Physiognomy
Plant Community Attributes
Physiognomy
•Architecture / Life Forms
•Leaf Area Index
•Phenology
•Plant Functional Types (PFTs)
Species Pattern
Physiognomy is a combination of the external
appearance of vegetation, its vertical structure, and the
growth forms of the dominant taxa.
Physiognomy is an emergent trait of the community.
•Vertical Structure
•Horizontal Structure
Species Composition
•Frequency
•Cover (Basal Area)
•Density
•Importance
Desert
Life Forms
Plant life form includes such
plant features as:
Size
Shape
Life span
Degree of woodiness
Degree of independence
General habit (morphology)
Position of apical buds
Leaf morphology
Phenology
Decid. Forest
Tundra
Life Forms
Contrary to what you might think, the great biomes of the
world share a remarkable amount of similarity in life
forms, regardless of wide taxonomic divergence.
Example: Chaparral from
Mediterranean, west coast of
U.S., west coast of South
America, and southern tip of
South Africa is almost
indistinguishable in
appearance (physiognomy).
Life Form Classification
Life Form Classification
Raunkiaer (1934)
Raunkiaer (1934)
One of the first to provide a comprehensive system of
plant life form classification based on their adaptations
for surviving the unfavorable season (winter cold or
summer drought).
Adaptations for survival linked to the protection
afforded to the sensitive apical meristems.
Recognized 5 groups: Phanaerophytes, Chamaephytes,
Hemicryptophytes, and Cryptophytes.
1=Phanaerophytes, 2-3= Chamaephytes,
4=Hemicryptophytes, 5-9=Cryptophytes
1
Leaf Area Index
Life Form Classification
Alternate System
The Leaf Area Index (LAI) is an important descriptor of
plant communities. It quantifies the amount of leaf overlap.
LAI is determined by collecting all of the leaves that
project in to a column of space that lies above an area of
ground (say 1m2), and their cumulative surface area is
measured:
LAI =
1=annual, 2=broadleaf evergreen + liana, 3=drought deciduous shrub,
4=winter deciduous broadleaf tree, 5=stem succulent, 6=bulbous
herbaceous perennial, 7=needle-leaf evergreen
Total leaf area (one surface only)
Ground area
Leaf Area Index
Phenology
LAI is strongly correlated to vegetation type:
Phenology is the study of the temporal aspects of recurrent
natural phenomena, and their relation to weather and
climate.
Vegetation Type
Tropical Rain Forest
Deciduous Forest
Boreal Conifer Forest
LAI
10-11
5-8
9-11
Grassland
Tundra
Semiarid Desert
Agriculture
5-8
1-2
1
3-5
Phenology is often used in physiognomic assessments to
refer to the vegetation as being:
Evergreen
Summergreen
Raingreen
Wintergreen
Plant Functional Types
Species Pattern
Box (1996) created a system of plant functional types
(PFTs) that are summarized on your handout.
Bisects are scale drawings of cut-away sections of forest.
They are useful in visually comparing and contrasting
different types of vegetation or stages of development.
PFTs are defined by vegetation type and traits of the
plants (branching pattern and leaf types).
He categorized all plants in to 15 PFTs and used these
to categorize different types of vegetation on a very
large scale (global). PFT was highly correlated to
climate and biome.
Vertical Structure
A bisect is generated by constructing a long thing strip
plot (usually 5-10m wide and 50-100m long) on the
ground and then drawing everything to scale that occurs
within that plot.
Beard and Richards were among the first to apply this
notion to the study of tropical forest in the 1930s & 1940s.
2
Bisect
Bisect
Comparing 2 Forests
Vegetation Height
a = height, eye to tree top
b = height, ground to eye
c = tree height
d = distance from eye to tree
θ = angle in degrees
a
Tan θ =
or a = d Tan θ
d
c=a+b
Vegetation height is an important aspect of
physiognomy and the bisect method. It is
frequently correlated with biome type.
Clinometer
(for measuring tree height)
Use a clinometer to determine
theta (see next slide).
a
c
θ
d
Improvised clinometer
b
level ground
Canopy Profiles
Canopy Profiles
Canopy profiles are frequently used to quantify canopy
denseness and coverage and were developed for the use
of wildlife habitat assessment.
Typical eastern deciduous forest
(3-4 layered)
Canopy profiles are essentially side-ways bar graphs
that summarize the amount of leaf coverage at different
heights within the vegetation.
They can be used stand alone or in conjunction with
bisects.
Typical taiga conifer forest
(1-2 layered)
3
Species Pattern
Species Composition
Horizontal Structure
Random
Regular
Clumped
One of the most descriptive elements of a community is an
identification of the "dominant" species.
Confirming
nonrandom pattern
(in horizontal
space) is the first
step in examining
vegetation
processes.
However, dominance is a generic word that really refers to a
whole suite of quantifiable parameters associated with
describing vegetation abundance.
All of these parameters first require that the community be
"sampled".
See http://www.orst.edu/instruct/bot440/wilsomar/HowToMeasure.htm
for a nice review of vegetation sampling methods.
