Clinal Genetic Growth Variation Within Two Douglas-Fir Breeding Zones Roy R. Sileo and Nancy L. Mandel
ABSTRACT- Twelve- and ten-year results of progeny tests of
1,275 wind-pollinated families of coastal Douglas-fir (Pseudo­
tsuga menziesii (Mirb.) Franco var. menziesii) are presented
along with maps of clinal genetic variation within two breed­
ings zones. Data originate from the two oldest progressive
tree-improvement cooperatives, called Vernonia and Molalla.
In both, the top 20 percent of the families were 7 percent
taller and 15 to 22 percent greater in volume than the mean
family. Division of the parent group at the outset into sets of
50 families at Vernonia and 25 families at Molalla revealed
that set means differed with origin within the breeding zone.
Scattergrams of all parents in each cooperative showed that a
downward shift of 1,000 feet in parent elevation, or a 10-mile
horizontal shift to the east or north, should provide 5 percent
more family height growth. Thus, there was evidence of
considerable clinal geographic variation within breeding zones.
Jsoheight patterns of clinal variation are complex and three­
dimensional, conforming to major topographic features in
each cooperative area.
How much genetic variation exists in populations of
coastal Douglas-fir? How large a zone should be used
for breeding or for seed orchards? New information on
both questions is now available from progeny tests
begun over a decade ago on 1,275 parent trees.
Although a variety of tree improvement programs are
used in the Douglas-frr region of Oregon and Washing­
ton, the "progressive" program, jointly sponsored by the
Industrial Forestry Association and USDA Forest Ser­
vice research, is by far the most common one (Sileo and
Wheat 1979). It is divided into successive phases, in the
first of which seedlings from wind-pollinated seed are
used to test progeny of very large numbers of parent
trees per breeding woe. Subsequent phases with cross­
pollinated seed are not discussed in this article.
Most of the progeny testing is done through 19
tree-improvement cooperatives that use the same basic
test designs. Hence, there is a broad and keen interest
within the Douglas-fir region concerning the outcome of
any data analyses involving the two oldest cooperative
programs. These are the Vernonia and Molalla coopera­
tives begun in 1966 and 1968, respectively, and named
from small Northwest communities which they surround.
Analyses of 1978 data from these pioneer programs
reveal how much genetic variation other owners might
expect to see in their own tests. Also, the computer
programs developed to analyze these two programs will
probably set most of the procedures likely to be used on
other owners' data.
Beyond such regional interests is the broader question
of defining boundaries and size of breeding zones. As
elsewhere a decade ago, the breeding zone of each
cooperative was delineated geographically from rather
scant ecological information. Can zones now be better
determined directly from the progeny tests by mapping
genetic variation? Campbell (1980) has recently shown
that genetic variation in growth was related in three
dimensions, with surprising precision, to the topography
in a small valley in the Oregon Cascades. He sampled
wind-pollinated parents at a density of about one tree
per 100 acres. A lower sampling density of one parent
216/JOURNAL OF FORESTitY/Aprill983
per 400 acres routinely used in the "progressive" pro­
gram might still provide a reasonably useful genetic
map to delineate breeding zones. We explore this possi­
bility in the present article.
Vernonia and Molalla Programs
Topographic data
The Vernonia Cooperative embraces an area of fea­
tureless hills west of Portland, Oregon, south of the
Columbia River, and mainly east of the summit of the
Coast Ranges. Saddle Mountain (3,536 feet) at its south
end is the most prominent topographic feature. The
Sunset Highway runs through the southern half. About
60 percent of the forestland in the area is owned by the
four cooperators.
The Molalla Cooperative is in the Cascade foothills
southeast of Portland. It lies south of the Clackamas and
north of the North Santiam drainages and includes the
Molalla drainage. Topography is mainly a gentle slope
in the north but with quite dissected, hilly lands in the
south. The four cooperators own about one-third of the
land within the cooperative" boundary.
Statistics about the two cooperative areas are:
Vernonia
Ownership
Elevational range
Dimensions
Landowners
Molalla
350,000 acres
300-2,700 feet
49 by 29 miles
Crown Zellerbach
LOngview Fibre
State of Oregon
International
Paper Co.
-----120,000 acres
900-2,800 feet
43 by 22 miles
Crown Zellerbach
Longview Fibre
State of Oregon
Publishers' Paper
Co.
