Douglas-Fir Rotations-Time for Reappraisal? Robert 0. Curtis, Forestry Sciences Laboratory, 3625-93rd
Ave. SW, Olympia, WA 98512, and David D.l\'Iarshall,
Department of Forest Resources, Oregon State University,
Corvallis, OR 97331.
F
orest management practices in the Douglas-fir region have
gradually evolved over the past century. This period has seen a
progression from unplanned liquidation through establishment
of effective fire control, attempted application of the seed tree
method (Isaac 1940) and selective cutting (Kirkland and
Brandstrom 1936, Isaac 1956, Smith 1970) in the 1920s and
1930s, ;yidespread and fairly successful use of staggered set­
tings in the 1940s and 1950s, and general adoption in subsequent
decades of large clearcuts with artificial regeneration and in­
creasingly shorter rotations.
entrenched ideas. This paper discusses extended rotations as a
possible means of reducing conflicts between timber production
and other forest values
.
Extended Rotations
Extended rotations deserve close attention by all owners, as
one option for which we do have some basis for estimating the
consequences. Extended rotations (combined with thinning and
other cultural practices) would mean a sharply reduced land area
Much of this sequence represents the accumulation of bio­
in the regeneration and early developmental stages (and hence,
logicalknowledge(Isaac 1938, 1943, Williamson and Twombly
aesthetically more appealing landscapes, reduced slash burning,
1983) and constructive evolution of forest practices. But the
most recent phase-large clearcuts combined with short rota­
reduced herbicide use) . They would also mean larger trees,
higher quality wood, higher values per unit of volume (and,
tions-has been a political disaster, however efficient it may
therefore reduced direct management and harvesting costs); and
have been in terms of immediate financial returns and speedy
longer thinning cycles, more naturally occurring snags
establishment of productive young stands
down material, better habitat for some wildlife, and perhaps
.
We now hear people and organizations talking seriously
about rotations as short as 40 yr. In round numbers it takes 10 yr
for a cut area to green up and begin to look like a forest again.
nd
improved long-term site productivity and hydrological benefits.
An associated benefit would be increased carbon storage, mak­
ing extended rotations a possible component of policies for
Forty-year rotations mean 25% of the landscape perpetually in
mitigating climatic change
a freshly cut condition. Whether or not this makes biological
sense, it creates horrendous public relations and political prob­
understood and are compatible with existing growth and yield
lems These are huge costs that are not included in conventional
.
present net value computations.
This is a major-perhaps the major-root cause of many of
our present problems.
The combination of social and political pressures (stemming
.
The associated thinning and regeneration methods are well
estimation systems. Thus we
can
estimate the consequences
through straightforward extensions of existing procedures.
Extended rotations also imply a renewed interest in and
widespread application of commercial thinning. Extending ro­
tations is probably the least disruptive of possible changes in
largely from the visual impacts of current forest practices) and
forest practices on public lands, which still contain much old
concerns raised by some scientists about certain biological
timber. Extending rotations involves obvious supply problems
for owners who have already removed most of their older age
aspects of current practices is forcing major changes in forest
management practices, with increased emphasis on amenity,
classes and must provide a continuous timber flow. Current
wildlife, and recreational values (DeBell and Curtis 1993). A
variety of alternative practices are being proposed or applied,
regulatory uncertainties are also a disincentive to long rotation
often referred to under the collective name of"New Forestry "
.
A general shortcoming of many of these practices is that we have
management
.
Feasibility of longer rotations depends partly on the effect it
little basis for quantitative estimates of the long-term results­
will have on timber yields. Forest Service minimum rotations
are set by the National Forest Management Act at culmination
eithercosts or benefits (if any). For some, this is totally lacking
of mean annual increment (MAI
.
Yet, this is certainly a time when we need to re-examine
=
production/age)--the point
at which average production over the rotation peaks. Other
WJAF 8(3) 1993
81
organizations use criteria that include other financial, tax, and
policy constraints. But the pattern of development of MAl is still
one of the underlying determinants.
Many people assume that MAl patterns and age of culmina­
tion are fixed and well-understood characteristics of a species.
Many also assume that intensive management and high produc­
tion necessarily mean short rotations. Both assumptions are
questionable.
The effects of extended rotations for coast Douglas-fir
(Pseudotsuga menziesii var menziesii) can be estimated, either
from predictions generated by the various existing stand simu­
lators, or from the results of experimental installations that
represent older stands that have had some sort of consistent
management. These two approaches ought to produce the same
answers, but won't necessarily because there are a lot of data
around that have not been incorporated in our present simulators
or adequately summarized and compared.
