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Rangeland Health: New Methods to Classify, Inventory, and Monitor Rangelands 4 Criteria and Indicators of Rangeland Health Rangeland ecosystems are continually responding to temporary changes in the physical and biotic environments. A system that assesses rangeland health must be able to distinguish between changes that result in the crossing of a threshold from those that are temporary because of normal fluctuations in physical or biotic factors. Some of these changes, that is, threshold shifts, may be difficult to reverse, but they do not necessarily entail a loss of the capacity to produce commodities and satisfy values. The process of rangeland degradation is complex and involves the interaction of changes in the physical, chemical, and biological properties of soils, as well as changes in plant vigor, species composition, litter accumulation and distribution, seed germination and seedling recruitment, total biomass production, and other ecological functions. Tueller (1973) reviewed the process of rangeland degradation and suggested 16 factors that operate at different stages of the degradation process. The process of rangeland improvement is just as complex. Multiple criteria and indicators will be needed to assess whether rangelands are healthy, at risk, or unhealthy. It is also clear that the evaluation of rangeland health is a judgment, not a measurement. Rangeland health, like range condition (SCS) or ecological status (USFS and BLM), is not a physical characteristic of rangelands that can be measured directly. The indicators of rangeland health, range condition (SCS), or ecological status (USFS and BLM) can, however, be measured. The evaluation of rangeland health will require judgments on the significance and meaning of the indicators that are measured. Evaluation of the preponderance of evidence from the evaluation of multiple indicators will be required for a meaningful assessment of rangeland health. The determination of whether a rangeland is healthy, at risk, or unhealthy should be based on the evaluation of three criteria: degree of soil stability and Desert needlegrass (Stipa speciosa)
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Rangeland Health: New Methods to Classify, Inventory, and Monitor Rangelands watershed function, integrity of nutrient cycles and energy flow, and presence of functioning recovery mechanisms. The process of rangeland change is complex, and multiple criteria should be used to determine whether rangelands are healthy, at risk, or unhealthy. No single criterion alone will be a sufficient basis for this determination. The committee recommends a three-phase approach for assessing rangeland health. Phase 1 is an evaluation of soft stability and watershed function. Phase 2 is an evaluation of the functioning of nutrient cycles and energy flows. Phase 3 is an evaluation of the probability that recovery mechanisms will occur on the rangeland being assessed. SOIL STABILITY AND WATERSHED FUNCTION The physical, chemical, and biological processes that occur in rangeland soils supply plants with nutrients and water. Microorganisms in the soil break down plant litter, releasing nitrogen, phosphorus, and other nutrients essential to plant growth. The texture, structure, and porosity of soil determine how much rain is captured and how much runs off during a storm. Soils are storehouses of water and nutrients for plants to draw on when they need them. The soft is a living system that is inextricably linked to nutrient cycles, energy flows, and other ecological processes of rangeland ecosystems. Soil Degradation There are three principal processes involved in soil degradation: physical, chemical, and biological. These processes are closely linked, and modification of one unavoidably alters the others. Physical degradation results in the deterioration of the physical properties of soils through compaction, wind or water erosion, deposition of sediments, and loss of soil structure. Biological degradation occurs when there is a reduction in the organic matter content of the soil, a decline in the amount of carbon stored as biomass, and a depression in the activity and diversity of the organisms living in the soft. Chemical degradation includes nutrient depletion, shifts toward extremes in the pH of the soft, increases in salt concentration, and contamination by toxic substances such as heavy metals (Lal and Stewart, 1990). Summaries of these phenomena and interactions can be found in basic soils texts (for example, Brady , Foth , Miller and Donahue , and Singer and Munns ). SOIL EROSION BY WIND AND WATER Soft erosion by wind and water is a major factor in the process of soft degradation on rangelands and has been recognized as such for a long
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Rangeland Health: New Methods to Classify, Inventory, and Monitor Rangelands time. It affects the physical, chemical, and biological properties of soils. Lincoln Ellison wrote: ''we know that range condition ceases to be satisfactory when accelerated soil erosion sets in, when destructive processes clearly exceed constructive processes. Hence a basic criterion of range condition is degree of soft erosion, and a minimal requirement for satisfactory condition is normal soil stability" (Ellison, 1949:790). Ellison considered the soft to be an index of the extent to which soft, plants, animals, and climate are knit together into an integrated whole. To Ellison, the presence of a well-developed soil was evidence of successful integration of climate and topography, vegetation, and animal life over a long time period. Ellison indicated, however, that accelerated soil erosion is evidence of disintegration and of a relatively recent change in the relationship between components of the range complex that were formerly well integrated. It is also an indication that a