Vital Landscape Attributes

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Reference: Aronson, J. & Le Floc'h, E. 1996. Vital landscape attributes: missing tools for

restoration ecology.Restoration Ecology 4: 377-387.

Vital landscape attributes: missing tools for restoration ecology

James ARONSON and Edouard LE FLOC'H

Centre d'Ecologie Fonctionelle et Evolutive

Centre National de la Recherche Scientifique

B.P. 5051, 34033 Montpellier cedex 01, France

Fax + 334 67.41.21.38

[email protected]

[email protected]

Abstract

Twenty three "vital ecosystem attributes" (VEAs) were previously proposed to aid inquantitative evaluation of whole ecosystem structure, composition and functional complexity over

time. We here introduce a series of 16 quantifiable attributes for use at a higher spatial scale and

ecological organisational level, the landscape. "Vital landscape attributes" (VLAs), should be useful

in evaluating the results of ecological restoration or rehabilitation undertaken with a landscape

perspective, provided that clear definitions and boundaries are agreed upon for the different spatial

and ecological entities involved. Like VEAs, VLAs should be sensitive to changes wrought by

human as well as non-human factors leading to ruptures in flow processes or vegetation `switches'.

They should be applicable over a wide range of landscape types and therefore aid in conducting

rigorous inter-landscape comparisons.

Three groups of VLAs are presented: 1) landscape structure and biotic composition, 2)

functional interactions among ecosystems within the landscape, and 3) degree, type and causes of

landscape fragmentation and degradation. Ecotones between ecosystems are touched upon by

several different VLAs. As conflicting terminology abounds in this area, we append a glossary

defining the problematic terms used.


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Introduction

Fifteen years ago, Forman & Godron (1981) called for distinct, measurable units to describe

landscapes. Today, "landscape ecologists" do measure spatial components and dimensions of

landscapes, but the concepts and units of measurement

appropriate to the study of ecological aspects of whole landscapes have not yet been adequately

developed. Many recent papers in this journal have cited the need for specific criteria to evaluate

restoration and rehabilitation projects undertaken with a landscape perspective (Brown & Lugo

1994; Dahm et al. 1995; Jackson et al. 1995; Kondolf 1995). However, there have been few

attempts at developing a practical approach with concrete methods.

Perhaps the first problem has to do with defining the word "landscapes". Geographers in

western Europe and North America tend to think of landscapes as something entirely subjective,

whereas ecologists grapple only with the objective, material aspects of what they also namelandscapes. Some authors (e.g., Berque 1990) have suggested - and rightly we think - that the

notion of landscape is subjective and objective at the same time, and can therefore be used in

different ways by different people. However, this arrangement requires that each author clearly

define his or her use of the term.

By most of its dozen-or-more `official' definitions, landscape certainly is generally

something that involves humans - as individual observers or as a society. In contrast, ecologists

place emphasis on biophysical features and the various interactions of an ecological and

evolutionary character that take place within a landscape.

Clearly, some kind of rapprochement is needed since, as Bertrand (1972) noted, dealing

scientifically with landscape means working at the crossroads between ecology and human

geography. Otherwise, ecologists may have to give up the term "landscape" altogether and coin a

new one to indicate what they are talking about. But the problem of interacting across disciplinary

lines would not have been eliminated by this tactic.

A second stumbling block for ecologists and geographers alike has been the failure to

clearly identify the place of landscapes in spatial or ecological hierarchies. Naveh & Lieberman

(1984), Orians (1986), Tongway (1991), Hobbs (1993), and Whisenant et al. (1995) have all written

of the need for quantifying landscapes as something discretely embedded within a well-definedhierarchy. However, they did not provide one!

Working with wetlands, Zedler (Pacific Estuarine Research Laboratory 1990), Swanson et

al. (1990), Kelly & Harwell (1990) and many of the contributors to Stetzner et al. (1994) worked

and reported results within a coherent conceptual hierarchy of fluvial units. For no apparent reason,

far less has been attempted to develop quantifiable traits and experimental approaches to studying


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and manipulating terrestrial systems with a nested approach (Hobbs & Saunders 1992; Hobbs &

Norton 1996). Yet, just as when `landscape' is used as a spatial entity, we need to know where the

authors draw boundaries around it on a map, so if this same word is denotes a level of ecological

complexity (Forman & Godron 1981, 1986), then we need a clear exposition of the ecological

hierarchy in which it appears (Aronson & Le Floc'h, 1996).

