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Past Changes, Present and Future Impacts,
and the Assessment of Community or
Ecosystem Condition
Robin J. Tausch
and others 1993a,b). Third is the accumulating information
on the potential impacts from the past, present, and future
human activities altering ecosystem dynamics (Denevan
1992' Tausch and others 1993b). Last is a general failure to
keep'the concepts of health or condition separate from the
ecological data and theories used or applied in making those
assessments (Scarnecchia 1995).
Abstract-Health, condition, and trend are widely used terms in
ecosystem management, but their use is highly variable. Their
application has been incompatible with the kinds of ecosystem
changes that have occurred during the Quaternary and with our
evolving understanding of ecosystem dynamics and present and
future impacts from human activities. To manage for sustainability
into the future, our concepts, definitions, and selection of standards
should be appropriate for what we know about the influence of past,
present, and future impacts. To avoid circularity in concepts and
assessments of health, they should be based on values that are
distinct from the sampled indicators and attributes applied in
making the assessments. Definitions and concepts are needed that
allow for the selection of standards of health and condition that are
more appropriate for the nonlinear trajectories of ecosystem change
and human alterations of those trajectories into the future.
Ecosystem Changes During the
Quaternary _ _ _ _ _ _ _ _ __
In much of our study and management of ecosystems we
have demonstrated a limited understanding of how ecosystems function and change over the long term, in part because
these efforts have usually occurred in a fragmented fashion
over the short term. As paleoecological information accumulates on long-term ecosystem dynamics, it is apparent that
a major part of why ecosystems behave as they do is rooted
in their history ofchange through the Quaternary (Betancourt
and others 1993; Tausch and others 1993b).
During the Pliocene, climate was generally more stable
than during the Pleistocene where there have been an
estimated 17 to 20 cycles of glacial advance and retreat with
associated environmental changes (Winograd and others
1992). Interglacial climates, such as those of the present,
only represented about 10 to 15 percent of the Quaternary
period (fig. 1 in Tausch and others 1993b). Species present
today are those that have managed to survive from the
Pliocene, through the pounding ofthe repeated glacial cycles
of the Pleistocene, followed by the human impacts of the
Holocene.
Associated with these climatic cycles have been dramatic
changes in species distributions and community dominance
patterns (Betancourt and others 1993) as each species responded individualistically to the environmental changes
(Foster and others 1990). The result has been a continual
shifting in the species composition and competitive interactions of communities (Foster and others 1990; Nowak and
others 1994a,b) that continues today. Communities have not
responded as single units.
Several conclusions could be summarized from the results
of paleoecological studies. Communities and ecosystems are
unique at each location and transient over time. They are
both dynamic and pluralistic because they function as a
mosaic of successional stages and functional processes scattered across the landscape. Communities potentially have
thresholds in the patterns of their successional trends and
can change rapidly in response to environmental changes if
those thresholds are crossed (Laycock 1991). Changes that
result from crossing a threshold can be persistent for long
References to ecosystem health, including range condition
and trend, are widely applied. to plant communities and
whole ecosystems. Despite their importance, the interpretation or understanding of terms such as good or poor health
vary greatly (National Research Council 1994; Scarnecchia
1995; West and others 1994; Unity in Concepts and Technology Task Group 1995a,b), are the subject of debate (Joyce
1993), and often do not supply answers to management
questions (Unity in Concepts and Technology Task Group
1995a,b). Ecosystem health is determined by reference to a
standard (West and others 1994). This standard varies, but
it is based on judgement of what represents healthy or
unhealthy condition from community composition. Clements
(1916, 1936) was the first to apply an ecological standard
based on plant succession. His monoclimax model, operating
within a climate assumed to be fluctuating around an
average, has largely dominated subsequent management
applications.
