Rangeland Health
RCA Issue Brief #10
August 1996
Are our rangelands healthy?
Methods to document "change on the range"
New ways to evaluate the ecological well-being of rangeland
Finding the answers
Literature cited
Did you know...
...that rangelands provide not only grazing for domestic animals, but also
important habitat for wildlife and opportunities for outdoor recreation?
...that rangelands trap and store carbon and thus reduce atmospheric greenhouse
gases, store water, and filter impurities from water? The vastness of American
rangelands--1 in every 4 acres of the United States--only serves to underscore
their importance.
Are our rangelands healthy?
That depends on whom you ask. Some argue that these lands are in better
condition today than at any time this century. Others, often using the same
data, claim that much of the Nation's rangeland is degraded and getting
worse. Many simply do not know but are concerned about both the health of
the land and the lack of definitive
information.
Most agree, however, that America--s rangelands deteriorated rapidly and
significantly during the latter part of the 19th century. Initial rangeland
condition assessments, based on visual observation, were descriptive in
nature. For example, in 1895--only a few decades after grazing began on
much of the Nation's rangeland--Jared G. Smith of the U.S. Department of
Agriculture wrote:
There has been much written during the past 10 years about the deterioration
of the ranges. Cattlemen say that grasses are not what they used to be;
that the valuable perennial species are disappearing, and that their place
is being taken by less nutritious annuals. This is true to a very marked
degree in many sections of the grazing country.
Methods to document "change on the range"
The succession-retrogression model
Observations such as Smith's
provided early ecologists and rangeland managers not only an assessment
of range condition, but also the foundation for the theories of succession
and retrogression. The succession theory holds, basically, that increasingly
developed soils and more complex mixes of plants replace less developed
soils and less complex mixes on the land. According to the theory, succession
ultimately results in a plant community in equilibrium with the environment,
particularly climate and soil. This is the "climax" plant community.
Disturbance of this plant community for any reason causes it to retrogress
to an earlier stage of development. Smith's description of turn-of-the-century
rangeland is a story of retrogression.
The ecological theories of succession and retrogression were developed into
a method of rangeland condition assessment in the 1940's. This method required
rangelands to be classified into range sites--areas of land capable of producing
a different kind or amount, or both, of climax vegetation. Range site descriptions
included information about soils, climate, topography, and other landscape
characteristics of the site, and a description of the climax plant community.
Using the succession-retrogression method, rangeland can be described as
being in "excellent," "good," "fair," or "poor"
condition, depending on how closely the current composition and production
of the vegetation on a site resemble the climax vegetation defined for the
site. This method of determining rangeland condition was first used in the
1940's to help ranchers determine the value of their land for livestock
grazing. This model worked well in the grassland region of the United States
where climax vegetation was mostly made up of highly productive and nutritious
grasses and forbs that also protected the soil from erosion. In this region,
rangeland classified in excellent condition, using this ecological theory,
also correlates to those lands that were most productive for livestock use,
especially cattle. Likewise, poor-condition rangeland, as described above
by Smith, was degraded for both ecological and livestock production reasons.
In the 1960s, range conservationists and scientists further developed this
classification system to include ecological condition and values. Where
the succession-retrogression model works, it is a powerful tool to explain
and predict how rangelands change with use and management.
Unfortunately, the succession-retrogression method of evaluating rangeland
condition has not worked so well to describe both ecological condition and
value for livestock grazing in other parts of the United States. The Society
for Range Management concluded in 1995 that "current range condition
assessments do not provide answers to the questions that Congress and the
public want answered about the status of our rangelands." Why are range
scientists re-examining the succession- retrogression method?
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Defining the climax plant community for a site is difficult at best
and impossible on some sites.
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The two-attribute approach--plant species composition and production--is
inadequate to address the complexity of rangeland ecosystems.
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Ecosystem change may not follow the linear pathway suggested by the
traditional succession-retrogression model.
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Succession or retrogression may not occur--or may occur slowly--on
some sites because of long-lived or otherwise dominant plants.
The state and transition model
The state and transition model is
of most value in explaining rangeland ecosystem change--
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when a system can evolve in several ways rather than follow a single
pathway;
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when change occurs very rapidly;
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when some changes are near-permanent; and
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when detailed explanation of the transitions that cause change is
required.
The vegetation types are called "states," and the processes that
cause states to change from one to another are called "transitions."
Where states are resistant to change, they are called "steady states."