We have previously presented a schematic model of ecosystem degradation, and the three

main responses available, with emphasis on arid and semiarid lands where degradation tends to be

widespread and severe (Aronson et al. 1993a). Applications of this model, and of a series of "vital

ecosystem attributes" (VEAs), to on-going field experiments in southern Tunisia, central Chile and

northern Cameroon were also described (Aronson et al. 1993b). A somewhat comparable overview

for aquatic systems, particularly streams and rivers, was provided by Kelly & Harwell 1990). Lefroy

& Hobbs (1993) have made an excellent contribution in the same vein, although they restrictedthemselves to agricultural systems where economic considerations are as or more important than

biodiversity or other environmental or aesthetic concerns.

In this paper, we introduce a series of measures to be used as a corollary to VEVEAVEAs;

we call them "vital landscape attributes", or VLAs. Like VEAs, VLAs should provide quantitative

indicators of levels of landscape degradation or - as is often said when ecologists are speaking of

landscapes - their "fragmentation" (Hobbs & Saunders 1991, 1992). In other words, they should

help to monitor and compare restoration or rehabilitation projects whether or not the project

designers fully realized the importance of a landscape perspective. No doubt such concerns are of

most relevance in areas where people are likely to continue being the primary ecological factor at

work.

VLAs should be sensitive, therefore, to perturbations wrought by both human or non-human

interventions, and also easily applicable over the full range of landscape types. They should help

reveal ruptures in spatial flow processes across landscapes and previous crossing of thresholds

leading to vegetation "switches" (Wilson & Agnew 1992; Wilson & King 1995). Ideally, they

should also reveal something about how local people are managing their environment, since the

`health' of a landscape has a great deal to do with the degree of good management that people have

attained and applied to their resource exploitation and production systems. No single index canprovide such information. Instead, large suites of indicators are required to thoroughly assess the

`health' and evolutionary direction (which we call "trajectory") of ecosystems and landscapes.

Change at these scales comes about from socioeconomic, but also climatic or biogeophysical

factors, and the myriad interactions among them.

Analogous to vital ecosystem attributes, VLAs should serve to identify and quantify


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landscape-scale traits that change in the course of degradation, restoration or rehabilitation. They

can play a critical role in "directing landscape dynamics" (Whisenant 1994, 1995), or piloting

ecosystem trajectories, by permitting the formulation and testing of hypotheses concerning the

organisation of landscapes, and their effects on individual ecosystems.

The main difficulty lies in identifying attributes that are truly appropriate to the landscape

scale and can, therefore, increase the sharpness or acuity with which we perceive interacting

components, trends, anamolies, etc. In other words, VLAs should help us resolve the complexity we

perceive in landscapes, both spatially and ecologically, so as to increase our ability to analyse,

compare and manage them in whatever context we are presented with. Accordingly, our approach is

purposefully somewhat simplistic so as to help inachieving rapid evaluations - or as a doctor might

say, diagnoses - of a landscape's current state and its probable evolutionary trajectory.

VLAs differ from VEAs primarily by dealing with two or more interacting ecosystems,and/or the ecotones occurring between them. Secondly, some VLAs must be defined that permit

quantitative description and analytical comparison of historical, cultural and other anthropogenic

dimensions of landscapes. While we do not dwell here on symbolic, perceptual, or other cultural

aspects of landscapes, we suggest, once again, that landscapes are not only a critically important

scale for evaluation and intervention by restoration ecologists, but also the meeting place between

ecology, human geography, environmental management and of course urban and rural landscape

design. It thus becomes inevitable to include both bio-pedo-physical and cultural/historical

variables when evaluating a landscape. However, our main goal here remains to establish a

preliminary list of VLAs for ecologists.

We now present 16 candidate VLAs. Depending on the study area and the priorities of the

restoration team, this list can and should be modified, as mentioned above. In what follows, an

ecosystem is considered as being contained within a landscape embedded in a biogeographical

matrix. (See Appendix for terms in italics.) The VLAs listed come under three headings:

a) structural and biotic composition, b) functional interactions among ecosystems, and c) degree,

type and causes offragmentation and degradation. Conversely, the level of landscape reintegration

achieved may be measured. Despite their importance, we devote little attention here to ecological

processes that affect populations of individual species (e.g., source-sink and neighborhood effects)(Dunning et al. 1992). Nevertheless, unless careful population-level studies are also carried out on

at least some key organisms, it will be very difficult to undertake reliable syntheses at higher levels

such as `community' or `ecosystem'.

In selecting and classifying VLAs, we have generally followed the criteria of Kelly &

Harwell (1990) and Aronson et al. (1993a). Identifying correlations among these various VLAs, and


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comparing them for various contrasted landscapes, with different past histories, are research

priorities for the future.