change of drastic proportions, over and above the normal amplitude of environmental stress, has taken place. EFFECTS OF SOIL DEGRADATION Soil degradation has profound effects on rangeland ecosystems. Smith (1989) concluded that site deterioration occurs mainly through deterioration of the soil's capacity to capture and store water, loss of the ability of the soil to supply nutrients, or the accumulation of salts or other toxic substances in the soil. Erosion and deposition of eroded sediments are, according to Smith (1989), major processes of site degradation; but degradation of the soil's structure, losses of nutrients to the atmosphere by gasification, movement of dissolved nutrients beyond the reach of plant roots by water percolation through the soft, or changes in the depths to water tables also cause rangeland degradation. Wilson and Tupper (1982) suggested that there are four classes of rangelands based on whether the soil is stable or unstable and whether vegetative productivity is good or diminished. Friedel (1991) wrote that site deterioration is best indicated by irreversible changes in the soft, and concluded that assessment of the soil surface is a critical element in the identification of thresholds of change on rangelands. Similarly, Pisser (1989) and Wilson (1989) emphasized the importance of soft erosion in rangeland assessments and recommended that soft criteria be incorporated into current assessments of range condition (SCS) and ecological status (USFS and BLM). Most recently, the Society for Range Management's Task Group on Unity in Concepts and Terminology (1991) recommended that the effectiveness of present vegetation in protecting a site against accelerated erosion by water should be assessed independent of the use of the site and that any site determined to be suffering accelerated erosion should be considered in unsatisfactory condition.
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Rangeland Health: New Methods to Classify, Inventory, and Monitor Rangelands OTHER EFFECTS OF SOIL DEGRADATION Soil degradation affects not only soil attributes but can also degrade other ecological processes. Loss of organic matter in the soil reduces nutrient stores and interrupts nutrient cycles. Accelerated soil erosion reduces the total organic matter and total nitrogen contents of soils and the capacity of rangeland soils to hold moisture (Croft et al., 1943). The formation of soil crusts and the development of erosion pavement (a hard, impermeable soil surface caused by erosion) can impede germination and growth of seedlings (Blaisdell and Holmgren, 1984; Troeh et al., 1991). Reduced water infiltration and water storage can reduce total vegetative biomass production and can result in shifts in species composition (Archer, 1989). SOIL STABILITY AND THE ENVIRONMENT Given the importance of soil stability, it is important to recognize that rangelands are often located in arid or other extreme environments where the processes of soil development are slow or impeded (Hugie et al., 1964; Passey et al., 1982; Wooldridge, 1963). Destructive processes such as wind and water erosion can easily exceed constructive process such as the accumulation of soil organic matter. Naturally destructive processes are thus highly probable on many rangelands (Friedel, 1991). Managers of rangelands must minimize the consequences of processes that destroy the soil if rangeland health is to be conserved. There are some arid, steeply sloping, or other sites in extreme environments, however, where destructive processes dominate and render even good management inconsequential. On such sites soil instability is manifest in the lack of soil horizons (the presence of a soil horizon is a characteristic of developed soil), little organic matter accumulation, and limited development of plant communities. Such sites have been unstable for millennia and will continue to be unstable long into the future. They are the result of processes that occur over geological time scales (tens of thousands of years) and can be considered naturally unhealthy or at risk. Management options that conserve or encourage the development of rangeland health on such sites are limited (see discussions by Retzer  and Birkeland ). These sites will require careful management to ensure improper use does not accelerate the destructive processes already operating on the site. Rangelands in less severe environments are exposed to varying degrees of soil degradation. Animal hooves may cause mild compaction of the soil in some locations. Prolonged wheeled vehicular traffic causes significant compaction on most soils. Abusive overgrazing not only may
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Rangeland Health: New Methods to Classify, Inventory, and Monitor Rangelands Overgrazing of livestock is an important factor in deterioration. Wind erosion takes a heavy toll on soil in this condition. Credit: U.S. Department of Agriculture. cause compaction but may remove plant cover and open the way for destructive erosion as well (Dormaar and Williams, 1990). Little research has been done to determine whether grazing causes loss of soil organic matter, but some studies have shown that wild and domestic grazing animals can influence soil processes (Pastor et al., 1988; Whicker and Defling, 1988). However, any factor that severely reduces soil cover opens the way for removal of organic matter via erosional events. EFFECTS OF SOIL DEGRADATION ON WATERSHEDS Soil degradation directly influences watershed function on rangelands. Precipitation that falls on rangelands ultimately infiltrates into the soil, evaporates, or becomes part of the overland flow and runoff to surface water (Branson et al., 1981). Figure 4-1 describes the pathways taken by rainfall on rangelands. The proportion of precipitation captured de-
