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Lesson 12: Community concepts and attributes • Plant community attributes Species composition Physiognomy Various approaches Plant functional types BIOME Model Phenology Diversity • Methods of describing plant communities – Discreet units: Plant associations – Continuum approach Some characteristics of vegetation • • • • • Physiogonomy: aspects of plant architecture, the general outward appearance of the vegetation base on plant growth forms. Species composition: the list of plant species in a community. Species diversity: richness, evenness, alpha and beta diversity. Phenology: the timing of major events in the life history of the component species. Productivity: biomass, annual productivity, allocation of productivity. Flora vs. vegetation? Flora vs. vegetation Flora: a list of the plant species in a region (e.g., the flora of Alaska). Vegetation: the mosaic of plant communities in a landscape or region. Thus vegetation is a collective term for all the plant communities in the same way that flora is a collective term for all the plant species. We describe plant communities not vegetation communities. Physiognomy • • • • Physiognomic approaches to describe vegetation are useful to help simplify the overwhelming complexity of species-level descriptions. Refers to the general appearance of the vegetation, usually incorporating features of its vertical structure and growth forms of the dominant plant species. Many approaches to describing physiognomy have been used. The current trend is toward development of plant functional types that have meaning as far as specific elements of ecosystem function. Profile diagrams (Davis and Richards) • • • • • • Richards, Tansley, Watt, and Beard described numerous Formations in tropical systems, aimed at the elimination of confusion in classification and terminology. One of the most diagrammatic approaches to describe physiognomy. Accurately measured transects through the forest, 200 m long and about 25 m wide. Often they would have to chop down the trees in order to get the necessary measurements of crown height and width. Herbarium collections could be made of the trees, which were often quite tall. This detail of the structure was impossible to portray with a photograph. Dansereaus “lollipop diagrams” • Transparency: “Dansereaus scheme based on…” Based on: • Plant growth form • Plant size • Plant cover • Leaf shape • Leaf function (deciduous vs. evergreeen) • Leaf texture (sclerophyll, succulent, etc.) Raunkiaers Life Forms Raunkier’s growth forms Raunkier’s growth forms Raunkiaers life forms based on position of perennating bud The guts of Raunkiaers system was the classification of plants according the position of the overwintering (perennating) bud: Phanerophytes: perrenating buds on aerial shoots, as is the case with most trees (1). Chamaephytes: buds near the ground surface, as is the case with most dwarf shrubs (2, 3). Hemicryptophytes: buds at the ground surface (4). Geophytes: buds beneath the ground surface and includes all plants with bulbs or tubers, such as lillies and potatoes (5, 6). Helophytes: submerged rhizomes. Many sedges have this type of bud (7). Hydrophytes: true aquatic plants with their buds in the water (8, 9). Therophytes: no buds. Desert annuals are therophytes. Raunkier’s growth forms Raunkier’s growth forms Raunkiaers biological spectra Raunkiaer used this system to catagorize all the plants in floras from different regions of the world. Here, we see the distribution of life forms for three very different regions, the a boreal area on the Labrador coast, a desert area in Aden, and a tropical island., Seychelles. We can see the dominance of hemicryptophytes in the north, chamaephytes in the desert, and phanerophytes with various leaf sizes in the Seychelles. The “normal spectrum” was developed from an analysis of random 1000 species from a list of world plants. Phanerophytes Chamaephytes Hemicrypto phytes Geophytes Hydrophytes Therophytes Labrador coast (boreal forest) 11 17 52 9 5 6 Aden (tropical desert) 33 27 19 3 Seychelles (tropical rainforest) 61 6 12 3 2 16 Normal spectrum 37 9 27 3 1 13 17 Bioclimatic diagram showing distribution of global vegetation based on life forms • • Transparency: “Fig. 4.18. The bioclimatic diagram after Dansereau.” Küchlers life form categories Plant Functional Types (PFTs) • • • It is not feasible to develop global models that include every ecosystem or every species. Therefore, various approaches are being used to group the multitude of plant species into more manageable units that are considered important with respect to ecosystem function. These groups are based on a variety of plant characteristics, including growth forms, life forms, taxonomic groups or other characteristics depending on the application. Numerous methods including: Solomon and Shugart 1993; Box 1996, Noble and Gitay 1996; Woodward and Cramer 1996; Smith et al. 1997. Response to the Global Change in Terrestrial Ecosystems (GCTE) need for a smaller group of “functional types” for global modeling efforts • • Cover of Smith et al. 1997. Plant Functional Types. Plant Functional Types of Box (1981) Partial (!) list of the plant functional types developed by Eugene Box. Widely accepted as perhaps the best statement to date of a consistent approach to describing plant