$125. PCT355+CT
(solld-sW ORGANON; dots•Willametle ORGANON; dash•DFSIM; dash/dot-SPS)
1.10
1.00
6
0.90
0.80
"
0.70
E
0.50
.§.
1;j
,
;;:
0.40
;;:
;:;;
0.20
li
,1/
'irl
.,.
0,30
0.10
0.00
I
...;. =-:.1.
. ..
-·-
.... ....
:Y
/
#
0.60
.
jj
r
80
60
40
20 .
120
100
140
AGE (years)
Figure 1. Estimated mean annual increment as ratio to maximum
on a good site (site II).
Comparisons of Simulator Predictions
Bulletin 201
We do not usually think of normal yield tables as "simula­
tors," but they are in a sense even though not very flexible ones.
From its initial publication in 1930 until fairly recently, Bulletin
201 (McArdle and Meyer 1930, McArdle et al. 1961) was the
bible of Douglas-frr foresters. Its influence still lingers.
Weknownow thatMcArdle's height curves were incorrectly
shaped. Most people today agree that King's (1966) are a better
regional average. Because of the way normal yield tables were
constructed, the volume curves are strongly affected by the
height curves. Substitution of King's curves for McArdle's in
the B201 yield tables gives considerably different development
patterns. Culmination occurs later, and the curves are relatively
flat over a considerable range ofliges (Curtis 1992a). They look
more like the curves produced by current simulators than do the
. originals.
·
S1 OS.
1.10
6
0.90
'
0.70
E
0.50
.§.
1;j
;:;;;;:
;;:
;:;;
of'
0.80
"
/;'
0.80
0.10
0.00
.. ····
v
,•'JZ
///
0.30
0.20
/
II
I•
0.40
There are three publicly available and widely'used simulators
. for the westside. These are ORGANON (Hann et al. 1992),
currently available in southwest Oregon and Willamette Valley
versions; DFSIM (Curtis et al. 1981); and SPS (Arney 1985).
. We can see what they say about the effect of harvest age by
plotting the ratio of MAI/MAimax over age. Figures 1, 2, and 3
show this for a management regime that includes precommercial
. and commercial thinning.
For site II, DFSIM and SPS say that a 40-yr harvest age will
produce about 75% of the potential cubic volume production;
ORGANON (southwest Oregon version) says only 55%. For
siteiii,DFSIMandSPS say about 60%, while ORGANON says
about40%. For site IV, DFSIM says about40%, while SPS and
ORGANON say about 30%.
If, instead, we plot MAl in cubic feet rather than the ratio to
maximum (Figure4), we see why the ORGANON estimates of
relative production are so different. Estimates of MAl aren't
really very different up to about age 60; the difference is in the
estimate of maximum MAl. Estimated age of culmination
comes somewhere around the point where each model runs out
//
·"
/
40
20
60
WJAF 8(3) 1993
80
100
120
140
AGE (years)
Figure 2. Estimated mean annual increment as ratio to maximum
on a medium site (site III).
Site 85. P355+CT
(soiJd-sW ORGANON; dots•Willametle ORGANON; dash•DFSJM; dashfdot•SPS)
· · ·�· ···........-. ....,... : =
1.10
1.00
•
82
·-:-:..":":o
· ··''T
1.00
·
ORGANON, DFSIM, SPS
PCT355+CT
(solld-sW ORGANON; dots•WJIIametle ORGANON; dash•DFSIM; dash/dot•SPS)
6
"
.§.
1;j
E
<
0.90
�..�. .
0.80
0.70
/
0.60
0,50
I
0.40
0.30
,'/
/j
/
/
0.20
1/J
0.10
/
0.00
20
40
60
80
100
120
140
AGE (years)
Figure 3. Estimated mean annual increment as ratio to maximum
on a poor site (site IV).
S105, PCT355+CT
(solld-sW ORGANON; dots•WIIIamette ORGANON; dash•OFSIM; dashfdot-SPS)
--r-r
200
y--r
I
!
-
<=
-c
-
....
....
r==r
. .
..
I
..
;::==:==:==:==:: : : :...:.. == ==!=..=. =.= ·=
.
1
-+--r
120 +--+-+-
..
. ..
.
.
.
· ·
.
