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An innovative contribution of landscape ecology to vegetation science

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An expansion of the foundations of the theory of landscape ecology can relocate its different approaches in a deeper biological vision. To this purpose, I directed my efforts towards comprehension of the landscape and of its main component-the
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  © 2005 Science From Israel / LPPLtd., Jerusalem  Israel Journal of Plant Sciences Vol. 53 2005 pp. 155–166  E-mail: v.ingegnoli@virgilio.it An innovative contribution of landscape ecology to vegetation science V ITTORIO  I NGEGNOLI    Department of Biology, University of Milan, Via Celoria 26, Milan 20133, Italy (Received 10 July 2005 and in revised form 20 January 2006) ABSTRACT An expansion of the foundations of the theory of landscape ecology can relocate its different approaches in a deeper biological vision. To this purpose, I directed my efforts towards comprehension of the landscape and of its main component—the vegetation mosaic—as a proper biological system.As suggested by Naveh, I have revised landscape ecology according to new sci-entificparadigms,rangingfromthePrincipleofEmergingPropertiestothe“orderthrough fluctuation”processes.Consideringthatalandscapeismuchmorethana set of spatial characters, I tried to focus its ecological elements and processes, proposing new concepts (e.g., ecocenotope, ecotissue), new functions (e.g., biologi-cal and territorial aspects of vegetation), and new applications (e.g., evaluation of vegetation, etc.).This improves vegetation science through (1) a critical review of the limits of phytosociology in studying the landscape, (2) a more coherent study of both natural and anthropogenic vegetation, (3) a better understanding of transformation processes, (4) a confirmationofthenecessitytoabandondeterministicconcepts(e.g., potential vegetation), and, especially, through (5) a new capacity for landscape vegetation diagnosis. Keywords : vegetation science, landscape ecology, biological territorial capacity (BTC), ecotissue, ecocenotope INTRODUCTIONImproving landscape ecology Today advancement in landscape ecology is particularly difficult.Thisyoungbranchofecologyneedstosynthe-size and advance beyond the different approaches its founders have given to it, primarily Naveh and Lieber-man (1984, 1994) and Forman (1986, 1995). Such an effort needs to study the landscape as a living entity. The landscape is much more than a set of spatial characters: it is a proper level of the hierarchy of life organization. To a certain extent, Naveh and Forman stated that the landscape may be definedasalivingsystem,buttheynever put this crucial concept at the base of the entire discipline of landscape ecology. Therefore, following the definitionoflandscapeasaliving entity, we may observe that (1) the theoretical sug-gestions of Naveh and Lieberman  (1984, 1994) about the importance of new scientificparadigmsinlandscapeecologyled to a revision of some ecological elements and even to new concepts,  and (2) practical applications result in a wider set of methods, consistent with the theoretical principles. One of the major consequences of widening the foundation of landscape ecology involves vegetation science. The main component of a landscape is vegeta-tion, the most important controller of the fluxofenergyand matter. Vegetation communities usually form the main mosaic of the landscape.   Israel Journal of Plant Sciences 53 2005 156 Limits of phytosociology At present, vegetation is definedasasetoflivingplant individuals, growing in a certain site in their natural disposition (Westhoff, 1970). In Europe, the study of vegetation is mainly founded on phytosociol-ogy (Braun-Blanquet, 1928) and (for the landscape) on geosynphytosociology (Biondi, 1996). But, beginning with Naveh and Lieberman (1984), many scientists realized the inadequacy of phytosociology in studying landscape. The principal weaknesses of phytosociology include the following points:1. After about 80 years of investigations there was no true innovation in the method of phytosociology. Thus phytosociological results became more and more incompatible with modern developments of science (Pignatti et al., 2002). Indeed, this line of investigation concentrated mostly on description of communities.2. It is impossible to properly show the order existing in a vegetation community only through a floristicdescription (e.g., phytosociologic tables, Pignatti et al., 1998). On the other hand, if the shorter algo-rithmic description of a system coincides with the description of the entire system, the system has to be classifiedasachaoticone(Pignattietal.,1998).Butvegetation is not a chaotic system!3. Classic phytosociology describes a typology of an idealized “natural” assemblage of plants rather than a study of vegetation in its full reality. It does not consider the coevolution and the interaction of veg-etation with man and the resulting new coenosis of anthropogenic vegetation. 