An example of a steady state is where long-lived or otherwise dominant plants
occur on a site. These steady-state plant communities change only as a result
of such transitions as long periods of above-average moisture or drought,
fire, an insect or disease outbreak, or human action. The site factors that
impose this high level of stability on a site are called "thresholds."
Examples of thresholds include:
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Soil erosion and nutrient loss so severe that some plants cannot grow.
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Invasion of a site by a plant that is so dominant that other plants
cannot compete.
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Change in the water cycle, such as more rapid runoff because of a
lower rate of water soaking into the soil, to the point that plant growth
is restricted during part of the growing season.
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Change in plant community structure--arrangement of plants on the
site--so that fire, a naturally occurring event that directs ecosystem change,
cannot occur or occurs in a more destructive way.
Ecological site descriptionsThe state and transition model provides
extensive knowledge of existing and possible states, transitions, thresholds
or other barriers to change, opportunities for management intervention,
and what changes can occur through mismanagement. All of this information
can and should be captured in the ecological site description.
As a result of new knowledge developed in the United States and other countries,
important changes have been made in the range site concept, including changing
the name from "range site" to "ecological site." This
is more than a semantic change. Ecological site descriptions include the
known plant community types that may occur on a site as well as the single
climax plant community. Ecological site descriptions should relate degree
of soil development, hydrologic and ecosystem functions, and other ecological
knowledge to the known plant communities. The ecological site description
also outlines the processes of change that may occur on a site as well as
showing change as a deviation from the climax or natural plant community.
Because of the more thorough evaluation of ecological factors at work on
an area of rangeland, the ecological site description provides information
needed for management of rangelands for many uses and values.
New ways to evaluate the ecological well-being
of rangeland
Both the succession-retrogression and state and transition models help explain
how rangeland ecosystems change, but change and ecological well-being are
not always the same thing. Two new concepts--rangeland health and site conservation
threshold--attempt to fill in the gaps.
Rangeland healthThe rangeland health model was developed by the
National Research Council (NRC) Committee on Rangeland Classification, which
was established to evaluate the methods used by Federal agencies to classify,
inventory, and monitor rangelands. The NRC recommended that the U.S. Departments
of Agriculture and the Interior jointly--
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define and adopt a minimum standard--independent of current or intended
use--of what constitutes acceptable range conditions;
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develop consistent criteria and methods of data interpretation to
evaluate whether rangeland management meets this standard; and
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implement a coordinated and statistically valid national inventory
to periodically evaluate the health of the Nation's rangeland.
In the NRC's 1994 report "Rangeland Health: New Ways to Classify, Inventory,
and Monitor Rangelands," the Committee defined rangeland health as
"the degree to which the integrity of the soil and ecological processes
are sustained." It recommended further that the "minimum standard
for rangeland management should be to prevent human-induced loss of rangeland
health." The Committee recommended that rangelands be considered--
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healthy "if an evaluation of the soil and ecological processes
indicates that the capacity to satisfy values and produce commodities is
being sustained";
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at risk "if the assessment indicates an increased, but reversible,
vulnerability to degradation"; and
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unhealthy "if the assessment indicates that degradation has resulted
in an irreversible loss of capacity to provide values and commodities."
Healthy rangeland can be described as land where erosion is not occurring
at an accelerated rate, where most precipitation infiltrates into the soil
and is used onsite for plant growth or flows as ground water to stream systems.
The plant community effectively and productively takes advantage of the
nutrients and energy that occur on the site. While plant species composition
is dynamic, there is a tendency on healthy rangelands for soils, the plant
community, and ecological functions to maintain or recover health following
release from natural (drought, insect outbreak, wildfire) or human-caused
stress.
What causes loss of rangeland health? The most common reasons are overgrazing
by domestic and wild animals, and change in the historical pattern of fire.
Overgrazing reduces the productivity and competitiveness of plants desired
by the grazing animals. Overgrazing can reduce plant cover and expose bare
soil to erosion. A shift in the competitive balance between plants may result
in a near-permanent change in plant species composition from plants desired
by grazing animals to plants that are seldom grazed. Woody shrubs and low-growing
trees often increase with overgrazing and lack of fire. Accelerated soil
erosion and near-permanent changes in plant species composition represent
a change in the values and commodities that can be obtained from an area
of rangeland, and, by definition, a loss of rangeland health.
