Forest Ecology and Management 258 (2009) 2153–2161
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Forest Ecology and Management
journal homepage: www.elsevier.com/locate/foreco
Growth and productivity of black spruce in even- and uneven-aged stands
at the limit of the closed boreal forest
Sergio Rossi *, Marie-Josée Tremblay, Hubert Morin, Germain Savard
Département des Sciences Fondamentales, Université du Québec à Chicoutimi, 555 Boulevard de l’Université, Chicoutimi (QC) G7H2B1, Canada
A R T I C L E I N F O
A B S T R A C T
Article history:
Received 8 June 2009
Received in revised form 17 August 2009
Accepted 18 August 2009
The increasing commercial interest and advancing exploitation of new remote territories of the boreal
forest require deeper knowledge of the productivity of these ecosystems. Canadian boreal forests are
commonly assumed to be evenly aged, but recent studies show that frequent small-scale disturbances
can lead to uneven-aged class distributions. However, how age distribution affects tree growth and stand
productivity at high latitudes remains an unanswered question. Dynamics of tree growth in even- and
uneven-aged stands at the limit of the closed black spruce (Picea mariana) forest in Quebec (Canada)
were assessed on 18 plots with ages ranging from 77 to 340 years. Height, diameter and age of all trees
were measured. Stem analysis was performed on the 10 dominant trees of each plot by measuring treering widths on discs collected each meter from the stem, and the growth dynamics in height, diameter
and volume were estimated according to tree age. Although growth followed a sigmoid pattern with
similar shapes and asymptotes in even- and uneven-aged stands, trees in the latter showed curves more
flattened and with increases delayed in time. Growth rates in even-aged plots were at least twice those of
uneven-aged plots. The vigorous growth rates occurred earlier in trees of even-aged plots with a
culmination of the mean annual increment in height, diameter and volume estimated at 40–80 years,
90–110 years earlier than in uneven-aged plots. Stand volume ranged between 30 and 238 m3 ha1 with
75% of stands showing values lower than 120 m3 ha1 and higher volumes occurring at greater dominant
heights and stand densities. Results demonstrated the different growth dynamics of black spruce in
single- and multi-cohort stands and suggested the need for information on the stand structure when
estimating the effective or potential growth performance for forest management of this species.
ß 2009 Elsevier B.V. All rights reserved.
Keywords:
Forest dynamics
Forest structure
Old-growth forest
Picea mariana
Regeneration
Stem analysis
1. Introduction
The boreal forest represents the widest reservoir of wood of the
northern hemisphere. In these environments, forest exploitation
has moved from south to north towards the remoter territories and
new forested regions. Because of long forest rotations, Canada has
repeatedly extended the area involved in forest management,
relocating its boundaries northwards to maintain adequate
production to meet the demand for timber (Ministère des
Ressources Naturelles, 2000). In Quebec, these boundaries have
crossed the 50th parallel, approaching the northern limit of the
closed forest of black spruce (Picea mariana). Although this species
has been extensively studied within its major managed area
(Johnson, 1992; Paquin and Doucet, 1992; Lussier et al., 2002),
north of the 50th parallel the studied stands become increasingly
rare because of their inaccessibility and presumed low growth and
regeneration potential (Perron, 2003; Ministère des Ressources
* Corresponding author. Tel.: +1 418 545 5011x2330; fax: +1 418 545 5012.
E-mail address: [email protected] (S. Rossi).
0378-1127/$ – see front matter ß 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.foreco.2009.08.023
Naturelles, 2000). This lack of study sites has led to a shortage of
information on the real productivity of the forest at high latitudes.
However, the increasing commercial interest in the northern
forests requires deeper knowledge of these biotopes that have an
evident ecological importance but basically still unknown
economic potential.
Natural forests of black spruce originate from fire, which kills
the previously established trees creating even-aged stands from
the aerial seed banks released by the semi-serotinous cones
(Lieffers, 1986; St-Pierre and Gagnon, 1992; Charron and Greene,
2002; Bouchard et al., 2008). In the absence of other intense
disturbances that could again kill the whole stand or in cases
where the fire interval exceeds tree lifespan, the stand is affected
by secondary disturbances: approximately 120–200 years after a
fire, the death and/or falling of larger trees begins to open up gaps
in the canopy (De Grandpré et al., 2000; Harper et al., 2003). Within
these gaps, dead trees are gradually replaced by other individuals
from a new cohort that modifies the stand creating a multi-aged
structure (Pham et al., 2004; Harper et al., 2006). This multi-aged
structure represents 70% of the stands in the eastern Quebec
(Boucher et al., 2003) and is expected to represent an important
S. Rossi et al. / Forest Ecology and Management 258 (2009) 2153–2161
2154
total precipitation of 946 mm. About 300 cm of snow covers the
ground from October to May, only disappearing completely in June.
The sum of the mean temperatures exceeding 5 8C is 970.9 8C day.
proportion of the forests of high latitudes. If and how age structure
within a stand affects tree growth and stand productivity of these
ecosystems remains a crucial but unanswered question.
In the past, the boreal forest was erroneously assumed to be a
mere mosaic of even-aged stands, frequently reinitiated by major
disturbances. This induced a widespread use of clear-cutting to
emulate the conditions created by nature. However, in the last
decade the previously overlooked small-scale events have been
clearly demonstrated (Kneeshaw and Gauthier, 2003) and, as a
result, the gap dynamics in the conifer-dominated populations of
North America has begun to be taken into account in ecosystembased forest management (Bergeron et al., 2002; Bergeron, 2004;
Brassard and Chen, 2006). Although the age-related changes in
forest structure have been analyzed for the Canadian boreal forest
(cf. McCarthy, 2001), to our knowledge there is still a lack of growth
models of black spruce at high latitudes.
