Douglas-fir growth can be increased report from Pacific Northwest shows By ROBERT F. STRAND, Forestry Supervisor
Central Research Division
Crown Zellerbach Corporation
Camas, Wash.
PORTLAND, 0RE.-Th e purpose of
applied forest research and develop­
ment is to provide information to
guide forest management decisions.
Decisions concerning use of fertil­
izers in forestry require reliable an­
swers to such questions as: How does
fertilization compare with other alter­
natives for producing more wood?
What fertilizer treatments have the
most favorable cost-benefit potential
for specific stand and site conditions?
We intend to discuss currently
available information and research in
progress concerning western Oregon,
western Washington and British Co­
lumbia. We also suggest work needed
to provide better basis for decisions
on forest fertilization.
About 20 years ago,
three University of Washington pro­
fessors, Dr. S. P. Gessel, Dr. P. G.
Haddock, and Dr. R. B. Walker, no­
ticed yellow-green foliage in extensive
stands of Douglas-fir and initiated research on nutritional needs of local
conifers. Their greenhouse studies
demonstrated the need of Douglas-fir,
western hemlock, and western redcedar for many nutrient elements;
their field trials in Douglas-fir indicat­
ed widespread nitrogen deficiency in
soils derived from glacial materials in
northwestern Washington.
Some private companies and land
management agencies took a lively interest in the progress of this research.
They initiated and expanded their own
research and operational efforts in
forest fertilization as evidence of
stand response to N fertilizers accu­
mulated and the certainty of contin­
ued rising stumpage prices increased.
Further impetus was provided by wellpublicized research and large-scale
fertilization in Scandinavia, particu­
larly by the Swedish Cellulose Co.
Recognizing a common need for
additional, but costly, information,
private companies, government agen­
cies, and the fertilizer industry have
joined in two cooperative, regional
programs to provide a cost-sharing
and coordinated approach to forest
fertilization research.
One program, the Regional Forest
Nutrition Research Project, is admin­
Background.
By RICHARD E. MILLER, Research Forester
Forestry Sciences Laboratory
Pacific Northwest Forest & Range Experiment Station
Forest Service, U. S. Department of Agriculture
Olympia, Wash.
istered by the College of Natural Re­
sources, University of Washington.
The goal is to develop guides for
planning of large-scale fertilizer appli­
cations to forest lands. With contribu­
tions from cooperators, the University
will establish and maintain a balanced
series of field fertilizer trials ( 10 8 ) in
western Oregon and Washington in
15- to 60-year-old forests of Douglas­
fir (720 plots) and hemlock ( 2 8 8).
The second program has been es­
tablished by the British Columbia For­
est Fertilization Board with members
from private forest industry, The Ca­
nadian Department of Forestry, and
the B.C. Forest Service. Tests are
planned or underway on Vancouver
Island. The major effort will be a se­
ries of fertilizer trials in 10­ to 40­
year-old Douglas-fir and western
hemlock stands on sites III and IV
( 100-year-index-age period) and ma­
jor soils on Vancouver Island.
Existing fertilizer trials. There are at
least 208 fertilizer trials in established
stands in western Oregon, Washington,
and British Columbia, and these trials
are potential sources of information
concerning growth and yield in managed stands. Each trial includes two
or more plots, which are at least one­
twentieth of an acre. In addition to
3,112 plots in these trials, there are at
least 2,500 smaller plots. Fertilizer
trials in regeneration studies are not
included in the accompanying table.
Near!)' all trials are in Douglas-fir
stands, most are on soils derived from
glacial material, and all tests include
nitrogen.
Tree response to
different nutrients.
Apparently, nitrogen is the most ef­
fective element for stimulating growth
of Douglas-fir and hemlock in western
Oregon, Washington, and British Co­
lumbia. Other elements, alone and in
combination with N or other ele­
ments, have not been adequately test­
ed to evaluate their potential impor­
tance. Other elements are likely to be­
come growth-limiting when inade­
quate natural supplies of N have been
corrected by fertilizer application.
