Investigator: Travis Whitney (Texas A&M University)
By the year 2030, Texas' population will almost double to 33 million people (Murdock, Hogue, Michael, White, & Pecotte, 1996). Rangelands alone make up over 60% (90 million acres) of the total land area of the state (Texas Farm Bureau, 1997). These rangeland holdings are becoming smaller, thus increasing the number of landowners per unit of land area. Over 202,000 Texas farms (76.7% of total farms) are less than 500 acres in size (American Farm Bureau, 1998). The growth in the number of land managers that want and need assistance from components of the Texas A&M Agriculture Program has and will continue to place greater demands on the system. The obvious answer to the problem of providing effective transfer of the increased amount of technology needed to foster better management decisions by rangeland producers is to provide more one-on-one, "on-ranch" contacts between highly qualified range specialists and producers. However, resource constraints continue to reduce on-site contacts with ranchers by specialists. One possible solution is to use electronic technology to gather and exchange information. Current technology provides a means to utilize the Internet with digital imagery and e-mail to overcome the time and cost limitations of personal contacts between specialists and clientele.
The Center for Grazinglands and Ranch Management (CGRM), in collaboration with the Texas Agricultural Extension Service (TAEX), is working with the University of Georgia to produce an Electronic Technology Transfer System (ETTS). This system will become a database for rangeland situations captured on digital imagery. This system will also provide producers and County Agricultural Extension Agents with a means to receive expert advise on rangeland attributes such as species identification, above ground forage biomass per acre, weed and woody plant density, and habitat management. Such a system would improve both the timeliness and accuracy of recommendations to a much larger number of individual landowners at a reduction in time and costs. Georgia Extension personnel believe that this system will deliver benefits such as decreasing diagnostic turnaround by an average of two days. There is great potential for use of this technology for many interactions between experts within the Texas A&M University Agricultural Program and clientele who need on-site assistance in making management decisions.
A pilot project was conducted that determined the effectiveness of selected electronic transfer technology, i.e., digital imagery, utilized by Range Extension Specialists in the state of Texas to assess rangeland conditions. Two ranches near Bryan, Texas, were selected to participate in this research project. The researcher took 35mm and digital photographs of the range sites as three "on-site" specialists constructed their recommendations. The specialists' recommendations and the photographs were then forwarded to the Center for Grazinglands and Ranch Management (CGRM) at Texas A&M University, College Station. The 35mm photographs were developed and scanned into a digital database using a flatbed scanner. The digital photographs from both cameras were then placed on the World Wide Web (WWW) and the five "in-office" Range Extension Specialists made their recommendations.
The first objective was to determine the relationship between "on-site" and "in-office" recommendations by Texas Range Extension Specialists using digital images. The findings related to above ground forage biomass per acre using only 35mm camera digitized images were as follows: 1. There were no statistically significant differences among the five "in-office" Range Extension Specialists when making quantitative rangeland observations for tonnage per acre, while using only 35mm digitized images. However, there was a high degree of variation in the observations. 2. The "in-office" Range Extension Specialists were inaccurate when estimating forage biomass per acre, even though their guesses did correspond with an increase in actual forage tonnage per acre. The findings related to tonnage, mesquite plants, and stems per acre and height and diameter of mesquite, using 35mm digitized images and digital camera images, were: 1. Only the height of mesquite observation gave evidence to suggest any differences among the "in-office" Range Extension Specialists. 2. There was a lot of variation within and among "in-office" specialists in all observations, except when observing the height of mesquite. 3. "In-office" Range Extension Specialists were inaccurate in making observations of all the range sites except for mesquite height and stem diameter sites. 4. The plant species significantly affected the Range Extension Specialists' accuracy in correctly identifying the plant.
The second objective was to determine the relationship between the quality of 35mm photographs and digital photographs. There was no difference in the type of camera used when making rangeland observations in this study.
