ERC process biologically and finan­
and to judge performance based on
dally viable. Moreover, in areas where
results instead of specialized tasks.
regeneration is reliable, the risks of
End result contracting is still relatively
end result contracting are manageable
new in the western United States and
because potential problems can be
should be considered experimental.
identified and addressed. Failure to
However, our results suggest that in
produce results can be traced to an ac­
areas where regeneration is reliable,
tivity or to natural conditions like
ERCs have the potential to reduce
drought. In contrast, in areas where
costs, improve innovation by in­
regeneration is difficult, it can be hard
volving industry in the proposal pro­
to determine if fault is due to the con­
cess, and imorove FS and industry re­
lati" . -x\o\1· , considering ERCs
tractor, the agency, or mother nature.
\\
s
The Umpqua and Winema ey...-.n-'
0 u'o C'{ cteo'd to assess the kind
ences with ERCs indicat
s \ \e ·
co'{ e _,ar would be appropriate
'{\\1\e
\1
\
cost-savings recoP' 0u\\
. �� t'\le '>le 'oee
ue in ERCs, how these activi'3
PIT study arP
1:\
"
'\1
sc " '
.:s depend on natural conditions,
'{e
'3
soWN
abled thr
' eo 'o'l
' \\1· and the legal and administrative con­
3
'\le
3\
c'{
e
'{
..::S
\
e
tiOJ·•-'
'QS
straints that may apply. The range of
' 'l
. 0 'o'l
3
e
. s -\\\e '1'l.
activities on the Umpqua and Winema
\1\ -\\ . ' v,_eS
expand
0e \
3
\'��'. c' \IS \ .r(\ '{\1\S'Sdual activities
National Forests differ considerably in
e
.,1\\SS 3
'{ SO'''
'"�'
part because these forests have dif­
ferent site conditions related to dif­
ferent management objectives which
were affected by administrative and
0
legal considerations.
LITERATURE CITED
OwEN, J. F, 1986. Stewardship contracting: A
management strategy for futuring in the Forest
Service. Unpubl. rep, Klamath National Forest,
CA, 55 p.
PoRTERJE, G .. L, ET AL. 1987. Stewardship con­
tracts. J. For. 85(8):29-32.
TARASCIO, F. 1988. Cost comparison stewardship
vs. standard contracts. Unpubl. rep. Umpqua
National Forest pap. 4 p.
USDA Fo REST SERVJCE. 1983. National produc­
tivity i mprovement study: Contracting/pur­
chasing. USDA For. Serv. Southern Region.
35 p.
WEAVER, F., ET AL. 1988. End result contracting
on the Winema National Forest. Unpubl. rep.
USDA For. Serv. pap. 17 p.
'-�e ,
'\lo'l'l e ------
Yield Comparison of Three
Douglas-Fir Plantations on
Former Farmland in
Western Washington
Marshall D. Murray and Constance A. Harrington, USDA
Forest Service, Forestry Sciences Laboratory, 3625 93rd Ave.
S. W., Olympia, WA 98502.
ABSTRACT. Yields of three Douglas-fir
plantations on
former farmland were substantially greater
than DFSIM yields for the plantations
based on site index estimates from adjacent
natural stands. Volume yield per acre of
trees 1.6 in. dbh and larger was 40 to 57%
greater in the actual plantations than in
the simulations. For trees 7.6 in. dbh and
larger, volume yield of the actual planta­
tions was 85 to 151% greater than the sim­
ulated yields. Mean annual increment of
the actual plantations was 56 to 69%
greater than the simulated values. In addi­
tion, top height was greater in two of the
plantations than predicted. Running a
second set of simulations with site index
estimates based on plantation trees reduced
the discrepancy in yields but still resulted
in substantial underpredictions. Some pos­
sible reasons for enhanced yield of the
plantations on former farmland are greater
site uniformity, reduced vegetative compe­
tition, and increased nutrient availability.
West. J. Appl. For. 5(4):00-00, October 1990.
