United States

Department of 

Agriculture

Forest Service

Pacific Northwest

Research Station

Research Paper

PNW-RP-547

June 2002

Thinning Shock and Response

to Fertilizer Less than Expected

in Young Douglas-Fir Stand at

Wind River Experimental Forest

Dean S. DeBell, Constance A. Harrington, and John Shumway
Dean S. DeBell is a research forester (retired), Constance A. Harrington is 

a research forester, and John Shumway is a research soil scientist (retired),

Forestry Sciences Laboratory, 3625 93rd Avenue SW, Olympia, WA 98512-9193.

Authors
DeBell, Dean S.; Harrington, Constance, A.; Shumway, John. 2002. Thinning 

shock and response to fertilizer less than expected in young Douglas-fir stand 

at Wind River Experimental Forest. Res. Pap. PNW-RP-547. Portland, OR: U.S.

Department of Agriculture, Forest Service, Pacific Northwest Research Station.

20 p.

Three thinning treatments (thinned to 3.7 by 3.7 m, thinned to 4.3 by 4.3 m, and 

an unthinned control treatment with nominal spacing averaging 2.6 by 2.6 m) were

installed in a 10-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) plantation growing on a low-quality site at the Wind River Experimental Forest in southwest

Washington. Two years after thinning, two fertilizer treatments were superimposed

on the design (0 and 224 kg per ha of nitrogen applied as ammonium nitrate). Diameter

growth increased with increasing spacing throughout the 6-year study period, and

it was also increased by fertilizer in both the thinned and unthinned (control) treatments. Thinning shock, a reduction in height growth after thinning, was expected at

this study site because severe thinning shock had been documented in earlier nearby

trials. Height growth was initially reduced slightly by thinning, but by the third 2-year

period after thinning, height growth in thinned, unfertilized treatments was equal to or

greater than height growth in the unthinned, unfertilized treatment. Fertilizer application increased height growth on average by 13 percent in the first 2 years after fertilization. In the third and fourth years after fertilization, however, fertilizer increased

average height growth by 9 percent, but the increase was substantial (16 percent)

only in the unthinned control treatment. The mild, ephemeral nature of thinning shock

in our study was in contrast to the severe, long-lasting shock in earlier studies at

Wind River. The milder shock in our study could be related to one or more of the

following: (1) thinning was done at an early age, (2) impacts of fire (natural or prescribed) preceding planting were minor, and (3) seed source of the planted stock

was appropriate for the location. Based on comparisons with other studies at Wind

River and elsewhere, we suspect that use of nonlocal, maladapted seed sources in

the earlier studies may have predisposed those trees to thinning shock. Furthermore,

we suspect that the much higher responses to fertilizer application reported in the

earlier studies may be associated with intense natural fires prior to planting, and the

reduced nutritional status of those sites may have been further exacerbated by the

use of maladapted seed sources.

Keywords: Thinning, thinning shock, fertilization, nitrogen, seed source, fire, 

Wind River.

Abstract
Long considered the “cradle of forestry research” in the Douglas-fir region, the Wind

River Experimental Forest in southwest Washington served as the type location and

initial trial site for many practices used in Pacific Northwest forests today. In several

instances, the results and trends in the Wind River studies were more dramatic than

those subsequently observed in other locations and in other species. Such differences have been particularly evident in growth responses to thinning and fertilization, two common silvicultural practices in young-growth stands of Douglas-fir

(Pseudotsuga menziesii (Mirb.) Franco). A few years ago, we established a new

study of thinning and fertilizing in a young plantation at Wind River to refine knowledge of thinning shock (a reduction in height growth after thinning) and the role that

nitrogen (N) fertilizer may play in overcoming it. Our study site is near the stands in

which severe thinning shock and dramatic growth increases with fertilization have

been observed. Three thinning treatments (thinned to 3.7 by 3.7 m, thinned to 4.3

by 4.3 m, and an unthinned control treatment with nominal spacing averaging 2.6 by

2.6 m) were installed in a 10-year-old Douglas-fir plantation growing on a low-quality

site. Two years after thinning, two fertilizer treatments were superimposed on the

design (0 and 224 kg per ha of nitrogen applied as ammonium nitrate). Diameter

growth increased with increasing spacing throughout the 6-year study period, and

it was also increased by fertilizer in both the thinned and unthinned (control) treatments. Height growth was initially reduced slightly by thinning, but by the third 2-

year period after thinning, height growth in thinned, unfertilized treatments was equal

to or greater than height growth in the unthinned, unfertilized treatment. Fertilizer

application increased height growth on average by 13 percent in the first 2 years

after fertilization. In the third and fourth years after fertilization, however, fertilizer

increased average height growth by 9 percent, but the increase was substantial

(16 percent) only in the unthinned control treatment. The mild, ephemeral nature of

thinning shock in our study was in contrast to the severe, long-lasting shock in earlier

studies at Wind River. The milder shock in our study could be related to one or more

of the following: (1) thinning was done at an early age, (2) impacts of fire (natural or

prescribed) preceding planting were minor, and (3) seed source of the planted stock

was appropriate for the location. Based on comparisons with other studies at Wind

River and elsewhere, we suspect that use of nonlocal, maladapted seed sources in

the earlier studies may have predisposed those trees to thinning shock. Furthermore,

we suspect that the much higher growth responses to fertilizer application reported

in the earlier studies may be associated with intense natural or prescribed fires prior

to planting, and the reduced nutritional status of those sites may have been further

exacerbated by the use of maladapted seed sources.

Summary
1

Long considered the “cradle of forestry research” in the Douglas-fir region, the Wind

River Experimental Forest served as the type location and initial trial site for many

practices used in Pacific Northwest forests today. In several instances, the results

and trends in the Wind River studies were more dramatic than those subsequently

observed in other locations and in other species. Such differences have been particularly evident in growth responses to thinning and fertilization, two common silvicultural practices in young-growth stands of Douglas-fir (Pseudotsuga menziesii (Mirb.)

Franco). 

Thinning affects tree growth primarily by reducing the number of stems per unit 

area and concentrating existing site resources on remaining crop trees. Diameter

growth is substantially increased, and height growth is usually unaffected or slightly

enhanced. In some instances, however, thinning causes a reduction in tree growth,

especially height increment. This phenomenon, sometimes called thinning shock,

was first measured quantitatively in a respacing trial in a 25-year-old Douglas-fir

plantation on the Wind River Experimental Forest by Staebler (1956a). The reduction in growth at that site, however, was substantial and continued for 10 to 15 years

after thinning, particularly in the widest spacings (Harrington and Reukema 1983).