This study concluded the following: (1) There were no statistically significant differences in observations among the five "in-office" Range Extension Specialists when making quantitative rangeland observations for above ground forage biomass per acre, while using only 35mm digitized images. However, there was a high degree of variation in the observations. This variation could be due to the lack of rangeland information concerning the range site and the quality of the picture. In addition, this variation may have been lower if there had been more samples per observation and an opportunity for the specialist to state "no estimate." Therefore, it was concluded that Texas Range Extension Specialists cannot accurately make rangeland observations from digital images if constrained to the conditions applied in this study, (2) Range Extension Specialists were inaccurate when estimating above ground forage biomass per acre. The specialists may have more accurately estimated the forage biomass if they had known the species, (3) The majority of the "in-office" specialists underestimated when estimating above ground forage biomass per acre, (4) Range Extension Specialists were inaccurate when estimating the number of mesquite plants and stems per acre. This was probably due to poor quality scenic images. In addition, some specialists may have given a threshold number of plants per acre. If the number of plants exceed a certain limit, then in practice, the specialist keeps the same recommendation and does not attempt to estimate accurately the number of plants above the threshold. Consequently, some of the specialists may not have had much practice in estimations above any given threshold, (5) The Range Extension Specialists were inaccurate when identifying various plant species. This is probably due to inefficient image quality and the "home" location of the individual specialists being different from the research sites. Some specialists were more familiar with species in their area, (6) There were no differences in the Range Extension Specialists' identification and estimations when viewing images taken with either the 35mm or the digital camera. The digital images appeared to be higher quality than the 35mm images, but this additional quality did not help the specialists.
The results of this research project revealed that this transfer of technology system, in its current state, is not efficient in determining rangeland situations, given the limitation of resolution of monitors likely to be available to the specialists. However, once this system is revised, it may have implications for success outside the realm of forage production. Additional uses might be: (1) a teaching tool, (2) evaluating body condition scores of livestock, (3) evaluating carcass quality and yield grades, (4) determining quality grades of agricultural commodities such as corn and cotton, (5) determining fuel forage loads for prescribed burning, (6) aid in the leasing of land, (7) aid in evaluating land for loans, and. Other disciplines, not directly related to rangeland, may be better able to use this research methodology. Examples include Entomology, Parasitology, Veterinary Medicine, Microbiology, Zoology, Physiology of Reproduction, Epidemology, Wildlife and Recreation, Food Science and Technology, Natural Resource Management, Soil and Crop Sciences, Geology, and Oceanography.
The researcher believes that this study can be improved and help begin assuring the sustainability of Texas' natural resources by providing needed monitoring capabilities and supporting producers in making timely decisions related to their individual environments. The following are recommendations for implementation: 1. Despite its limitations, it is recommended that training in the use of digital imagery be developed and implemented in each Texas Extension District for County Extension Agents and producers, 2. Develop and utilize a digital information page for the Range Extension Specialist to fill out electronically, 3. Instruct the Center for Grazinglands and Ranch Management to send photographs, intended for recommendation, to a specialist who is familiar with the particular species, location, and climate, 4. Use a zoom lens with a macro focus adjustment on single reflex cameras. 5, Use resolutions at a maximum of 1024 X 768 when using a digital camera because higher resolutions do not increase image quality and only require additional digital storage space, 6. Use the photo guides (Table 1 & Table 2) and the questionnaire for the producer (Table 3) that were developed from this study when implementing this research in the field. The following recommendations are for further study, 7. Determine the acceptance of this research by County Extension Agents and producers, 8. Determine the relationship between the observations of Range Extension Specialists and other individuals. 9, Determine rangeland forage utilization from digital photographs, 10. Estimate the percent utilizable forage per plot through digital imagery, 11. Evaluate the quality of forage through digital imagery, 12. Qualitatively determine the effectiveness of rangeland recommendations, and 13. All "in-office" specialists were expected to deliver a response on each range site in question. However, comments from them indicated that some were much more confident in their assessments than others. Thus, further study should evaluate the Range Extension Specialists' level of confidence in each estimation and the effects on their accuracy in estimating rangeland situations.
Monitoring Methods
From the 1930s through the 1950s, most producers were more concerned
about total pounds of red meat produced than increasing land productivity
or sustainability (McDaniel, 1997). Today, rangeland monitoring is becoming
more important as livestock production evolves into an intense monitoring
unit. Rangeland monitoring "records changes in resource status, usually
to assess the response to a management program at a particular site"
(Muir & McClaran, 1997). Data collected from rangeland inventories
is a valuable baseline on which to compare responses. Rangeland inventory
involves collecting information on "vegetation types, range sites
and condition, carrying capacity, soil types, utilization patterns, topography,
streams, habitat assessment for wildlife, and improvements (Muir &
McClaran, 1997).
