INTRODUCTION

Rangelands are those areas of the world which by reason of physical limitations - low and erratic precipitation, rough topography, poor drainage, and/or cold temperatures - are unsuited to cultivation and which are a source of forage for free-roaming native and domestic animals, as well as a source of wood products, water and wildlife. They include grasslands, shrub-steppe, desert scrub, savanna, open woodland, grazed forests, mountain meadows, riparian areas, wetlands and tundra. All areas of the world that are not barren deserts, farmed, or covered by bare soil, rock, ice, or concrete can be classified as rangelands (Holechek et al 1995).

Rangeland supports different vegetation types including shrublands such as deserts and chaparral, grasslands, steppes, woodlands, temporarily treeless areas in forests, and whatever grows on land today, sandy, rocky, saline, or wet soils, and steep topography for commercial farm and timber crops. Rangeland vegetation may be naturally stable or temporarily derived from other types of vegetation, especially following fire, timber harvest, brush clearing, or abandonment from cultivation. Weed and brush control, seeding and fertilization are infrequently used practices on rangelands (Heady and Childs 1994).

The terms range and rangeland have often been misused in the sense that they are often equated with livestock use and production alone. An important distinction is that range is a kind of land with many uses - it is not a land use. The multiple values of rangeland include forage for domestic and wild animals, water, wood fuels, wildlife cover, and aesthetics. Minerals are found on rangelands along with a variety of other products such as botanochemicals. There are many competing uses for rangelands - uses that are increasing with population growth, increasing urbanization and interests in preservation.

Range management is a discipline and an art that skillfully applies an organized body of knowledge accumulated by range science and practical experience for two purposes: (1)protection, improvement and continued welfare of the basic resources, which in many situations include soils, vegetation, endangered plants and animals, wilderness, water, and historical sites; and (2) optimum production of goods and service in combinations need by society (Heady and Child 1994).

Range constitutes an important land based resource for several reasons, the most important of which may be their wide distribution. About half of the terrestrial land resource onthe globe can be classified as range. Thus we are talking about a very extensive resource with relatively low biomass productivity. These lands must be managed wisely because of the increased demand for their products. Good management depends on careful inventory and monitoring of the resources found on these lands. Remote sensing possibly offers the onlyfeasible method for obtaining the information necessary for their wise use and management.

The range management profession places emphasis on ecological understanding of the following:

Figure 2

Figure 2 shows some of the relationships between rangeland ecosystems and management (Joyce 1989).

The photographs and images associated with this module are designed to allow the student to judge the usefulness of various forms of remote sensing to assist with rangeland management activities. A physical-measurement oriented list of range management activities that have some potential for being accomplished by remote sensing techniques is found below.

  1. Inventory and classification or rangeland vegetation.
  2. Determination of carrying capacity of rangeland plant communities.
  3. Determination of the productivity of rangeland plant communities.
  4. Condition classification and trend monitoring.
  5. Determination of forage and browse utilization.
  6. Determination of range readiness (time to graze).
  7. Kind, class and breed of livestock using a range area.
  8. Measurement of watershed values including measurements of erosion.
  9. Making wildlife censuses and evaluations of rangelands for wildlife habitat values.
  10. Evaluating the recreation use of rangelands.
  11. Judging and measuring the improvement potential of various range sites.
  12. Implementing intensive grazing management systems.
Table 1 suggests some of the scales of imagery useful for various rangeland applications.

Table 1. Representative fraction scales of imagery used by rangeland resource managers with suggested uses.

Notes - the first three scales have historically been obtained as aerial photographs. In the future much of this imagery will be obtained as multispectral airborne videography with submeter pixels and the analysis and interpretation will be accomplished by image processing and GIS (Tueller 1979).
While remote sensing cannot provide all of the data and management input to these various rangeland activities, in many instances a considerable part of the required information can be obtained. An important and natural starting place for this consideration is to evaluate the capabilities of remote sensing to assist in the identification, interpretation, classification and inventory of the various range plant communities found around the world.


RANGELAND VEGETATION/PLANT COMMUNITIES

Vegetation mapping using photointerpretation procedures has been attempted on rangelands in many parts of the world. There are numerous different kinds of rangeland vegetation. Types vary from shrub-dominated cold desert types, hot desert types, grassland and savannah and woodland savannah.

