Pores;;rlogy
Management
Forest Ecology and Management 102 (1998) 61-74
Forest succession over a 20-year period following clearcutting in
balsam fir-yellow birch ecosystems of eastern Quhbec, Canada
Louis Archambault
Namral
Resources
Canada,
Canadian
* , Jacques Morissette, Michhle Bernier-Cardou
Forest
Sercbice. Laurentian
Forestry Centre,
Quebec, Canada GIV 4C7
P.O. Box 3800, 1055 du PEPS, Sainte-Fey,
Received 19 December 1996; accepted 8 April 1997
Abstract
Vegetation development over a ZO-year period following clearcutting in balsam fir ( Abies balsumeu (L.) Mill.)-yeliow
birch (&r&z nZl&aniensis
B&t.) ecosystems was examined in a study area located in eastern QuCbec, Canada. Vegetation,
physiographic and soil data were collected in 10 mature ecosystems and in 30 ecosystems harvested 5 years ago (lo), 10
years ago (lo), or 20 years ago (10). The 40 ecosystems had similar physiographic and soil characteristics. They were
typically located on mesic sites situated on ground moraines thicker than 50 cm. Following harvesting, sites were invaded by
competing species. Mountain maple ( Acer spicatum Lamb.) was the most important competing species. Twenty years after
logging, it fully occupied the sites with 7040 stems ha-’ (diameter at breast height 2 1 cm). Its regeneration stocking
reached 88% with a density of 22775 stems ha- ‘. Wild red raspberry (Rubus idaeus L. var. srrigosus(Michx.)) and
fireweed (Epilobium
angustifofium L.) were abundant during a IO-year period after logging, but disappeared almost
completely afterwards. The abundance of competing species has considerably reduced site production for a period of 20
years and will probably continue to do so for 20 to 30 more years. The proportion of commercial deciduous species
increased from 36% of the total number of stems (diameter at breast height 2 1 cm) in mature stands to 89% in stands
harvested 20 years ago. Balsam fir and white spruce ( Picea glauca (Moench) Voss) advanced regeneration was considerably
reduced. Stocking of these species went down from 76% in mature stands to only 27% in 20-year-old stands. As a result, it
is unlikely that the harvested areas will naturally evolve toward the original climax balsam fir-yellow birch Forest type in the
foreseeable future. 0 1998 Elsevier Science B.V.
Kevword.~:
Competing vegetation; Man-made perturbation; Mountain maple
1. Introduction
The mixedwood ecozone extends over 86 500 km*
in the province of QuCbec, Canada (Minis&e des
Ressourcesnaturelles du Qubbec, 1994a).The boreal
mixedwood forest types present in this ecozone con* Corresponding author. Tel.: (418) 648-7230; Fax: (418) 648.
5849; E-mail: [email protected].
stitute a major source of fiber for the industry and
provide habitat for numerouswildlife species.However, little is known about the structure, composition,
processesand dynamics of these ecosystems(Conse3 de la recherche foresti&re du Quebec, 1995).
More specifically, the balsam fir (Abies b&mm
CL.1 A&)-yellow
birch (Bet&a alleghaniensis
Britt.) forest type is widely distributed in Q&XC. It
is among the most productive mixedwood forest
0378-1127/98/$19.00 0 1998 Elsevier Science B.V. All rights reserved
P/I SO378-1
127(97)00109-6
types in QuCbec (Ministkre des Ressources naturelles
du QuCbec, 1994b). In eastern Quhbec. it is considered as a forest type in its final stage of evolution
(climax), which is a forest type in equilibrium, with
its environment that can perpetuate itself without
major changes in its species composition. unless it is
affected by major disturbances (Saucier. 1989).
Until recently, clearcutting was a common logging practice in QuCbec. This harvesting method is
generally not suitable for the balsam fir-yellow
birch
forest type due to the invasion of the site by competing vegetation (Ministgre des Ressources naturelles
du QuCbec, 1994b). Mountain maple ( Acer .~picatum
Lamb.), wild red raspberry (R&US idcre~ts
L. var.
strigosus
Michx.). fireweed ( Epilohium angustifnlium L.). and beaked hazel (C01-914.s
crmuta
Marsh.) are among the most aggressive competing
species(Bell, 1991; Jobidon, 1995). They can occupy a site for many years, reduce advanced regeneration growth, and prevent regeneration of desirable
species.However, very little detailed information is
available on vegetation development after clearcutting in this forest type.
The development of better forestry practices requires knowledge of system responsesto natural and
man-madedisturbancesincluding patterns of succession. Information on the effects of silvicultural treatments on future site conditions, vegetation species
composition. structure and spatial distribution is re-
A
Study
quired to design strategies to achieve sustainable
forest management.The objective of this study is to
determine vegetation development over a 20-year
period after clearcutting in the typical balsam firyellow birch forest type of eastern Quebec~.The
information gathered in this study will serve as a
baselinefor the evaluation of new silvicultural praetices currently being developed in QuCbec to regenerate balsamfir-yellow birch stands.