Progeny test information
Details of the test design for each cooperative are:
Item
Parent trees
Progeny tested
per family
Test sites
Sets·
Replications per
site
Vernonia
Molalla
----------Number---------­
900
375
102
12
18 of 50 families
5 on 9 sites
108
9
15 of 25 families
4
2 on 3 sites
Progeny per family
per replication
Progeny in test
2
91,800
3
40,500
Test sites in both programs were chosen to sample
forest conditions over the whole breeding zone, span­
ning the range of elevations, sites, aspects, and soil
types. Competing vegetation was removed by scarifica­
tion or burning before sites were replanted. Only 3 of 12
Vernonia and 5 of 9 Molalla test sites were fenced
against deer. Because serious damage occurred to tWo
Vernonia and one Molalla site, the informational loss
caused us to delete this data from the analyses.
In the Vernonia program . each test site contained
progeny of all 900 parents. Similarly, the Molalla pro-
gram sites contained progeny of 375 parents. The large
number of parent trees per cooperative necessitated
breakdown into sets of 50 or 25--small enough to
minimize site variation within a set replication of 100
progeny planted at 12-foot spacing. Parent trees in any
one set tend to be restricted to a small locality, an
important feature in the subsequent analysis.
Both cooperatives were initially considered as a logi­
cal single breeding zone with potential for an elevational
split. No split was made, however, because parent trees
in each were mainly from a central I ,000-foot band with
small fractions located higher or lower. Three parent
trees were chosen per 1,000 acres of ownership. The
progeny test was designed to minimize overall cost
while providing a strong test of the parent performance
over all sites. A strong family test on any site was
purposely foregone. Many sites were used to assure a
good sampling of the management conditions over the
whole breeding zone and, in addition, to permit a strong
stability test of performance trends of those families that
excelled on either good or poor sites.
Analysis information
Data were taken in the field on standardized forms.
We performed the analysis under arrangements in which
computer costs were financed by landowners through an
acreage assessment. Computer programs developed for
this analysis are to be used later to process data from
other cooperatives. Each landowner in these two coop­
eratives received printouts of the following analyses:
Rankings: Family performance within each set was
ordered by height and diameter on individual sites
and over all sites.
Analysis of variance and least significant differ­
ences (LSD): Significance of differences was tested
for family performance by site and over all sites.
Families exceeding LSD from set means were noted
in an array.
Correlation matrix: For each set, correlation coeffi­
cients of family heights were calculated between
every possible pairing of sites to assist in judging of
data from damaged sites.
Eberhart-Russell ( 1966) stability analysis: This anal­
ysis identifies families that perform well only on high
or on low sites, in contrast to the "stable" families
that do well on any site. (Results for individual
families are too detailed for presentation in this
article.)
Scattergrams: Family mean heights over all.sites and
correlation statistics were plotted over parent tree
elevation, latitude, and longitude.
.
Response surfaces: A stepwise multiple regression
was · performed of family mean heights on parent
elevation, latitude, and longitude. The expected fam­
ily heights were calculated for the center of the
I ,640-foot square area in which one or more parent
trees were located. Isoheight lines provided a map of
genetic variation over the cooperative ownership.
Parent Rankings and Analysis of Variance
The magnitude of average family height differences
over all sites at age 12 and 10 years is shown for each set
in tables 1 and 2. Statistically each of the 33 sets in the
two cooperatives is independent, hence is listed sepa­
rately for average and range as well as average height of
the top 20-percent component. For example, set 1 of the
Table 1. Vernonia test mean heights and variation, by
sets of 50 families. Parents In each set are located
within a rectangular area of dimensions shown.
TOP 20 PERCENTOF FAMILIES
GROWTH
SUPERIORITY
Range
Mean In
In
Dimensions Mean
height
height height volume
Miles
- - - - - - - - Feet- - - - - - - ---Percent--­
12-YEAR DATA
14.14 12.66-16.041 15.55 10.0 28.4 2
1
2 X 1
13.91
9.94-15.84
15.02
8.0 11.9
2
8 X 5
15.58
6.5 20.4
3
2 X 3
14.07 12.50-15.58
13.88 12.37-15.78
14.89
7.3 13.4
4
5 X 9
13.61 12.23-14.86
14.53
6.7 26.7
5
1 X 2
13.61 12.01-15.22
14.69
8.0 34.0
6
12 X 10
7.6 22.5
MEAN 5 X 53
13.87 11.94-15.55
14.92
10-YEAR DATA
9.41-12.79
7.9 15.6
11.61
7
8 X 11
10.76
6.7 21.4
11.48
10.76
9.18-11.74
8
12 X 15
9.58-11.64
11.28
6.5 21.0
9
3 X 4
10.60
6.9 25.4
10
6 X 11
10.86
9.61-12.40 11.61
8.92-11.74
11.15
11
9 X3
9.3 24.6
10.20
8.92-11.09
10.92
7.8 44.2
12
3 X 11
10.14
9.02-11.64
10.86
8.2 19.0
13
5 X 2
10.04
6.4 14.8
14
5 X 1
8.63-10.73. 10.43
9.81
11.45
8.4 19.7
10.56
9.23-12.07
15 11 X 2
8.~10.92
10.59
6.6 14.8
9.94
16 23 X 2
10.40
8.6 18.6
9.58
8.13-10.73
17 23 X 4
8.53-11.38
10.53
9.2 20.7
9.64
18 46 X 7
11.02
1.7 21.9
MEAN13 X 6
10.23
9.02-11.38
Set
ALL FAMILIES
1 Top families are significantly different (p = 0.05) tram· mean families in all 18
sets.
