STAND STRUCTURE, SUCCESSION, AND USE OF SOUTHERN
ALBERTA'S ROCKY MOUNTAIN FORESP
ROBERT J. DAY
School of Forestry, Lakehead University, Thunder Bay, Ontario
Abstract. Structural analysis of the subalpine forest in southern Alberta shows that the
old-growth Picea-Abies forest has succeeded even-aged stands of Pinus contorta var. latifolia
Engelm. that became established after fire 150-200 or more years ago. Because P. contorta
regeneration fails beneath its own canopy, an irregular- to uneven-aged understory of Picea
engelmannii Parry X P. glauca (Moench) Voss. and Abies lasiocarpa (Hook) Nutt. becomes
established. As the even-aged P. contorta overstory ages, sporadic death of overmature trees
permits an irregular- to all-aged Picea-Abies forest to emerge and dominate, unless fire re­
initiates the succession to even-aged P. contorta. Extensive and frequent fires in the past,
mainly initiated by "dry" electrical storms, have prevented long-term successional development
and have maintained most of the forest in the early P. contorta-dominated phase of the suc­
cession. Introduction of effective fire protection is now permitting progress toward the late
successional phases. Widespread development of the Picea-Abies phase and the decadent Abies­
Picea phase that follows are forecast. The ecological effects of such fire-protection policies
are questioned. A silvicultural program of fire prescription is suggested for the maintenance of
the fauna and wilderness value of the mountain national parks. Silvicultural alternatives in
harmony with the ecology of the forest are suggested for the implementation of multiple-use
policies in the Rocky Mountain Reserve.
INTRODUCTION
rT-b,.,--,--<r7r--r----rrn-=-=o::=-I
Fire and logging in the late 19th and in the 20th
century (MacMillan 1909) have removed most of
the old-growth2 Picea engelmannii Parry X
NATIONAL PARKS
CANADIAN
./L�L/../.J.
. AMERICAN
.>_>).�,:>..
ROCKY MTN. FOREST
Picea
glauca (Moench) Voss.-Abies lasiocarpa (Hook)
Nutt. forest from the Rocky Mountain Forest Re­
serve in southern Alberta (Fig. 1). Some of the few
old-growth stands that remained in the Crowsnest
Forest were studied to assess their successional ori­
gin, development, and structure. Such a study has
provided a unique ecological record for future man­
agement and silviculture of the Rocky Mountain
Forest Reserve and the adjacent Waterton-Glacier
and Banff National Parks.
and Horton (1956, 1959) agree that this forest (Fig.
1) is mainly composed of even-aged
(5-year age
latifolia
Engelm.3 with a few stands of old-growth Picea­
Abies on sites that have escaped fire for 150-200
range),
fire-initiated
115°
1200
Bloomberg (1950), Cormack (1949, 1953, 1956),
Pinus contorta var.
110°
FIG. 1. Location of the Crowsnest Forest study area.
omitted many trees under 80 years. He found that a
quarter of the old growth was even-aged (40-year
age range),
range),
half was broadly-aged
(l20-year age
and the remainder was all-aged. Neither
years or more. These workers differ in their concept
Bloomberg nor Horton comment on the amazingly
of the structure and successional development of the
strong tendency their data show for development of
old growth. Bloomberg describes the old growth as
irregular-aged Picea-Abies old growth from even­
"part way between even-aged and irregular forest"
aged Pinus as the succession advances.
(lOO-year age range!), mainly because he excluded
In the past, successional development of this forest
trees below 3 inches (7.62 cm) dbh and so omitted
was limited by the pressure of natural fires caused
most trees under 150 years of age. Horton measured
mainly by "dry" electrical storms. In the mid-19th
all trees down to 1 inch (2.54 cm) dbh, but still
century European colonization may have increased
Received February 2, 1970; accepted September 28,
1970.
2 Mature forest with principal dominants at least 150200 years old.
a Future reference to Picea ellgelmannii X P. glauca,
Abies lasiocarpa, and Pinus con/orta may be by generic
name only.
fire incidence and severity (Table 1).