(Pseudotsuga menziesii)
During the past three decades land­
owners in western Washington have
planted Douglas-fir (Pseudotsuga men­
ziesii) on their farmlands to produce
Christmas trees or timber. Former
farmland, free of stumps and logging
debris, provides a good site for tree
planting. Site preparation, planting,
and postplanting treatments are pos­
sible with mechanical equipment and
uniform spacing can be achieved.
Early growth of trees on former
farmland may be greatly enhanced by
treatments associated with the pre­
vious land use, such as fertilization or
cultivation of an agricultural crop, and
by postplahting control of competing
vegetation. One of the best known ex­
amples of the association of tree
growth with previous land use is the
"old-field effect" on the growth of
loblolly pine (Pinus taeda) plantations
in the southeastern United States
(Haines, Maki, and Sanderford 1973 ,
Wahlenberg 1960). The effect w a s
named when i t was noticed that pine
seedlings planted on old fields often
grew faster than those planted on
cutover sites. A similar phenomenon
known as the "pasture effect," that is,
better tree growth on land previously
in pasture than on sites previously in
tree cover, has also been reported for
pine plantations in New Zealand and
Australia (Skinner and Attiwill 1981,
West 1984).
Does Douglas-fir planted on former
farmland produce greater yield than
that obtained from D o ugla s-fir
planted o n areas previously in tree
cover? To answer this question, the
yield of plantations on former farm­
land could be compared to those on
cutover land. We obtained establish­
ment histories for three Douglas-fir
plantations on former farmland. Un­
fortunately, plantations on cutover
land with the same soil, age, and
stocking as our plantations were not
available for comparison. In the ab­
sence of actual experimental data, we
u s e d a regional Douglas-fir yield
model to predict the yields that would
be expected on cutover land.
The DFSIM Douglas-fir stand simu­
lation program (Curtis et al. 1981) can
be used to predict development of an
average stand when site index, initial
stocking, and silvicultural treatment
are specified. Thus, DFSIM estimates
can be used to provide an indication of
the gains associated with previous ag­
ricultural use, site preparation, and
postplanting cultivation in these plan­
tations.
This report presents actual yield of
three Douglas-fir plantations estab­
lished on former farmland and com­
pares the actual yield with yield pre­
dicted by DFSIM for simulated planta­
tions on adjacent cutover land.
DESCRIPTION AND HISTORY OF
THE PLAl'ITATIONS
Three Douglas-fir plantations were
established on former farmland be­
tween 1957 and 1963 . The plantations
are located within 20 miles of each
other in Thurston and Lewis
Counties, WA, an area recognized as
one of the best timber-growing re­
gions in North America. The area's
potential for high productivity is the
WJAF 5(4)1990 123
'I
;\
result of fertile soils and favorable cli­
mate. Soils are derived from a variety
of parent materials and range from
average to excellent site quality for
Douglas-fir (Table 1). The maritime
climate is characterized by dry cool
summers and wet, mild winters.
Average annual precipitation in the
area of the plantations averages 50 in.
(Phillips 1964).
The plantations were disked or
plowed before planting and were cul­
tivated the f irst few years after
planting to control competing vegeta­
tion (Table 2). Stand characteristics
varied among the three plantations,
but all exhibited the uniform spacing
and an understory free of competing
vegetation shown in Figure 1.
METHODS
Diameter at breast height of live
trees within a sample area in each
plantation was measured and tallied
by l-in. classes. In the smaller Roch­
ester plantation, all live trees were
measured except for three rows of
trees on the outer edge surrounding
the plantation. In the larger planta­
tions at Cooks Hill and Evaline, 0.1-ac
sample plots were taken throughout
the entire plantation. Samples con­
sisted of 5 plots at Cooks Hill and 12
plots at Evaline. Twenty-four trees
throughout the range of dbh were
measured for height at each planta­
tion; two-thirds of the height trees had
dbh equal to or greater than the qua­
dratic mean stand diameter. A height­
diameter relationship was derived
from the height sample trees, and an
average height for each l-in. dbh class
was calculated. Cubic volume (total
stem inside bark) of each dbh class
was taken from a volume table for
second-growth Douglas-fir (Bruce and
DeMars 1974).
