FOREST STRUCTURE:
Key to function
ESRM 304
Why Sample Forest Vegetation?
 Need
information on forest vegetation for
making sound decisions

What is the recreation potential?
What silvicultural treatment will result in best critical habitat
enhancement?
What silvicultural treatment will result in best growth &
regeneration of the trees?
What species is / are most suitable for reforestation?
What is the value of the timber and the land?
Is there sufficient value in timber to offset cost of
silvicultural treatments?
What is the status of biodiversity on the area?
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What is the status of the forest as a carbon sink?
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Why Sample Forest Vegetation?
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Ultimate objective is to obtain quantifiable
information about the resource that allows
reasonable decisions on its destiny,
management, and use
Forest Systems
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Forests are dynamic, biological systems;
changing continuously
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Trees change in size (growth)
Trees die when old, when harvested, and/or when
damaged by pathogens (mortality)
New trees enter the system (recruitment)
Forest Systems
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Four major stages of stand development
o
o
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Stand initiation stage
 Grass-forb
 Seedling-shrub
Stem exclusion stage
 Sapling-pole
 Intermediate
Understory re-initiation (mature)
Old-growth stage
Provide different habitats and growth potential
Forest Systems
Major stages
of stand
development
Forest Systems
Stand
dynamics
vector
Visualizing Stand Dynamics
Lowland site,
St. Edward
State Park
in 2004 C.E.
SVS under
LMS v2.0
Developed
in Silviculture
Lab here in
SFR (then
CFR)
Visualizing Stand Dynamics
Lowland site,
St. Edward
State Park
50 years
later, i.e.
in 2054 C.E.
Forest Structure / Constitution
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Determined by:
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Size variability
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Diameter
Height
Crown
Frequency of occurrence; shape, location of size
distribution
Age; shape, location of age distribution
Spatial arrangement of trees in stand
Forest Structure / Constitution
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Five Typical Stand Structures
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Even-aged stand
Two-aged stand
Balanced uneven-aged stand
Irregular uneven-aged stand
Even-aged stratified mixture
Represent different management options /
potentials
Five Typical Stand Constitutions
o
Even-aged stand
Five Typical Stand Constitutions
o
Balanced uneven-aged stand
Five Typical Stand Constitutions
o
Even-aged stratified mixture
Need to see the forest for the trees !
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Individual tree measurement forms the basis
for all forest assessment / inventory
Many relationships can be derived from
individual tree attributes
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Species
Age
Diameter
Height
Direct measurement, sampling, prediction are
all involved
Individual Tree Measurement
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Diameter
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Most frequently measured diameter is Diameter Breast Height,
or, DBH for short
DBH is average stem diameter (in inches!) outside bark of a
tree measured at breast height above ground level
 In U.S., breast height is taken to be 4.5 ft.
 On steep slopes measure on the uphill side of tree
 Leaning trees require measurement along the bole
 Trees forking below breast height are treated as two
 Trees forking above breast height – avoid swells
 Other stem deformities – move above it
Most commonly used measurement device is the D-tape
DBH
Diameter Measurement
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Diameter classes
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Very often expedient to summarize inventory data
into size classes based on DBH
No matter the size of class used – still measure to
nearest 0.1” !
1-inch classes
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2” class (1.6 to 2.5”), 3” class (2.6 to 3.5), …
2-inch classes
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4” class (3.1 to 5.0”), 6” class (5.1 to 7.0), …
Diameter Measurement
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Diameter
(size)
distributions
QuickTime™ and a
decompressor
are needed to see this picture.
Diameter Measurement
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Basal Area
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Cross sectional area of the tree at breast height –
assuming stem circularity – always in square feet! (in U.S.)
Area of circle, A = p r 2
Basal area, g = p (DBH/2)2 (1/12)2 = 0.005454 DBH2
Average stand DBH is a useful statistic for management
Quadratic Mean DBH (QMD) is the diameter of the tree
corresponding to the tree of mean basal area
QMD  Dg 
g
0.005454
Individual Tree Measurement
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Age
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Trees in temperate zones grow one distinctive layer of
wood per year so age is found by counting these annual
rings
 Care is needed to avoid counting ‘false’ rings
Tree Age:
 Total Age: Elapsed time since germination of a seed or
time since budding of a sprout or cutting
 Breast-height age: Elapsed time since tree height
exceeded breast height
Stand Age:
 Plantation age: Elapsed time since planting – regardless
of seedling age
Even-aged vs. Uneven-aged
Individual Tree Measurement
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Tree Height
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Total height: distance from tree base to tip
(volume, biomass, site quality)
Height-to-crown: distance from tree base to base
of live crown
Merchantable height: Height to a minimum top
diameter
Instruments are called “hypsometers”
Direct measurement: Height poles
 Indirect measurement
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Similar triangles
Trigonometric principles (clinometer)
T
Height Measurement
Tree Height = DT + BD.
O
DT/OD = tan(TOD), therefore, DT = OD x tan(TOD)
DB/OD = – tan(DOB), therefore, DB = – OD x tan(DOB),
D
B
Tree Height = OD x tan(TOD) + [– OD x tan(DOB)], or,
Tree Height = OD x [tan(TOD) – tan(DOB)].
