High-Resolution Mapping of Inherent Growth Variation 1n Coastal Douglas-Fir Roy R. S11en.!./
Six high-resolution maps of genetic height variation for small breeding zones
in western Oregon are presented in this paper. Production of such maps is
becoming routine. Two maps were presented 1n the April 1983 issue of the
Journal of Forestry (Silen and Mandel 1983). Since then four more have been
produced as part of an analysis package as 5-, 10-, or 15-year data are
processed for progeny tests of breeding zones for the Progressive Tree
Improvement Program (Silen and Wheat 1980). Full or partial data on 26 more
breeding zones in Washington and Oregon are scheduled for analysis in 1984.
Within a reasonably short period, the 1. 3 million acres now mapped may expand
to over 3 million acres. Total height, or incremental height, is the only
genetic trait now routinely mapped. My purpose is to display the maps,
describe the data base and analysis, briefly discuss computer processing and
enhancement, and highlight patterns of geographic genetic variation co1111o
1 n to
the six maps. Implications for genetic programs are not covered.
Coverage
Figure 1 shows 8. 2 million acres in western Washington and Oregon in the
Progressive Tree Improvement Program. There are 90 breeding zones of 100,000
to 300,000 acres. Within zones, the sampling of parent trees 1s fairly
dense--usually two trees per square mile of forest ownership. For these six
maps the number of parent trees ranges from 161 to 900. In other words, there
are a lot of sample points per map. Parents are evaluated at 5-year intervals
from metric height measurements of progeny on 6 to 12 sites, each with 12 to
20 progeny. With over 100 progeny per parent the family mean is a fairly
precise statistical estimate of performance. This large number of individuals
per family probably accounts for the clarity with which patterns of geographic
genetic variation often appear when unprocessed family means are plotted on a
map. Sometimes the patterns are improved by computer enhancements, and
sometimes not.
Highlighted on the figure are five presently mapped Douglas-fir cooperative
program areas--Vernonia, Molalla, Burnt Woods, Gold Beach, and Dallas. The
sixth map applies to a program in western hemlock--the Tillamook Hemlock Tree
Improvement Program.
Vernonia Tree Improvement Cooperative
Figure 2 shows a 350,000-acre forest area directly west of Portland, Oregon,
of this Cooperative mainly owned by Crown Zellerbach Corporation, Longview
Fibre Corporation, International Paper Corporation, and the State of Oregon,
known as the Vernonia Tree Improvement Cooperative. The basic procedure for
constructing the genetic maps is to plot the family mean height at its
coordinate location, then draw in isoheight contour lines. The Vernonia map,
the first such map, was prepared by hand. With 900 parent trees to be plotted
.!./The
Author--Roy R. Silen, is genetics project leader, Forestry Sciences
Laboratory, Pacific Northwest Forest and Range Experiment Station, USDA Forest
Service, Corvallis, Oregon 97331.
581
and with decisions needed about map scales and background information such as
topographic contours, rivers, roads, and towns, the several trials of various
alternatives proved to be tedious. For the map shown, we used the height
growth increment from years 7 to 10 as the plotted variable, mainly to
eliminate the large variation in heights in the first 7 years caused by
animals, brush competition, and frost.
Without applying any computer enhancement techniques, the basic data itself
provides clear geographic patterns. Note that in the hilly area south of the
Nehalem River, nearly all family height growth over 200 cm can be included in
a 1- to 6-mile-wide band on the rolling ridgetop, at 1,200-1,500-feet
elevation, and that two parallel bands 1- to 6-miles wide downslope include
the 190-199 cm, and then the 180- to 189-cm trees in this valley bottom. On
this gentle, 10-mile slope there is a genetic cline from the Nehalem River
bottom to the ridgetop. Note the similar band of 200+ cm growth on the ridge
that parallels the Columbia River north of the Nehalem River. The parentage
at the western edge of the Willamette Valley and in the lowlands northward to
Vernonia are relatively slower growing. A most striking feature concerns the
70 families on the south end of the map located at 1,500- to 2,400-feet
·elevation on the southeast flank of Saddle Mountain, all with below average
growths of 178 to 190 cm.
Computer Aids
All this former handwork, except drawing of the 1soheight lines, is now done
by computer. Cooperators are asked for coordinates of parent tree using the
military grid found on all U. S. Geological Survey (USGS) Quadrangle sheets.
The metric grid on USGS maps is shown in 10,000-meter marginal tic marks. The
0,0 origin is somewhere in the Pacific Ocean to assure that all coordinates
are positive. The 10,000-meter grid (6.2 x 6.2 miles) will be prominent on
most subsequent maps. Up to 900 points were impossible to plot on a map of
useful scale, so the number of points was reduced by plotting the mean of all
families with parents in a 500-meter squilre. The density of points also made
necessary the coding of heights into classes represented by -single-digits.
