Physiognomy. Physiognomy is a combination of the external appearance of
vegetation, its vertical structure, and the growth forms of the dominant taxa.
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
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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.
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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)
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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
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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.
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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
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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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