2. Materials and methods
The study area covers approximately 200 km’
(Fig. 1) and is located in the eastern part 01’ the
province of QuCbec (Canada) in Forest Section L6.
Temiscouata-Restigouche. of the Great Lakes-St.
Lawrence Forest Regions of Rowe ( 1972). The area
also partially correspondsto ecoregions5c and 8a of
the ecoregion classification system used in Q&bec
(Thibault, 1985). Ecoregion 5c belongs to the balsam
fir-yellow birch domain and ecoregion 8a belongs to
the balsam fir-white birch (Bet&
papyr(fera
Marsh.) domain. However, the study area is more
representative of ecoregion 5c than ecoregion 8a.
The topography is moderately rolling with altitudes
ranging from 275 to 575 m. The parent material
area
lf
4-
;-,_
’
\
I
1
I
i
Fig. I. Location
U.S.A.
of the study area.
‘,
New
Brunswick
L. Archambault
et al. / Forest Ecology
originates from calcareous sedimentary rocks, shales,
sandstones, conglomerates and volcanites. The most
common landform features originate from glacial
activity and include ground and end moraines of
various thicknesses and residual material resulting
from rock weathering. Bedrock outcrops are present
but cover small areas. The mean annual temperature
varies between 0°C and 2.5”C and the growth season
extends from 150 days to 160 days. The total precipitation is relatively low, ranging from 900 mm to
1100 mm (Saucier and Robitaille, 1995).
2.2. Sampling design
Since no permanent sample plots were available,
vegetation development over the 20-year period after
clearcutting was assessed from plots established in
balsam fir-yellow
birch stands harvested at different
times. To minimize the effects of the variability of
permanent site characteristics on vegetation development, the study was conducted on a relatively small
area (200 km’) in ecosystems with similar physiographic (landform, percent slope and topographic
position) and soil characteristics. Our approach to
studying successional patterns is similar to the approach used by Brisson et al. (1988), Crowell and
Freedman (1994), and MacLean and Wein (1977).
Stand selection was carried out by scanning forest
cover type maps and aerial photographs produced in
1975, 1985 and 1993 by the Minis&e des Ressources
naturelles du Quebec. Potential mixedwood stands
were visited in 1994. Preharvest stand composition
was confirmed in the field by the presence of leftover balsam fir, white spruce (Picea glauca
(Moench) Voss), and white and yellow birch trees
and stumps. Sampling was conducted in 1995. A
total of 40 stands was selected: 10 harvested approximately 5 years ago (1990-19911, 10 harvested 10
years ago (1986-1987)
and 10 harvested 20 years
ago (1974-1977).
The 10 remaining stands were
mature stands that served as controls and were used
to evaluate the preharvest species composition. Harvesting was carried out by conventional clearcutting
(full-tree extraction).
Vegetation, physiographic and soil data were collected according to the procedure used in Quebec for
ecosystem classification (Minis&e
des Ressources
naturelles du Quebec, 1994~). A circular plot (0.04
and Management
102 (1998)
61-74
63
ha) was established on a transect located at random
in each ecosystem. The location of the transect in the
stand and the situation of the plot on the transect
were determined using a table of random numbers.
All living stems of diameter at breast height (DBH)
between 1 and 9 cm were recorded in a circular
subplot of 0.004 ha, whereas stems of larger DBH
were recorded in the entire plot. The percent coverage of all species was visually estimated using the
following scale: 81-lOO%, 61-80%, 41-60%, 2640%, 6-25%, l-5%, and + (one individual). In the
mature stands, height and DBH of three dominant or
codominant trees were measured. These trees were
bored 1 m aboveground for age determination. Three
dominant or codominant mountain maple trees were
selected for stem analyses. Disks were taken at
stump height, at 1.3 m and then every meter along
the stem.
Regeneration data were collected in 10 regeneration subplots (0.0004 ha) located 15 m apart on a
transect on which the 0.04 ha plot was located. The
transect was oriented perpendicular to the slope. The
first two regeneration plots were located in the 0.04ha plot, 7.5 m away from its center. All living tree
species between 5 cm and 7 m high were recorded
using the following classes: 5-30 cm, 30 cm-lm,
l-4 m and 4-7 m. The height of the tallest individual of each tree species was measured. The maximum height of the herb and shrub species considered
as important competitive species was recorded. The
proportion of seedbed types (micro-environment)
of
each regeneration plot was estimated visually (10%
classes).