DFSIM requires a value for 50-year
site index to be input for each stand
condition that is simulated. Plantation
trees growing on former farmland
may have different patterns of height
growth over time than the trees used
Table 1. Soil and site index information for three Douglas-fir plantations on former farmland
in western Washington.
Plantation
Soil
parent material
Rochester
Cooks Hill
Spanaway
Salkum
Eva line
Olympic
Glacial outwash
Highly weathered
glacial till
Highly weathered
basalt
1
2
3
Soil
series1
Natural
stand2
Plantation
trees3
133
130
143
108
126
110
124
108
131
Values of site index by soil series based on soil survey of Lewis County, WA (Evans and Fibich 1987).
Values estimated from heights and ages of site trees in a nearby natural stand of Douglas-fir.
Values estimated from heights and ages of site trees in the plantation.
to develop the height-age relation­
ships in King (1966); thus, it is not
known how stable estimates of 50­
year site index would be based on
these young trees. For this study, site
index values were estimated in three
ways: (1) based on site trees in a
nearby natural stand, (2) based on the
soil series-site index relationships
available for the area (Evans and Fi­
bich 1987), and (3) based on site trees
in the plantation. The natural stands,
ranging in breast-height age from 24
to 35 years, were on the same soil
series as the actual plantations. Site
index values for the natural stands
were obtained from regional Douglas­
fir site curves (King 1966). Site index
values for the plantations were back­
calculated from DFSIM to provide the
same height and age values as were
present in each plantation.
For all three plantations, the site
index value obtained from the natural
stand and the value associated with
the soil series were within 3 ft of each
other (Table 1). The site index estimate
based on the plantation site trees was
similar to the other estimates for the
Rochester plantation; however, the
plantation-based estimates from the
Cooks Hill and Evaline plantations
were 5 to 13 ft higher than the other
estimates. Two sets of DFSIM simula­
tions were run for each plantation.
The first set used the site index value
estimated from the nearby natural
stand, this assumed that the natural
Date of
planting
Planting
density
Postplanting
treatments
Plantation
Previous crop
Rochester
Strawberries
Previous crop
plowed under
Spring
1957
8 X 8ft
680 trees/ac
Cultivated first
few years
Cooks
Hill
Strawberries
February
19&3
8 X ft
680 trees/ac
Cultivated first
few years
Evaline
Pasture
Strawberries
plowed under,
cover crop of
oats and vetch
grown 1 year
and harvested,
soil disked
before planting
Soil disked
before planting
124
W)AF 5(4)1990
I
I
50-year site index
Soil
series
stand w a s cut and subsequently
planted with Douglas-fir at the same
spacing as the existing plantation. The
second simulations used the site index
value estimated from the plantation
trees themselves. If one assumes that
the site index values will be stable,
this set of simulations allows the effect
of an increase in site index to be sepa­
rated from other effects of planting on
former farmland.
Comparisons are based on breast
height ages, since these rather than
total ages are used in the DFSIM pre­
diction equations. For a given breast
height age, the comparisons were
made for the same number of trees per
acre 1.6 in. dbh and larger as the ac­
tual plantations.
The plantations took fewer years to
reach breast height than the regional
average values used by DFSIM to con­
vert breast height age to total age
(Table 3). As a consequence of rapid
early height growth, the actual planta­
tions were 2 to 4 years younger in total
age than the DFSIM values. Such age
differences are reflected in differences
in calculated MAl of the actual planta­
tions relative to that of the simulated
plantations.
RESULTS
Comparisons of actual plantation
growth with the values predicted by
DFSIM are shown in Table 4. All three
plantations had greater average dbh,
cubic volume, and mean annual incre-
Table 2. Establishment histories for three Douglas-fir plantations on former farmland in western Washington.