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Rangeland Health: New Methods to Classify, Inventory, and Monitor Rangelands FIGURE 4-1 The pathways taken by rain falling on vegetated land. Source: Derived from R. Brewer. 1989. The Science of Ecology. Philadelphia: Saunders College Publishing. pends on the energy, time of year, and total volume of precipitation during a particular rainfall event and by the properties of the soil on which it falls (Branson et al., 1981). Texture, structure, moisture content, vegetative or litter cover, and organic matter content are the most important properties of soil that influence infiltration (Satterlund, 1972). Degradation of watershed f-unction has direct effects on rangelands. Grazing, gathering of fuelwood and harvesting of woody and herbaceous vegetation, and fires all may have dramatic and direct effects on the infiltration of water into the soil. Standing vegetation, litter and duff (partly decayed organic matter), and organic matter incorporated into the soil all improve the ability of water to infiltrate the soil through various processes (Figure 4-2). A site that has lost its vegetation, litter, and ultimately, the organic matter incorporated into its soil tends to seal its surface and encourage water to run off as overland flow rather than be absorbed into the soil profile. As less water infiltrates the soil, less plant growth is possible, and therefore, soil cover and the amount of organic matter in the soil are reduced, leading to less infiltration. This process can lead to a self-rein-
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Rangeland Health: New Methods to Classify, Inventory, and Monitor Rangelands forcing cycle of watershed degradation as increased volumes of runoff accelerate soil erosion, which, in turn, reduces the infiltration of water into the soil and increases runoff (Shaxon et al., 1989). Loss of the nutrients that are attached to soil particles can lead to further degradation through the loss of soil fertility (Logan, 1990). Soil degradation, primarily through accelerated wind and water erosion, causes the direct and often irreversible loss of rangeland health. Soil degradation not only damages the soil itself but also disrupts nutrient cycling, seed germination, seedling development, and other ecological processes that are central to rangeland health. In addition, soil degradation can degrade watersheds, leading to the further loss of rangeland health as well as off-site damages to water quality. Criteria and Indicators of Soil Stability and Watershed Function The criteria and indicators that are selected to assess soil stability and watershed function must relate to two fundamental processes: soil erosion by wind and water and infiltration or capture of precipitation. These FIGURE 4-2 Diagram of a soil profile. Rangeland vegetation helps to create a layer of surface soil rich in organic matter, which serves as a basis for an extensive root system. In such a profile, water is better able to infiltrate the soil, limiting the effects of erosion.
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Rangeland Health: New Methods to Classify, Inventory, and Monitor Rangelands two processes interact with each other, and measurable indicators of their activities can provide data that can be used to evaluate the stability of soils and interpret whether watershed functions are adequate. The degree of soil movement by wind and water should be the criterion used to assess soil stability and watershed function; evaluation of soil movement should be based on multiple indicators of the condition of the soil surface. Soil erosion by wind and water is the most important form of soil degradation on rangelands, and erosion damage is often irreversible. The degree of soil movement by wind and water should be fundamental to the assessment of rangeland health. The use of soil surface characteristics such as rills and gullies, scours (bare soil caused by the scouring action of wind or water) and dunes, litter cover, flow patterns, and pedestaling (erosion of soil from around the base of a plant such that it appears to be on a pedestal) have long been used as indicators of soil stability. Table 4-1, which was developed by the Bureau of Land Management, is an example of the use of soil surface characteristics to assess soil stability. Table 4-2 lists the general surface soil characteristics that are useful indicators of the degree of the soil stability and watershed function. The development of rills and gullies, the degree of pedestaling, evidence of scouring by wind or sheet erosion (erosion caused by thin sheets of water running off unprotected soil), and deposition of eroded material in fans or dunes are all evidence of soil erosion and runoff. The presence and distribution of an organically enriched A-horizon (the uppermost layer of soil in which organic matter is deposited and the decay process occurs) is evidence of the balance between soil development and degradation. All of these indicators have been used in the past, and many are currently used by federal agencies to evaluate the stability of rangeland soils. Estimates of erosion rates on rangelands have been impeded by the lack of models that are well adapted to rangelands. New models that will better simulate rangeland conditions are being developed. Estimates of erosion rates by wind or water alone, however, will not be sufficient unless researchers can determine erosion rates that are acceptable for main taming rangeland health. In addition, estimation of erosion rates does not necessarily yield estimates of the proportion of precipitation that is effectively captured—an important criterion for the evaluation of water shed function. Development of soil crusts, for example, may simultaneously reduce soil loss and increase runoff. Development of predictive models that estimate rates of soil loss and infiltration, coupled with the establishment of natural rates of soil loss, could help to quantify the evaluation of soil stability and watershed function as part of rangeland assessments. Soil surface characteristics will