Vital Landscape Attributes (VLAs)

1. Type, number and range of landforms is a logical starting point. In Russia, Siberia and central

Europe, a long tradition exists for studying physical-chemical "geosystems" or "natural territorial

complexes" (Grin 1984; Rougerie & Beroutchachvili 1991). These concepts also recur in the

German notion of "landschaft" and the English phrase "natural landscape" as opposed to "cultural

landscape", and they have had a strong influence on French geographers as well. Swanson et al.

(1988) discussed geosystem processes or landform features that can affect ecosystems and

landscapes, including environmental gradients and the movement of material, organisms,

propagules and energy along them, and geomorphic processes that alter biotic features andprocesses. These same authors also pointed out that landforms also influence the frequency and

spatial pattern of non-geomorphically induced disturbances such as fire, wind and grazing.

2. The number of ecosystems present needs to be explicit, including both aquatic and terrestrial

types. These different ecosystems, and their boundaries, should be defined and located as carefully

as possible. This may be difficult in areas where landscape heterogeneity has been drastically

reduced by human activities over the past few centuries, and the natural boundaries between

ecosystems obscured. In most situations, however, a tentative listing can be achieved on the basis of

broad differences in landforms and/or extant biotic communities. When this is not possible, it may

be preferable to work initially with "land units" (see below).

Biotic communities can be typified according to mathematical indices of landscape

richness, evenness and patchiness (Romme 1982). McCoy et al. (1986) developed a quantitative

method to determine biotic boundaries along environmental gradients that requires only presence-

absence data and a series of multivariate analyses. This approach could well be applied to

landscapes by employing a series of transects along complete toposequences in such a way as to

represent the entire landscape (Aronson et al. in press a). Patchiness was also used by Romme

(1982) to reveal the interspersion and contrast of `communities' at the landscape scale. However,communities do not segregate neatly in accordance with ecosystems and, as mentioned above,

ecosystems and communities boundaries are often masked by past human activities. Accordingly,

caution must be employed.

Where legitimate doubt exists as to the distinctions that can be drawn between `landscape'

and `ecosystem', we may subdivide the territory under study into "land units" (Christian & Stewart


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1964). When more data are available, notably via quantification of various VEAs and VLAs, then

more precise terms can be substituted.

Spatial aspects of landscape pattern (or physiognomy, as some would call it) can indeed be

most readily - if not always satisfactorily - analysed in terms of land units, i.e., "ecologically

homogeneous tracts of land at the scale at issue" (Zonneveld 1989). By definition, a land unit may

either represent portions of a landscape in a given stage of "recovery" following a disturbance, or

else "permanent cultures of at least a decade", e.g., orchards, vineyards (Zonneveld 1989:79). They

can also be tracts of "wilderness", fallows, or anything else that lends itself to spatial cartography.

3. Type, number and range of land units are three simple measures of heterogeneity within a

landscape. Land units can also be characterized or categorized by more sophisticated indices, e.g.,

dominance and contagion within a landscape, and fractal dimension. O'Neill et al. (1988) have usedthis approach to discriminate between major landscape types in the eastern United States.

Dominance measures the relative frequency of a land unit in a landscape. The contagion index

measures the extent to which the different land uses are aggregated or clumped. Conveniently, the

fractal geometry of land units is highly correlated with the degree of human manipulation of a given

landscape. See O'Neill et al. (1988) for units of measurement and computation techniques.

It may be mentioned that many other workers in landscape ecology have applied

information theory and fractal geometry to quantifying shapes and boundaries in a landscape

(Turner 1989). Exceptionally, Turner & Ruscher (1988) and Odum & Turner (1990) used these

approaches to describe landscape changes in Georgia (USA) since 1920, thereby tracking changing

spatial dynamics and fractal dimensions over a considerable period of time. This seems a

particularly promising research direction to pursue.

4. Diversity, length and intensity of former human uses.

This type of investigation has been called, in France, the archeology of landscapes. In

attempting to `read' or decipher a landscape's current condition, it can be extremely useful to

identify the dates and duration of periods of particularly intensive exploitation of the study area in

the past.The age or longevity of different uses, and of intensive use in general, to which man has put

a landscape and its bio-resources, and the intensity of that use as well, are often critical variables in

the current state of `health' of the various ecosystems operating within the landscape under study.

The plant and animal species found in landscapes long since occupied by man have tended to

evolve certain commensal characteristics allowing them to subsist despite the repeated, intense


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perturbations cause by rural populations....otherwise they have disappeared. Thus, knowing

something about the history of land use by people is critical (Aronson et al. in press a,b).

