Color profile: Disabled
Composite Default screen
1794
Foliage and stand growth responses of
semimature lodgepole pine to thinning and
fertilization
Richard C. Yang
Abstract: The aim of this study was to quantify the interactive response of lodgepole pine (Pinus contorta Dougl. var.
latifolia Engelm.) to thinning and nitrogen (N) fertilization in midrotation stands by assessing foliar and stand growth
response relationships and determining the optimum fertilizer regime. The experiment design was a factorial
arrangement of treatments with two thinning intensities (thinned and unthinned control) and four N levels (0, 180, 360,
and 540 kg·ha–1). Foliage was sampled annually from trees in buffers for 4 years following treatment and plot trees
measured at a 5-year interval. Results indicated that the effect of fertilization on fascicle length and needle dry mass
disappeared 2 years after N treatment, while thinning effects on foliage emerged 3 years after fertilization. Both first
year fascicle length and dry mass were reliable predictors (r2 = 0.87 and 0.82, respectively) of subsequent stand
volume growth. Applications of N at 360 kg·ha–1 to thinned and unthinned plots, respectively, improved 10-year
periodic height increment by 20 and 19%, diameter at breast height by 29 and 34%, basal area by 21 and 36%, and
total volume by 25 and 28%. Fertilization of N at this level appears to be optimal based on foliar and mensurational
responses. High N loadings increased tree mortality and accelerated stand development and so it could be
advantageously used as a tool for managing overstocked stands.
Résumé : Cette étude visait à quantifier la réaction combinée du pin lodgepole (Pinus contorta Dougl. var. latifolia
Engelm.) à une éclaircie et à la fertilisation azotée dans des peuplements rendus à mi-révolution en évaluant les
relations entre la croissance foliaire et la croissance du peuplement et en déterminant le régime de fertilisation optimal.
Les traitements comprenaient deux intensités d’éclaircie (éclairci et témoin non éclairci) et quatre niveaux d’azote (0,
180, 360 et 540 kg·ha–1) dans un dispositif factoriel. Le feuillage a été échantillonné annuellement sur des arbres des
zones tampons pendant 4 ans après les traitements et à 5 ans d’intervalle sur les arbres situés à l’intérieur des
parcelles. Les résultats ont montré que l’effet de la fertilisation sur la longueur des fascicules et la masse sèche des
aiguilles disparaissait 2 ans après la fertilisation azotée tandis que l’effet de l’éclaircie sur le feuillage commençait à se
faire sentir 3 ans après la fertilisation. On pouvait se fier sur la longueur et la masse sèche des fascicules après 1 an
pour prédire la croissance subséquente en volume du peuplement (r2 = 0,87 et 0,82, respectivement). L’application de
360 kg·ha–1 d’azote dans les parcelles éclaircies et non éclaircies a augmenté l’accroissement en hauteur sur une
période de 10 ans de 20 et 19%, le diamètre à hauteur de poitrine de 29 et 34%, la surface terrière de 21 et 36% et le
volume total de 25 et 28%, respectivement. Ce taux de fertilisation azotée semble optimal sur la base de la réaction du
feuillage et des mesures de croissance. Des apports importants d’azote ont augmenté la mortalité des arbres et accéléré
le développement du peuplement et pourraient donc avantageusement servir d’outil pour aménager les peuplements trop
denses.
[Traduit par la rédaction]
Yang
1804
Lodgepole pine (Pinus contorta Dougl. var. latifolia
Engelm.), one of the most widespread conifers in Canada
and the western United States, occupies 22% of the total forest land in western Canada. This species grows under a variety of site conditions, but extensive, seral stands are most
commonly associated with relatively dry, nutrient-poor sites
(Wheeler and Critchfield 1985). On these sites, lodgepole
pine often regenerates densely following natural or human
disturbance. Because of the overdense regeneration, density
controls via juvenile spacing or commercial thinning are freReceived February 2, 1998. Accepted September 9, 1998.
R.C. Yang. Canadian Forest Service, Northern Forestry
Centre, 5320 122nd Street, Edmonton AB T6H 3S5, Canada.
e-mail: [email protected]
Can. J. For. Res. 28: 1794–1804 (1998)
I:\cjfr\cjfr28\cjfr-12\X98-148.vp
Wednesday, January 20, 1999 1:36:31 PM
quently prescribed for managing this species. Thinning, in
addition to increasing growing space, results in reduced
evapotranspiration and water stress, heavier snow accumulation (more moisture), earlier thawing of frozen soil, and a
prolonged period of decomposition and root activity in the
forest floor (Goodell 1952). By creating favourable environments for physiological activities, thinning exerts a longterm effect on stand development.
The extensive autecological association of lodgepole pine
with nutrient-poor sites suggests that amelioration of nutrient status through fertilization is an alternative to thinning
for stimulating stand growth. Favourable growth responses
of lodgepole pine to fertilization have been documented
(Cochran 1975, 1979; Yang 1985a, 1985b; Weetman et al.
1988; Brockley 1989, 1990, 1995; Brockley and Sheran
1994, Preston and Mead 1994). Results from these studies
clearly indicate that nitrogen (N) is the element that most
© 1998 NRC Canada
Color profile: Disabled
Composite Default screen
171.18;
123.55;
179.32;
178.42;
112.62;
110.58;
107.63;
88.18;
202.97;
194.52;
211.92;
224.71;
139.85;
132.81;
135.21;
134.93;
Note: Data are presented in the order mean; minimum; maximum. Values are based on nine replicates of each treatment combination.
