M. M. Kothmann, R. T. Hinnant, and C. A. Taylor, Jr.
Summary
Development and application of an effective control program for juniper using fire requires an understanding of the relationship between fire and grazing. The concepts that are important to understanding vegetation response are: sustainability, plant succession, seed bank, seed rain, plant vigor, deferred grazing, proper stocking, and grazing behavior of different kinds of animals. Forage may be consumed by livestock or used as fuel for burning. Deferment and proper stocking are keys to promoting improved vigor and composition of herbaceous vegetation and accumulating fuel for burning. The stocking rate and grazing schedule should allocate enough forage to livestock to provide ranch income and also allocate enough to fuel for effective burning. Ranchers can use a program such as The Grazing Manager to determine the most effective stocking rate and grazing schedule to reduce the cost of burning and increase the probability that burning can be implemented as required to control juniper regrowth.
Introduction
Grazing management and brush control have often been treated as separate issues by rangeland managers. When mechanical and chemical methods of brush control are used, it is possible, although not advisable, to ignore grazing management. However, increasing costs for mechanical and chemical brush control methods and the realization that these controls will be required every 15 to 20 years make them less viable as the sole alternatives. Juniper density is increasing across large areas of Texas and the rate of reinfestation from seed will continue to increase. This means more frequent application of control practices. In the absence of fire, pricklypear and other woody species are also increasing on Texas rangelands and mechanical control of juniper may actually help spread
pricklypear. Based on these considerations, fire is a promising long-term brush management tool. The objective for using fire should be control of woody plants; eradication is not a feasible alternative. When fire is to be used for brush management, grazing management must play a central role in designing and implementing the brush management program.
The kinds of expertise and management skill required to implement different juniper management practices varies considerably. Mechanical control of juniper requires the least amount of expertise but has high inputs of cultural energy and costs. Chemical control requires more expertise than mechanical, and is also expensive. Burning has the lowest level of cultural inputs and is potentially the least expensive method, but it requires the highest levels of expertise and a commitment to long-term management planning (Figure 1).
Vegetation serves a dual role as forage for grazing animals and as fuel for prescribed burns. The manager must balance the amount of forage that is used by grazing animals and the amount that is used for fuel. Vegetation used for forage can generate income; however, vegetation used for fuel is an expense incurred with the expectation of enhancing future income. Both the cost and effectiveness of a prescribed burning program depend upon the allocation of vegetation to either forage or fuel. If too much is allocated to forage, there will not be enough fuel to obtain effective brush suppression. However, if excess vegetation is allocated to burning, there may be little increased brush suppression but the cost of the burn may be significantly increased because of reduced animal production.
There is a potential trade-off of inputs for juniper control between cash and management. Those managers willing to make a commitment to developing their knowledge and managerial skills can reduce their costs for obtaining long-term juniper control. This raises two questions which we will evaluate in this paper. (1) What knowledge and managerial skills are required? (2) What tools are available to assist managers in developing effective grazing/burning management plans?
Considerations
Planning and implementing a successful prescribed burning program to provide long-term control of juniper requires basic knowledge in the areas of forage and animal production, grazing management, juniper ecology, and prescribed burning. Before beginning a burning program, the manager should obtain training in these concepts and techniques. It will also be wise to enlist the aid of someone trained and experienced with prescribed burning to assist with development of the burning plan and to supervise the first burns. Specialists in Natural Resources Conservation Service, Texas Agricultural Extension Service, and Texas Parks and Wildlife can provide such assistance.
Concepts
Several concepts are critical for developing effective prescribed burning programs.
Sustainability is like a stool with three legs. The three legs are the components: physical (primarily soil), biological (vegetation and animals), and economic (income and expenses). Sustainability of a ranching enterprise depends upon maintaining the productivity of soils, vegetation, and animals. Accelerated erosion resulting from inadequate cover reduces the depth, fertility, and productive potential of soils. Productivity of vegetation is related to the kinds, amounts, and health of plants present. When desirable forage plants are replaced by plants with low nutritive value, animal production will be reduced. Sustainable animal production requires managing for soil stability and desirable forage species. Many plant species, in addition to juniper, that increase on rangelands in the absence of fire have low forage value. A cost effective vegetation management program is essential for economic sustainability.
Plant vigor refers to the size and health of individual plants. Plants in good vigor exhibit rapid growth and produce good seed crops when conditions are favorable. Plants in low vigor are stunted and grow slowly even when conditions are favorable. Close frequent defoliation will reduce plant vigor. Following close defoliation, if growing conditions are favorable, plants produce new leaves and root growth declines. Frequent close defoliation reduces the root system resulting in plants that are much more susceptible to death from stresses such as burning or drought. Proper stocking and regular deferment prior to burning are important to establish good vigor in the desirable forage plants. Burning can reduce the vigor of woody plants much more than for grasses; thus, it shifts the composition of the vegetation towards less woody and more grasses.