Soil pits were excavated and complete soil descriptions were made in 10 randomly selected
ecosystems. Each of the six superficial deposit categories recorded on the ecological maps available for
the study area were sampled for soil description. Soil
samples from each horizon were collected for laboratory analyses. In addition, a soil sample of the humus
horizon and the C horizon were collected in the
remaining 30 stands for laboratory analyses. The pH,
organic content and nitrogen concentration were determined for each organic horizon. The proportion of
sand, silt and clay, pH, organic matter content, and
concentrations of potassium, calcium. sodium, magnesium, iron and aluminum were evaluated for each
mineral horizon. Soil physical and chemical analyses
64
procedures
(1978).
L. Archambault
are described
et al. /Forest
Ecology
in detail in McKeague
2.3. Statistical analyses
Analyses of variance were conducted to detect
changes in vegetation composition and structure following harvesting. The experimental design had four
ages (mature, 5, 10, and 20 years since harvest) and
10 plots per age class. The analyses of coverage,
number of species, DBH, basal area, density, and
regeneration density and stocking were based on a
single factor model where the effects of the number
of years following harvesting were considered fixed.
The model for the analyses of data from stem analyses of mountain maple, height of regeneration, and
seedbed types (micro-environment)
included one additional random effect, that of trees within the 0.04-ha
plots or the effect of regeneration subplots. These
latter linear models were considered mixed models
(Milliken and Johnson, 1984, Chap. 21). Whenever
possible, the random part of the model was reduced.
The validity of the assumptions on which the
analyses are based was evaluated from plots of the
residuals before model reduction. If necessary, variables were transformed to stabilize the residual variance and, whenever possible, the same transformation was used for similar analyses. For example.
mean DBH of stems larger than 10 cm required a
transformation; the same transformation was used for
all species even though it may not have been the best
transformation
for a particular species. The best
transformation was determined using the empirical
method (Montgomery, 1991, p. 104). The coverage
percentages were not transformed. The stocking of
regeneration was analyzed using the logistic transform of the number of regeneration subplots where
each species was present among 10 subplots (Cox,
1970). The logarithmic transform was satisfactory
for the other variables. Means and their approximate
confidence limits (95%) were computed on the logarithmic or logistic scale and then back-transformed.
When the logarithmic transform was used, data were
back-transformed
using the method proposed by
VCgiard and Ung (1993) to reduce the bias introduced by the transformation. To avoid inconsistencies between species or stratum specific densities or
basal area and totals for these variables, their arith-
and Mana,qment
102 C1998161-
74
metic means rather than their back-transformed ones
are presented in the tables and figures.
For each variable, four statistical tests were conducted. First, the general hypothesis of equality of
means between the four age groups of the model
(mature, 5, 10, and 20 years since harvest) was
tested. The second tested the hypothesis that the
slope of the best fitting straight line for the regression of the mean response (on the transformed scale
if applicable) over age since harvest was zero, excluding control stands. The third tested the lack of fit
to the straight line; algebraically, it is the quadratic
component of the regression of the mean response on
age, for ages 5. 10 and 20 years. The last contrast
compared the mean (transformed) response in the
mature stands with that observed 20 years after
harvest. When data were not available for a given
age group, for example when a species was absent
from all plots harvested, say. 5 years ago. appropriate contrasts were constructed to compare means that
were available. All tests were conducted with a
probability of Type 1 error of cz = 5%. To maintain
an overall significance level of S%, individual tests
of the non-fully orthogonal contrasts were conducted
at a reduced level of significance equal to the overall
level (5%) divided by the number of contrasts t a f
3 = 0.0167%) (Rosenthal and Rosnow, 1985). Statistical analyses were done using SAS software.
3. Results
3. I. Site characteristics
The site characteristics of the ecosystems considered for the study correspond to the typical balsam
fir-yellow
birch forest type of eastern Quebec
(Saucier, 1989). This forest type is generally found
in midslope position, on mesic sites situated on
ground moraines of variable thickness. The key
physiographic and soil characteristics of the selected
ecosystems were similar (Table 1). All the ecosystems were located on ground moraines generally
thicker than 50 cm. The landscape was gentty to
moderately rolling, and slopes averaged 12% (range
0% to 40%). The majority of the ecosystems (351
were situated in midslope position on terrains with
variable aspects. The other ecosystems were on flat
L. Archambault
Table 1
Summary
of physiographic
Physiographic
and soil variables
and soil characteristics
et al. / Forest Ecology
(mean f SE.)