A cold desert sagebrush/grass vegetation type characterized by big sagebrush (Artemisia tridentata tridentata) and Thurber's needlegrass (Stipa thurberiana).



A hot desert vegetation type characterized by creosote bush (Larrea tridentata) and bursage Ambrosia dumosa.











Also shown in large scale (1:600). Note the amount of bareground, the rocks and gravel on the soil surface. The cresote bush are recognizable by the near reddish tone and the irregular diffuse edges of the plants. The bursage plants are more symmetrical, gray green in color with less diffuse edges.









A species of grass in northern Australia. The dominant and almost only species in the grassland is Mitchell grass (Astrebla pectinata).







Mapping success has generally been high especially if those creating the map unit polygons were familiar with and had previously worked on the ground studying the vegetation. Success is much lower if the photo interpreter attempts to do this without the previous field experience. Vegetation mapping using digital image processing has also been attempted on rangelands with variable success (McGraw and Tueller 1983).


Image processing

On many heterogeneous rangeland environments supervised classification approaches have proved inadequate since the training sets do not adequately represent the various range plant communities. Often the heterogeneity of rangelands based on various soil types, land forms, latitudes, longitudes, aspects, slopes, precipitation patterns and soil types has precluded the obtaining of useful training sets for accurate classification. Unsupervised classification procedures with a high level of interaction with the interpreter have proven to be more valuable on rangelands. In this case the interpreter is able to examine the classifications and determine which spectral class or classes really represent the range plant community of interest. In many cases intermediate-to-large scale aerial photography can be used as ground data to determine classification accuracy. Accuracies for many range vegetation maps can be between 75 and 95 percent (McGraw and Tueller 1983).

Diurnal and seasonal variations often complicate image processing classification interpretations (Wilson and Tueller 1987 and Oleson and Tueller 1989). Time of year and time of day both strongly influence the brightness values obtained by satellite and airborne videography. The time of year is influence is often closely correlated with the phenology of the vegetation. When the perennial range grasses are green they give a much different spectral signature that when dry and mature.

Mapping from Satellite Data and Small Scale Aerial Photography

The relatively large Landsat Thematic Mapper pixels (80m and 30m) tend to preclude mapping with small minimum mapping units. Usually several hundred acres must be mapped in each polygon. However, certain ecotones between range plant communities can be easily identified at these resolution levels. Small scale aerial photography generally has greater utility.

Figure 6



For example, examine Figure 6 - a NASA high altitude photograph with a scale of about 1:110,000 although it varies considerably because of the abrupt elevations changes in the Shoshone Mountain Range, central Nevada. Note the readily identifiable ecotones between the pinyon-juniper woodland and the big sagebrush grass vegetation and between the bright red riparian zone vegetation along the Reese River in Nevada and the sagebrush grass vegetation. Note the lighter toned areas that consist of areas where the sagebrush/grass vegetation has been plowed under and seeded to perennial grasses as a range improvement project. In the color infrared photographs the big sagebrush vegetation appears quite blue since this species has very low reflectivity in the infrared.

Figure 7



In Figure 7 you will also see the boundary between a perennial grass seeding and the sagebrush/grass vegetation. This latter figure is a Landsat Thematic Mapper scene with 30m pixels. This scene has sufficient resolution for planning of an intensive grazing management system. A range manager can determine where to place fences and gates for the various pastures. The location of watering points can be used to establish the protocol for the grazing management system. The meadows and stream channel riparian vegetation are highly reflective in the infrared.