4. Until now, even in the representation of the ecologi-cal space, it has not been considered that an associa-tion must have an information content that is greater than the sum of the information acquired by the component species. This is due to the Principle of Emergent Properties (Odum, 1989), which allows a vegetation coenosis to become an attractor in its context (the landscape), where it evolves and has to sustain a role (Ingegnoli, 2002).Thus phytosociology gives insufficientinformationfor studying a complex living system like a landscape. For this purpose the contribution of landscape ecology to vegetation science is needed. This may be the main reason why Zev Naveh (personal communication) was the firsttorequestthatIwriteascientifictextonland-scape ecology, (Ingegnoli, 2002).In this paper I present a brief synthesis of the new paradigms expanding the theoretical foundation of land-scape ecology, as well as some of the methods available in studying vegetation. Two examples of natural and human environments are presented: (1) the vegetation of the Venice lagoon, and (2) the forested landscape unit of the Lavazé Pass (Trentino–AltoAdige). NEW PARADIGMS AND NEW CONCEPTSHierarchic levels of life and their characters Organisms or very complex self-organizing systems need to exchange material and energy with the environ-ment. They are able to perceive and process informa-tion, to transform and reproduce themselves, to have their history, and to participate in evolution. Life cannot exist without the presence of its environment. Life and its environment are a unique system, because the condi-tions allowing life are necessary both inside and outside an adapted distinguishable entity, like an organism. That is why the concept of life is not limited to a single organ-ism or to a group of species, and why we describe life organization in hierarchic levels. The landscape is one of these levels. Concerning this argument there is still some confu-sion . Organism  and  population  generally correspond to quite definiterangesofscale,ifweconsidertheirvitalspace per individual and their minimum habitat, re-spectively. The upper part of the “biological spectrum” (sensu Odum, 1971) also presents a quite definiterangeof scale corresponding to ecoregions  and ecosphere . Problems arise in the middle part of the biological spectrum, concerning communities , ecosystems , and landscapes . For many scientists these are usable levels at almost any scale (Allen and Hoekstra, 1992; Wiens and Moss, 1999), or at least they occupy the same wide range of scales. This is in contrast with the Principle of Emerging Properties, which affirmsthatthewholeis greater than the sum of its components. Philosophi-cally this was expressed by the epistemological school of Gestalt (i.e., perception of the form; Lorenz, 1978; Naveh and Lieberman, 1984). The differences among communities, ecosystems, and landscapes seem to be mainly in criteria of observation. There are three parallel hierarchies (Ingegnoli and Giglio, 2005), based on the biotic, on the environmental, and on the ecological (integrated) criterion. The last one is able to integrate the firsttwo,sinceanyecologicalsystem must include both a biological element and   its environment. Therefore, it seems probable that we have to consider two hierarchic levels in the middle biologi-cal spectrum: (1) the ecological system, composed of the community (biotic view), the ecosystem (functional view), and the microchore (i.e., the spatial contigu-ity characters, sensu Zonneveld, 1995), which we will name ecocoenotope , and (2) the landscape , formed by   Ingegnoli / Landscape ecology’s contribution to vegetation science 157a system of interacting ecocoenotopes. Consequently, a landscape  can be definedasasystemofintertwiningand coevolving natural and human ecocoenotopes re-peated in a characteristic way over the land.No doubt some of the characters of community and ecosystem are available also at landscape level, and that the inverse is also true. Only reductionism pretends to separate all the characters related to each level. In contrast, we can note that each biological level presents unique  characters and exportable characteristics. For example, processes allowing the definitionoflifeare exportable  characteristics: each specificbiologicallevelexpresses this process in a unique  way, depending on its scale, its structure, its functions, and its amount of infor-mation. Each system that presents unique  characteristics is an entity. We can findpropertiesuniquelycharacter-izing cell, organism, population, ecocoenotope, land-scape, ecoregion, and ecosphere. That is why we cannot describe the behavior of a landscape merely by scaling up an ecological system of communities (Fig. 1). The landscape level and its main structure To study the behavior of a landscape it is useful to focus on the main landscape apparatuses. The definitionof landscape apparatus (Ingegnoli, 2002) concerns func-tional systems of “tesserae” and/or ecotopes that form specificconfigurationsinthecomplexmosaic(i.e., ecotissue ) of a landscape. But how can we defineates- Fig. 1. Flow diagram representing ( above ) a plant community (i.e., association) according to Pignatti (1996). Note the two main complementary cycles: integration of spatial niches and formation of vegetation layers and humus.  