9.83;
9.52;
10.40;
9.01;
12.31;
12.41;
12.13;
11.98;
7.51;
6.11;
8.65;
6.76;
10.99;
11.35;
10.70;
10.12;
11.53
11.37
11.23
10.79
13.36
14.07
13.39
13.36
12.98;
12.68;
13.07;
12.80;
13.01;
13.05;
12.52;
12.92;
12.10;
9.84;
12.08;
10.98;
11.86;
12.58;
11.56;
12.10;
14.44
14.26
14.06
14.02
14.22
14.72
13.40
13.95
40.70;
40.19;
40.86;
44.05;
26.45;
25.62;
26.20;
25.91;
33.70;
32.36;
33.45;
38.42;
22.09;
22.10;
21.51;
17.81;
46.65
51.20
52.93
49.08
30.05
32.53
30.88
31.14
Total volume
(m3·ha–1)
Basal area
(m2·ha–1)
Height (m)
DBH (cm)
7956
9493
5947
9293
2406
2206
2273
2474
3276;
3543;
3008;
4947;
2005;
1605;
1872;
1939;
4985;
5393;
4375;
6351;
2132;
2028;
2161;
2198;
0
180
360
540
0
180
360
540
The experiment was a randomized complete block design with
factorial arrangement of treatments. Nine 60 × 80 m blocks were
subdivided into two sub-blocks, each consisting of four 9.5 m radius circular plots. A 6.9 m radius inner plot was established concentrically inside the 9.5-m plot. Interplot centres were 20 m apart
leaving a minimum 5-m buffer zone between plots to prevent
movement of N between plots.
Thinning was randomly assigned to a sub-block within each
block. Experience from other spacing and thinning studies suggested that 2000 stems/ha was probably an optimum stocking for
lodgepole pine in this region (Yang 1991). Prior to thinning, all
trees on the 9.5 m radius plot were first tallied by diameter; trees to
be thinned were selected based on vigour and spacing between
neighbouring crop trees. Plots were thinned with chainsaws during
Unthinned
Unthinned
Unthinned
Unthinned
Thinned
Thinned
Thinned
Thinned
Experimental design
Stems/ha
The study area was located about 50 km southeast of Hinton,
Alta. (53°25′N, 117°34′W), on the Weldwood of Canada Limited
(Hinton Division) Forest Management Area. Forests in this area
were within the Lower Foothills Section (B. 19a) of the Boreal
Forest Region (Rowe 1972). A densely stocked 40-year-old lodgepole pine stand of fire origin on Mercoal soil series (Dumanski et
al. 1972) was selected.
A dense ground cover consisted of Labrador tea (Ledum groenlandicum Oeder), bearberry (Arctostaphylos uva-ursi Spreng),
bunchberry (Cornus canadensis L.), and fireweed (Epilobium
angustifolium L.). The ecological association of this area was described as Pinus contorta – Picea mariana/Ledum groenlandicum/Pleurozium schreberi (Pl-Sb/Ledum/Pleurozium) (Corns and
Annas 1986; Beckingham et al. 1996). Topography ranged from
level to undulating (4–11% slope). The soil was a well-drained
Orthic Gray Luvisol developed on medium-textured Cordilleran
till.
N applied
(kg·ha–1)
Study area
Table 1. Initial density, diameter at breast height (DBH), height, basal area, and total volume by treatment combinations.
limits the growth of lodgepole pine. The responsiveness of
this species to N fertilizer may reflect low rates of N supply
resulting from erosion of the ecosystem N capital by repeated fire disturbances on sites where this species naturally
occurs.
In a previous study, Yang (1985a, 1985b) reported that
fertilization of lodgepole pine improved stand growth and
productivity in 30- and 70-year-old stands on two soils in
west-central Alberta. The study in the 30-year stands
showed improved diameter and volume growth following N,
phosphorus (P), and sulphur (S) applications; however, fertilization effects were obscured by a high and variable mortality associated with the excessive stand density commonly
found in fire-regenerated stands of this species. It was concluded that density control was required to accurately assess
fertilization effects on semimature lodgepole pine stands.
A study aimed to quantify the interactive response to thinning and N fertilizer in a midrotation stand was initiated in
1984 with the following objectives: (i) to ascertain semimature lodgepole pine foliage response to combined thinning and fertilization treatments and relationships between
foliar response and subsequent stand growth; (ii) to assess
the effects of fertilization and thinning (singly or in combination) on growth and mortality; and (iii) to determine the
optimum fertilizer regime for lodgepole pine on the soil type
studied.
1795
239.35
256.04
279.49
263.19
164.22
174.99
163.30
161.88
Yang
© 1998 NRC Canada
I:\cjfr\cjfr28\cjfr-12\X98-148.vp
Wednesday, January 20, 1999 1:36:32 PM
Color profile: Disabled
Composite Default screen
1796
Can. J. For. Res. Vol. 28, 1998
Table 2. Estimated parameters of height–diameter curves for thinning and fertilization treatments.
Unthinned
Unthinned
Unthinned
Unthinned
Thinned
Thinned
Thinned
Thinned
Estimated parametera
N applied
(kg·ha–1)
No. of
samples
a
b
c
MSEb
0
180
360
540
0
180
360
540
118
115
104
103
112
107
106
99
14.6281
15.9253
15.5884
15.0536
14.6341
15.9730
14.8010
14.4315
0.1195
0.1309
0.1137
0.1289
0.1161
0.1074
0.1129
0.1167
0.8779
1.5544
1.0728
1.0480
0.8607
1.1762
0.9497
0.8629
1.2609
1.0771
1.0341
1.1210
0.7263
0.8034
0.7567
1.0362
a
Function formula: H = 1.3 + a[1 – exp (–bD)]c, where H is total tree height (m), D is diameter at breast height outside bark
(cm), and a, b, and c are coefficients to be estimated.
b
MSE, Mean squared error.
the summer of 1984 to reduce stand basal area to 26 m2·ha–1 or approximately 2100 stems/ha (Table 1).