·
2 Family volume calculations assumed conical cross sections. Diameter for
each family ·was estimated from data on similar sized trees in plots near
.•
Corvallis, Oregon.
3 A1'9rage sets N-S and E-W dimension. Sets 1-6 c01'9r a 12- x 16-mile,
and 7-18 a 49- x 29-mi/e area.
Table 2. Molalla test mean heights and variation, by sets
of 25 families.
·
TOP20PERCENTOFFAMIUES
GROWTH.
SUPERIORITY
Dimensions Mean
Range
Mean In
In
height
height height volume
Miles --------Feet------- ---Percent--­
10-YEAR DATA
7.4
16.0
1
B X 11
10.63 8.89-11.64 1 11.41
18.0
8.1
10.76
2
3 X 6
9.94 8.53-11.19
18.6
3
7 X 9
10.33 9.55-11.64
11.22
8.6
4
4 X 5
10.40 9.45-11.91
11.19
7.6
18.4
11.22
8.2
18.6
5
2 X 4
10.37 9.51-11.87
6
5 X 4
10.86 9.15-11.94
11.55
6.3
14.9
11.22 10.27-13.15
7.6
16.4
7
2 X 4
12.07
5.7
12.7
11.42 10.5Q-12.60
12.07
8
11 X 14
12.1
12.10
5.7
9
6 X 13
11.45 10.6Q-12.20
6.5
14.8
10
1 X 2
12.83
12.04 11.19-13.02
7.3
16.2
11
9 X 3
10.79 9.74-11.74
11.58
11.68
8:5
19.0
12
2 X 4
10.76 9.25-11.94
11.48 10.37-12.37
12.17
6.0
14.1
13
1 X 2
5.8
13.3
11.38 10.69-12.73
12.04
14
1 X 4
11.02
7.7
1.5
2 X 3
10.23 8.95-11.61
15
2
7.1
15.0
MEAN 4 X 6
10.89 9.77-12.10
11.64
Set
ALL FAMILIES
1
Top tamUies are significantly different (p = 0.05) from mean families in all but sets 4, 9, and 10. 2
A1'9rage dimensions of sets 1-15. All 15 sets c01'9r a 43- x 22-mile area. Vernonia Cooperative shown in table 1 consists of 50
12-year-old families which range from 12.7 to 16.0 feet,
and have an average height over all sites of 14.1 feet.
Like all the sets in table 1 , top · families in set 1 are
statistically different from the set mean. Also listed is
an average height of 15.5 feet for the top 20 percent, a
April 1983/JOURNAL OF fORESTRY/217
~-
difference of 10.0 percent in height and 28.4 percent in
volume from the 14.1-foot average family in set 1.
Lastly, the parents are within a rectangle 2 miles from
north to south and 1 mile from west to east.
Genetic variation of these 1,275 families (tables 1
and 2) deserves a more detailed inspection than space
permits. Main interest of cooperators is the genetic
variation displayed by the top 20 percent of families in
each set. Practically, this selected group may approxi­
mate the balance desired between keeping a large ge­
netic base and achieving a reasonable selection intensi­
ty. In the average set, the top 20-percent group is about
7 percent taller and has 15 to 22 percent more volume
than the average family.