Below , the representation of a system of plant communities (Ingegnoli, 1997), the main difference with that above being the cycle related to the transforma-tion of the ecotissue.   Israel Journal of Plant Sciences 53 2005 158sera and an ecotope in this new perspective? A tessera is the smallest homogeneous unit visible at the spatial scale of a landscape, multifunctional but tridimensional. It corresponds to the old definitionofecotope(asthesum of physiotope and biotope) and it may represent the hierarchical level of ecocoenotope. In contrast, an ecotope is the smallest multidimen-sional unitary element that presents all the structural and functional characters of the concerned landscape. It is the minimum system of interdependent tesserae (In-gegnoli, 2002). A landscape subsystem formed by a set of tesserae of the same landscape function (e.g., protec-tion) can be considered a landscape apparatus.A primary well-known landscape function is rep-resented by the survey of human habitat (HH) versus natural and semi-natural habitat (NH). The HH can be definedasthewholeareainwhichhumanpopula-tions live or manage permanently, limiting or strongly influencingtheself-regulationcapabilityofnaturalsystems. Self-regulating and near-natural ecosystems (i.e., almost unchanged after human abandonment) are NH. In landscape ecology the management role of hu-man populations—if not directed against nature—may be considered as a semi-natural function. Life processes and systemic attributes As expressed by some scientists (Ingegnoli, 1980, 1993, 2001, 2002; Naveh and Lieberman, 1984,1994; Naveh, 1987; Leser, 1997; Meffe and Carrol, 1997), the land-scape presents life processes and systemic attributes of a self-organizing system at each biological level. Con-sequently a landscape (1) follows non-equilibrium ther-modynamic, and (2) is subjected to the irreversibility of time, the Principle of Emerging Properties, the ‘order through fluctuation’process(PrigogineandNicolis,1977; Naveh and Lieberman, 1984, 1994; Ingegnoli, 1991, 1993, 2002; Prigogine, 1996). Focusing our attention on the main transformation processes concerning the landscape, let us review the main aspects:  Hierarchical structuring . The behavior of a landscape and of all ecological systems is limited by (1) the poten-tial behavior of its components (lower level of scale), and (2) the constraints of the environment (upper level of scale). These conditions represent the fieldofexis-tence in which the system of ecocenotopes must reside.  Metastability.  An ecological system can remain within a limited set of conditions, but it may present alterations if these conditions change. The system may cross a critical threshold, approaching even radical changes (Ingegnoli, 2002). Therefore, different types of landscapes may be correlated with diverse levels of metastability.  Non-equilibrium thermodynamic.  Thermodynamic bonds may determine an attractor that represents a condition of minimum external energy dissipation in its proper fieldofexistence.Possiblemacro-fluctua-tions produce instabilities that move the system towards a new organizational state. This new state allows an increase of dissipation and moves the system towards new thresholds to reach a new attractor. All this could be represented as a cybernetic process of “order through fluctuation”.  Evolutionary changes.  The structuring of every biologi-cal system may be reached (i.e., the information may be transmitted) only if the finalstateofthesystemconsideredis less unstable (i.e., more metastable) than its initial state. The modalities by which these processes are realized may be different and not limited to a single scale. Coevolution.  The history of the interactions among the elements of a landscape in a given locality shows a par-ticular dominion that is characterized by the coherence of the reciprocal adaptation of the elements themselves. This process leads to a stabilization of the different homeostatic capacities of a landscape, which may be expressed with a particular degree of metastability.  Reproductive processes. Each level of life organization presents typical reproductive components: (1) a system that maintains information, (b) a mutation, (c) a protec-tion of renewed elements, (d) a selection phase, and (e) a crucial disturbance eliminating the old structure. Therefore a landscape is able to reproduce itself. Ecological Reproduction At the organizational level of landscape, or of eco- coenotope, how does reproduction occur? There is no doubt that it is different from the same processes at organism level; nevertheless it has to occur. Informa-tion to be transmitted has to be circumscribed in time and space, e.g., in a propagule-bank. An outbreak effect must appear, for example, a “zero event” (Oldeman, 1990) or “crucial disturbance” (e.g., fire),allowingthe“propagula” to substitute previous organic structures. For instance, through the renewal of the tesserae forming an ecotope, a landscape may reproduce