FOREST STRUCTURE: Key to function
ESRM 304
Why Sample Forest Vegetation?
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?
Need information on forest vegetation for making sound decisions
Why Sample Forest Vegetation?
Ultimate objective is to obtain quantifiable information about the resource that allows reasonable decisions on its destiny, management, and use
Forest 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)
Forest Systems
Four major stages of stand developmento Stand initiation stage
Grass-forb Seedling-shrub
o Stem exclusion stage Sapling-pole Intermediate
o Understory re-initiation (mature)o Old-growth stage
Provide different habitats and growth potential
Major stages of stand develop-ment
Forest Systems
Stand dynamics vector
Forest Systems
Visualizing Stand DynamicsLowland site,St. Edward State Parkin 2004 C.E.
SVS under LMS v2.0Developed in SilvicultureLab here in SFR (thenCFR)
Visualizing Stand Dynamics
Lowland site,St. Edward State Park50 yearslater, i.e.in 2054 C.E.
Forest 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
Forest Structure / Constitution
Five Typical Stand Structureso Even-aged stando Two-aged stando Balanced uneven-aged stando Irregular uneven-aged stando 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
Can 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
Individual 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
DBH
Diameter 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), …
Diameter Measurement
Diameter (size) distributions
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Diameter 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 = r 2 Basal area, g = (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
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
Individual 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 polesIndirect measurement
Similar triangles Trigonometric principles (clinometer)
DT/OD = tan(TOD), therefore, DT = OD x tan(TOD)DT/OD = tan(TOD), therefore, DT = OD x tan(TOD)DB/OD = – tan(DOB), therefore, DB = – OD x tan(DOB),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) + [– OD x tan(DOB)], or,Tree Height = OD x [tan(TOD) – tan(DOB)]. Tree Height = OD x [tan(TOD) – tan(DOB)].
Horizontal distance OD is measured with a tape.Horizontal distance OD is measured with a tape.Clino measures tangents of angles TOD, DOB in percent (100 x tan), soClino measures tangents of angles TOD, DOB in percent (100 x tan), so
Tree Height = OD x [TOD% / 100 – DOB% / 100], orTree Height = OD x [TOD% / 100 – DOB% / 100], orTree Height = OD / 100 x [TOD% – DOB%]Tree Height = OD / 100 x [TOD% – DOB%]
Height Measurement
Tree Height = DT + BD.Tree Height = DT + BD.
OO
TT
BB
DD
Slope correction for height measurementSlope correction for height measurement
OD/OD’ = cos(DOD’)OD/OD’ = cos(DOD’)
OD = OD’ x cos(DOD’)OD = OD’ x cos(DOD’)
Measure angle DOD’ with clinometer in degrees & plug into height Measure angle DOD’ with clinometer in degrees & plug into height
equation:equation:
Tree Height = [OD’ x cos(DOD’)] / 100 x [TOD% –DOB%]Tree Height = [OD’ x cos(DOD’)] / 100 x [TOD% –DOB%]
OO DD
D’D’
Individual 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
Site Index
James King (1966) published site index curves for Douglas-fir in the Pacific Northwest
Continuous 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 (PSP’s) is for:o Forecasting growth, i.e., developing and testing forest
simulation modelso Studying the effects of cultural practices, insect attacks,
weather, climate, etc.o 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
CFI is generally very low intensityo TSP’s will typically be used to supplement PSP’s
CFI plots must be representative of the forest; no special “reserve status”
Systematic sampling is often usedo Stratified sampling is often messed up by natural disaster,
natural changes in species composition
Sample size determination is difficulto Must be applicable now AND in the futureo Large enough to be precise for several forest attributeso Sampling intensities often range from 0.1% to 1%
Continuous 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
Continuous 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
periodico In a periodic survey, with periodic measurement
interval p, EVERY plot is measured every p yearso In an “annual” survey, 1/p plots will be measured
EVERY year
Summary Remarks
Measurement data collected from trees in a forest system yields information- Forest Structure / Function
o Four major stages of stand developmento Five major age constitutions
Sound data enables sound stand, forest, and landscape management decisions
Permanent Sample Plot LayoutLarge Tree measurement plotLarge Tree measurement plot
0.1 acre plot 0.1 acre plot 37.2 foot radius 37.2 foot radius white PVC pipe at plot center ; plot number white PVC pipe at plot center ; plot number
written on it w/ indelible inkwritten on it w/ indelible ink all trees within the plot have aluminum tagsall trees within the plot have aluminum tags first tree on plot marked with pink flaggingfirst tree on plot marked with pink flagging
Small Tree measurement plotSmall Tree measurement plot
0.025 acre plot 0.025 acre plot 18.6 foot 18.6 foot radiusradius
same plot center as large plotsame plot center as large plot trees are not taggedtrees are not tagged perimeter is not markedperimeter is not marked
Plot and Tree Enumeration Card Page of Date Team Forest Compartment Stand Plot Aspect Slope Elevation Tree Spp DBH Ht. Dist S (o) B. (%) T. (%) C. (%) Add-on Comment(s)
Upper 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 12:30 P.M. Bring warm clothes, sturdy footwear, rain
gear, etc.