Number
Mature
Elevation (ml
Topographic
position”
Slope (%I
Length of backslope
Humus type’
and Management
102 (1998)
61-74
65
of the 40 ecosystems
of years since harvesting
(n = 101
363 k 14
5(n=
10)
514+ 11
M%o,
14 * 2
143 f 16
USm-MS;,
14+3
148 f 15
HF%-HM,,
j
H~m-~u
1
10 (n = 10)
20 (n = 10)
439 $- 29
FCI ,-RS,, ,-MS,,,
9i2
120+21
401+
Hl++,O,
Hf%O,
h3,+2,
L~6,-sL,,,-s1L(2,
MY,,,
SICL, I,
Mho,
15
b,-‘?I,-MS(s,
12+3
120 * 21
Fw2,
Texture
(C horizot#
Drainage’
Lo,-SIL,,
MY
,-q3,
I 01
L(7)--SIL,,
%z,
Mw,lO,
I
“F. flat area; MS, midslope; RS, rounded summit: US, upper slope.
bNumbers in parentheses are frequencies.
‘FHM,
fibri-humimor;
FM, librimor:
HFM, humi-fibrimor:
HM. humimor.
“L, loam: SIL, silty loam; SICL, silty clay loam; SL, sandy loam.
‘MW. moderately
well drained.
areas, rounded summits and upper slopes. All soils
were moderately well drained. The most frequent
humus layer type (36) was humi-fibrimor. The other
types were fibri-humimor,
humimor and fibrimor.
The mean thickness of the humus layer averaged 6
cm, ranging from 2 to 24 cm. The soil texture of the
C horizon of 31 ecosystems was medium: loam (27)
and silty loam (4). Eight ecosystems were on
coarse-textured soils (sandy loam) and one ecosystem was located on a fine-textured soil (silty clay
loam). The mean gravel content of the C horizon was
relatively high (50%), ranging from 27 to 67%.
According to the results of the chemical analyses
performed on soil samples collected in 10 soil pits
(Table 21, all soils belonged to the podzolic order:
nine could be classified as humo-ferric podzols and
one as ferro-humic podzol.
3.2. Stand characteristics
and species composition
Ten mature balsam fir-yellow
birch stands were
considered to evaluate the preharvest species composition. Only two accessible stands that were never
harvested could be sampled. The other eight stands
were partially cut approximately 45 years ago. However, logging was generally carried out in the wintertime and horses were used to skid logs. This harvesting method considerably reduces damage to advanced regeneration and does not significantly affect
the natural forest succession. Therefore, it can be
assumed that the current species composition is representative of a balsam fir-yellow
birch ecosystem
type that has not been affected by man-made disturbances. In the mature stands, balsam fir was the most
important overstory species, representing 54% of the
total basal area (Table 3). White spruce, yellow birch
and white birch were the other major overstory
species that together accounted for 38% of the total
basal area. White birch density (DBH: l-9 cm)
decreased (P = 0.0149) after logging from 2375
stems ha-’ in the lo-year-old stands (not shown) to
875 stems ha-’ in the 20-year-old stands. Mountain
maple was the most important understory species in
the mature stands and the stands harvested 20 years
ago. Its density (DBH: l-9 cm) increased (P =
0.0005) after logging from 575 stems ha-’ in the
5-year-old stands (not shown) to 7025 stems ha-’ in
the 20-year-old stands. The mean age of the dominant and codominant balsam fir, white spruce, yellow birch and sugar maple ( Acer saccharum Marsh.)
trees sampled in the mature stands was 59, 100, 45,
and 86 years, respectively, and these were 16.7 m,
17.8 m, 16.3, and 15.0 m high, respectively.
The total number of species was 60, 53, 52, and
57 in the mature stands and the stands harvested 5,
10, and 20 years ago. The mean number of species
identified in the 0.04-ha plot was not significantly
different (P = 0.0740) between ages, ranging from
26.6 to 31.7. However, the percent coverage of the
most important competitive species varied over time
66
L. Archambault
Table 3
Selected stand characteristics
Species
et al./ Forest Ecology
(mean)
of mature
DBH:lO
(cm)
cm +”
Matureb
and Management
stands and stands harvested
20
species
13.7
17.2
16.2
21.1
13.7
15.0
10.8
-
Density: 10 cm +
(stem ha- ‘)
Basal area: 10 cm +
(m’ ha-‘)
Mature
Mature
20
Mature
20
-
50
125
475
75
875
25
25
-
470
25
60
85
140
128
3
50
18
25
45
58
27
25
-
15.8
0.7
1.2
2.8
2.7
5.8
0.1
1.0
0.4
0.6
2.3
0.8
0.6
0.3
-
2725
50
25
7025
50
300
3
10
15
-
0.0
0.2
0.1
-
20
Acer spicatum
Acer pens?;luanicum
Conlus cornuta
Understory
10.0
14.4
-
Salh
Sambucus pubens
Sorbus americano
15.0
14.0
-
-
-
All species
19.7
15.31
3100
9100
175
25
75
25
25
50
-
3
5
927
30
-.-*..