This paradigm has created problems for the interpretation and understanding of the present and future states of
the structure, function, and resilience of ecosystems. First,
since the late 1950's, communities have been known to
potentially have multiple endpoints (Olsen 1958). Second,
the accumulating information from the past shows that
climate has continually changed during the last 2 million
years ofthe Quaternary (Betancourt and others 1993; Tausch
In: Barrow, Jerry R.; McArthur, E. Durant; Sosebee, Ronald E.; Tausch,
Robin J., comps. 1996. Proceedings: shrubland ecosystem dynamics in a
changing environment; 1995 May 23-25; Las Cruces, NM. Gen. Tech. R:ep.
INT-GTR-338. Ogden, UT: U.S. Department of Agriculture, Forest SeTVlce,
Intermountain Research Station.
Robin J. Tausch is Project Leader, U.S. Department of Agriculture, Forest
Service, Intermountain Research Station, Reno, NY 89512.
97
periods (Tausch and others 1995). This landscape mosaic of
dynamic processes and successional change are central to
both understanding and managing ecosystems to maintain
their resiliency (Arrow and others 1995). An existing community may be as much or more the result of the conditions
of its formation as it is of the environmental conditions under
which it currently exists.
Clearly, the better we understand how communities came
to be through their history of development during the Quaternary, the better we will understand the nature of current
changes, including their scale and the driving forces behind
them. Management actions based on this understanding
will be more appropriate for maintaining healthy ecosystems.
are benchmark data that are from, as most are, a single
location and point in time (West and others 1994). How
benchmark communities can conflict with the assumptions
used in their application for condition determination can be
described by drawing on examples from history.
Example I-The benchmark site and the target site were
originally the same community at some arbitrary time in the
past, but the benchmark site is no longer relictual nor
representative of the target site because both have changed
over time. The changes have proceeded in different directions because the two sites have experienced different environmental changes and disturbances. The benchmark currently represents a community we think existed on the
target site in the past, or was possibly chosen because
someone's preference was for such a community to have
existed.
Paleoecological Implications for
Ecosystem Health _ _ _ _ _ __
Example 2-The benchmark site is actually a relic,
representing the potential for some other sites, but is not and
never has been representative of the potential for the target
site. There are many reasons why this can happen. An
improper identification of the potential community type
could occur because of error in identifying the history and
ecology of either the target site or the benchmark site. An
inappropriate selection of a benchmark site could occur
because of the desire to have one despite their scarcity or
absence.
Results from paleoecological research can provide guidance for the determination of ecosystem health and range
condition. Range condition in this case is a specific application of the concept of ecosystem health. When determining
the condition of a target community or site for management,
it is necessary to compare the area to a reference or standard
(West and others 1994). That standard is a benchmark that
represents the climax or some preferred community composition (Unity Task Group 1995a,b). A benchmark represents
an external standard for health assessment (West and
others 1994).
Two alternatives exist for selecting a benchmark for this
comparison. The first, and most preferred alternative is to
have an actual benchmark community that represents the
ecologic potential for the target community. With proper
management the successional direction taken by the target
community should result in its changing to increasingly
resemble the benchmark community.
Suitable benchmark communities are relatively rare because of climate changes and the extensiveness of past
human impacts on most ecosystems (Denevan 1992, Tausch
and others 1993a,b). Thus, the second method is to come up
with an estimation of what the benchmark community
would look like and what its species composition would be,
and to do so by some means such as a defacto expert system
(West and others 1994).
Paleoecological information reveals several potential problems with the methods used for selecting a benchmark
community, be it actual or estimated. The assumption is
that the benchmark community is a valid standard or
reference that is still representative of the potential for the
target community, and that it represents the community
composition needed to meet the management goals for the
site. Because benchmarks are scarce, extra effort is often
expended to find something that is representative. Once
benchmarks are selected, attempts are usually not made to
determine either accuracy or precision of their species composition and abundance, but are treated as if they are known
without error.