For example, we are currently engaged in comparing long-term ecosystem studies in

southern France and central Chile where an order of difference in magnitude separates the age since

energy- intensive systems of agricultural exploitation have been introduced and practised. In France

there are some 6 - 10 millenia of such history, as compared with only four to 460 years in central

Chile (Aronson & Le Floc'h 1996). What's more many of the most common plant species found in

central Chile are in fact originally from the Mediterranean Basin, where they evolved in co-

habitation with people. (N.B. It is be useful to speak of `positive feedback systems' in this context

but, technically, the term "coevolution" should be avoided.)

5. Diversity of present human uses of landscapes, or portions thereof, includes those activitesleaving no trace (hunting, hiking, mushroom collecting, etc.). This is not the same as the preceding

VLA, since they cannot be easily mapped or studied spatially. In any case, they require in-depth

studies of local people and their day-to-day activities and preferences. Typically, this is a VLA for

which the help of geographers or sociologists may be required.

6. Number and proportion of land use types refers initially to the uses to which people put different

pieces of land, with concrete physical consequences visable in the landscape. These are broad

categories such as plough-farming, pasturing, tree-farming, etc., and do not necessarily correspond

to specific geographical land units. The proportion of each land use type to overall land area can be

readily quantified. This calculation may have important social and political ramifications when

many different actors or interest groups are present in a given landscape.

By using ratios for this VLA, size-related variations can be overcome for the purpose of

inter-landscape comparisons. However, the problem with both proportions and ratios is that they

tend to encourage thinking in terms of linear relationships that in fact only rarely exist. To avoid

such oversimplification, a modified Shannon-Wiener Diversity Index (Westman 1985) can be used

to measure three indices of landscape pattern: proportion of land use type, mean size, and an overallindex of diversity, combining number and relative abundance within the landscape.

7. Number and variety of ecotones i.e., zones of high biological and energetic connectivity between

ecosystems, and of varying shapes and widths. As habitat boundaries and more-or-less permeable

barriers, ecotones have major impact on the movement of organisms and materials across


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landscapes (Hansen & di Castri 1992). For example, conserving a variety of ecotones of differing

shapes and sizes may lead to higher retention of nutrients and may influence nutrient cycling over

predominantly agricultural landscapes (Ryszkowski 1992). Hardt & Forman (1989) reported similar

results on reclaimed surface mines. More research on ecotones is needed in other kinds of

landscapes. In some areas (e.g., much of southern Europe, where lands are being `liberated' from

agriculture), there may be long-term value in not only conserving existing ecotones but also

artificially recreating semi-permeable barriers to animal or plant movements, as well as to water,

nutrient and energy flows. In theory, this could complement the sort of artificially fostered patch

dynamics practised with success by Hardt & Forman (1989) and by Ludwig & Tongway (1996).

8. Number and types of corridors or "wildlife corridors" are increasingly investigated, but seldom in

conjunction with human movements across landscapes; these are usually treated apart, and bydifferent investigators. In our view, more attention should be paid to the direction and orientation of

all travel routes traversing a landscape.

In past Oriental as well as Occidental and African cultures, great attention was paid to the

siting, routing and orientation of roads, bridges, tombs and other conveyors of human souls, or

bodies, or livestock, produce and the like. These routes were often determined by simple factors

such as topography, but also by more cryptic ones, such as wind and rainfall patterns, or the

behavior of certain rivers in exceptionally wet years. Telluric force lines were also considered in

some cases, and such efforts should not be neglected by modern day restorationists. Similarly,

determining exactly why animals followed one path rather than another merits our full attention.

For present purposes, however, we simply recommend some kind of census be undertaken

of all forms of movement corridors within a landscape (see below). An obvious follow-up to this

would be to monitor actual numbers of people, livestock or wild animals moving in each direction

along a corridor in, say, a 24-hour period, per week, or per year. The important thing is to

characterize how movements across the landscape were traditionally effected.

9. Diversity of selected critical groups of organisms (or "functional groups"; Krner 1993) is an

essential component to the characterization of habitats or communities (representing anapproximation of ecosystems). Birds, fish, crustaceans, higher plants, mycorrhizae, etc., could all be

considered as key groups of interest at the landscape level; there are often close, functional

correlations among groups. For example, it is widely held that abundance and diversity of birds in a

river valley are indicators of abundance and diversity of fish. Large animals are usually given

particular attention (Naiman 1988; Pastor et al. 1988). Some measures of beta (i.e., between sites of


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a similar type), and gamma (overall landscape) diversity should be obtained, e.g., on the basis of

presence-absence data (Wilson & Shmida 1984).