The ecosystem-based forest management is in part substituting
the traditional practices of clear-cutting to maintain functioning of
the boreal forests (Bergeron et al., 2002). The new practices should
attempt to more closely simulate the natural processes and
disturbances occurring in these environments. However, conservation, restoration, and management require knowledge on
features and dynamics of the stands in natural, pristine areas
(Kneeshaw and Gauthier, 2003). The aim of this study was to assess
changes in growth during stand development at both tree and
stand level by investigating (i) dynamics of tree growth and (ii)
stand volume in even- and uneven-aged stands of black spruce at
the limit of the closed boreal forest in Quebec, Canada.
2.2. Methods
Eighteen natural stands were selected from the inventory
maps at the scale 1:50 000 (Quebec Ministry of Natural
Resources) according to a stratified random selection. Stands
were divided according to their reported forest age and density
and samples were selected from each stratum independently in
order to obtain as wide as possible a range of stand ages and
densities. In each selected stand, sample plots were established
that were at least twice the area of the larger gaps (cf. McCarthy,
2001) and sampled during 2003–2005 (Table 1). Because tree
density varied among stands, plot sizes varied from 200 to
400 m2 so that all plots included at least 24 sampled trees (Rossi
et al., in press). As the area was inaccessible by road, stand
selection was based on the proximity of a lake at least 1 km in
length to permit access by floatplane. Because of their remote
location and the absence of evidence of human impact, the
stands were considered to have developed under the influence
of natural disturbances.
In each plot, height and diameter at breast height (DBH) were
measured on all living trees with a diameter at breast height (DBH)
larger than 9-cm and 2-cm-thick discs were collected from the
stem base. Discs were also collected along the stem of 10 dominant
black spruce [Picea mariana (Mill.) B.S.P.] trees at sampling heights
of 0.3, 0.6, 1 and 1.3 m from the collar. Above 1.3 m, discs were
collected at intervals of 1 m for the remaining length of the stem.
The dominant trees had upright stem, elevated DBH and heights
similar to those of the bigger trees of the stand. Trees with
polycormic stems, evident damage due to parasites and reduced or
partially dead crowns were excluded from the selection of the
dominant trees. However, in 11 trees (6% of the total), the last 2–
3 m from the top was polycormic; in this case, only the longer and
upright stem was used for measurements. Discs were air-dried and
sanded with progressively finer grade sandpaper. Tree-ring widths
were measured to the nearest 0.01 mm using a Henson measuring
system along two to four paths, according to the uniformity of the
tree rings on the disc. All ring width series were corrected by crossdating performed both visually and using the COFECHA computer
program (Holmes, 1983). Measurements were averaged for each
disc and tree ring.
2. Materials and methods
2.1. Study area
The study was conducted between Lac Mistassini and
Manicouagan Reservoir, at the limit of the closed boreal forest
in Quebec, Canada. The region has a gently rolling topography with
hills reaching 500–700 m a.s.l. on thick and undifferentiated glacial
till deposits. This area is part of the black spruce-feather moss
bioclimatic domain (Robitaille and Saucier, 1998), with a potential
vegetation composed mainly of black spruce and balsam fir (Abies
balsamea). The closest meteorological station is located in Bonnard
(508430 N, 718030 W, 506 m a.s.l.), 75 km from the study area. The
climate is continental, with cool, short summers and long, cold
winters with a 30-year mean annual temperature of 1.8 8C and
Table 1
Location, structure and characteristics of the 18 selected plots at the limit of the closed boreal forest in Quebec, Canada. The number of trees within plot is reported in
parentheses.
