Reports on researches in the Arctic utilizing IARC-JAXA Information System (IJIS)
and Satellite Data 2008. pp 39-42

Severe forest fire in Alaska and global environmental changes

Vegetation recovery for four years after large-scaled wildfire in Alaska
Team Ecology (P4)
Tsuyuzaki, S.1, Narita, K.2, Kodama, Y.3, Harada, K.4 & Ishikawa, M.1
1
GSEES, Hokkaido University (HU), 2 FEHS, Akita University, 3 ILTS, HU, 4 FSAES, Miyagi University

Wildfires take place in taiga, due mostly tolightning (Engelmark 1999). The initial stages after
wildfires greatly determine the forest dynamics. On
Picea mariana forests in Alaska, crown fire, that
incompletely burned the ground-surface cover, isordinal and promotes seedling regeneration (Bonan &Shugart 1989).
Picea mariana develops aerial
seedbank, and disperses more seeds after fire, and is
adapted to establish wet and nutrient-poor habitat thatis distributed more on north slopes in mountains (vanCleve et al. 1986). In discontinuous permafrost
regions, the scenarios of succession differ between
north and south slopes, due mostly to the presence of
permafrost on the north slopes, and vice versa.
Wildfire is likely to become larger and more intense(Dale et al. 2001). To predict the effects oflarge-scaled wildfire on revegetation, we haveresearched the followings from 2005 to 2008: 1)
Detecting plant community recovery patterns withdifferent fire severities, and 2) Characterizing
regeneration dynamics after wildfire. Based onthese results, we found out that recovery ofSphagnum mat was prerequisite for P. mariana forest
regeneration, in particular, after severe wildfires.

on the measurement to reconstruct pre-fire forest
structure. Outside the plots, 22 tree cores were
sampled by a borer or clippers in summer 2005.
Two seed traps (52 cm × 26 cm in surface area)
were set up on each plot in summer 2005. Seeds
were collected at every census. Seed germination
test was performed in an incubator [15oC/25oC (12hr/12 hr)] with continuous or 12-hr light.
In each plot, six 1 m × 1 m quadrats wererandomly set up. Canopy openness was estimatedby photos taken on each quadrat at 1.3 m above theground surface by a fish-eye lens in summer 2005
and 2008 (Frazer et al. 1999).
Albedo wasmeasured on each quadrat (Tsuyuzaki et al. in press),and duff thickness was estimated by a steel stake.
At every census, vegetated area was estimated oneach quadrat. The cover of each species was
30
Number of seeds/trap

1. INTRODUCTION

20

1

2. STUDY AREA AND METHODS
0
Number of seeds germinated/trap

A typical P. mariana forest on the north slope ofPoker Flat, ca. 50 km north of Fairbanks, interior
Alaska, is selected for monitoring, because of large
and severe fire, slope direction, and accessibility.
Wildfires (Boundary Fire) stroke this region insummer 2004. The field surveys were conducted in
May (spring) and July-August (summer) in every
year from 2005 to 2007 and summer 2008. The
total censuses were 7 times.
At the first census, we established 16 10 m × 10 m
plots. Based on fire severities, plots were assigned
as less-(L), moderately-(M), and heavily-(H) burned.
Stem survival and moss cover characterized L. M
was situated between L and H, i.e., most trees weredead but unburned plant cover remained somehow on
the ground surface. H is burned totally, i.e., allstems were killed and > 80% ground surface wasburned out. In each plot, we measured height anddiameter at breast height (DBH) for all alive and deadstems ≥ 1.3 m in height. Fallen trees were included

6

4

2

0
SevereModerate
Fire severity

Less

Figure 1. Picea mariana seeds captured by seed traps,
and germinated in lab-experiment per seed trap. Mean isshown with SE. Duration: ■ = 2005-2006, ■ =2006-2007,
and ■ = 2007-2008. In 2005 and 2006, the data werecomplied with spring and summer. Seed density was notdifferent between three fire severities (Tukey’s test), and thenumber of germinated seeds was different between years, andis not significantly different between severities.

recorded on burned (hereafter, i.e., BS) and unburned(US) ground surfaces, separately, at summer census.
When a tree seedling was observed in the quadrats,
the seedling was marked by a numbered flag, and wasrecorded on height, crown area and location. In
summer 2007, > 20 seedlings for P. mariana, Populus
tremuloides and Betula neoalaskana were excavated
to investigate allometry on stem height and biomass.
Detailed statistical analysis is not described in thisreport, due to page limitation.