Typically the range of heights is divided into five to ten classes represented
by the digits O through 9.
Computer maps are plotted on a 1:250,000 scale to correspond with a convenient
USGS map series. The coded values and a coordinate grid are plotted directly
on acetate sheets so that they can be overlaid on the USGS contour maps. The
isoheight lines are drawn on Xerox copies of the map plus overlay.
As
with the processing of satellite data, systematic and random variation can
sometimes be reduced by computer techniques. Krieging, a procedure that uses
a moving average, sometimes helps in smoothing out statistical variation. The
main statistical smoothing and data strengthening has been done with multiple
regression to predict an expected family height at the parents latitude,
longitude, and elevation. The method is described in a previous paper (Silen
and Mandel 1983). The method produces a response surface for which isoheight
contours are mapped.
Maps from Multiple Regression
The next map of the Vernonia area (figure 3) is based on parent tree values
estimated by multiple regression for their coordinate location. T this data
set there were significant effects of latitude and elevation squareo. The
582 response-surface map shows that parents in the north half would be expected to
perfonn better than average. The better perfonnance on the hills south of the
Nehalem River is also shown, as well as the poor performance of those
southeast of Saddle Mountain. The map becomes somewhat absurd in its
prediction that trees from the northeast corner should be 7-1/2 percent better
than average--a case of carrying trends too far.
The next map (figure 4) generated from 111Ultiple regression techniques applies
to the Molalla Cooperative. This cooperative of four landowners is located
southeast of Portland in the foothills of the Cascade Range and east of the
Willamette Valley. The forests range from about 1,000 feet to 2,600 feet.
The 375 selected parent trees are not well distributed and only about
40 percent of the mapped area is owned by the four landowners. But the data
is generally excellent and a number of factors were significant in multiple
regression analysis (latitude squared, latitude times elevation, elevation
squared, longitude times elevation, and longitude squared). The result was a
response surface of considerable complexity that fit the basic data reasonably
well.
The map shows a strong trend of better parent perfonnance to the north.
Parallel bands representing a change of 2-1/2 percent in total height at
10 years are spaced at 2- to 5-mile intervals. Best perfonnance in the north
is at 1,000 feet along the edge of the Willamette Valley. Performance drops
off upslope to about 1,800 feet, then improves again at elevations up to
2,500 feet. At the south end of the map the poorest perfonnance is from
parentage on the valley edge. Perfonnance there rises as parent elevation
increases. This is quite a complex geographic pattern. A feature of the
Molalla Cooperative data is that the top 10 of the 375 parent trees originate
in a 1- by 2-mile rectangle at 1,000 feet elevation near Colton, Oregon.
Burnt Woods Cooperative
The remaining four maps were constructed from basic data. No attempt has been
made at computer enhancements because newer data will soon become available
from 10- or 15-year measurements.
The Burnt Woods Cooperative (figure 5) tested only 161 parent trees on
70,000 acres owned by the State of Oregon and Starker Forests. The lands lie
west of Corvallis in an east-west oriented pair of drainages with flanking
highlands to north and south. Several points about the isoheight contouring
are of interest.
As with the Molalla Cooperative map, the top-perfonning parentage is confined
to a small area. One such area is south of Blodgett at 1,200 feet elevation.
Other areas of good parentage are associated with coves near the top of low
hills in the main drainages. At the northeast corner is a major ridge. A
clinal banding of the successively poorer growing parents occurs on the east
side of this ridge that forms the forest edge of the Willamette Valley, a
similar pattern to the Vernonia Cooperative map. The isoheight lines are
mainly oriented east to west paralleling the drainage pattern.
Gold Beach Cooperative
Several features seen in maps from the Gold Beach Cooperative (figures 6-8)
are unusual. The area is located astride the Oregon-California border and
583 includes a 15-mile-wide strip along 50 miles of the Pacific coastline. Two
major drainages are included--the Rogue River at the north and the Chetco
River at the south of the mapped area. The nine landowners in the Gold Beach
Cooperative own about 80 percent of the forest land. Sampling of
1,066 parents is more uniform than for any other of the six maps. This is
shown in figure 6 in which the coded values in each sampled 500-meter square
range from 2 to 6 with 4 the average value.
An enlargement of the Oregon-California border area is next shown with
isoheight lines (figure 7). The pattern of these lines is complex, but some
simplifications become obvious. The "average-growth" parentage along the
coast grades inland into "above-average" parentage, and then into islands of
"top" parentage, finally grading eastward into "average" and "below-average"
parentage.
