Vegetation Ecology

Eddy van der Maarel, Janet Franklin, Eddy van der Maarel, Janet Franklin

• Editore: Wiley-Blackwell
• Anno: 2012
• ISBN:
  9781118452486
• Edizione: 2
• Argomento: Biowissenschaften
• Categoria: Ökologie

Additional resources for this book can be found at: www.wiley.com/go/vandermaarelfranklin/vegetationecology. Vegetation Ecology, 2nd Edition is a comprehensive, integrated account of plant communities and their environments. Written by leading experts in their field from four continents, the second edition of this book:

• covers the composition, structure, ecology, dynamics, diversity, biotic interactions and distribution of plant communities, with an emphasis on functional adaptations;
• reviews modern developments in vegetation ecology in a historical perspective;
• presents a coherent view on vegetation ecology while integrating population ecology, dispersal biology, soil biology,
• ecosystem ecology and global change studies;
• tackles applied aspects of vegetation ecology, including management of communities and invasive species;
• includes new chapters addressing the classification and mapping of vegetation, and the significance of plant functional types

Vegetation Ecology, 2nd Edition is aimed at advanced undergraduates, graduates and researchers and teachers in plant ecology, geography, forestry and nature conservation. Vegetation Ecology takes an integrated, multidisciplinary approach and will be welcomed as an essential reference for plant ecologists the world over.

1

Vegetation Ecology: Historical Notes and Outline

Eddy van der Maarel¹ and Janet Franklin²

¹University of Groningen, The Netherlands

²Arizona State University, USA

1.1 Vegetation Ecology at the Community Level

1.1.1 Vegetation and Plant Community

Vegetation ecology, the study of the plant cover and its relationships with the environment, is a complex scientific undertaking, regarding the overwhelming variation of its object of study, both in space and in time, as well as its intricate interactions with abiotic and biotic factors. It is also a very modern science with important applications in well-known socio-economic activities, notably nature management, in particular the preservation of biodiversity, sustainable use of natural resources and detecting ‘global change’ in the plant cover of the earth.

Vegetation, the central object of study in vegetation ecology, can be loosely defined as a system of largely spontaneously growing plants. Not all growing plants form vegetation, for instance, a sown corn field or a flowerbed in a garden do not. But the weeds surrounding such plants do form vegetation. A pine plantation will become vegetation after some years of spontaneous growth of the pine trees and the subsequent development of an understorey.

From the early 19th century onwards, vegetation scientists have studied stands (small areas) of vegetation, which they considered samples of a plant community (see Mueller-Dombois & Ellenberg 1974; Allen & Hoekstra 1992). Intuitively, and later on explicitly, such stands were selected on the basis of uniformity and discreteness. The vegetation included in the sample should look uniform and should be discernable from surrounding vegetation. From early on, plant communities have been discussed as possibly or certainly integrated units which can be studied as such and classified. Most early European and American vegetation scientists did not explicitly make a distinction between actual stands of vegetation and the abstract concept of the plant community. This distinction was more important in the ‘Braun-Blanquet approach’ (Westhoff & van der Maarel 1978). This approach, usually called phytosociology, was developed in Central Europe in the early decades of the 20th century, notably by J. Braun-Blanquet from Zürich, and later from Montpellier. The Braun-Blanquet approach, also known as the Zürich–Montpellier school, became the leading approach in vegetation science. It has a strong emphasis on the typology of plant communities based on descriptions of stands, called relevés. This can be understood because of its practical use (see also Chapter 2). However, Braun-Blanquet (1932, 1964) paid much attention to the relations of plant communities with the environment and the interactions within communities (see Section 1.1.2), which is now incorporated in the concept of ecosystem.

A plant community can be conveniently studied while separated from its abiotic and biotic environment with which it forms an ecosystem, even if this separation is artificial. In a similar way, a community of birds, insects, molluscs or any other taxonomic group under study, including mosses and lichens, can be studied separately as well (see Barkman 1978). One can also describe a biotic community, i.e. the combination of a plant community and several animal groups (Westhoff & van der Maarel 1978).