Following thinning, crop trees within the 6.9 m radius were
tagged, and diameter at breast height outside bark (DBH) was recorded. Additionally, the height of 10 dominant or codominant
trees on each plot was measured and used to determine volume and
assess height–diameter relationships following treatment.
Nitrogen as ammonium nitrate was applied at four levels: 0,
180, 360, and 540 kg·ha–1. Treatments were randomly assigned to
plots within the half block. In addition to N, 40 kg·ha–1 of P as ammonium phosphate, and S as ammonium sulphate were applied
separately to each fertilized plot. Fertilizers were manually applied
to the 9.5 m radius plots using cyclone seeders in November 1985.
Data collection and analysis
Foliar sampling
Current foliage and soil were collected from the treated buffer
for 4 years (1985–1988). Foliar samples were collected from lateral branches within the upper one third of the live crown. Samples
were taken from two trees in each plot in winter when branches
were frozen and easy to break with shotgun pellets. The currentyear’s foliage was clipped off branches in the field, stored in plastic bags. A subsample of 100 needles were weighed, individual
needle lengths measured, and the sample oven-dried at 70°C for
16 h and reweighed. Soil from each plot was sampled using an auger to a fixed depth of 120 cm and segregated by seven depths
(L–F, 0–5, 5–15, 15–30, 30–61, 61–91, and 91–120 cm) for laboratory analysis. Nutrient concentrations of needles and soil were also
determined; results are reported separately.
Tree measurements
Diameter of all crop trees on the 6.9-m inner plots were measured at establishment and re-measured in the winter of 1989 and
1994, five and 10 years, respectively, after thinning and plot establishment (4 and 9 years after fertilizer application). Ten height
trees that varied in DBH were measured in each plot. Dead trees
on the thinned plot were noted and possible causes of death were
assessed.
Measured height trees in each treatment were lumped by treatment combination to develop height and DBH (H–D) curves. The
modified Weibull nonlinear function developed by Yang et al.
(1978) and adopted by the Alberta Land and Forest Services
(Huang 1994) was used.
Data analysis
Periodic increments in height (PHI), diameter at breast height
outside bark (PDI), stand basal area (PBAI), stand total volume
(PTVI), and mortality, along with needle length and mass of 100
fascicles, were analysed for treatment effects. The PHI and PDI
were computed as the difference between two successive measurements in height and diameter, respectively, of individual surviving
trees on plots. These differences were averaged to obtain treatment
responses for individual plots. Stand basal area and total volume
increments were similarly computed by summing up individual
surviving trees on each plot and converting plot values to a perhectare basis.
Individual tree volumes were calculated using the ecologically
based individual tree volume estimation procedures developed by
the Alberta Land and Forest Services (Huang 1994) along with
H–D curves developed for each treatment (Table 2). Mortality was
assessed on stems per hectare, basal area, and total volume. For
basal area and total volume mortalities, tree DBH at the first measurement was used.
Plot data were subjected to statistical analysis using versatile
general linear model (GLM) procedures (SAS Institute Inc. 1990).
Differences in treatment effects were then tested using Student–
Newman–Keuls multiple range test.
Fascicle length and dry mass
The response of fascicle length and mass to N fertilizer
and thinning in four consecutive years is shown in Figs. 1
and 2; F statistics for main factors and interactions are listed
in Table 3.
Fascicle length did not respond to thinning until 1987 (2
years after treatment). In contrast, a positive response to N
fertilizer occurred 1 year after treatment, reached a maximum after 2 years, and disappeared after 3 years (Table 3,
Fig. 1). Mean needle mass showed a similar pattern (Table 3,
Fig. 2). Thinning did not affect needle mass until 3 years
(Table 3). Interactions between fertilization and thinning
were not significant in all years examined.
Height increment
Thinning significantly affected 5- and 10-year PHI (Table 4);
in general, PHIs were smaller on thinned than unthinned
plots (Fig. 3a).
Thinning significantly reduced 5- and 10-year PHI. In
contrast, N fertilizer increased 5-year PHI by 18–29% in
unthinned plots and 9–51% in thinned plots, and 10-year
PHI up to 19 and 20%, respectively, on unthinned and
thinned plots. Periodic height increments increased with the
© 1998 NRC Canada
I:\cjfr\cjfr28\cjfr-12\X98-148.vp
Wednesday, January 20, 1999 1:36:33 PM
Color profile: Disabled
Composite Default screen
Yang
1797
Table 3. F statistics for fascicle length and needle mass to thinning and fertilization treatments.
Critical F value
Fascicle length
Fascicle mass
Factor
df
p = 0.05
p = 0.01
1985
1986
1987
1988
1985
1986
1987
1988
Thinned (T)
Fertilizer (F)
T×F
Error
1
3
3
64
3.99
2.75
2.75
7.04
4.10
4.10
0.04
0.34
0.99
21.78
0.54
9.13**
0.63
29.89
5.22*
21.52**
0.52
54.27
4.49*
0.52
0.43
51.49
1.50
0.27
0.98
0.047
1.75
5.93**
0.51
0.165
2.61
19.66**
0.26
0.336
4.45*
0.20
0.65
0.282
*Significant at the 5% probability level.
**Significant at the 1% probability level.
Table 4. F statistics of treatment effects on periodic stand parameters.