Loss of rangeland health, initiated by overgrazing, may continue even if
grazing management is improved unless some compensating event occurs. Fire,
which tends to kill the shrubs and trees that compete with grasses and forbs,
is such an event. Fortunately, rangelands can be maintained in a healthy
state with grazing, and properly managed grazing can sustain or enhance
rangeland health. Likewise, fire can be used to direct ecosystems toward
healthy states.
Rangeland health was recommended by the NRC as a minimum ecological standard.
Where rangeland health is preserved, a variety of management options and
uses may be appropriate.
Site conservation thresholdThe Society for Range Management (SRM)
Task Group on Unity in Concepts and Terms was formed in 1989 to "continue
to seek agency commonality and unity in technology and methodology relating
to rangeland condition and trend." In its 1995 report, the Task Group
recommended three strategies to improve rangeland condition assessments:
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Evaluate rangelands from the basis of the same land unit classification,
the ecological site.
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Evaluate plant communities likely to occur on a site on the basis
of their ability to protect the site against accelerated erosion.
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Select a desired plant community for an ecological site considering
both site conservation and management objectives for the site.
To assess the sustainability of rangeland management, SRM has recommended
the site conservation threshold concept: "The kind, amount, and/or
pattern of vegetation needed as a minimum on a given site to prevent accelerated
erosion." According to SRM, the threshold is the point where the erosion
rate increases significantly. Vegetation that provides, at a minimum, the
protection necessary to prevent accelerated erosion is considered by SRM
to be above the threshold and would be rated satisfactory or sustainable.
Vegetation that does not provide adequate protection would be rated unsatisfactory
or unsustainable.
The figure below combines the concepts developed by NRC and SRM. The "early
warning line" was proposed by the NRC as the point where negative changes
in ecosystem characteristics are first noticed--changes that may indicate
ecosystem degradation and a threat to long-term productivity of the site.
The "threshold of rangeland health" represents the point where
degradation is so severe that improvement will be possible only through
application of improvement practices such as chemical or mechanical control
of weeds or brush and seeding of desired species. The site conservation
threshold concept proposed by SRM represents the mid-point between the early
warning line and the threshold of rangeland health.
Arrows represent transitions between different ecological states or
conditions, which are represented as circles (A-E). Solid arrows represent
changes that are difficult to achieve. A shift from 'A' to 'B' indicates
that some deterioration has occurred; recovery is possible through good
management. A continuing shift to 'C' represents a loss of rangeland health;
recovery to healthy 'D' or at-risk 'B' condition is difficult but possible
if rangeland improvement practices such as brush or weed control and range
seeding are applied. 'E' represents rangeland that has continued to deteriorate;
soil erosion and other ecosystem changes associated with 'E' make recovery
to a more healthy condition difficult.
Source: National Research Council Committee on Rangeland Classification,
1994. The site conservation threshold is from the Society for Range Management,
1995.
Developing indicators to help rangeland managers identify states in the
zone between the early warning line and the site conservation threshold
may be the most important rangeland research work to be done. These are
the states that retain considerable capacity to respond to management of
ecological processes--control of grazing or prescribed burning. The zone
between the site conservation threshold and the threshold of rangeland health
would seem to represent situations where ecosystem functions are changing
in ways or rates that threaten sustained capacity to produce commodities
and satisfy values.
The rangeland health and site conservation threshold concepts represent
ways to evaluate the ecological condition of rangeland. Both require that
indicators representing "good" and "bad" characteristics
of ecosystem condition and trend be established and that the current status
of the ecosystem be judged against these indicators. Both concepts emphasize
that multiple indicators are needed to evaluate the health or sustainability
of the land.
Finding the answers
Are our rangelands healthy? Is our management accomplishing what we want?
To answer these questions about ecological quality of the Nation's rangelands,
a set of indicators that address key questions must be developed and used
in a statistical inventory. Indicators of range health must be scientifically
sound, yet understandable by the public and relevant to the public's interests
in rangelands. The Natural Resources Conservation Service (NRCS) Grazing
Land Technology Institute, working with scientists in other organizations,
is developing such indicators. The NRCS National Resources Inventory (NRI)
is the most likely vehicle for obtaining this information. Planning for
the rangeland health components of the 1997 NRI is underway.
Literature Cited
National Research Council. 1994. Rangeland Health: New Ways to Classify,
Inventory and Monitor Rangelands. National Academy Press. Washington, DC.
Society for Range Management. 1995. New concepts for assessment of rangeland
condition. Journal of Range Management 48:271-283.
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