Uniformity and distinctiveness. As mentioned above, the delimitation of stands of vegetation in the field is based on an internal characteristic, i.e. uniformity, and an external one, i.e. distinctiveness. Distinctiveness of a stand has been much discussed and interpreted. Distinctiveness implies discontinuity with surrounding vegetation. This is sometimes very obviously environmentally determined, for example in the case of a depression in a dry area, or the roadside vegetation between the road and a ditch in an artificial landscape. However, more usually the distribution of the local plant populations is decisive. This has been the case since H.A. Gleason (e.g. 1926) observed that species are ‘individualistically’ distributed along omnipresent environmental gradients and thus cannot form bounded communities. Note that this observation referred to stands of vegetation, even if the word community was used! The wealth of literature on ordination (see also Chapter 3) offers ample evidence of the ‘continuum concept of vegetation’ (McIntosh 1986).

Gleason and many of his adherers criticized the community concept of F.E. Clements (e.g. 1916), the pioneer in succession theory, who compared the community with an organism and, apparently, recognized plant community units in the field. However, this ‘holistic approach’ to the plant community had little to do with the recognition of plant communities in the field.

Shipley & Keddy (1987) simplified the controversy by reducing it to the recognition of different boundary patterns in the field. They devised a field method to test the ‘individualistic and community-unit concepts as falsifiable hypotheses’. They detected the concentration of species distribution boundaries at certain points along environmental gradients. In their study – as in other studies – boundary clusters are found in some cases and not in others. Coin­cidence of distribution boundaries occur at a steep part of an environmental gradient, and at places with a sharp spatial boundary or strong fluctuations in environmental conditions (see also Chapter 3).

The occurrence of different boundary situations as such is of theoretical importance. They can be linked to the two types of boundary distinguished by C.G. van Leeuwen and put in a vegetation ecological framework (see Westhoff & van der Maarel 1978; van der Maarel 1990). The first type is the limes convergens which can be identified with an ecotone sensu stricto or tension zone. Here species boundaries can be determined strictly by abiotic conditions, which shift abruptly, in space and/or in time, although interference between species may play a part (e.g. Shipley & Keddy 1987); the ecotone may also be caused or sharpened by plants, the so-called vegetation switch (Wilson & Agnew 1992). The opposite type of boundary, limes divergens or ecocline, is typically what we now call a gradient where species reach local distribution boundaries in an ‘individualistic’ way along gradually changing environmental conditions (van der Maarel 1990).

Despite the general appreciation of the individualistic character of species distributions, it has been recognized that ‘there is a certain pattern to the vegetation with more or less similar groups of species recurring from place to place’ (Curtis 1959). This was further elucidated by R.H. Whittaker (e.g. 1978). Indeed, the individualistic and community concepts are now generally integrated (e.g. van der Maarel 2005).

1.1.2 Plant Communities: Integrated, Discrete Units or a Convenient Tool

Concepts. Within the neutral definitions of plant community quite different ideas and opinions on the nature of the plant community have been expressed since the early 20th century and the discussion is still going on. The controversy between Clements and Gleason has been an important element in this discussion. Allen & Hoekstra (1992) posited that the contrasting viewpoints of the two masters were influenced by the differences in the landscapes where they grew up. Clements was brought up in the prairie landscape of Nebraska and viewed plant communities as units from horseback, while Gleason walked through the forest, from tree to tree, aware of the small-scale differences within the community. Thus, the different environments may have had a decisive influence on their ‘perspective’.

However, two outstanding European contemporaries of Clements and Gleason do not fit this interpretation. The Russian plant ecologist G.I. Ramenskiy, who is generally considered the father of ordination and who was a Gleasonian avant la lettre, demonstrated the individuality of species distributions along gradients with meadow vegetation. On the other hand, the Finnish forest ecologist A.K. Cajander developed an authoritative typology of Finnish forests (e.g. Trass & Malmer 1978). Apparently, emphasizing that continuities, or rather discontinuities, can be done in any plant community type and this has to do with intellectual attitude rather than upbringing and field experience. Westhoff & van der Maarel (1978) considered that the ‘organismal concept’ of Clements versus the ‘individualistic concept’ of Gleason, can rather be interpreted as the ‘social structure’ concept and the ‘population structure’ concept, respectively (see van der Maarel 2005).