Mapping from 1:24,000 or Larger Scale Resource Photography

The first features to be mapped and inventoried at this scale are the basic range plant communities. These can be defined in various ways. The Natural Resources Conservation Service (NRCS) of the U.S. Department of Agriculture maps the soil polygons and then describes the ecological sites that are found associated with these polygons. The ecological sites were originally called range sites and woodland sites but are now lumped under the general term ecological sites. The ecological site is defined as a kind of land with specific physical characteristics which differs from other kinds of land in its ability to produce distinctive kinds and amounts of vegetation in its response to management. In addition range managers define another important management term, the Desired Plant Community. The Desired Plant community is defined as follows: of the several plant communities that may occupy a range site, the one that has been identified through a management plan to best meet the plan's objectives for the site. For many years much of the aerial photography for range, forest and soil mapping applications was obtained at a representative fraction scale of 1:15,840 or exactly 4 inches to the mile. Now, however, most the aerial photography, mostly in color or colorinfrared, is obtained at a representative fraction scale of 1:24,000 designed to coincide with the USGS 7.5 minute topographic maps. This scale of imagery is very useful for mapping range plant communities and features of interest to rangeland management although in many cases larger scales near 1:10,000 would be ideal for such mapping. However, the ease of use and transference to both hard copy orthophotoquads of the same scale make these products very useful for rangeland applications. In addition the orthophotoquads are available in digital form for many rangeland areas. The soils polygons from the NRCS soil surveys are also plotted on these same orthophotoquads providing an additional important reference for management of rangeland resources.

Figure 8A


Figure 8B

Figures 8a and 8b show the identification and mapping potential for range plant community characterized with and overstory of Cliffrose (Cowania stansburiana) with an understory of black sagebrush (Artemisia nova). Figure 8a shows the 1:10,000 scale vertical aerial photograph while 8b shows how this vegetation appears on the ground. Note the pattern of the cliffrose and black sagebrush plants. By comparing this image with the ground scene one can measure the relative proportions of each species on the site. Cliffrose is an important winter browse for mule deer and so it is important to determine its status over time since the welfare of this species may influence deer populations.

Figure 9


Figure 9 shows a 1:500 scale aerial photograph where a fire has occurred in the pinyon/juniper woodland. Such a resource management feature is quite mappable at this scale. Note the darkened burned area on the left side of the image. This imagery allows the range manager or range scientist to examine vegetation patterns and the clumping of species groups or species within the range plant community.

As the ecological sites on a rangeland area are identified and inventoried there are a number of other features that must be identified and inventoried, if possible, in order to provide good data in support of range management. These include features such as fences and fence lines, watering points, important topographic features that influence the movement of domestic livestock and wildlife, rock outcrops, trails, and stream courses.

RANGELAND MONITORING

Range Condition and Trend

The basic rangeland inventory, much of it obtained from various sources of remote sensing, if done properly can serve as the first step in rangeland monitoring. Rangeland management has historically required range surveys to determine forage productivity and carrying capacity. This is still an important consideration in many parts of the world. However, if initial range surveys have been accomplished, either quantitatively or in a qualitative sense, then the carrying capacity has often been determined or set at some prescribed level. Most range managers include procedures for monitoring. in their management plans. Is the set carrying capacity proper and correct or is the level of grazing too low or too high? Is the range improving or is it deteriorating? If too high then there is the expectation that range deterioration is occurring due to overgrazing. Monitoring is designed to determine if the grazing is proper or too intense. Remote sensing has an important role to play in monitoring rangeland vegetation and soil characteristics.

Monitoring vegetation and soil conditions is an essential element of good range management. Because of limited funds and personnel for monitoring large expanses, ground-based monitoring is rarely possible on a regular basis. Multitemporal aerial photography or videography or digital images of various scales can provide an efficient means of recording both long- term (years or decades) and short-term (daily or seasonal) changes. The permanent record provided by images becomes an important element in range condition studies (Tueller 1978). Range condition and trend are important concepts that must be understood relative to the question of rangeland monitoring. Range Condition refers to a set of characteristics of the rangeland plant community relative to forage production, soil quality, topography and a specific plant species composition as related to some standard (Tueller 1991). It is how we wish the range to appear.

Range Trend refers to changes in the rangeland vegetation and soils, or plant succession on rangelands. Vegetation succession is often a predictable process. Monitoring of the rangeland vegetation presupposes that managers can describe and predict successional stages or seres based upon species reactions to specific natural or man-caused disturbances. Many methods, both objective and subjective, have been developed. A large number of them are both conceptually and statistically very sound while others lack soundness. The cost of objectivity is high while the cost for subjective methods is lower. Therefore, vegetation monitoring must be a practical trade off between cost and subjectivity. Remote sensing provides one possible techniques for narrowing the gap between objective and subjective measurement of range trend over large expanses of rangelands (Tueller 1995).

