Rangeland Health New Methods to Classify, Inventory, and Monitor Rangelands (1994) / Chapter Skim
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4 CRITERIA AND INDICATORS OF RANGELAND HEALTH
4 CRITERIA AND INDICATORS OF RANGELAND HEALTH
Pages 97-133
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From page 97... ...
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, spe cies composition, litter accumulation and distribution, seed germination and seedling recruitment, total biomass production, and other ecological functions. Tueller (1973)
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From page 98... ...
Phase 1 is an evaluation of soil stability and watershed function. Phase 2 is an evaluation of the functioning of nutrient cycles and energy flows.
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From page 99... ...
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 soil erosion, and a minimal requirement for satisfactory condition is normal soil stability" (Ellison, 1949:790~.
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From page 100... ...
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.
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From page 101... ...
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.
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From page 102... ...
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 function has direct effects on rangelands.
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From page 103... ...
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.
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From page 104... ...
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)
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From page 105... ...
The condition of this organically enriched Ahorizon 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.
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From page 108... ...
Multiple Indicators of Soil Surface Condition Needed The presence and distribution of the A-horizon, rills, and gullies; areas scoured by wind or water; and pedestals under rocks and plants are
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From page 109... ...
An evaluation of soil stability and watershed function, as determined by the use of measurable indicators of the condition of the soil surface, should become a fundamental component of all inventorying and monitoring programs for federal and nonfederal rangelands. An example of pedestal formation at an early stage.
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From page 110... ...
More data on soil properties related to soil stability and important ecological processes need to be included in soil surveys. Table 4-3 indicates possible soil characteristics that could be included in soil surveys related to plant growth.
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From page 111... ...
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From page 112... ...
Nutrient Cycling Nutrients follow cyclical patterns as they are used and reused by living organisms. Although the majority of available nutrients for plant growth is found in the soil (Brady, 1990)
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From page 113... ...
Nutrient cycling entails the extraction of nutrients from the soil by plant roots. Rangelands may support individual plants with root systems that occupy much of the soil profile or a mixture of different plants that have various root depths (Figure 4-3)
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From page 114... ...
a legume Poor fe~o~j; Ss, SfJer~fA~s s~f~Iosf~ Bd, buffalo grass (~chZoe J~c~lofJest Ap, western ragweed (~8ros~ psdosf~ch~; and Li, skeleton weed (L~oJes~~ C Source: A
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From page 115... ...
Interruption or slowing of nutrient cycling can lead to site degradation as a rangeland becomes increasingly deficient in the nutrients required by plants. An evaluation of the degree to which nutrients are conserved and the degree to which nutrient cycles operate should be important elements of a system of assessing rangeland health.
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From page 116... ...
Plant life-forms and species compositions determine the ability of the plant community to process sunlight energy under a variety of environmental conditions. Plant interactions with the physical environment also ~nfluence energy flow.
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From page 117... ...
An evaluation of nutrient cycles and energy flows, however, has not been part of traditional assessments of rangelands. Therefore, experience with useful criteria and indicators of nutrient cycles and energy flow on rangelands is much less than that with indicators of soil stability and watershed function.
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From page 118... ...
Data on species composition could be used to assess whether photosynthesis occurs during all or only a part of the growing season. Similarly, data on plant composition could be used to assess whether all or only a fraction of the available soil profile is occupied by plant roots.
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From page 119... ...
Department of the Interior (DOIJ should initiate a coordinated research effort, drawing onfederal agency and other scientists to develop, test, and implement indicators of the spatial and temporal distributions of nutrients and energy for use in rangeland health assessments. The lack of experience with and testing of specific indicators of nutrient cycling and energy flow is an important impediment to the development of a comprehensive system of determining whether rangelands are healthy, at risk, or unhealthy.
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From page 120... ...
JUDGMENT REQUIRED Until measurable indicators of nutrient cycling and energy flow are developed, evaluation of what constitutes a healthy, at-risk, or unhealthy distribution of plants, bare areas, rooting depths, and growth periods will depend primarily on informed judgments. The healthy end of the continuum consists of an unfragmented distribution of plants and litter with few bare areas, plants that fill the soil profile with roots, and plants that are capable of photosynthesis throughout the growing season.
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From page 121... ...
In assessing rangeland health, when judgments are used to place a higher value on one plant than another, emphasis should be placed on species that reduce soil erosion or fill nutrient cycling or energy flow niches. Such decisions must be made on a site-by-site basis.
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From page 122... ...
MICROSITES FOR SEED GERMINATION AND SEEDLING ESTABLISHMENT Finally, maintenance of biotic control over the abiotic environment (the nonliving part of the environment) through self-induced changes in plant community dynamics requires the presence of microsites (the area immediately surrounding a seed, which may be as small as a few millimeters in diameter)
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From page 123... ...
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.
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From page 124... ...
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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From page 125... ...
Distribution of Plant and litter Fragmented Fragmented nutrients and distribution distribution distribution energy unfragmented developing developed, with large barren areas between fragments Photosynthetic activity occurs throughout the period suitable for plant growth Rooting throughout the available soil profile Photosynthetic activity restricted Photosynthetic activity restricted during one or to one season more seasons only Roots absent from portions of the available soil profile Rooting in only one portion of the available soil profile 3. Recovery Diverse age-class Seedlings and young Decadent plants mechanisms distribution plants are missing predominate Plants are vigorous Plant vigor is Plant vigor is reduced poor Germination Developing crusts Soil movement or microsites are or soil movement crusting inhibit present and well degrade microsites most germination distributed
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From page 126... ...
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 composition and age-class distribution, microsites in which seeds can germinate are available, and seedlings are becoming established.
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From page 127... ...
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.
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From page 128... ...
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 researchers 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.
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From page 129... ...
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)
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From page 130... ...
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From page 132... ...
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)
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From page 133... ...
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.
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