The keys to successful monitoring include: 1) developing a good management plan, 2) developing clear ecological objectives, 3) being site specific, 4) monitoring the attributes that relate to the objectives, 5) understanding the quality and reliability of the data so that you can interpret correlations, and 6) using a feedback approach to adjust management (McDaniel, 1997). Monitoring can be used in two ways: 1) point-in-time comparisons, which are used to evaluate annual effects of grazing management within and between areas and 2) trend monitoring, which is used to trace changes over time. A major benefit of plant monitoring is the "ability to quantify the balance between vegetative and reproductive growth. This makes it possible to customize cultural management during the growing season" (Kerby, Horrocks, & Plant, 1993, p. 1178).
The following steps summarize the researcher's literature review into
a comprehensive unit and explain the techniques of rangeland photographic
monitoring.
Step 1: Perform a "needs assessment" of the ranch or rangeland
by asking the following questions: 1. How much capital, time, and labor
is available for a monitoring program? Rangeland monitoring can be as sophisticated
as integrating Global Positioning Satellite (GPS) Systems and experimentation,
or as basic as taking yearly photographs of changes in range condition.
2. What general attributes need to be monitored? Attributes are "characteristics
of the population that is [sic] measured during sampling such as species
composition, biomass, cover, frequency, slope, topography, soil texture
and crusting, streambed material, water quality, non-point-source pollution,
elevation, stream channel changes, physical disturbances, insect damage,
and brush and weed problems" (Muir & McClaran, 1997; University
of California, 1995). "Cover is the vertical projection of plant material
onto the ground when viewed from above and is expressed as a percentage"
(Muir & McClaran, 1997). Monitoring vegetative changes (number and
size) and reproductive characteristics (number of flowering plants and
fruits or flowers per plant) can also be performed (Palmer, 1987). Palmer
(1987) measured the effects of spring and summer burn, removal of woody
species, and no-treatment control on height of plants.
Step 2: Gather needed information for the rangeland sites in question. Various sources of information can include landscape, aerial, infrared, and global satellite photographs, ownership or sales history, past grazing management plans, historical livestock information (carrying capacity), historical climatic data, county soil surveys, U.S. Geological survey maps, and any previous range site maps of your area. A baseline inventory can be prepared from Government Accounting Office (GAO) reports, National Resource Inventories (NRI), Resource Planning Act (RPA), and/or Forest Land and Resource Management Plans (LRMP). Precision farming divides fields on the basis of information collected from GPS systems. Global Information systems (GIS) and GPS systems also aid in creating baseline inventories. Kvien (1999) stated "By linking GPS to yield monitoring devices, soil and pest sampling, remote sensing, and information such as topography, soil type, water patterns, previous and current cultural practices, a grower can create maps showing how these parameters vary within a field." Infrared aerial photography registers the Earth's surface temperature contrasts. This also aids in mapping rangeland and resources.
Step 3: Gather the needed equipment. The type of photographic monitoring being performed will determine the equipment needs. Basic short and long-term rangeland photographic monitoring of above ground biomass, density of plants per acre, height and stem diameter of woody species, and species identification requires most the following equipment: at least four flagged steel fence posts, four sections (12-18 inches) of re-bar rod, hammer or post driver, spray paint, permanent marker, 35mm or digital camera, film, and an erasable board or cardboard (McGinty & White, 1998).
Step 4: Take the photographs. The following information explains how, when, where, and what to monitor to deliver quality photographs. Photographic guidelines (Appendices C & D) were created for both a 35 mm and digital camera by the researcher's literature review, experiences from this project, and a photographer. These guidelines will help enhance the quality of rangeland photographs.
How to Select Cameras
Obtain either a 35mm camera or a digital camera. There are basically
two types of 35mm cameras: compact and single lens reflex (SLR). A compact
35mm camera has a focal length of about 2.5 to 3.5 feet to infinity. Therefore,
when monitoring distinctive plant characteristics that require a close-up
picture (less than 2.5 feet), a macro zoom lens is recommended. An SLR
camera has a near focal distance of about 1.5 feet, without a zoom lens
(Langford, 1998). When using a 35mm camera, use a fast color film such
as 100 or 200 speed. The speed refers to the film's sensitivity to light;
the 100 speed is one-half as sensitive to light as the 200 speed. Preferably
use Kodak Royal Gold 200ã because it is the best overall film, has
excellent resolution, fine grain, high power, saturated colors, and can
be used on both sunny and cloudy days (Langford, 1998).