All communities, however, continually change, but more
recently the directions of change have often been altered by
humans (Denevan 1992, Tausch and others 1993b). Thus,
many potential problems exist for the representativeness of
the selected benchmarks. A particularly relevant example
Example 3-The benchmark site is a valid relic and was
once representative of the subject site, but disturbance,
introduced species, or other environmental factors have
pushed the target site across one or more thresholds to
where the benchmark site is neither representative nor
attainable (Unity Task Force 1995a,b). The sustainable
potential communities possible for the target site have
changed, and current examples may not exist.
Example 4-The benchmark site is a valid relic that is
still representative of some past composition of the target
site. However, the benchmark community provides either
inadequate productivity or inadequately protects important
resources for current human needs (Unity Task Force
1995a,b). Other communities within the environmental constraints of the target site would perhaps be better able to
supply the resource demands on a sustainable basis.
Example 5-The benchmark site is a relic that is representative of what existed on the target site at some arbitrary
past time. However, the climate and other environmental
conditions under which the benchmark community developed no longer exist. This could include past processes and
stages of its development that are no longer possible, and
past interactions with species that are no longer present.
The benchmark site is now a relic that has persisted by
vegetation inertia such as persistence of long-lived perennial community dominants (fig. 4 in Tausch and others
1993b). As such it is on the edge of a threshold and easily
changed by even minor disturbance. Converting the target
site to the same community as the benchmark site would
take considerable effort, and the site would be difficult to
maintain due to inherent instability. The possible communities for the target site that are sustainable are new for the
location and probably did not exist in the past.
98
Example 6-When there is no actual benchmark site,
and the composition of one must be estimated, one or more
ofthe preceding five examples may still apply. An additional
possible problem is that the estimated benchmark community is not real, even though it was based on experience or
historical information. It possibly has never existed or at
least is not a possibility for any of the target sites to which
it has been applied.
The above complications may not always occur, but they
and related problems are common enough to contribute to
the current inappropriate use, confusion, and concern in the
assessment of health described by the Unity Task Force
(1995a,b) and the National Research Council (1994). Some
selections of a benchmark for condition determination have
been successful for management, but often because ofluck.
When a benchmark is used and any of the complications
described in the examples above occur, then the goals set for
the target site are in error in some way. All estimates of
health or condition based on comparison with the benchmark site will usually be negatively affected. The greater the
error in the selection of a benchmark, the more negative the
affects on any estimate of health, condition, or trend are
likely to be. Also, decades of experience (Unity Task Force
1995a,b) have shown that selection of pristine or climax
vegetation usually used for benchmarks is not a necessity
nor even particularly useful for assessing health or setting
management goals.
Benchmark communities selected for determining target
site health may have several problems. One has been the
lack of any established procedures at any point in the process
for judging the appropriateness of a benchmark community
or for determining its suitability for meeting management
needs. Lack of objective guidelines can lead to selections
based on appeal of some pristine condition or, a reliance on
some past magical time of supposed ecosystem perfection or
when things were still "natural"-communities that may
have never existed (Denevan 1992; Tausch and others 1993b).
Another problem arises when a static benchmark community is selected for health assessment and for management
direction. A static community represents a defacto selection
of, or a gamble on, the particular future environmental
scenario favorable to the selected benchmark. But based on
the accumulating climatic information we have for the past
2 million years, the least probable future event is for the
climate to remain the same. Therefore, any benchmark
picked is likely to be incorrect except over the relatively
short term because we have limited ability to predict climate
and environmental changes into the future.
changes vary in time and space as a mosaic of dynamic
processes of competition and community change scattered
across the landscape.
Trajectories of community change from pre-history are
increasingly being modified by impacts from human activities, resulting in new demands and problems (Golley and
others 1994). The changes are often unnoticed until major
differences have accumulated because the changes are occurring on spatial scales that encompass entire landscapes,
and are occurring on times scales where cause and effect can
be separated by one or more generations (Lee 1993).