1
Even-aged stands o f P. contorta with trees occa­
sionally able to survive for 300 years (Horton 1956)
are not likely to break up gradually and be succeeded
by irregular- or all-aged Picea-Abies when the risk
of fire is high. For example, with an average of about
FOREST IN SOUTHERN ALBERTA
Late Spring 1972
TABLE 1. Percentage areaa of fire-origin Pinus contorta
473
Random sampling was not feasible because of
limited study time and numerous measurements on
Period
Number
of years
Area of land with
fire-origin stands
(%)
Minimum forest area
burnt per year
each plot. All plots were established subjectively in
(%)
representative stands on two adjacent sites described
Ogilvie (1963):
(1) Picea-Abiesl Heracleum­
Equisetum on the coarse, alluvial, gleysolic soils of the
valley bottom; and (2) Picea-Abiesl Menziesia-Tia­
rella on the weakly podsolic sandy to clay-loam tills
1830--1870
40
12.8
0.32
1871-1890
20
23.3
1.16
1891-1910
20
36.1
1.80
1911-1930
20
4.4
0.22
by
of the moderate slopes adjoining the valley bottom.
aBased upon data from the northern section of the Rocky Mountain
Forest Reserve (Canada Dep. Resources and Development, Forestry
Branch 1931 (Unpubl. MS). Rate of growth survey.) Note that reburn
tends to reduce the percentage burnt per year in each successively older
period.
growth and five in early successional Pinus-Picea;
1.5% of the forest burned per annum, as was the
Crowsnest Forest.
case before 1911 (see Table 1), the "average" stand
would be burnt every 67 years! If protection can
reduce fire risk to less than 0.1% (already 0.46% ),4
the "average" stand will be burned less than once in
1,000 years. Irregular- or all-aged Picea-Abies old
growth should succeed and dominate most of the
sites now occupied by P. contorta.
Differing opinions on the ecological development
of this forest stimulated this work. According to
Bloomberg
(1950) fire initiation and a period of
dominance by P. contorta are essential for develop­
ment of thrifty Picea-Abies forest. He considered that
the Picea-Abies old growth was the final stage in
forest succession and states that "without the re­
vitalizing effects of fire on the soil" the forest will
degrade into "masses of stagnated vegetable growth"
Ten
other successional phases could not be found in the
and
self-perpetuating
climax.
Horton
(1959) described even-, broadly even-, and all-aged
stands, but was not convinced that the all-aged stands
were an advanced successional stage because of ev­
plots of
11 5,
used. The plot size was varied to include a minimum
of 100 dominant and codominant trees.
Individual tree species as small as 1 inch (2.54 cm)
dbh were numbered
and
mapped.
Seedlings
and
clumps of regeneration less than 1 inch dbh were
mapped and aged. The following measurements were
taken from the numbered trees:
(1) diameter at
breast height, basal diameter 6 inches above the soil,
total height, and length of live crown; (2) dominance
class according to position in the stand and crown
condition; and (3) basal age 6 inches above the soil.
Breast-height age was not used because Picea could
be as much as 100 years older at the base of the tree
than at breast height.
� 3383/HA.
fered, believing that the Picea-Abies old growth was
all-aged
Circular sample
11 10, and 1120 acre (0. 81, 0.40, and 0.20 ha) were
and "unwanted scrub species." Cormack (1953) dif­
an
were established in Picea-Abies old
plots
(a)
R
HEIGHT 29 YEARS
AFTER fIRE
§
x:
"X,
:
(b)
HEIGHT
56
YEARS
AfTER FIRE
�
§
idences of a long period of establishment in under­
stocked conditions. Barnes (1937) showed that sim­
ilar Picea-A bies old growth in the interior of British
,
Columbia regenerates from its understory and de­
velops a two-aged structure in the absence of fire.
Oosting and Reed (1952) described all-aged Picea­
Abies old growth in Wyoming on sites considered
fire free for seven centuries. Solution of these differ­
ences was the objective of this work.
METHODS
This study was made in the upper reaches of moun­
tain valleys between 5,500 and 6,500 it (1,676 and
X
1"-
�
I
9
40 FT.
I
1 2 M.
10
I
3
20
I
6
30
I
9
50 60
40
I
12
I
15
56
YEARS
FT.
I
18 M.
4791/HA.
Ie)
AGE 29 YEARS
Id)
AGE
AFTER FIRE
AFTER FIRE
§
§:
a
a
.:
a
1,981 m) elevation. Maximum timber volumes in the
Picea-Abies old growth are 30,000-50,000 bd ftl
30
20
I
6
§
acre (336-671 m3/ha) on the alluvial valley bottom
a
.:
and on the adjacent north and east-facing till slopes.