3. RESULTS
3.1 Fire severities
The altitude ranged from 244 m to 437 m, and theslopes faced 7.0o-43.5o from N to W with 4.8o-19.0o
slope angles. Before the wildfire, 5-54 P. mariana
stems ≥ 1.3 m, that accounted for 97% of total, hadestablished in the plots, and 81% of them wereburned and dead. The maximum tree height was
13.0 m. Alnus crispa, B. neoalaskana and Salix spp.,
established with low frequencies. The plant coveron the forest floor ranged from 0% to 100%,
indicating that the floor was patchily burned withvarious scales and thus was suitable for this study.
The age of tree cores was up to 174, and waslinearly correlated to height. The stem-diameter
growth indicated that drastic events, such as wildfires,
occurred 60 and 130-140 years before now. The
forest regeneration before the 2004 fire was not
simultaneously, and thus the previous fires were
presumably crown fire.
The canopy openness ranged from 57% to 95% on
the 80 quadrats in 2005, and from 45% to 82% in
2008. The relationships between albedo in 2005 (x)and 2008 (y) was expressed as: y = 1.20x - 18.92 (r2 =0.782, significant at P < 0.01). Plant cover on theforest floor decreased down to 40% by the fire evenon L. Duff thickness ranged from 3 cm to 73 cm.
On albedo, see Kodama’s report and Tsuyuzaki et al.
(in press).
In summary, the albedo did not return tothe pre-fire conditions until vegetation cover becomes
higher enough to reflect radiation.
3.2 Seed dispersal and germination
In summer 2007, cones were counted for 12 P.
mariana snags, and confirmed that the seeds werestill available on the snags. Seed traps constantly
captured P. mariana seeds until summer 2008 (Fig. 1).
B. neoalaskana was second dominant in the traps(data not shown). The other seeds were recorded
from forbs and grasses. Therefore, even after severe
wildfire, seed immigration from the snags was not
limited in the early stages.
However, thegermination of P. mariana annually decreased.
3.3 Plant communities in herb layer
For 3 years, there were > 44 taxa, consisting of 31
vascular plants (4 trees, 13 shrubs, 12 herbs, and 2
ferns) on the 96 quadrats. Sphagnum spp. werepredominant on US, although the cover declined in2008. Plant cover fluctuated little for trees, herbs
and mosses on US, while shrub cover significantly
increased on both US and BS. Shrubs, e.g., Ledum
groenlandicum, Vaccinium vitis-idaea, and V.
uloginosum, came from legacies through the last fire.
Since there were few seedlings on shrubs, vegetative
reproduction was most important for shrub
regeneration. Trees slightly increased in cover on

16
4
2
0

14

Density (m2)12
10

Picea mariana, n = 164

Populus tremuloides, n = 272

Picea mariana, n = 670

4
2
0

8
6

4
2
0

4
2

4
2
0

0
05/07

06/05

06/

07/05
Date

07/07

08/08

Salix spp., n = 71

Betula papyrifera, n = 38

05/07

06/05

06/

07/05

07/07

08/08

Date

Figure 2. The fates of seedlings emerged from Summer 2005 to Summer 2008. Green and brown columns indicate recruits anddeaths (/m2) in each census period. Blue lines show the fluctuations of seedling densities. Total numbers of seedlings (n) from2005 to 2008 are shown in each figure. On unburned surface, there were no seedlings for P. tremuloides and Salix spp., and were 3
for B. neoalaskana.

1

10

Aug 08Aug 07

Aug 06

Canopy area (cm2)

Aug 08Aug 07
Aug 052

Aug 06

3

May 07

4

May 06

Stem height (cm)5

Aug 05

100

6

1

1

0.1

0
Date

Date

Figure 3. Changes in stem height and crown area on tree seedlings for four years surveyed. ● = Picea mariana on burned
surface (BS), ● = P. mariana on unburned surface (US), ● = Populus tremuloides on BS, ● = Salix spp. on BS, and ● =Betula neoalaskana on BS. Height and crown area are significantly different for P. mariana between BS and US at P < 0.01
(repeated measures ANOVA), and are different between P. mariana and broad-leaved trees at P < 0.01.