The two questions posed at the beginning of this
article arose from observing the large variation of family
averages from set to set. For example, in the 10-year
Vernonia sets 7-18 (table 1), set 10 averages 10.9 feet
or 5 percent taller and set 17 averages 9. 6 feet or 6 .4
percent shorter than the overall average of 10.2 feet-a
range of 11.4 percentage points. The most striking case,
however, is the comparison of sets 2 and 10 in the
Molalla Cooperative (table 2). The sets differ by 19.2
percentage points. Over all sites, the tallest family in set
2 attained only the same average height as the shortest
family in set 10-11.2 feet. The top 20-percent group in
set 2 (10.8 feet) is shorter than the average of nine other
sets. The top 20-percent group in set 10 (12.8 feet),
however, exceeds the height of the tallest family in 13 of
the 15 sets! In fact, the average tree in set 10 exceeds
the tallest tree in nine other sets. All parent trees in set
10 occur on a 2-square-mile area. The concentration of
tall or short families in certain geographic locales is
investigated more thoroughly in subsequent sections of
this article.
Other results deal with the large variation among
planting sites and the comparisons between heights
three years ago and now. This tabulation illustrates
planting site variability:
AVERAGE FAMILY HEIGHT
Site
Best
Average
Poorest
Vernonia
Molalla
- - - - - - - Feet - - - - - - ­
17.45
15.45
10.70
10.89
4.79
5.87
The major factor in this threefold difference is dam­
age by frost and animals at the poorest sites or use of a
formerly plowed field for the best. Even the best grow­
ing families on the poorest sites grew far below the
average height over all sites.
The main information from the analysis of variance is
that all the Vernonia sets and 12 of the 15 Molalla sets
had significant family differences, indicating that even
the frugal statistical design of the test has met expecta­
tions.
Family Height l'ersus Parent Tree Origin
Indications of clinal genetic variation within the two
breeding zones led to production of scattergrams of
family height versus parent tree elevation, latitude, and
longitude. The linear regressions are shown in figure 1.
The indicated geographic effects on 10-year height in
Vernonia and Molalla tests are:
Progeny are 5.9 (Vernonia) and 6.3 (Molalla) inches
taller per 1,000 feet lower elevation of parents.
218/JOURNAL OF fORESTRY/April 1983
Elevation
::E
"'iii
360
~
~
:r
.
300
0..
260
>
1:
longitude
~
.
~
1000
Feet
2000
~·''-121 -­
~
~
0
-;.­
Latitude
~
.<:
r-
0
10
20
30
Minutes
40
0
10
20
30
40
Minutes
Figure I. Regressions of average family height over all test
sites on elevation, latitude, and longitude. The indicated
genetic effect is about lh-inch more progeny height as parent
trees occur one mile nonhward or eastward or 100 feet lower
in the two breeding zones. With 375 and 600 parent trees as a
data base, the difference from zero slope is beyond the 1-in­
100,000 level of significance. Proportion of variance explained
by regression (? values) is shown in parentheses.
Progeny are 0.45 and 0_29 inch taller per mile
northward location of parents.
Progeny are 0.58 arid 0.44 inch taller per mile
eastward location of parents.
A seed source shift of 1,000 feet downward or 10
miles northward or eastward would be accompanied by a
5-percent increase in progeny height. Some sets from
low elevations in northerly or westerly parts of both
cooperatives have particularly high numbers of tall fami­
lies (sets 7-10 in Vernonia and 9-10 in Molalla).
Conversely, those at south, east, or higher locations
have a high proportion of short families (sets 14, 17,
and 18 in Vernonia, and 2, 3, and 15 in Molalla
cooperatives).
.
With such large numbers of families, the linear ef­
fects shown infigure 1 turn out to be different frorn zero
slope beyond the 0.00001 level of statistical signifi­
cance. This constitutes a strong indication, if not proof,
of clinal genetic variation within two relatively small
geographic areas in northwest Oregon. Both latitudinal
and longitudinal effects are confounded by elevational
differences, however. Questions arise as to what the
detailed pattern of geographic genetic variation may be.
Of more importance is how much of the growth superi­
ority attributable to the position of a parent within the
breeding zones can safely be used in a tree improvement
program.
Detailed Mapping of Genetic Variation
The simplest approach to providing detailed patterns
of inherent growth rates would be to record the mean
family height i.wer all sites at the coordinate location of
each parent, then draw isoheight contours in the same
way a topographic contour map is made. An improve­
ment we .tried was to reduce tree-to-tree variation .bY
pooling several neighboring parents to produce an aver­
age height for a small locale. Such preliminary maps for
both cooperatives did show surprising conformity with
topography in many localities.
