are an increase in forage produced for livestock and enhanced livestock handling. However, since Gambel oak is a natural part of the vegetation, recurrent treatment is required to retain these advantages. Eradication of Gambel oak is rare by any method, and without complete kill prolific sprouting may occur from roots, rhizomes, and basal stems. Treated ranges many times assume a “thicket”like appearance several years after an initial oak control effort. These sprout thickets differ from the original mature oak stands in both their structure and response to control methods. Range managers are in need of effective control methods on these previously treated areas where abundant oak sprouts are difficult to control with conventional methods and present a major management problem. We suggest here some reasons for the difficulty in controlling Gambel oak and propose some possible alternatives for dealing with the Gambel oak sprouts. Problems in Controlling Gambel Oak Application of Ecological Principles Range scientists recognize that proper and wise management of ranges includes direct manipulation of the ecosystem. Such manipulation should be directed in ways that work in accord with the natural functioning of ecosystems and should be based upon ecological principles, that is, particularly competition and succession (Vallentine 1971). With increasing costs of fuels and herbicides, conventional methods of manipulating oakbrush ranges must continue to be cost effective, as well asenvironmentally sound. Yet, the demand for meat by an expanding world population is sure to place pressure on the livestock producer to increase the productivity of rangelands. Range scientists, in some cases, concede that it is unwise to continually confront natural ecosystem forces by Authors are graduate research assistant, Colorado State University, presently associate professor, Department of Agronomy, Oklahoma State University, Stillwater 74078; professor, Range Science Department, Colorado State University, Fort Collins; and range researcher, San Juan Basin Research Centef, Hesperus. This report is Contribution No. 2644 of the Colorado State University Experiment Station. JOURNAL OF RANGE MANAGEMENT 36(3), May 1993 attempting to remove Gambel oak over broad areas at a relatively high cost while ignoring the renewable forage resource supplied by the oakbrush. Perhaps it is time for researchers and managers also to consider the possible worth of Gambel oak and concentrate more on developing its benefits to ranchers and society in general. The time may be approaching when range scientists and ranchers can no longer afford, economically and politically, to continue viewing Gambel oak only as a noxious species. Site specific manip ulation of oak will continue to be important, but we will probably be unable to eradicate the species. Growth and Morphology of Gambel Oak Preformed shoots are characteristic of predeterminate species such as Gambel oak (Sweeney 1975, Dahl and Hyder 1977). These species have winter buds that contain a telescoped, fully formed shoot containing primordia of all leaves that will subsequently expand the following season. This 2-year process involves bud formation in the first year and elongation of the preformed components into a shoot the second year. Only a portion of the winter buds become active whereas others remain dormant. If new shoots are defoliated, for example, by early spring frost, other shoots often develop from dormant buds, depending on the degree of defoliation (Kozlowski 1971). Gambel oak generally produces two kinds of shoots, i.e., long and short. Long shoots have leaves separated by distinct internodes and bear lateral buds which may develop either into more long shoots or short shoots (Kozlowski 1971, Dahl and Hyder 1977). Gambel oak sprouts are predominantly long shoots, and are more difficult to control than mature oak which have predominantly short shoots (Engle 1978). This characteristic of sprouts accounts for most difficulties encountered in herbicide control. That is, Wilson et al. (1975) suggested that for best control with herbicides, woody plants should have a higher proportion of short shoots. Carbohydrates and translocatable herbicides are moved mostly to the growing young leaves at the tip of long shoots instead of to the roots and other storage tissues. Long shoots are more prevalent in young trees than in older trees, and by the fourth or fifth order of branching, the long shoots bear only short shoots perhaps because of a general decrease in vigor (Wilson 1970). Therefore, young plants with larger proportions of long shoots are more difficult to kill with translocated herbicides than older plants (Dahl and Hyder 1977). Oak trees ordinarily exhibit the intermittent type of growth common to most trees of temperate zones where height growth occurs in a single flush of growth (Zimmerman and Brown 1971). All the leaf primordia are preformed in the overwintering terminal bud and height growth is usually restricted to a single period early in the growing season. The length of shoot elongation also affects the species’ response to defoliation and herbicide applications. Mature Gambel oak have been reported to have a short period (24 to 27 days) of shoot growth, which is completed by the first week in July (Sweeney 1973, but Gambel oak sprouts have prolonged and numerous elongation periods (Engle and Bonham 1980). The duration of elongation in mature oak remains rather constant each year (Sweeney 1975). Gambel oak sprouts probably have a longer period of shoot elongation than do mature trees. Species of Quercus have a tendency to form “lammas shoots,” which presumably appear around Lammas Day or August I (Kozlowski 1971). This type of shoot results from bursting and elongation of a current-year terminal bud on the main shoot or branch. Marquiss (1969) reported a late summer regrowth of Gambel oak in late August. Lammas