Management decisions can only involve either maintaining or changing the many community trajectories in response to the new demands and problems. Better knowledge
of the past, present, and likely future of these trajectories
needs to be part of how we assess ecosystem health and how
we make management decisions. Our current knowledge,
however, is woefully inadequate. In many ways, we do not
know how the world works, what the problems are, how
serious they are, or how to cure them (Woo dwell 1994). The
result is a critical need for new information from monitoring
and the continuing development of new methods (Golley and
others 1994). This requires a broader, more forward-looking
focus than the concentration on a single benchmark as a
standard for both the assessment of health and the selection
of management actions.
An attempt to develop better guidelines for assessing
range health was recently published by the National Research Council (1994). This attempt was both confusing and
clarifying, leading Scarnecchia (1995) to refer to the Council's
proposal as "a change in terminology without a change in
conceptuality-a confounding step sideways out of the line
of fire." An example of the confounding was the concept of
thresholds in community composition as an integral part of
determining range condition. By the Council's definition, a
community near a threshold is a community at risk, but a
community must have crossed a threshold to be in poor
condition.
Increasing evidence shows that there are often thresholds
of change in communities (Laycock 1991). But the Council's
definition incorporating a threshold as a requirement for an
assessment of poor condition implies that all communities
have only one threshold, or maybe only one important
threshold. If any communities do not have a threshold, does
that mean they cannot ever be in poor condition? For situations where more than one threshold may occur, the Council
provides no way for determining which one should be used in
the identification of poor condition. Another implication is
that the threshold in the species composition of each community is located at just that point in a sere that identifies the
critical point for management.
A common characteristic of thresholds is that changes in
community composition are permanent, at least for management implications into the foreseeable future (Laycock 1991;
Tausch and others 1993b; Tausch and others 1995; Unity
Task Group 1995a,b). The result of a community crossing a
threshold is the change to ~ new species composition that is
functionally a new community. Resource needs and management goals can also dictate that many communities should
be interpreted as in "poor" condition well before they are
even at risk of crossing a threshold, else mitigation becomes
unlikely, if not impossible.
Paradigms Needed for the
Future
--------------------------------------
Procedures used for determining ecosystem health that
involve any sort of standard, including benchmarks, are
inadequate now and, unless changed will be inadequate for
the future. One needed change concerns use of benchmarks
of preferred community composition for health assessment.
Paleoecological evidence clearly shows that plant communities are trajectories of change from the past, through the
present, and into the future. The patterns and rates of these
99
The latest report from the Unity Task Group (1995b) also
provides recommendations for new guidelines that are based
first on the concept of an ecological site. The focus on a
benchmark is a little less stringent. Proper identification of
the ecological type allows for extrapolation of research and
management experience to other areas ofthe landscape with
the same ecological type. The Unity Task Group (1995a,b)
also adds to the definitions for a Site Conservation Threshold and a Site Conservation Rating specific to the ecological
site. These allow for identifying community status and
change on ecological sites critical to management that are
independent of thresholds.
The Task Group format also calls for the identification of
different community types for a particular ecological site,
but only those currently known to occur. They recommend
that one be selected from those identified to be the Desired
Potential Community, which is described in more general
terms than the benchmark has been in the past, but vegetation status is still determined in terms of similarity to, and
trend as movement toward or away from, the Desired Potential Community (Unity Task Group 1995a,b).
Remaining problems with the Task Group's definition of
the Desired Potential Community are related to those of a
benchmark in general. First, its selection involves significant proportion of value judgments, such as the selection of
a Desired Potential Community that is based on an assumption that climate and environmental conditions favorable to
it will be present in the future. The Task Group's definition
assumes that the communities identified as currently representative of the ecological site cover all the possibilities.
However, some or all of these communities could be relics of
past conditions and not possible in the future.
These guidelines also assume that we know enough about
the important ecological attributes and indicators of the
ecological site to recognize it over all the communities
currently occurring. For most sites such information is
probably not available because, first, the level of change is
ongoing, and second, no communities have ever been adequately identified and mapped (Estes and Mooneyhan
1994). Finally, the Task Group guidelines ignore the possibility that many, or even most, ofthe possible future communities may not yet exist (for example, they will only occur as
conditions change in the future).