We next smoothed family variation by a stepwise
regression that produced expected family average heights
for each 1,640-foot square containing one or more
parent trees. Then contoUr lines of isoheights were
drawn as was done earlier. by Campbell (1980). The
stepwise regression on family average heights included
only the contributions of latitude, longitude, and eleva­
tion, their products and their squares, that were signifi­
cant at the 0.05 level. The two regression equations are
noted in figure 2. The major effect iii both was from
latitude, which accounted for about three-fourths of the
30- to 36-percent total variation ex­
plained by the regression surfaces.
The Vernonia 12- and 10-year height
data had many more missing entries
than the Molalla data, and similar
procedures produced no correspond­
ingly fine isoheight detail. The
Vernonia data on average family
growth between years 7 and 10 are
not as much affected by early envi­
ronmental variation, and did provide
a topography-related map of genetic
variation.
The two maps of figure 2 show
the isoheight bands for each cooper­
ative area. The maps are noteworthy
in having many parallel bands of
isoheights that imply uniform gradi­
ents of geographic genetic change in
growth rate. Are these patterns re­
lated to topography and in turn to
environmental gradients? The iso­
lines obviously follow the general
v2~ 6.81><]0_,1-2
- s.3s·ro·''-£
landform in many instances, espe­
+ 1.10~JO~E'+4.40~10. D£
cially where parent tree sampling
- 2.31•10.' D'- 586
was dense. Unfortunately, there are
large unsampled areas on each map
L.• FMENT l.ATffiiDE IN 'fWI. (MII..IlN?I' 6R'ID,)
W~ERE. Yt=ffiEDICTW HEIGHTG~ E3E1WEEN
7AN.D 10 YEAR'5 IN CM.
D• FAA00"" l.ONGrTIJDf IN I(M.(MIUP.RY bi?IP,)
outside the cooperative ownership.
Yt= PR'I'DICTW 1UIN.. HEIGHT" AT 10 ~ EO=~ £!£VATION IN ME-TER;
For the Vernonia Cooperative, we
INCM.
noted that parents with slowest in­
Figure 2. lsoheight maps of family height. lsoheights are shown as percentage
herent growth fringed the Willamette
deviations
from overall mean family height in each cooperative area. Predicting
Valley and extended northward into
equations are given below each map.
the upper Nehalem drainage to
Vernonia. Parents expressing the best inher­
occasional. places where distinct banding occurred be­
ent growth lay in two bands at the summit of the
tween them, but a large portion of the area in the
flanking hills to the west and to the northeast of the
southern half followed a latitudinal rather than an
valley. The isoheight banding from best to poorest
elevational pattern.
growth rate was regular and parallel through the hills
Some Implications
west of the upper Nehalem-an expression of clinal
genetic variation. There was also a large expanse of
The substantial differences between average and best
parentage displayed in these progeny tests should not be
parents expressing fairly rapid growth on the Columbia
slope at the north end of the cooperative area. A
interpreted as genetic gains to be applied in future yield
particularly striking example of geographic variation is a
calculations. We are reporting on genetic differences
group of 60 parents from a 3-mile-square area east of
among small, open-grown tree families, averaging about
Saddle Mountain, all of which grew at relatively slow
10 feet tall and 2 inches in d.b.h., growing mainly
rates. A 15-percent range of geographic variation is
without tree competition on prepared and usually pro­
shown in figure 2.
tected sites on gentle topography. Their growth curves
For the Molalla Cooperative, consistently better than
are still changing rapidly. Such data can hardly apply to
mature, fully stocked forests growing on all kinds of
average growth was expressed by families from the
northern half of the cooperative area. Again, the pattern
topography.
was complex. In the northwest quadrant, best inherent
Still the inherent growth differences seen in tables 1
growth was indicated for parents from elevations below
and 2 are reassuring to the landowners who have in­
1,300 feet at the base of the Cascade slope, with
vested in the program. Under concepts that Were current
successively slower growth bands upslope to about 1,800
a decade ago, the programs have met expectations. The
feet. Above 1,800 feet, the inherent growth increased
test design was adequate, and an array of computer
again up to 2,400 feet, where some of the best parents
programs is now available for prompt analysis. A large
number of parent trees are tentatively identified for
were located. For the southern half, the slowest growth
of all was by progeny of parent trees fringing the
superior growth of their progeny in both cooperatives.
Willamette Valley at low elevations. Better growth again
Some are displaying superiority on good or on poor
occurred on trees from 2,200 to 3,000 feet. There were
sites. Crossing programs among parent trees were started
a decade ago and are continuing under various breeding
concepts that will place increasing dependence on this
THE AUTHORs-Roy R. Sileo is genetics project leader, Forestry
Sciences Laboratory, Pacific Northwest Forest and Range Exper­
kind of data.
iment Station, USDA Forest Service, Corvallis, Oregon 97331.
