QK 477.2 .FS C38 1990

EFFECT OF VEGETATION COMPETITION ON TREE SEEDUNG

ESTABUSHMENT AND GROWTH IN AN UPLAND, POST-FIRE

SUCCESSION IN INTERIOR AlASKA

A

THESIS

Presented to the Faculty

of the University of Alaska Fairbanks

in Partial Fulfillment of the Requirements

for the Degree of

MASTER OF SCIENCE

By

Timothy Carl Cater, B.S.

Fairbanks, Alaska

December 1990

EFFECT OF VEGETATION COMPETITION ON TREE SEEDUNG

ESTABLISHMENT AND GROWTH IN AN UPLAND, POST-FIRE

SUCCESSION IN INTERIOR ALASKA

A

THESIS

Presented to the Faculty

of the University of Alaska Fairbanks

in Partial Fulfillment of the Requirements

for the Degree of

MASTER OF SCIENCE

By

Timothy Carl Cater, B.S.

Fairbanks, Alaska

December 1990

ARLIS Alaska Resources Librarv & Information Services

Library Building. Suite 111 3211 Providence Drive

Anchorage, AK 99508·4614

_, .. . •'' '' .... ..__ • - ••••. 1. -·· ~ ~'··· -· .· ~ ·- ·-' -- .. -~ - ~-~-. -----.... ---·~ .. ....._.. __ . __ .. ~ .. _ ............. __ _..,...,....,_,,....,,.,......--~---=--~----~--.. ----·-· .. -----

r. '·· -~ ~ r: .1 :1 r .. 1 Ul..l - 0 b~i

EFFECT OF VEGETATION COMPETITION ON TREE SEEDLING

ESTABLISHMENT AND GROWTH IN AN UPLAND, POST-FIRE

SUCCESSION IN INTERIOR ALASKA

By

Timothy Carl Cater

RECOMMENDED:

Department Head

APPROVED: .£Sf?~~

tc&!tl9tJ

ABSTRACT

Location and density of naturally occurring Picea glauca seedlings were

measured five years following fire to document natural establishment patterns.

To estimate effects of competition on these patterns, _E. glauca and Betula

papyrifera were sown as seeds and transplanted as seedlings into distinct patches

of vegetation where either Equisetum arvense, Calamagrostis canadensis, or

Populus tremuloides was dominant (>90% cover). Naturally occurring P. glauca

seedlings preferentially established where E. arvense was dominant. Similarly, _E.

glauca and B. papvrifera establishment and growth were greater in E. arvense

patches and clipped plots. Thus, colonizing species inhibit establishment of late-

successional species, with E. arvense being a weaker competitor than C.

canadensis and _E. tremuloides. Accumulated above and below-ground biomass

were not good indicators of competitive ability. Environmental differences

between patch types were positively correlated with the bioassay results: C.

canadensis patches had thicker organic mats and cooler and wetter soils than

other patch types.

11l

TABLE OF CONTENTS

PAGE

Abstract ...................................................................................................... .iii

Table of Contents ..................................................................................... .iv

List of Figures .......................................................................................... vi

List of Tables .......................................................................................... viii

Acknowledgments ..................................................................................... ix

Introduction ................................................................................................ 1

Methods ....................................................................................................... 4

Study Area ...................................................................................... 4

Experimental Design ...................................................................... 5

Seed Sowing Experiment. ................................................. 6

Transplant Experiment ...................................................... S

Biotic and Abiotic Site V ariables .................................... 9

Transects ............................................................................ 10

Statis~ical Analyses ....................................................................... 11

Results ......................................................................................................... 13

Seed Sowing Experiment .............................................................. 13

Germination ........................................................................ 13

Survivorship ......................................................................... 13

Growth .................................................................................. 17

Transplant Experiment ................................................................. 20

IV

v

PAGE

Biotic Site Variables .................................................................... 24

Abiotic Site Variables ................................................................ 24

Transects ....................................................................................... 29

Discussion .................................................................................................. 31

Seedling Establishment and Early Growth .............................. 31

Abiotic Site Variables ................................................................. 33

Equivalence of Competitors ....................................................... 34

Indicators of Competitive Ability .............................................. 35

Conclusions ................................................................................................... 3 6

Management Implications ............................................................. 36

Suggestions for Future Work. ....................................................... 37

Literature Cited .......................................................................................... 38

LIST OF FIGURES

PAGE

Figure 1. Seedling germination (maximum number observed/total 14

seeds sown) and survivorship after two years (number

survivors/maximum number germinated) from sown seeds

of spruce and birch in seedbeds.

'

Figure 2. Seedling germination and survivorship after two years from 15

sown seeds of spruce and birch in seedbeds.

Figure 3. Growth parameters for spruce seedlings from sown seeds 18

in clipped and control treatments in three patch types.

Figure 4. Growth parameters for spruce seedlings from sown seeds 19

in clipped and control treatments in three patch types.

Figure 5. 1989 diameter growth and 1988 and 1989 height growth for 21

spruce seedlings transplanted into clipped treatments in

three patch types.

Figure 6. 1989 growth parameters for birch seedlings transplanted 22

into clipped treatments in three patch types.

Figure 7. Relative growth rate (In (total dry mass) - In (total - 23

current growth) for birch seedlings transplanted into

clipped treatments in three patch types.

vi

Vll

Figure 8. Above and below-ground biomass in mid-August 1989 in 25

three patch types.

Figure 9. 1989 seasonal and daily patterns of soil temperature at a 26

10 em depth in three patch types.

Figure 10. 1989 seasonal pattern of soil temperature at a 10 em depth 27

in clipped and unclipped treatments in three patch types.

Figure 11. a-c) 1989 seasonal pattern of soil moisture in organic and 28

mineral (top 5 em) soil layers and organic mat depth in

three patch types.

Figure 12. 1989 distribution of naturally occurring white spruce 30

seedlings > 1 yr old in a 2520 m2 area upslope from

experiment.

LIST OF TABLES

PAGE

Table 1. Probability values (from F-tests) from all ANOV As performed 16 (FER=.OS).

viii

ACKNOWLEDGEMENTS

I wish to acknowledge my advisor, Terry Chapin, who provided

guidance and assistance with all aspects of this work and was a constant role

model. I thank my other committee members, Keith Van Cleve and Les Viereck,

for a great deal of advice and careful editing. I also thank Joe Stehlik from the

Alaska State Forest Nursery for providing the white spruce seeds and the

transplant seedlings used in the bioassay experiments. The Institute of Arctic

Biology provided logistical support. All of the staff and faculty of the Institute of

Arctic Biology provided a superior place to work and study. I am indebted to my

fellow graduate students who provided unending help and moral support with the

multitude of tasks involved with completing a thesis. Lastly, I thank my

compatriot, Elizabeth Stockmar, for providing field assistance, as well as guidance

and support with life in general.

IX

IN1RODUCTION

In Alaskan post-fire succession, little is known about the role that

competition from colonizing species has in governing establishment and early

growth of late-successional tree species. Previous studies of taiga succession have

emphasized plant responses to successional changes in the physical environment

(e.g. light, moisture, nutrients; Van Cleve and Viereck 1983, Van Cleve et al.

1983, Van Cleve and Yarie 1986). However, competition was important in

determining seedling establishment and growth in primary succession on an

interior Alaskan flood plain (Walker and Chapin 1986). Similarly, studies in

other forest successions have shown that competition is an important control over

tree seedling establishment (Wilde et al. 1968, Webb et al. 1972, Niering and

Goodwin 1974, Harcombe 1977, Van Hulst 1979, Carter et al. 1984) as well as

influencing plant growth in general (Harper 1977, Connell 1983, Schoener 1983).