Stand
Latitude
Longitude
Altitude
(m)
Plot
size (m)
Sampling
year
Stand
structure
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
1
2
3
518000
518270
518200
518310
518420
518060
518200
518130
518020
518000
518000
518090
518220
518030
518110
518450
518410
518510
738000
718240
708060
708260
718090
718570
708470
718470
728360
728400
718110
718040
718350
728340
718040
708330
708460
708190
420
541
539
601
615
570
540
534
520
480
531
546
570
530
528
622
652
535
10 20
10 20
20 20
10 20
20 20
20 20
20 20
20 20
20 20
10 20
10 20
20 20
20 20
15 20
20 20
20 20
20 20
20 20
2003
2004
2004
2005
2004
2004
2005
2005
2003
2003
2005
2004
2004
2003
2005
2004
2004
2004
Even-aged
Even-aged
Even-aged
Even-aged
Even-aged
Even-aged
Even-aged
Even-aged
Uneven-aged
Uneven-aged
Uneven-aged
Uneven-aged
Uneven-aged
Uneven-aged
Uneven-aged
Uneven-aged
Uneven-aged
Uneven-aged
Number of trees in the plot
Black spruce
42
29
38
74
48
77
45
33
46
44
34
24
39
48
57
46
40
30
Dominant
height (m)
Mean
DBH (cm)
Stand
density
(trees ha1)
Stand
basal area
(m2 ha1)
11.00
13.02
13.24
12.73
14.70
15.10
12.25
12.68
14.48
16.93
17.22
16.28
13.09
15.77
14.64
13.15
12.06
9.05
11.49
12.76
13.39
12.82
14.41
14.18
11.41
13.22
12.41
15.64
14.51
13.39
12.33
13.51
13.41
13.88
12.66
11.57
2100
2300
950
3750
1200
2025
1125
825
1275
2350
1700
600
975
1600
1450
1275
1000
875
22.41
30.67
14.01
49.41
20.75
33.83
11.76
12.14
16.23
47.06
30.4
9.5
12.41
24.02
21.42
20.64
13.02
9.45
Other species
17
1
4
5
3
1
5
5
S. Rossi et al. / Forest Ecology and Management 258 (2009) 2153–2161
Estimations of height growth were made using the Carmean
(1972) method. This method produces the best estimates of the tree
height Hij at age tij assuming that the annual height growth within a
given stem section is constant and that, on average, the crosscut
occurred in the middle of a given annual height growth (Dyer and
Bailey, 1987). After having designated the growth rings at the ith
cross-section with the subscript j varying from 1 to ri for each tree of
age n, the assumptions are expressed mathematically by
Hi j ¼ hi þ
hiþ1 hi
h hi
þ ð j 1Þ iþ1
2ðr i r iþ1 Þ
r i r iþ1
and
ti j ¼ n ri þ j
where hi is the height at the ith cross-section, tij the tree age
associated with the jth inner ring at the ith cross-section and ri the
number of growth rings at the ith cross-section. Stem volume was
calculated by adding the volume of all tree sections envisaged as
truncated cones with the volume V being obtained by the formula:
V¼
pl
3
2
ða2 þ ab þ b Þ
where l is the height of the truncated cone and a and b the minor
and major radius (Van Laar and Akça, 2007).
2.3. Statistical analyses
Stands were classified as even- or uneven-aged according to the
distribution of tree age and the age of the older trees measured on
the plot (Rossi et al., in press). Growths in height, diameter and
volume were fitted with a sigmoid function using the NLIN
procedure (NonLINear regression) and Gauss iterative method in
SAS (SAS, 2003). The sigmoid function is defined as:
h
i
y ¼ A exp eKðtTiÞ
where y represents stem height, diameter or volume and t the tree
age. The three parameters are the upper asymptote A, the rate of
change of the shape K and the x-axis placement of the inflection
point Ti. The residuals were regressed onto the partial derivatives
with respect to the parameters until the estimates converged.
Several possible starting values were specified for each parameter,
so that the NLIN procedure evaluated each combination of initial
values using the interactions producing the smallest residual sums
of squares. Curve fitting was performed also for each site and the
estimated function parameters were correlated with dominant
height, stand age and stand density. Dominant height was defined
as the mean height of the 100 largest trees per hectare (Pardé and
Bouchon, 1988), which in this work corresponded to the two to
four largest trees per plot. Stand age was the period since the last
stand-replacing disturbance that, in each stand, was assessed as
the age of the oldest tree.
The volumes obtained by stem analysis on the dominant trees
were compared with the cylindrical volumes calculated using DBH
and height. This relationship, computed separately for even-aged
and uneven-aged stands, was employed for computing stem
volume of all trees in the plots and for estimating stand volume.
Stand volume was compared with stand density, dominant height
and stand age by means of forward multiple regressions to assess
the relevance of these independent variables in the model. The
analysis started with no variable in the model and gradually
added all variables. At each repetition, the method calculated Fstatistics that reflected the contribution of the variables to the
model, added the variable with largest F to the model. F-statistics
were then recalculated for the remaining variables, so repeating
the evaluation process until all variables were added one by one to
the model.
2155
3. Results
3.1. Stand description
A total of 835 trees were harvested for age determination. Plots
contained from 24 to 81 trees and showed a high variability in
density, estimated from 600 to 3750 trees ha1 (Table 1). Mean
DBH varied from 11.41 to 15.64 cm, which produced a basal area of
between 9.45 and 49.41 m2 ha1 with the greatest values observed
at the highest densities. Black spruce formed almost monospecific
stands in all plots except plot 2, where 36% of trees were Jack pine
(Pinus banksiana). Tamarack (Larix laricina) and white birch (Betula
papyrifera) were found as single specimens in stands 4 and 6,
respectively, while balsam fir was present in 30% of the plots, but
only represented a modest percentage of the total basal area of the
stand (Table 1).
Stands 1–8 had structures dominated by one or few age cohorts
and the majority of trees regenerated within 20–30 years after the
last stand-replacing disturbance (Fig. 1). These stands showed ages
of the older trees ranging between 77 and 188 years and were
considered even-aged. Plots 9–18 were uneven-aged stands, with
wider and irregular age distributions that included trees from
almost every class. Stand 12 showed a clearly bimodal structure. In
uneven-aged stands, the age of the older trees varied between 222
and 340 years and the within-plot age ranges and standard
deviations that were four times higher than in even-aged stands.
