Rangeland Health New Methods to Classify, Inventory, and Monitor Rangelands (1994) / Chapter Skim
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2 RANGELAND HEALTH
2 RANGELAND HEALTH
Pages 29-50
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From page 29... ...
The capacity of rangelands to satisfy the values of and produce commodities for these diverse groups depends on the integrity of the soil and ecological processes of rangelands. National assessments should provide accurate and accessible information about the status of rangeland ecosystems to all individuals and groups who have an interest in the values and commodities that rangelands provide.
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From page 30... ...
Rangelands, for the most part, do not receive such inputs. The capacity of rangelands to produce commodities and satisfy values depends on the integrity of nutrient cycles, energy flows, plant community dynamics, an intact soil profile, and stores of nutrients and water.
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From page 31... ...
At the same time that public debate over the use of the nation's rangelands has grown, a scientific debate over the use of current range condition (SCS) and ecological status (USES and BLM)
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From page 32... ...
At this site, heavy grazing and moderate drought combine to reduce grass cover, compact the soil, increase erosion and runoff, and create a patchy distribution of water and nutrients that leads to an increased density of mesquite and creosote bushes. Once the shift is made to a patchy distribution of mesquite and creosote bushes, the ecosystem does not revert to the original black grama grassland without human intervention.
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From page 33... ...
The black grama grassland has crossed a threshold to a desert shrubland. Even with human intervention, it may not be possible for the land to return to a black grama grassland, since soil nutrients and moisture essential to the grasses are limited to isolated pockets in which shrubs are firmly established.
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From page 34... ...
The capacity of rangelands to produce commodities and satisfy societal values depends on the interactions of climate, plants, and animals in a given physical landscape over time. These interactions are mediated by the soil and by internal ecological processes such as nutrient cycles, energy flows, and plant community dynamics.
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From page 35... ...
These decisions will be contentious, but they can at least be made in the context of conserving the health, and therefore the capacity, of rangelands to produce commodities and satisfy values, regardless of their use. Categories for Rangeland Assessments Rangeland ecosystems are dynamic systems, and fitting rangelands into categories based on ecological criteria is a difficult but essential task for national assessments of rangelands.
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From page 36... ...
healthy if an evaluation of the soil and ecological processes indicates that the capacity to satisfy values and produce commodities is being sustained, (2) at risk if the assessment indicates an increased vulnerability to degradation, and (3)
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From page 37... ...
Even with restoration, however, some loss of capacity to produce commodities and satisfy values may be permanent. The boundaries between healthy, at-risk, and unhealthy states of a rangeland should be distinguished based on changes in the soil and ecological processes that determine (1)
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From page 38... ...
Changes in grazing management can result in rapid positive changes in the composition of plant communities and the amount of annual biomass that is produced if the changes in use and management are accompanied by a series of years with above-average precipitation. Changes in the vegetation will occur more slowly or may not occur at all under climatic conditions that are not favorable for seedling establishment and growth.
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From page 39... ...
These changes in plant composition were considered normal adjustments as a result of grazing. Ellison considered destructive change to be beyond the limits of normal change and to be induced by accelerated erosion, which was evidence of a basic change in the relationship between components of the rangeland ecosystem a change of drastic proportions over and above the normal range of environmental stresses.
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From page 40... ...
Light grazing decreases the cover of palatable perennial grasses, including Themeda triandra and Eragrostis racemosa, and increases the cover of unpalatable perennial or annual grasses, such as Cymbopogon excavatus. These changes signal that the rangeland is at risk of shifting across a threshold to a different combination of spe Shown are a spikelet and a tuft of Themeda triandra.
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From page 41... ...
Simply reducing grazing pressure, once the threshold is crossed, is no longer sufficient to regain the initial state. Management techniques such as soil reclamation and reseeding with perennial grasses would be required, but they may not necessarily lead to a recovery to the initial state.
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From page 42... ...
First, as the use of the term "threshold" suggests, the shift from one ecological state to another across the boundary is not easily reversed. Second, as the use of the term "health" suggests, changes in the soil or ecological processes result in a change in the capacity of the rangeland to satisfy values or produce commodities.
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From page 43... ...
Identification of at-risk rangelands would enable range managers to take-appropriate action before the health of the rangeland and the capacity of the rangeland to produce commodities and satisfy values is impaired. The transition from a healthy rangeland (state A)
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From page 44... ...
trees and the shrubs that surround them. Mesquite is becoming common and more dominant in ecosystems throughout the southwestern United States, although historically it was a minor component of rangeland ecosystems.
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From page 45... ...
Grazing contributes to this trend as cattle eat mesquite seeds, depositing them in dung, a nutrient-rich environment ideally suited to germination. The rangeland crosses a threshold, becoming a subtropical thorny woodland.
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From page 46... ...
A short-lived drought or temporary heavy grazing, for example, may result in a reduction in biomass production. Increased amounts of rainfall or improved grazing management may produce a shift to a different plant community within a complex that produces a different mix of commodities and values.
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From page 47... ...
Even with such corrective action there may be permanent loss of capacity to produce commodities and satisfy values, at least within practical time frames and costs. Future options to use and manage the site may be lost as well.
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From page 48... ...
Rangeland health is a measure of whether the capacity of rangelands to produce commodities and satisfy values is being conserved. An assessment of rangeland health is not intended to quantify the suitability of particular rangelands for particular purposes.
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From page 49... ...
Differences between the capacities of different rangelands to produce commodities and satisfy values do not necessarily imply differences in health as defined here. Rangeland health estimates the risk of the loss of the capacity to produce commodities and satisfy values by evaluating the integrity of the site's ecological processes and soils.
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From page 50... ...
This unhealthy state, however, has not been induced by humans, and even the best management of these landscapes may not be sufficient to achieve healthy conditions. The primary concern of range management should be preventing loss of health on rangelands where human use and management can improve or degrade rangeland health.
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