The procedures built into assessments are currently inappropriate, which confounds the process, (Scarnecchia 1995).
Basically, our failure has been to not keep the value-based
concepts of health, condition, or ecological status (EMAP
from West and others 1994) separated from both ecological
theory and ecological data. Scarnecchia (1995) points out
that to accomplish this separation it is necessary "that the
concept [of health] per se be devoid and independent of any
ecological theory, including theories involving succession,
climax, stable states, and thresholds" (emphasis from
Scarnecchia 1995). He additionally stresses that a concept of
ecosystem health or condition "must be designed to apply,
but not consist of, regionally applicable, partially validated,
ever evolving ecological theories" (Scarnecchia 1995). There
are no directly measurable indicators of ecosystem health,
only measurable changes over time in indicators and attributes of ecosystems. These changes must be interpreted
using values that include cultural factors (Unity Task Group
1995a,b), to develop an appropriate assessment of health.
The assessment of ecosystem health thus involves three
important, functionally discrete modules: (1) the social values upon which the associated concepts of ecosystem health
or condition are based; (2) the ecological theories available
for the ecosystem; and (3) the ecological data on attributes
and indicators available for the ecosystem. When we fail to
keep these three functionally discrete parts separate, we end
up with the confounded and confused process described by
Scarnecchia (1995). Inventory, monitoring, selection of the
Site Conservation Threshold, determination of the Site
Conservation Rating, and the assessment of condition for all
possible communities are critical to the process of health
determination. However, they need to be based as much as
possible on attributes and indicators that are as independent as possible from a particular plant community and from
values of health.
The procedures for determining a benchmark community
as a standard for health assessment can be used to provide
examples of how confounding can occur. Whether some onthe-ground benchmark is present or absent, the process
comprises values as much as it comprises ecological theory
or ecological data. Essentially, whenever there is a gap in
either ecological data or theory, values tend to fill in the gap,
confounding the process. Their identification as values is
then usually lost. Even estimated benchmarks, however, are
often treated as if they represent actual ecological data.
The Unity Task Group (1995a) report indicates a need for
the development of a statistically valid inventory and condition assessment of rangelands. Statistical procedures for
inventories of attributes and indicators (typical offield data)
are established and widely used. Changes in those attributes and indicators over time can also be analyzed by
conventional statistics. However, a statistically valid summary for the assessment of condition or ecological status,
with its necessity for a high proportion of incorporated
values and opinions, requires different assumptions and
statistical techniques.
Assessing of an ecosystem's health should focus on the
current trajectory of change. This requires baseline data and
the application of adaptive management through the monitoring of future changes (West and others 1994) of not only
all known communities for an ecological site, but for unrealized ones as they occur. Expanding on a description by Lee
(1993), ecosystem health, range condition, and ecosystem
sustainability are not fixed endpoints as a benchmark community is often interpreted, but directions (values) for guiding constructive change.
Again paraphrasing Lee (1993), these ideas (values) are
worthwhile because they set a standard for responsible
management. When the concepts of health are used appropriately, the focus will be on managing the ongoing trajectories of change in ecosystems and not on achieving a particular benchmark. The standard of comparison will be more
functional than compositional.
Assessments need to be accomplished in the three parts
described by Scarnecchia (1995). First are the field collection
and statistical analysis of the ecological data on the ecosystem. Second is the application of available ecological theory
for interpretation of analysis results. This is needed to
improve our ecological understanding of what the states and
changes measured mean for anticipating possible affects
that future changes or trends will have on the structure,
100
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Golley, F., Baudry, J., Berry, R. J., Bornkamm, R., Dahlberg, K,
Mansson, A M., King, J., Lee, J., Lenz, R., Sharitz, R., and
Sevdin, U. 1994. What is the road to sustainability? Renewable
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Joyce, L. A 1993. The life cycle of the range condition concept.