3.2. Dynamics of tree growth
Tree growth in height, diameter and volume followed a sigmoid
pattern (Fig. 2). A gradual initial increase was followed by a more
rapid growth rate, which was attained at older ages in trees of
uneven-aged stands. Volume increased more slowly than height
and diameter and remained at very low values for 15 and 45 years
in even-aged and uneven-aged stands, respectively. After the sharp
increase, growth rate slowed down and height, diameter and
volume fluctuated around a maximum value. Although an evident
heteroscedasticity appeared mainly at younger ages, the standard
deviations remained constant after curves reached their plateau
(Fig. 2). In even- and uneven-aged stands, after 140 and 320 years,
respectively, abrupt changes in means and standard deviations
were caused by the reduction in the number of trees reaching these
ages and used for producing the last parts of the curves. A
comparison between the growth curves in the uneven-aged stands
revealed only three trees out of 100 with an initial growth rate
clearly higher than that of the other trees of the stand (data not
shown). These trees could be belonged to the first cohort
established after the stand-replacing disturbance.
Evaluation of the nonlinear regressions was based on statistics
for goodness of fit, fitting behaviour and examination of the
residuals. The regressions explained a proportion of variation
varying between 0.42 and 0.75, with lower R2 calculated for stem
volume because of the higher variability in the data (Table 2).
Standard errors represented 0.3–3.5% of the parameter values with
higher errors estimated for K. In general, the absence of patterns in
the distributions of the residuals confirmed the model quality and
goodness of fit. However, in even-aged stands, the beginning of the
curve was distant from the origin and predicted values overestimated the observations for the first 10 and 5 years of height and
diameter growth, respectively.
Growth dynamics modelled by the sigmoid functions are
reported together with the mean annual increments in Fig. 3. The
first 10 years of growth are removed from the plot because of
the observed inaccuracies of the curve fitting. Although functions
attained similar asymptotes, the shape was related to stand
structure with uneven-aged stands characterized by more
S. Rossi et al. / Forest Ecology and Management 258 (2009) 2153–2161
2156
Fig. 1. Tree age frequency distribution from 18 stands at the limit of the closed boreal forest in Quebec, Canada.
Table 2
Parameters of the sigmoid function (A, upper asymptote; K, rate of change; Ti, x-axis placement of the inflection point) and R2 for models fitted by nonlinear regressions with
tree height, diameter and stem volume for even- and uneven-aged stands at the limit of the closed boreal forest in Quebec, Canada. Values in parentheses represent the
standard error of the estimated parameters.
R2
Variable
Structure
A
K (102)
Height
Even-aged
Uneven-aged
11.29 (0.04)
11.67 (0.06)
3.62 (0.05)
1.81 (0.02)
31.76 (0.26)
86.32 (0.51)
0.75
0.70
Diameter
Even-aged
Uneven-aged
15.76 (0.07)
18.62 (0.13)
4.33 (0.08)
1.48 (0.02)
27.21 (0.28)
96.33 (0.68)
0.66
0.71
Stem volume
Even-aged
Uneven-aged
82.36 (1.15)
78.18 (0.98)
3.14 (0.11)
2.37 (0.07)
56.96 (0.74)
127.79 (0.89)
0.47
0.42
Ti
S. Rossi et al. / Forest Ecology and Management 258 (2009) 2153–2161
2157
Fig. 2. Individual growth in height, diameter and stem volume of black spruce trees from even- and uneven-aged stands at the limit of the closed boreal forest in Quebec, Canada.
flattened curves and with an increase delayed in time, as also
indicated by the lower K-parameter (Table 2). Vigorous growth
rates occurred earlier in trees of even-aged plots, with a
culmination of the mean annual increment in height and diameter
estimated by Ti-parameter at 32 and 27 years, 62 years earlier on
average than in uneven-aged plots. A longer delay was observed for
mean annual increment in volume, which culminated at 57 years
in even-aged plots and at 128 years in uneven-aged plots (Fig. 3).
Growth rates were always higher in trees of even-aged plots, with
maximum increments at least twice those of trees in uneven-aged
plots. Although mean annual increments in height and diameter
converged towards similar values at older tree ages, at 180 years
after stand initiation uneven-aged plots still showed 27% lower
growth rates in volume than those of even-aged plots.
Dominant height was correlated with the A-parameter of the
sigmoid functions for height and volume growth while no
significant correlation (p > 0.05) was observed either with the
other function parameters or with diameter growth (Table 3).
Stand age was negatively and positively correlated with K and Ti,
respectively for height, diameter and volume growth, but with
different levels of significativity. At tree level, no correlation was
detected between stand density and the estimated parameters of
the sigmoid functions (p > 0.05).
3.3. Stand volume
Linear relationships were detected between the cylindrical
volume and the stem volume of the dominant trees (Fig. 4). The
regressions accounted for 96% and 97% of the variation in stem
volume in even-aged and uneven-aged stands, respectively, with
slopes of 0.30–0.32. The higher slope estimated for uneven-aged
stands were connected to some big trees, which were lacking in
even-aged stands (regression coefficients are reported in Fig. 4).
Very high variations in stand volume were observed between
the 18 plots, with ranges varying between 30 and 238 m3 ha1
and 75% of stands showing volumes lower than 120 m3 ha1
(Table 4). In average, even-aged plots showed higher stand volumes
with 96 m3 ha1 estimated for even-aged stands and 85 m3 ha1
estimated for uneven-aged stands. However, because of the very high
standard deviation, this difference should be considered irrelevant.
Table 3
Pearson correlation coefficients calculated between the three parameters of the sigmoid functions (A, K, Ti) fitted to the growths in height, diameter and volume with stand
characteristics (dominant height, stand density and stand age).
Height growth
Dominant height
Stand age
Stand density
ns, not significant.
*
p < 0.01.
**
p < 0.001.
***
p < 0.0001.