10. Range and modalities of organisms regularly crossing ecotones is a related VLA directly

affecting trajectories of more than one ecosystem. This can be quantified simply by using the

number of entities involved and one of several existing indices of similarity chosen to compare

them. It would be important to quantify the number and frequency of these trans-landscape

movements to help understand the dynamics which drive them.

11. Cycling indices of flows and exchanges of water, nutrients and energy within and among

ecosystems. We have proposed cycling indices (Finn 1976, 1982) as a VEA (Aronson et al. 1993a),

but they probably apply better at the level of landscapes. In either case, they should be used toevaluate whether or not nutrient and water `leaks' are becoming more or less important, both within

and among adjacent ecosystems as a result of past actions or current restoration efforts.

Since "ecosystem health" (Leopold 1948; Costanza et al. 1992) and "ecosystem integrity",

may well rely on a full complement of biological diversity being present, all tending to serve in

"leak plugging" (von Voris et al. 1980; Main 1981), and thereby maintaining ecosystem structure

and functioning, the study of "leakiness" at both the ecosystem and landscape levels can be a very

powerful tool. Ultimately it should reveal what proportions of available energy, water and nutrient

resources are being captured and recycled and where; a serious research committment is required

for this and indeed, such enquiries should receive high priority.

12. Pattern and tempo of water and nutrient movements among contiguous ecosystems is an

important VLA for which the traditional units of limnology and hydrology (cubic meters of water

moving past a point per minute or cubic centimeters of silt charge in the water) are not appropriate.

However, Band et al. (1991) offered some useful guidelines and quantitative measures for

modalities of water circulation in a watershed, including rainfall and surface run-off patterns, water

table dynamics, etc.).

13. Level of anthropogenic transformation of a landscape indicates relative homogenization of a

landscape as a function of cumulative human activities. In French, and other Romance languages,

this is called "anthropisation" or "artificialisation". "Banalisation" is a related concept. In English,

no single words exist to convey these notions. In ecology, however, they are simply a special kind


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of disturbance or perturbation and can to a large degree be lumped together. Plant and animal

populations respond quickly to this kind of selective pressure; communities and ecosystems having

achieved some sort of metastability despite prolonged human presence will presumably give an

accurate reflection of the degree of anthropogenic transformation that obtains (Hobbs & Hopkins

1990; Aronson et al. in press a, b).

Means of quantifying this VLA depend on the origin and severity of the processes involved.

If quantitative or semi-quantitative measures can be agreed upon, this VLA can be used both when

comparing between two or more landscapes in a given matrix, or else to characterize the range and

proportions of past and ongoing artificialisation among land use units in a given landscape. This, of

course, implies determining a "landscape of reference", however imperfect.

Just as an ecosystem undergoing rapid transformation will present varying vegetation

`facies' that are more or less removed from the "ecosystem of reference", it is important to clarifyhow much or how far each part of a landscape has been altered in the time frame of concern. Here

in the Mediterranean Basin, of course, heterogeneity at all scales of analysis is the byword for all

ecosystems and, until recently, all landscapes. Therefore, it is important to seek all available data on

the past history of the specific study areas (see VLA 4). This approach was exemplified in the

recent issue of this journal devoted to the Kissimme River project (Dahm 1995), where a detailed

historical account of the study area was presented (Koebel 1995) prior to discussing the orientation

and various details of the restoration project itself.

One of the emergent properties of the landscape that should be become more apparent

through study of this VLA is the relative degree of homogeneity to be found at the landscape unit

level, and this can be expected to increase in situations of declining (or abolished) land use, at least

in areas where ecosystem resiliency has not been totally destroyed. In the milder, subhumid portions

of mediterranean Europe, this situation is generally perceived as a degradation of, or at least

unwelcome departure from traditional landscapes that people have known in the 20th century. In

drier parts of the same region (southern Spain, Greece, etc.), the greater aridity probably intensifies

and accelerates the undesireable side-effects of prolonged human use, and extant ecosystem

resilience is apparently much lower as a rule. Particular attention should be given to whether one ormore "thresholds of irreversibility" have been crossed in the process of anthropogenic

transformation.

Land abandonment may also have direct consequences for some native plants, animals and,

of course, people. In the case of southern France and adjacent parts of Spain and Italy, the hazard of

disastrous fires raging out of control during the dry summer months increases rapidly as woodlands


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and shrublands become inpenetrable (Etienne et al. in press).

To give one more example, we cite a land-mapping study carried out in southern Tunisia

(Le Floc'h 1979), wherein the number of man-hours spent working per hectare and per year proved

a very useful indicator both for research and management purposes. This parameter is well-known

in cultural anthropology and rural economy as well and should prove useful in the present context

as well.