The data have also provided a preliminary look at
Nancy L. Mandel is project mathematical statistician.
direct mapping of genetic variation as a basis of refining
6
April 1983/JOURNAL OF fORESTllY/219
breeding zone boundaries. Even with data from such
small progeny trees, it is clear from the clines in figure
1 that the breeding zones are not genetically uniform.
About 30 percent of the total genetic variation appears
to be attributable to such geographic variation.
Figure 2 is clear confirmation of a three-dimensional
clinal genetic variation that conforms to general land­
forms as first shown in Campbell's (1980) study. The
detail of the topographic fit is not as good as he
demonstrated with a highly controlled experiment and
parent tree sampling four times as dense as in our
sampling. Yet our isoheight maps from commercial
progeny tests clearly reflect main topographic features,
in several cases with remarkable fidelity. The maps
further suggest that genetic isoheight contours might
actually have been even more detailed, if parent tree
sampling had been as dense and uniform as in Camp­
bell's study. But without such speculation, delineation
of breeding zone boundaries directly from our progeny
test data appears practical even at the parent tree density
sampling routinely used in the progressive program.
Finally, the data suggest that much of the genetic
variation within the breeding zones is actually racial or
geographical.
The most asked question about such a detailed clinal
variation pattern in inherent growth is "why?" The
cooperative plots are simply not designed to provide an
answer. At best the genetic gradients might be shown to
relate to climatic and other environmental gradient pat­
terns, but climatic data in the two cooperative areas are
too sparse for such detailed analyses. Hence, we can
only speculate.
Our most plausible speculation is related to relative
growing season length in various locales. Areas that
have evolved inherently slow-growing populations, such
as those fringing the Willamette Valley, have growing
seasons truncated by early onset of summer drought,
often by mid-June. Best inherent growth rates have
evolved at low elevations in relatively moist locales with
generally deep soils, or alternatively on broad ridgetops
also with heavy rainfall and deep soils. By comparison
with the average, such locales may provide moisture for
growth longer into the droughty summers typical of
western Oregon. Similar hypotheses that inherently su­
perior growth occurs in areas of optimum environment
have been proposed for slash pine (Squillace 1966).
Whatever the reason, the present data and particularly
Campbell's (1980) data suggest a surprisingly high
genetic precision in the ability of natural populations to
fit local environments.
The finding of such a detailed pattern of racial
variation within breeding zones raises a confusing prob­
lem for the geneticist. How should three-dimensional
clinal variation be handled in a genetic program?
A more immediate and practical problem arises in the
two cooperatives. Because a disproportionate number of
top parents originate from a few locales, landowners of
these favored locales may have little enthusiasm for
using a standard improved seed from parents elsewhere
in the cooperative. For example, the average family of
the set-10 area in the Molalla Cooperative is superior in
growth rate to the tallest family in most other sets. In
contrast, a seed mix for the entire breeding zone, made
up strictly of parentage from a tallest fraction of all
families, might be of concern to landowners of the
(Continued on page 227)
220/JOURNAL OF fORESTllY/April 1983
Whole-Tree Utilization
System for Thinning
Young Douglas-Fir
Jerry J. Kammenga
ABSTRACT - The Washington State Department of Natural
Resources is commercially thinning naturally established
40-year-old Douglas-fir (Pseudotsuga menziesii) stands which
were once considered too small to be merchantable. Efficient,
cost-effective thinning is accomplished by whole-tree chipping
in the woods. The logging system includes a portable chipper,
a chain-flail delimber, two rubber-tired grapple skidders, and
three rubber-tired or tracked tree-to-tree feller-bunchers with
accumulators. This system provides total utilization of the
harvested material. An average of 100 to 125 green tons of·
pulp chips with less than 7-percent bark can be produced in
an eight-hour shift. Approximately 1,000 stems per acre,
averaging 4 inches in diameter at breast height, are removed
to leave 200 of the best trees. This stocking gives adequate
growing space and provides operational maneuverability. The
feller-buncher operators are trained to select trees by follow­
ing rules that describe leave trees. Stand damage can be kept
within acceptable limits, preferably under 5 percent of the
leave trees, by requiring prelocated skid trail systems and rub
trees. Successful tree selection and avoidance of stand dam­
age depend upon operator cooperation.