Diameter growth
Volume growth
A
K
Ti
A
K
Ti
A
K
Ti
0.85***
0.28 ns
0.03 ns
0.29 ns
0.90***
0.36 ns
0.22 ns
0.90***
0.41 ns
0.42 ns
0.25 ns
0.29 ns
0.27 ns
0.90***
0.36 ns
0.31 ns
0.61*
0.42 ns
0.86***
0.03 ns
0.30 ns
0.13 ns
0.82**
0.25 ns
0.01 ns
0.93***
0.35 ns
2158
S. Rossi et al. / Forest Ecology and Management 258 (2009) 2153–2161
Fig. 3. Gompertz functions representing individual growth in height, diameter and volume and their mean annual increments of black spruce in even- and uneven-aged
stands at the limit of the closed boreal forest in Quebec, Canada.
Forward multiple regressions performed with stand density,
dominant height and stand age gradually included all independent variables in the model but the relevance of each variable in
predicting stem volume was different (Table 5). At the first step,
stand density produced an R2 accounting for 69% of the
variability in stand volume. The relevance of the second
variable, the dominant height, was still statistically significant
(F = 22.64, p < 0.001) and estimated as 18% at partial R2. Stand
age was not significant (F = 0.50, p > 0.05) and produced an
irrelevant increase in R2. Multiple regressions indicated that
stand density (SD) and dominant height (H) were sufficient to
provide a suitable model for predicting stand volume (SV) by
Table 4
Stand age (i.e. period since the last stand-replacing disturbance) and volume of the
18 selected plots at the limit of the closed boreal forest in Quebec, Canada.
Fig. 4. Linear regressions between stem volume and the cylindrical volume
calculated using DBH and height of dominant trees from 18 even-aged and unevenaged stands at the limit of the closed boreal forest in Quebec, Canada.
Stand
Stand age (years)
Stand volume (m3 ha1)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
77
84
107
149
158
177
182
188
222
232
250
280
283
285
296
324
329
340
82.94
119.63
55.37
190.99
80.37
151.23
43.55
44.35
61.05
238.7
139.92
41
46.72
100.23
75.72
75.79
42.4
30.39
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S. Rossi et al. / Forest Ecology and Management 258 (2009) 2153–2161
Table 5
Summary of the forward regression for stand volume (m3 ha1) regressed against stand density (trees ha1), dominant height (m) and stand age (years) in black spruce at the
limit of the closed boreal forest in Quebec, Canada.
Step
1
2
3
Partial R2
0.696
0.182
0.004
Model R2
0.696
0.879
0.883
F
36.76
22.64
0.50
p
<0.0001
<0.0003
0.4891
accounting for 87% of variance according to the following fitted
equation:
SV ¼ 153:11 þ 5:69 102 SD þ 11:23 H
4. Discussion
This work analyzed growth and productivity of black spruce at
the limit of the closed boreal forest, comparing dynamics of tree
growth and forest structure. Results showed more vigorous growth
rates in trees of even-aged plots, whereas delayed culminations of
mean annual increments in height, diameter and volume were
observed in uneven-aged plots. In the boreal forest of high
latitudes, the development of an extensive and thick moss layer
prevents the establishment of seed-originated seedlings in mature
stands but favours the growth of a dense regeneration produced by
layering (Viereck and Johnson, 1990; Rossi et al., in press). Black
spruce is characterized by shade-tolerance, showing growth in as
little as 10% of full light intensity and by a continuous initiation of
adventitious roots following the steady accumulation of organic
matter at the base of the stem (Viereck and Johnson, 1990; Krause
and Morin, 2005). These features allow saplings to maintain their
presence in the understorey for more than 100 years (Messier et al.,
1999; Rossi et al., in press). At lower light intensities, advance
regeneration of this long-lived species can maintain low production rates by retaining branches and foliage longer and drastically
reducing height and diameter growth (Takahashi, 1996; Claveau
et al., 2002), which clearly explains the observed differences in tree
growth between even- and uneven-aged stands. The strategy
allows suppressed trees to avoid costs of construction for new
tissues, reduce outlay for nonphotosynthetic organs, and wait with
slow growth until a small-scale disturbance occurs to open the
canopy (Messier et al., 1999).
Age is usually reported as one of the most important
variables in growth and yield modelling. In black spruce forests,
an intense disturbance resulting in a single cohort can be
followed after 120–200 years by low-intensity disturbances that
produce multi-cohort structures (Groot et al., 2004; Rossi et al.,
in press). If the stand structure is unknown, the variable age can
be misleading because the slow tree growth in multi-cohort
stands is the result of the initial suppression by and competition
with the dominant layer. Mean annual increments of trees in
uneven-aged stands represented only 30% of the value measured
in trees of even-aged stands. Consequently, when estimated
without including stand structure, mean growth rates could
provide incorrect information about effective or potential tree
performances. These findings have to be considered when
estimating black spruce growth for future management decisions in high-latitude boreal forests.