Figure 8 covers the pattern for the 50-mile stretch of coastline. There is a
5- to 15-mile-wide band of average parentage (slant shading) that parallels
the coastline. The eastern edge of the sampled area has below-average
arentage (vertical shading). Each of the two major drainages has a basically
simple pattern. The east-west orientation of the Rogue River is characterized
by slow-growing parentage at the river mouth, then relatively fast-growing
parentage (heavy shading) for about 15 miles upstream in the valley bottom.
On either side of this faster growing band is a 1- to 4-mile-wide band of
average-growth parentage, and still more distant from the river is a band of
slow-growing pa entage. This pattern is like that for the east-west drainage
in the Burnt Woods Cooperative map. The Chetco River, with north-south
orientation, has the same banding pattern except that the valley bottom has
slow-growing parentage banded by average, then slow-growing parentage to the
west and fast-growing parentage to the east and south.
The most interesting feature has to do with location of the fastest growing
parentage. Other than an area of such parentage described for the Rogue
River, nearly all such parentage occurs either near the Oregon- California
border, or on a ridge paralleling the ocean north of the Rogue River. Note
how the small areas of best growing parentage ·are within island-like isoheight
contours of better than average parentage. Of these two areas, the one nearer
the Oregon-California border is interesting because it delineates nearly all
the extension of the range of coast redwood into southern Oregon. An
ecologist from the Siskiyou National Forest, USDA Forest Service, has
suggested that the coastal strip of average parentage corresponds to the
narrow range of western redcedar along the southern Oregon Coast. Figure 9
shows the isoheight lines drawn on a 1:250,000-scale USGS map of the type sent
to each Cooperator.
Dallas Tree Improvement Cooperative
This cooperative (figure 10) of seven landowners is located south of the
Vernonia Cooperative and west of Salem, Oregon. It fringes the Willamette
Valley for about 40 miles.
About 300 parent trees at elevations below
1,500 feet provide the data base. Only about 35 percent of the land area is
sampled leaving large gaps with no parent tree sampling.
Even so, the pattern is consistently one of increasingly slower growing
parentage as sampling approaches the edge of the Willamette Valley. We see an
isoheight line following the forest edge that includes all the below-average
584
parentage. The band of average parentage is 3- to 6-miles wide, with better
growing parentage generally westward. This is the similar pattern as reported
for the Vernonia and Burnt Woods Cooperatives. With so much of the forest
area unsampled, a lot of the isoheight lines are shown as dashes between solid
lines where sampling occurred.
Tillamook Hemlock Tree Improvement Cooperative
A cooperative involving five landowners of western hemlock forests along the
north coast of Oregon (figure 11) provides 5-year data for the last map. The
coastal strip samp'led with 300 trees varies from O to about 12 miles in width
along 70 miles of coastline. The pattern seems quite clear: Virtually all
parentage of below average performance can be delineated with a band
paralleling the coastline extending into each estuary about to the limit of
tidewater. Inland from this tidewater line are parent trees of average
performance. At intervals along the coast are island-like isoheight lines
that delineate the above-average parentage. Most of these islands of faster
growing parentage involve upland basins, ridges, and south-facing slopes
somewhat back from the coastline.
Discussion
There are some features in common to all six maps that support the concept of
a highly precise adaptation to local environments (Silen 1982):
1. Clinal variation is the rule. There are clear examples of gradual
changes of inherent growth along gradients of moisture or ¢emperature.
2. Fastest or slowest inherent growth rates are geographically localized.
There are clear examples in each of the six cooperative areas.
3. The correspondence of genetic isoheight lines with topographic features
is clear in many cases, and best where sampling of locales is dense.
Prime examples are the gradient of lesser growth toward the timber edge
of the Willamette Valley, the tidal relationship of slower growth in the
western hemlock area, the cline associated with the slope of the
Cascades, the band of similar performance along the 50 miles of coastline
near the Oregon-California border, and the faster growing parentage
associated with the redwood area in Curry County.
4. The north-south orientation of many isoheight bands follows predictions
from general regional studies. East-west valleys of the Burnt Woods and
Gold Beach cooperatives, however, demonstrate the overriding effects of
local topography.
5. All six cooperative maps display a 10- to 15-percent difference in
progeny height associated with geography. How much of this genetic
variation is applicable to use for upgrading growth in the area of poorer
growth on each map is a major question.