The Washington State Department of Natural Re­
sources manages 30,000 acres of young naturally estab­
lished Douglas-fir near Hood Canal in Mason County.
In the average stand, the trees are about 40 years old and
mixed with some lodgepole pine. Stocking varies from
800 to 1,200 stems per acre, and d.b.h. from 2 to 12
inches. Dominant trees average 80 feet in height, basal
area is 155 square feet per acre, and total stem volume
is 5,000 cubic feet per acre. The trees grow on shallow,
glaciated gravel soil presently classed as 100 (class III)
on a 50-year site index. The depth above the hardpan is
18 inches. This thin soil causes severe root competition
and grafting. Growth rates are slowing. In 20 years,
total wood fiber production will be an estimated 16
percent (site index 90-dass IV equivalent) below po­
tential unless measures are taken to provide growing
space. The dominants still have sufficient crown to
respond to management.
Field observations of a 1976 fertilization show imme­
diate growth rate changes from 16 to 10 rings per inch
for a broadcast application of 200 pounds of nitrogen
per acre. An economic analysis indicates that the
management of these stands can increase their present
net worth by 70 percent. At an 8-percent rate of return
over 20 years, a present net worth of $1 ,450 per acre
increases to $2,450 per acre with thinning and fertiliza­
tion. A low-investment thinning is needed to maintain
the present growth rate and to concentrate this growth
on the best trees.
This article reports an operational case study con­
ducted with these purposes:
• To determine the adaptability of readily available
CJ983 SOCIETY OF AMERICAN fORESTEllS
As can be seen m table 1, the diameters and volumes
may appear to skew to the right (skewness > 0) and may
not have the proper peakedness (kurtosis -=/=- 3.0); how­
ever, the deviation from the normal distribution is not
significant at the 5-percent level.
Other even-aged pure stands may not deviate signifi­
cantly from the normal distribution, and therefore can
also benefit from our procedure. Some uneven-aged or
mixed stands may follow a reverse J-shape or other form
of the Weibull function (Bailey and Dell 1973) but still
have a high correlation between diameter and volume
(Moser and Hall 1969, Embry and Gottfried 1971). In
such stands the linear regression estimator is still the
best among other estimator's (such as the ratio estimator,
stratified sampling estimator, and PPS estimator) in
volume estimation with the auxiliary variable d.b.h. for
a sample size of four (Ek 1971). Therefore, our proce­
dure can still be useful. Our estimate should still be
better than the standard regression estimate. However,
the optimal spacing in rank among selected trees in the
second phase of double sampling within a nonnormal
population needs further study.
Because positive transformations in d.b.h. do not
change the ranking of trees by diameter, basal area or
other functions of d.b.h. are not needed for ranking,
even though the regression model may fit better by the
transformation of d.b.h. If the correlation between vol­
ume and d.b.h. is already high, little can be gained
from transformations. For example, the correlation be­
tween diameter and volume among our 100 trees was
0.9756, and the correlation between basal area (calcu­
lated from diameter) and volume was 0.9897. The
Improvement in precision due to use of basal area over
use of d.b.h. in the regression model was of little
practical value.
Our procedure is not limited to volume estimation
alone. Any forest measurement which has a high corre­
lation and a high cost ratio with the diameter measure­
ment can benefit from the procedure. Detailed biomass
studies on high-quality hardwood trees (Schneider 1973)
can be expensive. The extremely high cost ratio would
make our procedure attractive. Fortunately, a high corre­
lation between biomass and d.b.h. (Baumgras 1980,
Wiant et al. 1977) ensures the superiority of the regres­
Sion estimator. Other studies, such as those of foliar dry
weight (Rogers and Hinckley 1979), branch weight, and
branch leaf weight (Ek 1979), could also use our proce­
dure to reduce sampling costs.
Another example: in the first phase of aerial photo
inventories, volume estimations are made, then all plots
can be ranked according to their volume. Plots selected
during the second phase are measured directly. Regres­
sion estimates are computed for all samples and for data
subsets with one-at-a-time omission. Finally, the confi­
dence interval is calculated by the jackknifing
method. •
Literature Cited
BAILEY, R. L., and T. R. DELL. 1973. Quantifying diameter distributions
with the Weibull function. For. Sci. 19:97-104.
BAUMGRAS, J. E. 1980. Biomass yields from Allegheny hardwood thinning.
USDA For. Serv. Res. Pap. NE-466, 7 p.
COCHRAN, W. G. 1977. Sampling Technique. Ed. 3. John Wiley and Sons,
New York, N.Y. 428 p.