Multi-cohort ecosystem-based management is being developed
and implemented in the boreal forest of Canada. Knowledge of tree
growth in stands with heterogeneous multi-aged structures is an
integral part of this management approach. However, the available
growth models of uneven-aged stands for Eastern Canada refer
mainly to the southern boreal mixedwood forest (Bergeron and
Harvey, 1997; Harvey et al., 2002). On the contrary, models of
growth for black spruce are yield curves derived from essentially
Intercept
5.74
153.11
165.04
Independent variables
Density (102)
Dominant height
Stand age (102)
6.29
5.69
5.94
11.23
11.02
4.97
even-aged study plots and specify volume increment as a function
of stand age (Morin and Gagnon, 1992; Pothier and Savard, 1998;
Groot et al., 2004). Although suitable for correctly describing the
growth dynamics in younger single-cohort stands, these models
may fail if applied in stands older than 150–200 years, when trees
of the secondary cohorts have attained the dominant canopy.
However, at high latitudes, the closed boreal forest appears
homogeneously sized in both even-aged and uneven-aged stands,
with diameter and height distributions similar across all stages of
stand development (Rossi et al., in press). Consequently, an
accurate assessment of the age structure is indispensable to
identify the stand structure at these latitudes.
Although boreal forests can originate from regeneration
following major disturbances (Viereck, 1983; Cogbill, 1985), the
importance of the smaller-scale, secondary disturbances has been
recognized also for these ecosystems. In the absence of other
intense disturbances that could kill the whole stand or in cases
where fire interval exceeds tree lifespan, death and/or falling of the
larger trees, caused by biotic or abiotic factors such as windthrow,
insect outbreaks or fungal root and butt rots, open the canopy and
create gaps (Smith et al., 1987; Liu and Hytteborn, 1991;
Kuuluvainen, 1994; De Grandpré et al., 2000; Harper et al.,
2003). The dead trees are gradually replaced by other shadetolerant individuals leading to structural and compositional
changes in the stand. Since tree species diversity is rather limited
in the boreal forest, stand development occurs mainly through
changes in structure (Harper et al., 2002). Until 340 years since
stand initiation, plots were observed to be strongly dominated by
black spruce while signs of progression to a different composition
were lacking, with the exception of balsam fir, whose presence
could not assure the development of a spruce-fir mixed stand,
typical of the southern and eastern parts of Quebec. Shadeintolerant tree species could also occur at these latitudes
(Robitaille and Saucier, 1998). However, the sporadic presence
of Jack pine, tamarack and white birch suggested that the gaps
opened by the small-scale, secondary disturbances were of
reduced dimensions (Pham et al., 2004).
The forests characterized by gap dynamics are supposed to have
relatively constant structural features and a number of trees
continuously decreasing with age (inverse J-shaped age structures). These characteristics should be maintained by both the
repeated small-scale disturbances and the continuous recruitment
of new individuals. However, such theoretical distribution is rarely
found at stand level (Hett and Loucks, 1976; Kuuluvainen et al.,
1998) and in Quebec is more frequent in balsam fir-dominated
stands (Boucher et al., 2003). On the contrary, in old-growth
forests, multi-cohort stands with irregular or multimodal distributions are more frequent (Steijlen and Zackrisson, 1987;
Zackrisson et al., 1995; De Grandpré et al., 2000; Lilja et al., 2006).
With increasing time since stand initiation, windthrow could be a
significant factor contributing to the forest dynamics in coniferous
stands and black spruce is especially vulnerable because of its
shallow root system. According to De Grandpré et al. (2000), this
disturbance may contribute to the development of the observed
multi-layered structure because it does not affect homogeneously
all the individuals in a stand.
2160
S. Rossi et al. / Forest Ecology and Management 258 (2009) 2153–2161
Both dominant height and stand density were reliable
indicators of forest productivity and predictors of wood production
of black spruce, accounting for 84% of the variability. These two
variables are simple stand characteristics, easy and inexpensive to
measure in most situations. Height of the largest trees is the most
widely accepted and used indicator of site productivity (Rayner,
1992; Vanclay, 1992) and is independent of the amount of stems in
even-aged stands and within a wide range of density (Lanner,
1985). Nevertheless, this work demonstrated also that stands with
elevated density supported the highest basal areas and volumes,
irrespective of their age. At these latitudes, the variations in stem
diameter are small and 80% of the trees show DBH ranging
between 9 and 15 cm in both even-aged and uneven-aged stands
(Rossi et al., in press). Thus, it is possible that the stand volume is
affected mainly by the number of stems rather than their size.
In young, even-aged plots, stand volume over time always
increases (Assmann, 1970). After maturity, death of the trees
belonging to the first cohort could lead to a drastic decreasing of
periodic growth increments and wood losses (Pothier et al., 2004).
In our study, no influence of the stand age on stand volume was
detected. However, in uneven-aged stands of black spruce, the
long-term yield trajectory has complex dynamics with a decline
followed by more or less constant stand volume over time (Garet
et al., 2009). These nonlinear patterns, observed on permanent
sample plots, could not be detected by the linear relationships
employed in this work.
5. Conclusion
Management practices for the boreal forest often rely on the
assumption that commonly natural stands have an even-aged
structure originating from stand-replacing disturbances. Thus,
clear-cutting is assumed to be the most appropriate practice for
emulating the natural disturbance regimes. In Canada, this has
become the subject of heated debated according to the emerging
concepts of ecosystem-based management (Brassard and Chen,
2006). Selective-cutting is in part substituting the traditional
practices to reduce disturbances and more closely simulate the
natural processes occurring in boreal environments. These new
practices attempt to artificially maintain or recreate multilayered uneven-aged structures in stands whose growth
potentials have to be correctly evaluated (Bergeron et al.,
2002). If effective management decisions are going to be made
for exploiting the high-latitude forests, studies on the real
growth rates in both even- and uneven-aged stands must be
undertaken.