Digital cameras vary according to price, options, settings, and maximum resolutions. A digital camera with a maximum resolution of 1800 X 1200 costs about $900 while a camera with a resolution of 1152 X 864 costs around $500. Resolution is the number of pixels (individual points of color) contained on a display monitor per inch, expressed in terms of the number of pixels on the horizontal axis by the number on the vertical axis (Langford, 1998). A camera resolution of 1280 X 1024 is recommended when photographs (viewed by a monitor) are used to monitor plant densities or structures where individual plants have to be counted or identified in a plot or range site. If digital images will be printed on high quality photo paper, then a camera resolution above the printer's capabilities is recommended so that quality is not reduced.
How to Select Monitors and Scanners
Computer monitors vary according to screen size, maximum resolution,
number of bits, and dot pitch. Most 17 inch monitors can display images
at 1280 X 1024 or 1600 X 1200 resolutions, with up to 32 bit true color
settings and .25 to .28 mm dot pitch. The smaller the dot pitch, the sharper
the image due to more dots (pixels) per horizontal line. In addition, the
number of bits of color that are produced per pixel affects image quality.
A 24-bit monitor, when compared to a 16-bit monitor, has a higher possible
number of colors per pixel (Grimm, 1996). Most scanners can scan at a resolution
above both monitors and printers. Therefore, the cost is determined by
the quality of the image editing software and other built-in programs.
How to Monitor
When monitoring above ground forage biomass, "select an
appropriate plot size that matches the type of vegetation to be sampled"
(Table 4).
Table 4
A legible plot sign should be included in each photograph that identifies the pasture name or range site and date (White & Richardson, 1995). In addition, select representative areas, randomly select specific sites within the areas, and try to avoid being biased. Utilization zones (table 5) are best mapped at the end of a grazing season, when utilization is the greatest. These zones identify key areas for "sampling and management, the recognition of problems in livestock distribution, and range improvement decisions" (Muir & McClaran, 1997).
The number of photographs needed for each range site is determined by what will be monitored. When monitoring total above ground forage biomass per acre, take one elevated scenic picture, one picture at 10-12 feet (at a 45° angle), and two pictures, near vertical, at three feet from the designated plot. The vertical picture will help indicate leaf area index, ground cover, and basal area. Basal area is an important characteristic because it "measures long-term effects of climate, soil condition and grazing" (National Academy of Sciences-Natural Resource Council, 1962, p. 48). If it is necessary to photograph a plant for identification purposes, then take another picture as close as your camera will allow, while using a black background for contrast. In addition, use a stake marked at 6" increments to determine height of the plants. Height can also be measured using a golf, tennis, and softball as references (University of California, 1995).
Various forage plots may be clipped so that the rancher/producer can begin to create a visual image of actual tonnage per acre. Muir and McClaran (1997) defined forage as "plants that are available and palatable to grazing animals." Proper clipping techniques are required to help ensure adequate results of what is actually being monitored or evaluated. Biomass is usually determined on a dry-matter basis and is used to assess range condition and carrying capacity (Muir & McClaran, 1997). Muir and McClaran (1997) reveal that biomass is the weight of the plant material within a particular area and may be collected on an individual species basis or total weight. If there is more than one species in the plot, and each species has about the same nutritional quality, then the plant material can be collected on "total weight." "Estimations can be quite accurate… but when there are mixes of long and short grasses, fine and course, or mixtures of clovers and grasses, estimation is not reliable" (National Academy of Sciences-Natural Resource Council, 1962, p. 81).
When clipping plots, it is important to know the four basic biomass categories: 1) living - actively growing material, 2) recent dead - current year's growth, 3) old dead - previous season's growth, and 4) litter - detached plant material lying on soil surface (e.g. dead grass, freshly fallen leaves, twigs, bark, and fruits) (Muir & McClaran, 1997). It is also important to know individual species and forage value composition to be more accurate in determining utilization.
Clipped plots are oven dried at 140 degrees Farenheight for a minimum of 24 hours (White & Richardson, 1995). It is important to note that the percent water moisture variability can be large due to the species, state of growth, growth form, season, and soil and atmospheric moisture levels (Muir & McClaran, 1997). In addition, Muir and McClaran (1997) explain that the weight of the plants may refer to 1) the green weight (freshly cut plants), 2) air-dried weight (dried in the shade or oven at 60 degrees Celsius and contain about 10-12% moisture, and 3) oven-dry weight (dried at 140° F).