Preplanting
treatments
,I
. I
Autumn
1958
6
X
8ft
900 trees/ac
Cultivated first
few years
Planting stock
Nursery-grown
Douglas-fir
seedlings
probably 2
years old
Nursery-grown
1-year-old
Douglas-fir
seedlings
Nursery-grown
2-year-old
Douglas-fir
seedlings
Comments
Very few missing
trees, dead
trees may have
been replaced
Very few missing
trees, early
survival was
excellent
Dead trees not
replaced, skips
in some rows
{I
J
mean diameter between the actual
and simulated values. However,
number of trees 7.6 in. and larger and
their corresponding cubic volume
were still underpredicted by 67 and
53%.
DISCUSSION
Figure 1. The Rochester plantation
25 years after planting;
ment for trees 1.6 in. dbh and larger
and substantially greater cubic volume
and numbers of trees 7.6 in. dbh and
larger than the simulated plantations.
The differences in values between the
two simulations for each plantation
were roughly proportional to the dif­
ferences between the site index values
used.
Rochester
Mean diameter of all trees 1. 6 in.
and larger was 1.3 in. larger in the
plantation on former farmland than
that predicted in either of the simula­
tions (Table 3). Mean diameter of trees
7. 6 in. dbh and larger did not differ
between the plantation and the simu­
lations; however, the actual plantation
had more than two and a half times as
many trees in the larger diameter
grouping than predicted by either of
the simulations. Similarly, actual cubic
volume in trees 7.6 in. dbh and larger
was 151% greater in the simulation
using site index from the natural stand
and 182% greater than the value pre­
dicted using the plantation-based esti­
mate of site index.
Cooks
Hill
Top height of Cooks Hill plantation
was 4. 0 ft taller and mean diameter of
Table 3. Average number of years for domi­
nant trees to reach the branch whorl at or
immediately below breast height (4.5 ft).
Actual valu es
Plantation
From
seed
From
planting
Pacific
Northwest
average1
(from seed)
.................. (yr) ................ .
¡
Rochester
Cooks Hill
Evaline
1
6
3
5
4
2
3
8
7
7
.
Values from King (1966); based on the site
index values estimated from an adjacent natural
stand.
tree spacing is 8 by 8 ft.
all trees (1.6 in. dbh and larger) was
1.0 in. greater than the values pre­
dicted by DFSIM with the natural
stand site index value (Table 4). Asso­
ciated with these differences were in­
creases in cubic volume (in trees 1.6
in. and larger) and mean annual in­
crement of 40 and 63%. Mean diam­
eter of trees 7.6 in. dbh and larger was
0.3 in. smaller in the actual plantations
than in simulation based on the nat­
ural stand site index; however, the
plantation on former farmland had
93% more trees and 85% more stem
volume in this size category than the
corresponding DFSIM simulation.
The simulation based on the higher
plantation site index estimate resulted
in DFSIM predicting a larger mean di­
ameter for trees 7.6 in. dbh and larger
than was present in the actual planta­
tion. However, the number of trees
7 . 6 in. a n d larger and the c u b i c
volume ( i n this size category) were
still underpredicted by 62 and 40%.
Evaline
Top height of the Evaline plantation
was 5.9 ft taller and mean diameter of
all trees (1.6 in. dbh and larger) was
1.4 in. greater than the values pre­
dicted by DFSIM with the natural
stand site index estimate (Table 4).
The actual plantation also had 40%
more cubic volume and 63% higher
mean annual increment (in trees 1. 6
in. and larger) than the simulation.
The actual plantation only had a 0.2
in. greater mean diameter of trees 7.6
in. and larger than the simulation
based on the natural stand site index;
however, this simulation underpre­
dicted the number of trees and the
cubic volume in this size category by
104 and 115%.
. Using the plantation-based estimate
of site index reduced the difference in
The differences in the yields pro­
duced by the three Douglas-fir planta­
tions on former farmland and the
yields predicted by DFSIM were sur­
prisingly large. These differences
should be considered as examples of
the possible benefits associated with
"agricultural effects" on tree growth.
The agricultural effects at Rochester
apparently resulted in increased
stockability of the site, while the ef­
fects at Cooks Hill and Evaline in­
creased site quality (measured by top
height) and stockability. The DFSIM
stand simulator was developed with
the use of extensive data, all of which
came from natural stands and planta­
tions established on cutover forested
land. Our plantations, on the other
hand, had stand establishment histo­
ries not common in the Douglas-fir re­
gion. Thus, the presence of these agri­
cultural effects does not indicate that
DFSIM produces inaccurate yield pro­
jections for more typical stands.