Understanding these competitive interactions is important because post-fire

succession is :common in Alaska. Before fire suppression (pre-1939), Barney

(1971) estimated that interior Alaskan forests (140,000,000 ha; Viereck 1973)

burned at the rate of 0.6 to 1.0 million hajyear. Following fire suppression

(1940-1970), approximately 400,000 hajyear burned while approximately 240,000

ha/year have burned between 1970-1980 (Viereck and Schandelmeier 1980).

Thus, the majority of interior Alaska has burned in the last 200-250 years (Barney

1971, Viereck 1973). Fires may recur as often as 50-110 years in white spruce

1

forests (Yarie 1981), with the majority of fires occurring on south-facing slopes

(Viereck 1973).

2

Competition was defined by Grime (1973) as "the tendency of neighboring

plants to utilize the same quantum of light, ion of a mineral nutrient, molecule of

water, or volume of space." Thus, competitive interactions, or inhibition, arise

from resource pre-emption (Werner 1976, Grace 1987) and result in a reduced

resource availability (Tilman 1985).

Many competition studies use species that are morphologically similar or

have taxonomic relatedness in order to maximize the degree of niche overlap

(Goldberg and Werner 1983, Schoener 1983). However, all autotrophic plants use

essentially the same resources (Harper 1977, Chapin 1980). Thus, all co-occurring

plants can be potential competitors (Aarssen 1983, Agren and Fagerstrom 1984,

Shmida and Ellner 1984, Hubbell and Foster 1986, Goldberg 1987).

The three competitor species used in this study were chosen because (1)

they are prominent in post-fire succession and (2) they appeared to differ

strikingly in the extent to which they excluded white spruce (Picea glauca

[Moench] Voss) and paper birch (Betula papvrifera Marsh.), the future dominant

species of similar sites (Viereck 1973, Van Cleve and Viereck 1981). Also,

grasses have been shown to be important competitors during white spruce

regeneration (Stiell 1976, Gardner 1983), with bluestem (Calamagrostis

canadensis) being a particularly effective competitor (Waldron 1966, Eis 1981).

In early succession in taiga forests, distinct patches of vegetation

dominated by one species are present, a situation that is analogous to pair-wise

competition experimental designs. However, plants are probably responding to

diffuse competition (MacArthur 1972) from all species in a patch (Fowler 1981,

Goldberg and Werner 1983, Mitchley 1987). Thus, conclusions will be made

relative to patch types instead of single competitor species.

As in other competition studies, a field neighborhood experimental design

was used (Goldberg 1987) and competitor abundance manipulated. The

responses of spruce and birch to these altered environments were compared to

their behavior under natural, unmanipulated conditions (Connell 1983).

Conclusions from competition experiments were compared with natural patterns

of spruce seedling establishment to test the hypothesis that competitive"

interactions are important in controlling establishment and early growth of late-

successional tree species in a post-fire succession in Alaska.

3

METHODS

Study Area

The study was conducted from 1988-1989 in the Bonanza Creek

Experimental Forest near Fairbanks, Alaska (64°45'N, 148°20'W) as part of the

boreal forest Long-Term Ecological Research (LTER) program. The study site

(LTER site # UP1a) had burned five years prior to study (29 May-15 June 1983)

as part of a 3500 ha wildfire (Juday 1985). Located on a south-facing slope, the

site was previously occupied by a 170-year-old white spruce stand (Foote and

Viereck 1985). As documented for wildfire in Alaska by Viereck and

Schandelmeier (1980), the forest floor burned unevenly resulting in a patchy

mosaic of varying seedbed conditions. In general, the area was moderately

burned with interspersed patches of severe burn (Foote and Viereck 1985).

Severe burning can cause significant changes in the nutrient status and chemical

properties of the forest floor (Smith 1970, Dubreuil and Moore 1982, Dyrness et

al. 1989) and has been positively correlated with white spruce seedling growth on

an interior Alaskan floodplain (Wurtz 1988). Charcoal was present in humus

layers as observed for other white spruce stands in Manitoba (1955).

Zasada (1985) showed seed beds to be important to seedling establishment

in the Rosie Creek Fire area with most seedlings occurring on ash and/ or organic

seedbeds of 2.5 em or less and on organic seedbeds > 5 em deep when a good

seed source was available. White spruce seedlings were present in 1984 at 124-

766 seedlings/ha depending on burn severity (Foote and Viereck 1985) and

4

5

distance from seed source (Zasada 1985).

As in other descriptions of taiga succession (Van Cleve and Viereck 1981),

the study area had a shrub /herb layer dominated by horsetail (Equisetum arvense

L.), bluestem (Calamagrostis canadensis [Michx.] Beauv.), and quaking aspen

(Populus tremuloides Michx. (nomenclature of Hulten 1968, Viereck and Little

1986). Most of the plants present regenerated from underground organs the year

after the fire (Viereck and Foote 1985) leading to nearly pure patches of

bluestem and aspen 1-10m in diameter. These patches were separated by areas

of horsetail containing scattered individuals of fireweed (Epilobium angustifolium

L.), bluebells (Mertensia paniculata [Ait.] G. Don), raspberry (Rubus idaeus L.),

and wild rose (Rosa acicularis Lindl.). Ceratodon purpureus (Hedw.) Brid. and

Marchantia polymorpha L. were common. The shrub/herb stage usually lasts

approximately 25 yrs until deciduous trees become dominant, although white

spruce may be conspicuous in the understory. White spruce is usually dominant

after 100 yrs, often with a birch tree component (Van Cleve and Viereck 1981,

Van Cleve and Viereck 1983).

Experimental Design

A bioassay approach (Chapin et al. 1986) was used to determine the

influence of competition on spruce and birch. Three sets of 15 replicate patches

of vegetation were selected with each set of patches having one of three

competitor species (horsetail, bluestem, or aspen) as the dominant ( > 90%

vegetative cover) species. Each set of patches contains true replicates for

comparisons among patch types (Hurlbert 1984). However, caution should be

used in extrapolating these results to the entire Rosie Creek fire, or to fires in

general, since only one burned site was used.

6

Within each patch, a 4.1 m X 4.5 m plot was established. All above-

ground vegetation was removed (clipped treatment) in half of all 45 (3 patch

types X 15 replicates) plots. The adjacent half was the unclipped treatment. The

clipped treatment was maintained by removing all non-experimental vegetation

with hand clippers every 1-2 weeks during the 1988 and 1989 growing seasons.

Seedling survivorship and growth responses were recorded as functions of (1)

presence/absence of competing vegetation and (2) biomass per unit area of the

patch type. Since the dominant species of the patch types have different growth

forms, these two estimates may be better indicators of resource use than the

number or size of neighboring individuals (Goldberg 1987).

Seed Sowing Experiment

On 31 May-3 June 1988, six 20 em X 20 em seedplots were established in

both the clipped and unclipped halves of all ( 45) plots. Seedplots were at least

0.9 m from the plot boundaries with 10 em separating each seedplot (the

experimental unit in the analyses). I randomly assigned three treatments: (1)

control (unseeded), (2) no scarification, and (3) scarification with each treatment

containing two of the six seedplots. Control and no scarification seedplots were

left undisturbed, while scarified seedplots were scraped twice in perpendicular

directions with a 3-toothed trowel to create an organic and mineral soil seedbed.