This opinion is supported by experi­
mental results from studies where
growth on N-treated plots was less
than growth on plots with comparable
amounts of N plus other elements
such as phosphorus, potassium, or sul­
fur. Although western hemlock, west­
ern redcedar, and Sitka spruce have
also responded to fertilizer, the fol­
lowing discussion of growth responses
is limited to those in Douglas-fir
stands after nitrogen application.
In general, cubic volume responses
by Douglas-fir to nitrogen range from
0 to more than 100 per cent over the
pretreatment growth rate and Q!:.Ob­ 7
average about 30 per cent during
a 5­ to 7-year period. For example,
results from replicated experiments at
four locations ranging from site II to
IV demonstrate that nitrogen appli­
cations totaling 200 to 300 pounds per
acre provided growth increases over
unfertilized plots of 257 to 7 80 cubic
feet per acre (17-63 per cent) in peri­
odic growth during 5- to 7- year peri­
ods. Moreover, continued response is
most likely. Significant to pulp users
is the fact that production of wood by
weight on fertilized plots of Douglasfir is only slightly less (6-8 per cent)
than production by volume.
Effect of stand age. Douglas-firs up to
300 years of age have responded to
nitrogen fertilizer. Two separate analyses of data from hundreds of plots
in the 15­ to 90-year range showed
similar basal area increase by all age
classes.
Although increases in total volume
and basal area may be similar in both
immature and mature stands, the rei­
ative gain in merchantable volume or
in value is not clear. Greater financial
returns may result from treating older
stands, since (1) growth increases can
be readily harvested in intermediate
or final cutting, and (2) value of
growth commonly increases with
stand age. However, fertilizing young
stands to accelerate production of
commercial-size timber can also pro­
duce remarkable value growth.
Information currently available
suggests benefits from fertilizing a
wide range of age classes. If nutrientdeficient sites exist in all age classes,
then assignment or priority to one age
(Continued on next paJ?e)
Reprinted from the October 1969 issue of FOREST INDUSTRIES
Reproduced by the Forest Service, U. S. Departm nt of Agriculture, for official
use
2 9
FERTILIZATION
class or another appears more relat d
to the distribution of age classes
available to the forester and his spe­
cific management objectives.
In overstocked stands of Douglas­
fir, large trees generally respond more
than smaller trees to fertilizer. There is
evidence that this may increase rate
of natural thinning. The effect of fer­
tilizing overstocked stands of hemlock
and redcedar or mixture of these spe­
cies with Douglas-fir is being investi­
gated to ,develop possible alternatives
to costly precommercial thinning.
Effect of stocking, Nitrogen fertilizer
has increased Douglas-fir growth per
acre over a wide range of stocking
levels. Whether fertilization is more
likely to produce a greater in::rease
TABLE I FERTILIZER TRIALS IN ESTABLISHED, CONIFEROUS STANDS IN WESTERN BRITISH COLUMBIA, WASHINGTON, AND OREGON (AS OF JULY
1969)
Trials
Province or State
Organization
Western British Columbia
Canadian Department of
Plots
1
32
5
100
6
83
22
168
908
495
1
118
1
5
2
1,705
16
173
29
14
295
68
6
5
60
20
4
5
36
188
776
507
45
15
7
36
214
64
631
3,1121
Fisheries & Forestry
Cominco, Ltd., and British
Columbia Forest Service
Crown Zellerbach Corp.
MacMillan Bloedel, Ltd.
Pacific Logging Co., Ltd.
& Cominco, Ltd.
University of British
Columbia
Crown Zellerbach Corp.
Western Washington
U. S. Forest Service,
Pacific Northwest Forest
& Range Exp. Sta.
University of Washington
Washington Department
Natural Resources
Washington State University
Weyerhaeuser Timber Co.
Crown Zellerbach Corp.
Western Oregon
Oregon State University
Roseburg Lumber Co.
U.S. Forest Service,
Pacific Northwest Forest
& Range Exp. Sta.
Total
Of this total 2,796 plots (90 per cent) are in
Doug/as-fir forests and 2,052 66 per cent) on
soils developing from g/acia material.
1
[
in total or merchantable volume with
one level of stocking or another is not
known. With low stocking levels, for
example those following moderate to
heavy thinning, fertilizer application
can compensate for the initial loss of
total increment which is commonly
associated with thinning.
