GROWTH AND YIELD

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GROWTH ANDYIELD How will myforest grow? Dr.
Glenn GloverSchool of Forestry Wildlife
SciencesAuburn University
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GROWTH ANDYIELD Purpose of this presentationTo
introduce you to concepts and methods of
estimating growth and yield of forest stands and
how you can use these in management of your forest
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YIELD
is the amount of standing or existing volume,
weight, mass or other characteristic of interest
at a specified point in time
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Pine stand _at_ age 15 years 81 tons/ac of standing
merchantable fiber.
At age 20 same stand108 tons/ac of standing
merchantable fiber.
YIELD at age 15 is 81 tons/ac YIELD at age 20
is 108 tons/ac
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Stand thinned at age 20 removing 54 tons/ac At
age 27 stand has 100 tons/ac standing
Standing Yield _at_ age 27 100 t Total Yield at
age 27 is 100 t 54 t (thinned) 154 t/ac
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GROWTH
is the change in size, volume, weight or other
characteristic of interest over a specified time
period
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At age 15 years -- 81 t/ac yield At age 20
years -- 108 t/ac yield Periodic Growth over
five years 108 tons - 81 tons 27 tons 10
cords _at_ 2.7 tons/cord (5400 lb/cord) Average
ANNUAL Growth is (27 tons/ac) / 5 yrs 5.4
t/ac/yr 2 cords/ac/yr
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Basic conceptsof growth and yield using an
exampleplanted pine stand Example540
trees/acre plantedSite Index 65 feet at base
25 yrs
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Example Planted Pine StandNumber of trees/acre
by age
No thinning
540 trees/ac planted
400 tpa_at_ 16 yrs
300 tpa _at_ 22 yrs
500 tpa_at_ 8 yrs
200 tpa _at_ 30 yrs
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Example Planted Pine StandNumber of trees/acre
by age
No thinning
540 trees/ac planted
Realisticmortality trends
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Example Planted Pine StandNumber of trees/acre
by age
Thinning
540 trees/ac planted
Thin
Thin
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Example YIELD Curve
Lineargrowthphase
No Thinning
68 cds _at_ 35 yrs
54 cds _at_ 25 yrs
23 cds _at_ 15 yrs
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Example YIELD Curve
183 tons _at_ 35 yrs
147 tons _at_ 25 yrs
61 tons _at_ 15 yrs
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Maximum CURRENT annual increment
CAI This years growth
10 tons/ac (3.7 cords) at 16 and 17 years
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Maximum MEAN annual increment
MAI Yield/Age
or average up tothisyear
5.9 tons/ac/yr (2.2 cords) at 25 and 26 years
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Maximum MEAN annual increment
Thin?
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Biological maturity or maximum average
production
Current increment Mean increment
Economicmaturityconsiderstimevalue ofmoney
Economic maturity
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Age 25 Yield in tons/ac
800 160 t/ac540 148 t/ac350 130 t/ac
Unthinned
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80
Age 25 years
70
Age 10 years
60
50
Base age 25 yrs
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62 tons difference 23 cords
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41.3
Site prep only SP Herbaceous
control
26.3
29.5
10.8
19.6
8.8
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Site Index 60 ft (SP) Site Index
90 ft (SP HC)
SI90
90
SI60
26.3
60
19.6
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Yield at age 22 years
SI90 200 t/acSI60 100 t/ac
Double yield!?
NO!
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Site Index 60 ft Site Index 90
ftAdjusted curve
90
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26.3
60
19.6
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Adjusted yield
No thinning
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Types of Growth Yield Projections

• Growth Percent
• Stand Table Projection
• Growth and Yield Equations and Models

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Growth percent is a simpleexpression of growth
relativeto a starting value over aspecified
time period
Annual Simple Growth percent (Yield _at_ Age2 -
Yield _at_ Age1) X 100(Yrs in period X Yield _at_ Age1)
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Simple Growth PercentExample
Yield at age 15 yrs 47 tons Yield at age 20
yrs 69 tons Annual Growth (69 t 47 t) X
100 9.36 /yr (5 X 47 t)
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Simple Growth Percent Example Future Yield
Current Yield X ((AG X years) 1)
10047 tons X ((9.36 X 5 years)1) 69.0
t 100 69.8 tons X ((9.36 X 5 years)1)
101.4 t 100
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Simple Growth Percent Example(used to estimate
timber basis for tax) Yield at age 35 yrs 143
tonsWhat was yield 12 years ago? Assume 6
average annual growth Previous Yield Current
Yield ((AG X years) 1) 100
143 tons ((6 X 12 years)1) 83 t
100
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Stand Table Projection
Stand table projection uses a current diameter
distribution (stand table) and Recent Past
Growth (usually from increment cores) to
project or estimate future diameter
distribution(and growth and yield)
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Stand Table Projection
Stand Table Projection worksbest in thrifty
growing UNEVEN-AGED stands (for 10 years in
South), but can beused in EVEN-AGED standswith
CAUTION for short time periods (5 years in South)
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Example Stand (and Stock) Table
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Projected Stand Table
Using Growth Index Ratio RGrowth dbh class
size
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Current and Future Yield
No mortality
t tons
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Growth and Yield Equations
Mathematical equations that estimate yield
based on Stand ageSite index (indicator of
site quality)A measure of density (basal
area or number of trees)
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Growth and Yield Equations
Example--Bennett (1970) Slash Pine ln(V)
5.98812 121.713/S 19.758/A (cu. ft.)
0.89683 ln(B) V Volume Yield S Site
Index (base age 25 years) 60 ftA Age at
desired yield, in years 25 yr B Basal at
age A 150 sf (predicted
from another equation) V 2128 cubic feet 27
cords (_at_ 80 cf/cord)
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Diameter DistributionGrowth and Yield Models
Uses a series of equations to predict
distribution of number of trees by diameter
class for stand characteristics such as --
age-- stand basal area-- site index
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391 trees
346 trees
Generate stand tableEstimate height by
dbhCalculate yield (volume or weight)
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Individual TreeGrowth and Yield Models
A computer program links components of growth
tosimulate growth of individualtrees, then
aggregates thesetrees to provide
stand-level(per acre) growth and yield
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Individual TreeGrowth and Yield Models
The system isprimarily driven by
COMPETITIONamong neighboring trees
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Individual Tree Models
(from PTAEDA, VPISU)
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There is an adagethat states ALL MODELS ARE
WRONG, BUT SOME MODELS ARE USEFUL
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Most growth and yield models are developed from
(and predict) ideal stands. Models are
mathematical equations that CANNOT completely
mimic complex biological processes. Models MUST
be usedwith CARE, CAUTIONand EXPERIENCE
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In ConclusionThe proper inventory of products
(and other resources) on your forest and the
judicious projection of how your stands will grow
can help you make better decisions about your
forest.
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Making Good Decisionsis a KEY to
SuccessfulManagement ENJOY YOUR FOREST!