7

One non-scarified and one scarified seedplot were randomly selected and

sown with 404 viable spruce seeds/plot (10,100 seeds/m2). The other non-

scarified and scarified seedplots received 140 viable birch seeds/plot (3500

seeds/m2). Sowing rates were based on field germination and survival rates of

Walker et al. (1986). Spruce seeds were collected adjacent to the burn area in

1983 and 1984 by the Alaska State Forest Nursery; birch seeds were collected in

1987 from an area 4 km north of the University of Alaska Fairbanks. Both sets

of seeds were cleaned and stored at -10°C until sown. Prior to sowing, laboratory

germination tests were conducted to obtain the proportion of viable seeds (spruce

80%, birch 95% ). Quantities sown were determined by weighing seeds and were

based on groups of 100 seeds (n=6; spruce: 3.2 X 10-3 g/seed ± 2.65 X 10-4,

birch: 2.93 X: 104 g/seed ± 5.81 X 10-5).

Germinants were counted at least monthly in 1988 and three times during

1989 on each seedplot. It was planned to subtract germinants from the adjacent,

control seedplots from the counts to allow for seedlings from natural seed rain,

but no naturally regenerating seedlings were found. The maximum number of

gerrninants counted for each seedplot on any one date during 1988 was used as a

measure of germination. On 8-10 August 1989, all live germinants in each

seedplot were harvested and counted. Above-ground stem height and root length

of ten randomly selected germinants were recorded (all were measured if fewer

than ten survived). Gerrninants were separated into roots, stems, and leaves,

dried at 70°C for at least 48 hr, and weighed.

Transplant Experiment

8

Spruce seedlings were grown for one year in a greenhouse at the Alaska

State Forest Nursery in Palmer, Alaska from seed collected in 1983 adjacent to

the burned area. They grew in a 1:1 soilless medium of Sphagnum peatmoss and

coarse vermiculite in 1000 cm3 cones and were watered as necessary with water

containing soluble fertilizer (NPK 9:45:15 for the first four weeks and NPK

20:20:20 afterwards). Natural light was supplemented (430 lux, 16 h photoperiod)

until the natural photoperiod exceeded 16 h. Greenhouse temperatures were

20±2°C.

In July 1987, seedlings were placed outside to harden off for winter

(watered with NPK 9:45:15). The following June, spruce seedlings were

transported to Fairbanks and acclimatized in the shade for ten days. Four

seedlings were transplanted (7-8 July) into both subplots (clipped and unclipped)

of all 45 plots. Birch seedlings were grown under the same conditions ( 440 cm3

cones) from locally collected seed sown in May 1988 and four seedlings were

transplanted (3-5 August) into both clipping treatments in 42 plots (15 horsetail,

14 bluestem, 14 aspen). Within each subplot, each seedling was located at least

0.9 m from the subplot's boundaries and the seed sowing experiment and was

separated by 25 em from other seedlings. Spruce seedlings that died after one

month (24%) were replaced. Extra birch seedlings were not available to replace

ones that died (29% ). Browsed seedlings were not included in the analyses.

9

For both species, stem diameter at 1 em and total height above ground

were measured in August 1988. In August 1989, all measurements were repeated,

and the birch seedlings harvested at ground level. Seedlings from each seedplot

were separated into 1988 stems and 1989 leaves and stems and all parts were

dried at 70°C for at least 72 hrs and weighed. Individual weights from a seedplot

were pooled for analyses.

Biotic and Abiotic Site Variables

On 17 August 1989, accumulated biomass in each patch type was

quantified by harvesting all above-ground biomass in a 0.25 m2 quadrat one meter

inside each unclipped subplot. Samples were oven-dried at 70°C until a constant

weight was reached. Also, below-ground biomass was estimated by collecting

three randomly located soil cores from both clipping treatments in 42 plots. Each

core contained the organic soil layer and the top 10 em of mineral soil (the

rooting depth of transplanted seedlings). Roots were separated using a 0.5 mm

mesh sieve, oven-dried at 70°C for at least 72 hrs and weighed. The three core

samples from each clipped plot were pooled for analyses.

Several abiotic variables were measured to document effects of removing

all above-ground biomass and to quantify environmental differences among patch

types. (1) Each time a plot was visited (at least every two weeks), soil

10

temperature at a ten em depth was measured in both clipping treatments with a

30 em long soil thermometer. (2) Soil characteristics were measured by sampling

the organic layer and the top 5 em of the mineral layer four times in 1989. Cores

were 10 em in diameter and were taken at least ten days after a rainfall. On each

date, organic layer depth, soil moisture (% dry mass after oven-drying organic

soils at 70°C and mineral soils at 110°C until a constant weight was reached), and

bulk density of each soil layer were calculated. (3) On 28 July 1989, total solar

radiation at ground level was measured within one hour of solar noon (1300;

AST) in the unclipped half of 15 experimental plots (five of each patch type)

using a Li-Cor (Li-185) radiometer.

Transects

To document natural patterns of spruce seedling establishment, thirty two-

meter-wide transects 90 m in length were established adjacent to each other

approximately 300 m upslope from the experimental plots. The transects

extended away from an unburned stand of mature, seed-producing white spruce

trees. In each transect, each spruce seedling older than one year was counted.

Both distance from seed source and the dominant species of competing vegetation

in the seedling's immediate vicinity (25 em radius) were recorded. Vegetative

cover estimates were visually made every ten meters in a one m2 quadrat.

Seedling densities in each patch type were standardized relative to the cover of

that patch type in the sampled area in order to make comparisons across species

11

(Neu et al. 1974). Most seedlings encountered established the year after the fire

under very different conditions from those present during this study. Primarily,

very little horsetail, bluestem, and aspen were present (Viereck and Foote 1985)

which is simulated by the clipping treatment.

Statistical Analyses

Germination and survivorship of seedlings from sown seed were analyzed

using model I 3-way analyses of variance (ANOVA; SYSTAT version 4, Wilkinson

1988). Data were transformed where necessary to meet the assumption of

homoscedasticity (P = .05, Bartlett's test; Zar 1984 ). Significance of the three

factors (patch type, clipping, and scarification) was tested using Bonferonni

adjusted probabilities (P=.05/7 = .007) to control the familywise error rate

(FER) at .05 (Wilkinson 1988, Day and Quinn 1989). To compare results

between spruce and birch, 4-way ANOV As were used with species as the fourth

factor (FER= .05).

For germination and spruce survivorship, when patch type significance was

detected (P < .007), differences between level means were tested using Tukey

multiple comparisons (Zar 1984, Day and Quinn 1989). For birch survivorship,

the Kruskal-Wallis test was used since data were rank-transformed (Conover and

Iman 1981, Zar 1984). Both tests had overall significance levels = .05.

If the clipping or scarification factors were significant, Dunnett's test was

used to make planned, pair-wise comparisons between level means within each

12

patch type (P = .05; Zar 1984, Day and Quinn 1989)

Growth data from both bioassay experiments were analyzed using Model I

3-way analysis of covariance (AN COY A; FER= .05) on data that were

transformed where necessary. Total number of surviving seedlings was used as a

covariate to account for intraspecific competition. I confirmed the assumption of

homogeneity of slopes between the covariate and each factor in the analyses

(patch type, clipping, scarification; Zar 1984, Wilkinson 1988). The covariate was

removed when not significant, and ANOVAs were performed using the same

multiple comparison procedures described for germination and survivorship. If

significant covariance was detected, the Bryant-Paulson generalization of Tukey's

method was used (significance level = .05) to compare adjusted level means

(Bryant and Paulson 1976, Neter et al. 1985, Day and Quinn 1989).

All other analyses were performed with Model I 2-way ANOV As

(FER= .05) using transformed data where necessary and the multiple comparison

tests described for germination and survivorship. If any of the Al'\l"OV A or

ANCOVA analyses showed no significance, no multiple comparisons were

performed unless visual inspection indicated a possible significant difference

between untransformed level means as suggested by Zar ( 1984) and Wilkinson

(1988).

