Lesson 12 - Alaska Geobotany Center

Lesson 12: Community concepts andattributes• Plant community attributesSpecies compositionPhysiognomyVarious approachesPlant functional typesBIOME ModelPhenologyDiversity• Methods of describing plant communities– Discreet units: Plant associations– Continuum approach

Some characteristics of vegetation• Physiogonomy: aspects of plant architecture, the generaloutward appearance of the vegetation base on plant growthforms.• Species composition: the list of plant species in acommunity.• Species diversity: richness, evenness, alpha and betadiversity.• Phenology: the timing of major events in the life history ofthe component species.• Productivity: biomass, annual productivity, allocation ofproductivity.

Flora vs. vegetation?

Flora vs. vegetationFlora: a list of the plant species in a region (e.g., the flora ofAlaska).Vegetation: the mosaic of plant communities in a landscape orregion.Thus vegetation is a collective term for all the plantcommunities in the same way that flora is a collective termfor all the plant species.We describe plant communities not vegetation communities.

Physiognomy• Physiognomic approaches to describe vegetation are useful tohelp simplify the overwhelming complexity of species-leveldescriptions.• Refers to the general appearance of the vegetation, usuallyincorporating features of its vertical structure and growth forms ofthe dominant plant species.• Many approaches to describing physiognomy have been used.• The current trend is toward development of plant functional typesthat have meaning as far as specific elements of ecosystemfunction.

Profile diagrams (Davis and Richards)• Richards, Tansley, Watt,and Beard describednumerous Formations intropical systems, aimed atthe elimination of confusionin classification andterminology.• One of the mostdiagrammatic approachesto describe physiognomy.• Accurately measuredtransects through theforest, 200 m long andabout 25 m wide.• Often they would have tochop down the trees inorder to get the necessarymeasurements of crownheight and width.• Herbarium collections couldbe made of the trees, whichwere often quite tall.• This detail of the structurewas impossible to portraywith a photograph.

Dansereau s “lollipop diagrams”• Transparency: “Dansereau s scheme based on…”Based on:• Plant growthform• Plant size• Plant cover• Leaf shape• Leaf function(deciduous vs.evergreeen)• Leaf texture(sclerophyll,succulent,etc.)

Raunkiaer s Life FormsRaunkier’s Raunkier’s growth growth forms forms

Raunkiaer s life forms based on position ofperennating budThe guts of Raunkiaer s system was theclassification of plants according theposition of the overwintering(perennating) bud:Phanerophytes: perrenating buds on aerialshoots, 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 surfaceand includes all plants with bulbs or tubers,such as lillies and potatoes (5, 6).Helophytes: submerged rhizomes. Manysedges have this type of bud (7).Hydrophytes: true aquatic plants with theirbuds in the water (8, 9).Therophytes: no buds. Desert annuals aretherophytes.Raunkier’s Raunkier’s growth growth forms forms

Raunkiaer s biological spectraRaunkiaer used this system to catagorize all the plants in floras from different regions ofthe world.Here, we see the distribution of life forms for three very different regions, the a borealarea 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 alist of world plants.PhanerophytesChamaephytesHemicryptophytesGeophytesHydrophytesTherophytesLabradorcoast111752956(borealforest)Aden(tropicaldesert)332719317Seychelles(tropicalrainforest)616123216Normalspectrum379273113

Bioclimatic diagram showing distribution of global vegetationbased on life forms• Transparency: “Fig. 4.18. The bioclimatic diagram• after Dansereau.”

Küchler s life form categories

Plant Functional Types (PFTs)• It is not feasible to develop global models that include everyecosystem or every species. Therefore, various approaches arebeing used to group the multitude of plant species into moremanageable units that are considered important with respect toecosystem function.• These groups are based on a variety of plant characteristics,including growth forms, life forms, taxonomic groups or othercharacteristics depending on the application.• Numerous methods including: Solomon and Shugart 1993; Box1996, Noble and Gitay 1996; Woodward and Cramer 1996; Smith etal. 1997.

Response to the GlobalChange in TerrestrialEcosystems (GCTE)need for a smaller groupof “functional types” forglobal modeling efforts• Cover of Smith et al. 1997. Plant• Functional Types.

Plant Functional Types of Box (1981)Partial (!) list of the plantfunctional types developed byEugene Box.Widely accepted as perhaps thebest statement to date of aconsistent approach todescribing plant andcommunity physiognomy.However, it is still quite a long listand not particularly useful forglobal modeling effortsbecause of its complexity.• Table14 -1, p. 274, Smith et al. 1997

Vegetation types based on the plant functionaltypes of Box• This list of 15 globalvegetation types isderived from the PFTsof Box.•Table 8-2, p. 190, BBPGS,•Modified from Box 1996

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 thesmallest number of plant functional types, constraints anddriving variables that could still simulate broad features ofpresent vegetation of the Earth…”• This model then could be used to help predict thevegetation under altered climate scenarios, either in thepast or in the future.

Bioclimatic indices derived from climatic data in the Biomemodel• Table 14 -3, p. 280, Smith et al. 1997The limits of vegetation types were defined by various tolerance limits or climaticrequirements 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 bioclimaticindex were identified.