Journal of Range Management 46: 132-138.
Laycock, W. A 1991. Stable states and thresholds of range condition
on North American rangelands: A viewpoint. Journal of Range
Management 44: 427-433.
Lee, K N. 1993. Greed, scale mismatch, and learning. Ecological
Applications 3: 560-564.
National Research Council. 1994. Rangeland health. National Acad emy Press. Washington DC.
Nowak, C. L., Nowak, R. S., Tausch, R. J., and Wigand, P. E. 1994a.
A 30,000 year record of vegetation dynamics at a semi-arid locale
in the Great Basin. Journal of Vegetation Science 5: 579-590.
Nowak, C. L., Nowak, R. S., Tausch, R. J., and Wigand, P. E. 1994b.
Tree and shrub dynamics in northwestern Great Basin woodland
and shrub steppe during the Late-Pleistocene and Holocene.
American Journal of Botany 81: 265-277.
Olsen, J. S.1958. Rates of succession and soil changes on southern
Lake Michigan sand dunes. Bot. Gaz. 119: 125-170.
Scarnecchia, D. L. 1995. Viewpoint: The rangeland condition concept and range science's search for identity: a systems viewpoint.
Journal of Range Management 48: 181-186.
Tausch, R. J., Burkhardt, J. W., Nowak, C. L., and Wigand, P. E.
1993a. Viewpoint: lessons from the past for managing tomorrow's
range ecosystems. Rangelands 15: 196-199.
Tausch, R. J., Chambers, J. C., Blank, R. R., and Nowak, R. S. 1995.
Differential establishment of perennial grass and cheatgrass
following fire on an ungrazed sagebrush-juniper site. In: Roundy,
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multiple successional pathways: Legacy of the quaternary?
Journal of Range Management 46: 439-447.
Unity in Concepts and Terminology Task Group. 1995a. Evaluating
rangeland sustainability: the evolving technology. Rangelands
17: 85-92.
Unity in Concepts and Terminology Task Group. 1995b. New
concepts for assessment of rangeland condition. Journal of Range
Management 48: 271-282.
West, N. E., McDaniel, K, Smith, E. L., Tueller, P. T., and Leonard, S.
1994. Monitoring and interpreting ecological integrity on arid
and semi-arid lands of the Western United States. New Mexico
Range Improvement Task Force Rep. 37, New Mexico State
University, Las Cruces.
Winograd, I. J ., Coplen, T. B., Landwehr, J. M., Riggs,A C., Ludwig,
K. R., Szabo, B. J., Kolsar, P. T., and Revesz, K M. 1992.
Continuous 500,000 year climatic record from vein calcite in
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functioning, and resilience of the ecosystem. Third is
incorporating a framework of social values within which
ecological data and theories can be organized into an assessment (Scarnnechia 1995).
All three parts must be involved and are always intimately interlinked. The ultimate successes of ecosystem
management, for example, hinge on people because we are
an integral part of ecosystems (Box 1995). Interaction between social values and ecological theory can also affect how
we view ecosystems, which will influence the types of ecological data collected. However, unless we consistently recognize all three parts of the process, and focus on standards
based on monitoring ecological attributes and indicators
rather than on achieving fixed benchmark communities, the
resulting confounding of our assessments will prevent accurate and timely understanding of the ecosystem changes.
This will inhibit proper management to maintain ecosystem trajectories of change that sustain their functions and
resiliency.
Acknowledgments _ _ _ _ _ __
Appreciation is extended to Carl Freeman, John Emlen,
Dennis Hanson, James Lyons-Weiler, Debra Palmquist, and
James A. Young for their review of the manuscript. Additional thanks go to Carl Freeman, John Emlen and James
Lyons-Weiler for specific insights and criticisms that have
resulted in important improvements. Faults remain mine.
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