Woody and Weed Plants per Acre
When monitoring the number of woody and/or weed plants per acre,
it is recommended to take one to two scenic pictures (preferably from an
elevated position, i.e., top of a truck, ladder, or hillside), one picture
at 10-12 feet, and one at 3-5 feet from the designated plot. Take another
picture, with a black background, at 6-12" for species identification
purposes. Panoramic views can be created by setting up a photo point and
taking a picture on each side of that point. The two pictures can then
be placed side-by-side to give a larger view of the site.
"Attributes that involve counting, particularly density, are subject to error, where it's difficult to distinguish discrete individual plants" (Muir & McClaran, 1997). When counting the number of plants per plot, Muir and McClaran note that "woody plants that feature multiple stems or vegetation propagation present challenges in counting for densities and overlooking or counting an inferior species in the quadrant will compromise the accuracy of frequency data."
When to Monitor
Monitoring can be done yearly and/or seasonally. McGinty &
White (1998) explain that the desired time for annual monitoring is in
the fall before the first killing frost. For seasonal monitoring, take
photographs at "late winter or spring green-up, mid-summer, and at
frost or before and after grazing a pasture, and/or when controlling brush
or weeds" (McGinty & White, 1998, p.2). The exact day that you
re-monitor is not as important as the stage of plant growth because seasons
vary from year to year (University of California, 1995). In addition, utilization
is more difficult to assess in the spring and early summer because there
are more species (varieties) and more selective grazing (Bell, 1973). Therefore,
key species may be heavily used.
When monitoring changes in rangeland condition, either annually or seasonally, photo-points need to be developed (White & Richardson, 1995). Once the location is selected to be monitored, it needs to be permanently marked with a highly visible steel fence post or metal stake (re-bar). This site can be recorded on aerial photographs or ranch/pasture layout maps. Detailed notes that describe the location and situation should be taken at each photo-point (White & Richardson, 1995). This may include compass bearing and distance from a highly visible land mark or GPS coordinates if available. In addition, use a data information sheet to record any observations of the site. A questionnaire for the producer (Table 3) was constructed by the researcher's literature review and discussions with Range Extension Specialists.
When taking pictures, stand so that you do not cast a shadow onto the plot or scene. In addition, stand so that the sun is to your right or left to produce sidelighting. This will help emphasize textures, contours, and overall form. Shadows and textures are eliminated if the sun is behind you (Langford, 1998). The best time to take rangeland photographs is on a slightly overcast day, 3-4 hours after sunrise or 3-4 hours prior to sunset. This time of the day gives appropriate shadowing. If pictures are taken early a.m. or late p.m., the colors are distorted and the photographs are more difficult to interpret. There is a blue tint just before sunrise that exaggerates green colors (Langford, 1998). Early morning light shows an orange tint and late afternoon light, just prior to sunset, is reddish-orange to gold color (Langford, 1998).
What Plant Characteristics to Monitor A Range Extension Specialist in the field (on-site) combines various aspects of the rangeland to construct a recommendation. The range specialist combines quantitative clues such as species identification, number of plants per acre, number of stems per plant, soil condition, and climate, with qualitative "feel" inferences. The "in-office" specialist must make recommendations based solely on what the photographer sees and feels. Therefore, the "on-site" photographer must be aware of the various clues that are used by the specialists. Grazing and brush management are tremendously large and diverse subjects with many aspects and interactions. The following information is intended to deliver basic concepts and provide a background for recognizing various attributes that need to be monitored.
Grazing Management
Identifying plant species is important when constructing recommendations
for grazing management practices. Rangeland forages, consisting primarily
of grasses and legumes, differ in nutritional quality, total forage yield,
seasonal distribution of yield, rate of maturity, area of adaptation, hardiness,
degree of revegitation, disease resistance, seeding vigor, quality of seed,
and overall leaf, stem, root structure, palatability, digestibility, and
nutrient content. Forages can be classified as tropical or subtropical,
warm or cold season, and/or annual, biennial or perennial. They can also
be identified by their growth patterns (decumbent or erect), vegetative
reproductive structures (stolons or rhizomes), and specific characteristics
such as inflorescence types, leaf attachment and arrangement (alternate,
opposite, whorled), blade complexity (simple, toothed, trifoliated, pinnately,
or palmately), and shape of leaves, pedals, and blade margins of leaves
and pedals (Barnes, Miller, & Nelson, 1995), structure, or absence,
of sheath collar, ligule, auricle, and/or pubescence (leaf hair).