Environmental constraints of the PFT s in theBIOME modelA table could then be constructed that showed the environmental contraintsfor 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 thecombination of PFTs ineach of the majorvegetations types in theBIOME model.

Vegetation redistribution of Europe under a changed climate aspredicted by the BIOME model using two different climate models asdrivers• 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 climatechangescenarios, 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 standsof vegetation is the most basic survey method and central to allclassification methods.• Usually the information collected includes a list of plant species(vascular plants, bryophytes, lichens) with estimates of theirpercentage cover. (The fungi, algae and microflora are usuallyanalyzed by specialists in these fields.)• The relevé method of the Braun-Blanquet approach is the mostthorough method and will be discussed in Lesson 14.

Braun-Blanquet sorted Example tableTable approach of Species to vegetation classificationBraun-Blanquet sorted-tableanalysis method

Species diversityThere are two meanings of diversity in the literature:(1) (The most common application of the term.) The total number ofspecies in a community, more accurately called richness.(2) (Probably the more accurate way to use the term.) A measure thatcombines richness with relative abundance or evenness:– Richness: the number of species per unit area.– Evenness: the distribution of individuals among the species. This ismaximized when all the species have the same number of individuals.– Diversity: A combination of richness and evenness, i.e. richnessweighted by evenness.If community A has 5 species with uneven numbers of individuals,and community B has 4 species with equal numbers ofindividuals, A will have higher species richness, but B may have ahigher diversity.

Simpson s and Shannon-Wiener s indices ofdiversity• The Simpson index (C)is calculated:C = (p i) 2where p i is the proportion of all individuals in the sample that belong tospecies i.The Simpson index weights the most abundant species more heavily thanrare species• The Shannon-Wiener index (H ) is an index of the total amount ofinformation in a sample.H = - (p i)(ln p i),where p i is the proportion of all individuals in the sample that belong tospecies i.The Shannon-Wiener index varies from 0, for a community with onespecies only, to values of 7 or more in rich forests.

Examples of how the diversity indices vary with differentabundance 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 “withinhabitat diversity”. It is often considered the number of plantspecies in a given habitat. This can be waited by theabundance of the species as in the Shannon-Weiner indexof diversity.• Beta diversity is the “between habitat diversity”. It is thediversity of plant communities or the amount of speciesturnover along a ecological gradient. It is often consideredthe diversity of plant communities in a landscape.

PhenologyThe study of the time of appearance of characteristic periodicevents in the life cycles of organisms and how these eventsare influenced by factors, such as temperature, latitude,and altitude. For example, the timing of flowering and leaffall in plants.

Phenology diagram for Acomastylis rossii in different habitats onNiwot Ridge, ColoradoShows the timing ofvarious events inthe life history of aspecies.The example showshow snow affectsthe timing ofgrowth in onespecies.Early season eventsare shifted aboutone month later,but seed dispersalis initiated at aboutthe same time.

Phenophase diagrams 1983,Niwot Ridge, ColoradoShow the timing of eventsfor a variety of climate,plant, insect, birds andmammals

Phenological diagrams ofin selected species in aTrifolium-Melampryumcommunity, Göttingen,Germany

• BiomassIndices of biomass– Clip harvest– Harvest and regression method for trees• Productivity• Percentage cover– Scalar estimates– Measurement• Leaf area index• Vegetation indices (e.g. NDVI, normalized differencevegetation 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, BBPGSVegetation occurs indiscreetrecognizable units.Several species cooccuralong theenvironmentalgradient.Ecotones are rathernarrow portions ofthe gradient.Ecologists focus onclassification ofplant communitiesoften have this view.

“Association-unit” view of plantcommunities• Associations are repeating assemblages of plants that canbe found in similar habitats.• These assemblages can be classified according to the totalfloristic composition of the communities.

Major proponents of the “discreet unit” orassociation viewBraun-Blanquet Clements

The Braun-Blanquet viewIn Europe, during the 1930 s, Braun-Blanquetdeveloped a method of describing andclassifying vegetation into discreet units,that he called Associations.This method became the central concept ofthe Zurich-Montpellier School ofphytosociology. It gained wideacceptance throughout Europe and muchof the world. We will discuss this methodin some depth in another lesson.In North America, no single method ofclassifying vegetation ever developed.Braun-Blanquet

Clement s view• Clements, recognized discreet units. In1898 he wrote thePhytogeography ofNebraska, and later described much ofthe vegetation of North America, namingregional formations, associations andseral stages. He described climaxassociations, and wrote about thecauses of succession.• His views were immensely popularduring the 1930s and 1940s.• He metaphorically described plantassociations in terms of an organismwith a birth and death which occurred inthe process of succession. He used themetaphor, probably excessively, todescribe the interdependent nature of theassociated species.• Later ecologist have derided this“organismic” view.• There was somewhat of a revival of someClements ideas with the advent of theGaia hypothesis.Clements

Continuum view• Fig. 8-2a, p. 185, BBPGSSpecies tend to come and go along an gradient according toeach species individualistic response to the environmentalvariable.This individualistic view of species response to environmentalgradients was first suggested by Henry Gleason in the US in1926, although Ramensky presented a similar concept earlilerin Russia.