Acknowledgements
This work was funded by Consortium de Recherche sur la Forêt
Boréale Commerciale, Fonds de Recherche sur la Nature et les
Technologies du Québec and Conseil de Recherches en Sciences
Naturelles et en Génie du Canada. The authors thank J.-G. Girard, V.
Levasseur, P. Tremblay and M. Matboueriahi for technical support,
R. Pilli for his helpful suggestions on the manuscript and A. Garside
for checking the English text.
References
Assmann, E., 1970. The Principles of Forest Yield Study. Pergamon Press, Oxford, UK.
Bergeron, Y., 2004. Is regulated even-aged management the right strategy for the
Canadian boreal forest? Forestry Chronicle 80, 458–462.
Bergeron, Y., Harvey, B., 1997. Basing silviculture on natural ecosystem dynamics:
an approach applied to the southern boreal mixedwood forest of Quebec. Forest
Ecology and Management 92, 235–242.
Bergeron, Y., Leduc, A., Harvey, B.D., Gauthier, S., 2002. Natural fire regime: a guide
for sustainable management of the Canadian boreal forest. Silva Fennica 36,
81–95.
Bouchard, M., Pothier, D., Gauthier, S., 2008. Fire return intervals and tree species
succession in the North Shore region of eastern Quebec. Canadian Journal of
Forest Research 38, 1621–1633.
Boucher, D., De Grandpré, L., Gauthier, S., 2003. Dévelopment d’un outil de classification de la structure des peuplements et comparaison de deux territoires de
la pessière à mousses du Québec. Forestry Chronicle 79, 318–328.
Brassard, B.W., Chen, H.Y.H., 2006. Stand structural dynamics of North American
boreal forests. Critical Reviews in Plant Sciences 25, 115–137.
Carmean, W.H., 1972. Site index curves for upland oaks in the Central States. Forest
Science 18, 109–120.
Charron, I., Greene, D.F., 2002. Post-wildfire seedbeds and tree establishment in the
southern mixedwood boreal forest. Canadian Journal of Forest Research 32,
1607–1615.
Claveau, Y., Messier, C., Comeau, P.G., Coates, K.D., 2002. Growth and crown
morphological responses of boreal conifer seedlings and saplings with contrasting shade tolerance to a gradient of light and height. Canadian Journal of
Forest Research 32, 458–468.
Cogbill, C.V., 1985. Dynamics of the boreal forests of the Laurentian Highlands,
Canada. Canadian Journal of Forest Research 15, 252–261.
De Grandpré, L., Morissette, J., Gauthier, S., 2000. Long-term post-fire change in
the northeastern boreal forest of Quebec. Journal of Vegetation Science 11,
791–800.
Dyer, M.E., Bailey, R.L., 1987. A test of six methods for estimating true heights from
stem analysis data. Forest Science 33, 3–13.
Garet, J., Pothier, D., Bouchard, M., 2009. Predicting the long-term yield trajectory of
black spruce stands using time since fire. Forest Ecology and Management 257,
2189–2197.
Groot, A., Gauthier, S., Bergeron, Y., 2004. Stand dynamics modelling approaches for
multicohort management of Eastern Canadian boreal forests. Silva Fennica 38,
437–448.
Harper, K.A., Bergeron, Y., Drapeau, P., Gauthier, S., De Grandpré, L., 2006.
Changes in spatial pattern of trees and snags during structural development
in Picea mariana boreal forests. Journal of Vegetation Science 17, 535–546.
Harper, K.A., Bergeron, Y., Gauthier, S., Drapeau, P., 2002. Post-fire development of
canopy structure and composition in black spruce forests of Abitibi, Québec: a
landscape scale study. Silva Fennica 36, 249–263.
Harper, K.A., Broudreault, C., De Grandpré, L., Drapeau, P., Gauthier, S., Bergeron, Y.,
2003. Structure, composition, and diversity of old-growth black spruce boreal
forest of the Clay Belt region in Quebec and Ontario. Environmental Reviews 11,
S79–S98.
Harvey, B.D., Leduc, A., Gauthier, S., Bergeron, Y., 2002. Stand-landscape integration
in natural disturbance-based management of the southern boreal forest. Forest
Ecology and Management 155, 369–385.
Hett, J.M., Loucks, O.L., 1976. Age structure models of balsam fir and eastern
hemlock. Journal of Ecology 64, 1029–1044.
Holmes, R.L., 1983. Computer-assisted quality control in tree-ring dating measurement. Tree-Ring Bulletin 43, 69–78.
Johnson, E.A., 1992. Fire and Vegetation Dynamics: Studies from the North American Boreal Forest. Cambridge University Press, UK.
Kneeshaw, D., Gauthier, S., 2003. Old growth in the boreal forest: a dynamic
perspective at the stand and landscape level. Environmental Reviews 11,
S99–S114.
Krause, C., Morin, H., 2005. Adventive-root development in mature black spruce and
balsam fir in the boreal forests of Quebec, Canada. Canadian Journal of Forest
Research 35, 2642–2654.
Kuuluvainen, T., 1994. Gap disturbance, ground microtopography, and the regeneration dynamics of boreal coniferous forests in Finland: a review. Annales
Zoologici Fennici 31, 35–51.
Kuuluvainen, T., Syrjänen, K., Kalliola, R., 1998. Structure of a pristine Picea abies
forest in northeastern Europe. Journal of Vegetation Science 9, 563–574.
