Ecosystem Restoration: Theory, Practice,
and Evidence
Wayne Tyson
Evidence—Successful Ecosystem
Restoration Defined
Abstract—“Garbage in, garbage out,” applies to almost everything but ecosystem restoration. Nature is so forgiving that on
all but the worst sites, regardless of the quality of the theoretical
foundation, the hyperbole, and the practice applied, something is
bound to happen eventually.
Another dictum, “gold in, garbage out” does apply, however.
Elaborate and expensive programs do not guarantee performance.
We are tempted to take full credit when Nature compensates for
our inadequacies and blame her whenever performance fails to
meet expectations. Sound theory, integrity in practice, and evidence in proof of previously predicted performance (feasibility)
can, like a good cutting horse, ultimately improve the stock of
theory, practice, and performance.
Given a sound theoretical foundation and corresponding
practice, ecosystem restoration should be a snap. Why, then,
are there so many failures and disappointments? What
distinguishes sound from flawed theory, good practice from
poor, successful from unsuccessful ecosystem restoration?
A sculptor, asked how he was able to create such fine
works, once said, “I just cut away the ugly part.” If theory,
practice, and evidence of performance are parts of a feedback continuum, the first step in improving results is to
identify the ugly parts, the flaws, over which we have some
control. Flaws in theory feed flaws in practice which produce disappointing results.
Flaws in performance or in our interpretation of evidence
can be due to poor theory and practice, but also to unrealistic expectations, as in mitigation requirements. So a realistic determination of what is feasible must be part of the
picture. Wishing—demanding a specific level of performance
not supported by the capabilities and limitations of the site
and technology—creates an illusion of failure. Conversely,
failing to demand what is feasible allows flawed performance to masquerade as successful.
If we are to reduce the number of failures and disappointments in ecosystem restoration, we must find a practical
course toward betterment. Working with the wrong paradigm will not achieve this. Therefore, a paradigm-shift
will be needed.
Before we can grapple with these issues, we need a definition of a restored ecosystem. Better men than I have
proposed a pretty good one. St. John (1989) has modified
Ewel’s (1987) criteria, and I really can’t improve upon these
efforts. Ewel and St. John define what a restored ecosystem
is, and in so doing, establish the criteria for evaluating evidence which can be used to judge the validity of the theory
and practice employed on any one project.
I will quote or paraphrase from St. John (1989), who
quotes Ewel (1987) and adds his own comment. Ewel suggests that sustainability, low invasibility, productivity,
nutrient retention, and biotic interactions define a successful restoration project ecosystem.
Sustainability
Ewel and St. John agree that the restored community
must be capable of perpetuating itself without outside subsidy. For example, a restored ecosystem must not require
fertilizer or irrigation.
Resistance to Invasion
Ewel concluded that because natural communities make
complete use of resources, they resist invasion by alien species. “While some [alien] invasion always occurs,” St. John
points out, “especially following…disturbance…the community should progress toward reduced invasibility with time.”
Productivity
Ewel considers the rate of production of biomass per unit
time to be an integrating measure of several important ecosystem processes. St. John agrees with him that the restored
community should equal the pre-disturbance community in
productivity; he points out that allowances will have to be
made for stage of development and for species composition.
I would add that productivity cannot exceed the productive potential of the restored site. If productivity is to be
related solely to the pre-disturbance community, a restored
community may be capable of more or less productivity
than the original site (pre-disturbance or comparable site).
Nutrient Retention
In: Roundy, Bruce A.; McArthur, E. Durant; Haley, Jennifer S.; Mann,
David K., comps. 1995. Proceedings: wildland shrub and arid land restoration symposium; 1993 October 19-21; Las Vegas, NV. Gen. Tech. Rep.
INT-GTR-315. Ogden, UT: U.S. Department of Agriculture, Forest Service,
Intermountain Research Station.