14. Spread of disturbance across a landscape, and ecological disturbance regimes in general, need to

be studied since "disturbances operate at many scales simultaneously, and their interactions

contribute to the observed landscape mosaic" (Turner 1989). Ecosystem and landscape managers

should learn to expect and indeed plan for risk of unexpected disturbance and chance events in

their multiscale, multidimensional projects (Allen & Hoekstra 1987; Bodkin 1990). To do so, theyneed to have a notion of the indigenous disturbance regimes of given ecosystems and their potential

impact on whole landscapes.

15. Number and importance of biological invasions deal with a kind of disturbance for which the

indigenous ecosystem was theoretically not `designed' to cope. Vitousek (1989) has elegantly

demonstrated the profound impact of certain invasive organisms on certain ecosystems. At the

landscape level, this impact may well be greater than at the ecosystem level. Many restoration

efforts therefore logically begin with straightforward eradication efforts aimed at eliminating

noxious animals or plants introduced intentionally or inadvertently in the past. However, the

environmental impact of those invaders is not always well determined. These invaders may be the

only organisms of a functional type to be able to survive under present conditions and can serve an

important intermediary role while a range of native species is being reintroduced.

An effective complement would be to rate landscape units, or even whole ecosystems,

according to their "resistance to invasive (plant or animal) species", as recommended by Zedler and

coworkers (Pacific Estuarine Research Laboratory 1990) in their manual for evaluating coastal

wetlands in southern California. Of course such ratings must be periodically reviewed as the extent

of the "eternal external threat" (Janzen 1986) changes. The rate of plant invasion now occurring forthe first time in the Galapagos Islands, for example, could hardly have been predicted ten years ago.

16. Nature and intensity of the different sources of degradation, whether legal or illegal. An

example of how to use this self-explanatory VLA would be to quantify the sources and current

levels of pollution by their relative importance, duration, origin, or other ecological or socio-


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economic criteria. In some areas, illegal activities such as poaching or tree-stealing may be

particularly influential but hard to quantify.

With the last attribute in this list, we returned to our colleagues in the realm of sociology,

cultural anthropology and human geography. All of these disciplines have much to contribute to the

emerging "science of landscapes", especially in areas where restoration or rehabilitation must co-

exist with local populations' social, economic and other cultural needs.

We note that Ruzicka & Miklos (1990) combine ecological and socioeconomic variables in

their LANDEP system for "landscape optimization" planning. Other examples of this kind of

thinking are given in Young's (1992) volume on "sustainable investment and resource use", and the

well-known work of Costanza and co-workers (Costanza & Daly 1992). See also the

interdiscipinary syntheses undertaken by Zube et al. (1975), Raveneau (1977), Brown & Lugo

(1994) and Jackson et al. (1995) for examples of how to at least juxtapose, if not fully integrate,data from various disciplines ranging from ecology to rural sociology and economics.

Discussion

In this paper, we have proposed a preliminary list of 16 vital landscape attributes or VLAs

to complement our previous list of vital ecosystem attributes, or VEAs. These should aid in refining

existing models of spatial and ecological hierarchies relevant to restoration and landscape ecology.

More concretely, developing quantifiable, sensitive, reliable, and universal VLAs appears to be an

essential step in the advancement of a landscape perspective in restoration and rehabilitation

ecology. Whether the goal is "ecologically sustainable landscapes" (Forman 1990), the preservation

of biodiversity (Franklin 1993), or else "sustainable development", the landscape seems a crucial

scale at which to work, both conceptually and practically. We hope that VLAs will provide a useful

tool for such endeavors.

Acknowledgements

We warmly thank Sandra Brown, Shivcharn Dhillion, Richard Hobbs, Byron Lamont, Bill Niering,

Dan Simberloff and Steven Whisenant for comments and criticisms on earlier versions of the

manuscript.


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Appendix: Glossary

Ecosystem trajectories

The sampling, evaluation and indeed monitoring of ecosystems (see below) as living,

evolving systems, often far from thermodynamic equilibrium, is greatly facilitated by adapting the

notion of trajectories. We see this as an integrative concept grouping succession, as defined by

Clements (1916), as well as all other paths or itineraries imagined or engineered by people for any

given ecosystem or set of ecosystems. On a short time scale, some ecologists may argue that

ecosystems simply change without necessarily following a trajectory. However, with sufficient

perspective, any and all changes an ecosystem undergoes in a given period of time can be seen as

comprising a `trajectory'.

It may be argued that any path taken by an ecosystem from one state to another is, bydefinition, succession. However, as commonly understood, succession is something autogenic (Cf.