Definitions. One or more of these different plant community concepts are reflected in the many plant community definitions available. The definition by Westhoff & van der Maarel (1978) is representative of phytosociology as it was developed in Central Europe, notably by J. Braun-Blanquet, and in Northern Europe by G.E. Du Rietz. However, it also reflects ideas from early Anglo-American plant ecology, both in Great Britain (A.G. Tansley) and the USA (F.E. Clements), notably the emphasis on the interrelations between community and environment and on species interactions: ‘a part of a vegetation consisting of interacting populations growing in a uniform environment and showing a floristic composition and structure that is relatively uniform and distinct from the surrounding vegetation’.

Several later definitions of the plant community reflected the outcome of the more recent debates on the holistic and individualistic concepts, and on the reality of emergent properties. They may emphasize the co-occurrence of populations (Looijen & van Andel 1999), interactions between individuals (Parker 2001), or the ‘phenomenological’ coincidence (Grootjans et al. 1996). ‘Emergent properties’ are causing the whole to be more than the sum of its parts, such as dominance–diversity relations (Whittaker 1965; Wilson et al. 1998). Weiher & Keddy (1999) proposed the term ‘assembly rules’. Grime (2001) paid attention to the mechanisms of plant community assembly. Details and more literature on aspects of integration are found in van der Maarel (2005).

In conclusion, a plant community is generally recognized as a relatively uniform piece of vegetation in a uniform environment, with a recognizable floristic composition and structure, that is relatively distinct from the surrounding vegetation. Even if the populations of the participating species are usually distributed individualistically in the landscape, they may well interact within the community and build up an integrated unit with emergent properties. At the same time, plant communities can be convenient units for conveying information about vegetation and its environment.

1.1.3 Vegetation Survey and Sampling

Whatever our aim, approach and scale of observation, vegetation – whether loosely defined or approached as a plant community, or as a unit in a higher level of integration – should be described and analysed. Vegetation characteristics are either derived from plant morphological characters, usually called structure, or from the plant species recognized, the floristic composition. In Chapter 2, R.K. Peet & D.W. Roberts present a detailed account of community description. Amongst the many different objectives, there are four common ones:

1 phytosociological: community classification and survey, dealt with in Chapter 2;

2 ecological: correlation of the variation in vegetation composition with variation in environmental factors, dealt within Chapter 3;

3 dynamical: study of vegetation changes; see Chapter 4;

4 applied: nature conservation and management, t...

Indice dei contenuti

• Cover
• Companion Website
• Title page
• Copyright page
• Contributors
• Preface
• 1 Vegetation Ecology: Historical Notes and Outline
• 2 Classification of Natural and Semi-natural Vegetation
• 3 Vegetation and Environment: Discontinuities and Continuities
• 4 Vegetation Dynamics
• 5 Clonality in the Plant Community
• 6 Seed Ecology and Assembly Rules in Plant Communities
• 7 Species Interactions Structuring Plant Communities
• 8 Terrestrial Plant-Herbivore Interactions: Integrating Across Multiple Determinants and Trophic Levels
• 9 Interactions Between Higher Plants and Soil-dwelling Organisms
• 10 Vegetation and Ecosystem
• 11 Diversity and Ecosystem Function
• 12 Plant Functional Types and Traits at the Community, Ecosystem and World Level
• 13 Plant Invasions and Invasibility of Plant Communities
• 14 Vegetation Conservation, Management and Restoration
• 15 Vegetation Types and Their Broad-scale Distribution
• 16 Mapping Vegetation from Landscape to Regional Scales
• 17 Vegetation Ecology and Global Change
• Supplemental Images
• Index