RESULTS

Seed Sowing Experiment

Germination

Birch seeds germinated better than spruce seeds, especially in bluestem

patches (P .05) increase germination, while it

consistently did improve germination in horsetail and aspen (Fig. 2). Removal of

above-ground vegetation did not significantly affect germination (Fig. 2, Table 1).

Survivorship

Spruce survivorship was always greater than birch survivorship (P < .05) in

all three patch types (Fig. 1). Also, overall survivorship was significantly inhibited

(P < .05) in bluestem and aspen relative to horsetail. The positive effect that

scarification had on germination was not detected for survivorship after two years

(Table 1). Significantly increased survivorship (P < .05) due to clipping was seen

only for birch in horsetail patches (Fig. 2).

The· seed sowing e;qJerimems demonstrate that germination is lower in

bluestem and higher on scarified seedbeds. However, only patch type is

important in controlling survivorship after two years (except for birch in clipped

horsetail patches) with horsetail consistently having the most favorable

environment of the three patch types. Above-ground competition appears to be

important only to birch survivorship in horsetail patches.

13

15 7

-1 2--'-

,........_ "-0 ?'-. -......._.., z 9+ 0 1-

,........._

0'

(< -,-- 1 , .. uv l - 0 1qr,.; ~~~

Table 1. Probability values (from F-tests) from all ANOV As performed (FER

=.05).

Seed Saving Experiment

Species Patch Clip- scari-Type ping fication

(:il (f'Il (f.;l.l (:if.;] El:Xt:l. E::IX:lt: f.;I..x:lt: f'l:Xt:t.x:lt: Irsm:!I:2Dlli;t12n

GerJIIinat~on

Spruce .002 .024

17

Growth

Growth of spruce gerrninants also tended to be greater when sown in

horsetail compared to gerrninants in bluestem and aspen. \Vhile germinants in

bluestem and aspen did not differ (Fig. 3). Total biomass and total length (above-

ground stem height + root length), but not root:shoot biomass ratio, exhibited

this pattern (Fig. 3). Similarly for birch gerrninants, total biomass, but not total

length or root:shoot biomass ratio, was significantly greater in horsetail than in

the other two patch types (Fig. 4 ).

Clipping of competing vegetation consistently caused increased growth

(P < .05) of spruce germinants in aspen patches and tended to increase spruce

growth in horsetail patches (Fig. 3). Birch's response to clipping \Vas like spruce's

except that gerrninants differed in horsetail and bluestern instead of aspen:

gerrninants in the clipped horsetail patches accumulated significantly more

biomass (P < .05) and were longer in both clipped horsetail and bluestern patches (Fig. 4 ). Also, clipping had no detectable effect on allocation ( root:shoot ratio)

for spruce (Fig. 3) or birch (Fig. 4).

The consistent significance of total number of surviving seedlings (Table 1)

as the covariate in the growth analyses suggests intraspecific competition among

gerrninants was important. No significant interactions among the three factors

were detected (Table 1 ).

14.- a14 SPRUCE 0.4-r T CJ UNCLIPPED

-CLIPPED ; a a a

1? _J_ b -' 0 12 * E 14 14 b ~ 0.3 + u 10 +

~ -._.,

11 ..,.. T 13 15 Vl

ll -T - 1l - Vl . I ll (;> -

20T

l r i E 15 +

.... '-' w -10-,_ z

;::: 5 + 0 ....

* a

3

T

0 -'-------'--'

3.5 T i

' I_ 3.0+ c 0

a...,5+ • -· i Ol ~

:n .., 0 + (/) -· < :::;:

Q 1.5 + Cl ,_

Z 0

I j 1. T

_J r ;::: 0.5 + 0 I .... r

* a

14

5

-:-;

I j

BIRCH

c::::J UNCLJPPED -CLIPPED

* a

5

a

4

--:-,

b b

O.O .L' __ H_O_R_S-ETAIL BLUESTEM ASPEN

PATCH TYPE

0.8 T

0.7+ Q

~ 0.5 + (/')

~ 0.5' ::::;

0.4.,. 8 Q 0 . ..J7 (/')

~ 0.2+

0.1

0.0

a

I , ~I --,

I I

a a

r r

~ I

: >

'-HORSETAIL SLUESTEM ASPEN

PATCH TYPE

Fig. 4. Growth parameters for birch seedlings from sown seeds in clipped and control treatments in three patch types. Statistics as in Fig. 1.

19

20

Transplant Experiment '

The patch type into which spruce seedlings were transplanted affected

(P

"--·-~····--·----~·-...--~-~-J.~ ·~-~---~---..:~,·~"--·"-_:# ___ :~ __ ., __ ..,._;_._ ___ ....._.___. ... :~~:--~--'"---'--.SPRUCE a

15 14 b b

0 • 0 _!_I ___ __:_j HORSETAIL BLUESTEM ASPEN

PATCH TYPE

10.0 T a a a -

t '* :..___; UNCLIPPED ......-, 8.0 + 'l i]1 - CLIPPED o!l

:~! E I (.) ~ *I -.......; .

I 3 6.0+ ;II ,-1

0 0:: 0 I- 4.0 I 0 w :r:: 2. 0

i I I I + ;

I r.

.,.

-::-! ·-: * *I: *

:1 i l

i I II ' * r ·~ ! ; i ~~ T i I I I i I

I I

I I I

i I II

0.0 1 988 1989 1988 1 989 1 988 1 989

HORSETAIL BLUESTEM ASPEN

PATCH TYPE

-

21

Fig. 5. 1989 diameter growth and 1988 and 1989 height growth for spruce seedlings transplanted into clipped treatments in three patch types. Statistics as in

Fig. 1.

E

1.5T I

r 1.3+

E 0' ~ 1. 7" :r .... ;;:: ;f 0.8 +

BIRCH :-- UNCLIPPED

~ 1. 6- * - CLIPPED a

'-

: 1 .4 ~ b b - II

1.2__:_ 0'> ;----r:

* - lj_!l i T 0) 1 0 ° I , .__, . --:- i .1· . '!""""'

i · : .L I w - i f!l ' I ~ 0.8...:... :I !l! I I a::: I I i I ; I

' ' 1 1 i

0 r' I '. I I f- .0- I I I I 3: ! ~ ! • 0 - I ;

6 o.4~ u > f- 0.2--:-

24

Biotic Site Variables

Above-ground biomass of all vegetation in each patch type was not

significantly (P=.061) different among patch types. However, aspen had a much

higher average (906 gjm2) than horsetail (186 g/m2) or bluestem (258 gjm2); the

lack of statistical significance is probably due to the high variance associated with

the aspen samples (Fig. 8). Similarly, aspen had significantly more (P < .001) root

biomass than horsetail and bluestem patches which were not significantly different

from one another. In horsetail patches, clipping significantly stimulated (P < .05)

root growth (Fig. 8).

Abiotic Site Variables

Bluestem soils were colder (P < .05) than soils in horsetail and aspen

patches on three of the sampled dates in 1989. Horsetail and aspen soils were

not significantly different (P> .05) from each other (Fig. 9). Temperature

differences among patch types appear to be less common after solar noon (Fig.

9). The clipped treatment consistently created significantly warmer (P < .05) soils,

especially in bluestem patches (Fig. 10).

Bluestem soils were often wetter (P < .05) and had a thicker organic mat

than in aspen patches. But only occasionally did bluestem patches have a deeper

organic mat or wetter soils than horsetail patches (Fig. 11 ). Bulk density was not

significantly different among patch types (Table 1). Clipping did not significantly

affect soil moisture or bulk density (Table 1).