Further up these slopes and on south and west as­
pects, timber volumes fall to 15,000 bd ft/acre (168
� �o
"'
�
10 20
30 40 YRS.
�
•
Canadian Institute of Forestry. 1955. Forest fire pro­
30 40
50 60,,(RS.
\
_Pinus
..... - __
m3/ha) or less.
tection in Canada.
10 20
-X-
Abies
- -x·· Picea
FIG. 2. Structure of the young Pinus-Picea forest 29
and 56 years after fire.
ROBERT J. DAY
474
Ecology, Vol. 53, No. 3
A soil pit was dug for variations in profile and
evidences of charcoal.
(a)
(c)
OLD-GROWTH
OLD-GROWTH
RECENT
SUCCESSIONAL
ALLUVIUM
TILL SLOPES
ALLUVIUM
RESULTS
Young Pinus-Picea stands
The stand-structure curves for Pinus-Picea stands
initiated by fire 29 and 56 years ago are given in
, ,
"-
: 'x,�.x
-"x..,
Fig. 2. The age-class distribution curves of these
stands are of similar general form even though the
2c, d). In both stands, Pinus contorta and Picea en­
gelmannii X P. glauca, regeneration became estab­
AGE.
-
(20-YEAR PERIODS)
lished in large numbers immediately after an intiating
fire. Pinus is superior in numbers, grows rapidly, and
forms a canopy three to four times the height of
the Picea that it dominates (Fig. 2a, b). Establish­
,/"
\
..
;
proportion of their component species differs (Fig.
��
_�
'-�---x--
FIG. 4. Periodic diameter growth of Pinus and Picea
on (a) old-growth till slopes, (b) old-growth alluvium,
and (c) recent successional alluvium.
ment of Pinus regeneration ceases approximately 30
years after the initiating fire (Fig. 2c, d). Natural
thinning of Pinus begins at this time and progresses
as the dense young stand develops. In the 56-year-old
stand 350 dead pine per acre (865 per hectare)
were counted. Picea regeneration is reduced,
but
establishment continues throughout this phase. Abies
regeneration is minimal immediately after the fire
and increases very slowly in this phase.
The age-structure curves of the young Pinus-Picea
in Fig. 2c and 2d suggest three distinct waves of
seedling remigration and ecesis:
1st
Pinus-superabundant
Picea-Abies may have had a similar ongm pattern
to the young Pinus-Picea. The age ranges in Fig. 3c
are overlong owing to combination of old-growth
stands with a range of origin times in the data. The
differences between the shape of the curves in Fig.
2c and 2d and those in Fig. 3 are caused by subse­
'
quent regeneration (particularly Abies) and mor­
tality (principally Pinus) in the overstory.
A comparison of the basal age-diameter growth
measurements in both the old-growth Picea-Abies
and in the young Pinus-Picea again suggests similar
seed
supply
released
origin patterns
(Fig. 4). Essentially similar initial
from serotinous cones after fire, immediate ecesis of
growth patterns for both Pinus
numerous
(slow) indicate that the former species dominated
seedlings
then
cessation,
rapid
early
(fast) and Picea
the old-growth 200-250 years ago in the same way
growth and dominance.
2nd Picea-abundant seed from residuals released
it now dominates young successional Pinus stands.
seasonally after the fire, ecesis of seedlings less nu­
Diameter growth patterns in the old growth indicate
merous than Pinus initially, but continues through­
that Picea assumed dominance 50-70 years after
out the phase, slow growth dominated by Pinus.
3rd Abies-little seed because of destruction by
(Fig. 4c).
fire, slow remigration.
These waves can be readily recognized in the ad­
vanced age classes of the Picea-Abies old growth in
Fig. 3c. Such similarity suggests that the old-growth
� 2242/1IA.
k.'!\b/RA.
�
:!
(b)
,
!i
:i
..... _-.!!!!!!.
D!N4ETER
(l-INCHCLASStll)
1: "\i
i i
i i
i: iI
!
I
: i
1 \
: 1
\.���.x·x.
38"�.�
\i
(el
i
i
i
4
I
i
i
i
i
\.
,.
Old-growth Picea-Abies stands
Problems in dating the fires that initiated the Picea­
Abies were more severe than in the young Pinus be­
· 'I
·
o:
624/1L\. �
:
initiation by fire in exactly the same way as it is now
assuming dominance in the 56-year-old Pinus stand
cause of (1) presettIement origin, (2) possibility of
several initial burns, (3) death of dominant Pinus,
ME
(lll-lWCIASSES)
Despite these problems, patterns of species compo­
sition were similar. Though Pinus ages ranged from
150 to 250 years, most dominant trees were 220-240
years old, which suggested origin in fires about 230
years ago (1730's).