and community physiognomy. However, it is still quite a long list and not particularly useful for global modeling efforts because of its complexity. • Table14 -1, p. 274, Smith et al. 1997 Vegetation types based on the plant functional types of Box • •Table 8-2, p. 190, BBPGS, •Modified from Box 1996 This list of 15 global vegetation types is derived from the PFTs of Box. BIOME model (Prentice et al. 1992) • • • • Modelers require an even simpler approach. Prentice et al. developed the BIOME model. Goal is to “find the simplest possible model with the smallest number of plant functional types, constraints and driving variables that could still simulate broad features of present vegetation of the Earth…” This model then could be used to help predict the vegetation under altered climate scenarios, either in the past or in the future. Bioclimatic indices derived from climatic data in the Biome model • Table 14 -3, p. 280, Smith et al. 1997 The limits of vegetation types were defined by various tolerance limits or climatic requirements of the dominant plant functional types in each vegetation unit. The various tolerance or plant requirements were related to ecophysiological mechanisms. Bioclimatic indices that were tied to these ecophysiological requirements were identified. And the element(s) in the climate data base that could be used to calculate the bioclimatic index were identified. Environmental constraints of the PFTs in the BIOME model A table could then be constructed that showed the environmental contraints for the PFTs in the BIOME model: •Table 14 - 4, p. 282, in Smith et al. 1997 Assembling “vegetation types” from PFTs • Table 14 -5, p. 283, Smith et al. 1997. This table shows the combination of PFTs in each of the major vegetations types in the BIOME model. Vegetation redistribution of Europe under a changed climate as predicted by the BIOME model using two different climate models as drivers • Plates 1, 2, and 3, Cramer 1997 in Smith et al. 1997. Using the table of environmental constraints, and global maps of future climate conditions under various climatechange scenarios, it is possible to map the distribution of future vegetation types. The model is able to create new vegetation types from the PFTs if a new climate permits such a situation. Species composition • • • Detailed lists of species composition within representative stands of vegetation is the most basic survey method and central to all classification methods. Usually the information collected includes a list of plant species (vascular plants, bryophytes, lichens) with estimates of their percentage cover. (The fungi, algae and microflora are usually analyzed by specialists in these fields.) The relevé method of the Braun-Blanquet approach is the most thorough method and will be discussed in Lesson 14. Example of Species Braun-Blanquet sorted tableTable approach to vegetation classification Braun-Blanquet sorted-table analysis method Species diversity There are two meanings of diversity in the literature: (1) (The most common application of the term.) The total number of species in a community, more accurately called richness. (2) (Probably the more accurate way to use the term.) A measure that combines richness with relative abundance or evenness: – – – Richness: the number of species per unit area. Evenness: the distribution of individuals among the species. This is maximized when all the species have the same number of individuals. Diversity: A combination of richness and evenness, i.e. richness weighted by evenness. If community A has 5 species with uneven numbers of individuals, and community B has 4 species with equal numbers of individuals, A will have higher species richness, but B may have a higher diversity. Simpsons and Shannon-Wieners indices of diversity • The Simpson index (C)is calculated: C = (pi)2 where pi is the proportion of all individuals in the sample that belong to species i. The Simpson index weights the most abundant species more heavily than rare species • The Shannon-Wiener index (H) is an index of the total amount of information in a sample. H = - (pi)(ln pi), where pi is the proportion of all individuals in the sample that belong to species i. The Shannon-Wiener index varies from 0, for a community with one species only, to values of 7 or more in rich forests. Examples of how the diversity indices vary with different abundance of species • • Fig. 8-5, p. 195, BBPGS Put Table 8-4, p. 194 below the figure Alpha and Beta diversity • Whittaker (1972 ) defined alpha diversity as the “within habitat diversity”. It is often considered the number of plant species in a given habitat. This can be waited by the abundance of the species as in the Shannon-Weiner index of diversity. • Beta diversity is the “between habitat diversity”. It is the diversity of plant communities or the amount of species turnover along a ecological gradient. It is often considered the diversity of plant communities in a landscape. Phenology The study of the time of appearance of characteristic periodic events in the life cycles of organisms and how these events are influenced by factors, such as temperature, latitude, and altitude. For example, the timing of flowering and leaf fall in plants. Phenology diagram for Acomastylis rossii in different habitats on Niwot Ridge, Colorado Shows the timing of various events in