Critical F value
Period
measured
5-year
10-year
Mortality
Factor
df
p = 0.05
p = 0.01
Height
DBH
Basal
area
Thin (T)
Fertilizer (F)
T×F
Error
T
F
T×F
Error
1
3
3
64
1
3
3
64
3.99
2.75
2.75
7.04
4.10
4.10
3.99
2.75
2.75
7.04
4.10
4.10
10.68**
3.08*
0.74
0.089
7.69**
5.16**
0.83
0.127
51.24**
1.45
0.07
0.292
284.80**
19.75**
2.84*
0.067
17.90**
1.45
0.47
2.639
56.08**
1.65
0.37
6.322
Total
volume
Stems/ha
Basal
area
Total
volume
3.24
3.27*
0.76
82.246
25.92**
3.15*
0.23
191.14
26.48**
1.19
0.89
235 600
132.37**
3.96*
2.24
316 900
15.39**
0.72
0.21
2.9066
137.38**
6.73**
1.22
3.124
12.06**
0.76
0.34
57.871
98.81**
6.96**
1.56
75.144
*Significant at the 5% probability level.
**Significant at the 1% probability level.
level of N applied up to 360 kg·ha–1; additional N depressed
height growth and was detrimental to height increment especially on thinned plots (Fig. 3a). Nitrogen also affected H–D
relationship; large trees (DBH > 20 cm) were taller on fertilized plots than trees of the same diameter on unfertilized
plots, except those on thinned and the heaviest N-fertilized
plots (Figs. 4a and 4b). The H–D ratio was greatest at the
lowest N applied plots.
Diameter growth
Diameter increment increased significantly in response to
thinning after both 5- and 10-years (Table 4). The 5-year
PDI ranged from 0.56 to 0.83 cm on unthinned plots in comparison to 1.37 to 1.78 cm on the thinned plots. The magnitude of 5-year PDI on thinned plots was similar to that of
10-year PDI on unthinned plots (Fig. 3b).
In contrast, fertilization did not affect 5-year PDI despite
a positive effect on thinned plots. Nevertheless, PDI increased significantly in response to N fertilization after 10
years (Table 4). Interactions between thinning and fertilization treatments were significant at the 5% level; interactions
are shown in Fig. 3b where PDI response patterns to fertilization differed between thinned and unthinned plots. On
unthinned plots, PDI increased with N applied up to
360 kg·ha–1 and decreased beyond this level while PHI increased with N applied up to 540 kg·ha–1 on thinned plots.
After 10 years, the negative effects of 540 kg·ha–1 on PDI
had largely disappeared; N improved PDI by 19–34% and
27–38%, respectively, on unthinned and thinned plots.
Stand basal area and total volume
Thinning significantly increased basal area increments after 5 and 10 years (Table 4). In contrast, fertilization had no
effects on either 5- nor 10-year PBAI. There was no
thinning × fertilization interaction (Fig. 5a). Stand basal area
responded most to the 360 kg·ha–1 N treatment in both absolute (net increment from the unfertilized control) and relative (percentage of net increment over initial basal area
(Table 1)) measures (Fig. 6a). Despite an initially reduced
stock, basal area on thinned and fertilized at 360 kg·ha–1 N
plots outgrew those on unthinned plots after 10 years.
Fertilization was the only factor that increased PTVI after
5 years, but both thinning and fertilization increased PTVI
after 10 years (Table 4). There was no thinning × fertilization interaction (Fig. 5b).
Fertilization produced up to 11.7 and 6.6 m3·ha–1 extra
wood, respectively, on unthinned and thinned plots after 5
years and up to 23.0 and 17.1 m3·ha–1 after 10 years (Fig. 6b).
Absolute volume increments due to fertilization were smaller
on thinned than on unthinned plots; relative growth on those
thinned surpassed those on unthinned after 10 years.
Mortality
Three measures of periodic stand mortality showed the
same treatment response: thinning significantly decreased
5-year periodic mortality assessed on number of stems per
hectare, stand basal area, and stand total volume. Fertilization did not affect periodic mortality; but both thinning and
fertilization significantly influenced stand mortality 10 years
after treatment (Table 4). Interactions between fertilization
and thinning were not significant (Table 4, Fig. 7).
Correlations between foliar and periodic stand growth
responses
Average fascicle length 1 year after fertilization was significantly correlated with 5-year PHI (r = 0.238, p = 0.04)
© 1998 NRC Canada
I:\cjfr\cjfr28\cjfr-12\X98-148.vp
Wednesday, January 20, 1999 1:36:34 PM
Color profile: Disabled
Composite Default screen
1798
Can. J. For. Res. Vol. 28, 1998
Fig. 1. Means and standard errors of fascicle length following
fertilization in (a) unthinned and (b) thinned plots. Values inside
the bars are percentages relative to the control.
Fig. 2. Means and standard errors of fascicle mass following
fertilization in (a) unthinned and (b) thinned plots. Values inside
the bars are percentages relative to the control.
(a)
(a)
(b)
(b)
and PTVI (r = 0.239, p = 0.04) as well as 10-year PTVI (r =
0.238, p = 0.04). Average needle lengths in the second
growing season were associated with 5-year PBAI (r =
0.281, p = 0.017) and PTVI (r = 0.316, p = 0.007) as well as
10-year PBAI (r = 0.381, p = 0.001) and PTVI (r = 0.433,
p = 0.0001). Little association was found between new needle length in the third growing season and tree or stand
growth with the exception of diameter growth (r = 0.237,
p = 0.04). The relationships between needle dry masses and
tree stand growth were similar to those of fascicle length. In
addition, needle mass in 1988 correlated with 10-year PDI
(r = 0.250, p = 0.034) as well as PBAI (r = 0.251, p =
0.034).