itself, following the typical sequence of reproductive pro-cesses (Table 1). From the point of view of vegetation science we have to underline the concept of ecological memory (Bengtsson et al., 2003). It could be divided into a within-patch memory and external memory to show the different ecological processes. The within-site processes can be viewed as assembly rules (e.g., propa-gule-bank, biological legacies, etc.), while among-site processes may include such landscape functions as   Ingegnoli / Landscape ecology’s contribution to vegetation science 159dispersal filters,pioneerbelts,oldtreesources,distancefrom source, and range of disturbances. Crucial distur-bances can be natural or human.Re-colonization also plays an important role in self-reproduction. Pioneer phases tend to be stochastic, but pioneer dynamics are oriented by strain conditions that depend on the structure and dynamic of the landscape unit. Time has a considerable functional importance: therefore, the recreative phases of the elements of a spe-cificlandscapehavetoavoidtoo-rapidtransformations.Even human colonization is able to reproduce typical ecotopes and landscapes almost all over the world. In doing this, cultural tradition plays an important role, even in an ecological sense. NEW FUNCTIONS AND NEW METHODSCrucial importance of vegetation in the evaluation of a landscape In reality, landscape ecology cannot represent the com-plexity of the landscape level only through an ecologi-cal mosaic. The new disciplinary model proposed by Ingegnoli (2002) is based on the ecotissue  (or ecological tissue) concept, a complex multidimensional structure built up by a main mosaic (generally formed by the vegetation coenosis) and a hierarchic set of correlated and integrated mosaics and information of different temporal and spatial scales. The role of vegetation coenosis is in accordance with a non-equilibrium thermodynamic. Whereas an energy concentration (i.e., photosynthetic plants) pro-duces structure and organization in a landscape matrix with increasing entropy, the “order through fluctuation”process creates a patch that acquires a specificlandscaperole. This may be the principal way through which ecological systems become heterogeneous (Ingegnoli, 1980, 1999; Forman and Moore, 1991). Consequently, a correct evaluation of the ecological state of a landscape is impossible without the evaluation of its vegetation. But this evaluation has to be in accordance with the above-mentioned landscape ecological principles, as follows: 1. First of all, the definitionofvegetationmustbe:the complex   of the plants  of a landscape element, con-sidered in their aggregation capacities and in their relations with environmental factors. Therefore, a cultivated tessera has to be considered as vegetation not only for its weeds (e.g., Secalinetea, Cheno- podietea ), but even for the cultivation itself (e.g., Triticum   aestivum ,  Hordeum   vulgare ), without which the weeds do not succeed and the tessera does not become the habitat for many natural species (e.g., Coturnix coturnix, Alauda arvensis ). Besides, this type of vegetation is a crucial ecological component for human populations.2. Therefore, the following statement: “Vegetation is organized in communities” (Pignatti et al., 2002) (Fig. 2) is necessary but not sufficient.Vegetationis organized in ecocoenotopes and in systems of interacting ecocoenotopes (i.e., landscape), thus involving both the hierarchic levels of the middle biological spectrum. Consequently, in Fig. 1 we may observe the emergence of other processes impossible to consider at the community level, e.g., the ecotope web, patch conditions, landscape disturbances, etc. 3. Finally, the processes of transformation of vegetation need to be synthesized following the studies of Falin-ski (1998) modifiedbyIngegnoli(2002),asshowninTable 2. The main processes are (1) Steady attractor, (2) Transitory variations, (3) Instability processes, (4) Destructive processes, (5) Recreative processes. Thus, a complete understanding of the transformation mo-dalities of the vegetation in a landscape need a proper ecological function able to quantify these changes. The biological territorial capacity of vegetation The linkage between the ecological balance of a land-scape and the ecological metastability has a very impor-tant dynamic significance.Tryingtoevaluatethemeta-stability of a landscape, one has to refer to the concept of biodiversity  (in this case, landscape diversity) and to the concept of latent capacity of homeostasis  of an eco-coenotope. We start from this second concept. Table 1Comparison of the main processes of reproduction of an animal population and of a landscape minimum unitPopulation renewal Reproduction process Ecotope renewalPredisposed gonads Reservoir of information Ecological memory (e.g., propagule bank)Chromosome crossing over Mutation Local disturbancesNest or parental cares Young structure protection Nursery nichesCompetition and predation Selection Competition and predationDeath, often deferred Old structure death Crucial disturbance
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