1

c:;- 1 200 + I I E l

1000 + * ~ I U1 U1 . g 200 +

16 T

15+

f 14 +

I

13 ~ ' '

12 + I T

A.-A. HORSETAIL

0·---- 0 BLUESTEM ·-·ASPEN

7

7

2 2 I 3

3 7

3 8 1i 1'7 10 11 - 7 .... 2 4 1 4 ; 4 T T 6 ;; • - 7 6 ~.... , •.

.... IL II . I -"-.- .- 14 - /~ - · r/ + '• • f - \!/ I

~11 + u ~ 0 10 ~

T ~' '-· - i :t . -~· .:. - - - ,' ' II ' -' • :r>' : ;..· I ; j. ·-t-'7' - -

~: - - 'I v -~ ..) '' - : ... - ', . ' ' '-----""

' ' !';", - ; ' . : 2. -- ~· .. ~ ;.-' 9 1 1 ' - 4

:_.'-- '.) -· " w 0::: :J f-

7:0 T

i T *

IS+

' + I I

tO+ -·~· 1 r

,...--..._ 5-

u 0 J '--"

w 0:::::

20 .....-

:::J 1- IS + " I

J5QT

125-!-

100 ' T

75 +

~ 50 Vl 0

E >- 2.5 + '-v •O ,, '-'

w 0::

0

::J 60 T f-V1

0 ::E 50+ -' 0 V1 .d.Q +

30 +

20 -r-

10 -r-

ORGANIC LAYER c::::J HORSETAIL

a b - BLUESTEM

j a css:sl ASPEN a

'I b a a b ,, T I I ab b

II cb a

I i I !

j I I

I I

MINERAL LAYER a a a

r r T ij8a II : 0 ~ I 'I I! ,, ! j I!

i;l . ; i r . i l

i I I

b

!

a a a

b

ab

0 "2 1

14 4 JUNE JULY

b

5! r aaa b .-- i able § 4 + . 'i t ~I ' a.. · i a • a ..... 31 . a , n c:t:: . : I I T w I I I ~ .... ' I ~ 2~ I, il I u i 'I ;! IJ z l 'i I 23 . I I . II a: 1 _;_ , , . : 1 0 . ,., :i ;,

I . ' 'I o i ,, : i I 1 4 JUNE 4 JULY 1 7 AUG

20 T ' c i

::J -

"' i 2 15 1 ~ i z I 0 • - I .... . < ' CS10+ < ' c:t:: -' w > w -' 5 + 0 z

1 a a : !

T

n :::J 0 c:t::

" I I

o ! I HORSETAIL BLUESTEM ASPEN

PATCH TYPE

28

Fig. 11. a-c) 1989 seasonal pattern of soil moisture in organic and mineral (top 5 em) soil layers and organic mat depth in three patch types. n = 15 for each patch type. Means followed by the same letter are not significantly different (P >. 05) for that date. d) Light attenuation in three patch types, n = 5 for each patch type. Statistics as in Fig. 1. (radiation at ground level in the clipped treatments (100%) was 2100 U E*cm-1*s-2).

Light tended to be less attenuated (not significantly) in horsetail patches

than in bluestem or aspen (Fig. 11).

Transects

29

Density of naturally occurring spruce seedlings decreased as distance from

seed source increased (Fig. 12). This pattern corresponds to that of spruce seed

rain documented in the Rosie Creek burn by Zasada (1985). Of the 1,167

seedlings encountered, 90% were associated with horsetail. This result partly

reflects greater abundance of horsetail in the sampled area (Fig. 12). However,

when the frequencies of associations are standardized to reflect each competitor

species' abundance in the sampled area, spruce seedlings were found much more

often than expected (association index greater than 1.0) near horsetail and much

less often (association index less than 1.0) than expected near bluestem or any

other species: present (Fig. 12). Aspen was absent where seed rain was great

enough to perform transects, so its effects on the natural distribution of naturally

occurring spruce seedlings could not be evaluated.

' ~ 275 ~;~ IE 250 +I

• I • 225 +: I... ;. I

~ 200 +; § 175 + i c: ' '

--; 150 +; ,_ . ~ 125 !: 2: 100 +' ~ 75 f! ::::; • I 8 SOfj ~ 25ti

aD

ASSOCIATED SPECIES

== ALL SPECIES - HORSETAIL

:::::1 OTHER

25 35 45 55 65 80 T

75 85 95 105

t C HORSETAIL f 70 + - BLUESTEM ] tl ~MOSS

60 • IS2l OTHER ~~~ ..-.. .:; l T ! ~ ..,~Q 1 I ~ : ] .• ~ :1 ~ 40-i- ! ii :/ 2; : !/ ~ ] 'i u ·I . :· •I ., ,., '

: i)J !f :: il

' il--0 ! .

] .I :I

I

i l

~ u li I 'I n " 1 .i

,I

~ 'I :i I ·I :;r ., !! ill ' I

30 . 40 50 60 70 80 90 100 1 1 0

DISTANCE FROM SEED SOURCE (m)

30

.3.0.,. . +-+ HORSETAIL _2-.:::_ MOSS

--·=OTHER

6 5.7

~ , ·-· BLUESTEM .....-.. / ~ --- -·~' + I + 1

~ ~ ~ . + .:::l > .... o.,.. + ~ 8 .• + §~ :;;: +

~ f.) ;;;; 0 ;;,..1 ~., 4 :n

:::::

. . 5 "'7

i.J~-

..2 I I -·· '' _,, ··==· •• ; ~ + ... , .

~ 0 "- ; I ~ ' .• =\· =~ . i :i . ~ \ ;

0,0 : •• ..!~············I 25 35 45 55 65 75 85 95 105 JISTANCE FROM SEED SOURCE (m)

Fig. U. 1989 distribution of naturally occurring white spruce seedlings > 1 yr old in a 2520 rrl- area upslope from experiment. n= 14 for each distance class. b) Cover (%) of primary species in sampled area, means± SE. c) Association index of spruce seedlings for primary species in sampled area. A value > 1 indicates greater probability of finding seedling near a species than predicted by its cover in the sampled area (aspen not tested).

DISCUSSION

Seedling Establishment and Early Growth

The preferential establishment of naturally occurring spruce seedlings in

patches of horsetail as well as their exclusion by bluestem and other species

demonstrates the importance of understory vegetation in determining patterns of

post-fire forest regeneration. Similar correlations of tree seedling density and

distribution with different herb patches have been found in eastern deciduous

forests (Maguire and Forman 1983). In old-field successions, seedling distribution

is greatly influenced by the distribution of vegetation patch types, bare ground

(Harrison and Werner 1984 ), and height of competing vegetation (Werner and

Harbeck 1982).

The experimental results suggest that a lower level of competition appears

to be present in horsetail resulting in preferential establishment and growth of

spruce and birch germinants and transplanted seedlings. Thus, in these forests

where the understory survives and resprouts after fire, the species composition

likely determines the pattern of overstory development via inhibitory interactions.

Similar results have been found in other successions (Niering and Egler 1955,

Neiring and Goodwin 1974, Harcombe 1977, Van Hulst 1979, Peet and

Christensen 1980, Eis 1981, Walker and Chapin 1986). However, Uchino et al.

(1984) have shown that high rates of nitrogen fixation are associated with

horsetail. Thus, the soil nitrogen status may be more favorable in horsetail

patches allowing for facilitory interactions.