Results of several Weyerhaeuser
studies suggest that fertilizer com­
bined with thinning produced more
cubic-foot increase than that pro­
duced by either of the two treatments
alone.
30
Future research and development
should devote much more effort to
manipulating growing-stock levels in
combination with fertilization.
Effect of site quality. Nitrogen has in­
creased Douglas-fir growth over the
full range of site quality from I+ to
V -. Understandably, growth increases
from fertilizer will be greatest where
lack of available nutrients-and not
other factors-limits forest growth.
There is no generally applicable evi­
dence that more response to fertilizer
occurs by fertilizing the upper, mid,
or lower range of site quality. Recent
analyses by Crown Zellerbach and the
University of Washington show no
consistent pattern in basal area
growth response over the range of site
lii and lower. Such analyses, which
combine growth data from stands dif­
fering widely in site quality as well as
stocking, age, and initial condition at
time of fertilizing, are worthwhile at­
tempts to gain generalizations from
vast amounts of data.
However, concurrent differences in
other factors commonly mask the
true and independent effect of site
quality, Moreover, site index alone is
probably too crude a measure of nu­
trient status of a stand to provide a re­
liable basis predicting fertilizer needs
and thus to assign priority for exten­
sive fertilizer operations.
In specific or local areas where few­
er growth-determining factors vary,
closer relationships between response
and site quality are to be expected.
For example, the University of Wash­
ington data from the glaciated area
near Shelton show very strong growth
increases from 300 pounds of nitro­
gen on SI 90 locations and ever small­
er gains through and including SI 140
stands. By adding nitrogen to these
low quality sites, we can achieve much
larger responses in volume production
than by adding the same quantity to
nearby, medium quality sites.
Selection of stands to fertilize. Forest
managers need to know in which
stands they can obtain best return
from fertilizer investments. As noted
previously, comparable responses are
reported from a wide range of stand
age and stocking. Currently, there is
no reliable basis for selecting stands
by site index or site quality except for
some local areas.
Considering current knowledge,
Northwest land managers would risk
less in fertilizing those stands with site
and stand conditions similar to those
in which successful fertilizer trials are
located. By this criterion, the glaci­
ated area around Puget Sound presents
a minimal risk for investment because
(1) there are very few trials where a
good response to nitrogen has not
been found and ( 2) large numbers of
trials are located on typical and ex­
tensive soil-site conditions.
In the absence of field trial results,
foresters have attempted to use soil
and foliar analyses along with soil sur­
vey information to diagnose nutrient
deficiencies. Soil and foliar analyses
have been useful in agriculture only
after considerable field experience has
established a close correlation be­
"This beginning certainly justifies a much larger investment
in research and development to be sure that we use fertilization's
full potential for increasing wood supply at reasonable cost."
About This File:
rThis file was created by scanning the printed pLiblication.
.
; M1s ca n identified by the software have been corrected; )
_
./
' howeyer,
some mistakes may remain.
·
tween tree growth and the nutrient
concentration in the soil or plant.
Experience has shown that the
need for fertilizer will frequently be
indicated by low nutrient concentra­
tions in soil or foliage; however, high
concentrations may not preclude the
possibility of fertilizer response. Cur­
rent research at the University of
Washington and Oregon State Uni­
versity is attempting to improve these
diagnostic tools for Northwest forests.
Rates of nitrogen application. Many
short-term trials show a nearly con­
stant of linear increase in growth re­
sponse per unit of nitrogen added be­
tween 100 and 200 pounds N per
acre. Above 200 to 300 pounds N per
acre, there is usually a gradually de­
creasing response per pound of N.
U.S. Forest Service data, however,
suggest that heavier applications may
extend the period of response and thus
shift the optimal amount of N to a
higher rate of application than current
short-term data suggest.
Presently, the best generalization is
that the optimal rate of N fertilization
would lie between 150 and 300
pounds per acre for a response dura­
tion of 5 to 7 years. Certainly, the bal­
anced design of the regional trials will
help determine best rates for differ­
ent climatic and stand conditions.
Placement, cost, and form of N. In
mountainous forests of the Pacific
Northwest, broadcast application by
aircraft-helicopter or fixed wing­
has proven practical and economical.