Wayne Tyson, Land Restoration Associates, P.O. Box 34069 Hillcrest
Station, San Diego, CA 92163-4069.
Ewel states that the conservation of nutrients is relatively
greater in natural than disturbed communities. St. John
cites the difficulty and expense of direct methods of measurement, but describes indirect techniques that are more
feasible.
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Biotic Interactions
Ewel says that the entire range of critical biological components should be in evidence, emphasizing pollinators and
symbionts.
This five-point approach is a means of providing ample
evidence of ecosystem health, and St. John has pointed out
that circumstances can alter cases. The complete restoration of any disturbed ecosystem takes time.
Completeness, at least in the near term, may not be
as large an issue in restoration as many consider it to be.
The initial reintroduction of those species which are able
to maintain viable populations under site conditions as
modified according to sound restoration theory may be
sufficient—particularly if species diversity and productivity increase over time to a level approaching (sometimes
exceeding) that of the pre-disturbance or comparable (example) habitat.
Function may be a more valid measure, since part of
restoration planning consists of creating conditions by use
of some organisms to produce habitat in the future for species for which suitable habitat does not yet exist. If that
function is present under the applicable conditions of Ewel,
normally the remaining conditions can be anticipated.
The degree to which a restored ecosystem resembles the
pre-disturbance or exemplar system is a gross measure of
its validity. But just as the constituents of undisturbed ecosystems vary, so do restored ecosystems, as do disturbed ecosystems which are not actively restored, from Mt. St. Helens
to “old fields” of various kinds. Restoration may be more
the management for acceleration of a powerful, inexorable
process of nature than it is an expression of the creative
genius of mankind. It may be that simply being on that
acceleration curve is sufficient.
There is a continuum from very slow to very rapid postdisturbance recovery of damaged ecosystems, from years
to centuries to millennia, depending upon whether we are
thinking of the oil fields of Kuwait or a rich bottom-land
post-flood environment—of whether the disturbance was
total or slight, the site potential great or minimal.
Through simple logic, concluding that if results are consistently good the theory that drove the practice and the
practice itself must be good, we can evaluate the validity
of theory and practice. Similarly, we can conclude that
theory and/or practice may have flaws if restoration projects
founded on them are consistently flawed.
The concept of consistency is important. Anybody can
be lucky or unlucky, more or less, fifty percent of the time.
One could have an isolated, sterile site in a tough environment with a low budget, an indifferent client, and an uncooperative contractor. Or one could have good site conditions
with excellent natural recruitment, a favorable weather pattern, a reasonable budget, and an enthusiastic contractor.
Figure 1—A 1 1/2:1 road cut restored using
a low-cost but technically adequate concept.
are difficult to achieve, particularly in a highly competitive
academic environment. People despise boring detail; they
like pictures.
In Figure 1, a 1 1/2:1 road cut is shown, just after treatment according to “Restoration Theory A.”
Figure 2 shows (photo is taken from a different position;
use the tall pine tree and houses on the horizon for reference) the Theory A project site ten years later, just prior
to re-grading and re-treatment according to “Restoration
Theory B.”
Figure 3 shows the same site ten years after treatment
according to “Restoration Theory B.”
Theory A was a low-cost but technically adequate concept
which relied upon site modification and no irrigation or
maintenance; Theory B employed a more costly, fairly standard hydraulically applied seed and fiber mulch, irrigation,
and maintenance.
Theory and Practice
Theory and practice need not, and probably should not,
be judged entirely upon direct empirical evidence. Theoretical foundations for theoretical structures and practices
can be evaluated by disciplined logic in an atmosphere of
intellectual integrity. The problem is that such conditions
Figure 2—The same road cut 10 years later. The
perspective of this picture differs from Figure 1.
Use the tall pine tree and the houses on the horizon for reference.
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Figure 3—The same road cut 10 years after a
more expensive, more complicated, but less successful attempt at restoration.