Treatment responses relative to those from unthinned and
unfertilized control plots were analysed (Table 5); relative
fascicle length and mass were highly correlated with relative
10-year PTVI.
Foliage and stand responses
The patterns of fascicle length growth in response to fertilization and thinning treatments were similar to results reported by Cochran (1975) who applied N, P, and S at 673,
336, and 101 kg·ha–1, respectively, to a 40-year-old lodgepole pine stand in southern Oregon. Cochran (1975) observed that needle length increased markedly during the first
season after application and decreased in the second growing season. Causes of discrepancy in response duration between this and Cochran’s study are unclear. Difference in N
© 1998 NRC Canada
I:\cjfr\cjfr28\cjfr-12\X98-148.vp
Wednesday, January 20, 1999 1:36:46 PM
Color profile: Disabled
Composite Default screen
Yang
1799
Fig. 3. Means and standard errors of 5- and 10-year periodic
(a) height and (b) diameter at breast height (DBH) increments
following fertilization in unthinned (NT) and thinned (T) plots.
Values inside the bars are percentages relative to the control.
Fig. 4. Effects of four N fertilization levels on height–diameter
relationships in (a) unthinned and (b) thinned plots.
(a)
(b)
sources (ammonium nitrate vs. urea) and application season
(November vs. May) as well as year-to-year variation in
weather patterns may all contribute to the discrepancy. Evaluating N sources and application seasons, Brockley (1995)
reported no difference in needle mass response to these two
N sources and a 27% increase in needle mass in response to
a fall application.
Compared with the well-documented foliar responses to
fertilization, reports of lodgepole pine foliar responses to
thinning are scarce. Needle mass increased by 29% three
years after thinning a 22-year-old balsam fir (Abies balsamea (L.) Mill.) stand in Quebec (Piene 1978). Results
from this study showed that the effect of thinning on needle
length and mass became significant 3 and 4 years, respec-
tively, after the stand was thinned (Table 3). On thinned
plots, fascicle length and mass responses occurred only
when combined fertilization. In unfertilized plots, the 1988
needle mass in thinned plots was actually slightly smaller
than unthinned plots (Fig. 2).
The disappearance of fertilization effects on fascicle
length and mass 2 years after treatment (Table 3, Figs. 2a
and 2b) and the emergence of thinning effects on foliage
length and mass 3 years after fertilization suggest that the effects of fertilization on foliar development are rapid and
short lived, while thinning effects are gradual and long lasting. Fertilization may affect the number of needles after
treatment. Therefore, total foliage mass may continue to increase even though the length and mass of individual fertilized needles is not different than unfertilized needles. A
© 1998 NRC Canada
I:\cjfr\cjfr28\cjfr-12\X98-148.vp
Wednesday, January 20, 1999 1:36:54 PM
Color profile: Disabled
Composite Default screen
1800
Can. J. For. Res. Vol. 28, 1998
Fig. 5. Means and standard errors of 5- and 10-year periodic
(a) basal area (m2·ha–1) and (b) stand total volume (m3·ha–1)
increments following fertilization in unthinned (NT) and thinned
(T) plots. Values inside the bar are percentages relative to the
control.
(a)
Fig. 6. Five- and 10-year absolute and relative stand (a) basal
area (m2·ha–1) and (b) total volume (m3·ha–1) increments of three
fertilized treatments over unfertilized one in unthinned (NT) and
thinned (T) plots. Annotated labels to the right of response
curves denote thinning (NT, T), measured periods (5 and 10
years) and absolute (A) or relative (R) increment.
(b)
combined treatment of thinning and fertilization, consequently, would be expected to significantly enhance foliar
development and consequently tree and stand growth.
Assessing stand basal area and volume responses to fertilization requires long-term observation; consequently, stand
mensurational responses are often predicted from foliar
responses during the first year after fertilization. Previous
studies have shown significant positive correlations between
first-year increases in needle mass and subsequent stemwood responses (Timmer and Morrow 1984; Brockley
1989). Weetman et al. (1988) found that needle mass in the
first growing season following fertilization generally corresponded with subsequent 4-year basal area response in
lodgepole pine. A significant positive correlation (r = 0.61)
was obtained between first-year needle mass response and
relative third-year tree volume response in British Columbia
(Brockley 1989). Hunter et al. (1987) reported a strong correlation between volume increment and needle mass. All
these reports suggest that tree and stand growth responses of
lodge pine can be predicted based on foliage development
following treatment.
Correlation analysis (data not shown) on needle length
and mass and subsequent stand increments indicated that
fascicle length and fascicle mass in 1987, two years after
© 1998 NRC Canada
I:\cjfr\cjfr28\cjfr-12\X98-148.vp
Wednesday, January 20, 1999 1:37:03 PM
Color profile: Disabled
Composite Default screen
Yang
1801
(a)
(b)
(c)
Fig. 7. Means and standard errors of 5- and 10-year stand
mortality following fertilization in unthinned (NT) and thinned
(T) plots: (a) number of stems/ha, (b) basal area (m2·ha–1), and
(c) total volume (m3·ha–1). Values above error bars are
percentages relative to the control.
fertilization, were highly correlated (p < 0.001) with 10-year
PBAI (r = 0.433) and PTVI (r = 0.422). Those correlation
coefficients illustrated a high association between foliar parameters 2 years after fertilization and subsequent stand development; however, the relationships were not high enough
to be reliable predictors. It appears that absolute values of
fascicle parameters and PTVI were not sensitive enough for
developing a relationship for prediction.
In contrast, analysis of percentage increments relative to
the control and relative fascicle length and mass (Table 5)
suggested that both fascicle length and mass within 2 years
after fertilization were closely correlated (r ranged from 0.84
to 0.93) with 10-year relative PTVI and that both can be
used for predicting stand volume response.