"autogenic restoration" (Whisenant 1994)). In contrast, the term trajectory implies a subject that

`throws' or `guides' an object, which is accordingly `thrown' or `trajected'. Thus, trajectory seems a

useful term for describing what happens to an ecosystem that is undergoing ecological restoration

or rehabilitation.

Ecosystem

The term ecosystem was defined by Tansley (1935) as a biotic community and its

biogeophysical environnment, including all the interactions between and among them. Lindeman

(1942) wrote that an ecosystem could occur "within a space-time unit of any magnitude" (emphasis

added). Recently, however, ecologists have grown dissatisfied with the lack of an intrinsic scale in

this definition: either a more precise definition is needed, which indicates clearly the position of the

ecosystem within a larger hierarchy, or else `ecosystem' must be abandoned as an independent,

discrete entity (O'Neill et al. 1986). Naturally, we opt for the former. We follow Cousins (1993)

who argues that an `ecosystem' can be defined as a "subjectively determined [emphasis added]

aggregate with boundaries given by an observer...in a hierarchy of functional objects". That is to say

that some number of visable or measurable attributes must be selected as criteria for delineatingecosystems within a landscape.

Landscape

The same process as described for ecosystem must also apply to landscape, if we are to

avoid semi-mystical usages of these two terms. Objective or subjective barriers must also ultimately


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be drawn between adjacent landscapes. Most hierarchies constructed by ecologists have

tended to jump from ècosystem' to biome, without stopping at `landscape'. The reason for this may

be an unspoken desire to avoid dealing with `the human dimension' of landscapes. Some

geographers, social scientists, and the general public tend to define `landscape' as something

profoundly unquantifiable, a stew of human culture and symbolism, combined with, or carved out

of, hard-edged (i.e., physical, biogeochemical) determinants of `natural', i.e., non-human origin. The

Penguin Dictionary of Human Geography (Goodall 1987) notes ten concepts of landscape which

differ slightly in emphasis, but are not mutually exclusive. In general, landscape is thought of as

something comprising ecological, geographical and cultural components (Troll 1971). In passing, it

should be noted that ecologists have at least that many different definitions of ècosystem', but tend

to eliminate all that cannot be seen or touched objectively in both cases.

To cite one example of a geographer's thoughts on landscape, Augustin Berque (1984,1986, 1990) writes of landscapes as being both the ìmprint' of the past, and the matrix of current

(and future) human activities in a given area. In other words, landscape is both objective and

subjective at the same time. Berque argues that landscapes should be seen primarily as the ongoing

relationship between people and their "milieu" or habitat. They are not simply a setting in which

people (and other organisms) act out their lives; rather they are also the living matrix which makes

those lives possible and determines the possibilities available to them. Landscapes are in turn

continuously being altered and modelled by the cumulative effects of the organisms present within

them, especially people (Cf. Troll 1971; Naveh & Lieberman 1984).

As ecologists we must reject Berque's position for two reasons. First, with regards

landscapes, his definition fails to meet the Popperian criterion that hypotheses should be amenable

to rigorous testing via experimentation (Cf. Pickett et al. 1994, however, for a critique of Popper in

the modern context). As an alternative approach, we follow Forman & Godron (1981, 1986) who

defined landscape as something physical, tangible and, therefore, measureable. For these authors,

and indeed most working ecologists today, a landscape is a heterogeneous portion of land (of some

undetermined area, but often several square kilometers wherein occurs a "recognizable cluster of

ecosystems that interact in ways producing spatially repeated patterns" (Forman & Godron 1986).

Slightly different definitions are found in Swanson et al. (1988), Urban et al. (1987), and Turner(1989).

Matrix

In his timely call to pay more attention to ecosystems and landscapes, Franklin (1993) made

extensive use of the term matrix. He follows the prevailing paradigm in landscape ecology when he


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writes of nature reserves and parks as occurring within a "landscape matrix" that he defines as the

"unreserved portion of the landscape" (Franklin 1993:204). By "unreserved", he means that portion

of the landscape with which he is not concerned.

According to this formulation, there is no indication of hierarchical scaling, and landscape

and matrix are synonymous. While urging more attention be paid to higher levels of organization

(ecosystem, landscape and matrix), Franklin fails to show how to quantifiy or even distinguish

among them practically.

We propose that the word `matrix' should be used, in the present context, to describe a new

hierarchical scale, just above landscapes. As we have seen, landscapes are the result, the "imprint",

of past human activities in a given setting. The matrix is thus the biological or, better still, the

biogeophysical environment in which a landscape comes to be created. In other words, working

with a certain vegetation type, geological substrate and prevailing climate - all of which togetherconstitute the matrix in our hierarchy -, people create landscapes. (In the context of general ecology

and biogeography, the notion of biome is nearly synonymous.)