Horizontal distance OD is measured with a tape.
Clino measures tangents of angles TOD, DOB in percent (100 x tan), so
Tree Height = OD x [TOD% / 100 – DOB% / 100], or
Tree Height = OD / 100 x [TOD% – DOB%]
Slope correction for height measurement
D
O
D’
OD/OD’ = cos(DOD’)
OD = OD’ x cos(DOD’)
Measure angle DOD’ with clinometer in degrees & plug into height
equation:
Tree Height = [OD’ x cos(DOD’)] / 100 x [TOD% –DOB%]
Some Stand Attribute Definitions
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Trees per unit area (TPA) – Average number of
live trees existing on a characteristic unit of area.
The most basic measure of stand density. (In
U.S.A., units are Trees Per Acre.)
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Height – (H, AveHt) Arithmetic mean height of all
trees in a stand.
Some Stand Attribute Definitions …
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Diameter Breast Height (DBH) – average diameter
of a tree stem (trunk, or bole) measured 4.5 feet
above general ground level on flat or gently
sloping terrain, otherwise measured from the
uphill side on sloping terrain. (In U.S.A., units are
inches.)
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Mean DBH (AveDBH) - The simple arithmetic
mean DBH of all trees in the stand.
Some Stand Attribute Definitions …
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Basal area (ba, sometimes g) – cross-sectional area
of a tree stem at breast height, assuming circular
cross-sectional shape. (In U.S.A., units are square
feet.)
Stand Basal Area (SBA, BA, or G) – sum of
individual tree basal areas in a stand.
Quadratic Mean DBH (DBHq, QMD, or sometimes
Dg) – the DBH of the tree with mean basal area
Some Stand Attribute Definitions
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Height in relation to age - Site Quality
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Trees are resource integrators
Site Index: The average height of undamaged
dominant trees at a reference age
Dominant tree height insensitive to crowding
Reference, or base, or index age chosen
appropriately
Species dependent
Sometimes dominant trees are unavailable;
challenge esp. in mixed stands
Requires trees on the site
Site Index
James King
(1966)
published
site index
curves for
Douglas-fir
in the
Pacific
Northwest
Continuous Forest Inventory
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The ONLY way to get a complete historical
record on forest change is to monitor
permanently monumented plots
Data from Permanent Sample Plots (PSP’s) is
for:
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Forecasting growth, i.e., developing and testing forest
simulation models
Studying the effects of cultural practices, insect attacks,
weather, climate, etc.
Studying how biodiversity, wildlife habitat quality, etc. …
change over time
Chief purpose is to assess change so forest
stewards are alerted to potential need for
changing practices or policies
Continuous Forest Inventory
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CFI is generally very low intensity
o
TSP’s will typically be used to supplement PSP’s
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CFI plots must be representative of the forest; no
special “reserve status”
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Systematic sampling is often used
o
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Stratified sampling is often messed up by natural disaster,
natural changes in species composition
Sample size determination is difficult
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Must be applicable now AND in the future
Large enough to be precise for several forest attributes
Sampling intensities often range from 0.1% to 1%
Continuous Forest Inventory
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Plot locations are usually determined using a transparent grid
with pin pricks on an appropriately scaled grid, then overlain
onto a photomosaic or other map of the ownership, then
transferred to 9 x 9” photos to take into the field
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Distance & bearing to plot center is determined from the
photo or map from a known permanent location (primary
control) to avoid bias
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Plot center is marked with aluminum stake, re-bar, or PVC
pipe
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Trees on plot are stapled, nailed and / or painted near breast
height
Continuous Forest Inventory
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Five percent of all plots (randomly selected) are
normally “check-cruised” for accuracy
Measurement interval is typically 3 to 10 years
Repeat measurement cycle is either annual or
periodic
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In a periodic survey, with periodic measurement interval
p, EVERY plot is measured every p years
In an “annual” survey, 1/p plots will be measured
EVERY year
Summary Remarks
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Measurement data collected from trees in a
forest system yields information
- Forest Structure / Function
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Four major stages of stand development
Five major age constitutions
Sound data enables sound stand, forest,
and landscape management decisions
Permanent Sample Plot Layout
Large Tree measurement plot
Small Tree measurement plot
 0.1 acre plot  37.2 foot radius
 white PVC pipe at plot center ; plot number
written on it w/ indelible ink
 all trees within the plot have aluminum tags
 0.025 acre plot  18.6 foot
radius
 same plot center as large plot
 trees are not tagged
 perimeter is not marked
 first tree on plot marked with pink flagging
Plot and Tree Enumeration Card
Page
Date
Forest
Team
Compartment
Stand
Plot
Aspect
Slope
Elevation
Tree
Spp
DBH
Ht.
Dist
S (o)
B. (%)
T. (%)
C. (%)
Add-on
of
Comment(s)
Upper Canopy Surveys
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Field Trip to St. Edward State Park
Tue 11 May
Depart from behind Bloedel Hall (C-10
parking lot) promptly at 12:30 P.M.
Bring appropriate clothes, sturdy footwear,
rain gear, etc.