We are not aware of other reports of
enhanced yield of Douglas-fir on
former farmland. Since information is
not available from controlled experi­
ments, we can only speculate on the
reasons for the greater yield observed
in our plantations. Possible reasons
for improved yield include greater site
uniformity, reduced competition
during establishment, and increased
nutrient availability. The relative im­
portance of these and other possible
reasons for improved growth will
probably vary from plantation to plan­
tation depending on the specific man­
agement history and site conditions.
Site uniformity implies that trees
can be planted on an even spacing and
that each tree has more nearly equal
growing conditions. Consequently,
unfavorable conditions that cause
poor growth can be minimized, unuti­
Jized spots can be reduced, and yield
increased proportionately.
Part of any agricultural effect is
probably due to reduced competition
during the establishment period. Veg­
etative competition can reduce growth
of planted trees. Weed cover in 28- to
3 2-year-old red pine (Pinus resinosa)
plantations in Wisconsin caused more
than 50% loss in expected volume of
merchantable timber (Wilde et al.
1968). Cultivation can eliminate com­
peting annual vegetation as well as
destroy native root systems, thus re­
ducing or eliminating competition for
light, soil moisture or nutrients from
WJAF 5(4)1990
125
Table 4. Comparison of values from 3 Douglas-fir plantations on former farmland with values predicted from DFSIM.
Plantation
Rochester
Actual
DFSIM (natural stand)4
DFSIM (plantation)s
Cooks Hill
Actual
DFSIM (natural stand)4
DFSIM (plantation)s
Evaline
Actual
DFSIM (natural stand)4
DFSIM (plantation)s
1
2
3
4
s
trees 1.6" dbh +
Per ac
trees 7.6" dbh +
Total
age
(yr)
BH
age
(yr)
Hoi(),
(ft)
Dg. 2
(in.)
Trees
(no.)
CVTS3
(ft)
MAl
(cu ft)
Dg2
(in.)
Trees
(no.)
CVTS3
27
29
29
21
21
21
57.0
58.2
57.2
7.3
6.0
6.0
630
630
630
3910
2695
2590
145
93
89
8.4
8.5
8.4
253
100
94
2195
875
780
24
28
28
21
21
21
68.5
64.5
68.4
7.4
6.4
6.7
640
640
640
4810
3445
3920
200
123
140
8.6
8.9
9.2
276
143
170
2960
1595
2120
25
27
26
20
20
20
71.0
65.1
71.1
8.6
7.2
7.7
460
460
460
5010
3185
3910
200
118
150
9.3
9.1
9.7
334
164
200
4315
2005
2820
(ft)
Mean height of the 40 largest trees per acre. Quadratic mean stand dbh. Cubic volume total stem. DFSIM estimates using a site index value based on site trees in a nearby natural stand. DFSIM estimates using a site index value based on site trees in the plantation. larly of nitrogen and phosphorus­
sprouting stumps and residual trees which are often present on recently may have contributed to the greater
cutover areas (Wahlenberg 1960). growth and yield of these plantations.
In addition to reduced competition,
Although these old-field plantation
other residual effects of cultivation
comparisons with simulated stands do
that may influence tree growth in­ . not allow us to quantify the effects of
clude changes in soil physical and
pre- and post-stand establishment
chemical characteristics as well as al­
treatments, they suggest that inten­
teration of the soil microbiology asso­
sive site preparation and early vegeta­
ciated with the change in vegetation
tion control may produce growth
0
gains of considerable magnitude.
and management. Oldfield sites have
less woody debris both above and
below ground, which immobilizes nu­
LITERATURE CITED
trients during its decay(Ralston1978).
BRUCE, D., AND D. J. DEMARS. 1974. Volume
Soils on old field sites have also been
equations for second-growth Douglas-fir.
reported to have higher pH and
USDA For. Serv. Res. Note PNW-239. 5 p.
higher phosphorus levels than soils
CURTIS, R. 0., G. W. CLENDENEN, AND D. J.