Vegetation Sampling
In statistics, we collect data on a small subset (sample)
in order to make inference about the whole
(population).
Likewise, we do the same in vegetation ecology.
Because it would be impossible to count every tree in
the woods (census), we sample a smaller number and
make inferences about the whole forest.
Quadrats
A quadrat is simply a predefined area repeatedly used to
sample the vegetation of an area (usually placed at random).
Quadrats can be rectangular, square, or circular in shape and
vary in size depending upon the type of vegetation being
sampled (trees require large quadrats, mosses require small
quadrats).
The standard sample unit in vegetation ecology is the
quadrat.
Quadrats
Quadrats
Reel tapes can be used to lay out plots of any size in
forest environments. A compass is used to square off
corners and maintain 90-degree azimuths.
90º
25 m
Small quadrats can be constructed as frames (wood or
PVC); larger ones are laid on the ground using tapes.
There is an extensive literature regarding the size and
shapes of quadrats, which we will skip here.
25 m
4
Transects
Transects
Transects are simply lines (usually tape measures) that are
used to create a linear scale against which to sample (see
previous and following pictures).
Example of a transect
being used in a forest
environment.
Example: 35m transect with 5 randomly located (left vs.
right as determined by coin flip) 5×5m quadrats
m0
5
10
15
20
25
30
35
Species Abundance
Frequency
Quadrats and transects can be laid out within the vegetation
and data collected on species abundance. The three most
important parameters are:
Frequency
Cover (or basal area)
Density
Often, these parameters are combined to form a synthetic
index called an Importance Value (IV). An IV is determined
for each species in the community. Species with the highest
IVs are the most "important".
Frequency
A
D
m0
D
D
5
10
15
It has the advantage that it can be done quickly and does
not require one to determine how many individuals are in
the quadrat (only whether it is present/absent).
As a single parameter, frequency tends to be inaccurate for
rare species or those with a clumped distribution. It is also
uninformative for very common species.
Cover is the percentage of ground covered by a given species.
25
30
35
A
DA
A
Consider vegetation
containing 5 species:
A, B, C, D, E
The presence of each letter
in a quadrat represents an
individual of that species.
Frequency is the percentage of quadrats in which a species
appears.
Cover
BE
D
20
Note use of red-white
surveyor's chaining pin
to hold end of tape
secure.
D
A
In this example,
frequencies are:
A = 60%
B = 20%
C = 0%
D = 100%
E = 40%
E
Cover can be measured as aerial (canopy) cover (most easily
done from above with vegetation of short stature such as
grasslands or old-fields).
Cover can also be measured as basal cover or basal area--the
area occupied by the base of a plant (e.g., tussock grass or
tree).
Aerial photographs are very useful for measuring cover, but
can be quite time consuming.
5
Basal area (BA), or crosssectional area, is most often
determined for trees.
Cover
A =
0.4%
B =
64%
C =
9%
D =
12%
E =
15%
Basal Area
It is reported for each species as
the sum of tree areas per unit
ground area (but can also be
converted to a percentage; RBA).
Measure the diameter at breast
height (DBH) and determine the
cross-sectional area (using
formula for circle) for all trees in
plots. Sum by species & express
per unit area.
For example, the BA of white oak
might be 1.8 m2 ha-1.
Basal Area
Typically, for trees, one
measures the DBH using a
specially calibrated "dtape" (to read diameter
instead of circumference).
Density
Density is the number of individuals per unit area
(e.g., density of white oak = 112 stems ha-1).
Density can be measured only for species with
distinct individuals (e.g., trees).
Example: for 3 plots, each 10×10m, the density of
species A = 12 stems per 300m2 or 400 stems ha-1.
Example: d = 31.5 cm
A
BA = π(d/2)2 = 779.3 cm2
A A
B
Importance
Importance refers to the relative contribution of a species
to the entire community.
It can be used in an informal way to refer to the
intuitively determined dominant species. Plant ecologists
generally refer to an importance value (IV) for a species
and define this precisely as the sum of cover, density,
and frequency. More often it is relativized (RIV) as:
Relative Cover + Relative Density + Relative Frequency
RIV =
3
A
A
AA
A
A
B
B
A
A
A
B
Importance
For plant communities where
individuals are hard to identify (e.g.,
old-fields that are dominated by clonal
herbs), importance values do not
employ density as a measure of
abundance. Instead,
RIV =
Relative Cover + Relative Frequency
2
6
Community Summary Table
Community data are typically summarized in a table:
Species
FREQ
RFREQ DEN
RDEN
BA
16
36.36
652
66.67
Acer saccharum
4
9.09
23
2.35
Carya ovata
7
15.91
47
4.81
Fraxinus americana
14
31.82
198
20.25
Quercus alba
3
6.82
58
5.93
Quercus prinus
44
100
978
100
TOTALS
RBA
2.4
14.5
9.8
22.1
9.6
58.4
IV
4.11
24.83
16.78
37.84
16.44
100
RIV
107.14
36.27
37.50
89.91
29.19
300
35.71
12.09
12.50
29.97
9.73
100
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