The height, diameter, and age-frequency distribu­
\
"
\,.�
-', x
lI. x.i\.ix l·
and (4) possibility that Picea burn residuals remain.
tions in Fig. 3 reveal the present structure of the old
�
growth. Picea dominates, rising as much as 10-15 ft
(3.3-4.6 m) above the tallest Pinus which forms both
a subordinate and codominant layer. Overstory Picea
FIG. 3. Structure of the old-growth forest.
and Pinus comprise most of the basal area although
Late Spring 1972
475
FOREST IN SOUTHERN ALBERTA
neither species is as numerous as the Abies and Picea
lings doubles after canopy breakup (900 Abies and
that form an irregular-aged and sized understory. In
250 Picea per acre (2,224 and 6 18 respectively per
the understory Abies is four times as numerous as
hectare) beneath the canopy; 1,700 Abies and 400
Picea (Day 1970) .
Picea per acre (4,201 and 988 respectively per hec­
The bell-shaped (normal curve) frequency distri­
tare) after breakup) .
butions for Pinus are typical of an even-aged or
DISCUSSION
broadly even-aged stand component (Fig. 3). The
absence of regeneration, low vitality in the overstory
The results of this study support the theory that
(live crown ratios were 25 % for Pinus as opposed
the old-growth Picea-Abies stands of the Crowsnest
to 55% for Picea), and presence of many dead co­
Forest are an advanced stage in the fire-initiated,
dominant trees indicate that Pinus is passing out of
secondary succession that induces the young Pinus­
Picea stands in the region. The results also clearly
show that the old-growth Picea-Abies is not a se1f­
the stand.
The irregular frequency distribution curves for
Picea in Fig. 3 suggest that this species behaves both
perpetuating climax community, but is fire dependent,
as an even-aged, secondary successional pioneer and
and in the absence of fire will advance toward a later
as a semisuccessful, irregular-aged, late successional
Abies-Picea phase. Though not adequately repre­
species. The low proportion of Picea to Abies in the
sented, projection of stand data suggests that the
(1: 4 average) and poor representation
Abies-Picea phase will have an entirely different
in the larger height and diameter classes of the under­
structure from that found in the overstory of the Pi­
story suggest that Picea will be less well represented
phases. Thus, though the supply of Picea seed is
cea-Abies old growth. Measurements in patches of
Picea-Abies old growth with a breaking-up overstory
indicate that the Abies-Picea phase will probably have
more than adequate in old growth (Day 1970) , in­
the all-aged structure of the understory from which
understory
in numbers or volume in more advanced successional
ability to compete with Abies in the advanced suc­
it is formed. Eventual domination of the forests of
cessional phases mark it as a fire-dependent species
this region by the Abies-Picea is deprecated by this
(Bloomberg 1950) .
writer because the following attributes are expected:
The I-shaped (-log) frequency distribution curves
(a) poor physiognomy related to an all-aged structure
for the Abies understory are typical of an all-aged
with little Picea and abundant Abies in all canopy
stand component (Knuchel 1953). It could be as­
layers; (b) low vitality caused by overstory recruit-
sumed that Abies will dominate the advanced phases
of this succession except that Abies rarely becomes
an effective canopy dominant (Fig. 3a). The few
-- !!m!!.
!!£!!.
specimens that live 200 or more years are always
---_.-•..
20-30 ft (6 . 1-9.1 m) beneath the Picea canopy and
are senescent and infected with both stem and root
illY.
PHASE
1
55
YEARS AFTER FIRE
rot.
Further advanced successional phases
These stages are nonexistent or of very rare oc­
currence in the Crowsnest Forest because few stands
will escape fire for more than 250 years. The break­
up of the Pinus canopy in itself probably predisposes
the forest to fire. With the windthrow of the Pinus,
\
tops and branches could provide fuel for a fire haz­
ard not previously encountered in this successional
system. It is only a matter of time before a dry­
For lack of extensive areas in this phase, plots
were measured in patches of Picea-Abies old growth
where the Pinus overstory had been windthrown.