DEMARs. 1981. A new stand simulator for coast
on forested sites (Haines, Maki, and
Douglas-fir: DFSIM user's guide. USDA For.
Sanderford 1973). The pasture effect
Serv. Gen. Tech. Rep. PNW-128. 79 p.
has been associated with increased
EvANS, R. L., AND W. R. F!BIOi. 1987. Soil survey
availability of nitrogen and phos­
of Lewis County area, Washington. USDA Soil
Conserv. Serv. 466 p. 108 maps.
phorus (Skinner and Attiwill1981). In HAINEs, L. W., T. E. MAl<!, AND S. G. SANDER­
the three Douglas-fir plantations, fer­
FORD. 1973. The effect of mechanical site prepa­
tilizers were probably. used on the ration treatments on soil productivity and tree
previous agricultural crop. Thus in­
(Pinus tacda L. and P. e/liottii Engelm. var. el­
liottil) growth. P. 379-395 in Proc. Fourth N.
creased nutrient availability-particu­
126
WJAF 5(4) 1990
Am. For. Soils Con£. B. Bernier and C. H.
Winget (eds.). Les Presses de l'Universite
Laval, Quebec.
KING, J. E. 1966. Site index curves for Douglas-fir
in the Pacific Northwest. Weyerhaeuser For,
Pap. 8. Weyerhaeuser Company, Centralia,
WA. 49 p.
PHILLIPS, E. L. 1964. Washington climate for
Oark, Cowlitz, Lewis, and Skamania counties.
Agric. Ext. Serv. Bull. E.M. 2462. Wash. State
Univ., Pullman. 42 p.
RALSTON, C. W. 1978. The southern pinery:
Forests, physiography, and soils. P. 6-13 in
Proc. symp. on principles of maintaining pro­
ductivity on prepared sites, T. Tippin (ed.),
Southeast. area State & Private For., Atlanta,
GA.
SKINNER, M. F., AND P. M. A'mwJU... 1981. The
productivity of pine plantations in relation to
previous land use 1. Growth responses in agri­
cultural and forest soils. Plant & Soil 60:161­
176.
W. G. 1960. Loblolly Pine-its
use, ecology, regeneration, protection, growth
and management. Duke Univ., School of For.,
Raleigh, NC. 603 p.
WEST, G. G. 1984. Establishment requirements of
Pinus radiata cuttings and seedlings compared.
NZ J. For. Sci. 14:41-52.
W!WE, s. A., B. H. SHAW, AND A. w. FEDKEN­
HEUER, 1968. Weeds as a factor depressing
forest growth. Weed Res. 8:196-204.
WAHLENBERG,
Table 4. Comparison of values from 3 Douglas-fir plantations on former farmland with values predicted from DFSIM.
Plantation
Rochester
Actual
DFSIM (natural stand)4
DFSIM (plantation)s
Cooks Hill
Actual
DFSIM (natural stand)4
DFSIM (plantation)s
Evaline
Actual
DFSIM (natural stand)4
DFSIM (plantation)s
1
2
3
5
trees 1.6" dbh +
BH
age
(yr)
HMl,
(ft)
Dg.2
(in.)
Trees
(no.)
CVTS3
(ft)
MAl
(cu ft)
Dg2
(in.)
Trees
(no.)
CVTS3
27
29
29
21
21
21
57.0
58.2
57.2
7.3
6.0
6.0
630
630
630
3910
2695
2590
145
93
89
8.4
8.5
8.4
253
100
94
2195
875
780
24
28
28
21
21
21
68.5
64.5
68.4
7.4
6.4
6.7
640
640
640
4810
3445
3920
200
123
140
8.6
8.9
9.2
276
143
170
2960
1595
2120
25
27
26 20
20
20
71.0
65.1
71.1
8.6
7.2
7.7
460
460
460
5010
3185
3910
200
118
150
9.3
9.1
9.7
334
164
200
4315
2005
2820
sprouting stumps and residual trees
which are often present on recently
cutover areas (Wahlenberg1 960).