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Rangeland Health: New Methods to Classify, Inventory, and Monitor Rangelands continue to provide the best available information with which to evaluate soil stability. THE A-HORIZON The A-horizon is the soil layer where organic matter from plant litter, animal manures and other sources begins to decompose and becomes incorporated into the soft. The condition of this organically enriched A horizon has important effects on soil stability, nutrient cycling, energy flows, and recovery mechanisms. The condition of the A-horizon, for example, greatly influences how rapidly water can infiltrate into the soil or safely be stored at the surface of the soil. The nutrients released through the biological activity that occurs in the A-horizon are critically important to the productivity of the site. The A-horizon may not be evenly distributed across the landscape, and it may occur as a thin layer and only in association with living plants in some desert situations. In most rangelands, the presence and distribution of an organically enriched A-horizon can serve as a useful indicator of soil development on a site. The absence or fragmented distribution of an A-horizon indicates that soil is not developing or accumulating on the site. On the other hand, it may indicate that soil formation occurs only in relation to a few prominent grasses or shrubs. RILLS AND GULLIES Rills and gullies provide channels for the rapid flow of water from the site. This water may contain soil and organic matter as well as nutrients in solution. Evidence of the development and activity of rills and gullies is a useful indicator of the degree of soil erosion and water infiltration on a site. The physical features of rills and gullies—including their depths, distributions, or degree or the development of a dendritic pattern (branching), which is evidence of active erosion—can be used as indicators of the seriousness of erosion and runoff. SHEET AND SCOUR EROSION Sheet erosion by water and scour erosion by wind can remove or reduce the depth of the A-horizon from large areas of rangelands. Continued erosion by these processes results in the loss of subsoil layers beneath the A-horizon as well. Scour erosion by wind may result in abrasive damage to plants as the soil and organic particles blow across the land surface. Sheet and scour erosion can occur without the development of rills or gullies. The degree of development of patches of bare soil as a
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Rangeland Health: New Methods to Classify, Inventory, and Monitor Rangelands Table 4-1 Surface Soil Characteristics of the Bureau of Land Management Characteristic Class 1 Class 2 Class 3 Class 4 Class 5 Soil movement Subsoil exposed over much of area; may have embryonic dunes and wind-scoured depressions Soil and debris deposited against minor obstructions Moderated movement of soil is visible and recent; slight terracing Some movement of soil particles No visual evidence of movement Surface rock and/or litter Very little remaining (use care on low-productivity sites); if present, surface rock or fragments exhibit some movement and accumulation of smaller fragments behind obstacles Extreme movement is apparent; large and numerous deposits against obstacle; if present, surface rock or fragments exhibit some movement and accumulation of smaller fragments behind obstacles Moderate movement is apparent and fragments are deposited against obstacles; if present, fragments have a poorly developed distribution pattern May show slight movement; if present, coarse fragments have a truncated appearance or spotty distribution caused by wind or water Accumulation in place; if present, the distribution of fragments shows no movement caused by wind or water Pedestaling Most rocks and plants are pedestaled and roots are exposed Rocks and plants on pedestals are generally evident; plant roots are exposed Small rock and plant pedestals occurring in flow patterns Slight pedestaling, in flow patterns No visual evidence of pedestaling
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Rangeland Health: New Methods to Classify, Inventory, and Monitor Rangelands Characteristic Class 1 Class 2 Class 3 Class 4 Class 5 Flow patterns Flow patterns are numerous and readily noticeable; may have large barren fan deposits Flow patterns contain silt, sand deposits, and alluvial fans Well defined, small, and few with intermittent deposits Deposition of particles may be in evidence No visual evidence of low patterns Rills and gullies May be present at depths of 8 to 15 cm (3 to 6 inches) and at intervals of less than 13 cm (15 inches); sharply incised gullies cover most of the area, and 50 percent are actively eroding Rills at depths of 1 to 15 cm (0.5 to 6 inches) occur in exposed areas at intervals of 150 cm (t feet); gullies are numerous and well developed, with active erosion along 10 to 50 percent of their lengths or a few well developed gullies with active erosion along more than 50 percent of their length Rills at depths of 1 to 15 cm (0.5 to 6 inches) occur in exposed places at approximately 300-cm (10-foot) intervals; gullies are well developed, with active erosion along less than 10 percent of their length; some vegetation may be present Some rills in evidence at infrequent intervals of over 300 cm (10 feet); evidence of gullies that show little bed or slope erosion; some vegetation is present on slopes No visual evidence of rills; may be present in stable condition; vegetation on channel bed and side slopes SOURCE: Adapted from U.S. Department of the Interior, Bureau of Land Management. 1973. Determination of Erosion Condition Class, Form 7310-12. May. Washington, D.C.: U.S. Department of the Interior.