Shock was also severe in another thinning (and fertilizing) test at Wind River, even

resulting in negligible response in diameter growth (Miller and Reukema 1977).

Nitrogen (N) fertilizer applications in the Pacific Northwest usually cause an increase

in tree growth and stand productivity by increasing total nutrient resources available

at a forest site. Regionwide trials indicate 70 percent of Douglas-fir stands show

moderate to large growth increases after N application at 224 kg per ha, and

response is slightly more consistent and somewhat greater in thinned than in

unthinned stands (Chappell and others 1992, Peterson and others 1986). Miller and

others (1986) evaluated these same regionwide trials and found that stands growing

on sites of low quality had greater relative (and absolute) response to fertilizer than

did stands on sites of high quality. They also suggested that N application would be

most beneficial biologically when crown development is rapid and trees begin to

fully use other site resources. Some of the most impressive growth responses to

N applications have occurred in Douglas-fir plantations at Wind River (Miller and

Reukema 1977, Miller and Tarrant 1983).

Where N fertilizer has been applied in experimental stands that manifested thinning

shock, the shock symptoms have been reduced or mitigated (Brix 1993, Crown and

others 1977). Such benefits were particularly evident in a thinning-fertilizing test in a

20-year-old plantation at Wind River; thinning reduced height growth by 25 percent,

and diameter growth showed no improvement over a 5-year period, whereas fertilizing the thinned trees nearly doubled height growth and increased their diameter

growth by 84 percent (Miller and Reukema 1977).

Some foresters, recognizing that many of the above-described results of the Wind

River studies differ at least in degree from the norm, have suggested that the poor

site quality and a harsher climate at Wind River than is typical for its latitude and

elevation may contribute to such differences in response. Silen and Olsen (1992)

Introduction
comment, however, that although the Wind River valley is surrounded by mountains,

and thus has greater precipitation and a shorter growing season than would be

expected for its elevation, the “climate is typical of major valleys for much of the

area along the west slopes of the Cascade Range in Oregon and Washington.”

A few years ago, we established a new study of thinning and fertilizing in a young

plantation at Wind River to refine knowledge of thinning shock and the role that N

fertilizer may play in overcoming it. Our study site abuts the stand in which substantial thinning shock and dramatic growth increases with fertilization were reported by

Miller and Reukema (1977) and is within a few kilometers of another study where

severe and long-lasting thinning shock has been observed (Harrington and Reukema

1983, Staebler 1956a). Responses in the new study, however, were more moderate

than anticipated–thinning shock was minor and response to fertilizer was low in relation to earlier trials. We therefore compared characteristics of the new study with

older Wind River trials and developed some hypotheses regarding site and stand

factors associated with differences in the nature of responses. This paper describes

the new study, presents 6-year results, and offers thoughts on factors influencing

responses and the implications for management elsewhere.

The study area is a long, narrow 23-ha plantation on the Wind River Experimental

Forest near Carson, Washington. It is located along a gentle (10 to 15 percent)

east-facing slope at 650 m elevation. Precipitation averages 2540 mm per year, but

only about 10 percent falls during the May 1-September 30 period of the growing

season. Soils at the study site are moderately deep to deep, well-drained loams of

the Stabler series, and have developed from volcanic ash and pumice. Vegetation 

is transitional between the western hemlock (Tsuga heterophylla (Raf.) Sarg.) and

Pacific silver fir (Abies amabilis Dougl. ex Forbes) zones (Franklin and Dyrness

1973), and between the western hemlock/salal (Gaultheria shallon Pursh) and

Pacific silver fir/salal habitat types (Brockway and others 1983). Larger Douglas-fir

trees in the plantation averaged a little over 10 m tall at a breast height age of about

15 years; thus, Douglas-fir productivity is site class IV on a 50-year base (King 1966).

The study area was previously occupied by an old-growth stand of mostly Douglasfir, western hemlock, and Pacific silver fir. It was logged by tractor in 1973, and

logging slash was tractor piled on landings and burned. In late April and early May

1975, the unit was planted with 2-1 Douglas-fir grown from seed collected in seed

zone 440, the same seed zone as the study area. Target planting density was 740

trees per ha (about 3.7 by 3.7 m), but abundant natural regeneration also contributed

to stocking. Other tree species that became established on the site (originating as

new seedlings or advanced regeneration) were western hemlock and Pacific silver

fir; shrub species included vine maple (Acer circinatum Pursh) and Pacific dogwood (Cornus nuttallii Aud.); and ground vegetation was made up mostly of salal,

Oregongrape (Berberis nervosa Pursh), huckleberry (Vaccinium spp.), 

and beargrass (Xerophyllum tenax (Pursh) Nutt.).

2

Study Methods

Study Area
The study site was divided into three blocks of about equal size, and precommercial

thinning prescriptions were developed to provide a range of stand densities within

each block. The prescriptions were applied at random to the subsections delineated

for various thinning treatments within each block. A contract crew conducted the

operational thinning in fall 1984; the slash generated by the thinning was left in

place. Three distinct thinning levels were achieved: T0, an unthinned control with a

nominal spacing of 2.6 by 2.6 m, averaging 1,462 trees per ha; T1, with a nominal

spacing of 3.7 by 3.7 m, averaging 744 trees per ha; and T2, a nominal spacing of

4.3 by 4.3 m, averaging 536 trees per ha. In spring 1987, two growing seasons after

thinning, two N fertilizer treatments were added to the experimental design: F0,

unfertilized control, and F1, ammonium nitrate applied by hand at 224 kg of N per ha.

Before the 1985 growing season, 27 temporary plot centers were established, and

the 25 trees closest to the center stake were tagged and measured for height and

diameter. One 25-tree plot was located in each unthinned control area (except for

one block which had been thinned throughout), and two or three plots were located

in each of the other thinning treatments in each block. These 25-tree plots provided

a measure of treatment effects on diameter growth for the first two growing seasons

after thinning and served to identify spots where fixed-area plots were subsequently

installed.

In fall 1986, 43 permanent fixed-area plots of two sizes were established: 14 large

(0.2 ha) plots and 29 small (0.03 ha) plots; the smaller plots were installed primarily

to assess short-term response to fertilizer. All trees were tagged and measured for

diameter at breast height (d.b.h.), and a sample of trees on each plot were measured for total height. One or more large plots were positioned within each of the

three thinning treatments (T0, T1, and T2); none of the large plots received fertilizer.

Most of the smaller plots (24) plus a 3-m surrounding buffer received fertilizer application, and the others (5) served to complete the replicated design for assessment

of tree growth at all thinning and fertilizer levels in all three blocks. Trees were

remeasured for diameter again at the end of the 1990 growing season. 