Lanner, R.M., 1985. On the insensitivity of height growth to spacing. Forest Ecology
and Management 13, 143–148.
Lieffers, V.J., 1986. Stand structure, variability in growth and intraspecific competition in a peatland stand of black spruce Picea mariana. Holarctic Ecology 9,
58–64.
Lilja, S., Wallenius, T., Kuuluvainen, T., 2006. Structure and development of
old Picea abies forests in northern boreal Fennoscandia. Ecoscience 13,
181–192.
Liu, Q.-H., Hytteborn, H., 1991. Gap structure, disturbance and regeneration in a
primeval Picea abies forest. Journal of Vegetation Science 2, 391–402.
Lussier, J.-M., Morin, H., Gagnon, R., 2002. Mortality in black spruce stands of fire or
clear-cut origin. Canadian Journal of Forest Research 32, 539–547.
McCarthy, J., 2001. Gap dynamics of forest trees: a review with particular attention
to boreal forests. Environmental Reviews 9, 1–59.
Messier, C., Doucet, R., Ruel, J.-C., Claveau, Y., Kelly, C., Lechowicz, M.J., 1999.
Functional ecology of advance regeneration in relation to light in boreal forests.
Canadian Journal of Forest Research 29, 812–823.
Ministère des Ressources Naturelles, 2000. La limite nordique des forêts attribuables. Rapport final du comité Gouvernement du Québec.
Morin, H., Gagnon, R., 1992. Comparative growth and yield of layer- and seed-origin
black spruce (Picea mariana) stands in Quebec. Canadian Journal of Forest
Research 22, 465–473.
Paquin, R., Doucet, R., 1992. Croissance en hauteur à long terme de la régénération
préétablie dans des pessières noires boréales régénérées par marcottage, au
Québec. Canadian Journal of Forest Research 22, 613–621.
Pardé, J., Bouchon, J., 1988. Dendrométrie. ENGREF, Nancy, France.
S. Rossi et al. / Forest Ecology and Management 258 (2009) 2153–2161
Perron, J.-Y., 2003. Tarif de cubage général: volume marchand brut. Direction
des inventaires forestiers, Ministère des Ressources naturelles, de la Faune
et des Parcs, Québec, Canada.
Pham, A.T., De Grandpré, L., Gauthier, S., Bergeron, Y., 2004. Gap dynamics and
replacement patterns in gaps of the northeastern boreal forest of Quebec.
Canadian Journal of Forest Research 34, 353–364.
Pothier, D., Raulier, F., Riopel, M., 2004. Ageing and decline of trembling aspen
stands in Quebec. Canadian Journal of Forest Research 34, 1251–1258.
Pothier, D., Savard, F., 1998. Actualisation des tables de production pour les
principales espèces forestières du Québec. Ministère des Ressources Naturelles,
Direction de la Recherche Forestière, Québec.
Rayner, M.E., 1992. Evaluation of six site classifications for modelling timber yield of
regrowth karri (Eucalyptus diversicolor F. Muell.). Forest Ecology and Management 54, 315–336.
Robitaille, A., Saucier, J.-P., 1998. Paysages régionaux du Québec méridional. Les
Publications du Québec, Québec.
Rossi, S., Tremblay, M.-J., Morin, H., Levasseur, V., in press. Stand structure and
dynamics of Picea mariana on the northern border of the natural closed boreal
forest in Quebec, Canada. Canadian Journal of Forest Research.
SAS, 2003. SAS System Version 9.1.3. SAS Institute Inc, Cary, NC.
Smith, V.G., Watts, M., James, D.F., 1987. Mechanical stability of black spruce in the
clay belt region of northern Ontario. Canadian Journal of Forest Research 17,
1080–1091.
2161
Steijlen, I., Zackrisson, O., 1987. Long-term regeneration dynamics and successional
trends in a northern Swedish coniferous forest stand. Canadian Journal of
Botany 65, 839–848.
St-Pierre, H., Gagnon, R., 1992. Régénération après feu de l’épinette noire (Picea
mariana) et du pin gris (Pinus banksiana) dans la forêt boréale, Québec. Canadian
Journal of Forest Research 22, 474–481.
Takahashi, K., 1996. Plastic response of crown architecture to crowding in
understorey trees of two co-dominating conifers. Annals of Botany 77,
159–164.
Van Laar, A., Akça, A., 2007. Forest Mensuration. Springer, Dordrecht, The Netherlands.
Vanclay, J.K., 1992. Assessing site productivity in tropical moist forests. Forest
Ecology and Management 54, 257–287.
Viereck, L.A., 1983. The effects of fire in black spruce ecosystems of Alaska
and Northern Canada. In: Wein, R.W., MacLean, D.A. (Eds.), The Role
of Fire in Northern Circumpolar Ecosystems. John Wiley & Sons Ltd,
New York.
Viereck, L.A., Johnson, W.F., 1990. Picea mariana (Mill.) B.S.P., black spruce. In: Burns,
R.M., Honkala, B.H. (Eds.), Silvics of North America. U.S. Department of Agriculture, Forest Service, Washington, DC, p. 675.
Zackrisson, O., Nilsson, M., Steijlen, I., Hörnberg, G., 1995. Regeneration pulses and
climate–vegetation interactions in nonpyrogenic boreal Scots pine stands.
Journal of Ecology 83, 469–483.