the life history of a species. The example shows how snow affects the timing of growth in one species. Early season events are shifted about one month later, but seed dispersal is initiated at about the same time. Phenophase diagrams 1983, Niwot Ridge, Colorado Show the timing of events for a variety of climate, plant, insect, birds and mammals Phenological diagrams of in selected species in a Trifolium-Melampryum community, Göttingen, Germany Indices of biomass • Biomass – Clip harvest – Harvest and regression method for trees • • Productivity Percentage cover – Scalar estimates – Measurement • • Leaf area index Vegetation indices (e.g. NDVI, normalized difference vegetation index) Productivity gradients • Fig. 8-7, p. 199, BBPGS Ways to describe plant communities • Association approach • Continuum approach Association Approach • Fig. 8-1, p. 183, BBPGS Vegetation occurs in discreet recognizable units. Several species cooccur along the environmental gradient. Ecotones are rather narrow portions of the gradient. Ecologists focus on classification of plant communities often have this view. “Association-unit” view of plant communities • • Associations are repeating assemblages of plants that can be found in similar habitats. These assemblages can be classified according to the total floristic composition of the communities. Major proponents of the “discreet unit” or association view Braun-Blanquet Clements The Braun-Blanquet view In Europe, during the 1930s, Braun-Blanquet developed a method of describing and classifying vegetation into discreet units, that he called Associations. This method became the central concept of the Zurich-Montpellier School of phytosociology. It gained wide acceptance throughout Europe and much of the world. We will discuss this method in some depth in another lesson. In North America, no single method of classifying vegetation ever developed. Braun-Blanquet Clements view • • • • • Clements, recognized discreet units. In 1898 he wrote thePhytogeography of Nebraska, and later described much of the vegetation of North America, naming regional formations, associations and seral stages. He described climax associations, and wrote about the causes of succession. His views were immensely popular during the 1930s and 1940s. He metaphorically described plant associations in terms of an organism with a birth and death which occurred in the process of succession. He used the metaphor, probably excessively, to describe the interdependent nature of the associated species. Later ecologist have derided this “organismic” view. There was somewhat of a revival of some Clements ideas with the advent of the Gaia hypothesis. Clements Continuum view • Fig. 8-2a, p. 185, BBPGS Species tend to come and go along an gradient according to each species individualistic response to the environmental variable. This individualistic view of species response to environmental gradients was first suggested by Henry Gleason in the US in 1926, although Ramensky presented a similar concept earliler in Russia. Major proponents of the continuum approach Gleason Curtis Whittaker Henry Gleason • • • Student of Cowles; primarily a taxonomist, with a strong grounding in the 'physiographic ecology' of Cowles. He also conceived plant associations in terms of floristic composition, but he viewed these associations blending into each other continuously with no discreet boundaries. Disputed Clement's organismic approach and developed the individualistic hypothesis, which stressed the importance of species over community aspects. He was considered a heretic and a "good man gone wrong" from 1926 until the late 1940's and early 1950's when Cain, Curtis, Whittaker and others began developing ideas of continuum approach. Gleason developed his views while studying the plant communities along the length of the Mississippi River Valley. A broader view of Gleason: Nicholson (1990) • Later in life, Gleason acknowledged the advantage and practical importance of identifying and classifying plant communities (Nicholson, 1990, p. 152) and even did not object to something very similar to monoclimax hypothesis of Clements as long as the history and individual nature of species were recognized as the prime movers of ecological succession (Nicholson, p, 152-153). Development of the American continuum view of plant communities: Gleason, Curtis, and Whittaker • Although Gleason was scarcely recognized at the time of his 1926 paper, mainly because of the dominance of Clementsian ideas at the time, he eventually had a tremendous influence on American plant ecology. • In the 1950s, John Curtis and his colleagues at the University of Wisonsin developed methods of indirect ordination of plant communities, whereby stands of vegetation were organized mathematically by the floristic similarity to each other. In the next 40 years, these mathematical approaches almost totally replaced methods of classification based on table analysis. • About the same time that Curtis was working in Wisconsin, Robert Whittaker was looking at vegetation along continuous elevation gradients in different areas of the USA. He also adhered to the continuum school of phytosociology, but he had a broader view also recognized the validity of the association approaches used in Europe. He edited a classic book entitled Classification of Plant Communities which