A
ln
,lTl+
4-7m
t-4m
CORVLUS
CORNUTA
10
A
A
A
0
:
i
Mature
of years
Fig. 2. Changes in percentage cover
important competitive
species.
266
0.1
0.4
-
29.4
6.5
30
1
A
..
,y..
g: ..*,.....
5
10
-...-*
15
x)
EPILOBIUM
ANGUSTIFOLIUY
the harvest in the 4-7 m stratum. It was also higher
(P = 0.0002) in the 20-year-old stands(58%) than in
the mature stands(24%). Following a slight increase
from 47% to 55% between 5 and 10 years, the
coverage of this speciesin the l-4 m stratum decreased(P = 0.0092) to 27%, 20 years after logging.
The coverage of beaked hazel remained relatively
low (< 10%) in all strata and did not vary over time
(0.1822 I P s 0.6793). It was not different from that
of the mature stands (0.1178 I P 5 0.9028). The
coverage of wild red raspberry in the 0.5-l m
stratum decreased(P = 0.0001) over time from 60%,
5 years after harvest, to 2%, 20 years after logging.
The coverage of fireweed in the same stratum decreasedover time, but this trend was not significant
(P = 0.0365). Five years after logging, the percent
coverage of fireweed was 21% in the 0.5- 1 m
stratum. Wild red raspbeny and fireweed were virtually absent from the mature stands and the stands
harvested 20 years ago.
3.3. Regeneration
Number
-
-
20 years ago: M = 10.
(Fig. 2). The percent coverage of mountain maple
increased (P = 0.0001) substantially with time since
RUBUS IDAEUS
67
Density: l-9 cm
(stem ha- ’ )
Abirs balsamea
Acer rubrum
Acer saccharum
Bet&a allrghaniensis
Be&la papwifera
Picea glauca
Prunus penqkanica
Thqa occidentalis
“DBH: diameter at breast height.
bMature stands: n = 10, stands harvested
61-74
20 years ago
Overstory
20.8
17.9
18.4
22.3
16.5
23.8
25.0
species
10.7
-
102 (1998)
since
behavior
harvesting
after harvesting
for the most
The total stocking (5 cm-7 ml and the stocking
of the 5-30 cm height class of balsamfir regenera-
68
L. Archambault
rf al. /Forest
Ecology
and Management
tion were much lower (P = 0.0003. 0.0001) in the
20-year-old stands as compared with the mature
stands (Fig. 3). In the l-7 m height class, balsam fir
stocking increased between 5 and 10 years after
harvest and then decreased until 20 years after harvest (P = 0.0167). The total stocking of white birch,
a shade intolerant species, decreased (P = 0.0027)
over time following logging. The stocking of white
birch in the l-7 m height class increased between 5
and 10 years after harvest and then decreased until
20 years after harvest (P = 0.0004). The stocking of
white spruce, yellow birch and sugar maple was
relatively low, did not vary over time and was not
different from that of the mature stands (0.0348 5 P
I 0.8279). However, there was a tendency for sugar
maple, a shade tolerant species, stocking to increase
over time and for yellow birch, an intermediate in
shade tolerance species, to decrease over time. The
total stocking of mountain maple always remained
very high (over 74%). It did not vary over time
(P = 0.4858) and was not different from the mature
stand stocking (P = 0.3 135). Mountain maple stocking in the 5-30 cm and the 30 cm-lm height classes
ABdES
SUBAMEA
90
70
v
60
50
.
v . .. .
40
.
I------a
.._.__
A
* \
“t
MabJm
5
M
,o
50
40
30
SUJ
eo-
10
50
70
so
v
30
20
10
0
15
70.
60.
PKXAQLAlKX
BEWA
MLEGMNlENSlS
50
40
-7.
L._,
30
‘;:
b
~~
.-F
5-3ocm
soan-lrn
l-7m
Tow
hl- 74
decreased between 5 and 10 years after logging and
then increased until 20 years after harvest (P =
0.0106, 0.0112).
The total density and the density of the 5-30 cm
height class of balsam fir regeneration (Fig. -t) was
much lower (P = 0.0009, 0.0001) in the 30-year-old
stands as compared with the mature stands. Balsam
fir density in the l-7 m height class increased
between 5 and 10 years after logging and then
decreased until 20 years after harvest (P = 0.0099).
All densities of white spruce were low and its total
density was lower in the 20-year-old stands than in
the mature stands (P = 0.0118). Yellow birch densities (5-30 cm, 30 cm-lm, total) tended to decrease
after logging. but these trends were not significant
(0.0296 < P i 0.1685). White birch density in the
l-7 m height class increased between 5 and 10 years
after logging and then decreased until 20 years after
harvest ( P = 0.0002). Although not significant (P =
0.0179). the same trend was observed for the total
density of this species. Densities of sugzu maple
tended to increase over time but no statistical tests
could be performed. The total density of mountain
Bo
.. . ..