Change Detection

Base line data can be acquired from some combination of both ground and remotely sensed data. In the past this has often involved the use of point samples on the ground using various kinds of measurement techniques to quantify the vegetation followed by extrapolation of the data from these points to larger expanses of rangelands. After the base line sample has been obtained then subsequent sets of ground and remotely sensed data can measure range trend and provide evidence for range managers that the trend is either upward, downward or stable. If the trend is downward then the range manager can reduce livestock numbers, instigate more uniform grazing practice by fencing, herding, or developing new watering points, or develop an intensive grazing management system involving appropriate combinations of rest, rotation and deferment.

Changes in Satellite Data or Large Scale Aerial Photography

Vegetation changes of a general kind can be measured using satellite images or large scale photography.. An example is the ability to document the occurrence of wildfire sites over large areas. For example, a study of 11 NASA high altitude color infrared photographs determined that the burn size varied from 26.8 to 113.2 acres in size. Perimeters for these burns varied from 0.9 to 10.9 miles in length, creating new ecotones. Recent burns covered only 1.9 percent of the total area (Tueller, 1992). Burns become obscured as the vegetation changes and must be examined on recent imagery, say every three to five years for successfully determining the rate and extent of wildfires on rangelands.

Changes in Photographic and Videographic Data (Large Scale/Near Earth) and Overgrazing Validated at a Piosphere or Fence Line.

Range managers often use piospheres (watering points) or fence lines between landscapes with different stocking rates and/or range management practices. These sites can provide validation sites to extrapolate remotely sensed data to sites not examined in the field. This is of great importance due to the extensive nature of rangeland resources around the world.

Figure 10A


Figure 10B



Figure 10a shows a typical fenceline comparison involving an area on the right of the fence that has been overgrazed because of a combination of legally permitted livestock plus wildhorses whereas on the left the area has been grazed by cattle only. Such comparisons can serve to allow proper interpretation of remotely sensed data by qualified rangeland resource managers (Tueller 1991 and 1995).

Often range managers use various procedures to calibrate the use of large scale/near earth imagery for evaluating vegetation changes on rangelands. Figure 10a shows a fence line in the Great Basin salt desert shrub vegetation that has been heavily grazed on the right hand side and more judiciously grazed on the left.

Figure 11A


Figure 11a is an oblique showing another calibration technique where measurements are made at regular distances outward from a rangeland watering point. Near the watering point the vegetation is made up mostly of annual weedy species such as cheatgrass (Bromus tectorum), and mustard (Descurania sp.) and unpalatable shrubs such as green rabbitbrush. (Chrysothamnus naseosus)

Figure 11B


Figure 11C


Outward several miles from the watering point the range is in excellent condition. Figure 11C shows what the range appears like at 6 miles from the watering point. Here there are few weedy annuals and the range is in excellent condition with an overstory of big sagebrush (Artemisia tridentata) and several perennial grasses, bluebunch wheatgrass (Agropyron spicatum) being the dominant. These differences when validated on the ground with minimal sampling can be detected and measured on various scales of imagery.

Figure 12A


Figure 12B


Both aerial photography (Figure 12a;1:800) and aerial videography (Figure 12b;0.7m pixels) provide a means of measuring vegetation changes on rangelands. Aerial photography provides higher resolution and greater clarity. However, aerial multispectral videography with submeter pixels are slowly improving and will likely be the procedure of choice for many future rangeland applications.

Grazing Management Planning on a Small Scale Aerial Photograph or Satellite Image

Good management of rangeland resources requires that the range is evenly grazed over large areas. The distribution and timing of grazing is necessary for the implementation of useful intensive grazing management systems. Large scale images (1:60,000 to 1:150,000) are useful for the development of such systems. Useful intensive grazing management systems normally involve concepts of rest, rotation and deferment of grazing use spread over several pastures or paddocks (Fig. 7). The general lay of the land, the plant communities, topography, fences or required fences and necessary watering points can be examined on various kinds of imagery either hard copy or digitally via an image processing system. One can identify and interpret those management features available on the landscape or determine those that should be developed and specified for use in a grazing management system.