- -+
_,' -· --+
---r·---+----<•tc-' ··_· _�-....s....c
-·- -+-···
_-+' _:'"c.:'•+--+-i---J
· ·-·
- --! _-·
, %-'f''-r--1-----!--+--+-+--+-r--J
l£-'
I
R--+-r--1-----!--+----+-+--+-+--J
100+--+SQ+----+
lj
/
+--,'/-!+-+--+--+-f--t---+-+--+--+--+--1
20
jiJ
60
+----+
,/-!+ +--+-+--+----!-+ --+-+--+-i---J
20
60
8()
100
120
AGE (years)
Figure 4. Estimated mean annual increment in cubic feet on a
medium site (site III).
Figure 5. First thinned at age 60, mean annual increment of this
low site (site IV) stand is still increasing at age 117.
of data and extrapolates off into thin air. This is around 70 yr or
so for DFSINI and SPS, and around 100 for ORGANON. (Some
part of the differences between ORGANON on the one hand and
DFSINI and SPS on the other may also be associated with real
Mt. Walker Thinning
solid•unthinned, dashed-1hlnned
differences in growth patterns for the geographic areas repre­
sented)
.
One conclusion is that all three simulators say that the !vW
curves are relatively flat at advanced ages Once one approaches
.
the maximum, there is a fairly wide range of ages that produce
about the same cubic volume yields For national forest lands at
.
least (which are predominantly lower site), we probably won't
lose much in the long run by going to quite long rotations - say
100 to 150 yr or more.
Comparisons of Remeasured Plot Data
60
70
60
Pending a more complete assembly and analysis of existing
90
100
110
120
AGE (years)
data for older stands, we do have some examples that are
thought- provoking (Others have been presented by Newton
.
and Cole 1987)
.
Figure 6. Observed mean annual increment in Mt. Walker
thinning study, site IV (poor).
Mt. Walker
This is a site IV stand near Quilcene, WA, with two unthinned
Stampede Creek LOGS. MAl and PAl.
(dash-thinned PAl, dots-thinned MAl, solld•unlhinned PAl and MAl)
plots and four plots that were thinned in the mid- 1930's and
again in the 1950's (Worthington 1966) These wereremeasured
.
in 199 1 at age 1 17 (Figure 5) MAl is still increasing (Figure 6).
.
The thinned stands have considerably larger trees and have
developed a multispecies and multilayer structure that should be
more acceptable to wildlife biologists than the denser and more
uniform conditions on the unthinned plots
.
Stampede Creek LOGS
This is one of nine installations in the levels-of-growing­
stock (LOGS) study series (Curtis and Marshall l 986). All nine
are showing more or less the same patterns over a range from site
II to1IV and in both plantations and natural stands. Stampede
Creek is site ill. At age 53, periodic annual increment (PAl=
periodic growth/yr in period)-which is an estimate of current
growth rate--(s still roughly twice the mean annual increment
in all treatments (Curtis 1992b, Figure 7) This stand is a long
.
way from culmination.
300
j
>.
<;'
tJ s. c
.s
E
"
z
260
200
150 100
:
+----+--==-.:"". r,;;;iii
-
50
,.. ...
......
0
30
35
I
. iHtltHr:t
iiitttt
.•••.•.••
r
I
I
45
50
I
55
AGE (years)
Figure 7. Observed mean annual increments and periodic annual
increments for treatments 1, 3, 5, 7, and control in the Stampede
Creek levels-of-growing-stock study,site III (medium). (Volumes
removed in calibration cut included.)
WJAF 8(3) 1993
83
Black Rock (Oregon State University)
This series of plots is mostly site II. The area was logged and
burned aro).lnd
1910 and regenerated naturally. The plots were
first thinned.(by the late Alan Berg of OSU) at about age 48, and
are now about
80 years of age.
None of those plots for which data have been summarized
have yet clearly culminated. As an example, MAI and PAI
31
values for plot 27-an unthinned plot adjacent to plot
(discussed below), though of slightly lower site index-are
shown in Figures 8 and 9. (The fluctuations ih PAI values reflect
both year-to-year variation in growth and mortality and mea­
surement inaccuracies associated with very short measurement
intervals.)
Plot 31 provides a striking example of what may be possible.
This is a l-ac plot thinned at age 48 to
50 stems/ac, removing
two-thirds of the standing volume. It was then underplanted with
hemlock. Today it has a pronounced two-storied structure, is a
10), and is making astonishing
visually beautiful stand (Figure
growth.