A
.v.
El
Bo
102 (19%)
20
:sQ;,;::::::-*
.
1
I
Mature
5
10
15
20
.-I.,
20o
10
I
L
i.:::;
. . . . ,J.*
-...._,.
1
Malure
5
10
15
2-J
Number
Fig. 3. Changes
in stocking
of regeneration
of years
after harvesting
since
harvesting
for the most important
commercial
species and Acer spcutum.
L. Archambault
et al. / Forest Ecology
maple was high in all ecosystems ranging from
21525 to 33 150 stems ha-‘. It did not vary over
time (P = 0.2829) and was not different in the 20year-old stands as compared with the mature stands
(P = 0.8022). The mountain maple density in the
5-30 cm and the 30 cm-lm height classes decreased
between 5 and 10 years and then increased until 20
years after harvest (P = 0.0072, 0.0001).
The mean and maximum heights of balsam fir
(Fig. 5) increased between 5 and 10 years after
harvest and then decreased slightly until 20 years
(P = 0.0090, 0.0013). The mean height of balsam fir
was higher in the 20-year-old stands as compared
with the mature stands (P = 0.0036). The mean and
maximum heights of the two birch species increased
over time and were higher in the 20-year-old stands
than in the mature stands (0.0001 I P I 0.0004).
The mean and maximum heights of sugar maple and
mountain maple were higher in the 20-year-old stands
than in the mature stands (0.0001 < P I 0.0083).
The maximum height of mountain maple increased
over time (P = O.OOOl), whereas its mean height
.
AMES
BACSAMEA
-0.-
Nan-tm
and Management
102 (1998)
69
61-74
increased from 5 to 10 years and then slightly decreased until 20 years after harvest (P = 0.0018).
The maximum height of the other two major
competing species (not shown), wild red raspberry
and fireweed, increased between 5 and 10 years and
then decreased until 20 years (P = 0.0020, 0.0001).
Wild red raspberry increased from 0.88 m to 0.95 m
between 5 and 10 years after harvest and then decreased to 0.46 m 20 years after logging. For fireweed, these heights were 1.l 1, 1.34 and 0.79 m,
respectively.
Seedbed types changed over time. The percentage
of seedbed made of dead wood and mixed litter
(leaves and needles) decreased over time (P =
0.0001, 0.0001). The percentage of dead wood decreased from 28.4% to 12.4% and the percentage of
the mixed litter went down from 66.2% to 16.8%
between 5 and 20 years after harvest. The percentage
of seedbed made of leaf litter increased from 23.7%
to 62.3% between 10 and 20 years after logging
(P = 0.0001). clearly indicating an invasion of the
site by deciduous species. The percentage of mixed
Ii
PICEAGLAUCA
SEWA
ALLEGHNIEMSIS
Number of years since harvesting
Fig. 4. Changes
in density of regeneration
after harvesting
for the most important
commercial
species and Acer spicatum.
70
..BETULA
ALLEWANIENSIS
.T
,:,*
65.
ACER
SPfCATUM
4.
3.
.
,.a.‘.
2
.
‘-
.
----9
Number of years since harvesting
Fig
5. Changes
in mean and maximum
height
of regeneration
after
harvesting
for the most important
commercial
species and
Acrr
Apicatum.
litter was higher (P = 0.0001) in the mature stands
(70.1%) than in the 20-year-old stands(16.8%). The
proportion of rotten wood was also higher (P =
0.0052) in the mature stands (12.8%) as compared
with the 20-year-old stands(5.6%).
3.4. Mountain maple charucteristics
The results obtained from stem analyses conducted on dominant or codominant mountain maple
trees showed that this speciesestablisheswell following harvesting. The mean age of the trees corresponds to the period of time elapsed since harvest
(Table 4). The oldest trees were found in mature
stands,which shows that this speciescan also establish and survive in ecosystemsrelatively undisturbed
by man. The oldest individual was found in a mature
stand. It was 53 years old, measured5.6 m and had a
diameter at stump height of 5 cm. Growth of mountain maple was vigorous, height and diameters(stump
Table 4
Acrr
spicutum
tree characteristics
Characteristic
Age (stump height)
Age (breast height)
Height (m)
DSH (crnlb
DBH (cm)’
(mean)
Number
--
of years since harvesting
Mature
5”
10
20
28.9f25.7-32.6)
25.1 (21.4-29.4)
6.5 (6.0-7.2)
6.5 (5.8-7.3)
5.2 (4.5-6.1)
3.7 (3.4-4.3)
1.7 (1.4-2.0)
9.ats.o-IO.11
6.5 (5.5-7.6)
2.8 ~2.5-3.0)
3.112.8-3.5)
1.8 (1.5-2.1)
21.1 (1X.8-23.81
18.2 (15.6-21.3)
“In each group the number of observations
varied between
‘DSH, diameter at stump height.