Breakup of the overstory released the Abies-Picea
understory, and Abies dominated all diameter classes
2
155
YEARS AFTER FIRE
PHASE
3
255
YEARS AFTER FIRE
4
355
YEARS AFTER FIRE
\
up to 30,000 bd ft/acre (336 m3/ha) of logs plus
lightning strike reinitiates the succession.
PHASE
,
\
\
\"
"
- - --. __ e. - - • __ ----.:::--..-...-=::: __
'.
\
\
\"
"
PHASE
....
- -- - ---- - - - ---."'::: :::- .-__ '1.-",::,:,: _________
_
up to 10 inches (25. 4 cm) dbh. Picea was smaller in
size and fewer in number than Abies and slow in
releasing. Eimmeration of the reproduction under 1
inch (2. 54 cm) · dbh showed that the number of seed-
AGE
(lO-YEAR CLASSES)
FIG. 5. Hypothetical forest succession for Rocky Moun­
tain Forest in southern Alberta.
ROBERT J. DAY
476
Ecology, Vol.53, No.3
ment only through the heavy suppression of the
phase with volumes between 30,000 and 50,000 bd
understory,
ftl·acre (336-671 m3/ha) .
poor nutrient cycling caused by mor
humus formation; and (c) absence of the herbiv­
Q[ous fauna because of lack of the disturbance phases.
'1:he following stylized hypothesis is suggested for
Phase 4 (3 55 years after fire)
post-burn successional behavior of a typical stand
(Fig. 5).
tiating fire have died, and Pinus has been completely
Phase I-Young Pinus (55 years after fire)
stand is uneven- to all-aged Abies-Picea.
The Pinus and Picea that established after the ini­
eliminated from the stand (probably would occur as
a minor component where windthrow is severe) . The
Dense even-aged Pinus of declining vigor
(Fig.
4) dominates the burned-over area. The Picea that
established after the burn is less numerous and forms
a canopy about a quarter the height of the dominat­
ing Pinus. Pinus regeneration is absent because of
inability to establish beneath its canopy, and heavy
intraspecific competition is eliminating the weaker
codominant and intermediate Pinus in the overstory
by natural thinning. Picea regeneration is still be­
coming established and its vigor in the understory is
increasing (Fig. 4). Abies is sparse in the under­
story, but establishes itself easily and grows well
wherever seed permits it to invade.
The superabundant seed supplied from storage in
serotinous cones and inherent ability to establish and
grow rapidly on the exposed post-burn site account
for initial advantage of Pinus. Reinvasion of Picea
from seed cast by residuals is slower because of a
reduced seed supply, establishment problems on the
exposed site, and an inherently slower growth pat­
tern (Day 1963a) . Because of the loss of Abies seed
in the fire (dehiscent cones) and elimination of re­
siduals (thin resinous bark) the seed supply is min­
imal. Sporadic survivors must
develop
a seeding
population before reinvasion is possible.
Phase 2 (155 years after fire)
Superior growth of the larger members of the
irregular-aged Picea understory that has established
Longer­
lived Picea emerges through a subordinate canopy
layer composed mainly of Abies. Abies is unlikely
to be able to compete with Picea in the overstory
because of its early predisposition to disease which
is probably caused by inability to withstand evapora­
tive stress. Vigor is low because trees can only be­
come dominant after a lifetime of stagnant and sup­
pressed growth, and because of a buildup of mor
humus,
probably
reduces
nutrient
cycling.
Early
death and disease in this stagnant phase suggest that
timber volumes will fall to about one-third those
measured in phase 3.
The hypothesis in Fig. 5 is based on the results of
measurements in the young Pinus-Picea stands (Fig.
2) and in the old-growth Picea-Abies stands (Fig.
3) . Previous work also supports the hypothesis. The
establishment of Pinus contorta after fire is reported
by Parker (1942), Candy (1951), Crossley (1952,
1955), and Horton (1955). The subsequent regen­
eration of Picea and Abies under the Pinus is dis­
cussed by Bloomberg (1950), DeGrace (1950a, b),
Cormack (1953), and Horton (1956). The gradual
replacement of the Pinus contorta overstory by a
Picea understory is described by Horton (1956) and
is supported by other data (Canada Dep. Resources
Development, Forestry Branch, unpublished
data). The development of old-growth forest with a
broadly even-aged overstory after the Pinus declines
and dies is described by Bloomberg (1950), DeGrace
(1950a, b), Cormack (1956), and Horton (1959).
and
steadily since the initiating fire now pennits Picea
Only the final phase of the diagram lacks corrobora­
the declining Pinus canopy.
tion in Canada. It is supported by data from Oosting
Abies, which could only remigrate slowly after the
and Reed (1952) for subalpine Abies-Picea stands
fire because of the destruction of seed and residuals,
in the Medicine Bow Mountains of Wyoming.
to
begin dominating
is now developing an aggressive all-aged understory
from a new generation of mother trees.