Both first-year fascicle length and fascicle mass proved to
be reliable predictors of subsequent stand volume growth;
linear regressions explained 87 and 82%, respectively, of
variation in 10-year mean relative PTVI (Figs. 8a and 8b).
Multiple regression analysis (data not shown) indicated that
91% of the variation was accounted for by relative fascicle
length and mass in 1986; fascicle length 2 years after fertilization explained an additional 5% of the variation.
The strong relationship between first-year foliar response
and subsequent stand growth bears some management implications. Relative volume growth rates were lower on fertilized–thinned plots than on fertilized–unthinned plots after 5
years, but growth rates were higher after 10 years (Fig. 6b).
The reversal trend of relative growth rates confirms the beneficial effect of combined thinning and fertilization.
Height increments
Compared with other stand parameters, height growth response to thinning and fertilization is less often reported and
is more controversial partly because height is more time
consuming to measure and less accurate than diameter.
Thinning initially reduced height increment while N fertilizer
applied to 360 kg·ha–1 increased it. For both measurement
periods, PHIs of all four fertilization levels on unthinned
plots were consistently larger than those of the corresponding level on thinned plots (Fig. 3a). A temporary decline in
height growth of crop trees immediately after thinning
(“thinning shock”) has been reported in several tree species
(Brockley 1989). However, reports of the effects of thinning
on lodgepole pine height growth have been variable and inconclusive (Johnstone 1985), probably reflecting the important influences of both age and site quality on height growth.
Thinning, which results in more growing space, might even
reduce height growth, particularly on good sites, because
tree crowns on good sites expand so rapidly that diameter
accelerates at the expense of height growth (Johnstone
1983). There are some indications that some crowding is required to maximize the height growth of lodgepole pine
(Dahms 1973; Johnstone 1981, 1982, 1983).
© 1998 NRC Canada
I:\cjfr\cjfr28\cjfr-12\X98-148.vp
Wednesday, January 20, 1999 1:37:09 PM
Color profile: Disabled
Composite Default screen
1802
Can. J. For. Res. Vol. 28, 1998
Table 5. Pearson’s correlation coefficients for relative periodic height, diameter at breast height (DBH), basal area, and total volume
increments with relative fascicle length and mass within 3 years following treatment.
Period
5-year
10-year
Relative fascicle length
Relative fascicle mass
Relative
increment
1986
1987
1988
1986
1987
1988
Height
DBH
Basal area
Total volume
Height
DBH
Basal area
Total volume
0.667
–0.039
0.142
0.621
0.337
0.149
–0.024
0.933***
0.631
0.205
0.425
0.772*
0.431
0.368
0.248
0.889***
–0.297
0.739*
0.682
0.366
–0.380
0.812*
0.750*
0.098
0.592
0.107
0.275
0.687
0.309
0.296
0.138
0.904***
0.592
0.273
0.467
0.747*
0.409
0.426
0.309
0.840***
–0.329
0.785*
0.688
0.359
–0.256
0.754*
0.778*
–0.096
Note: All measures are treatment means relative to mean of unthinned, unfertilized control plots (n = 8). Asterisks show the coeffiecients that are
significantly different from 0 (*, p < 0.05; **, p < 0.01; ***, p < 0.001).
Table 6. Summarized 10-year results for survival tree density, mean diameter at breast height (DBH), total stand volume, mean tree
volume, tree volume increment, and mean DBH of dead trees by treatment.
Unthinned
Unthinned
Unthinned
Unthinned
Mean for unthinned
Thinned
Thinned
Thinned
Thinned
Mean for thinned
N applied
(kg·ha–1)
Density
(stems/ha)
Mean
DBH (cm)
Total
volume
(m3·ha–1)
0
180
360
540
3499
3722
3046
3982
3562
2058
1835
1968
1909
1942
11.23
11.49
12.27
10.76
11.44
14.50
15.19
14.96
15.00
14.91
266.25
272.82
293.69
310.99
285.94
201.98
208.27
213.10
214.20
209.39
0
180
360
540
Application of 360 kg·ha–1 N effectively promoted PHI
to 51 and 20%, respectively, after 5 and 10 years on
thinned plots compared with 29 and 19% on unthinned plots
(Fig. 3a). This implies that fertilizer can be used to reduce
the short-term impacts of thinning shock and that
fertilization should be considered in commercially thinned
midrotation stands to accelerate stand recovery and
development.
The modified Weibull function fitted well to measured
height and diameter data (Table 2). The three parameters in
the Weibull function have physical significance: parameters
a, b, and c define respectively the asymptotic maximum, location, and shape of the curve (Yang et al. 1978). Estimated
a and c parameters for the 180 kg·ha–1 N had the largest
value among four N treatments on both thinned and
unthinned plots. The differentiated shape parameters of H–D
curves responding to four levels of fertilization are graphically depicted in Figs. 4a and 4b. Nitrogen fertilization influenced not only height growth but also changed bole shape
and stem profile. Comparing the H–D relationships at the
four N levels, 180 kg·ha–1 N had the largest H–D ratio;
higher N application rates reduced the ratio. Figures 3a, 4a,
and 4b all suggest an adverse effect of high N (540 kg·ha–1)
on height growth, especially on thinned plots. Whether the
Mean tree
volume
(m3)
10-year
tree volume
increment
(m3/tree)
Mean
DBH of
dead trees
0.0761
0.0733
0.0964
0.0781
0.0810
0.0981
0.1135
0.1083
0.1122
0.1080
0.0181
0.0210
0.0268
0.0217
0.0219
0.0302
0.0411
0.0396
0.0415
0.0381
6.58
6.70
7.49
6.77
6.88
10.49
10.31
9.12
10.00
9.98
adverse effect is temporary or permanent requires further
observation.