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Rangeland Health: New Methods to Classify, Inventory, and Monitor Rangelands RESEARCH NEEDED The secretaries of USDA and DOI should initiate a coordinated research effort, drawing on federal agency and other scientists to develop, test, and implement indicators of recovery mechanisms for use in rangeland health assessments. Explicit evaluations of recovery mechanisms have not been part of rangeland assessments to date. The lack of development and testing of measurable indicators of change in recovery mechanisms is an important impediment to a comprehensive evaluation of rangeland health. There is an urgent need to develop measurable indicators and methods of evaluation that can be incorporated into routine assessments of rangelands. The indicators discussed here are embryonic and are suggested by the committee to stimulate research, development, and refinement of useful indicators of self-induced recovery mechanisms. MEASUREMENT AND EVALUATION OF INDICATORS OF RANGELAND HEALTH The indicators of rangeland health for each of the criteria listed in Table 4-2 are only a subset of those that the committee could suggest. Past investigators have used all of the indicators as part of rangeland assessments. In many cases, the data currently collected as part of range condition (SCS), ecological status (USFS and BLM), and apparent trend (SCS) evaluations can be reinterpreted as indicators of rangeland health. The overlap between the indicators of rangeland health investigated by the committee and currently used indicators is given in Table 4-6. Identification of Boundaries A fundamental problem with assessing rangeland health involves identification of the boundaries between healthy, at-risk, and unhealthy rangelands. Table 4-7 illustrates one way these boundaries could be identified using indicators of soil stability and watershed function, distribution of nutrients and energy, and recovery mechanisms—the three-phase approach recommended by the committee. The illustration in Table 4-7 and the discussions that follow are offered as a useful starting point. These distinctions will have to be refined and validated through research. SOIL STABILITY AND WATERSHED FUNCTION Healthy rangelands, in this example, exhibit no evidence of accelerated soil erosion by wind or water. There is no evidence of the formation of rills and gullies, pedestals, or sheet or scour erosion, and there is no evi-
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Rangeland Health: New Methods to Classify, Inventory, and Monitor Rangelands Table 4-6 Indicators of Rangeland Health Currently Used as Indicators of Range Condition (SCS), Ecological Status (USFS and BLM), or Apparent Trend (SCS) Same or Similar Indicator Used for Same or Similar Indicator Used for Proposed Rangeland Health Indicator Range Condition (SCS) and Ecological Status (USFS and BLM) Apparent Trand (SCS) A-horizon Rills, gullies DM Pedestaling DM Scouring or sheet erosion DM Sedimentation, dune formation RM Plant distribution Litter distribution and incorporation RM Rooting depth RM Photosynthetic period RM Age class RM Plant vigor DM Germination microsites NOTE: DM, direct measure of indicator used; RM, related measure of indicator used. dence that water or wind-eroded materials have been deposited on the site. The A-horizon of the soil appears to be stable and is present uniformly over the site. At-risk rangelands show evidence of soil movement, but such movement is primarily within the site itself. Rills and gullies may be forming, but they are not yet well developed or integrated into a dendritic pattern. If pedestaling is present, it is not so severe that the roots are exposed. Similarly, scours and dunes are small and not well developed, if they are present, and there is little evidence of sediment deposits on the site. Soil particles, organic matter, nutrients, and water are redistributed on the site, but they are not yet lost from the site. Evidence of soil movement off the site, however, indicates an unhealthy state. Rills and gullies are well developed and active, and they display a developed dendritic pattern. Pedestaling is severe enough that roots are exposed, scours and dunes may be active and widespread, and large areas may be devoid of the A-horizon of soil. There is clear evidence of soil degradation and transport of nutrients, water, and organic matter off the site.