Seed bank is the total number of viable seeds that are present in the soil. Seeds of different species remain viable for different periods of time. Different plant species have different strategies for seed production. Annual species produce a large number of seeds and the plants die. They start over from seed every year. Perennial grasses produce fewer seeds than annuals but the plants survive from year to year. Their seeds are viable for a few years; thus, regular additions to the seed bank are required. Some plants such as mesquite produce seeds that can remain in the soil for many years and still germinate. Juniper produces large numbers of seeds which generally remain viable for less than two years. Juniper seeds are transported by many animals and birds. An area with mature juniper trees will have a many juniper seeds in the soil. If it is cleared, these seeds will germinate and reinfest the area. Thus, follow-up treatment must be planned.
Seed rain is seed produced from somedistance away added to the seed bank. The seeds may be produced by plants growing in the immediate area, or they may be transported into the area by wind, water, animals, or birds. The distance that seed can be transported depends upon the method of transport. Birds and varmints are primary carriers of juniper seed. Since juniper seeds remain viable in the seed bank for only 1-2 years, the rate of seed rain is very important in determining the rate of reinfestation that may occur after an area has been cleared of mature trees and the seed bank depleted of viable seeds.
Plant succession results in natural changes in species composition on a site. Plant succession results from the processes of growth, competition, reproduction, establishment of new plants, and death of existing plants. Climate, soils, fire, and grazing are the primary factors that determine the direction of successional changes on rangelands. Climate and soils are not subject to direct management control but fire and grazing can be managed to direct plant succession.
In the absence of fire, evergreen species like juniper accumulate nutrients and shade competing species. Grasses and woody plants that shed their leaves in the fall release much of the nutrients they accumulate each year during the dormant period. Perennial grasses are very efficient in recapturing available soil nitrogen when the new growing season starts. Evergreen species are not adapted to a release and recapture growth strategy as are grasses. Thus, they are suppressed by burning which forces nutrient release and reduces their height advantage; whereas, burning promotes grasses.
Deferred grazing is the practice of removing all livestock from a pasture for an adequate period of time to allow forage species to grow and reproduce without being grazed. The pasture may then be grazed to utilize the accumulated forage. Deferment is a very important component of a prescribed burning program. It provides for the accumulation of adequate amounts of fine fuel and improves continuity of fuel which contribute to an effective burn. It also allows desirable forage plants to increase in vigor and seed production. Not all rotational grazing systems will provide deferment. If the rotation is too rapid, the non-grazed periods will be too short for the desirable forage plants to recover from the previous defoliation and reproduce. Recovery of a plant that has been closely defoliated involves regrowth of leaves followed by resumption of root growth which will lag new leaf production. If defoliation occurs too frequently as in rapid rotations, root growth will be greatly reduced and plant vigor decreased.
Proper stocking is essential for an effective burning program. The total number of animals on the ranch must be set at a level that will allow forage accumulation for burning without overgrazing some of the pastures. Stocking rate determines the degree of use on the vegetation. The criteria for evaluating proper stocking is the degree of use on the key species, i.e., the most important forage plants. Since forage production varies greatly among years and seasons, it is difficult to determine a correct stocking rate. When prescribed burning is planned, forage must be allocated for fuel as well as for grazing. The Grazing Manager (TGM) is a computer program designed to assist a manager with planning and monitoring grazing to achieve proper stocking.
Range condition is based on the kinds of plants present. Heavy stocking will reduce range condition; however, moderate stocking with periodic deferment will improve range condition, if the density of woody plants is controlled. When combined with proper stocking, the use of deferment before and after burning is an effective method to improve range condition. Forage production declines as range condition decreases and as juniper density and stocking rate increase.
Kind of animal, eg., cattle, sheep, goat, etc., will affect the degree of use on different plant species and the structure and distribution of fuel for burning. Cattle prefer grasses and will not use much browse. Thus, as cattle grazing increases, the availability of grasses will decrease. Sheep prefer forbs and grasses and, if stocked too heavily, will graze preferred areas very closely causing discontinuities in fuel which will reduce the effectiveness of fire. Since grasses are the primary source of fine fuel for burning, stocking with cattle and sheep should be light to moderate. Goats utilize browse effectively and do not graze grasses closely unless stocked extremely heavy. Goats can be stocked to increase livestock production without greatly reducing the amount or continuity of fine fuel. Goats will utilize seedling juniper and when used in combination with burning, they can improve the level of juniper control. Continuous heavy stocking with goats is not recommended. Heavy stocking with goats during the winter after mature trees have been controlled can be an effective means of reducing the number of seedling juniper that establish. During spring and summer, goats will prefer grasses and forbs to juniper. However, during the winter when grasses are dormant their preference for juniper increases.
Example
Let’s assume a deep upland soil, nearly level, with 25 inch annual average precipitation. Suppose we start with an open grassland with a good stand of bunch grasses with moderate use and no fire. Woody vegetation currently consists of scattered liveoak mottes, an orchard stand of mature mesquite trees, and scattered large pricklypear plants. The nearest mature juniper plants are 2 miles away in some steep rough canyons. Pricklypear will increase the number of seed in the seed bank and the number of young plants. Mesquite will produce many seeds which will remain in the seed bank for many years. Liveoak will probably be stable or increase very slowly. Juniper will invade the site by seed rain. Wind and water will not move the seed up slope, thus, birds will be the primary vector. Initially only a few juniper plants will establish under trees, fences, and other areas where birds may perch. As juniper plants nearer this site mature and begin to produce seeds, both the rate of seed rain and plant establishment will increase. These changes will not be greatly affected by grazing management. If the site is properly stocked, burning will be a viable option for suppression of juniper and pricklypear.
Suppose we start with the same site in the same initial condition as described in the previous example, except with heavy stocking. The bunch grasses will be closely grazed and new leaves will be grazed soon after they are produced. The root system of these grasses will get shorter and thinner with the result that these plants will not be able to compete effectively for soil water and nutrients. Existing short grasses, annual grasses, and woody vegetation will utilize the resources formerly used by the bunch grasses. Bare patches will appear in the pasture and the amount of herbaceous vegetation present will be low and discontinuous. The rate of juniper invasion may be similar to the previous example, but in this case, there will be no fine fuel to initiate a burning program for control.
Inventory
The first step in planning a prescribed burning program is for the manager to inventory the current condition of both herbaceous and woody vegetation. The current status of the vegetation and the stocking rate will determine the potential for using prescribed burning and what may need to be changed prior to burning. The current status of the vegetation will determine the kind of plan that should be developed. If the manager cannot identify the primary forage species and does not understand basic concepts of plant ecology, assistance should be obtained from someone who has such training. Proper grazing management both before and after a burn is required for success.
Several different scenarios relative to stocking rate, range condition, and juniper age and density will be described to illustrate the influence of these three factors on the potential for and the approach to prescribed burning. The examples are ordered from the lowest to highest potential for burning.
Heavy stocking, poor range condition, dense mature juniper.
Under these conditions there is almost no potential for initiating a prescribed burning program until the mature juniper have been mechanically controlled and grazing management is improved. A burn should be scheduled within a few years after the mechanical control to kill young juniper plants that were missed and those established from the seed bank. Following the initial juniper control, using intensive goat grazing during the winter will help maintain control.
Heavy stocking, poor range condition, light infestation of young juniper.
Initially the potential for prescribed burning is low; however, improved grazing management may provide adequate fuel before juniper becomes dense enough to seriously reduce forage production. Initiating a control program before the juniper reach maturity and begin producing seeds is important. Years of heavy stocking reduces range condition, soil condition, and plant vigor. The pasture may not produce enough fuel to support an effective fire even if it is rested for a year prior to burning. In these cases, stocking rates should be reduced and pastures provided deferment to increase plant vigor and seed production of desirable species prior to burning. Burning prior to correcting grazing management problems will not yield good results. Pastures should not be grazed during the year prior to burning and they should be rested after the burn until the desirable forage species have matured. If they are grazed during the first growing season after the burn, the few remaining desirable forage plants and new seedlings will receive heavy use and may be killed. Implementing a prescribed burning program under these conditions will incur higher deferment costs than on moderately stocked good condition ranges. However, making these management changes is the first step to stopping deterioration of vegetation and soils and to begin improving range condition.
Moderate stocking, fair condition, dense mature juniper.
Prescribed burning may not be effective until the mature juniper have been killed. Burning may be feasible after only one growing season of deferred grazing to increase fuel load and increase seed production of desirable forage species. However, growing season deferment followed by dormant season grazing should be practiced prior to and following the burn to improve continuity of fuel, plant vigor, and seed production of desirable species. Cost of implementing burning on this kind of pasture will be intermediate to the poor condition and good condition pastures. The procedures recommended here are designed to improve range condition as well as to control juniper.
Moderate stocking, good condition, light juniper infestation.
It should be feasible to initiate burning during the first year. This type of pasture will have good species composition and the seed bank should have ample seed of desirable species for good establishment following a burn. Deferment cost will be minimal for these pastures since the amount of forage that normally remains after grazing is nearly adequate for burning. Since forage production potential on these pastures is high, it may be possible to apply moderate grazing during the spring and summer prior to the burn. Grazing may be resumed during the first growing season after the burn when standing crop is adequate. These pastures should receive periodic deferment as part of a planned grazing schedule to maintain range condition.
When and how often should I burn?
Many rangelands currently support moderate to dense stands of mature juniper. Implementing burning these lands frequently will require mechanical control of the large trees. Small trees could be left for clean-up by prescribed burning. Some of the dense juniper stands may be left for wildlife cover on steep shallow sites. The contribution of mature trees to seed rain should be considered. If there are many mature plants on neighboring properties, the presence of some on your land may have little additional effect on the rate of reinfestation by juniper seedlings.
The ideal time to develop and initiate a prescribed burning program is when all of the juniper plants are small. The smaller the plants, the easier they are to kill with fire. Research at the Sonora Research Station indicates that it may take 10 to 20 years for seedling juniper plants to reach reproductive maturity. As the size of the juniper canopy increases, forage production is progressively reduced and burning becomes difficult. The rate of growth and increase in density of juniper are directly proportional to the amount of rainfall; thus, in the eastern Edwards Plateau burning will need to be more frequent than on the western edge.
Prescribed burning is generally conducted during the winter when most grasses are dormant. Research is being conducted on the Sonora Research Station to evaluate the effects of summer burning. Because of higher summer temperatures and lower humidity, risk related to control of fire is greater than for winter burning. Burning during spring or fall is not recommended. Temperature, humidity, wind speed, and topography of the site of the burn will greatly affect the intensity and behavior of a fire. Only an experienced individual should develop and implement a fire plan. If you do not have experience, attend a short course, read publications describing procedures for prescribed burning, and assist an experienced crew in conducting a burn.
The optimal frequency for burning depends upon the rate of reinfestation and growth of juniper canopy. A plan should be developed to rotate burning among the pastures at a frequency that will prevent young plants from maturing and producing seed and becoming so large that the fire will not kill them. This means that each pasture should be burned every 5-10 years. Burning will not be possible in some years because of too much rain, too dry, too windy or other factors. This means that in good years for burning, several pastures may need to be burned to make up for skipped years. If the proportion of forage allocated to grazing is high, there will be few years with enough to support an effective burn, or only a small portion of the ranch can be deferred for burning. This will result in a longer burning rotation that may result in plants becoming too large for control by burning.
Developing a Grazing Plan
An effective grazing plan will have several attributes. It will balance forage demand with the current year’s forage production, distribute grazing uniformly across pastures and provide deferment for selected pastures during critical growth periods. Desirable forage species will not be grazed closely during the primary growing periods in any of the pastures. These goals can be achieved using the grazing management program, TGM. With it you can determine the stocking rate that will allocate enough forage to burning to achieve the necessary burning rotation. An effective stocking strategy will set total forage demand at a level to provide adequate fine fuel for prescribed burning on 1/5 to 1/10 of the area needing control in all but drought years when burning should probably be skipped. Extra pastures can be burned during years with above normal forage production.
When and how long should pastures be deferred?
The primary growth periods for the key forage species should be identified. Determine when they initiate growth and when they reproduce. Deferment periods should start during early growth and extend until seed set. Plants in good vigor respond effectively to shorter deferment periods than plants on low vigor. Ranges in poor condition with low vigor plants will require 4-6 month deferments to be effective. The length of the deferment will vary with the species. For grasses like sideoats gamma, deferment periods from May through July and August through October will be effective if moisture is available. For tall grasses like little bluestem and indiangrass, which are more prevalent in the eastern Edwards Plateau, deferments from June through October will be required. Properly stocked pastures in good condition will not need deferment as frequently as poor condition pastures which need to improve.
Productive pastures with uniform cover of herbaceous vegetation may be grazed lightly prior to burning and then grazed again after the burn as soon as adequate forage regrowth is present. Deferment may follow later during the growing season. On the other hand, poor condition pastures will need more deferment to accumulate adequate amounts of fine fuel prior to burning and will need deferment during the growing season immediately after the burn to allow establishment of desirable plants. An exception may be made if livestock are grazed in the pasture immediately after the burn to eat pricklypear that was singed by the burn. However, the livestock should be removed when the grasses begin rapid growth.
Conclusions
Long term juniper control will require repeated application of control practices. Burning has the potential to be an effective low cost control method but it requires greater levels of expertise than other control methods. It is advisable to study prescribed burning techniques, to understand basic concepts, and to obtain experience prior to implementing a prescribed burn. Implementation of a prescribed burning program to provide long term control of juniper will require attention to grazing management. Grazing management required for an effective prescribed burning program will also be effective for improving range condition. An additional benefit from prescribed burning, compared to mechanical control, is that other problem species such as prickly pear will also be reduced.
Comments: Allan McGinty, Professor and Extension Wildlife Specialist