’ DBH, diameter at breast height.
Numbers in wrentheses
are 95% confidence limits.
1.8 (1.6-2.0)
1.8 (1.6-2.0)
0.6 (0.5-0.7)
28 and 30.
5.9 (5.4~6.fJ
7.4 (6.S8.3)
5.5 (4.7-6.43
-_-
L. Archambault
et al./Forest
Ecology
height and breast height) increased significantly after
harvesting (P = 0.0001). Twenty years after harvesting, mountain maple height and diameters were comparable to those observed in the mature stands
(0.1287 I P I 0.6652).
4. Discussion
4. I. Species composition
Clearcut logging caused major changes to the
species composition of harvested balsam fir-yellow
birch ecosystems as compared with their pre-harvest
species composition. In mature stands, balsam fir,
white spruce, yellow birch and white birch represented 92% of the total basal area and 25% of the
total number of stems. The comparison with the
basal area 20 years after harvest cannot be made
because stands were too young, but these species
then accounted for only 13% of the total number of
stems. As observed by Hatcher (1960) Frisque et al.
(1978) and Rue1 (1992) in clearcut coniferous (balsam fir) stands, harvesting was also responsible for
an important increase in the proportion of deciduous
species in boreal mixedwood stands. There has been
a complete shift in the relative proportion of commercial deciduous and coniferous species. In mature
stands, coniferous species (balsam fir, white spruce)
accounted for 64% of the total number of overstory
species stems and commercial deciduous species (red
maple ( Acer rzzbrum L.), sugar maple, yellow birch,
white birch) accounted for 36% of the total number
of overstory species stems. In the 20-year-old stands,
the same coniferous and deciduous species accounted for 8% and 89%, respectively, of the total
number of overstory species stems.
Mountain maple is a common species of boreal
mixedwood ecosystems in eastern Canada (Blouin
and Grandtner, 197 1; Bell, 1991; Jobidon, 1995). It
is a very aggressive species and can cause important
losses of production. It is able to subsist under heavy
canopy suppression and to gain dominance upon
release. Mountain maple suppresses advanced growth
of balsam fir and spruce and its leaf litter prevents
seeding-in by these coniferous species. After harvesting, it can invade cutover areas and completely
occupy a site for periods of 30 to 60 years (Vincent,
and Management
102 (1998)
61-74
71
1965; VallCe et al., 1976; BCdard et al., 1978). The
opening of the canopy following a spruce budworm
(Choristoneuru fumiferuna Clem.) epidemic also favors its propagation (Batzer and Popp, 1985). Mountain maple reproduces mainly by sprouting, but layering and seeding can occur (Post, 1965; Vincent,
1965). In this study, it fully occupied the cutover
areas and became the most important species accounting for more than 75% of the total number of
stems (DBH 2 1 cm) in the 20-year-old stands. Furthermore, its percent coverage was very high, reaching 27% and 58% in the l-4 m and 4-7 m height
classes, respectively. Mountain maple formed a very
dense canopy allowing very little light penetration,
considerably reducing advanced regeneration growth
and preventing establishment of new regeneration.
Twenty years after logging, the abundance of
mountain maple and the low density of the commercial species considerably reduced site production.
Yield tables for mixedwood plantations are not available in Quebec. However, according to yield tables
for softwood
plantations
in southern Quebec
(Bolghari and Bertrand, 1984) the site quality index
(height in meters at 25 years) for white spruce, a
widely planted species, varies between 6 and 12 at
25 years. For example, a 20-year-olid white spruce
plantation on a medium-quality site (site quality
index of 9 m at 25 years) has 3 106 stems ha- ’ As a
comparison, the total density of the commercial
overstory species was only 1849 stems ha- ’ .
The coverage of beaked hazel remained relatively
low during the 20-year period after harvesting and its
impact on establishment and growth of desirable
regeneration was probably reduced. Like Rue1 (1992)
and Winder and Watson (1994) we observed that
wild red raspberry and fireweed were early colonizers and caused severe competition for a limited time.
These two species were only abundant in the first 10
years after logging and then almost completely disappeared from the canopy.
4.2. Regeneration
Logging caused significant damage to advanced
regeneration. Balsam fir and white spruce were particularly affected. The total stocking of balsam fir
was reduced from 69% in the mature stands to 27%
in the 20-year-old stands. Its density went down
12
L. Archamhault
et al. /Forest
Ecology
from 6925 stems ha-’ to 1375 stems ha ’ . The total
density of white spruce was also reduced significantly from 500 stems ha-’ in the mature stands to
100 stems ha-’ in the 20-year-old stands. Stocking
and density of the commercial deciduous species
(red maple, sugar maple, yellow birch, white birch)
were less affected and were comparable in the mature stands and in the stands harvested 20 years ago.