There is ready acceptance by geneticists of stable racial differences in
growth rate occurring along major latitudinal or elevational transects where
pollen exchange is unlikely. Here is added evidence that clinal variation is
maintaineo over distances so short that pollen exchange must occur. Any of
585 the six cooperative areas have as great or greater environmental variation as
might occur over whole states in the eastern United States. Obviously the
species would benefit from a similar precise genetic and environmental matchup
as occurs along the major environmental gradients. It would appear that such
a matchup is occurring even though the mechanism isn't understood.
Most Ranger Districts in the Pacific Northwest will soon have high-resolution
maps of inherent growth variation.
Literature Cited
Silen, R. R. Nitrogen, corn, and forest genetics. The agricultural yield
strategy--implications for Douglas-fir management. Gen. Tech. Rept.
PNW 137. USDA Forest Service, Pacific· Northwest Forest and Range Experiment
Station, Portland, Oregon 20 p; 1982.
Silen, R. R.; Mandel, N. L. Clinal genetic growth variation within two
Douglas-fir breeding zones. Journal of Forestry. 81:216-220; 1983.
Silen, R. R.; Wheat, J. G. Progressive Tree Improvement Program in coastal
Douglas-fir. Journal of Forestry. 77:78-83; 1979.
r
586 MSMllllGTON
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Figure 1. --Twenty-three tree improvement cooperatives are outlfned fn western
Oregon and Washington, fnvolving 8.2 million acres and 44 landownfng
organizations. .Cooperatives for which maps of genetic varfation are presented
are shaded. Progeny test data from 161 to 1,066 parent trees were used to
prepare the six maps.
587
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Figure 2. --Vernonia Cooperative in the Coast Ranges west of Portland involved
900 parent trees tested on 12 sites by four landowners. This was the first
map attempted, so was prepared by hand methods. Decreasing progeny heights in
a cline from the hills of the Coast Range to the edge of the Willamette Valley
is a prominent feature of the map. Figures are centimeters of incremental
growth from 7 to 10 years.
588
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Figure 3.--Yernonia Cooperative map was prepared from 7- to 10-year
incremental growth predicted for each parent location by the regression
equation shown in the box below the map. The equation reduces statistical
variation, thus smoothing the data of the previous map which shows the
unprocessed data.
589
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Figure 4.--Molalla Cooperative is in the foothills of the Cascade Range
southeast of Portland. Progeny from 375 parents were tested on nine sites.
The 10-year total heights produced the multiple regression equation in the box
below the map. The equation was used to estimate heights at parent
coordinates. Note that northern parents show superior heights. Clinal
variation is displayed up the slope of the foothills.
590
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Figure 5.--Burnt Woods Cooperative in the hills of the Coast Range west of
Corvallis displays coded 5- to 10-year progeny height in 10-cm increments
based on 161 parents tested on eight sites (1•260 cm; 7•320 cm). Drainage
orientation and isoheight lines are mainly east-west. Note concentrations of
fastest growing families south of Blodgett and steep clinal variation in
northeast corner associated with the rain shadow created by Little Grass
Mountain.
591
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Figure 6.--Gold Beach Coo erative along the Oregon and California Coasts
embraces acreage of nine andowners with 1,0
. 66 tested trees. The better
distribution of parents is shown by the coded progeny heights. Note the
east-west alignment of the Rogue Rfver and northeast-southwest alignment of
the Chetco River for details explained in the text.
592
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Figure 7.--An enlargement of figure 6 in the area of the Oregon-California
border. Isoheight lines delineate locations of above-average (4'sl and
top-performing (S's) parent trees. Average parentage are fn a 3- to 6-mfle
coastal band, with top-performing parentage fnside islands of above-average
percentage.
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Figure 8.--Gold Beach Cooperative. Mapping for about 50 miles of coastline
forests displays the band of average-growth parentage along the coast, a
contrasting pattern for the Chetco and Rogue valleys, and islands of
above-average parentage near the California border and on a ridge north of the
Rogue River.
594
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Figure 9.--All cooperative members receive more detailed maps of the kind in
this figure. Coded parental infoMnation and isoheight contours are drawn on a
USGS 1:250,000-scale topographic map.
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Figure 10. --Dallas Valley Cooperative. The map, like that of the Vernonia
Cooperative area, displays a banding of below-average parentage fringing the
Willamette Valley. Successive bands of average growth and above-average
growth are indicated westward into the Coast Ranges.
596
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Figure 11.--Tillamook Hemlock Cooperative. Below-average parentage can be
delineated by a line along the coast into each estuary to about the limit of
tidewater. Average-growth parentage is found inland of this line. Several
scattered island-like areas of parentage with above-average growth occur in
basins, south slopes, and ridges somewhat back from the coast.
597