In spring 1991, past annual height increments were assessed retrospectively. On

the larger plots (0.2 ha), the 20 tallest trees per plot were selected, and the height 

at whorls representing the end of growing seasons 1980 through 1990 were measured. On small plots (0.03 ha), the 10 tallest trees per plot were measured in a similar way. All selected trees were in dominant or strong codominant crown positions.

All data related to growth after treatment were summarized and analyzed in terms 

of three 2-year growth periods: period 1 (1985 and 1986) included the first 2 years

after thinning but before application of fertilizer; period 2 (1987 and 1988) included

the third and fourth years after thinning and the first 2 years after fertilization; and

period 3 (1989 and 1990) included the fifth and sixth years after thinning and the

third and fourth years after fertilization. Only data from trees surviving through 1990

were used in the analyses of growth; mortality was minimal (3 percent), unrelated to

treatment, and caused primarily by root rot disease.

3

Treatments

Plot Installation and

Data Collection

Data Analysis
4

Comparison with 

Other Studies

Quadratic mean diameter growth during period 1 was analyzed by using data from

the temporary 25-tree plots; fertilizer had not yet been applied and the data were

analyzed as an unbalanced randomized block with three blocks and three thinning

treatments by using a general linear model (SAS Institute 1988). Diameter growth

for combined periods 2 and 3 was evaluated with data collected on the permanent

plots. The analysis, which was done by using a mixed model procedure (SAS

Institute 1996), was an unbalanced, 3 by 2 split-plot factorial (fertilizer treatment 

was the subplot) with three random blocks.

The retrospective height growth data were used to examine the effects of thinning

intensity and N fertilizer on mean height growth of the tallest trees–dominants and

large codominants–during the three 2-year periods mentioned above. In period 1,

fertilizer had not yet been applied; thus, the data were analyzed as an unbalanced

random block with three blocks and three thinning treatments. Height growth data

for periods 2 and 3 were analyzed as an unbalanced, 3 by 2 split-plot factorial with

three random blocks. In addition, the retrospective height measurement data for 

the 2 years prior to thinning (1983 and 1984) were evaluated for pretreatment 

differences in growth.

Preplanned comparisons of mean diameter growth and height growth were made

among thinning treatments within each fertilizer treatment for all periods, and also

between fertilizer levels within each thinning treatment for periods 2 and 3. Means

were considered significantly different if p ≤ 0.10.

To compare the tree growth in this study with growth in other studies in the area, we

compiled a list of the other thinning and fertilization trials in young-growth stands in

the Wind River Experimental Forest. We then evaluated each study to determine its

fire history and, if planted, the site preparation method and seed source used. We

ascertained the mapped soil unit for each study area from a geographic information

system layer provided by the Gifford Pinchot National Forest and asked a soil scientist familiar with the area to convert the mapping units to the best-fit soil series used

by the Natural Resources Conservation Service.

Precipitation during the growing season (May 1 through September 30) was calculated for the initial response period for each study from the records for nearby

weather stations located at the Wind River Nursery (1953-1977) and the Carson

Fish Hatchery (1978-1997). Long-term records for these stations were available

online at www.wrcc.dri.edu. Mean, minimum, and maximum precipitation values 

for the growing seasons that corresponded with the years of growth measured 

were evaluated to examine the possibility that growth for individual studies might

have been influenced by one or more years of unusually dry or wet conditions. 

The oldest study did not have weather records available for examination.
Table 1—Tree and stand characteristics immediately after thinning

Diametera Height Prior height growthb Stocking 

Thinning

treatment Mean Rangec Mean Range Mean Range Mean Range

- - Centimeters - - - - - - - - - - - - - Meters - - - - - - - - - - - - - Trees per hectare - -

T0 6.0ad 5.2 - 6.5 4.2a 3.7 - 4.5 1.5a 1.3 - 1.6 1462a 1005 - 1825 

T1 6.2a 6.0 - 6.4 4.4a 4.2 - 4.5 1.4a 1.4 - 1.5 744b 706 - 810 

T2 6.0a 5.5 - 7.4 4.2a 3.8 - 4.8 1.4a 1.3 - 1.6 536c 508 - 568 

a Quadratic mean diameter.

b Height growth in 1983 and 1984, 2 years before thinning, based on retrospective measurement of height increment.

c Ranges are based on plot means.

d Means in a column followed by the same letter are not significantly different at p ≤ 0.10.

5

Results and

Discussion

Tree and Stand

Characteristics After

Thinning

For each study, we determined initial stand conditions (age, height, diameter, and

density) and the type of treatment (for thinning treatments, the new stand densities

and for fertilizer treatments, the rate and type of fertilizer used). Mean tree growth

for each treatment was obtained and compared to that in untreated plots. For several

studies, the published reports did not contain all the information we required; when

possible, we consulted unpublished reports from our office files. Data from Installation 171 of the Forest Regional Nutrition Research project were obtained from the

Stand Management Cooperative, College of Forest Resources, University of

Washington, Seattle, Washington. 

Despite the operational nature of the precommercial thinning, tree characteristics

were fairly uniform among plots immediately after thinning within each treatment

(table 1). Although mean tree size is commonly increased somewhat with level of

thinning (because smaller trees are cut), the young, undifferentiated stage of this

plantation apparently mediated against such effects associated with treatment

implementation. Thus, the uniform initial conditions in the three thinning treatments

should have provided a sensitive test of treatment differences in growth rates of

trees of similar size. In addition, height growth during the 2 years before treatment

(based on retrospective measurements) was remarkably similar among thinning

treatments (p = 0.91, table 1). Measurements obtained in the fixed-area plots indicated that T1 had, on average, only about one-half the trees that were present in

T0, the control; and T2 had only about one-third as many as the control. All thinning

treatments differed significantly from each other in tree density, with no overlap

among plots in trees per hectare in the different thinning treatments. 
6

Diameter Growth Assessment of data from the 25-tree temporary plots revealed that diameter growth

in the first 2 years increased with the amount of thinning (fig. 1). Growth in the heavier thinning (T2) was about 10 percent greater than in the unthinned control (T0).

Growth in the lighter thinning (T1) averaged 5 percent greater than that of the control but did not differ significantly from either the control or the heavier thinning.

Quadratic mean diameter growth response increased in combined periods 2 and 3.

In unfertilized plots, diameter growth response averaged 18 percent greater in the

heavier thinning than in the unthinned control. Response to thinning in the fertilized

plots was greater in absolute amount but similar in relative terms, increasing from

about 10 percent in T1 to 18 percent in T2. Response to fertilizer application was

significant overall and was similar in all thinning treatments, averaging about 32 

percent. 