Figure 10. This good site (site II) stand, thinned to 50 stems/ac at
age 48, is making remarkable growth and is still increasing in
mean annual increment at age 81. It is a visually attractive stand,
with an average diameter of 28 in. and excellent stem quality.
Volume increment of plot 31 in cubic feet is shown in Figure
11, in board feet inFigure 12. (This doesn't include the hemlock
Black Rock
31
(thinned): MAl and PAl, cu.
ft.
(solid • MAl, dashed· PAl)
27 (unthlnned):
Black Rock
MAl and PAl, cu. ft.
360
(solid • MAl, dashed • PAl)
34{)
..,.
!
c:
..
.E
.. E
.,
z
360
300
34{)
280
320
II
I I
300
280
240
220
200
I ' 'I
180
160
I
I
,-
I
I
,,
I
I
I\
-
I
- ..........
180
\1
160
'
l't
I
200
t...,
I
I I I
220
'
/
I
50
55
50
75
70
65
60
55
50
eo
2200
I
I
1400
800
··\
...
,
,
\
1200
1000
I
II
1Soo
"
a;
z
70
!
75
80
85
I
,,
I
I
I
I
,"
I
1
...--
-
--
.E
.,
z
.--55
50
65
70
75
eo
85
AGE (years)
Figure 9. Observed mean annual increment and periodic annual
increment in board feet on Black Rock plot 27 (no thinning), site
III+ (medium).
WJAF 8(3) 1993
1600
1-
1400
E
,
•
2000
..
l---
50
2200
c:
-
45
(thinned): MAl and PAl, bd. ft.
I\ .
l \..;,.. __ .,.,...
1eOO
..
600
31
2400
t5
E
400
84
I,
I
(solid • MAl, dashed • PAl)
'i
..
2000
"'
E
I
I
Figure 11. Observed mean annual increment and periodic annual
increment in cubic feet on Black Rock plot 31 (very heavy
thinning), site II (good).
Black Rock
2400
1eOO
.E
I
AGE (yeats)
85
(solid • MAl, dashed • PAl)
E
I
I
65
!I
I
I
I
I
45
,,
I
i
I
Black Rock 27 (unthlnned): MAl and PAl, bd. ft.
"'
.
100
Figure 8. Observed mean annual increment and periodic annual
increment in cubic feet on Black Rock plot 27 (no thinning), site
III+ (medium).
e.
c:
II I
:
t
120
AGE (years) -o
·-
120
45
t5
I
J
,
;ll
I
100
tii
I
140
I
140
I.
240
I
I
I
260
II i
I I i
I II
II
I
260
i
!
i
320
' /
1200
/V
.......•'\'
\"'
\
\ I
'I
1000
800
600
400
45
50
55
50
65
70
75
50
85
AGE (years)
Figure 12. Observed mean annual increment and periodic annual
increment in board feet Scribner on Black Rock plot 31 (very
heavy thinning), site II (good).
component, which is still too small for board foot volume.) After
need data and analyses to evaluate the potential of very heavy
an initial reduction caused by the heavy thinning, current
thinning in 40- to 50-year-old plantations as a means of meeting
increment has been steadily increasing relative to mean annual
interim supply needs while shifting to longer rotations. From a
increment. At age 81, growth is
accelerating. If we compare
long-term timber standpoint, we may even come out ahead.
production at age 81 with production of two 40-yr rotations, the
81-yr rotation has produced about 1.25 times the cubic volume
of two 40-yr rotations. But, the 81-yr-old stand has an average
diameter of 28 in. with long clear boles, compared to an average
diameter of around 12 in. at age40. In terms of value production,
the 81-yr-old stand probably has a 2:1 advantage.
Also note that the thinning at age 48 took out two-thirds of
the existing volume, and that the regeneration costs that would
follow clearcutting are avoided. (Berg did underplant, but this
had negligible effect on volume up to age 81.) This suggests that
under some conditions one might be able to make a fairly
painless transition from short rotation management to longer
rotations.
Most of our future stands will be plantations with some sort
of early density control and will have somewhat different
characteristics at age 40 than did this stand. But, early manage­
ment may not greatly change these relationships. Early density
control will make future stands more resistant to windthrow than
naturally regenerated stands and therefore more amenable to
drastic treatments such as that applied to Black Rock plot 31.
Literature Cited
A 'IEY, J.D. !985. A modeling strategy for the growth projection of managed
stands. Can. J. For. Res. !5(3):51!-518.
CURTIS, R.O. 1992a. A new look at an old question-Douglas-fir culmination
age. West. J. Appl. For. 7(4):97-99.