DUNCAN, G. T. 1978. An empirical study of jackknife-constructed confidence
regions in nonlinear regression. Technometrics 20:123-129.
DURBIN, J. 1959. A note on the application of Quenouille's method of bias
reduction to the estimation of ratios. Biometrika 46:551-558.
EK, A. R. 1971. A comparison of some estimators in forest sampling. For.
Sci. 17:2-13.
EK, A. R. 1979. A model for estimating branch weight and branch leaf weight
in biomass studies. For. Sci. 25:303-306.
EMBRY, R. S., and G. J. GOTTFRIED. 1971. Height-diameter equations for
Arizona mixed conifers. USDA For. Serv. Res. Note RM-191, 2 p.
HUMMEL, F. C. 1951. Instruments for the measurement of height, diameter,
and taper of standing trees. For. Abs. 12:261-269.
MILLER, R. G. 1974. The jackknife-a review. Biometrika 61:1-15.
MosER, J. W., and 0. F. HALL. 1969. Deriving growth and yield functions for
uneven-aged forest stands. For. Sci. 15:183-188.
O'CONNELL, M. J., and H. A. DAVID. 1976. Order statistics and their
concomitants in some doubling sampling situations. P. 451-466 in Essays in
Probability and Statistics. S. Ikeda, et al. (eds.) Shinko Tsusho, Tokyo,
Japan. 716 p.
QUENOUILLE, M. H. 1965. Notes on bias in estimation. Biometrika
52:647-649.
RAo, J. N. K. 1968. Some small sample results in ratio and regression
estimation. J. Ind. Stat. Assoc. 6:160--168.
RAO, J. N. K., and J. WEBSTER. 1966. On two methods of bias reduction in
the ·estimation of ratios. Biometrika 53:571-577.
ROGERS, R., and T. H. HINCKLEY. 1979. Foliar weight and area related to
current sapwood area in oak. For. Sci. 25:298-303.
SCHNEIDER, G. 1973. Biomass and macro-nutrient content in a 31-year-old
black walnut plantation. Mich. Academician 2:33-42.
WIANT, H. V., C. E. SHEETZ, A. C. COLANINO, J. C. DEMoss, and F.
CASTANEDA. 1977. Tables and procedures for estimating weights of some
Appalachian hardwoods. W.Va. Univ. Agric. and For. Exp. Stn. Bull. 649T,
36 p.
YANG, Y. C., and W. J. YANG. 1955. Volume estimation from sample trees.
J. Taiwan For. 1(2):3--17.
THE AUTHORs--Yong C. Yang is professor, Department of For­
estry, National Taiwan University, Taipei, Taiwan 107, Republic
of China. Fan H. Kung is professor, Department of Forestry,
Southern Illinois University, Carbondale 62901.
Clinal Genetic Growth Variation within Two Douglas-Fir Breeding Zones (from page 220)
remainder of the cooperative area. Such parentage would
come mainly from sites with a more mild and moist
mtcroclimate or with a longer growing season than the
planting site. Since growth and hardiness are usually
mversely related, there is concern that the seed mix may
not be hardy enough for areas with severe microcli­
mates. Such risks of maladaptation are much more
dtfficult to assess than benefits from improved inherent
growth rates, though no less important.
Fortunately, enough genetic variation is displayed
within the sets, even from small localities, that a good
tree improvement program could continue, if need be,
Without using the racial component. For example, 12 of
the 33 sets that cover areas of less than 10 square miles
have little more genetic variation than the 12 sets whose
parents range over 50 or more square miles. Such data
assure the landowner that a program will be productive
even if parentage is strictly local.
Ten-year data uncover many questions without solv­
ing them. Fifteen-year data may reduce or even settle
many present uncertainties. Meanwhile, the prospect of
directly delineating breeding zones from genetic data
appears to be an important bonus from the large parent
tree base used in these programs. •
Literature Cited
CAMPBELL, R. K. 1980. Genecology of Douglas-fir in a watershed in the
Oregon Cascades. Ecology 60: I ,036--1,050.
EBERHART, S. A., and W. A. RUSSELL. 1966. Stability parameters for
comparing varieties. Crop Sci. 6:36--40.
SILEN, R. R., and J. G. WHEAT. 1979. Progressive tree improvement program
in coastal Douglas-fir. J. For. 77:78-83.
SQUILLACE, A. E. 1966. Racial variation in slash pine as affected by climatic
factors. USDA For. Serv. Res. Pap. SE-21, 10 p.
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