Phase 3-Old growth (255 years after fire)
Pinus is decadent or dying and Picea dominates.
As the dominant Pinus die, Picea from the inter­
mediate classes fill the gaps above an all-aged Abies­
Picea understory. Abies is about four times as nu­
merous as Picea in the understory because it appears
to be better adapted to lower light levels (Baskerville
IMPLICATIONS
The present objective of eliminating wild fires by
both the Alberta Department of Lands and Forests
and the Parks Branch of the Canada Department of
Northern Affairs and National Resources will lead
to the elimination of an ecological pressure that has
been responsible for the evolution of the forest com­
munities that characterize the region since the re­
traction of the Cordilleran ice.
Park management
1965) and higher root competition levels than Picea.
Though Picea seeds and germinates readily, mor­
Fire protection ,to preserve a "wilderness" will al­
tality is severe. Timber volume culminates in this
low the gradual development of present forest stands
FOREST IN SOUTHERN ALBERTA
Late Spring 1972
477
toward the Abies-Picea phase which will become
forest ecology. The silviculturalist can then provide
w!despread in time. Forest will also establish on
authorities responsible for land use ,with the best
land now kept clear by repeated fire and the pro­
means of achieving the diverse objectives of man.
portion of parkland available for the famous her­
bivorous fauna (Cervus canadensis nelsonii Bailey,
Odocoileus hemionus h emionus Rafinesque, O. vir­
ginianus ochrouvus Bailey, and Alces alces andersonii
Peterson) and their predators will be greatly reduced
(Stelfox and Taber 1969).
A well-planned, silvicultural program of fire pre­
scription and control is needed to maintain the dis­
turbance phases of the succession so that a healthy,
viable "wilderness" will remain for future genera­
tions.
Forest manugement
The
primary
objective
of
management
of
the
Rocky Mountain Reserve is for water yield, with
secondary objectives for timber production, recre­
ation, and game management. The ecological be­
havior of the forest suggests the following alterna­
tives for its component species.
A fire-origin, even-aged structure and rapid, early­
growth pattern suggest management as an even-aged
crop on short rotation. Carefully planned clearcut­
ting (to avoid erosion) followed by prescribed fire
(fuel permitting) and aerial seeding or scarification
and cone scattering would appear to be the best
silvicultural methods for this species.
Picea engelmannii Parry X P. glauca (Moench) Voss.
Ability to establish immediately after fire, as well
as beneath the canopy of the successional and old­
growth stands, suggests management as an even- or
irregular-aged crop. Specific microenvironment re­
quirements (Day 1936b) and susceptibility to micro­
environmental hazards (Day 1963a) would permit
management by clearcutting old growth on moist
protected slopes and on small clearcut blocks and
strips provided that adequate seedbed is prepared by
prescribed burning or scarification. On exposed s�opes
or the valley bottom scarification before felling or a
form of shelterwood felling with scarification is sug­
gested. Alternatively, Picea could be managed as an
all-aged crop with Abies by group selection.
Abies lasiocarpa (Hook) Nutt.
of
an
all-aged
understory
Cormack, R. G. H. 1949. A study of trout streamside
cover in logged-over and undisturbed virgin spruce
woods. Can. J. Res. 27:78-95.
---.
1953. A survey of forest succession in the east­
ern Rockies. Forest. Chron. 29:218-232.
---.
1956. Spruce-fir climax vegetation in southwest­
ern Alberta. Forest. Chron. 32:346-349.
Crossley, D. I. 1952. Discing overdense lodgepole pine
regeneration. Can. Dep. Res. Develop., Forest. Br.,
Silv. Leafl. 66. 3 p.
. 1955. Mechanical scarification and strip clear­
cutting to induce lodgepole pine regeneration. Can.
Dep. N. Aff. Nat. Res., Forest. Br., Tech. Note 34.
13 p.
Day, R. J. 1963a. Spruce seedling mortality caused by
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---.
---
Pinus contorta var. latifolia Engelm.
Formation
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�
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