If diameter growth in period 1 and combined periods 2 and 3 (fig. 1) is added to 

initial diameter (table 1), it is apparent that trees nearly doubled in diameter in the

unthinned, unfertilized plots between ages 10 and 16–to nearly 12 cm. During the

Figure 1—Diameter growth by thinning and fertilizing treatment. Letters centered over the thinning treatment designations indicate differences in growth in period 1 (prior to application of the fertilizing treatments) among the three thinning treatments. Letters on top of the bars indicate differences in growth in

periods 2 plus 3 by thinning treatment within a fertilizing treatment (bars topped by the same letter are

not significantly different at p ≤ 0.10; lower case letters refer to the F0 treatment and uppercase letters 

to the F1 treatment).
same period, trees in fertilized plots with the heavier thinning grew to 14.4 cm. Thus,

when combined, the two cultural practices increased tree diameter by about 20 percent in 6 years.

In contrast to diameter growth, height increment of the selected tallest trees during

the first 2-year period after thinning decreased slightly with the intensity of thinning

(table 2). Height growth in the heavier thinning treatment was about 11 percent

lower than in the unthinned control plots.

In the second 2-year period, height growth in the thinned treatments of the unfertilized plots continued to be slightly lower than in unthinned plots on average (table 2),

but such reductions did not approach significance (p = 0.49). Differences among

thinning treatments in fertilized plots were negligible. Thus, trees in all treatments

recovered from shock by the end of the fourth growing season if not earlier. Response

to fertilizer overall was highly significant. Differences between fertilized and unfertilized plots were largest (14 percent and 16 percent) in the unthinned and more

heavily thinned plots, and only 9 percent in the lighter thinning treatment.

In the third 2-year period, there were no differences among thinning treatments in

height growth in unfertilized plots (table 2); therefore, trees had recovered from the

shock evident in earlier measurements. In fertilized plots, however, height growth

decreased with thinning, and growth in the heavier thinning was significantly lower

than in unthinned plots. Although such a pattern may seem odd, especially given 

the similarity of growth among thinning treatments in period 2, the renewed reduction in growth with thinning can most likely be linked to development of increased

competition from understory shrubs and herbs in thinned and fertilized plots. In a

study near Shawnigan Lake on Vancouver Island, Stanek and others (1979) found

that the treatment with the heaviest thinning (about two-thirds basal area removed)

plus fertilization at 224 kg of N per ha resulted in greater understory biomass than

the other thinning and fertilizing treatments tested in the Shawnigan Lake study;

bracken fern (Pteridium aquilinum L.) biomass was more than six times greater

7

Height Growth

Table 2—Height growth of Douglas-fir as related to thinning and fertilization treatments by 2-year 

periods

Period 1† (1985-86) Period 2 (1987-88) Period 3 (1989-90)

Thinning

treatment Before fertilization Unfertilized Fertilized Difference Unfertilized Fertilized Difference 

Meters

T0 1.42a 1.64a 1.87a 0.23* 1.50a 1.74a 0.24*

T1 1.33ab 1.61a 1.76a .15 1.55a 1.66ab .11 

T2 1.27b 1.56a 1.82a .25* 1.50a 1.58b .07 

† After thinning.

Means in a column followed by the same letter are not significantly different at p ≤ 0.10.

* The difference between fertilized and unfertilized was significant at p ≤ 0.10.
and salal biomass more than double after 5 or 6 years as compared with biomass 

of these two species in the unthinned, unfertilized (control) treatment. A comparison

at Shawnigan Lake involving one unreplicated plot showed that understory removal

during the first 5 years after thinning and fertilizing increased tree growth (in this

case, the measure was d.b.h.) (Brix 1993). Recent observations on a subsample of

plots in our study were consistent with the understory competition hypothesis; that

is, understory plants appeared to be taller and denser in the heavily thinned plots

that had received an application of N fertilizer (224 kg of N per ha). As trees grow

and crowns expand, however, the understory will become shaded and less vigorous,

and the relations of height growth to treatment are likely to change.

Over all periods and thinning treatments, fertilization increased height growth and

was statistically significant, but means between the fertilized and unfertilized treatments differed significantly only for the unthinned plots (T0). Lack of significant

growth responses to fertilizer in the thinned plots (T1 and T2) is probably related

to increased competition for moisture and nutrients associated with enhanced

development of the understory.

During the 6 years after thinning, mean height of the selected tallest trees more

than doubled–increasing from 4.2 to about 8.7 m, on average, in unfertilized plots

and to about 9.0 m in fertilized plots (tables 1 and 2). Initial reductions in height

growth associated with thinning faded after the first 2 years; by the sixth year, trees 

in the T2 thinning differed in total height from those in unthinned plots by only 2.6

percent in the unfertilized plots and 3.9 percent in the fertilized plots. Mean tree

heights in fertilized plots at all thinning levels were taller than those in the unfertilized, unthinned plots; therefore, fertilizer application more than compensated for 

any height growth reduction associated with thinning. Still, the increase in mean 

tree height associated with combined heavy thinning and fertilization amounted to

only 2 percent after 6 years, or in the most productive combination (no thinning but

fertilization), only 5 percent; thus, compared with an increase in diameter of about

20 percent, effects of the two cultural practices on height growth were minor.

We determined that eight other silvicultural studies at Wind River would be of interest to compare with the results in our study (table 3); these studies were located on

Trout Creek Hill (as was our study site) or in the nearby drainages of Planting Creek

or Martha Creek (fig. 2). These studies were spacing and species mixture trials on

Trout Creek Hill (studies 2a and 2b in figure 2 and table 3); the thinning and fertilization trial in a plantation adjacent to our study on Trout Creek Hill (study 3); the wide

spacing (study 4), “spot” thinning (individual tree release) (study 6), and fertilization

trials (study 5) in the plantation in the Planting Creek area; the “spot” thinning (study

7) and dominance thinning (study 8) trials in natural stands in the Martha Creek

area; and a fertilization trial in a natural stand (study 9) on Trout Creek Hill. The

studies are all in the same general area and differ little in elevation (fig. 2). In addition, although not identical, they share the same general soil type (ash-influenced,

deep, well-drained, mostly loamy soils). The weather stations are nearby and at 

similar or somewhat lower elevations (fig. 2).

8

Comparing Results with

Other Studies at Wind

River and Elsewhere
Height and diameter growth in our study were similar to those measured in the

nearby young spacing trials on Trout Creek Hill (studies 2a and 2b in table 3); thus,

we have some confidence that the growth rates in our study were not atypical for

the area. Early responses to both thinning and fertilizing treatments, however, differed substantially among these other studies at Wind River. The specifics of those

studies are discussed below.