31

32

Spruce seed predation by birds and/ or small mammals was observed

(disturbed seedbeds) in both clipping treatments in all patch types. This is

probably responsible for birch's higher germination rates while spruce's greater

seed size is probably responsible for its higher rates of survivorship (Harper 1977)

compared to birch after two years. Although scarification was not important to

establishment after two years, germination was greater on scarified seedbeds.

Similarily, white spruce regeneration in interior Alaska has been shown to be

significantly greater on mineral soils (Zasada and Gregory 1969, Dobbs 1972,

Putnam 1985, Walker et al. 1986) relative to untreated organic seedbeds. ·Also,

Zasada ( 1980) showed that white spruce seedlings were taller and had larger basal

diameters on mineral surfaces than on organic surfaces after five years.

Above-ground competition appears to be important for birch but not for

spruce as indicated by birch's increased growth and spruce's general lack of

response. Both types of results have been shown elsewhere: Shaw et al. ( 1987)

showed that shaded sitka spruce seedlings grew taller than unshaded seedlings,

but Wurtz ( 1988) showed white spruce seedlings to be relatively unaffected by

shading. Also, Wurtz ( 1988) showed significantly greater basal diameter growth

of white spruce seedlings (after three years) upon removal of associated

vegetation.

The seed sowing experiment demonstrates that simultaneous establishment

of mid and late-successional species, like birch and spruce, is possible on these

sites. Similarly, simultaneous establishment of other mid and late-successional

species has been shown to occur early in old-field successions (Braun-Blanquet

1932, Beckwith 1954) and in a primary succession on an interior Alaskan flood

plain (Walker et al. 1986). Thus, patterns of succession on these sites must

reflect differential growth and/ or longevity, not sequential establishment.

33

Results from this study are also consistent with the hypothesis that the shade

tolerance of late-successional species like spruce tends to be greater than that of

mid-successional species like birch (Harper 1977, Bazzaz 1979), as ·walker and

Chapin (1986) demonstrated for white spruce and balsam poplar (Populus

balsamifera L.) in a primary succession in Alaska. A low maximum potential

growth rate, common for species that occur in limited resource environments

(Chapin 1980) and later in succession (Grime 1977, Chapin 1980), may explain

the low biomass and cover of late-successional species during initial stages of

succession (Egler 1954 ).

Abiotic Site Variables

Environmental differences between patch types do not consistently explain

these results although several trends appear to be important as has been shown

by Van Cleve and Viereck (1981). Increased birch growth (and spruce rarely) in

horsetail patches and clipped plots may be due to increased mineralization and

decomposition rates resulting from increased soil temperature. These interactions

have been demonstrated in the taiga (Van Cleve and Viereck 1981, Van Cleve et

al. 1983, Van Cleve and Yarie 1986) as well as in tundra soils (Chapin et al.

34

1979). Increased soil temperature has been shown to increase root elongation

rates in greenhouse-grown Alaskan taiga tree species, as well as being correlated

with the seasonal pattern of root elongation by taiga tree seedlings (Tryon and

Chapin 1983). Also, Dyrness et al. (1989) and Wurtz (1988) demonstrated that

early white spruce seedling growth is controlled by soil temperature. Similarly,

Grossnickle (1987) demonstrated that cold soils inhibit seedling growth.

Higher soil temperatures were not consistently correlated v..1th differences

in soil moisture, although bluestem tended to have a thicker organic mat and

cooler and wetter soils. Drought conditions due to higher temperatures and

subsequently higher evaporation rates should increase the likelihood of

competitive inhibition due to competition for water (Van Cleve et al. 1983).

However, drought conditions were probably not present since the average

monthly precipitation rate (recorded at a weather station upslope from

experimental plots) between May and August was very near (45.8 rnrn in 1988,

33.9 rnrn in 1989, Viereck, unpubl.) to the 30 year (1959-1989) monthly average

(38.3 rnrn) ·for the same time period in Fairbanks (United States Department of

Commerce 1988, United States Department of Commerce 1989). Nevertheless,

drought stress may still be an important factor during average growing conditions.

Equivalence of Competitors

Both experiments suggest that horsetail is a weaker competitor than

bluestem and aspen and that birch is inhibited more by competition than spruce.

35

Thus, competitive pair-wise interactions between species with different growth

forms are not equal as also found by Miller and Werner (1983). Wilson (1989)

also documented unequal competitive interactions between two co-occurring

grasses. In contrast, Goldberg and Werner (1983), who used competitor species

of similar growth forms, did not document unequal patterns between species.

These results also confirm that dense grass clones can effectively inhibit seedling

establishment as shown for bluestem by ·waldron (1966) and Eis (1981). Also,

McQuilkin (1940) demonstrated similar interactions during pine seedling

establishment in little bluestem (compared with bare and scarified soil).

Indicators of Competitive Ability

Species identity is a better indicator of competitive ability than either

above-ground (Goldberg and \Verner 1983), below-ground biomass (Goldberg

1987) or light attenuation. Thus, the amount of above and below-ground biomass

of a patch type does not appear to be an adequate predictor of plant responses to

competition although alternative explanations can be made for any field

experiment (Bender et al. 1984 ). However, root competition has been shown to

inhibit seedling growth of late-successional species in other studies (Lutz 1945,

Walker and Chapin 1986). Similarly, Tilman (1989) demonstrated that

competition for nutrients is an important mechanism in determining growth of a

bunchgrass on unproductive, nitrogen-poor soils in Minnesota.

CONCLUSIONS

In an upland post-fire succession in interior Alaska, natural establishment

patterns of spruce indicate that horsetail patches provide a better environment

than bluestem and other species present (aspen not tested). Bioassay experiments

demonstrate that spruce and birch can simultaneously establish, but show greater

survivorship and accumulate more biomass in horsetail patches. Also, competitive

interactions significantly affected the establishment and early growth of spruce

and birch. Both sets of results lead to the conclusion that the species of

understory vegetation present have unequal, inhibitory effects on the

establishment and growth of spruce and birch and are important in determining

patterns of forest regeneration in interior Alaska.

Bluestem patches tended to have a thicker organic mat and cooler and

wetter soils than horsetail and aspen patches. These trends correspond to the

lower growth exhibited in bluestem patches. Thus, differences in the plant-

mediated microenvironment appears to control establishment and growth on

these sites.

Management Implications

A. burn's intensity may be very important to forest regeneration. Previous

work has shown that areas that are intensely burned are more likely to be

established by horsetail. Similarily, lightly or moderately burned areas are more

likely to be colonized by species present before the fire. This information

36

37

combined with the results from this study suggest that artificial regeneration

techniques may not be necessary if a site is intensely burned. Also, any artificial

regeneration techniques which increase colonization by bluestem should be

avoided. Gathering the depth of the existing organic layer may be the most

effecient information to collect before considering artificial regeneration.

Suggestions for Future Work

Several areas of study warrant further work. First, determine if the

regrowth of colonizing species is similar following fires in other areas. Tree cores

taken from a mature forest may show that various distributions of mid and late-

successional trees exist, thus implying that vegetation competition is important.

One might use various temperature treatments in bluestem patches to determine

if temperature or competition is the more important factor. Also, to test for the

importance of nutrient competition, use bioassay experiments to determine if

tissue nutrient concentrations of tree seedlings varies among patch types

The.possibility of site conditions present before a fire controlling

subsequent regrowth patterns also exists. To document this, immediately mapping

former vegetation patterns (from burned remains) following fire and monitoring

subsequent regeneration of both colonizer species as well as tree species may be

very important.

LITERATURE CITED

Aarssen, L. W. 1983. Ecological combining ability and competitive ability in

plants: towards a general evolutionary theory of coexistence in systems of

competition. American Naturalist 122:707-731.