Pictures don’t tell everything, but in this case they tell
quite a bit. Theory A produced a sequence of actions more
or less consistent with what might be called “Theory A
Practices.” The result was not an exact duplication of the
site’s original vegetation, but a functional ecosystem comparable to the original was achieved immediately (this could
not be validated for about three years, however). It was selfsustaining throughout the ten years of its existence, and
still declining in invasibility, maintaining (subject to fluctuations in productive capacity) the level of productivity it
reached after about five years, retaining nutrients, and increasing in diversity when it was re-graded and replaced
by the “Theory B” restoration project.
Theory B produced a similarly consistent sequence of
actions which, however, did not result in a functional ecosystem comparable to the original. An illusion of success
was maintained until the irrigation system and maintenance program were phased out, but the artificially maintained vegetation quickly declined (no sustainability), the
site remains dominated by alien species (little resistance
to invasion), productivity declined, nutrients declined and
remain low (poor nutrient retention), and diversity declined
and remains at a low level (low level of biotic interaction).
This case may be unique but it illustrates a universal
principle. Highly hyped methodologies are not always what
they seem, and are seldom equally valid in all situations.
Money doesn’t guarantee success. Sound habitat restoration theory can work where highly hyped methodologies
don’t.
If the evidence is good, one can take credit; if bad, one
can blame the Ides of March or other “slings and arrows
of outrageous fortune.” The vagaries of weather, for example, can be deadly to a restoration project, but within
limits, weather is part of the context in which a restoration
project must be designed to work. Although weather can’t
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be predicted, climate can be understood and considered as
the context in which the restoration project must function.
Each site has a potential, difficult to delineate precisely
but simple enough to get a rough handle on, that can be
called its productive capacity. Productive capacity also
eludes precise description, but it can be determined within
useful boundaries.
This “fuzzy” logic is a difficult pill for most scientists to
swallow, because they have been trained to adore precision.
But nature is sloppy. This infatuation with precision in
dealing with a very ragged process may be at the root of
many of our troubles. To compound the confusion, every
factor in this equation is in a constant state of flux. Is it
wise to attempt to describe, much less deal with, such a
squishy and “unreliable” process using a system of thought
tightly bounded by several decimal places of precision?
The other factor in this “maybe”-ridden equation is what
we might call technical feasibility—that is, given the site
and environmental, not to mention political, social, and psychological conditions of each project—what are the boundaries of what can be done? You guessed it, the boundaries
of technical feasibility also elude precise definition, but they
at least can be determined within useful limits.
The purpose of getting this rough handle on this jiggly
process is to define our ignorance. This is what is known
as “brilliance.” It may be the soul of genius. It seems like
a playful paradox, but lack of concern with his or her own
brilliance has characterized every “genius” I have known
or read about, and every “ordinary” person who has done
extraordinary things. It’s like Chinese handcuffs—the more
you struggle, the more tightly you are held. To know, you
must let go, relax. This is a tall order for most people of
“western” cultures, but it came quite naturally to my native
American ancestors and many eastern cultures.
In a very broad sense, ecosystem restoration may best
be described as re-setting basic conditions so that natural
systems can recover lost or interrupted functions faster.
The world or regional subset ecosystems will eventually
restore some kind of biological complex to any disturbed
site, but it may take centuries or millennia. When we do
finally grasp the importance of understanding our ignorance,
we may come at last to the conclusion that it would have
been far cheaper to leave it alone in the first place.
References
Ewel, J. J. 1987. Restoration is the ultimate test of ecological theory. p. 31-33 in: W. R. Jordan, M. E. Gilpin, and
J. D. Aber (eds.) Restoration ecology: a synthetic approach
to ecological research. Cambridge University Press,
Cambridge.
St. John, T. V. 1989. Practical application of Ewel’s criteria
for a successful restoration. Proc. Symp. Society for Ecological Restoration, pp. 376-380. 1st Ann. Conf. Jan. 16-20,
Oakland, CA.