Miller and Reukema (1977) found that thinning the adjacent planted stand (study 3

in figure 2 and table 3) from 1,110 to 730 trees per ha (about 3.7 by 3.7 m) reduced

height growth by 25 percent as compared to trees in unthinned plots and had negligible effect on diameter growth (-4 percent) during the first 5 years. Applying fertilizer

to the thinned stand, however, nearly doubled height growth and increased diameter

growth by more than 30 percent during the same period. There was no unthinned,

fertilized treatment to compare with the new study, however.

9

Figure 2—Location of nine silvicultural trials in young-growth stands on the Wind River Experimental Forest and two weather stations (WS1 and WS2) nearby. The numbers in the figure are

associated with the studies listed in table 3; 2a and 2b refer to two different trials planted 1 year

apart. Major roads are shown as bold lines. Contours are shown as dashed lines with the interval between contour lines 400 m in elevation.
10

Table 3—Comparison of site and stand characteristics and tree growth in nine silvicultural studies at Wind River in southwestern Washington 

Site information Initial stand conditions Postthinning Fertilization

Growth Response Response 

Study number Site Fire Seed and namea class history sourceb Age Ht. D.b.h. Density Density Ht. D.b.h. Ht. D.b.h. N Ht. D.b.h. Comments

Years m cm Trees per hectare m/yr cm/yr - Percent - kg/ha - Percent -

Plantations: 

1 TCH IV Old growth PS 13 4.2 6.0 1,460 T0 1,460 0.8 0.9 - - - - 224 15 22 Thinning response based 

this study logged, T1 740 0.8 1.0 13 10 224 8 37 on 6 years. Fertilization 

some piles T2 540 0.7 1.1 5 20 224 10 30 response based on 4 burned years. N applied as AN.

2 a and b TCH IV Old growth PS 13 4.9 6.7 1,110 - - 0.7 0.8 - - - - Initial spacing trial nearby 

Units 4 and 8c logged, slash 14 5.0 6.5 1,110 - - 0.7 1.0 - - - - (not thinned). Growth 

piles burned 14 4.8 6.6 620 - - 0.7 1.1 - - - - based on 5 years.

3 TCH V Old growth PU 20 6.1 7.4 1,400 T0 1,400 0.5 0.6 - - - - - - Ht responses adjusted 

M and Rd logged, T1 730 0.4 0.6 -25 -4 336 191 84 for a covariate. Fertilizer 

boadcast response based on 6 burned trees. Response based

on 5 years. N applied as urea.

4 PC V Major wildfires PU 28 8.8 10.0 1,600 T0 1,600 0.5 - - - - - - T0 comparison not 

WSTe 1902, 1927 Tx 140 0.2 - - -60 - - available for diameter as 

to all treatments thinned. 

890 Response based on 5 

years.
11

Table 3—Comparison of site and stand characteristics and tree growth in nine silvicultural studies at Wind River in southwestern Washington (continued)

Site information Initial stand conditions Postthinning Fertilization

Growth Response Response 

Study number Site Fire Seed and namea class history sourceb Age Ht. D.b.h. Density Density Ht. D.b.h. Ht. D.b.h. N Ht. D.b.h. Comments

Years m cm Trees per hectare m/yr cm/yr - Percent - kg/ha - Percent -

5 PC V Major wildfires PU 36 13.7 14.2 1,550 T0 1,500 0.4 0.3 - - - - 157 54 79 All plots unthinned. 

Fertilization 1902, 1927 314 74 152 N applied as AN. trialf 471 60 160 Responses based on 

4 years.

6 PC V Major wildfires PU 28 9.8 11.6 1,550 T0 1,550 0.4 0.4 Dominant trees in T3

Spot thing 1902, 1927 T1 -1Ch 0.4 0.4 -9 -2 grew 8% more in ht and

T2 -2C 0.4 0.5 -9 2 22% more in d.b.h than 

T3 -3C 0.4 0.5 -13 11 T0. Codominant trees in 

T3 had 38% less ht 

growth and 6% less d.b.h. growth than in T0. 

Responses based on 6years. 

Natural stands:

7 MC IV Old growth Nat. 41 20.4 19.6 -- j T0 -- j 0.3 0.2 - - - - Ht trees damaged in T1

Spot thini logged, slash T1 -1Ch na 0.3 - - 23 and T2. Dominant trees 

broadcast T2 -2C na 0.3 - - 46 in T3 had equal ht 

burned T3 -3C 0.2 0.4 -20 54 growth and 50% more 

d.b.h. growth than in T0. 

Codominant trees in T3

had 37% less ht growth and 11% more d.b.h. growth than in T0. Growth based on 5 years.
12

Table 3—Comparison of site and stand characteristics and tree growth in nine silvicultural studies at Wind River in southwestern Washington (continued)

Site information Initial stand conditions Postthinning Fertilization

Growth Response Response 

Study number Site Fire Seed and namea class history sourceb Age Ht. D.b.h. Density Density Ht. D.b.h. Ht. D.b.h. N Ht. D.b.h. Comments

Years m cm Trees per hectare m/yr cm/yr - Percent - kg/ha - Percent -

8 MC IV Old growth Nat. 10 2.2 3.3 11,300 T0 11,300 0.4 0.6 - - - - Growth for dominant 

Dom. think logged, slash TSl 1,240 0.3 0.6 1 28 trees only. Growth rates 

broadcast TDl 1,260 0.4 0.7 -5 71 adjusted for initial differburned ences in tree size. Plots

not replicated. Growthbased on 5 years.

9 THC IV Old growth Nat. 50 24.3 18.4 2,120 2,120 0.3 0.2 - - - - 224 as 6 53 All plots unthinned, 

RFRNPm logged, slash urea growth on 3 urea and 2

Inst. 171 broadcast 224 as 41 55 AN plots compared to 1 

burned AN control plot. Growth 

based on 4 years. 

a Major locations are Trout Creek Hill (TCH), Planting Creek (PC), and Martha Creek (MC). Ht = height, d.b.h. = diameter at breast height, AN = ammonium nitrate. Study numbers

match those in figure 2.