Note that several different landscapes can conceivably arise within a given matrix, as when,

for example, populations from two different ethnic groups live and work in proximity one to the

other. Each landscape is therefore the result of interactions between a matrix and the activities of a

given cultural group.

Fragmentation of landscapes

This term (Hobbs & Saunders 1991, 1992) describes a generally gradual phenomenon

marked by the rupture of certain linkages, i.e., a reduction in `connectivity' (Merriam 1984; Baudry

& Merriam 1988) among ecosystems in a given landscape. Such a rupture will naturally have

profound consequences for the trajectories of each ecosystem, and the structure, composition and

functioning of the landscape itself. In theory, even subtle consequences of landscape fragmentation

should be measurable at inter-and intra-community levels within ecosystems, and among

ecosystems as well.

Reintegration of landscapes

This term (Hobbs & Saunders 1991, 1992) denotes a conscious effort to reestablish pre-

existing relationships of connectivity among contiguous ecosystems in cases where human activites

have caused ruptures and fragmentation. It suggests that a return to former ecosystem trajectories,

or something close to them, can be achieved by revising management practices (and, perhaps, land


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tenure, zoning laws, etc.). For this to work, all of the local `actors' must agree to cooperate in the

common interest.

Much of the discussion surrounding landscape reintegration and biological conservation in

densely populated areas has centered on "movement corridors" for wildlife (e.g., Henein &

Merriam 1990; Saunders et al. 1991). However, although corridors may have strong public appeal,

and therefore be useful for eco-activist lobbying or environmental reeducation, they are only a small

part of the problem of reintegration (Simberloff et al. 1992). In a broad sense, landscape

reintegration involves restorations, rehabilitations and reallocations, applied in different places and

proportions, according to local context and contingencies.

We have used the terms restoration, rehabilitation and reallocation in the plural, since the

same ecosystem can occur more than once in a given landscape, especially in areas where human

activities have a long history. In restoration projects concerned with the landscape as well asecosystems, it may be necessary to treat land units of a given ecosystem type differentially. In some

cases, they may be treated in an identical fashion but at different paces, to achieve a mosaic of land

units in different stages of a given trajectory.

Artificial `rejuvenation' of selected land units

In areas of agricultural abandonment, such as are common throughout western Europe

today, landscapes show a tendency to

closed canopies, and to lose open spaces. As a result, they lose biodiversity at all hierarchical levels.

It may thus prove worthwhile to attempt to maintain some open spaces by a variety of techniques

we would group under the heading "artificial rejuvenation". The most obvious way to achieve

`rejuvenation' of a given land unit is by engaging in cutting, plowing, burning, etc. in order to

eliminate certain species or functional groups, and thereby temporarily halt, or slow, secondary

succession. For example, in some countries, controlled fires are routinely used to maintain prairies

or other grassland-type systems.

In Figure 1 we have tried to show how rejuvenation relates to restoration, rehabilitation and

reallocation. In some cases (Figure 1, a1

) following degradation (or abandonment), with or without

subsequent intervention, a trajectory can follow the same pattern, in reverse, as that shown by thepre-disturbance ecosystem or other ecosystem of reference. However, other possible trajectories

exist (see Figure 1, a2) that may or may not converge at some point, and will no doubt proceed at

different paces.

In rehabilitation efforts, one or more thresholds of irreversibility can be crossed (Figure 1,

b1 and b2). Furthermore, different trajectories should be anticipated in different phases of


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restoration or rehabilitation (i.e., a1 vs. a'1 vs. a''1 and a2 vs. a'2 vs. a''2). Reallocations can lead to

entirely new uses for land units; rejuvenation is a site-specific managerial activity that should be

considered as part of a holistic landscape reintegration project. It is for this reason that "ecosystems"

is given in the plural in this figure.

Landscape of reference

We propose a term both analogous to and complementary with "ecosystem of reference". It

seems useful to have a standard of comparison and evaluation when working with complex

systems, even though their past history is not fully knowable and any given ecosystem (or

landscape) or reference selected will necessarily be arbitrary. To be acceptable to local people, the

landscape of reference may be chosen on the basis of the cultural, social and economic context at

some moment' in the past.


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Figure 1. Schematic representation of alternative ecosystem trajectories over three phases,

illustrating the notions of restoration, rehabilitation, reallocation, and rejuvenation as well as that of

"thresholds of irreversibility". See text for further details).

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