BS, mostly by broad-leaved seedlings. A grass,Calamagrostis canadensis, and a moss, Ceratodon
purpureus, significantly increased in cover on BS for
the four years. Epilobium angustifolium (fireweed)
increased greatly in cover to 2006, but decreased
gradually thereafter.
3.4 Seedling emergence, survival, and growth
In total, 1215 tree seedlings were marked for thefour years (Fig 2). P. mariana was most abundant,i.e., 834 seedlings in the quadrats, and germinatedmore on US. Three broad-leaved tree taxa, P.
tremuloides, B. neoalaskana and Salix spp., totaled
318 seedlings. All of these seedlings established onBS, except 3 B. neoalaskana seedlings on US.
Stems ≥ DBH for broad-leaved tree species were lessin the surveyed plots, indicating that these seeds camefrom the external environments.
On P. mariana seedlings emerged in 2005, seedlingsurvival did not differ greatly between BS and US.
On broad-leaved trees, the survival was more than
50% by 2008. Therefore, the survival rates were not
low for all the species. This indicated that safe site
for seedling emergence is rather important.
Stem growth, measured by height and crown area,
was significantly higher on the three broad-leaved
trees than on P. mariana on BS (Fig. 3). In addition,
on P. mariana, stem growth was significantly slower
on the US than on BS.
A few examples of the allometric equations aredescribed below.
Stem height (y) and aboveground biomass (x)Picea mariana
On US: y = +0.508x – 0.326
On BS: y = +0.465x –0.090
Populus tremuloides on BS: y = +0.593x – 0.428
Betula neoalaskana on BS: y = +0.532x –0.330
The differences were significant between BS and
US for P. mariana, and between species on BS(ANCOVA). We also evaluated the relationships
between aboveground and belowground biomass, andbetween stem and leaf biomass. The significant
differences in the slopes of allometry indicated that
resource allocation differed between P. mariana andbroad-leaved tree species on BS. Broad-leaved trees
allocated more to belowground than to aboveground,and to stem than to leaf. Furthermore, broad-leaved
trees allocated aboveground biomass more to height
growth than P. mariana. These results indicated thatbroad-leaved trees acquired light more effectively
than P. mariana, and did not have to allocate more to
aboveground organs. One cause seemed to be lower
allocation plasticity of P. mariana, showing from thebiomass allocation did not differ between the two
habitats.
In conclusion, the establishment ofbroad-leaved trees proceeded if the ground wasburned completely.

4. DISCUSSION
4.1 Seed immigration and seedling establishment
P. mariana seeds were captured fluently by seedtraps from 2005 to 2007 and the seedlings emerged
well.
However, the seed germination rates
decreased in 2008. P. mariana provides viable seeds
for several years, by producing semi-serotinous cones(Bonan & Shugart 1989). The cones on snags
support this trend. The seed immigration was
unlikely to be limited for P. mariana regeneration
immediately after wildfire, although viable seeds
decreased annually. The decline in viable seeds
suggested that more seeds came from the aerial
seedbank on the canopy. Between Yukon andBritish Columbia, seedling recruitment on P. mariana
is highest in the first 5 years after fires, while
additional establishment is not observed after 10
years (Johnstone et al. 2004). Number of seedlingrecruits declined annually on Poker Flat, indicatingthat tree regeneration patterns on P. mariana should
be determined for the first several years after fire.
All broad-leaved trees observed in Poker Flatproduce long-distance wind-dispersed seeds. The
seeds of these broad-leaved trees immigrated fromthe external environments, since the mature stems
were least in the surveyed area. These mean thatseed supply will persist for broad-leaved trees.
Furthermore, the intensive forest fire, that removes
duff layer, promotes the seedling establishment of
those broad-leaved trees.
4.2 Environmental changes
If moss mat, mostly consisting of Sphagnum,
remains on the ground surface after wildfire, soil
temperature keeps low. However, the complete
removal of moss mat promotes soil temperature
increase and/or melting permafrost (Yoshikawa et al.
2002). Albedo also declines by fire, and is mostly
determined by plant cover on the ground surface inPoker Flat (Tsuyuzaki et al. in press). Fire severity,
in particular, on the forest floor, must be mentioned to
predict regeneration. Surface temperature increases
after fire, due to increase in canopy openness anddecrease in albedo on a P. mariana forest (Chambers
et al. 2005). In addition, Sphagnum cover is likely
to influence permafrost distribution. Therefore, a
trigger on environmental changes is considered to be
derived from Sphagnum layer. The dominance ofSphagnum spp. is related to P. mariana forest
expansion (Fenton et al. 2007).
4.3 Regeneration patterns
The seedling survival did not differ greatly
between P. mariana and broad-leaved trees, and thegrowth rates were significantly higher forbroad-leaved trees. Mean annual biomass increment
is higher in dry sites than in wet sites along achronosequence on P. mariana forests in Manitoba,
Canada, but carbon pools in bryophyte, understory
and forest floor are less for the dry sites (Wang et al.
2003). The allometric relationships suggested that P.
mariana has low allocation plasticity, and thus thegrowth is limited on the burned ground surface.
On Poker Flat, plant cover removal from theground surface determines seedling colonization andvegetation recovery. Canopy openness influences
the distribution pattern and productivity ofherbaceous plants on the forest floor (Whigham
2004). However, initial tree composition after fire
had little effects on understory composition in the
coniferous forests of eastern Canada, while soil burnseverity affected temporal changes in understory
species (Lecomte et al. 2005). Those suggest that
forest regeneration after large-scaled fire differs fromweak fire, including crown fire. Fire severity may
change successional sere on P. mariana forests