Mortality
The effect of thinning on mortality was significant after 5
and 10 years (Table 4) because thinning effectively removed
suppressed and unhealthy trees and left only vigorous trees.
Mortality, mainly caused by thinning injuries and windfall of
codominant trees (average DBH 9.98 cm), was lower on
thinned than unthinned plots (Figs. 7a–7c). However, among
thinned plots, mortality was significantly higher on fertilized
plots than on unfertilized control. The causes of the higher
mortality on fertilized and thinned plots warrant further
investigation.
Compared with the thinned plots, mortality on unthinned
plots was substantial. The mortality, based on field observation, occurred on subdominant and suppressed trees with an
average DBH of 6.88 cm (Table 6). Despite substantially
higher mortality on high N plots, average sizes of dead trees
were similar among four treatments. There were no negative
impacts of high N fertilization on stand volume increment
after 10 years (Fig. 5b). It appears that high N augments the
self-thinning process in overstocked stands and hastens
© 1998 NRC Canada
I:\cjfr\cjfr28\cjfr-12\X98-148.vp
Wednesday, January 20, 1999 1:37:10 PM
Color profile: Disabled
Composite Default screen
Yang
Fig. 8. Relationship between relative 10-year stand volume
increment (PTVI) and (a) relative fascicle length (rfl86) and
(b) relative fascicle mass (rfm86) produced in 1986, one year
after fertilization. All values are relative to unthinned,
unfertilized control plots.
1803
return based on 10-year results is beyond the scope of this
paper. However, as biological responses provide the base for
economic analysis, the 10-year results may shed some light
on financial returns of various treatments.
Ten years after treatment, fertilized and unthinned plots
had 80 m3·ha–1 more wood than fertilized and thinned plots,
but usable volume should be discounted because small trees
are not harvestable. In contrast, thinning removed small
trees; so surviving trees on thinned plots would be
harvestable. In addition, average tree size was larger (31 and
36%, respectively, by DBH and volume) in thinned plots
than in unthinned plots (Table 6). Large-size logs reduce
logging costs and increase utilization rate and value. The increased value on thinned plots may partially offset the extra
volume advantage of unthinned plots.
Thinning improves stand light and moisture (Brix 1971)
and redistributes available resources to crop trees, while fertilization adds needed nutrients. Crop trees capitalize on
those resources; extend foliar length; and increase foliar
mass (Figs. 1 and 2), foliage quantity, and photosynthetic efficiency (Brix 1981, 1983). The substantial gain of 76% or
0.0175 m3 individual tree volume on thinned over unthinned
plots in 10 years (Table 6) demonstrates the beneficial effect
of combined thinning and fertilization on tree growth and
stand development.
The author thanks Mr. S. Lux and Mr. C. Rentz for their
assistance in field and laboratory work, Y. Kalra and F.
Radford for conducting foliar and soil analyses, and Dr.
I.G.W. Corns for reviewing the manuscript. Special thanks
are extended to Dr. Robert Brockley of the B.C. Ministry of
Forests and two anonymous reviewers for their critical reviews and valuable suggestions on an earlier version of the
manuscript.
stand development and could be used as a tool in managing
those overstocked stands.
Heavy N fertilization also increased mortality in thinned
plots, which suggests that other factors, such as nutritional
imbalance, may be involved (Fig. 7). Foliar graphical analysis (Timmer and Stone 1978) will be useful in looking at the
response of nutrients other than N following N fertilization.
Effect of combined thinning and fertilization
Fertilization and thinning are management tools, and the
use of those tools should be evaluated and justified by associated cost and benefit. A detailed discussion on economic
Beckingham, J.D., Corns, I.G.W., and Archibald, J.H. 1996. Field
guide to ecosites of west-central Alberta. Can. For. Serv. North.
For. Cent. Spec. Rep. No. 9.
Brix, H. 1971. Effects of nitrogen fertilization on photosynthesis
and respiration in Douglas-fir. For. Sci. 17: 407–414.
Brix, H. 1981. Effects of nitrogen fertilizer source and application
rates on foliar nitrogen concentration, photosynthesis, and
growth of Douglas-fir. Can. J. For. Res. 11: 775–780.
Brix, H. 1983. Effects of thinning and nitrogen fertilization on
growth of Douglas-fir: relative contribution of foliage quantity
and efficiency. Can. J. For. Res. 13: 167–175.
Brockley, R.P. 1989. Response of thinned, immature lodgepole
pine to nitrogen fertilization: three-year growth response. FRDA
Rep. No. 36. Canada–B.C. Forest Resource Development
Agreement, B.C. Ministry of Forests, Victoria.
Brockley, R.P. 1990. Response of thinned, immature lodgepole
pine to nitrogen and boron fertilization. Can. J. For. Res. 20:
579–585.
Brockley, R.P. 1995. Effects of nitrogen source and season of application on the nutrition and growth of lodgepole pine. Can. J.
For. Res. 25: 516–526.
Brockley, R.P., and Shernan, F.J. 1994. Foliar nutrient status and
facicle weight of lodgepole pine following nitrogen and sulphur
© 1998 NRC Canada
I:\cjfr\cjfr28\cjfr-12\X98-148.vp
Wednesday, January 20, 1999 1:37:14 PM
Color profile: Disabled
Composite Default screen
1804
fertilization in the interior of British Columbia. Can. J. For. Res.
24: 792–803.