As discussed by Anderson in the Au­
gust issue of FOREST INDUSTRIES, total
cost of applying urea over large acre­
ages is approaching 10 cents per
pound of nitrogen. Nitrogen is spread
exclusively as dry pellets or prills, al­
though Crown Zellerbach and the
Union Oil Co. in cooperation with the
Forest Service are experimenting with
foliar sprays.
Urea prills are most commonly
used, because nitrogen in this form is
46 per cent of the payload as com­
pared with 33 per cent as ammonium
nitrate. Moreover, there is as yet no
evidence for Northwest conditions
that nitrogen as urea is any less effec­
tive per pound than that in other
forms. Current data analysis by the
University of Washington and studies
comparing urea versus ammonium ni­
trate by Crown Zellerbach may pro­
vide new information shortly.
Season of application. Season of appli­
cation can affect both growth response
and total cost of application. Of par­
ticular importance to growth response
are the climatic conditions between
time of application and peak of nutri­
ent use by the tree, Climate strongly
affects possible loss of applied nitro­
gen and thus net amount of fertilizer
available to plants; it also affects nu­
·trient uptake and other factors influ­
encing tree growth.
Comparable growth responses ap­
parently result from both spring and
fall application of N. Analysis of data
from Crown Zellerbach plots suggests
that the more the rainfall during the
first growing season, the more the re­
sponse; to a lesser extent, the later the
application within the January-to-June
period, the less the response over a
4-year period.
Several trials have been initiated to
determine the best season for apply­
ing fertilizers. Further background
study is necessary to tell us what tim­
ing of application and kinds of N fer­
tilizers to apply to reduce risk of N
losses and increase the N uptake.
Since weather conditions have a
strong influence on stand response to
fertilizers, reliable long-range weather
forecasts may be useful in scheduling
fertilizer investments.
However, season for maximum
growth response must be balanced
against season of minimum applica­
tion costs. There are obvious advan­
tages to fertilizer manufacturers and
applicators to extend sales and appli­
cation throughout the year. Accord­
ingly, greater economic benefits may
result from accepting some loss in in
crement to take advantage of season­
al fluctuation in application costs.
Nitrogen losses. The fate of applied
nitrogen is of current concern. Leach­
ing loss of N could result in nitrate
contamination of surface or subsur­
face water. Although current knowl­
edge indicates this is highly unlikely
with amounts and materials used in
forest fertilization, there is too much
public concern about water pollution
to forge ahead in operational fertili­
zation without additional studies and
monitoring.
Studies at the University of Wash­
ington suggest that leaching and vol­
atilizing losses are relatively unimpor­
tant in their study areas located on
glacial soils. Recent laboratory work
by Crown Zellerbach, however, sug­
gests that gaseous losses to the atmos­
phere after urea application could
amount to over 80 pounds of a 200­
pound-N-per-acre treatment. We
need to know the extent and effect of
fertilizer losses. This knowledge will
fix the amount and direction of effort
needed to prevent losses through new
fertilizers and closer timing and rates
of application.
Conclusion. We know at least the fol­
lowing at this time:
1. Nitrogen fertilizer can increase
growth of Douglas-fir on a wide range
of stand age, stocking levels, and site
quality.
2. Other elements have not been ad­
equately tested to evaluate their im­
portance.
3. In
general, cubic-volume re­
sponses by Douglas-fir to nitrogen
range from 0 to over 100 per cent
and probably average about 30 per
cent during a 5- to 7-year period.
4. Optimum rates of N appear to
lie between 150 and 300 pounds per
acre for a response duration of 5-7
years.
5. Existing fertilizer trials are po­
tential sources of information about
growth and yield in managed stands.
They are local examples to help man­
agers select stands for treatment.
This beginning certainly justifies a
much larger investment in research
and development to be sure that we
use fertilization's full potential for in­
creasing wood supply at a reasonable
cost.
Our wood-producing land base will
shrink due to increasing demands by
other users of forest land. The land
manager will need this fertilization
tool if he is to maintain a low-cost
supply of raw material to keep this
region's forest industry competitive in
1111
a world market.
31