b PS = planted, source was same seed zone, PU = planted, unknown or nonlocal seed source, Nat. = naturally seeded stand.c Study C-45, data on file, Olympia Forestry Sciences Laboratory.d Miller and Reukema 1977.e Staebler 1956a, Harrington and Reukema 1983.f Reukema 1968, Miller and Tarrant 1983.g Krueger 1959, Reukema 1963 (report on study P27 on file, Olympia Forestry Sciences Laboratory, 16 p.).h Treatments in the spot thinning removed 1, 2, or 3 competitors; stand density not estimated.i Staebler 1956b, Reukema 1961, Reukema 1963 (report on study P20 on file, Olympia Forestry Sciences Laboratory, 18 p.).j Stand density not measured, the stand was described as well stocked, dense, and crowded.k Isaac 1926 (report on study P20 on file, Olympia Forestry Sciences Laboratory, 14 p.), Steele 1955.l TS = thinning based on spacing, TD = thinning to release dominant trees.m RFNRP = Regional Forest Nutrition Research Project. Data on file with: Stand Management Cooperative, College of Forest Resources, University of Washington, P.O. Box 352100,

Seattle, WA 98195-2100.
Similar contrasts are also evident in studies in the nearby Planting Creek area of

Wind River Experimental Forest. Height growth of trees on thinned plots in the widespacing trial (study 4 in table 3) where thinning shock was first quantified (Staebler

1956a) was about 60 percent less than that of control trees during the first 5 years;

during the 6- to 10-year period, trees in most thinning treatments recovered somewhat although height growth remained about 16 percent lower than that in control

trees (Harrington and Reukema 1983). Height growth in the widest spacing (9.1 

by 9.1 m) did not recover until 11 to 15 years after the thinning.

A trial of varying degrees of individual tree release (study 6) adjacent to the wide

spacing trial in the Planting Creek area and in the same plantation showed overall

reductions in height growth of 9 to 13 percent during the first 6 years after treatment

at age 28 (Krueger 1959). Response varied by crown class, however. Dominant

trees released from three competitors grew more than unreleased dominant trees

(about 8 percent in height and 22 percent in diameter), but codominant trees

released from the competition of three surrounding trees exhibited a severe reduction in height growth (38 percent) and a modest reduction (6 percent) in diameter

growth as compared to growth of unreleased codominant trees.

A fertilization trial in an unthinned area, also adjacent to the wide spacing trial in

Planting Creek (study 5 in table 3), yielded one of the largest and most long-lasting

responses to N fertilizer ever documented (Miller and Tarrant 1983); during the first

4 years, height growth was increased 54 to 74 percent and diameter growth 79 to

160 percent with 157 to 471 kg of N per ha applied as ammonium nitrate (Reukema

1968). Volume responses were 51 to 111 percent and continued undiminished for at

least 15 years (Miller and Tarrant 1983).

Thus, initial reductions in height growth after thinning were less, and increases in

diameter growth were greater in our study than in the above thinning trials in older

plantations. And though fertilization caused significant increases in diameter and

height growth in our study, such responses were markedly less than those obtained

in the adjacent plantation or in the Planting Creek area. On the other hand, diameter

growth response to thinning in the two studies in the natural stand at Martha Creek

(studies 7 and 8 in table 3) was quite positive (Reukema 1961, Staebler 1956b,

Steele 1955) and increased with degree of thinning release; the greatest release

resulted in 54 and 71 percent greater diameter growth than trees on unthinned

plots. Height growth was similar for all treatments in one trial (study 8 had a maximum difference among treatments of 5 percent in 5-year height growth). Height

growth in response to thinning in the other trial (study 7) is more difficult to assess

as the sample of trees measured for height growth was small and several height

trees were damaged. Dominant trees in the treatment with the greatest degree of

release (T3) had height growth rates equal to those of the unthinned trees. The fertilization trial in the natural stand on Trout Creek Hill (study 9) reported substantial

4-year diameter growth responses to N application (more than 50 percent greater 

in fertilized than in unfertilized plots) and positive but varying responses in height

growth.

13
We next consider the similarities and differences in the site and stand conditions

among the various trials and discuss the possible reasons for the observed differences in response to treatments. The nearby plantation trials that manifested more

severe thinning shock and greater response to fertilizer application differed from our

study plantation as follows: stands at thinning or fertilizing in the earlier trials were

older, site quality as determined by early growth rate was lower, effects of recent

wildfires or site preparation burns were more severe, and geographic sources of

planting material were nonlocal and now considered to be maladapted. In the following discussion, we examine these matters as well as precipitation, soil, and other

site factors to see if similarities and differences in such factors offer explanations

consistent with the observed responses of the various studies at Wind River. In

addition, results from thinning and fertilizing studies in Douglas-fir stands at other

locations in western Oregon, Washington, and British Columbia are discussed as

appropriate. 

In contrast to the previous suggestion by Harrington and Reukema (1983) that thinning shock is more likely when stands on poor sites are heavily thinned later than

the recommended age for precommercial thinning, we now believe that stand age 

is unlikely to be the major cause of the observed differences in thinning shock or in

response to fertilizer. It is true that our study was precommercially thinned within the

preferred age range of 10 to 15 years (Reukema 1975) and the other studies with

substantial thinning shock were thinned at 20 to 28 years. When we compare the

results from the spot thinning at Martha Creek in a 41-year-old, fully stocked natural

stand (study 7 in table 3) with the results from the same treatment at Planting Creek

in a 28-year-old plantation (study 6 in table 3), however, we see much better early

response in diameter growth of dominants, codominants, and intermediates in the

older stand (Reukema 1961, Staebler 1956b); and as discussed above, dominant

trees at Martha Creek had equal height growth in unthinned and heaviest thinning

treatments (study 7 in table 3). Moreover, shock was ephemeral (Rocky Brook,

thinned at age 27 years) or absent (Stampede Creek, thinned at age 32 years) in

other stand-level Douglas-fir thinning studies when the initial thinnings were done at

older ages (Williamson 1976, Williamson and Staebler 1971). Regionwide analyses

have indicated that response to N fertilizer is similar across age classes, although

there is a trend for greater response in younger stands (Chappell and others 1992).

The fertilizer trial established in a 50-year-old natural stand on Trout Creek Hill

(study 9 in table 3) also showed height and diameter responses to N (particularly

ammonium nitrate) that were generally much greater than those of our study. We 

do not intend to suggest that stand age (and associated tree and stand traits) does

not affect responses to thinning and fertilization–only that age seems unlikely to be

the major contributing factor in differences in type and magnitude of responses

observed in our study versus those of earlier Wind River studies.

Reported instances of thinning shock in Douglas-fir stands all have occurred on

sites of poor quality (IV and V). In addition, west of the Cascade Range in Oregon

and Washington, the response of Douglas-fir to N fertilizer is greater on low-quality

than high-quality sites (Miller and others 1986). Site quality was estimated to be site

V in the severely shocked nearby plantations (study 4, Staebler 1956a; Harrington

and Reukema 1983; study 3, Miller and Reukema 1977), whereas it appears to be

site IV in our study. Note, however, that the Miller and Reukema study and our study

are immediately adjacent, and soils and microclimate are nearly identical.

