our rangelands healthy?
to document "change on the range"
ways to evaluate the ecological well-being of rangeland
Did you know...
provide not only grazing for domestic animals, but also important habitat
for wildlife and opportunities for outdoor recreation?
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.
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
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"
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.
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.
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
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-
Defining the climax plant community for a site is
difficult at best and impossible on some sites.
The two-attribute approach--plant species composition and
production--is inadequate to address the complexity of rangeland
Ecosystem change may not follow the linear pathway
suggested by the traditional succession-retrogression model.
Succession or retrogression may not occur--or may occur
slowly--on some sites because of long-lived or otherwise dominant
The state and transition model--The state and
transition model is of most value in explaining rangeland ecosystem
when a system can evolve in several ways rather than
follow a single pathway;
when change occurs very rapidly;
when some changes are near-permanent; and
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
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:
Soil erosion and nutrient loss so severe that some plants
Invasion of a site by a plant that is so dominant that
other plants cannot compete.
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.
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 descriptions--The 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
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 health--The 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
define and adopt a minimum standard--independent of
current or intended use--of what constitutes acceptable range
develop consistent criteria and methods of data
interpretation to evaluate whether rangeland management meets this
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--
healthy "if an evaluation of the soil and ecological
processes indicates that the capacity to satisfy values and produce
commodities is being sustained";
at risk "if the assessment indicates an increased, but
reversible, vulnerability to degradation"; and
unhealthy "if the assessment indicates that degradation
has resulted in an irreversible loss of capacity to provide values and
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-perma- nent 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
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.
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 threshold--The
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:
Evaluate rangelands from the basis of the same land unit
classification, the ecological site.
Evaluate plant communities likely to occur on a site on
the basis of their ability to protect the site against accelerated
Select a desired plant community for an ecological site
considering both site conservation and management objectives for the
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.
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
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.
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
Finding the answers
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.
National Research Council. 1994. Rangeland Health: New Ways
to Classify, Inventory and Monitor Rangelands. National Academy Press.
Society for Range Management. 1995. New concepts
for assessment of rangeland condition. Journal of Range Management
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