Forage quality is very dependant on growth stages and maturity. It is important to know essential elements in various forage plants as well as the amount and degree of fluctuation in plant quality in different stages of growth (Bell, 1973). Climate also affects forage quality. Climate is the "primary factor in determining range forage production" (National Academy of Sciences-Natural Research Council, 1962, p. 12). More than 91% of the year-to-year variation in the ungrazed standing crop in the grasslands of Tuscon, Arizona, is accounted for by rainfall in the June-September grazing season (Muir & McClaran, 1997). "Drought usually inhibits tillering and branching of forages and hastens the death of the established tillers" (Barnes, et. al., p.91). Pittman (1980) observed that a higher temperature usually accelerates the rate of leaf appearance and senescence, stimulates true stem formation, and depresses formation of new tillers, resulting in more rapid aging and lower digestibility. It was suggested that increases in temperature result in thinner leaves, decreased tillering, increased lignin, and decreased soluble carbohydrates in plant cell walls (VanSoeste, 1968, in Pittman, 1980). In addition, crude fiber decreases in both temperate and tropical grasses with reductions in available moisture (Gifford & Jensen, 1967, in Pittman, 1980). Also, inverse relationships between forage digestibility and soil moisture have been reported for alfalfa (Medicago sativa L.) (Pittman, 1980). The conditions of limited moisture, high temperature, and long days all appear to be associated with low forage quality (Pittman, 1980). Tropical and subtropical grasses are usually lower in forage quality than temperate grasses and legumes (Pittman, 1980).
Weed and woody species are also identified by their structures, location, and adaptation. The density, size, and maturity of these species, soil characteristics, climate, and location within the state and particular site, are used to construct recommendations for control. Weeds and woody species have different growth stages, re-growth points, and levels of hardiness to treatments and environments.
After forage supply and quality have been evaluated, then proper stocking rates can be established. Stocking rate is the actual number of animals on a management unit throughout the time period of grazing (Muir & McClaran, 1997). The kind, size, age, and physiological needs of livestock, and forage wastage, grazing pressure, forage quality, and management objectives are factors that affect forage demand (White & Troxel, 1988). Animal units (AU) are used as a basis to "standardize and express stocking rates among different classes of livestock with similar dietary preferences" (Muir & McClaran, 1997, p.2). Animal Unit Equivalents (AUE) provide a basis to express carrying capacity, but there is a problem. Range herbivores differ widely in the kinds of forages that they consume (Lyons, Forbes, & Machen, 1996). For example, AUE suggests that five whitetail deer can eat the same amount as one cow (Table 6). This cannot be absolutely true because deer eat mostly browse and cows eat mostly grass (Muir & McClaran, 1997).
A more precise measurement of daily forge demand can be derived from a stock unit equivalent (SUE) table using a non-lactating 1,000-pound cow in the last one third of pregnancy as a standard (White & Troxel, 1988). This animal requires 17.3 mega calories of metabolized energy which converts to a daily forge demand of 19.6 pounds of 53.6% digestible forge (White & Troxel, 1988). Tables 7 and 8 illustrate how the SUE is calculated and how it is used to determine daily forge demand of cattle.
Carrying capacity can also be estimated by "using an average daily forage consumption of 26 lbs. of dry matter per day (approximately 40 lbs. on a fresh weight basis) per animal unit" (Scrifes, C.J., Durham, G.P., & Mutz, J.L., 1977, in Whitson, R.E., Hamilton, W.T., & Scrifes C.J., 1979). An Animal Unit Month (AUM) is defined as the "amount of forage required by an animal unit (a mature cow weighing 1,000 lb. with unweaned calf) for one month assuming average daily consumption of 26 lbs. of dry matter. Therefore, by convention, an AUM equals 780 lb. of dry forage" (Tanner, G., 1996). An accepted rule in proper grazing management is to "take half and leave half," and as half of the forage that is utilized is not totally consumed by the grazing animal, the amount of total forage that is actually needed for an AUM is 3,120 lbs. (780 ¸ .25) (Tanner, G., 1996).