In addition to reduced competition,
other residual effects of cultivation
that may influence tree growth in­
clude changes in soil physical and
chemical characteristics as well as al­
teration of the soil microbiology asso­
ciated with the change in vegetation
and management. Old field sites have
less woody debris both above and
below ground, which immobilizes nu­
trients during its decay (Ralston1 978).
Soils on old field sites have also been
reported to have higher pH and
higher phosphorus levels than soils
on forested sites (Haines, Maki, and
Sanderford 1 973). The pasture effect
has been associated with increased
availability of nitrogen and phos­
phorus (Skinner and Attiwill1 981). In
the three Douglas-fir plantations, fer­
tilizers were probably used on the
previous agricultural crop. Thus in­
creased nutrient availability-particu­
W]AF 5(4)1990
trees 7.6" dbh +
Total
age
(yr)
Mean height of the 40 largest trees per acre. Quadratic mean stand dbh. Cubic volume total stem. DFSIM estimates using a site index value based on site trees in a nearby natural stand.
DFSIM estimates using a site index value based on site trees in the plantation.
126
Per ac
_
larly of nitrogen and phosphorus­
may have contributed to the greater
growth and yield of these plantations.
Although these old-field plantation
comparisons with simulated stands do
not allow us to quantify the effects of
pre- and post-stand establishment
treatments, they suggest that inten­
sive site preparation and early vegeta­
tion control may produce growth
gains of considerable magnitude.
0
LITERATURE CITED
BRUCE, D., AND D. J. DEMARS. 1974. Volume
equations for second-growth Douglas-fir.
USDA For. Serv. Res. Note PNW-239. 5 p.
CURTIS, R. 0., G . W. CLENDENEN, AND D. J.
DEMARs. 1981. A new stand simulator for coast
Douglas-fir: DFSIM user's guide. USDA For.
Serv. Gen. Tech. Rep. PNW-128. 79 p.
EVANS, R. L., AND W. R. FmiCH. 1987. Soil survey
of Lewis County area, Washington. USDA Soil
Conserv. Serv. 466 p. 108 rna ps.
HAINES, L. W., T. E. MAKI, AND S. G. SANDER·
FORD. 1973. The effect of mechanical site prepa­
ration treatments on soil productivity and tree
(Pinus tacda L. and P. e/liollii Engelm. var. el­
liottir) growth. P. 379-395 in Proc. Fourth N.
(ft)
Am. For. Soils Conf. B. Bernier and C. H.
Winget (eds.). Les Presses de l'Universite
Laval, Quebec.
KiNG, J. E. 1966. Site index curves for Douglas-fir
in the Pacific Northwest. Weyerhaeuser For.
Pap. 8. Weyerhaeuser Company, Centralia,
WA. 49 p.
PHILLIPS, E. L. 1964. Washington climate for
Clark, Cowlitz, Lewis, and Skamania counties.
Agric. Ext. Serv. Bull. E.M. 2462. Wash. State
Univ., Pullman. 42 p.
RALSTON, C. W. 1978. The southern pinery:
Forests, physiography, and soils. P. 6-13 in
Proc. symp. on principles of maintaining pro­
ductivity on prepared sites, T. Tippin (ed.).
Southeast. area State & Private For., Atlanta,
GA.
SKINNER, M. F., AND P. M. ATI1WILL. 1981. The
productivity of pine plantations in relation to
previous land use 1. Growth responses in agri­
cultural and forest soils. Plant & Soil 60:161­
176.
WAHLENBERG, W. G. 1960. Loblolly Pine-its
use, ecology, regeneration, protection, growth
and management. Duke Univ., School of For.,
Raleigh, NC. 603 p.
1984. Establishment requirements of
Pir111s radiala cuttings and seedlings compared.
NZ J. For. Sci. 14:41-52.
WILDE, S. A., B. H. SHAW, AND A. W. FEDKEN­
HEUER. 1968. Weeds as a factor depressing
forest growth. Weed Res. 8:196-204.
WEST, G. G.