Major proponents of the continuumapproachGleason Curtis Whittaker

Henry Gleason• Student of Cowles; primarily a taxonomist,with a strong grounding in the'physiographic ecology' of Cowles. Healso conceived plant associations interms of floristic composition, but heviewed these associations blending intoeach other continuously with no discreetboundaries.• Disputed Clement's organismic approachand developed the individualistichypothesis, which stressed the importanceof species over community aspects.• He was considered a heretic and a "goodman gone wrong" from 1926 until the late1940's and early 1950's when Cain, Curtis,Whittaker and others began developingideas of continuum approach. Gleasondeveloped his views while studying theplant communities along the length of theMississippi River Valley.

A broader view of Gleason: Nicholson (1990)• Later in life, Gleason acknowledged the advantage and practicalimportance of identifying and classifying plant communities (Nicholson,1990, p. 152) and even did not object to something very similar tomonoclimax hypothesis of Clements as long as the history and individualnature of species were recognized as the prime movers of ecologicalsuccession (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 becauseof the dominance of Clementsian ideas at the time, he eventually had a tremendousinfluence on American plant ecology.• In the 1950 s, John Curtis and his colleagues at the University of Wisonsin developedmethods of indirect ordination of plant communities, whereby stands of vegetation wereorganized mathematically by the floristic similarity to each other. In the next 40 years,these mathematical approaches almost totally replaced methods of classification basedon table analysis.• About the same time that Curtis was working in Wisconsin, Robert Whittaker waslooking 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 viewalso recognized the validity of the association approaches used in Europe. He edited aclassic book entitled Classification of Plant Communities which summarized theapproaches from many schools and attempted a synthesis of ideas.• In Europe, during this period, vegetation science was and still is dominated by theassociation approach of Braun-Blanquet.

Whittaker s data of tree species occurrence along moisture gradients in theSiskiyou Mountains, Oregon and Santa Catalina Mountains, ArizonaSiskiyou Mtns.Santa Catalina Mtns.• Show Robert Whittaker s data for the abundance of all tree species alongelevation/moisture gradients in two mountain ranges.• These data tend to support the view of Gleason. A number of other studieshave also supported this view.• Over the last 45 years, there have been heated debates between plantcommunity ecologists regarding whether the views of the associationapproach are valid at all.

Anglo-American reaction to the European vegetation analysismethods“…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 haveoften 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 northernmontane vegetation, either unistratose or havign a relatively simple stratification. If one looksthrough illustrations in Braun-Blanquet s Pflanzensoziologie one cannot but be struck by the highproportion 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 Gleason s idea of themature association as being in a high degree individualized in its relationship to habitat. If this viewis accepted, it follows that the environment is infinitely variable, associations must be so also. Thegrouping of stands into abstract association can only be approximate and th abstract association isundefinable and ipso facto unclassifiable.”R.C. McLean and W.R. Ivimey-Cook 1973Textbook of Theoretical Botany

European reaction to the “Anglo-American” view“Whether because of the Tansley and Chipp book or because of the forceful andconvincing writing of a group of American plant ecologists, or, perhaps more likely,because of the linguistic provincialism of the English-speaking people even amongscientists, an “Anglo-American school of plant ecology developed, and for nearly ahalf-century has practically dominated vegetation science in English speaking partsof the world. The remarkable developments in continental and Soviet geobotany andphytosociology have remained little-known and scarcely understood by mostEnglish-speaking ecologists and disciples and students. Even Fuller and Conrad sEnglish translation of Braun-Blanquet s work (1932) produced scarcely a ripple in theself-contained complacency of the Clementsian and Tansleyan schools of thought inthis field.”Fosberg, 1974Introduction 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 samplingmethods are keys to which view is supported.• Association views are essential to describing, classifying, and mappingthe variation in vegetation. These units are somewhat subjective in nature.The methods of Braun-Blanquet have been applied now throughout theworld to widely divergent vegetation and offer a consistent globalframework for the classification and analysis of vegetation.• The continuum view more realistically describes the transitions in realvegetation, particularly across long gradients. Ordination methods areuseful for detailed studies of the relationship of vegetation to complexenvironmental gradients.

Summary• Some characteristics of vegetation:– Species composition (Braun-Blanquet)– Physiognomy (Davis, Richards, Dansereau, Kuchler, Raunkaier, Box, PlantFunctional 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 ofplants that can be found in similar habitats. These assemblages can be classifiedaccording to the total floristic composition of the communities. Major proponentsincluded Braun-Blanquet, Clements, Daubenmire.• In the “Continuum view” species have individualistic responses along anenvironmental gradients. Major proponents included Gleason, Curtis, and Whittaker.• A modern synthesis of the continuum and association views recognizes that bothview have validity and application for different aspects of community analysis

Literature for Lesson 12Gleason, H.A. 1926. The individualistic concept of the plant association. Bulletin of theTorrey 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 271-288 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 andcommunity analysis in vegetation science: some historical perspectives. Vegetatio69: 5-15.