Cochran, P.H. 1975. Response of pole-sized lodgepole pine to fertilization. USDA For. Serv. Pac. Northwest For. Range Exp. Stn.
Res. Note No. PNW-247.
Cochran, P.H. 1979. Response of thinned lodgepole pine after fertilization. USDA For. Serv. Pac. Northwest For. Range Exp. Stn.
Res. Note No. PNW-335.
Corns, I.G.W., and Annas, R.M. 1986. Field guide to forest ecosystems of west-central Alberta. Canadian Forest Service, Northern
Forest Centre, Edmonton, Alta.
Dahms, W.G. 1973. Tree growth and water use responds to thinning in a 47-year-old lodgepole pine stand. USDA For. Serv.
Pac. Northwest For. Range Exp. Stn. Res. Note No. PNW-194.
Dumanski, J., Macyk, T.M., Veauvy, C.F., and Lindsay, J.D. 1972.
Soil survey and land evaluation of the Hinton, Edson area, Alberta. Alta. Inst. Pedol. Rep. No. S-72-31.
Goodell, B.C. 1952. Watershed-management aspects of thinned
young lodgepole pine stands. J. For. 50: 374–378.
Huang, S. 1994. Ecologically based individual tree volume estimation for major Alberta tree species. Rep. No. 1. Alberta
Environmnetal Protection Lands and Forest Service, Forest
Management Division, Edmonton.
Hunter, I.R., Hunter, J.A.C., and Graham, J.D. 1987. Pinus radiata
stem volume increment and its relationship to needle mass, foliar and soil nutrients, and fertiliser input. N.Z. J. For. Sci. 17:
67–75.
Johnstone, W. 1981. Effects of spacing 7-year-old lodgepole pine
in west-central Alberta. Can. Can. For. Serv. North. For. Res.
Cent. Inf. Rep. No. NOR-X-236.
Johnstone, W. 1982. Juvenile spacing of 25-year-old lodgepole
pine in western Alberta. Can. Can. For. Serv. North. For. Res.
Cent. Inf. Rep. No. NOR-X-244.
Johnstone, W. 1983. Natural lodgepole pine in western central Alberta. Part II. Juvenile spacing. In Lodgepole pine: regeneration
and management. Edited by M. Murray. USDA For. Serv. Gen.
Tech. Rep. No. PNW-157. pp. 8–11.
Johnstone, W. 1985. Thinning lodgepole pine. In Proceedings of
Lodgepole Pine the Species and Its Management. 8–10 May
1984, Spokane, Wash., and 14–16 May 1984, Vancouver, B.C.
Edited by D.M. Baumgartner, R.G. Krebill, J.T. Arnott, and G.F.
Weetman. Washington State University Cooperative Extension,
Pullman. pp. 253–262.
Can. J. For. Res. Vol. 28, 1998
Piene, H. 1978. Effects of increased spacing on carbon mineralization rates and temperature in a stand of young balsam fir. Can. J.
For. Res. 8: 398–406.
Preston, C.M., and Mead, D.J. 1994. Growth response and recovery of 15N-fertilizer one and eight growing seasons after application to lodgepole pine in British Columbia. For. Ecol. Manage.
65: 219–229.
Rowe, J.S. 1972. Forest regions of Canada. Can. For. Serv. Publ.
No. 1300.
SAS Institute Inc. 1990. SAS/STAT user’s guide, version 6. 4th ed.
SAS Institute Inc. Cary, N.C.
Timmer, V.R., and Morrow, L.D. 1984. Predicting fertilizer growth
response and nutrient status of jack pine by foliar analysis. In
Forest Soils and Treatment Impacts. Proceedings of the 6th
North American Forest Soils Conference, June 1983, Knoxville,
Tenn. Edited by E.L. Stone. University of Tennessee, Knoxville.
pp. 335–351.
Timmer, V.R., and Stone, E. L. 1978. Comparative foliar analysis
of young balsam fir fertilized with nitrogen, phosphorus, potassium and lime. Soil Sci. Soc. Am. J. 42: 125–130.
Weetman, G.F., Fournier, R.M., and Schnorbus, E. 1988.
Lodgepole pine fertilization screening trials: four-year growth
response following initial predictions. Soil Sci. Soc. Am. J. 52:
833–839.
Wheeler, N.C., and Critchfield, W.B. 1985. The distribution and
botanical characteristics of lodgepole pine: biogeographical and
management implications. In Proceedings of Lodgepole Pine,
the Species and Its Management, 8–10 May 1984, Spokane,
Wash., and 14–16 May 1984, Vancouver, B.C. Edited by D.M.
Baumgartner, R.G. Krebill, J.T. Arnott, and G.F. Weetman.
Washington State University Cooperative Extension, Pullman.
pp. 1–13.
Yang, R.C. 1985a. Ten-year growth response of 70-year-old
lodgepole pine to fertilization in Alberta. Can. For. Serv. North.
For. Res. Cent. Inf. Rep. No. NOR-X-266.
Yang, R.C. 1985b. Effects of fertilization on growth of 30-year-old
lodgepole pine in west-central Alberta. Can. For. Serv. North.
For. Res. Cent. Inf. Rep. No. NOR-X-268.
Yang, R.C. 1991. Early stand development of lodgepole pine
spaced at age 7 in west-central Alberta. For. Can. North. For.
Cent. Inf. Rep. No. NOR-X-322.
Yang, R.C., Kozak, A., and Smith, H.G. 1978. The potential of
Weibull-type functions as flexible growth curves. Can. J. For.
Res. 8: 424–431.
© 1998 NRC Canada
I:\cjfr\cjfr28\cjfr-12\X98-148.vp
Wednesday, January 20, 1999 1:37:14 PM