Forage Utilization

For short term rangeland monitoring and for assessing the success of intensive grazing management systems it is necessary to periodically evaluate the forage utilization on portions of pastures or grazing allotments. This is mostly done on the ground by laying out cages to protect the grasses and forbs from grazing. Then at the end of the grazing season these plants are harvested and comparison made with grazed sites of the same size to determine the level of utilization. The idea is to implement the same grazing intensity over all portions of the pasture or allotment. There is also the need to determine that specific pastures in an intensive grazing management system have been utilized to a certain level.

Figure 13


Figure 13 shows how cages are used to measure utilization on the ground. The grazed sites can be calibrated with appropriate imagery to show which areas of the range have been grazed to certain levels.

SUMMARY

Various kinds of remotely sensed data can be used singly or in concert with one another or with other kinds of ancillary data to provide input to range management.

Figure 14

Conventional aerial photography at resources scales (1:10,000 - 1:24,000) will continue to be used along with new image processing systems/algorithms, digitized satellite images, airborne multispectral videography, and hyperspectral remote sensing. These images and data acquired from them will be used by trained rangeland resource managers to supplement the information required for good range management. Maps will tend to give way more and more to layers in Geographic Information Systems, and Geographic Positioning Systems (GPS) will be routinelym used for accurate and rapid georeferencing. As the remotely sensed and other data sets become more commonplace they will be used in various analysis procedures within the GIS framework to provide useful, and when necessary, real-time information to those managing the world's rangelands. Rangeland resource managers should become familiar with and keep up with new remote sensing technologies in order to utilize them for good rangeland resources management.

CREDITS

This module and exercises were written by Paul T. Tueller, Department of Environmental and Resource Sciences, University of Nevada Reno. TIF files and graphic editing by Andy Yuan.

REFERENCES CITED

Heady, H.F. and R. D. Child. 1994. Rangeland Ecology and Management. Westview Press, Boulder, Co. 519 pp.

Holechek, J. L., R. D. Pieper and C. H. Herbel. Range Management Principles and Practices. Second Edition. 1995. Regents/Prentice Hall, Englewood Cliffs, New Jersey. 526 pp.

Joyce, L.A. 1989. An analysis of the range forage situation in the United States: 1989-2040. USDA-FS Gen. Tech. Rep. RM-180.

McGraw and J. F. and P. T. Tueller. 1983. Landsat Computer-aided analysis Techniques for Range Vegetation Mapping. Journal of Range Management 36(5):627-631.

Oleson, S. G. and P. T. Tueller. 1989. Diurnal Radiance and Shadow Fluctuations in a cold Desert Shrub Plant Community. Remote Sens. Envirion. 29:1-13

Tueller, P.T. 1978. Large scale 70mm photography for range resources analysis in the western United States. Proceedings. 11th International Symposium on Remote Sensing of environment. Ann;. Arbor. pp. 1057-1514.

Tueller, P. T. 1979. Rangeland remote sensing interpretation problems. Proceedings of Remote Sensing for Natural Resources: A symposium. Moscow, ID pp. 450-465

Tueller, P. T. 1982. Remote Sensing for Range Management. Chapter 12, pp. 125-140. IN: Johannsen and Sanders (eds.) Remote Sensing for Resource Management. Soil Conservation Society of America.

Tueller, P. T. 1989. Remote sensing technology for rangeland management applications. Journal of Range Management42:442-453.

Tueller, P.T. 1991. Remote sensing applications for monitoring rangeland condition. J. Grassl. Soc. South Afr. 8(4):160-167.

Tueller, P.T. 1992. Great Basin Annual Vegetation Patterns Assessed by Remote Sensing. Proceedings of the Symposium: Ecology , Management and Restoration of Intermountain Annual Rangelands. pp. 128-132.

Tueller, P. T 1995. Remote Sensing in theManagement of Rangelands. Annals of the Arid Zone 34(3):191-207.

Wilson, R. O. and P. T. Tueller. 1987. Aerial and Ground Spectral Characteristics of Rangeland Plant Communities in Nevada. Remote Sensing of Environment 23:177-191.