As a result, the proportion of commercial deciduous
species became more important than the proportion
of coniferous species. The total stocking of coniferous species (balsam fir and white spruce) went down
from 76% in mature stands to only 27% in the
20-year-old stands. For the commercial deciduous
species, the stocking increased slightly from 40% in
mature stands to 51% in stands harvested 20 years
ago. Furthermore, the deciduous species completely
overtopped the coniferous species. The maximum
heights of yellow birch, white birch and mountain
maple were 4.8 m, 5.6 m, and 4.3 m, respectively, as
compared with 1.2 m and 0.2 m for balsam fir and
white spruce. respectively.
Mountain maple remained the most important regeneration species with
a total stocking of 88% and a total density of 22775
stems ha- ’ , 20 years after logging.
4.3. Successional trends
The dynamics of boreal ecosystemsis controlled
by cyclic natural and man-madeperturbations (Lortie. 1979; Bergeron and Dubuc, 1989; Attiwill, 1994).
Insect outbreaks, logging and fire are the main factors dictating the successionalpathways of boreal
ecosystems.These factors or combinations of these
factors, at different levels of intensity, affect future
stand composition in ways that are difficult to predict. In this study, logging and spruce budworm
outbreaks were the key successional elements of
disturbance.Over the last 75 years, fire did not affect
the ecosystemsconsideredfor the study.
Clearcut logging greatly disturbed the natural successionof the balsam fir-yellow birch forest type. It
is unlikely that the harvested areas will naturally
evolve toward the original climax forest type in the
foreseeablefuture. Mountain maple will continue to
completely overtop balsamfir and white spruce for a
long time, probably for at least another 20 to 30
years. The proportion of deciduous species in the
and Management
102 (1998)
6/-
74
next mature successional stage will be more important. White birch and sugar maple will become preponderant overstory species, whereas the relative
abundance of balsam fir and white spruce will be
reduced substantially. Yellow birch will persist in the
canopy and its importance should be comparable to
the mature stands.
Spruce budworm plays an important role in the
renewal of boreal forests of northeastern America. It
is the most important insect defoliator of coniferous
forests of eastern Canada and it is responsible for
extensive mortality in balsam fir-white spruce stands
(Blais, 1983: MacLean, 1980). The study area experienced two major spruce budwotm outbreaks between 1940 and 1990 (Hardy et al., 19871. The
ecosystems considered in the study experienced various numbers of years of light to severe annual
defoliation (9-23 years). Total fir and spruce mortality ranged from 0 and 50%. It can. therefore, be
assumedthat the spruce budworm played a role in
the current speciescomposition of the mature stands.
as well as in the preharvest speciescomposition of
the harvested stands. However. since the proportion
of deciduous species increased substantially after
logging and becausethe spruce budworm does not
defoliate deciduousspecies,it is hazardousto predict
its future role in the dynamics of these ecosystems.
Predictions made in this study regarding the
long-term successionaltrends of the harvested stands
should, however, be taken with caution since the
period after cleat-cutting is only 20 years. It is well
known that ecosystemsconstantly change in ways
that are only partially predictable, and that multiple
pathways are possible(Averill et al.. 1995). A large
number of endogenousand exogenous factors that
operate over wide ranges of size, frequency, predictability. timing and magnitude can influence succession (Attiwill, 1994; Cook, 1996), Therefore.
some additional changes may occur that can influence the final outcome in the succession.
These results clearly show that new silvicultural
practices must be designedto insure regeneration of
the original speciesand avoid competition problems
after logging. Shelterwood cutting, with and without
site preparation, and seed-tree cutting with site
preparation are methods currently being tested in
eastern Quebec, but results are not available yet.
However. a major problem with shelterwood cutting
L. Archambault
et al. /Forest
Ecology
is the high susceptibility of balsam fir to windthrow
due to the importance of the red heart root. Logging
with careful attention to advanced regeneration and
soils, which is now mandatory in even-aged forests
on QuCbec public lands (Minis&e
des For&s du
QuCbec, 19921, is another regeneration method that
must be evaluated. This technique is generally efficient in protecting desirable advanced regeneration,
but it may not prove very useful in decreasing
competition problems in balsam fir-yellow
birch
ecosystems due to the ability of mountain maple to
invade harvested areas.
Acknowledgements
The authors would like to thank Dr. Jean-Louis
Btlair for professional advice and field assistance,
and Mr. StCphane Tremblay for help in statistical
analyses. We are also grateful to Mr. Jean-Baptiste
Breton for indispensable assistance in field sampling,
and to Mr. Magella Gauthier and Mr. Ren6 Turcotte
who performed soil analyses.
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