summarized the approaches from many schools and attempted a synthesis of ideas. • In Europe, during this period, vegetation science was and still is dominated by the association approach of Braun-Blanquet. Whittakers data of tree species occurrence along moisture gradients in the Siskiyou Mountains, Oregon and Santa Catalina Mountains, Arizona Siskiyou Mtns. Santa Catalina Mtns. • • • Show Robert Whittakers data for the abundance of all tree species along elevation/moisture gradients in two mountain ranges. These data tend to support the view of Gleason. A number of other studies have also supported this view. Over the last 45 years, there have been heated debates between plant community ecologists regarding whether the views of the association approach are valid at all. Anglo-American reaction to the European vegetation analysis methods “…the predominance of sociological literature [in Europe] might disguise the fact that opposition exists, and partly because they illustrate the difficulties which workers in other parts of the world have often felt in trying to apply European ideas of vegetation to their own regions. It cannot be denied that European ideas of plant association are ased to a large extent on northern montane vegetation, either unistratose or havign a relatively simple stratification. If one looks through illustrations in Braun-Blanquets Pflanzensoziologie one cannot but be struck by the high proportion which deal with montane vegetation and how few with vegetation of complex character. In dealing with mixed forests difficulties begin to appear…[The]results agree with Gleasons idea of the mature association as being in a high degree individualized in its relationship to habitat. If this view is accepted, it follows that the environment is infinitely variable, associations must be so also. The grouping of stands into abstract association can only be approximate and th abstract association is undefinable and ipso facto unclassifiable.” R.C. McLean and W.R. Ivimey-Cook 1973 Textbook of Theoretical Botany European reaction to the “Anglo-American” view “Whether because of the Tansley and Chipp book or because of the forceful and convincing writing of a group of American plant ecologists, or, perhaps more likely, because of the linguistic provincialism of the English-speaking people even among scientists, an “Anglo-American school of plant ecology developed, and for nearly a half-century has practically dominated vegetation science in English speaking parts of the world. The remarkable developments in continental and Soviet geobotany and phytosociology have remained little-known and scarcely understood by most English-speaking ecologists and disciples and students. Even Fuller and Conrads English translation of Braun-Blanquets work (1932) produced scarcely a ripple in the self-contained complacency of the Clementsian and Tansleyan schools of thought in this field.” Fosberg, 1974 Introduction to Mueller-Dombois and Ellenberg, Aims and Methods of Vegetation Ecology A modern synthesis of the continuum and association views • • • Many studies have been done that support both views. Scale and sampling methods are keys to which view is supported. Association views are essential to describing, classifying, and mapping the variation in vegetation. These units are somewhat subjective in nature. The methods of Braun-Blanquet have been applied now throughout the world to widely divergent vegetation and offer a consistent global framework for the classification and analysis of vegetation. The continuum view more realistically describes the transitions in real vegetation, particularly across long gradients. Ordination methods are useful for detailed studies of the relationship of vegetation to complex environmental gradients. Summary • Some characteristics of vegetation: – Species composition (Braun-Blanquet) – Physiognomy (Davis, Richards, Dansereau, Kuchler, Raunkaier, Box, Plant Functional Types) – Species richness, evenness, and diversity (Simpson and Shannon-Wiener indices) – Phenology (phenology diagrams) – Biomass and productivity (harvests, productivity, cover, LAI, NDVI, etc.) • In the “Association-unit” view of plant communities are repeating assemblages of plants that can be found in similar habitats. These assemblages can be classified according to the total floristic composition of the communities. Major proponents included Braun-Blanquet, Clements, Daubenmire. In the “Continuum view” species have individualistic responses along an environmental gradients. Major proponents included Gleason, Curtis, and Whittaker. A modern synthesis of the continuum and association views recognizes that both view have validity and application for different aspects of community analysis • • Literature for Lesson 12 Gleason, H.A. 1926. The individualistic concept of the plant association. Bulletin of the Torrey Botanical Club, 53: 7-26. Clements, F.E. 1928. Nature and structure of the climax. Journal of Ecology, 24: 253-284. Cramer, W. 1997. Using plant functional types in a global vegetation model. Pages 271288 in Smith, T.M., H.H. Shugart, and F.I. Woodward. 1997. Plant Functional Types. Cambridge, Cambridge University Press. Noy-Meir, I. And E. van der Maarel. 1988. Relations between community theory and community analysis in vegetation science: some historical perspectives. Vegetatio 69: 5-15.