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Rangeland Health: New Methods to Classify, Inventory, and Monitor Rangelands DISTRIBUTION OF NUTRIENTS AND ENERGY In Table 4-7, the nutrients stored in litter, plant, and root biomass are well distributed and litter is being decomposed and incorporated into the soil throughout the rangeland considered to be healthy. Photosynthetic activity, which is represented by actively growing plants, is also well distributed across the site. The rangeland considered at risk, however, shows evidence that the spatial and temporal distribution of nutrients and energy is becoming fragmented across the site. Litter may be present, but it tends to accumulate in depressions or around prominent grasses or shrubs. The plant and root biomass is beginning to show a fragmented pattern, and barren areas develop between patches. In the rangeland considered unhealthy, this fragmented distribution of nutrients and energy is pronounced. Litter is sparse, accumulating and being incorporated Table 4-7 Relationship between Health Criteria and Thresholds Phase Healthy At Risk Unhealthy 1. Soil stability and watershed function No evidence of soil movement Soil is moving, but remains on site Soil is moving off site 2. Distribution of nutrients and energy Plant and litter distribution unfragmented Fragmented distribution developing Fragmented distribution developed, with large barren areas between fragments Photosynthetic activity occurs throughout the period suitable for plant growth Photosynthetic activity restricted during one or more seasons Photosynthetic activity restricted to one season only Rooting throughout the available soil profile Roots absent from portions of the available soil profile Rooting in only one portion of the available soil profile 3. Recovery mechanisms Diverse age-class distribution Seedlings and young plants are missing Decadent plants predominate Plant vigor is poor plants are vigorous Plant vigor is reduced Plant vigor is poor Germination microsites are present and well distributed Developing crusts or soil movement degrade microsites Soil movement or crusting inhibit most germination
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Rangeland Health: New Methods to Classify, Inventory, and Monitor Rangelands into the soil only in depressions or around prominent grasses or shrubs. Plant and root biomass is restricted to patches, and there are large barren areas between the patches. The distribution of nutrients and energy over time is also used to distinguish between states in Table 4-7. Photosynthetic activity occurs during most of the period when temperature and moisture make photo synthesis possible in rangelands defined as healthy. The diversity of plants with different growing periods is sufficient to ensure that at least some plants are actively photosynthesizing during most of the period when the temperature and moisture are at levels such that photosynthesis can occur. Similarly, the plant community structure supports a diversity of rooting depths, so that plants use the nutrients and water available throughout the soil profile. In the at-risk category, the period of time when photosynthesis occurs is reduced, and the portion of the soil profile occupied by the roots of the plants that are present is restricted. In the unhealthy category, photosynthesis is restricted to a portion of the period when moisture is available, and the plant roots occupy only one layer in the soil profile. RECOVERY MECHANISMS In Table 4-7, rangelands that show evidence that plant community dynamics are sufficient to at least maintain the current community structure and function are classified as healthy. There is a diverse species com position and age-class distribution, microsites in which seeds can germinate are available, and seedlings are becoming established. Plants are vigorous and show no signs of deformed growth patterns. At-risk rangelands are distinguished by missing age classes, reduced plant vigor, and restricted seedling recruitment. Rangelands in the unhealthy category are characterized by the predominance of old or deteriorating plants, the loss of microsites for seed germination, and the absence of seedlings. Preponderance of Evidence from Measured Indicators The decision to classify a rangeland as healthy, at risk, or unhealthy should be a judgment based on the preponderance of evidence from an evaluation of multiple and measurable indicators. Data must be collected and reported for all the measurable indicators to allow for independent analyses of the final classification decision. Consistently reported data on measurable indicators will be more valuable than a final judgment. It is unreasonable to expect that all indicators will simultaneously fall into the healthy, at-risk, or unhealthy category. It is more likely, for example, that the soil of a particular rangeland may show no evidence of move-
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Rangeland Health: New Methods to Classify, Inventory, and Monitor Rangelands ment by wind and water, suggesting that the site is healthy, while the distribution of litter, plants, and roots across the site may be becoming patchy, suggesting that the site is moving toward the at-risk category. In such cases a judgment must be made. The development of a patchy distribution of litter and plants suggests a reduction in the effective soil cover, which may lead to accelerated erosion or increased vulnerability to serious soil erosion during an intense rainstorm, and so the site is best considered at risk. Alternatively, seed germination and seedling recruitment may indicate that the patchy distribution will be short-lived, and so the site is best considered healthy. Each indicator represents an important piece of the puzzle. Taken together they provide the information needed to assess rangeland health. New Models of Rangeland Change Needed The secretaries of USDA and DOI should initiate a coordinated research effort, drawing on federal agency and other scientists to develop, test, and implement new models of rangeland change that incorporate the potential for difficult to-reverse shirts across ecological thresholds. A theory is accepted until unexplained anomalies overwhelm the proponents of the current theory or until an alternative theory is proposed to explain the anomalies. Recent findings in the field of community ecology have questioned the applicability of climax theory to all rangelands. Lay cock (1989), Westoby (1980), Westoby and colleagues (1989), and others have reviewed the anomalies