14

Considering Reasons

for Contrasting Results

Stand Age

Site Quality
Furthermore, publications on the Planting Creek thinning studies (study 4,

Harrington and Reukema 1983; study 6, Krueger 1959) indicate that the site for the

plantation trees was classified as site V, whereas the site for the adjacent fertilizer

study (study 5) was considered to be site IV (Miller and Tarrant 1983). One of the

other more distant studies (Rocky Brook) that showed only ephemeral shock (first 

2 years after thinning) was also site IV (initially reported as site V by Williamson

(1976) but subsequently determined to be site IV by Curtis and Marshall (1986)) and

another (Shawnigan Lake) was borderline between site IV and site V (Brix 1993,

Crown and Brett 1975, Crown and others 1977). The thinning in the young natural

stand at Martha Creek (study 8), which was considered to be site V, showed large,

early positive responses in diameter growth and little or no difference in height

growth (Steele 1955). In addition, the other thinning trial at Martha Creek (study 7)

that had excellent initial diameter growth response to release was on site IV ground

(Reukema 1961, Staebler 1956b). Thus, it does not appear that differences between

site IV and site V per se are strongly related to the observed differences in thinning

shock. And all studies mentioned previously–whether on site IV or site V land–responded

substantially more to fertilizer than did trees in our study. 

The Wind River area has fairly droughty summers with often 2 or more months 

with minimal precipitation; thus, precipitation during the growing season is generally

considered to be one of the factors that can account for year-to-year differences in

growth rates. If differences in precipitation influenced response to silvicultural treatment, we might expect a lower tendency for shock to be exhibited in periods of

above-average precipitation. Growing season precipitation (May 1 to September 30)

in the years after thinning and fertilizing treatments averaged 270 mm per yr (based

on 41 years of record) and varied substantially (minimum of 117 mm, maximum 433

mm). Precipitation levels, however, do not help explain the observed differences in

response to thinning, as the two trials that had the greatest shock had about average

growing season precipitation (mean of 253 mm per yr in study 4) or above-average

growing season precipitation (298 mm per yr in study 3) the years after thinning.

Growing-season precipitation in our study averaged 221 mm per yr for the 6 years

after thinning with a minimum value one year of 166 mm. 

Recent fire history differed among the various study areas in that the Planting Creek

area had been burned intensely in the Yacolt fire of 1902 and reburned in 1927, and

it is probable that the older trial adjacent to our study (study 3, Miller and Reukema

1977) had received a hot prescribed burn because of heavy slash remaining after

clearcutting the previous old-growth stand. In contrast, burning in our study was 

limited to piles on a few landings, and there was little if any burning over most of 

the area. Other studies that exhibited only mild and ephemeral shock, however, also

had experienced rather severe burns. The Shawnigan Lake site had a fire history

similar to the Planting Creek area. It had burned in 1925, was salvage logged in

1927, regenerated naturally, and reburned in 1942 to the point that the ground was

devoid of slash and had little humus (Crown and Brett 1975). Yet thinning shock

lasted only 2 years and recovery was so rapid that increased growth in the third

year more than made up for the initial reductions. Although we believe that fire 

history is unlikely to account for differences in thinning shock, we suspect that it

may play a role in influencing response to N fertilizer. All the Wind River plantation

studies that had large positive responses to N fertilization, as well as the very

15

Precipitation

Fire Severity
16

Seed Source

responsive, 50-year-old natural stand on Trout Creek Hill (study 9 in table 3) were

established after one or more wildfires or slash fires after harvest of old-growth

timber. The effects of these fires on soil properties would have been much more

intense than occurred in our study area where the only recent fires were restricted

to log landings. 

The planted stands in the Planting Creek area that exhibited severe shock (study 4,

Harrington and Reukema 1983, Staebler 1956a) or dramatic early and long-lasting

response to N fertilizer (study 5, Miller and Pienaar 1973, Miller and Tarrant 1983,

Reukema 1968) are known to have originated from a seed source from Roy,

Washington. This seed source is about 140 km NNW and about 500 m lower in 

elevation than the areas at Wind River where it was planted; this nonlocal seed

source is now considered to be poorly suited to the area. Moreover, the thinning and

fertilizer trial adjacent to our study (study 2, Miller and Reukema 1977) was established in 1952, and considering the date of establishment and rather poor growth of

the plantation in comparison with our study and other nearby plantings (studies 2a

and 2b in figure 2 and table 3), it seems probable that it too was established with a

nonlocal and maladapted seed source. Conversely, the stands that had only mild,

ephemeral shock (similar to that in our study) or no shock were established naturally

(study 8, Staebler 1956b), had abundant natural fill-in (Crown and Brett 1975,

Williamson 1976), or were planted with presumably suitable stock (Crown and Brett

1975). Thus, we think it is likely that poor adaptation associated with nonlocal seed

sources may predispose trees to experience more severe and long-lasting shock

after thinning. It is also probable that maladapted seed sources (in addition to burning

history) contribute to the particularly large responses to fertilizer observed in earlier

trials at Wind River; the plantations in which these studies were established tend to

be chlorotic and have fewer years of foliage and less dense foliage than plantations

established in recent years with known suitable seed sources. Moreover, genetic

researchers1 have observed general chlorosis in plantings for the Douglas-fir

heredity study, much of which consisted (by design) of nonlocal sources at any

given installation. 

Thinning shock–as manifested in reduced height growth–was minor and of short

duration, and diameter growth was positively impacted by thinning in this trial. Of

several possible reasons for differences between this experience and that in other

nearby studies, we do not think that its younger age, slightly higher inherent site

index (IV vs. V), and lack of recent fire offer adequate explanations. The maladapted

seed sources used in planting the Planting Creek area and, presumably, also the

adjacent stand studied by Miller and Reukema (1977), however, remain a likely

cause of the differences between our study and the earlier trials at Wind River in 

the magnitude and duration of “thinning shock.” Because N fertilizer seems to compensate for initial height growth reductions where it has been tested and companion

fertilizer studies have given much greater response on sites where thinning shock

was most severe, we suspect that either low available native N or a decreased

ability of trees to extract it after thinning also may be contributing factors.

1 Roy Silen and Frank Sorenson. 2001. Personal communications.

Principal plant geneticists (retired), USDA Forest Service, Pacific 

Northwest Research Station. Forestry Sciences Laboratory, Corvallis, 

OR 97331.

Management

Implications
17

The lower than expected height and diameter growth response to fertilizer in our

study and its shorter duration may be linked more closely to lack of recent fire, and

presumably higher levels of available native N, at our study site. The nearby fertilization test in an older natural stand (study 9 in table 3) gave much higher growth

response to applied N, but the site had been logged and burned intensely (oldgrowth logging slash broadcast burned) immediately before stand establishment.