CURTIS, R.O. l 992b. Levels-of-growing-stock cooperative study in Douglas­
fir: Report no. !!-Stampede Creek: A 20-year progress report. USDA
For. Serv. Res. Pap. PNW-442. 47 p.
CURTIS, R.O., G.W. CLENDENEN, and D.J. DE rARS. !981. A new stand
simulator for coast Douglas-fir: DFSIM user's guide. USDA For. Serv.
Gen. Tech. Rep. PNW-128. 79 p.
CURTIS, R.O., and D.O. MARSHALL. 1986. Levels-of-growing stock coopera­
tive study in Douglas-fir: Report No. 8-The LOGS study: Twenty year
results. USDA For. Serv. Res. Pap. PNW-356. 1!3 p.
DEBELL, D.S., and R.O. CuRTrs. !993. Silviculture and new forestry in the
Pacific Northwest. (Manuscript submitted to Journal of Forestry and on
file at Forestry Sciences laboratory, Olympia, WA. )
HANN, D. W., C.L. OLSEN andA.S. HESTER. !992. ORGANON user's manual­
Edition 4.0, Southwest Oregon version; Edition l.O, Western Willamette
Valley version. Dept. of F or. Resour., Oregon State University, Corvallis,
OR. 113 p.
IsAAc, L.A. 1938. Factors affecting establishment of Douglas-fir seedlings.
USDA Circ. No. 486, Wash., DC. 45 p.
IsAAc, L.A. !940. Mortality of Douglas-fir seed trees on cutover lands. P. 11­
12 in PNW For. Exp. Stn., For. Res. Notes No. 31. IsAAc, L.A. !943.
Conclusions
IsAAc, L.A. 1943. Reproductive habits of Douglas-fir. Charles Lathrop Pack
Culmination age in Douglas-fir is later than_many people
think, and very short rotations involve substantial losses in long­
term production. The MAl curve is relatively flat near and
b eyond culmination, suggesting that a considerable range of
rotation ages would produce about the same MAl. The upper
limits on this range of ages with roughly constant MAI are not
known (nor are those of potential response to thinning).
We need to rethink the whole question of harvest age and
rotation length, as part of the current general reappraisal of
management practices. Political and socialpressures are forcing
radical change, and traditional narrow economic analyses have
little relation to current realities. Extending rotations may be one
of the least disruptive and most effective ways to adapt.
We have a lot of young plantations coming on, and we need
to be thinking now about how we are going to handle these. We
need to extend the range of our simulators, and in particular we
Western J. Applied Forestry
Foundation, Washington, DC. 107 p.
IsAAC, L.A. 1956. Place of partial cutting in old-growth stands of the Douglas­
fir region. USDA For. Serv., PNW For. and Range Exp. Stn., Portland,
OR. 48 p.
KrNo, J.E. 1966. Site index curves for Douglas-fir in the Pacific Northwest.
Weyerhaeuser For. Pap. 8. Weyerhauser For. Res. Center, Centralia, WA.
49 p.
KIRKLAND, B.P., and A.J.F. BRANDSTROM. !936. Selective timber management
in the Douglas fir region. USDA For. Ser., Wash. DC. 122 p.
McARDLE, R.E., and W.H. tvlEYER. !930. The yield of Douglas-fir in the
Pacific Northwest. U.S. Dept. of Agr. Tech. Bul. 201. 64 p.
McARDLE, R.E., W.H. wlEYER, and D. BRUCE. 1961. The yield of Dougla>-fir
iR the Pacific Northwest. USDA Tech. Bull. 20! (rev). 72 p.
NEWTON, M., and E.C. CoLE. 1987. A sustained-yield scheme for old-growth
Douglas-fir. West. J. Appl. For. 2(!):22-25.
s urn, D.M. 1970. Applied ecology and the new forest. P. 3-7 in Proc. West.
Reforest. Coord. Comm., Western For. and Conserv. Assoc.
WILLIAMSON, R.L., and A.D. TwoMBLY. 1983. Pacific Douglas-fir. P. 9-12 in
SilviculturaJ systems for the major forest types of the United States. R.M.
BuRNS, (ed.). USDA For. Serv. Agric. Handb. No. 445. 19! p.
WoRTHfNGTON, N.P. 1966. Response to thinning 60-year-old Douglas-fir.
USDA For. Serv. Res. Note. PNW-35. 5 p.
8(3):81-85. 1993.
WJAF 8(3) 1993
85