Restoring conifers by natural
regeneration on slopes exposed
during highway reconstruction,
Glacier National Park, Montana,
USA
RAYMOND C. SHEARER1* AND JENNIFER M. ASEBROOK2
1 Forestry
Sciences Laboratory, US Department of Agriculture, Forest Service, Rocky Mountain Research
Station, Missoula, MT 59807-8089, USA
2 Glacier National Park, US Department of Interior, National Park Service, West Glacier, MT 59936, USA
* Corresponding author. E-mail: rshearer@fs.fed.us
Summary
In 1991, about 70 years after construction, the 16-km Lake McDonald section of the Going-to-theSun Road in Glacier National Park was rebuilt. The road, which is at the base of steep north-westfacing slopes, follows the 975 m contour above Lake McDonald within forests originating after
wildfires. Tree composition is mostly western red cedar (Thuja plicata Don ex D. Don) and western
hemlock (Tsuga heterophylla (Raf.) Sarg.) with a minor component of six other conifer species.
Trees were expected to disperse enough seeds to naturally regenerate road cuts on four land-types
with developed soils, but not on the fifth land-type with rock and scree. From 1987 to 1995, red
cedar and hemlock dispersed 4466 potentially viable (filled) seeds m–2 on cut slopes while other
species added 74 filled seeds m–2. From 1991 to 1995, after reconstruction, an average of 3294 filled
red cedar seeds fell m–2, in addition to 511 western hemlock m–2 and 61 m–2 for six other species.
On cut slopes from 1992 to 1998, of land-types with developed soils, seeds germinated after
snowmelt, usually from early May until the surface dried. Almost no seeds germinated and no
seedlings survived on the rock/scree land-type. Due to the harsh environment on cut slopes, most
seedlings died. In spring 1999, red cedar and hemlock seedlings were small and inconspicuous and
required an average of 312 and 173 filled seeds for each surviving seedling.
Introduction
Successful restoration of disturbed forestlands is
a worldwide concern. Afforestation of abandoned agricultural lands (Lockhart et al., 2003;
© Institute of Chartered Foresters, 2003
Jõgiste et al., 2003) are examples of large-scale
restoration, while this article on conifer natural
regeneration on cut slopes above a mountain road
exemplifies small-scale restoration of degraded
sites. Because of its broad scope, the study of
Forestry, Vol. 76, No. 2, 2003
200
F O R E S T RY
natural processes within the field of restoration
ecology is an important and complex topic. The
recovery and maintenance of processes is the key
to ecosystem resilience and repair (Bradshaw,
1997; Whisenant, 1999).
In 1982, the United States Congress passed the
National Surface Transportation Assistance Act to
upgrade and rehabilitate deteriorating road
systems in national parks within the US
Department of Interior (Shearer et al., 1996).
Reconstruction of the spectacular 84 km Goingto-the-Sun Road in north-western Montana’s
Glacier National Park was a high priority. Scheduled first was the 16-km Lake McDonald section
(west central) built in the 1920s and the only road
within the park kept open all year. A continuous
forest, principally western red cedar (Thuja plicata
Don ex D. Don) and western hemlock (Tsuga heterophylla (Raf.) Sarg.), grows on both sides of the
road. Park planners developed a strategy to revegetate treated areas, including road cuts, using
recommendations made by an interagency core
team of managers and scientists from the Park and
the US Department of Agriculture, Forest Service.
Photographic and written records document
natural recovery of vegetation, including conifers,
on cut slopes after initial construction 70 years
earlier. However, specific seedfall, seed germination and seedling development were not recorded.
Except on rocky sites, conifers were anticipated
to naturally regenerate road cuts exposed during
reconstruction because of the abundant seed
source, moderate climate and favourable soil
conditions.
Both western red cedar and western hemlock
produce frequent heavy cone crops in the Upper
Columbia River Basin (Gashwiler, 1969;
Minore, 1990; Packee, 1990; Feller and Klinka,
1998). Associated conifer species also periodically produce substantial cone crops (Haig et
al., 1941; Boe, 1954; Schmidt et al., 1976;
Graham, 1990). Natural regeneration of mixed
conifers in cedar–hemlock forests is usually
prompt and abundant (Ferguson, 1994),
especially when the litter/duff layer is reduced to
expose mineral soil (Haig et al., 1941). For
example, following clearcut and burn treatments on a western red cedar forest cover type
in western Montana every established seedling
required 13 filled seeds (Shearer, 1976). But,
restoring vegetation on fresh road cuts is much
less certain than on surfaces exposed by fire or
following forest management treatments.
Objectives of this opportunistic case study
were to document conifer seed-fall and subsequent regeneration on road cuts by estimating
(1) the number of conifer seeds dispersed from
1987 to 1995 in forest above and below cut
slopes; (2) the number of dispersed conifer seeds
that germinated on cut slopes from 1992 to 1998;
and (3) the number of conifer seedlings that survived on cut slopes in 1999.
Materials and methods
Study area
The Lake McDonald section of the Going-to-theSun Road (48° 35 N lat., 113° 55 W. long.)
follows the 975-m contour above the east shore
of the lake and is at the toe of slopes that average
about 35°. Forests surrounding the road were
initiated by three fire events (Barrett, 1988):
84 per cent after 1735, 10 per cent after 1813
(centre) and 6 per cent after 1929 (southern). The
forest is classified as western red cedar–western
hemlock (Eyre, 1980), both at the eastern
extreme of their natural ranges (Habeck, 1968).
Basal area is composed of 85 per cent western red
cedar and western hemlock; 10 per cent Rocky
Mountain Douglas-fir (Pseudotsuga menziesii var.
glauca (Beissn.) Franco) and western larch (Larix
occidentalis Nutt.); and 5 per cent western white
pine (Pinus monticola Dougl. Ex D. Don), spruce
(probably hybrids of Engelmann (Picea engelmannii Parry ex Engelm.) and white (Picea glauca
(Moench) Voss), lodge-pole pine (Pinus contorta
var. latifolia Engelm.) and sub-alpine fir (Abies
lasiocarpa (Hook.) Nutt.) (Shearer and Potter,
1994). Habitat types as classified by Pfister et al.
(1977) are Thuja plicata/Clintonia uniflora,
Tsuga heterophylla/Clintonia uniflora and Abies
lasiocarpa/Clintonia uniflora.
Lake McDonald creates an environment
favourable for plant growth and soil development
(Habeck, 1968). Mean annual precipitation is
~800 mm, maximum temperatures average –3°C
in January and 26°C in July, and the frost-free
period is about 104 days (Finklin, 1986). Soils
were formed from ice and water deposition
associated with glaciers (Martinson and Basko,
R E S T O R I N G C O N I F E R S B Y N AT U R A L R E G E N E R AT I O N
201
Table 1: Land-type number and description, land-type characteristics and percentage of road length within each
land-type, Lake McDonald section, Going-to-the-Sun Road, Glacier National Park, USA
Land-type number and description
Characteristics
%
1.
2.
3.
4.
5.
Moist soil
Moist, clayey soil
Droughty surface soil; cool, good air drainage
Dry soil; cool, poor air drainage
Little soil
35
10
7
41
7
Silty and fine sandy glacial till
Clayey glacial till
Sub-irrigated alluvial fan
Glacial drift and outwash
Rock and scree
1983). Glacial tills originated from Precambrian
argillite, shale and limestone. Volcanic ash
deposits, up to 25 cm deep, improved soil
development, fertility and moisture-holding
characteristics, which promoted vegetation
growth in these red cedar–hemlock forests.
Martinson and Basco (1983) identified several
‘land-types’ (soils integrated with vegetation,
drainage and climate) along this section of road.
These (Table 1) were condensed into five general
land-types (Shearer and Potter, 1994).
Methods
Ten sample points with two on each of the five
land-types were randomly selected along the Lake
McDonald section of the Going-to-the-Sun Road
(Shearer and Potter, 1994). Figure 1 shows the
approximate location of seed traps and regeneration plots in relation to the road.
Conifer seed-fall was estimated using 0.4-m2
rectangular seed traps, four placed on the forest
floor at each of the 10 sample points (Shearer and
Potter, 1994). Two seed traps spaced ~15 m apart
were positioned ~8 m from the edge of the road
prism, within the forest above the road cut, and
two below the road fill (Figure 1). Depending on
availability of personnel and climatic factors,
contents of seed traps were emptied from three to
nine times per year during the snow-free period
from 1987 to 1995, placed into labelled paper
sacks and stored at room temperature. Later,
seeds were separated by species and X-rayed.
From X-rays, seeds were classified as filled
(potentially viable with a developed embryo),
empty, or damaged. Unless specified, this paper
refers only to filled seeds.
In 1991, near each of the 10 groups of seed
traps, four 0.25-m2 plots were randomly estab-
lished approximately at road level on fresh cuts
above the ditch (Figure 2). Germination of conifer
seeds and seedling mortality were counted once a
month, May to September, 1992–1998. Plastic
toothpicks were placed at the right of new
seedlings for identification, a different colour for
each measurement. When seedlings died these
markers were removed. At the first measurement
in the spring, the multicolour toothpicks marking
surviving seedlings from the previous year were
replaced with a single colour to identify the year
of germination. A final seedling count was made
in May 1999.
Analysis
Seed dispersal data for each conifer species were
not normal and were highly variable between
years. Each species was analysed using the following: (1) the number of seeds from paired traps
averaged for a plot mean; (2) plot means ranked
within each year to address large differences
between years; (3) yearly ranks for each plot averaged across years to produce an aggregate rank;
and (4) possible differences in seed-fall among
land-type/road position analysed using KruskalWallis test statistics (Daniel, 1990). Because there
were only two plots for each land-type/road
position combination, Monte Carlo methods
were used to estimate significance levels for
Kruskal-Wallis test statistics (Mehta and Patel,
1996).
Large numerical differences in seed germination and seedling survival on cuts defied meaningful statistical analysis because of low sample sizes.
Hence, data were only summarized. Ratios of
number of filled seeds per germinant and per surviving seedling for 1999 data were calculated for
each land-type.
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F O R E S T RY
Figure 1. Schematic of Lake McDonald section, Going-to-the-Sun Road, Glacier National Park, Montana,
USA shows location of seed traps and conifer natural regeneration plots. Mean road dimensions: pavement
width, 6.7 m; shoulders, 0.7 (0.3–0.9) m; front slope to ditch, 1.2 m; ditch, 0.13 m; back-slope measures
1.5–1.8 m at a ratio of 3 : 1 (2 : 1 maximum).
Results
Seed dispersal
About 70 per cent of the western red cedar seeds
and 90 per cent of all other species dispersed in
September and October before snow began to
accumulate. From 1987 to 1995, an average of
6989 total seeds m–2 of all species fell along the
road, and 4519 seeds m–2 (65 per cent) of these
were filled (Table 2), ranging from 2342 seeds
m–2 in 1995 to 0.3 seeds m–2 in 1989. Composition of filled seeds during the study was: red
cedar, 74.4 per cent; hemlock, 23.9 per cent;
Douglas-fir, 0.7 per cent; larch, 0.5 per cent;
spruce, 0.2 per cent; and combined lodge-pole
pine, western white pine and sub-alpine fir,
0.2 per cent (Table 2). These percentages were
similar to the composition of the basal area: red
cedar, 63 (294 m2 ha–1); hemlock, 22 (103 m2
ha–1); Douglas-fir, 6 (28 m2 ha–1); larch, 4 (21 m2
ha–1); and the other four conifers, 5 (23 m2 ha–1).
Both basal area and percentage of seeds were
greatest below the road for red cedar and spruce,
and greatest above the road for hemlock,
Douglas-fir and western larch.
Western red cedar and western hemlock produced over 98 per cent of all conifer seeds during
the 9 years of this study (Table 2). From 1987 to
1995 red cedar dispersed 97 per cent of its seeds
in 1993 and 1995, while hemlock distributed 99
per cent in 1987, 1992, 1993 and 1995. Seed-fall
from other conifers occurred mostly in 1993 and
1995. Few seeds matured in 1989 or 1994.
From 1987 to 1995, significant variation in
seed-fall occurred by land-type and road position
combinations (Table 3) for western red cedar
R E S T O R I N G C O N I F E R S B Y N AT U R A L R E G E N E R AT I O N
203
Figure 2. Section of the Going-to-the-Sun Road showing typical shoulders, ditch and cut slope where four
0.25 m2 natural regeneration plots were established to count conifer seed germination and seedling survival,
7 May 1997, Glacier National Park, Montana, USA. Seed traps were placed in the forest above and below
the road.
Table 2: Mean number (standard deviation) of filled seeds m–2 dispersed by species and year of cone production
in forests paralleling Lake McDonald section, Going-to-the-Sun Road, Glacier National Park, USA
Year
WRC
WH
1987
0.6 (1.5)
565.3 (751.9)
1988
0.1 (0.4)
0.6 (1.6)
1989
0.0
0.0
1990
69.6 (108.1)
4.4 (7.2)
1991
2.5 (5.7)
4.0 (13.2)
1992
32.1 (68.0)
196.4 (285.2)
1993 1107.6 (1337.7) 141.5 (204.4)
1994
5.1 (8.4)
0.7 (1.2)
1995 2146.4 (1740.6) 168.7 (191.6)
Total 3364.1
1081.6
DF
WL
0.9 (1.6) 2.4 (4.8)
0.1 (0.5) 0.8 (2.0)
0.0
0.0
0.9 (2.5) 1.9 (4.0)
7.1 (8.4) 3.4 (7.4)
0.0
0.3 (0.1)
3.8 (6.6) 11.2 (18.0)
0.0
0.1 (0.4)
18.0 (21.3) 4.1 (8.6)
30.8
24.2
SPR
LPP
WWP
1.8 (2.5)
0.2 (0.7)
0.0
2.8 (11.8)
0.2 (0.7)
0.0
0.9 (2.6)
0.1 (0.4)
1.5 (2.8)
7.5
0.1 (0.5)
0.4 (1.7)
0.3 (2.0)
0.0
3.1 (5.1)
0.3 (0.8)
0.7 (1.9)
0.2 (0.9)
1.4 (5.7)
6.5
0.0
0.1 (0.5)
0.0
0.1 (0.4)
1.7 (5.0)
0.1 (0.4)
0.4 (1.1)
0.0
1.6 (3.1)
4.0
SAF
Total
0.1 (0.4) 571.2
0.0
2.3
0.0
0.3
0.0
79.7
0.0
22.0
0.0
229.2
0.1 (0.5) 1266.2
0.0
6.2
0.4
2342.1
0.6
4484.6
Species abbreviation: WRC, Western red cedar; WH, western hemlock; DF, Douglas-fir; WL, western larch; SPR,
spruce; LPP, lodge-pole pine; WWP, western white pine; SAF, sub-alpine fir.
seeds (P < 0.01) and for western hemlock seeds (P
= 0.02) but not for other conifers (P > 0.15). Red
cedar and hemlock composed nearly 99 per cent
of filled seeds that fell on land-types 1–4 and
70 per cent of seeds that fell on land-type 5. Red
cedar seed-fall ranged from a high of 5836 m–2 on
land-type 4 below the road to a low of 44 m–2 on
land-type 5 above the road. During the same
period hemlock seeds ranged from an average
high of over 2700 m–2 on land-types 2 and 4
above the road to an average low of 2 filled seeds
m–2 on land-type 5 below the road.
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F O R E S T RY
Table 3: Mean sum (standard deviation) of filled conifer seeds m–2 by species that fell from 1987 to 1995 by
land-type and location of seed traps in relation to Lake McDonald section, Going-to-the-Sun Road, Glacier
National Park, USA
Land-type
Location
1. Silty, fine sandy till
Above
Below
Above
Below
Above
Below
Above
Below
Above
Below
2. Clayey till
3. Sub-irrigated alluvium
4. Drift and outwash
5. Rock and scree
WRC
WH
DF
3722 (980)
5746 (1298)
3178 (877)
5700 (1180)
4570 (1137)
1802 (386)
2871 (703)
5836 (1292)
44 (8)
97 (18)
1710 (332)
947 (104)
2933 (495)
306 (49)
1004 (152)
432 (61)
2783 (547)
444 (88)
4 (1)
2 (0.4)
14 (2)
28 (6)
88 (20)
41 (8)
33 (7)
45 (7)
14 (3)
27 (7)
10 (1)
7 (2)
After road reconstruction in 1991, conifers
growing adjacent to the road dispersed abundant
seeds in 1992, 1993 and 1995 (Table 2). During
the 5 years after treatment, red cedar accounted
for 85 per cent of dispersed filled seeds (3294
m–2), hemlock 13 per cent (511 m–2), Douglas-fir
0.7 per cent (29 m–2), larch 0.5 per cent (19 m–2)
and the four other species 0.7 per cent (13 m–2).
Substantially more filled seeds (4766 m–2) fell on
land-types 1–4 than on land-type 5 (87 m–2).
There was no statistical difference by land-type
for other conifers.
Seed germination
Germination on road cuts began after snowmelt,
usually the second week of May. In 1997, germination began later in May because of more snow.
Western red cedar seeds germinated more rapidly
than western hemlock seeds. An average of 62, 30
and 5 per cent of red cedar seeds germinated in
May, June and July while 23, 52 and 22 per cent
of the hemlock seeds germinated in the same
period. Too few seeds of other species fell on these
sites to make similar comparisons. In spring
1992, few red cedar seeds and no hemlock seeds
germinated following the poor cone crop in 1991
(Table 4). Germination increased for both species
in 1993 after greater seed-fall in 1992. In 1994
and 1996, 8 per cent of filled red cedar seeds and
10 per cent of filled hemlock seeds germinated
following abundant cone production the previous
years.
For each seedling that germinated in the spring
WL
56 (7)
8 (2)
4 (1)
3 (0.4)
48 (9)
6 (1)
61 (9)
46 (5)
7 (2)
3 (1)
from 1992 to 1996 on land-types with developed
soils, an average of eight filled western red cedar
seeds (range 4–48) and 13 filled western hemlock
seeds (range 8–21) fell from 1991 to 1995 cones
(Table 4). Fewer seeds fell on land-type 5, and
only one hemlock and one Douglas-fir seedling
were counted there from 1992 to 1996. The percentage of subplots with germinants on landtypes 1–4 increased each year of the 5-year
period. For example, red cedar germinated on
50 per cent of the plots in 1993, 88 per cent in
1994, and 100 per cent in 1998; hemlock germinated on 69 per cent of the plots in 1993 and
1994 and 88 per cent in 1996. However, on replication 1, land-type 3, red cedar seeds germinated
there only in 1996 and hemlock seeds germinated
there in 1993, 1996 and 1998.
Seedling survival
By 1999, vegetation covered cut slopes treated
during reconstruction on land-types 1–4, but not
on rocky land-type 5. Surviving conifers were
inconspicuous among the post-treatment vegetation. All red cedar and hemlock appeared small
and frail. However, the few spruce and Douglasfir seedlings present were more robust on these
adverse sites.
Conifer seedling survival on road cuts in May
1999 varied greatly. Survival ranged from a high
of 130 seedlings m–2 (51 per cent of all living
seedlings including three-quarters of all red cedar
and over one-third of all hemlock and spruce) on
land-type 1 (replication 1) to none on land-types
R E S T O R I N G C O N I F E R S B Y N AT U R A L R E G E N E R AT I O N
205
Table 4: On land-types 1–4, the mean number of filled western red cedar (WRC) and western hemlock (WH)
seeds m–2 that fell on cut slopes from 1991 to 1995, the number of those seeds that germinated m–2 from 1992
to 1996, and their seeds : germination ratio; also seedling survival m–2 in May 1999 and their seeds : seedling
survival ratio, Lake McDonald section, Going-to-the-Sun Road, Glacier National Park, USA
Year of dispersal/
germination
Seeds
dispersed m–2
Seeds
germinated m–2
Ratio
1999 seedling
survival m–2
Ratio
WRC
1991–1992
1992–1993
1993–1994
1994–1995
1995–1996
Total
3.1
40.1
1384.4
6.3
2680.8
4114.7
0.6
5.9
173.9
0.0
354.0
535.3
1:5
1:7
1:8
–
1:8
1:8
0.0
0.1
0.2
–
12.9
13.2
–
1 : 401
1 : 6922
–
1 : 208
1 : 312
WH
1991–1992
1992–1993
1993–1994
1994–1995
1995–1996
Total
4.9
245.5
176.9
0.9
210.9
639.1
0.0
11.9
10.9
0.1
27.6
50.5
–
1 : 21
1 : 16
1:9
1:8
1 : 13
–
0.5
0.0
0.0
3.2
3.7
–
1 : 491
–
–
1 : 66
1 : 173
Species
3 (replication 1) and 5 (both replications). Survival was 15 per cent on land-type 2, 9 per cent
on land-type 3 and 16 per cent on land-type 4.
Each red cedar germinant required an average
of eight filled seeds in 1994 and 1996, and each
hemlock germinant needed 16 seeds in 1994 and
eight in 1996 (Table 4). By May 1999, the
number of red cedar seeds per living seedling
inflated to 6922, and 208 for seeds dispersed in
1993 and 1995, while each surviving hemlock
seedling required 491 and 66 for seeds dispersed
in 1992 and 1995. Red cedar and hemlock made
up 95 per cent of surviving conifer seedlings in
1999, and spruce, Douglas-fir, and larch composed the remainder. From 1991 to 1995 on landtypes 1–4, seeds : seedling ratios were 312 : 1 for
red cedar and 173 : 1 for hemlock.
Seed and seedling mortality
After snowmelt on land-types 1–4, a slow-moving
film of water, resulting from subsurface water disrupted by the road cuts, flowed freely down many
exposed cut slopes. This run-off persisted from a
few days to several weeks. Initially, many seeds
washed from the cuts into the ditch. As vegetation re-established and organic matter accumulated, most seeds were held in place. While soils
were saturated, many seedlings died from causes
associated with excess water and possibly disease.
Between monthly examinations, some seedlings
disappeared while others succumbed to disease or
animal feeding. When soils dried, usually during
July and August, some seedlings perished from
lack of moisture. But the greatest decrease in
seedlings occurred from October to May when
53 per cent of the red cedar and 40 per cent of the
hemlock seedlings died. Some frost heaved before
winter snow covered the plots, others were
wrenched from the soil or broken by snow creep,
and many died from causes associated with excess
water in the spring. About 25 per cent of western
red cedar and western hemlock seedlings died the
year they germinated.
Discussion
During this 9-year study western red cedar dispersed seed from two outstanding, one moderate,
five poor and one failure cone crops, while
western hemlock had one outstanding, three
good, three poor and two failure cone crops. In
1989, nearly all conifer seed and pollen cones
were killed by low temperature and wind chill
associated with an extreme Arctic front that
swept throughout the Northern Rockies on
1 February (Shearer and Potter, 1994; Shearer
and Kempf, 1999). In 1993 and 1995 an average
of 1627 red cedar seeds m–2 fell from stands
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F O R E S T RY
composed of 367 m2 ha–1 basal area of red cedar.
In 1987 an average of 565 hemlock seeds m–2
were dispersed from the same stands containing
129 m–2 basal area of hemlock. At two sites near
Vancouver, British Columbia, Feller and Klinka
(1998) report high seed-fall for combined viable
red cedar and hemlock seeds m–2 dispersed in
1990 and again in 1994 was about 1000 for one
stand with basal area of 173 m2 ha–1 and 200 for
a second stand with basal area of 82 m2 ha–1.
Ratios of red cedar and hemlock seed-fall to their
basal area between the Montana and British
Columbia sites are similar for years of good cone
crops.
After road reconstruction, western red cedar
and western hemlock dispersed over 3700 filled
seeds m–2 from 1991 to 1995. Most of these seeds
fell before mid-November when residual snow
usually began to accumulate (Shearer and Potter,
1994). A few seeds continued to disperse through
the winter and the next growing season. Seed germination on plots may have been delayed slightly
because snow cleared from the road by park
crews added to the accumulation on lower cut
slopes and required more time to melt (Figure 2).
Road cuts are more hostile environments for
germination of and survival of conifer seeds than
seedbeds on nearby natural surfaces because
seeds and seedlings are often subjected to more
extreme physical and biological conditions that
limit survival. Although many viable seeds dispersed from heavy cone crops in 1993 and 1995,
few germinated and only occasional seedlings survived through 1999. Dense mats of mosses that
developed on cut slopes seemed to prevent continuing germination of conifer seeds within these
clumps.
Until cuts re-established vegetation, many
seeds were carried off the plots by water that
flowed gently across the surface for up to several
weeks after snowmelt. High seedling losses from
October to May were attributed to frost heaving
before snow cover and to snow creep that pulled
young seedlings from the ground. During the five
years of measurements, eight and 12 filled seeds
were required for each germinating red cedar and
hemlock. However, by May 1999, that ratio
expanded to over 300 red cedar and 160 hemlock
seeds for each surviving seedling.
Characteristics of moisture and vegetation
observed on cut slopes closely fit the land-type
definitions shown in Table 1. Land-type 1 maintained wet or moist cut slopes much of the
summer and mosses became a major component
of the vegetation. Sixty per cent of the surviving
conifer seedlings in 1999 grew on land-type 1.
Surfaces of land-types 2 and 4 also remained
moist much of the summer and sustained a high
component of mosses among the vegetation, but
each had ~15 per cent of the surviving conifer
seedlings in 1999. Land-type 3 was much drier
with sparse vegetation and 9 per cent of the
surviving conifer seedlings in 1999. Little vegetation of any kind and no conifer seedlings were
observed on land-type 5.
Once-a-month site visits from May to September were not frequent enough to identify specific
causes of most seedling mortality. However, we
know a majority of them died over winter and
excess water was associated with death of many
seedlings in May and June. Other seedlings failed
to survive drying soils from late July to early September most years.
Conclusions
Cut slopes exposed in 1991 during reconstruction
of the Lake McDonald section, Going-to-the-Sun
Road, created uncertain environments for restoring conifers on five land-types. In the first 5 years
following treatment, plenty of potentially viable
seeds fell on the exposed backslopes. Only a small
percentage of these seeds germinated, early
seedling survival was low, and initial seedling
development of surviving conifer seed was slow.
Eight years after road reconstruction, conifer
seedlings were not conspicuous among dominant
shrubs and forbs developing on the cut slopes,
and it is likely that it will be many years before
they become evident and add greater variety to
the vegetation along this scenic road.
The hypothesis that seed-fall from bordering
forest trees is sufficient to regenerate conifers that
rapidly add texture to other vegetation is rejected
if the object is to quickly attain this goal. Tree
planting with nursery stock that is compatible
with these harsh sites will be necessary. However,
if speed is not an objective and the manager is
satisfied to know natural conifer regeneration is
present and increasing slowly below overtopping
vegetation, then this hypothesis is accepted.
R E S T O R I N G C O N I F E R S B Y N AT U R A L R E G E N E R AT I O N
Acknowledgements
We are indebted to Rachel Potter and Laurie Kurth for
supervising data collection; Leon Theroux and Jack
Schmidt for seed identification, X-ray and analysis, and
data handling; Rudy King for statistical advice and
methods for data analysis; Kristen Schaffer and Carol
Wolfe for helping with manuscript preparation; and
James Cramer for figures.
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