Based on our study and comparison with earlier research, we believe that regardless of reasons for shock, precommercial thinning in plantations established from

appropriate genetic stock should result in negligible shock, even on poor quality

(site IV or V) forest land. Fertilizing sites that have low available N at about the

same time as thinning may be desirable because responses have been good and

any tendency toward shock has been overcome.

In the broader context of technology development and management-research interrelations, we acknowledge the value of Wind River Experimental Forest not only as

a cradle of initial forestry research but also as a location where responses of trees

and shrubs to cultural practices have sometimes been particularly large and long

lasting. Such dramatic responses have stimulated both early management interest

in the practices and the development and testing of related scientific hypotheses.

And although we recognize that management decisions, that is, to act or not to act,

must always be made based on the information available at the time, results of the

present followup study should caution us not to base long-term expectations and

decisions about practices on either short-term responses or on results from only one

or two studies–even when applying the practices in the same geographic location as

the initial study. Other seemingly unrelated management changes—such as genetic

makeup of new stands or current utilization standards and approaches to hazard

reduction or site preparation–could lead to major differences in response to a practice. Some form of research, adaptive management, or operational monitoring is

therefore desirable as a standard component of forest management operations.
18

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Shawnigan Lake: a synthesis of project results. Victoria, BC: Forestry Canada

Pacific Forestry Centre, BC Ministry of Forests, Research Branch. 64 p.

Brockway, D.G.; Topik, C.; Hemstrom, M.A.; Emmingham, W.H. 1983. Plant 

association and management guide for the Pacific silver fir zone, Gifford Pinchot

National Forest. R6-Ecol-130a-1983. Portland, OR: U.S. Department of

Agriculture, Forest Service, Pacific Northwest Region. 122 p.

Chappell, H.N.; Omule, S.A.Y.; Gessel, S.D. 1992. Fertilization in coastal Northwest forests: using response information in developing stand-level tactics. In:

Chappell, H.N.; Weetman, G.F.; Miller, R.E., eds. Forest fertilization: sustaining

and improving nutrition and growth of western forests. Contrib. 73. Seattle:

University of Washington, College of Forest Resources, Institute of Forest

Resources: 98-113.

Crown, M.; Brett, C.P., eds. 1975. Fertilizer and thinning effects on a Douglas-fir 

ecosystem at Shawnigan Lake: an establishment report. Rep. BC-X-110.

Victoria, BC: Department of Environment, Canadian Forest Service. 45 p.

Crown, M.; Quenet, R.V.; Layton, C. 1977. Fertilization and thinning effects on a 

Douglas-fir ecosystem at Shawnigan Lake: 3-year growth response. Rep. BCX-152. Victoria, BC: Department of Environment, Canadian Forest Service. 36 p.

Curtis, R.O.; Marshall, D.D. 1986. Levels-of-growing-stock cooperative study in 

Douglas-fir: report no. 8–the LOGS study: twenty-year results. Res. Pap. PNW356. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific

Northwest Research Station. 173 p.

Franklin, J.F.; Dyrness, C.T. 1973. Natural vegetation of Oregon and Washington. 

Gen. Tech. Rep. PNW-8. Portland, OR: U.S. Department of Agriculture, Forest

Service, Pacific Northwest Forest and Range Experiment Station. 417 p.

Harrington, C.A.; Reukema, D.L. 1983. Initial shock and long-term stand development following thinning in a Douglas-fir plantation. Forest Science. 29(1): 33-46.

King, J.E. 1966. Site index curves for Douglas-fir in the Pacific Northwest. Pap. 8. 

Centralia, WA: Weyerhaeuser Company Forestry, Western Forestry Research

Center. 49 p.

Krueger, K.W. 1959. Diameter growth of plantation-grown Douglas-fir trees under 

varying degrees of release. Res. Note 168. Portland, OR: U.S. Department of

Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment

Station. 5 p.

Miller, R.E.; Barker, P.R.; Peterson, C.E.; Webster, S.R. 1986. Using nitrogen 

fertilizers in management of coast Douglas-fir. I. Regional trends of response. In:

Oliver, C.D.; Hanley, D.P.; Johnson, J.A., eds. Douglas-fir: stand management for

the future. Contrib. 55. Seattle, WA: University of Washington, College of Forest

Resources, Institute of Forest Resources: 290-303.
19

Miller, R.E.; Pienaar, L.V. 1973. Seven-year response of 35-year-old Douglas-fir 

to nitrogen fertilizer. Res. Pap. PNW-165. Portland, OR: U.S. Department of

Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment

Station. 24 p.

Miller, R.E.; Reukema, D.L. 1977. Urea fertilizer increases growth of 20-year-old 

thinned Douglas-fir on a poor quality site. Res. Note PNW-291. Portland, OR:

U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and

Range Experiment Station. 8 p.

Miller, R.E.; Tarrant, R.F. 1983. Long-term growth response of Douglas-fir to 

ammonium nitrate fertilizer. Forest Science. 29(1): 127-137.

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future: proceedings of a symposium. Contrib. 55. Seattle, WA: University of

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304-309.

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PNW-208. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific

Northwest Forest and Range Experiment Station. 4 p.

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fertilizer. Res. Note PNW-86. Portland, OR: U.S. Department of Agriculture,

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Reukema, D.L. 1975. Guidelines for precommercial thinning of Douglas-fir. Gen. 

Tech. Rep. PNW-30. Portland, OR: U.S. Department of Agriculture, Forest

Service, Pacific Northwest Forest and Range Experiment Station. 10 p.

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region. Gen. Tech. Rep. PNW-298. Portland, OR: U.S. Department of

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Journal of Forestry. 54(5): 339.

Staebler, G.R. 1956b. Effect of controlled release on growth of individual Douglasfir trees. Journal of Forestry. 54(9): 567-568.
Stanek, W.; Beddows, D.; State, D. 1979. Fertilizer and thinning effects on a 

Douglas-fir ecosystem at Shawnigan Lake on Vancouver Island: some observations on salal and bracken fern undergrowth. Rep. BC-R-1. Victoria, BC:

Department of Environment, Canadian Forestry Service. 11 p.

Steele, R.W. 1955. Thinning nine-year-old Douglas-fir by spacing and dominance 

methods. Northwest Science. 29(2): 84-89.

Williamson, R.L. 1976. Levels-of-growing-stock cooperative study in Douglas-fir: 

report no. 4–Rocky Brook, Stampede Creek and Iron Creek. Res. Pap. PNW210. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific

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20
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