Download Lesson 12 - Alaska Geobotany Center

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.