Agren, G. I., and T. Fagerstrom. 1984. Limiting dissimilarity in plants:

randomness prevents exclusion of species with similar competitive abilities.

Oikos 43:369-375.

Barney, R. J. 1971. Wildfires in Alaska-some historical and projected effects and

aspects. In: "Fire in the Northern Environment - a Symposium," pp. 51-59.

Pacific Northwest Forest and Range Experiment Station, Portland, Oregon.

Bazzaz, F. A. 1979. The physiological ecology of plant succession. Annual

Review of Ecology and Systematics 10:351-371.

Beckwith, S. L. 1954. Ecological succession on abandoned farm lands and its

relation to wildlife management. Ecological Monographs. 24:349-379.

Bender, E. A., Case, T. J. Case, and M. E. Gilpin. 1984. Perturbation

experiments in community ecology: theory and practice. Ecology 65:1-13.

Braun-Blanquet, J. 1932. Plant sociology: The study of plant communities.

McGraw-Hill, New York. 439 pp.

Bryant, J. L., A. S. Paulson. 1976. An extension of Tukey's method of multiple

comparisons to experimental design of random concomitant variables.

Biometrika. 63:631-638.

38

39

Carter, G. A., J. H. Miller, D. E. Davis, and R. M. Patterson. 1984. Effect of

vegetative competition on the moisture and nutrient status of loblolly pine.

Canadian Journal of Forest Research 14:1-9.

Chapin, F. S., III. 1980. The mineral nutrition of wild plants. Annual Review of

Ecology and Systematics 11:233-260.

------, K Van Cleve, and M. C. Chapin. 1979. Soil temperature and nutrient

cycling in the tussock growth form of Eriophorum vagina tum. Journal of

Ecology 67:169-189.

------, P. M. Vitousek, and K. Van Cleve. 1986. The nature of nutrient limitation

in plant communities. American Naturalist 127: 48-58.

Connell, J.H. 1983. On the prevalence and relative importance of interspecific

competition: evidence from field experiments. American Naturalist.

122:661-696.

Conover, w.: J., and R. L. Iman. 1981. Rank transformations as a bridge

between parametric and nonparametric statistics. The American

Statistician. 35:124-132.

Day, R. W., and G. P. Quinn. 1989. Comparisons of treatments after an analysis

of variance in ecology. Ecological Monographs. 59:467-468.

Dobbs, R. C. 1972. Regeneration of white and Engelmann spruce: a literature

review with special reference to the British Columbia interior. Canadian

Department of the Environment, Canadian Forestry Service, Pacific

Forestry Research Centre, Information Report BC-X-69.

40

Dubreuil, M. A., and T. R. Moore. 1982. A laboratory study of postfire nutrient

redistribution in subarctic spruce-lichen woodlands. Canadian Journal of

Botany. 60:2511-2517.

Dyrness, C. T., K Van Cleve, and J. D. Levison. 1989. The effect of wildfire on

soil chemistry in four forest types in interior Alaska. Canadian Journal of

Forest Research. 19:1389-1396.

Egler, F. E. 1954. Vegetation science concepts I. Initial floristic composition, a

factor in old-field vegetation development. Vegetatio 4:412-417.

Eis, S. 1981. Effect of vegetation competition on regeneration of white spruce.

Canadian Journal of Forest Research.l1:1-8.

Foote, M.J. and L.A. Viereck. 1985. Burn severity: Its impact on natural

revegetation following the Rosie Creek fire. Pp. 26-29 In: Juday and

Dyrness (eds.). Early results of the Rosie Creek fire research project.

Agricultural and Forestry Experiment Station, University of Alaska

Fairbanks, Fairbanks, Alaska, USA.

Fowler, N. 1981. Competition and coexistence in a North Carolina Grassland.

Journal of Ecology. 69:843-854.

Gardner, A. C. 1983. White spruce regeneration options on river floodplains in

the Yukon Territory. Canadian Forestry Service, Pacific Forest Research

Centre, Information report BC-X-240. 27 p.

Goldberg, D. E., and P. A Werner. 1983. Equivalence of competitors in plant

communities: a null hypothesis and a field experimental approach.

American Journal of Botany 70:1098-1104.

Goldberg, D. E. 1987. Neighborhood competition in an old-field plant

community. Ecology 68:1211-1223.

41

Grace, James B. 1987. The Impact of Preemption on the Zonation of Two Typha

Species Along Lakeshores. Ecological Monographs 57(4):283-303.

Grime, J. P. 1973. Competition and diversity in herbaceous vegetation - a reply.

Nature 244:310-311.

1977. Evidence for the existence of three primary strategies in plants and

its relevance to ecological theory. American Naturalist. 111:1169-1194.

Grossnickle, S. C. 1987. Int1uence of flooding and soil temperature on the water

relations and morphological development of cold-stored black spruce and

white spruce seedlings. Canadian Journal of Forest Research. 17:821-828.

Harcombe, P. A. 1977. The influences of fertilizers on some aspects of

succession in a humid tropical forest. Ecology 58:1375-1383.

Harper, J. L. 1977. Population Biology of Plants. Academic Press, London. 892

pp.

Harrison, J. S., P. A. Werner. 1984. Colonization of oak seedlings into a

heterogeneous successional habitat. Canadian Journal of Botany. 62:559-

563.

Hubbell, S. P., and R. B. Foster. 1986. Biology, chance, and history and the

structure of tropical rain forest tree communities. Pages 314-340 In: J.

Diamond and T. J. Case, editors. Community ecology. Harper and Row,

New York, New York, USA.

Hulten, E. 1968. Flora of Alaska and neighboring territories. Stanford

University Press, Stanford, California, USA

Hurlbert, S. 1984. Pseudoreplication and the design of ecological field

experiments. Ecological Monographs 20:231-250.

42

Juday, G. P. 1985. Preface: The Rosie Creek fire and its research opportunities.

Pp. vii-ix In: Juday and Dyrness (eds.), Early results of the Rosie Creek

fire research project 1984. University of Alaska Fairbanks Press,

Fairbanks, Alaska, USA.

Lutz, H. J. 1945. Vegetation on a trenched plot twenty-one years after

establishment. Ecology 26:200-202.

MacArthur, R. H. 1972. Geographical Ecology. Harper and Row.

Maguire, D. A and R. T. T. Forman. 1983. Herb cover effects on tree seedling

patterns in a mature hemlock-hardwood forest. Ecology 64:1367-1380.

McQuilkin, W. E. 1940. The natural establishment of pine in abandoned fields

in the Piedmont Plateau Region. Ecology 21:135-147.

Miller, T. E., and P. A. Werner. 1987. Competitive effects and responses

between plant species in a first-year old-field community. Ecology

68:1201-1210.

Mitchley, J. 1987. Diffuse competition in plant communities. Tree 2:104-106.

Neter, J. W. Wasserman, and M. H. Kutner. 1985. Applied Linear Statistical

Models. Richard D. Irwin, Inc., Homewood, Ill. 1127 pp.

43

Neu, C. W., C. R. Byers, and J. M. Peek. 1974. A technique for analysis of

utilization-availability data. Journal of Wildlife Management 38:541-545.

Niering, W. A., and F. E. Egler. 1955. A shrub community of Viburnum lentago,

stable for twenty-five years. Ecology 36:356-360.

Niering, W. A., and R. H. Goodwin. 1974. Creation of relatively stable

shrublands with herbicides: arresting "succession" on rights-of-way and

pastureland. Ecology 55:784-795. ,

Peet, R.K. and N.L. Christensen. 1980. Succession: A population process.