that are not well explained by successional theory. It still appears, however, that the area in the United States containing anomalous grassland vegetation is smaller than the area where successional theory can be used to model plant community dynamics. New models are being proposed to better explain the dynamics of rangeland vegetation. Researchers in arid areas, notably, in Australia and South Africa, are advancing new theories to explain the responses of plants to grazing and other environmental factors. Concepts of population dynamics that are derived from the field of animal ecology are being applied to rangeland vegetation, and concepts of alternating stable communities are challenging the Clementsian model of successional change (Clements, 1916). A state and transition model proposed by Westoby and colleagues (1989) seems well adapted to rangelands where episodic events may well be the primary factors responsible for determining vegetation composition. Despite these advances, there does not appear to be a single coherent theory that can explain all of the current anomalies or that has been sufficiently tested to replace current successional concepts. The facts that cur rent successional theory apparently adequately explains vegetation dy-
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Rangeland Health: New Methods to Classify, Inventory, and Monitor Rangelands namics on a significant portion of rangelands and that no new comprehensive theory has yet emerged have restrained efforts to replace the successional models currently used to rate range condition (SCS) or ecological status (USFS and BLM). The development of new models and theories of rangeland change requires research. There is a need to fund such research at an interdisciplinary level, integrating range science theories with theories from the other ecologies. The drive to specialize is not unique to range science or ecological research; however, this does impede the transfer of new and possibly helpful ideas between specialized fields. In addition, current ecological research is oriented toward the development of new ideas rather than the testing of new ideas for a variety of rangeland types. This' testing of new ideas is essential to determine which new ideas might hold promise as a theoretical foundation for rangeland management. The lack of a single, coherent theory of community structure and development that can replace current climax, succession, and retrogression models is the result of the fact that such potential theories cannot be sufficiently tested on a sufficiently large number of sites and, in so doing, allow re searchers to gain confidence that such theories could replace the currently held ones. There is a need for inexpensive inventory, classification, and monitoring methods with links to current ecological theory. These links must be robust so that as ecological theories change, the data can still be interpreted using new theories. This will involve a multiple-attribute approach to the design of the inventory. The development of such methods will require funding of interdisciplinary research that links all branches of ecological research. Further more, research to demonstrate the applicability of newly developed models over a variety of rangeland types is required. This area of research must be the testing ground for models that might hold promise as an improved theoretical framework for classifying, inventorying, and monitoring rangelands. Better Understanding of Rangeland Soils Needed The secretaries of USDA and DOI should initiate a coordinated research effort, drawing on federal agency and other scientists to increase understanding of the relationship between soil properties and rangeland health. Knowledge of soils has been used in assessments of rangelands primarily as an aid in the classification of rangelands. A range site (SCS), ecological site (BLM), or ecological type (USFS) is often defined by the presence of one or more characteristic soil types. While much research and experience supports the relationship of soil
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Rangeland Health: New Methods to Classify, Inventory, and Monitor Rangelands surface characteristics to rangeland health, basic knowledge of the effects of other soil properties such as organic matter content or water-holding capacity on nutrient cycling, energy flow, recovery mechanisms, and other elements of rangeland health is limited. The effects of grazing management and other management practices on soil properties are also not well understood. Basic and applied research is needed to increase understand Lug of how changes in soil properties affect rangeland health. Research on cropland soils has attempted to identify those soil properties that are most important in determining crop yield and vulnerability to degradation. Much research has also been devoted to determining the impact of tillage, crop sequence, residue management, organic amendments, fertilizers, cover crops, and other elements of farming systems on soil properties. Research pertaining to the coupling of rangeland soils with rangeland vegetation and disturbance of the rangeland ecosystem is needed. Although recent work has addressed the influence of soil organic matter on rangeland productivity (Burke et al., 1989), additional research detail Lug soil organic matter at specific sites is necessary to more closely de scribe the nutrient dynamics of range sites. Study of the relationships of other soil properties to plant growth and species composition is limited in the literature on rangeland soils. Some reports have addressed this area (Passey et al., 1982), but many questions remain. For example, at what level do plant types (species, community, landscape) and soil types (series, family, subgroup) most closely correlate? The influence of soil degradation on plant parameters (for example, yield, species composition, and regenerative power) is not well researched for rangeland soils. The influences of plowing or soil removal, grazing intensity, and climatic degradative factors (water and wind erosion) have not been determined for rangelands. All of these questions have a direct bearing on rangeland health. Field Evaluation of Proposed Indicators To explore the usefulness of the criteria and indicators discussed above, the committee developed a three-phase matrix as a workable approach to implementing its recommended three-phase concept of rangeland health evaluation. The matrix is presented in Table 4-8. The committee attempted to develop measures of the indicators that involve simple and, in many cases, visual estimates. The committee conducted limited field tests of a three-phase evaluation of rangeland health using the matrix. Eighteen limited field tests were carried out by six members of the