Grazing intensity affects quality and availability of key species. Scientific studies show past and present grazing intensities by livestock play a major role in determining the type of vegetation on a particular site (Joseph, Holechek, Possadas, & Valdez, 1997). An eastern Colorado study showed that both diet quality and forge intake were reduced under heavy grazing (Holechek, 1997). Continuous overgrazing has several effects: 1) causes a decrease in annual production of pasture vegetation and palatable grass species, 2) replaces perennials with annual species that are short-lived, 3) compacts soil, and 4) decreases animal health and consequent fall in meat and milk production (Friedman & Friedman, 1994). In addition, both heavily grazed and ungrazed areas often will be less diverse than moderately grazed areas (Office of Arid Lands Studies, 1997). Livestock will consume more high quality grasses and forbes with moderate grazing. Also, if "leaf area is low due to continuous overgrazing, the root system will become small, weak, and shallow" (White & Wolf, 1996, p. 3).
As forge use increases, to an extent, "animal production per acre increases due to less forage being wasted" (Rayburn, 1992, p. 1). Average daily gains per animal are nearly constant until about 50% of the pasture is used. Rayburn (1992) explains that major decreases in production per head occur as pasture use approaches 80%, resulting in reduced animal production per acre. In addition, grazing intensity has different effects on different forage species Some species can be grazed to a half-inch stubble height and while others can only be grazed to a 3-4 inch stubble (table 9) (Rayburn, 1992).
Brush and Weed Management Brush and weed control are important management objectives, especially in Texas. It is stated, "A total of 42 million acres are significantly invaded by noxious species, making Texas the national leader in the need for brush and weed control techniques" (Hamilton, 1998, p. 235). Adams (1997) found that 95% of the ranchers surveyed said that brush encroachment was the most limiting factor in making a living, ranked above drought and productivity. Also, most research shows that "for every pound of weeds controlled, there is a gain of at least one pound of grass" (Dorsett, 1998, p. 186).
Numerous treatment methods are available to control the wide variety of brush and weeds. "The diversity of problem plant species on grazinglands and the large number of potential treatment alternatives makes the decision process for selecting the appropriate brush and weed control technique difficult, especially when using herbicides" (Hamilton, 1998, p. 234). Therefore, Tom Welch and Wayne Hamilton developed a brush and weed control program called EXSEL (Expert System for Brush and Weed Control Technology Selection, Version 1.09). EXSEL is a forward chaining/decision support system designed to recommend the best mechanical and chemical range brush and weed control treatments for 163 problem plants in Texas. In addition, it also provides an analysis of prescription burn potential and will produce a pre-burn checklist. The user may select the plant kill efficacy level, force the system to consider certain types of treatments, or let the system choose the best alternative (Hamilton, Welch, Myrick, Lyons, Stuth, & Conner, 1993).
The Texas Agricultural Extension Service (TAEX) has developed a Brush Busters program that helps individuals make more effective treatments for mesquite, cedar, and prickly pear by detailing appropriate control methods. Identification of the species is important in this program because treatment recommendations will vary. An example is Blueberry and Redberry Cedar. Blueberry cedar is more common in central and south central Texas and is identified by blue berries. Redberry cedar is common in west, west central, and north central Texas, and is identified by red berries and small specks of white wax on leaves and twigs (Ueckert & McGinty, 1996). Ueckert and McGinty (1996) state that "Leaf and soil spot spray work best on trees less than three feet tall." In addition, cutting blueberry at ground level is effective, but redberry must be grubbed below the soil surface (Ueckert & McGinty, 1996). Noffke and McDaniel (1997) found that salt cedar mortality was influenced by the growth form of the plant based on tree height and number of stems. The taller, stemmier plants were more resistant to treatment.
Mesquite is controlled in various ways. The Texas Agricultural Extension
Service (Ueckert & McGinty, 1995) recommends the following:
If most of your mesquites have a few well-defined
stems or trunks coming out of the ground, you'll find that the stem spray
method works best for you…. The stem spray method is best on young mesquite
with smooth bark and few basal stems. This is a low volume treatment technique
and can be used anytime of the year (best in spring and summer)…. If your
mesquites are bushy, have many stems at ground level, and are less than
6-8 feet tall, try the leaf spray method (high volume method)…. The leaf
spray method should be applied in the spring when the leaves change color
from a light pea green to a uniform dark green….. In addition, spray when
the soil temperature has reached 75° F.