Vegetatio 43:131-140.

Putnam, W. E. 1985. Direct seeding techniques for regenerating white spruce in

interior Alaska. M.S. Thesis. University of Alaska, Fairbanks. 157 p.

Rowe, J. S. 1955. Factors influencing white spruce reproduction in Manitoba and

Saskatchewan. Canada Department of Northern Affairs and National

Resources, Forestry Branch, Forest Research Division, Technical Note No.

3. 27p.

Schoener, T. W. 1983. Field experiments on interspecific competition. American

Naturalist. 122:240-285.

Shaw, C. G., R. C. Sidle, and A. S. Harris. 1987. Evaluation of planting sites

common to a southeast Alaska clear-cut. III. Effects of microsite type and

ectomycorrhizal innoculation on growth and survival of Sitka spruce

seedlings. Canadian Journal of Forest Research. 17:334-339.

Shmida, A., and S. Ellner. 1984. Coexistence of plant species with similar niches.

44

Vegetatio 58:29-55.

Smith, D. W. 1970. Concentrations of soil nutrients before and after fire.

Canadian Journal of Soil Science. 50:17-29.

Stiell, W. M. 1976. White spruce: artificial regeneration in Canada. Canadian

Forestry Service, Forest Management Institute, Information Report FMR-

X-85. 263p.

Tilman, D. 1985. The resource ratio hypothesis of succession. American

Naturalist 125:827-852.

1989. Competition, nutrient reduction and the competitive neighborhood

of a bunchgrass. Functional Ecology 3:215-219.

Tryon, P. R., and F. S. Chapin, III. 1983. Temperature control over root growth

and root biomass in taiga forest trees. Canadian Journal of Forest

Research 13:827-833.

Uchino, F., T. Hiyoshi, and M. Yatazawa. 1984. Nitrogen fixing activities

associated with rhizomes and roots of Equisetum species. Soil Biology and

Biochemistry 16:663-667.

United States Department of Commerce. 1989. Climatic summary of United

States supplement for 1959 through 1988, Alaska. Climatography of the

United States. Weather Bureau, Washington, D. C.

United States Department of Commerce. 1989. Local climatological data annual

summary with comparative data, Fairbanks, Alaska. National Oceanic and

Atmospheric Administration Environmental Data Service, Washington,

45

D.C.

Van Cleve, K., and L.A. Viereck. 1981. Forest succession in relation to nutrient

cycling in the boreal forest of Alaska. In:D.C. West, H.H. Shugart and

D.B. Botkin (eds). Forest succession, concepts and application.

Springer-Verlag, New York. Pp. 185-210.

------, and L.A. Viereck. 1983. A comparison of successional sequences following

fire on permafrost-dominated and permafrost-free sites in interior Alaska.

In: Permafrost: Fourth International conference, Proceedings. National

Academy of Sciences. Washington, D.C. National Academy Press. Pp.

1286-1291.

------, and J. Yarie. 1986. Interaction of temperature, moisture, and soil chemistry

in controlling nutrient cycling and ecosystem development in the taiga of

Alaska. K. Van Cleve, F.S. Chapin III, P.W. Flanigan, L.A. Viereck, and

C.T. Dyrness ( eds.). In: Forest Ecosystems in the Alaskan taiga. A

synthesis of structure and function. Ecological Studies 57:160-169.

Van Cleve, K., C.T. Dyrness. L.A. Viereck, J. Fox, F.S. Chapin, III and W.

Oechel. 1983. Taiga ecosystems in interior Alaska. Bioscience 33:39-44.

Van Hulst, R. 1979. On the dynamics of vegetation: succession in model

communities. Vegetatio 39:85-96.

Viereck, L.A. 1973. Wildfire in the Taiga of Alaska. Quaternary Research 3:465-

495.

------, and M.J. Foote. 1985. Effects of the Rosie Creek Fire on selected

environmental factors in the Bonanza Creek Pp. 30-33 In: Juday and

Dyrness ( eds.). Early results of the Rosie Creek fire research project.

Agricultural and Forestry Experiment Station, University of Alaska

Fairbanks, Fairbanks, Alaska, USA.

------, and E. L. Little, Jr. 1986. Alaska trees and shrubs. University of Alaska

Fairbanks University Press, Fairbanks, Alaska, USA.

------, and L. A. Schandelmeier. 1980. Effects of fire in Alaska and adjacent

Canada - a literature review. United States Department of the Interior,

Bureau of Land Management, BLM - Alaska Technical Report 6.

Waldron, R. M. 1966. Factors affecting natural white spruce regeneration on

prepared seedbeds at the Riding Mountain Forest Experimental Area,

Manitoba. Canada Department of Forestry and Rural Development,

Forestry Branch Departmental Publ. No. 1169. 41 p.

Walker, L.R. and Chapin, F.S., III. 1986. Physiological controls over seedling

growth in primary succession on an Alaskan Floodplain. Ecology

67:1508-1523.

46

------, Zasada, J. C. and Chapin, F. S., III. 1986. The role of life history processes

in primary succession on an Alaskan floodplain. Ecology 67:1243-1253.

Webb, L. J., and J. G. Tracey, and W. T. Williams. 1972. Regeneration and

pattern in the sub-tropical rainforest. Journal of Ecology 6:675-695.

Werner, P. A. 1976. Ecology of plant populations in successional environments.

Systematic Botany 1:246-268.

Werner, P. A. and A. L. Harbeck. 1982. The pattern of tree seedling

establishment relative to staghorn sumac cover in Michigan old fields.

American Midland Naturalist 108:124-132.

Wilde, S. A., B. H. Shaw, and A. W. Fedkenheur. 1968. Weeds as a factor

depressing forest growth. Weed Research 8:196-204.

47

Wilkinson, Leland. 1988. Systat: The system for statistics. Systat, Inc., Evanston,

Illinois, USA.

Wilson, J. B. 1989. Root competition between three upland grasses. Functional

Ecology. 3:447-451.

Wurtz, T. L. 1988. Effects of the microsite on the growth of planted white

spruce seedlings. Ph D. Dissertation. University of Oregon. 200 p.

Yarie, J. 1981. Forest fire cycles and life tables: a case study from interior

Alaska. Canadian Journal of Forest Research 11:554-562.

Zar, J. H. 1984. Biostatistical analysis. Prentice-Hall, Englewood Cliffs, New

Jersey, USA.

Zasada, J. C., and R. A. Gregory. 1969. Regeneration of white spruce with

reference to interior Alaska: a literature review. Res. Pap. PNW-79.

USDA Forest Service, Pacific Northwest Forest and Range Experiment

Station. Portland, Oregon.

Zasada, J. C., and D. F. Grigal. 1978. The effects of silvicultural system and

seed bed preparation on natural regeneration of white spruce and

associated species in interior Alaska. In: C. A. Hollis and A. E. Squillace

(eds.) Proceedings: Fifth North American Forest Biology Workshop.

USDA Forest Service. p. 213-220.

Zasada, J. C. 1980. Some considerations in the natural regeneration of white

spruce in interior Alaska. In: Proceedings Forest Regeneration at High

Latitudes, USDA Forest Service, Pacific Northwest Forest and Range

Experiment Station, General Technical Report PNM-107. p. 25-29.

48

Zasada, J. C. 1985. Production, dispersal, and germination of white spruce and

paper birch and first-year seedling establishment after the Rosie Creek

fire. Pp. 34-37 In: Juday and Dyrness (eds.). Early results of the Rosie

Creek fire research project. Agricultural and Forestry Experiment Station,

University of Alaska Fairbanks, Fairbanks, Alaska, USA.