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Rangeland Health: New Methods to Classify, Inventory, and Monitor Rangelands TABLE 4-8 Rangeland Health Evaluation Matrix Indicator Healthy At Risk Unhealthy Phase 1: Soil stability and watershed function A-horizon Present and distribution unfragmented Present but fragmented distribution developing Absent, or present only in association prominent plants or with other obstructions Pedestaling No Pedestaling of plants or rocks Pedestals present, but on mature plants only; no roots exposed Most plants and rocks pedestaled; roots exposed Rills and gullies Absent, or with blunted and muted features Small, embryonic, and not connected into a dendritic pattern Well defined, actively expanding, dendritic pattern established Scouring or sheet erosion No visible scouring or sheet erosion Patches of bare soil or scours developing Bare areas and scours well developed and contiguous Sedimentation or dunes No visible soil deposition Soil accumulating around plants or small obstructions Soil accumulating in large barren deposits or dunes or behind large obstructions Phase 2: Distribution of nutrient cycling and energy flow Distribution of plants Plants well distributed across site Plant distribution becoming fragmented Plants clumped, often in association with prominent individuals; large bare areas between clumps
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Rangeland Health: New Methods to Classify, Inventory, and Monitor Rangelands Indicator Healthy At Risk Unhealthy Litter distribution and incorporation Uniform across site Becoming associated with prominent plants or other obstructions Litter largely absent Root distribution Community structure results in rooting through out the available soil profile Community structure results in absence of roots from portions of the available soil profile Community structure results in rooting in only one portion of the available soil profile Distribution of photosynthesis Photosynthetic activity occurs throughout the period suitable for plant growth Most photosynthetic activity occurs during one portion of the period suitable for plant growth Little or no photosynthetic activity on location during most of the period suitable for plant growth Phase 3: Recovery mechanisms Age-class distribution Distribution reflects all species Seedlings and young plants missing Primarily old or deteriorating plants present Plant vigor Plants display normal growth form Plants developing abnormal growth form Most Plants in abnormal growth form Germination Microsites present and distributed across the site Developing crusts, soil movement, or other factors degrading microsites; developing crusts are fragile Soil movement or crusting sufficient to inhibit most germination and seedling establishment
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Rangeland Health: New Methods to Classify, Inventory, and Monitor Rangelands committee in Arizona, New Mexico, Colorado, Wyoming, Montana, and Nebraska between April and July 1991. An analysis of the results revealed three important points in evaluating rangeland health by the approach proposed by the committee. SOIL STABILITY AND WATERSHED FUNCTION ARE THE MOST IMPORTANT CRITERIA Soil stability and watershed function should have greater weight than other criteria in the determination of rangeland health; soil movement off site should mean the rangeland is unhealthy. The degradation of soil and watershed function that accompanies movement of soil by wind and water can lead to irreversible changes in productivity and site potential, at least within a practical time scale and within the realm of economically feasible reclamation efforts. The irreversibility of such erosion losses has been repeatedly cited as a major concern in croplands, and forests as well as rangelands (Bormann and Likens, 1979; Ellison, 1949; Klock, 1982; Larson et al., 1983; Pierce, 1991; Sheridan, 1981; Wight and Siddoway, 1982). Because of the danger of irreversible effects from soil and watershed degradation, the evaluation of soil stability and watershed function should have greater weight in the final evaluation of rangeland health than do the other two phases of evaluation. The result of the phase 1 evaluation should be the maximum rating a rangeland can receive. That is, if an evaluation of phase 1 results in an unhealthy rating, evaluation of the other components should not result in a final rating of at risk or healthy. Uncertainty in Interpreting Indicators The precise placement of the boundaries between healthy, at risk, and unhealthy, however, is not clear. Placement of rangelands into healthy, at risk, or unhealthy classes will require judgment. As in any classification scheme, there will be borderline cases that are difficult to place into one class or another. The scientific understanding required to develop and interpret changes in indicators of rangeland health is currently better developed for phase 1 than it is for phases 2 and 3. There is substantial experience in using soil surface characteristics as indicators of soil stability, and new models of soil erosion on rangelands are being developed. The addition of currently used evaluations of soil surface characteristics, as described in this report, to all current and ongoing range condition (SCS), ecological status (USFS and BLM), and apparent trend (SCS) assessments would be
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Rangeland Health: New Methods to Classify, Inventory, and Monitor Rangelands a useful first step toward an assessment of rangeland health—a step that could be taken immediately. The scientific understanding needed to develop and interpret measurable indicators of changes in nutrient cycling, energy flow, and self induced recovery mechanisms is less well developed—an effort to develop and test such is urgently required. Finally, the difficulty in standardizing the boundaries between states of rangeland health must not impede efforts to expand the data collected during rangeland inventorying and monitoring. Standardizing rangeland health assessments will require systematically assembled data on measurable indicators. Collection of such data will allow tests of the utility of such measures in identifying healthy, at-risk, and unhealthy rangelands.
Representative terms from entire chapter: