DEPAR TMENT OF AGRICULT URE

United States 

Department of 

Agriculture

Forest Service

Pacific Northwest 

Research Station

Research Paper

PNW-RP-585

August 2010

The Density and Distribution 

of Sitka Spruce and Western 

Hemlock Seedling Banks in 

Partially Harvested Stands 

in Southeast Alaska

Louise S.Y. Levy, Robert L. Deal, and John C. Tappeiner
The Forest Service of the U.S. Department of Agriculture is dedicated to the principle of 

multiple use management of the Nation’s forest resources for sustained yields of wood, 

water, forage, wildlife, and recreation. Through forestry research, cooperation with the 

States and private forest owners, and management of the National Forests and National 

Grasslands, it strives—as directed by Congress—to provide increasingly greater service to a 

growing Nation.

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Authors

Louise S.Y. Levy formerly was coordinator of the Sustainable Forests Education 

Cooperative, Cloquet Forestry Center, University of Minnesota, 175 University 

Road, Cloquet, MN 55720. Robert L. Deal is a research forester, U.S. Department 

of Agriculture, Forest Service, Pacific Northwest Research Station, 620 SW Main 

Street, Suite 400, Portland, OR 97205. John C. Tappeiner is professor emeritus, 

College of Forestry, Department of Forest Resources, Oregon State University, 321 

Richardson Hall, Corvallis, OR 97331.

Cover photograph by Karen Waddell.
Abstract

Levy, Louise S.Y.; Deal, Robert L.; Tappeiner, John C. 2010. The density and 

distribution of Sitka spruce and western hemlock seedling banks in partially 

harvested stands in southeast Alaska. Res. Pap. PNW-RP-585. Portland, OR: 

U.S. Department of Agriculture, Forest Service, Pacific Northwest Research 

Station. 20 p.

This study’s objective was to document and describe the current seedling bank 

of Sitka spruce (Picea sitchensis (Bong.) Carr.) and western hemlock (Tsuga 

heterophylla (Raf.) Sarg.) stands in southeast Alaska that were partially cut 

between 1900 and 1984. We investigated the following: (1) What are seedling 

bank densities? (2) What are seedling size- and age-class distributions? (3) Do 

seedbed type, treatment, and understory vegetation affect seedling density and 

species composition? and (4) What are seedling growth rates?

Density was high for both Sitka spruce (22,000 seedlings/ha) and western 

hemlock (223,000 seedlings/ha) and varied widely between sites. There were 

always fewer spruce than hemlock. Ninety-five percent of spruce and 94 percent of 

hemlock were less than 0.5 m tall. Spruce had a mean age of 8 years (range 1 to 41 

years) and hemlock 19 years (range 1 to 110 years). Both species were four times 

as common on logs as on undisturbed forest floor. Under closed-canopy conditions 

at the 15 sites harvested between 1900 and 1958, the average annual height growth 

rate was 2.3 cm for hemlock and 1.7 cm for spruce. At the two open-canopy sites, 

harvested in 1983 and 1984, annual height growth rates increased to 8.2 cm for 

hemlock and 10.2 cm for spruce. 

Our results suggest that the seedling bank of both species is established 

and well stocked, thus providing advanced regeneration for the postharvest 

stand. Because forest managers have increasing concern about effects of 

clearcut harvesting in Pacific Northwest forest ecosystems and renewed interest 

in maintaining or restoring biodiversity, other silvicultural methods warrant 

examination.

Keywords: Natural regeneration, seedling banks, Sitka spruce, western 

hemlock, southeast Alaska, partial cutting.
Summary

Concern about the effects of clearcut harvesting on forest ecosystems in southeast 

Alaska has increased interest in alternative methods for regeneration and timber 

management such as partial cutting or uneven-age management. In this study, 

spruce and hemlock seedling banks following partial cutting were very dense and 

compare favorably with naturally regenerated clearcuts in the region. Advance 

regeneration left after cutting grew rapidly and was a significant and dominant 

component of the current stand. Thus, the existence of a seedling bank in the 

partially cut stands provided a new cohort of trees that could easily release and 

grow following another cutting or disturbance event. This would suggest that partial 

cutting in this forest type is a sustainable silvicultural system that could maintain 

current tree species composition and structure on a long-term basis. It is important 

to remember that the stands we studied were cut to provide specific wood products 

such as spruce (Picea sitchensis (Bong.) Carr.) sawtimber and hemlock (Tsuga 

heterophylla (Raf.) Sarg.) pilings. Cutting occurred without a planned silvicultural 

system with little effort taken to ensure spruce regeneration. Nevertheless Sitka 

spruce was maintained in these stands and included both new and advance spruce 

regeneration. Therefore, well-planned silvicultural systems based on partial cutting 

will likely provide rapidly growing trees for timber production and maintain stand 

mixtures of spruce and hemlock trees similar to old-growth forests. Our results 

show that the establishment of new regeneration and the growth of larger advance 

regeneration trees of both hemlock and spruce can maintain species composition 

similar to that of study plots before cutting. The results of this study strongly 

indicate that silvicultural systems using partial cutting can be successfully applied 

in western hemlock–Sitka spruce forests in southeast Alaska. By leaving spruce 

seed-trees, disturbing soil judiciously, planning entries to regulate overstory 

density to promote seedling establishment, and possibly planting spruce seedlings 

where the seed source is poor, we believe sizable new cohorts of spruce can also 

be regenerated in these systems while maintaining the attributes of uneven-aged 

stands.

Partial cutting in 

the spruce and 

hemlock forest type 

is a sustainable 

silvicultural system 

that could maintain 

current tree species 

composition and 

structure on a longterm basis.
1

Density and Distribution of Sitka Spruce and Western Hemlock Seedling Banks in Partially Harvested Stands in Southeast Alaska

Introduction

The natural regeneration of trees is a fundamental process for long-term forest 

growth and development. Natural regeneration plays an important role in a forest’s 

response to disturbances such as windthrow and fire, and it may be part of a 

silvicultural system for timber management. The success of natural regeneration 

depends on a variety of factors including plentiful seed, suitable seedbeds for 

germination and establishment, and a microenvironment that enables early 

seedling survival and growth.

Climatic conditions are ideal for natural regeneration in southeast Alaska’s 

temperate rain forests. Moisture is plentiful, and temperature extremes are moderate (Harris et al. 1974, Ruth and Harris 1979). In general, despite seed predation by 

squirrels (Yount 1997), seed availability does not appear to be a limiting factor in 

this region, as the major tree species—western hemlock (Tsuga heterophylla (Raf.) 

Sarg.) and Sitka spruce (Picea sitchensis (Bong.) Carr.)—are both prolific producers 

of light seeds that are easily transported by wind (Godman 1952; Harris 1967, 1969, 

1990; James and Gregory 1959; Packee 1990).

Since the early 1950s, forest managers in Sitka spruce–western hemlock stands 

in southeast Alaska almost exclusively have used even-age silvicultural systems 

(i.e., clearcutting and natural regeneration). However, recent regionwide forest 

management plans in Alaska (USDA FS 1997) have created guidelines for timber 

management using alternatives to clearcutting. These plans have sparked interest 

in assessing the effects of partial cutting in the spruce-hemlock forests of southeast 

Alaska. Information on the density and species composition of the seedling bank 

(i.e., advance regeneration) is needed to understand how partial cutting will affect 

the tree species composition following partial cutting. In particular, it is important 

to know if Sitka spruce, a moderately shade-tolerant species, has established 

advance regeneration that might enable forest managers to use partial cutting or 

uneven-age silvicultural systems to maintain spruce. Sitka spruce is a major component of southeast Alaska forests and historically has been the most economically 

valuable species. It is important that Sitka spruce continue to be maintained in these 

forests.

Successful natural regeneration of western hemlock and Sitka spruce following clearcutting has been well documented in this region (Anderson 1955, Harris 

and Farr 1974, Ruth and Harris 1979, Zasada and Packee 1995). From other studies (Alaback 1982, Christy and Mack 1984, Deal et al. 1991, Harmon 1987) and 

personal observation, we knew that Sitka spruce seedlings occur in the understory 

of coastal Pacific Northwest forests. Deal et al. (1991) documented the presence 

of Sitka spruce seedlings (< 1.30 m) in three stand-reconstruction plots located in 

It is important to 

know if Sitka spruce, 

a moderately shadetolerant species, has 

established advance 

regeneration that might 

enable forest managers 

to use partial cutting or 

uneven-age silvicultural 

systems to maintain 

spruce. 
2

Research paper pnw-rp-585

mature and old-growth hemlock-spruce forests in southeast Alaska. In these three 

stands, he found an average of between 0 and 27,900 seedlings/ha. However, prior 

to this study, there was no detailed information on the composition of seedling 

banks of southeastern Alaska forests and how seedling banks might be affected by 

partial cutting.

The objective of this study was to document and describe the seedling bank of 

Sitka spruce and western hemlock in partially cut stands in southeast Alaska. We 

studied the density, size, age, seedbed, and growth rates of Sitka spruce seedlings 

and compared them to western hemlock seedlings, a species known to be very 

shade tolerant. Specifically, we investigated the following: (1) What are the densities of established seedling banks? (2) What are the seedling size- and age-class 

distributions? (3) Are density and species composition affected by seedbed (logs or 

forest floor), treatment (cut and uncut), and understory shrub cover? and (4) What 

are the seedling growth rates?

Related Studies

This study was one of three research projects making up the retrospective portion 

of the USDA Forest Service study “Alternatives to Clearcutting in the Old-Growth 

Forests of Southeast Alaska.” A detailed background description and status report 

of the Alternatives to Clearcutting project is provided by McClellan (2004). Information and results from the three research projects can be found in Deal (1999, 

2001), Deal and Tappeiner (2002), Deal et al. (2002), Palkovic (1998),1 Yount (1997), 

and this paper. In particular, note that although this study documents and describes 

the current advance regeneration seedling bank under mostly closed-canopy conditions (15 of 17 sites), Deal and Tappeiner (2002) described the postharvest response

of Sitka spruce and western hemlock advance and postharvest regeneration in these 

partially cut stands. 

Materials and Methods

Study Area

Our study sites were located throughout the Tongass National Forest in southeast 

Alaska, which lies between latitudes 54° and 60° N and longitudes 130° and 138° 

W. This area is characterized by steeply rising coastal mountains and densely 

forested islands (Harris et al. 1974, Taylor 1935). The climate is maritime. Strong 

winds from the Pacific are common, particularly during fall and winter. The 

1

 Palkovic, P. 1998. Patterns of tree mortality, wounding, and disease in partially harvested 

stands in southeast Alaska. Unpublished report. On file with: Juneau Forestry Sciences 

Laboratory, 11305 Glacier Highway, Juneau, AK 99801.
3

Density and Distribution of Sitka Spruce and Western Hemlock Seedling Banks in Partially Harvested Stands in Southeast Alaska

significance of this climate for the forest is that lack of 

moisture does not limit regeneration, wildfires are rare, 

and windthrow of trees is common (Harris et al. 1974). 

Average annual temperature and precipitation ranges 

from 8 °C and 145 cm (Juneau) to 11 °C and 384 cm 

(Ketchikan). Monthly precipitation values range widely, 

temperatures somewhat less so (table 1). Soils in southeast 

Alaska are immature Spodosols, developed predominantly 

from granites, diorites, and limestones, and are typical 

of areas that have undergone recent glacial recession 

(Borman et al. 1995, Ruth and Harris 1979, Taylor 1935). 

The forest floor is typically a mix of undisturbed and 

disturbed (mineral soil, tip-up mounds) areas, and downed 

wood in all stages of decay.

Table 1—Monthly rainfall and temperature 

averages for southeast Alaska 

Precipitation	 Temperature

Low	 High	 Low	 High

Month Centimeters Degrees Celsius

January 5.08 29.21 -5.55 1.11

February 3.81 25.40 -3.06 1.94

March 3.81 25.40 -0.56 3.33

April 3.81 20.32 2.50 5.83

May 2.54 22.86 10.30 14.70

June 1.91 17.78 10.80 18.80

July 2.54 20.32 15.30 19.40

August 5.08 29.21 15.70 18.50

September 5.08 45.72 8.89 11.60

October 8.89 53.34 4.72 7.78

November 6.35 38.10 -0.56 9.44

December 5.08 35.56 -3.06 1.67

Source: National Oceanic and Atmospheric Administration, U.S. 

Department of Commerce.

Site Selection

The 17 sites in this study were logged between 1900 and 1958, except for two sites 

logged in the mid 1980s (table 2). The sites were selected by using both historical 

records and aerial photographs. Additionally, the sites were chosen with the following goals in mind (table 2, fig. 1):

• Sample a range of time since cutting. 

• Sample a range of cutting intensity including an uncut area. 

• Have relatively uniform topography, soils, forest type, and plant associations.

• Reflect distribution throughout the Tongass National Forest.

Examination of stumps and residual trees showed that all sites were mixed 

spruce-hemlock stands before logging. Most sites were within 20 to 300 m of the 

shoreline, and slopes were less than 20 percent. Each stand was surveyed to find a 

range of current stand densities and cutting intensities, with number and size of cut 

stumps and overstory trees noted (Deal and Tappeiner 2002). An uncut control area 

and three partially cut areas (light, medium, and heavy) were located in a 10-ha 

treatment area (also referred to as a “stand”). Two examples of the range of cutting 

intensities within a site are 49 to 96 percent cut (24 m2

/ha to 85 m2/ha) at Hanus 

Bay and 17 to 36 percent cut (9 m2/ha to 26 m2/ha) at Big Bear Creek. 

Because this study was a retrospective not a controlled study, quantification 

of cutting intensity was determined a posteriori once the range of cutting intensity 

had been calculated for each site. The cutting intensities are relative and reflect the 

variability found at each site. For additional detail on cutting intensity, please see 

Deal et al. (2002) and Deal and Tappeiner (2002). Four randomly located, 0.2-ha 
4

Research paper pnw-rp-585

circular overstory plots were installed within each treatment area at each site. The 

term “overstory plot” is used to distinguish these plots from the seedling bank 

plots described in this paper. All data were collected between late June and early 

September in 1995 and 1996. 

Seedling Bank Data Collection

For this study we defined seedlings as being < 3 m tall and < 2.5 cm (diameter 

at breast height). All western hemlock and Sitka spruce seedlings were counted 

in eight 1-m2 seedling plots in each overstory plot. The eight seedling plots were 

divided evenly between two seedbed types—logs and undisturbed forest floor. 

Surveys on seedbed cover conducted during this study showed the mean forest 

coverage of logs and forest floor was 2200 m2/ha and 7730 m2/ha, respectively. 

Four seedling plots were located at the first log nearest the center of the overstory 

plot in the four cardinal directions. Each forest floor seedling plot was adjacent to 

this log. At the Thomas Bay site, seedlings on mineral soil seedbeds from skid trails 

were included for comparison. Shrub cover was estimated to the nearest 10 percent 

by visualizing a horizontal plane covering the seedling plot and did not account for 

layering of foliage.

Table 2—Site descriptions for 17 selectively harvested sites in southeast Alaska 

Current stand composition

Research site	 Cutting datea	 Average shrub cover	 Basal area	 Spruce	 Hemlock

No. of 0.2-ha plots/site Percent m

2

/ha - - - - Percent - - - -

BB, Big Bear Creek (4) 1958 46 53–79 15–47 53–85

CP, Canoe Passage (4) 1927 41 44–66 2–13 74–92

EP, Elf Point (4) 1927 33 42–116 2–4 72–96

FC, Finger Creek (4) 1941 8 58–75 5–60 40–95

FB, Florence Bay (4) 1914 33 56–83 18–75 25–82

GP, Glass Peninsula (4) 1911 25 60–84 11–34 28–83

GR, Granite (4) 1983 58 13–70 0–7 93–100

HB, Hanus Bay (4) 1922 28 56–83 6–62 38–94

KL, Kutlaku Lake (4) 1920 16 58–139 5–49 35–95

MB, Margarita Bay (4) 1958 47 41–63 4–24 76–96

PB, Portage Bay (4) 1918 13 47–56 5–33 67–95

RF, Rainbow Falls (4) 1942 36 44–66 0–28 63–100

SB, Salt Lake Bay (4) 1928 62 63–87 17–73 27–83

SK, Sarkar (4) 1925 24 57–76 0–11 89–100

TB, Thomas Bay (3) 1984 35 49–70 1–17 83–99

WC, Weasel Cove (4) 1900 28 53–75 0–24 67–100

WH, Winter Harbor (4) 1932 21 73–95 2–33 67–98

a

 Cutting date is year of harvest. 

Source: Deal et al. 2002, Deal and Tappeiner 2002.
5

Density and Distribution of Sitka Spruce and Western Hemlock Seedling Banks in Partially Harvested Stands in Southeast Alaska

Figure 1—Location of 17 study sites in the Tongass National Forest, southeast Alaska. Site letter 

codes are referenced from table 2 (from Deal et al. 2002).

Size-class distribution was determined by classifying all counted seedlings into 

eight height classes (0 to <5 cm, 5 to <25 cm, 25 to <50 cm, 50 to <100 cm, 1.0 to 

<1.5 m, 1.5 to <2.0 m, 2.0 to <2.5 m, and 2.5 to ≤3.0 m). Ages and heights were 

measured on a subset of counted seedlings, usually one to two seedlings per sizeclass per seedling plot. Ages were measured by counting whorls on spruce and bud 

scars on hemlock, or by cutting a disc from the base of the seedling stem. Growth 

rings were counted in the laboratory with a stereo-microscope.
6

Research paper pnw-rp-585

Data Analysis

All statistical analyses were performed with SAS (1996). Seedling density was 

analyzed for each site separately to determine between-site variation. Because the 

data had a Poisson distribution with overdispersion, we used the drop-in-deviance 

test in a generalized linear model analysis for the individual site analysis of current 

seedling-bank density (McCullagh and Nelder 1989). 

For the 15 sites harvested between 1900 and 1958, seedling density data from 

cut and uncut plots were pooled for density calculations after analysis of variance 

(ANOVA) of the sites showed that cutting treatment had no significant impact on 

seedling bank densities for either species (hemlock p = 0.68, spruce p = 0.28). That 

is to say, from the perspective of the current seedling bank, as defined in this study, 

the canopies of the unharvested control plots and the harvested treatment plots 

were closed and thus essentially identical in understory conditions. By contrast, 

in the two recently harvested sites at Granite and Thomas Bay (cut in 1983 and 

1984, respectively), tree canopy closure had not yet occurred. Therefore, seedling 

size-class distribution was calculated separately for the cut and uncut plots to obtain 

information on the early growth rates of new trees under open canopy. Seedling 

density per hectare was calculated by using predicted values from the individual 

site regression analysis.

Seedling bank density was analyzed for response to seedbed (log or forest 

floor), treatment (cut or uncut 0.2-ha plot) and shrub cover (measured at each 

seedling plot). Sites were analyzed separately using generalized linear models to 

determine response variability among sites. When the 17 sites were combined 

to determine the regional response of seedlings to these variables, ANOVA was 

used because of the increase in sample size (n = 17). A square root transformation 

was done to normalize the distribution of means (mean number of seedlings per 

seedbed). Predicted values (95 percent confidence interval) were calculated for each 

seedbed in cut and uncut plots. On sites where shrub cover was present, representative values of 25 percent cover and 75 percent cover were used in the analysis 

because estimates of cover clustered around these values.

Size-class distribution was determined by calculating the number of seedlings 

in each size class and the proportion of seedlings found between 0.5 and 3 m tall. 

Size-class distribution was calculated by using predicted values from the site-bysite regression analysis and was analyzed for each site separately and then combined. Age-class distribution was determined by calculating the ages of sampled 

seedlings for each height class.
7

Density and Distribution of Sitka Spruce and Western Hemlock Seedling Banks in Partially Harvested Stands in Southeast Alaska

Results

Our most important results are as follows:

• Spruce and hemlock seedling banks are generously stocked.

• There are more spruce and hemlock seedlings on logs than on the forest floor.

• A higher percentage of understory vegetation cover results in a lower density 

of spruce and hemlock seedlings.

• Seedling bank density declines dramatically after seedlings reach 25 cm 

in height; however, some spruce and hemlock up to 3 m tall persist in the 

understory.

Seedling Density

Seedling density for both Sitka spruce and western hemlock was high and differed 

widely among sites, and there were always fewer spruce than hemlock seedlings 

(table 3). Mean spruce seedling density ranged from 3,000 to 46,000 seedlings/

ha, on 15 of 17 sites, with the lowest and greatest mean density found at Margaret 

Bay and Big Bear Creek (0 and 114,000/ha, respectively). Mean hemlock seedling 

density at all sites was extremely high, ranging between 47,000/ha and 419,000/

ha, on 15 of 17 sites; two sites averaged more than 700,000/ha. Although hemlock 

seedlings at Margaret Bay were plentiful (47,000/ha) this site had the lowest seedling density for hemlock as well as for spruce.

Table 3—Seedling density size class data for hemlock and spruce seedlings at 17 sites in southeast Alaska 

Spruce	 Hemlock

Site	 Density	 Seedlings 0.5 to 3.0 m	 Density	 Seedlings 0.5 to 3.0 m

Thousand seedlings/ha Percent Thousand seedlings/ha Percent 

Big Bear Creek 114 (43–299) 5 171 (92–317) 5

Canoe Passage 8 (4–17) 8 707 (170–2,930) 2

Elf Point 9 (2–41) 7 113 (101–322) 4

Finger Creek 36 (15–86) 0 181 (101–322) 3

Florence Bay 7 (4–14) 8 92 (52–163) 3

Glass Peninsula 46 (20–108) 2 67 (32–139) 0

Granite 33 (17–64) 19 163 (88–300) 17

Hanus Bay 15 (9–27) 0 273 (151–494) 0

Kutlaku Lake 4 (1–11) 0 67 (23–191) 9

Margarita Bay 0 (0) 0 47 (21–107) 13

Portage Bay 3 (1–9) 0 88 (52–147) 5

Rainbow Falls 13 (6–26) 0 320 (162–632) 2

Salt Lake Bay 23 (15–36) 5 59 (35–100) 0

Sarkar 15 (8–26) 0 419 (268–656) 1

Thomas Bay 24 (14–41) 3 723 (398–1,315) 25

Weasel Cove 6 (2–20) 15 159 (80–314) 9

Winter Harbor 13 (6–31) 149 (100–223) 3

Note: Values are means with range in parentheses.

Spruce and hemlock 

seedling banks are 

generously stocked.
8

Research paper pnw-rp-585

Size- and Age-Class Distribution

Size-class distribution of the conifer seedling banks roughly followed an “inverse-j” 

curve (fig. 2). The overwhelming majority of spruce (95 percent) and hemlock (94 

percent) seedlings were ≤0.5 m tall. The proportion of the total seedlings taller than 

0.5 m was less than 10 percent for all but two sites for spruce and three sites for 

hemlock (table 3).

The mean age was 19 years (range 1 to 110 years) for hemlock seedlings 

(n = 350) and 8 years (range 1 to 41 years) for spruce seedlings (n = 140) (table 4). 

In the three smallest size classes (0 to < 0.5 m), the age range was about the same 

for both species (1 to 19 years for spruce and 1 to 15 years for hemlock). In the 

larger size classes, between 0.5 m and 3.0 m, however, the age ranges in each size 

class were more variable in general, especially for hemlock. For example, ages of 

western hemlock in size class 6 ranged from 14 to 110 years, whereas ages for 

Sitka spruce ranged from 8 to 31 years (table 4).

Seedling Bank Microsites

The combined data set (all 17 sites) showed no significant difference in seedling 

density between the cut and uncut plots for either species. Seedbed was the only 

variable that affected hemlock and spruce seedling density (ANOVA, hemlock 

F = 15.23 p = 0.0001, spruce F = 3.49 p = 0.05). Seedlings of both species occurred 

four times as often on logs as on the forest floor. Although consistently more 

seedlings occurred on logs than on the forest floor, no pattern emerged for either 

species when seedling density was compared to percentage of log cover per hectare 

of forest. At a given percentage of log cover, seedling density for both species ranged 

widely. For example, at three sites with an average log cover of 2150 m2

/ha, average 

spruce density ranged from 4,000 to 15,000 seedlings/ha and hemlock density 

ranged from 67,000 to 419,000 seedlings/ha.

Table 4—Average age of Sitka spruce and western hemlock seedlings in eight 

size classes in southeast Alaska

Spruce	 Hemlock

Height size class	 Mean, SE (n)	 Min.	 Max.	 Mean, SE (n)	 Min.	 Max.

1 (0 < 5 cm) 4 ± 0.2 (61) 1 10 4 ± 0.2 (60) 1 10

2 (5 < 25 cm) 7 ± 0.3 (48) 4 15 7 ± 0.2 (112) 3 14

3 (25 < 50 cm) 13 ± 1.1 (15) 6 19 10 ± 0.9 (11) 6 15

4 (50 < 100 cm) 17 ± 1.4 (20) 6 32 18 ± 1.2 (66) 5 48

5 (1.0 < 1.5 m) 21 ± 2.3 (15) 7 33 34 ± 3.4 (38) 7 95

6 (1.5 < 2.0 m) 22 ± 4.4 (5) 8 31 40 ± 3.5 (37) 14 110

7 (2.0 < 2.5 m) 19 ± 0.9 (3) 18 21 41 ± 5.3 (22) 14 99

8 (2.5 ≤ 3.0 m) 35 ± 6.0 (2) 29 41 50 ± 7.0 (11) 30 99

SE = Standard error.
9

Density and Distribution of Sitka Spruce and Western Hemlock Seedling Banks in Partially Harvested Stands in Southeast Alaska

Figure 2—Size-class distribution and standard error of western hemlock (TSHE) and Sitka spruce (PISI) seedlings at six selectively 

harvested sites in southeast Alaska. The year below the site name is the cutting date and sites are arranged from oldest to most recently 

cut. These sites represent the range of size-class distributions found in this study. The eight size classes are defined as follows: 0 to 

<5 cm, 5 to <25 cm, 25 to <50 cm, 50 to <100 cm, 1.0 to <1.5 m, 1.5 to <2.0 m, 2.0 to <2.5 m, and 2.5 to <3.0 m.

Glass Peninsula

1911

Size class

1 2 3 4 5 6 7 8

Seedlings (thousands)

0

10

20

30

40

50

60

Kutlaku Lake

1920

Size class

1 2 3 4 5 6 7 8

Size class

1 2 3 4 5 6 7 8

Size class

1 2 3 4 5 6 7 8

Size class

1 2 3 4 5 6 7 8

Seedlings (thousands)

0

10

20

30

40

50

PISI 

TSHE 

Rainbow Falls

1942

PISI 

TSHE 

Margaret Bay

1958

PISI 

TSHE 

Big Bear Creek 

1958

PISI 

TSHE 

Size class

1 2 3 4 5 6 7 8

PISI 

TSHE 

Seedlings (thousands)

0

10

20

30

40

50

200

300

400

Seedlings (thousands)

0

10

20

100

200

Seedlings (thousands)

0

10

20

30

40

50

Seedlings (thousands)

0

10

20

30

40

50

100

150

Granite

1983

PISI 

TSHE 
10

Research paper pnw-rp-585

The most common variable affecting seedling densities was seedbed, but 

treatment and shrub cover were also significant at some sites (table 5). The 

significance of these three variables differed between both species and sites. 

Seedbed alone was significant at 3 of the 7 sites for spruce and at 7 of the 10 

sites for hemlock, but at sites where treatment or shrub cover was significant, 

another variable was almost always also significant.

Table 5—Significance of seedbed, treatment, and shrub cover on spruce 

and hemlock seedling density at 17 sites in southeast Alaska 

Site	 Seedbeda	 Treatmentb	 Shrub coverc

Big Bear Creek Spruce ** **

Hemlock **

Canoe Passage Spruce

Hemlock

Elf Point Spruce * * *

Hemlock *

Finger Creek Spruce ** *

Hemlock *

Florence Bay Spruce

Hemlock

Glass Peninsula Spruce **  

Hemlock **  ** **

Granite Spruce *

Hemlock **

Hanus Bay Spruce **

Hemlock ** * *

Kutlaku Lake Spruce *

Hemlock *

Margarita Bay Spruce

Hemlock **

Portage Bay Spruce

Hemlock **

Rainbow Falls Spruce **

Hemlock ** **

Salt Lake Bay Spruce *

Hemlock

Sarkar Spruce

Hemlock

Thomas Bay Spruce

Hemlock * ** **

Weasel Cove Spruce

Hemlock **

Winter Harbor Spruce

Hemlock *

* Indicates p ≤ 0.05, ** indicates p ≤ 0.01, sites with no asterisk are where none of the variables 

significantly influenced seedling density.

a

 Seedbed = log or undisturbed forest floor.

b

 Treatment = cut or uncut.

c

 Shrub cover = percentage shrub cover.
11

Density and Distribution of Sitka Spruce and Western Hemlock Seedling Banks in Partially Harvested Stands in Southeast Alaska

At four sites for each species, treatment, combined with either or both seedbed 

and shrub cover, had a significant effect on seedling densities. At one of these four 

sites, Glass Peninsula, all three variables (seedbed, treatment, and shrub cover) were 

significant for both species. At one site, Finger Creek, treatment was the only significant variable affecting hemlock seedling density.

Analysis of each site showed shrub cover, combined with either or both seedbed 

or treatment, significantly affected seedling density for spruce at two sites and for 

hemlock at four sites. At Glass Peninsula, all three variables were significant for both 

species (46,000 spruce and 67,000 hemlock seedlings/ha). At two sites for spruce 

(15,000 seedlings/ha at Hanus Bay and 13,000 seedlings/ha at Rainbow Falls) and 

one site for hemlock (149,000 seedlings/ha at Winter Harbor) shrub cover was the 

only variable significantly affecting seedling density (table 5).

High levels of shrub cover were associated with decreased seedling density. For 

example, at Hanus Bay, the seedling density model predicted seedling density ranging 

from 2,000 to 11,000 seedlings/ha for spruce and from 36,000 to 130,000 seedlings/ha 

for hemlock (seedlings under 75 percent or 25 percent shrub cover). 

An example of the variability in seedling density at each site is illustrated here for 

Elf Point (table 6). At this site, seedbed was the only significant variable for hemlock. 

There were 9.5 times as many hemlock seedlings on logs (200,000 seedlings/ha) than 

on undisturbed forest floor (21,000 seedlings/ha). All three variables were significant 

for spruce at this site. Spruce density ranged between 3,000 seedlings/ha under 75 percent shrub cover on undisturbed forest floor in the uncut plot to 12 million seedlings/ha 

under 25 percent shrub cover in the cut plots. At eight sites for spruce and four sites for 

hemlock, there were no significant variables explaining seedling densities. These sites 

(table 5) were located throughout the study area. 

Table 6—Seedling density for specific microsite conditions, harvest treatment, and shrub 

cover, at the Elf Point installationa

 

Hemlock	 Spruce

Conditionsb	 Density (95% CI)	 Conditions	 Density (95% CI)

Thousand seedlings/ha Thousand seedlings/ha

Forest floor 21,000 (2,000–200,000) Forest floor / cut / 75% 60 (0–11,000)

Forest floor / cut / 25% 800 (10–62,000)

Forest floor / uncut / 75% 3 (0–4,000)

Forest floor / uncut / 25% 50 (0–22,000)

Log 200,000 (10,000–420,000) Log / cut / 75% 900 (40–21,000)

Log / cut / 25% 12,000 (3,000–49,000)

Log / uncut / 75% 50 (0–10,000)

Log / uncut / 25% 700 (8–53,000)

a

 This site was chosen to represent the variability in seedling density under different conditions.

b

 Microsite conditions are forest floor and logs; harvest treatments are cut or uncut; 75 percent and 25 percent refer to percentage 

cover of understory vegetation.
12

Research paper pnw-rp-585

Seedling Growth Rates

Growth rates were uniformly low for spruce and hemlock seedlings in multiaged, 

closed-canopy stands (“All sites,” table 7). These stands were harvested between 

38 and 96 years prior to being surveyed for this study, and crown expansion had 

closed the canopy. In these closed-canopy stands, both species grew faster on logs 

than on undisturbed forest floor, and hemlock grew slightly faster than spruce. 

Hemlock seedlings in the understory of closed-canopy stands maintained a growth 

rate comparable to spruce seedlings in size classes between 0 and 0.25 m (table 4); 

however, height growth slowed down in taller size classes.

Owing to recent logging, crown closure at two of our study sites (Thomas Bay 

and Granite) had not yet occurred at the time of our survey; thus they were removed 

from the “All sites” analysis and assessed separately. At Thomas Bay, seedlings of 

both species on all seedbeds grew faster (min. annual growth rate 2.7 cm for spruce 

seedlings on logs) than seedlings in closed-canopy stands (max. annual growth rate 

1.7 cm for hemlock seedlings on undisturbed forest floor and spruce seedlings on 

Table 7—Age, height, and annual height growth for spruce and hemlock seedlings ≤ 3 m tall 

and ≤20 years old, on logs, undisturbed forest floor, and skid trails, in southeast Alaska

Log	 Forest floor	 Skid trail

	 	 Mean	 SE	 n	 Mean	 SE	 n	 Mean	 SE	 n

All sitesa

Hemlock

Age (yr) 8.0 0.40 134 7.4 0.50 56 — — —

Height (cm) 26.4 2.90 137 15.5 2.80 56

Height growth (cm/yr) 2.3 0.20 132 1.7 0.20 56 — — —

Spruce

Age (yr) 7.0 0.60 76 3.8 0.40 27 — — —

Height (cm) 15.7 3.70 74 3.8 0.38 27

Height growth (cm/yr) 1.7 0.20 74 1.2 0.20 27 — — —

Thomas Bayb

Hemlock

Age (yr) 8.5 1.30 19 8.2 0.90 10 7.2 0.35 11

Height (cm) 40.7 9.90 19 70.7 13.40 10 51.5 13.30 11

Height growth (cm/yr) 4.1 0.57 19 8.2 1.40 10 7.0 1.80 11

Spruce

Age (yr) 8.1 1.00 12 8.2 1.10 6 6.3 0.92 6

Height (cm) 23.8 5.60 12 46 14.60 6 77.8 25.10 6

Height growth (cm/yr) 2.7 0.42 12 5.0 1.00 6 10.2 3.10 6

a

 Values under “All sites” were calculated from data collected at 15 sites partially logged between 1900 and 1958. These sites 

were multiaged, closed-canopy stands.

b

 Thomas Bay was partially harvested in 1984 and was used as a comparison to the 15 multiaged, closed-canopy sites.

Growth rates were 

uniformly low for 

spruce and hemlock 

seedlings in multiaged, 

closed-canopy stands.
13

Density and Distribution of Sitka Spruce and Western Hemlock Seedling Banks in Partially Harvested Stands in Southeast Alaska

Table 8—Percentage of spruce and hemlock seedlings 

between 0.5 and 3 m, and percentage shrub cover at 

17 sites in southeast Alaska

Seedlings 0.5–3.0 m	 Average

Site	 Spruce	 Hemlock	 shrub cover

Percent

Finger Creek 0 3 8

Portage Bay 0 5 13

Kutlaku Lake 0 9 16

Winter Harbor 0 3 21

Sarkar 0 1 24

Glass Peninsula 2 0 25

Hanus Bay 0 0 28

Weasel Cove 15 9 28

Elf Point 7 4 33

Florence Bay 8 3 33

Thomas Bay 3 25 35

Rainbow Falls 0 2 36

Canoe Pasage 8 2 41

Big Bear Creek 5 5 46

Margarita Bay 0 13 47

Granite 19 17 58

Salt Lake Bay 5 0 62

logs) (table 7). Mean annual growth on undisturbed forest floor (8.2 cm for hemlock 

and 5.0 cm for spruce) was almost twice that on logs (4.1 cm for hemlock and 2.7 

cm for spruce) for both species. However, the fastest average annual growth rate 

found in this study was for spruce seedlings on disturbed soil (10.2 cm).

Sites at which we found the tallest seedlings (where more than 10 percent were 

taller than 0.5 m), had, in some cases, a higher percentage of shrub cover than sites 

with no seedlings taller than 0.5 m (table 8). At seven sites there were more spruce 

than hemlock between 0.5 m and 3.0 m. The average shrub cover at those seven 

sites was 40 percent, compared to 27 percent at the other 10 sites. At 8 of the 10 

sites with 27 percent average shrub cover, there were no spruce seedlings taller 

than 0.5 m. 

Discussion

Seedling Density

Both spruce and hemlock seedling banks were very dense, even overstocked by 

management standards, and compare favorably with naturally regenerated clearcuts 

in the same region (U.S. Forest Service regeneration survey data on file at Forestry 

Sciences Laboratory, Juneau, Alaska). The one exception was at Margarita Bay 
14

Research paper pnw-rp-585

where there were no spruce seedlings in any of the four treatment plots (one uncut 

and three cut), although overstory, cone-producing spruce trees were present in all 

four plots. Hemlock seedling density at this site was also the lowest in our study 

(table 3).

Margarita Bay was logged about 40 years earlier, and on the cut plots, there 

was a dense second canopy layer of hemlock and spruce, but no ground vegetation 

(including no seedling bank) beneath the seed trees. This site was a heavily cut, 

hemlock-dominated stand and is currently densely stocked. In contrast, the uncut 

plot had a multilayered vertical structure including thick understory vegetation. 

With time, we expect that there will be canopy openings in the cut plots from 

windthrow or timber harvest and that a spruce-hemlock seedling bank will develop.

It is unclear why seedling density differed so much among sites. Seed source 

and overstory species composition do not explain the variation. For example, Big 

Bear Creek (114,000 spruce seedlings/ha [table 3] and 15–47 percent current spruce 

basal area [table 2]) had 2.5 times the spruce density of Glass Peninsula (46,000 

spruce seedlings/ha [table 3] and 11–34 percent current spruce basal area [table 2]). 

Thomas Bay and Granite, harvested in 1984 and 1983, respectively, had the lowest 

spruce basal area of any of the sites (table 2), while also having some of the highest 

spruce seedling densities (table 3). These two sites still exhibited characteristics of 

recently harvested stands, open canopy and disturbed mineral soil from skid trails, 

which may explain why the spruce seedling density was so high relative to the 

number of spruce seed trees in the overstory.

Size- and Age-Class Distribution

The “inverse-j” curve distribution of both spruce and hemlock seedling banks 

is typical of tree seedling population dynamics in all-aged (uneven-aged) forests 

(Smith 1986). It was not surprising that hemlock seedlings should persist in the 

understory of these closed-canopy stands, as hemlock is shade tolerant, and its 

persistence in the understory for more than 100 years is not uncommon (Packee 

1990). Sitka spruce is considered moderately tolerant to tolerant of shade (Harris 

1990, Minore 1972), and our study documented that spruce can persist as long as 

30 years and even up to 41 years of age. 

Ott (1997) reported that spruce’s ability to maintain itself in mature stands was 

substantially less than that of hemlock. For example, Ott (1997) found that although 

western hemlock seedlings (< 2.5 cm d.b.h.) occurred on 46 to 92.3 percent of his 

understory vegetation plots at each of three study sites, Sitka spruce seedlings 

only occurred on 2 to 21 percent of understory vegetation plots. By comparison, 

we found many spruce seedlings at our sites although most of them were < 0.5 m 

Sitka spruce is considered moderately 

tolerant to tolerant of 

shade, and our study 

documented that 

spruce can persist 

as long as 30 years 

and even up to 41 

years of age.
15

Density and Distribution of Sitka Spruce and Western Hemlock Seedling Banks in Partially Harvested Stands in Southeast Alaska

tall. Little information is available on the growth of advance regeneration spruce. 

However, Ott (1997) documented that mean and median heights for both western 

hemlock and Sitka spruce were greater in gaps than under closed-canopy forest. 

Our results are similar to his.

Seedling Bank Microsites

Seedlings of both species can occur on a range of microsites, although it appears 

that logs are microsites that favor seedling establishment (Christy and Mack 1984, 

Deal et al. 1991, Harmon and Franklin 1989, McKee et al. 1982, this study). It is not 

clear why this is so. The more frequent occurrence of spruce and hemlock seedlings 

on woody seedbeds in naturally regenerated, uneven-aged stands may be related 

to high precipitation and shallow soils. Harmon and Franklin (1989) suggested that 

elevated sites afford freedom from competition from shrubs such as salmonberry 

(Rubus spectabilis (Prush)) and layers of shorter vegetation.

In the coastal forests of southeast Alaska, light is considered the primary 

factor affecting survival and growth of understory vegetation, as precipitation is 

abundant throughout the growing season and temperatures are moderate (Ruth 

and Harris 1979). Previous studies show that establishment of shrub seedlings in 

the forests was strongly related to photosynthetically active radiation at the forest 

floor (Tappeiner and Alaback 1989) as was the growth of hemlock, spruce, and 

Vaccinium seedlings in and adjacent to windthrow gaps (Alaback and Tappeiner 

1991).

Although seedling bank density is greater on logs, high densities of both species occur on other substrates as well. For example, at our sites we found an average 

of 20,000 western hemlock and 2,000 Sitka spruce seedlings/ha on forest floor. 

In recently harvested stands, spruce clearly regenerates well on heavily disturbed 

areas such as skid trails where mineral soil was exposed (Deal et al. 1991, Harris 

1990, Ruth and Harris 1979, Yount 1997). Windthrow mounds and pits, disturbed 

soil from the root systems of windthrown trees, are another source of exposed 

mineral soil, yet we rarely observed either spruce or hemlock seedlings more than 

a few years old growing in the mineral soil of mounds and pits. Perhaps there is 

a functional difference, such as soil movement in pits and mounds, between the 

exposed mineral soil from windthrow and from logging.

It appears that growing conditions in the understory become limiting after 

seedlings become 25 to 50 cm tall. There were high densities of seedlings in size 

classes one and two (0 to 25 cm), but the height distribution decreased rather 

abruptly after these size classes (fig. 2, table 3). Ages at these size classes were quite 

variable, ranging from 7 to 95 years for hemlock class 5 and 7 to 33 years for Sitka 
16

Research paper pnw-rp-585

spruce class 5. Thus, it appears from the size class distributions (fig. 2), taller and 

older seedlings that die are replaced as new seedlings are continually established.

Seedling Growth Rates

At Thomas Bay, harvested 1984, both conifer species clearly responded to 

postharvest stand conditions with increased seedling growth rates, compared to 

seedlings of similar age in closed-canopy stands on either logs or undisturbed soil. 

Suppressed hemlock 50 to 60 years old commonly develop into vigorously growing 

trees after release, although ability to respond decreases after age 100 (Packee 

1990). Deal (1999) found advance regeneration spruce grew rapidly and slightly 

better than hemlock after partial cutting. If the advance regeneration at these 

closed-canopy sites can respond to increased light made available by windthrow 

or harvest, they should be in a good position to occupy the new growing space.

Management Implications

Seedlings and saplings in the understory do not grow as rapidly as seedlings in 

clearcuts. What is important, however, is their potential for growth after overstory 

density is reduced. These seedlings and saplings should not be expected to grow 

at the maximum rates that are seen after clearcuts, but rather to maintain their 

potential for growth should they be released. More work is needed to determine the 

response of advance regeneration to release from competition with overstory trees.

Advance regeneration left after cutting grew rapidly and was a significant and 

dominant component of the current stand (Deal and Tappeiner 2002). Most of the 

current stand structure and growth came from residual trees and little growth was 

seen for newly established trees (Alaback and Tappeiner 1991). Thus, the existence 

of a seedling bank in the partially cut stands provides a new cohort of trees that 

could easily release and grow following another cutting or disturbance event. This 

would suggest that partial cutting in this forest type is a sustainable silvicultural 

system that could maintain current tree species composition and structure on a 

long-term basis.

Concern about the effects of clearcut harvesting on forest ecosystems in southeast Alaska and throughout the Pacific Northwest (Gray and Spies 1997) has led to 

discussion of alternative methods such as partial cutting or uneven-age management 

for regeneration during timber management. With a shift in forest land management to include biodiversity of forest ecosystems, other methods of harvesting and 

regenerating these stands need to be examined. 

 Deal (1999) found 

advance regeneration 

spruce grew rapidly 

and slightly better 

than hemlock after 

partial cutting.
17

Density and Distribution of Sitka Spruce and Western Hemlock Seedling Banks in Partially Harvested Stands in Southeast Alaska

This study indicates that partial cutting could be implemented as part of a new 

silvicultural system in southeast Alaska. By leaving spruce seed-trees, disturbing 

soil judiciously, planning entries to regulate overstory density to promote seedling 

establishment, and possibly planting spruce seedlings where the seed source is poor, 

we believe sizable new cohorts of spruce can also be regenerated in these systems 

while maintaining the attributes of uneven-aged stands. 

Acknowledgments

This project is a contribution from the USDA Forest Service study “Alternatives 

to Clearcutting in the Old-Growth Forests of Southeast Alaska,” a joint effort of 

the Pacific Northwest Research Station, the Alaska Region, the Tongass National 

Forest, and Oregon State University College of Forestry. We thank field crew and 

research associates Patricia Palkovic, Ellen Anderson, and David Bassett. 

English Equivalents

If you know: Multiply by: To find:

Centimeters (cm) .394 Inches

Meters (m) 3.28 Feet

Square meters (m2

) 10.76 Square feet

Hectares (ha) 2.47 Acres

Square meters per hectare (m2/ ha) 4.37 Square feet per acre

Degrees Celsius (°C) 1.8 °C + 32 Degrees Fahrenheit

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