Title: FOREST STRUCTURE: Key to function
1FOREST STRUCTURE Key to function
2Why 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?
- What is the status of the forest as a carbon
sink?
3Why Sample Forest Vegetation?
- Ultimate objective is to obtain quantifiable
information about the resource that allows
reasonable decisions on its destiny, management,
and use
4Forest Systems
- Forests are dynamic, biological systems changing
continuously - Trees change in size (growth)
- Trees die when old, when harvested, and/or when
damaged by pathogens (mortality) - New trees enter the system (recruitment)
5Forest Systems
- Four major stages of stand development
- 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
6Major stages of stand develop-ment
Forest Systems
7Stand dynamics vector
Forest Systems
8Visualizing 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)
9Visualizing Stand Dynamics
Lowland site, St. Edward State Park 50
years later, i.e. in 2054 C.E.
10Forest Structure / Constitution
- Determined by
- Size variability
- Diameter
- Height
- Crown
- Frequency of occurrence shape, location of size
distribution - Age shape, location of age distribution
- Spatial arrangement of trees in stand
11Forest Structure / Constitution
- Five Typical Stand Structures
- Even-aged stand
- Two-aged stand
- Balanced uneven-aged stand
- Irregular uneven-aged stand
- Even-aged stratified mixture
- Represent different management options /
potentials
12Five Typical Stand Constitutions
13Five Typical Stand Constitutions
- Balanced uneven-aged stand
14Five Typical Stand Constitutions
- Even-aged stratified mixture
15Can we see the trees for the forest?
- Individual tree measurement forms the basis for
all forest assessment / inventory - Many relationships can be derived from individual
tree attributes - Species
- Age
- Diameter
- Height
- Direct measurement, sampling, prediction are all
involved
16Individual Tree Measurement
- Diameter
- Most frequently measured diameter is Diameter
Breast Height, or, DBH for short - DBH is average stem diameter (in inches!) outside
bark of the 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
17DBH
18Diameter Measurement
- Diameter classes
- 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
- 2 class (1.6 to 2.5), 3 class (2.6 to 3.5),
- 2-inch classes
- 4 class (3.1 to 5.0), 6 class (5.1 to 7.0),
19Diameter Measurement
- Diameter (size) distributions
20Diameter Measurement
- Basal Area
- 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
21Individual Tree Measurement
- Age
- 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
22Individual Tree Measurement
- Tree Height
- 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
- Similar triangles
- Trigonometric principles (clinometer)
23Height Measurement Tree Height DT BD.
DT/OD tan(TOD), therefore, DT OD x
tan(TOD) DB/OD tan(DOB), therefore, DB OD
x tan(DOB), 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
24Slope correction for height measurement
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
25Individual Tree Measurement
- Height in relation to age - Site Quality
- 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
26Site Index
- James King (1966) published site index curves
for Douglas-fir in the Pacific Northwest
27Continuous Forest Inventory
- The ONLY way to get a complete historical record
on forest change is to monitor permanently
monumented plots - Data from Permanent Sample Plots (PSPs) is for
- 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
28Continuous Forest Inventory
- CFI is generally very low intensity
- TSPs will typically be used to supplement PSPs
- CFI plots must be representative of the forest
no special reserve status - Systematic sampling is often used
- Stratified sampling is often messed up by natural
disaster, natural changes in species composition - Sample size determination is difficult
- 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
29Continuous Forest Inventory
- 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 - Distance bearing to plot center is determined
from the photo or map from a known permanent
location (primary control) to avoid bias - Plot center is marked with aluminum stake,
re-bar, or PVC pipe - Trees on plot are stapled, nailed and / or
painted near breast height
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31Continuous Forest Inventory
- 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 - 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
32Summary Remarks
- Measurement data collected from trees in a forest
system yields information - - Forest Structure / Function
- Four major stages of stand development
- Five major age constitutions
- Sound data enables sound stand, forest, and
landscape management decisions -
33Permanent Sample Plot Layout
- Large 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
- first tree on plot marked with pink flagging
- Small Tree measurement plot
- 0.025 acre plot ? 18.6 foot radius
- same plot center as large plot
- trees are not tagged
- perimeter is not marked
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35Upper Canopy Surveys
- Field Trip to St. Edward State Park
- Tue and Wed (24th 25th)
- Depart from behind Bloedel Hall (C-10 parking
lot) promptly at 1230 P.M. - Bring warm clothes, sturdy footwear, rain gear,
etc.