towards mixed conifer and/or broad-leaved forests.
To clarify plant community-climate interactions
with micro-and macro-spatiotemporal changes, weneed further observations on: 1) changes in plantcommunity structures for longer term, 2) seedlingsurvival and growth related to Sphagnum recovery,and 3) determinants on Sphagnum recovery. To
predict carbon balance as well as regeneration pattern,
we have to mention Sphagnum layer more details.
The keystone species on the north slopes of interior
Alaska must be Sphagnum spp. To clarify thedeterminants on Sphagnum recovery, we set up
litterbags to estimate Sphagnum litter decompositionin summer 2008.
By combination with themeasurements of Sphagnum growth, we estimate safe
site for growth and turnover of Sphagnum.

REFERENCES
Bonan GB, Shugart HH. 1989. Environmental factors andecological processes in boreal forests. Ann.Rev.Ecol.Syst.
20, 1-28
Chambers SD, Beringer J, Randerson JT, Chapin III FS. 2005.
Fire effects on net radiation and energy partitioning:
contrasting responses of tundra and boreal forest
ecosystems. J.Geophys.Res. 110, doi: 10.1029/2004JD
005299Dale VH, Joyce LA, McNulty S, Neilson RP, Ayres MP,
Flannigan MD, Hanson PJ, Irland LC, Lugo AE, Peterson
CJ, Simberloff D, Swanson FJ, Stocks BJ, Wotton BM.
2001. Climate change and forest disturbances. BioScience51, 723-734
Engelmark O. 1999. Boreal forest disturbances. In: Walker LR(ed.). Ecosystems of the world 16: Ecosystems of disturbed
ground. Elsevier, Amsterdam. pp. 161-186
Fenton, N.J., Beland, C., de Blois, S., Bergeron, Y. 2007.
Sphagnum establishment and expansion in black spruce(Picea mariana) boreal forests. Can. J. Bot. 85: 43-50.
Frazer GW, Canham CD, Lertzman KP. 1999. Gap Light
Analyzer (GLA), ver. 2.0. Simon Fraser Univ, Burnaby,
BC/Inst Ecosyst Studies, Millbrook, NY
Johnstone JF, Chapin III FS, Foote J, Kemmett S, Price K,
Viereck L. 2004. Decadal observations of tree regeneration
following fire in boreal forest. Can.J.For.Res. 34, 267-273
Lecomte N, Simard M, Bergeron Y, Larouche A, Asnong H,
Richard PJH. 2005. Effects of fire severity and initial treecomposition on understorey vegetation dynamics in aboreal landscape inferred from chronosequence andpaleoecological data. J.Veg.Sci. 16, 665-674
Tsuyuzaki, S., Kushida, K., Kodama, Y. (in press) Recovery of
surface albedo and plant cover after wildfire in a Picea
mariana forest in interior Alaska. Climatic Change doi:
10.1007/s10584-008-9505-y
van Cleve K, Chapin III FS, Flanagan PW, Viereck LA,
Dyrness CT. 1986. Forest ecosystems in the Alaskan taiga.
Springer-Verlag, NYWang C, Bond-Lamberty B, Gower ST. 2003. Carbon
distribution of a wel-and poorly-drained black spruce fire
chronosequence. Global Change Biol. 9, 1066-1079
Whigham DF. 2004. Ecology of woodland herbs in temperate
deciduous forests. Ann.Rev.Ecol.Evol.Syst. 35, 583-621
Yoshikawa K, Bolton WR, Romanovsky VE, Fukuda M,
Hinzman LD. 2002. Impacts of wildfire on the permafrost
in the boreal forests of Interior Alaska. J.Geophys.Res. 107,
8148, doi:10.1029/2001JD000438