15-YEAR PROGENY TEST RESULTS
VERNONIA, MOLALLA, BURNT WOODS, ANO UMPQUA COOPERATIVES
13
by Roy R. Silen
IFA-PNW Program cooperators with younger programs can take considerable
comfort from the optimistic recent analyses of 15-year data from Vernonia,
Molalla, Burnt Woods, and Umpqua Cooperatives. The 15-year test results of
these Cooperatives, involving 2,035 parents, provide the first large-scale use
of volume information by the Cooperatives. Diameter measurements have not
been taken for programs at the 5- or 10-year measurement because groundline
diameter measurements needed to obtain accurate volumes were too costly.
Measurements of volumes in small trees using breast-height diameters are hard
to interpret due to the spurious apparent change in taper of trees in the
2-o meter range.
This summary of 15-year measurements covers growth statistics of heights, diameters, volumes, as well as F values, family and individual tree heritabilities, plantation x family interactions, parent-offspring correlation, and gain trends. Midparent-offspring correlations results are presented as separate articles in this issue. Studies of age-age correlations and spacing-genotype interactions are planned but have not been attempted at this writing. Growth Statistics.
Table l is complex. It provides a summary for two Cooperatives of the range, F value, and heritabilities by set for heights, diameters, and volumes. Also shown are family x plantation interactions and survival, set by set. The reader might be overwhelmed by such massive tabular data unless features of broad interest are highlighted. One such feature of the table is the consistently larger tree families of the Molalla Cooperative versus Vernonia Cooperative at age 15 years. Every set mean of the Molalla Cooperative has a larger average volume.
There are valuable silvicultural lessons, as well as genetic ones, in these data. High plantation survival at age 15 in both Cooperatives is noteworthy. By coincidence, Set 10 in both Cooperatives is unusual in that its mean volume is greater than that of the largest tree in several other sets. This provides an example of geographic genetic variation in both Cooperative areas since the two normal distribution of family means hardly overlap the distribution of the contrasting sets.
Parents in each set occur within an area of a few square miles. With few exceptions, the F values are statistically significant, an indication of real family differences within nearly every set. Again, Set 10 for Molalla can be singled out as an exception.
It has no significant family differences--all families are inherently fast growing. However, Set 10 shows a highly significant family x plantation interaction meaning faster-growing families on one site are slower growing on another site. The 15 -year data indicates most sets are beginning to show such an interaction, whereas 10- or 5-year measurements showed few significant family x plantation interactions. This follows trends previously seen on the 70-year-old Douglas-fir heredity study, in which family plantation interactions were weak for the first quarter century, but are now very pronounced. Cooperators in the program will find hours of interesting perusal with the other details of this table. Heritabilities and Genetic Gains for Volume.
Table l also shows that family heritabilities were high in most sets. Based
on four Cooperatives with 15-year data, an average volume gain prediction is
12.9 percent, using a 1:5 selection. The gain prediction by Cooperative is:
Volume gain
(percent)
Cooperative
Vernonia
Holalla
Burnt Woods
12.3 11. l 13.5 Umpqua Coast
14.6 ..
"
Even at the low 1:5 selection differential, genetic gains in growth rate are
better than the 10-percent figure hoped for 15 years ago.
Height Gain Changes Over Time
The question of how gain predictions change with tree age of the evaluation
plantations is basic to tree improvement. Although most foresters would
rather have predictions of gain based on volume growth rate, only height data
was collected in earlier years on most Cooperatives. Hore accurate estimates
would be based on repeated volume measurements of the same trees. Only a
preliminary estimate is readily available, however, from another kind of
data. This estimate is based on segregating the 5-, 10-, and 15-year height
measurements on which heritability and gain estimates are already made
(Table 2).
There are 13 Cooperatives with 5-year height data, 3 with
10 years, and 4 with 15-year data. The three averages of 5.44, 4.91, and 3.70
gain suggests that the trend over a 10-year period is clearly negative.
The
linear regression with r
-.49 would indicate a 1.7-percent smaller gain in
height growth rate at 15 years than at 5 years. This may simply reflect the
larger tree sizes on which gains are based as trees age.
=
Keep in mind that percent gains in volume growth rate may be nearly 3 times as
large as for height growth rate.
Relationship of F Value to Heritability
In such analyses one runs into interesting side issues.
A considerable number
of 5- or 10-year measurements done prior to.1983 did not have heritability
computations. Heritability estimates will be needed for further analyses. We
wondered if we might make heritability estimations graphically from a curve
derived by plotting the family and individual heritability values against
corresonding F values.
Figure l shows such a plot.
The precision of this
plot for the family F values versus heritability left little doubt that an
algebraic relationship was involved. The simple algebraic relationship turned
out to be H (heritability)
=
l -
l.
F
Upon further checking, it appears now
that we had simply reinvented the wheel; it has been derived before. However,
it is quite likely that relatively few Northwest practicing forest geneticists
have had occasion to stumble on this simple, useful relationship, so it is
mentioned here.
Individual tree heritabilities has appreciable variability at
each F value.
[
------- ---·---
Table l.
---- -----
Su111nary of 15-year statistics for two Cooperatives.
IS-Yur Analysis S111Wry ry
15-Yur M.llyi;ls
VE1811MIA axftAATlVE CIO test sit.es} ID.ALLA llO'E'RATIVE (8 tint sites>
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16
Figure 1.
VERNONIA AND MOLALLA 15-YEAR HEIGHTS
COMPARISON OF F VALUE AND HERITABILITY
(FAMILY AND INDIVIDUAL)
LOO·
+
.90
-
80
•
70
•
•
•
•
60 ­
•
50.
•
40 ­
•
30 ­
•
20
.....
Mollala
Vernonia
•
+·
...,"i>
+
.....
.
.....
.+ +
¢' + .
,.,
E-<
+
+
++
.
"'
=
.....
•
+
•
+
+
10 ­
+
+
.+
0------------ ------------------ - ---------------------------- ---­
.
-.10
-
0
1. 0
2.0
3.0
F VALUE
4.0
5.0
6.0
17
T ble 2.
Average genetic gain in height growth rate of 20 breeding zones at last evaluation age.
EVALUATION AGE
15-year
10-year
5-vear
Breeding unit
Gain
Grants Pass
4. 15
Tyec Gain
Breeding unit
Gain
Snow Peak
3.97
Burnt loklods
3.72
4. 77
Snow Peak High
5.26
Vernonia
4. 13
Snoqua1mie 2
7. 78
Dallas Valley
5.50
Molalla
3.19 Nor lh Uipqua 3
6.10
lilpqua Coast
3. 76 North lilpqua 4
4.02 Riddle 2
3.70 Butte Falls 4. 71 Gold Beach 1
4.84 Gold Beach 2
5.49 Gold Beach 3
4.76 Coquille 17
7.62 South lilpqua 3
4.70 Cowlitz (Noble fir)
8.14 x
5.44
r
=
0.49
a
=
6.32
Breeding unit
4.91
b
=
-0. 17 3.70