Tsuyuzaki S., Narita K., Kodama Y, Harada K & Ishikawa M. (Team Ecology, P4) 2010.
Vegetation recovery for five years after large-scaled wildfire in Alaska.

平成21年度IARC­JAXA情報システム(IJIS)及び衛星データ等を利用した北極圏研究業務委託 成果報告書. pp. 51­56
Severe forest fire in Alaska and global environmental changes

Vegetation recovery for five years after large-scaled wildfire in Alaska
Team Ecology (P4)
Tsuyuzaki, S.1, Narita, K.2, Kodama, Y.3, Harada, K.4 & Sawada, Y 5
1
Graduate School of Environmental Earth Science, Hokkaido University, 2 Faculty of Education and
Human Studies, Akita University, 3 Institute of Low Temperature Science, Hokkaido University, 4 School ofFood, Agricultural and Environmental Sciences, Miyagi University, 5: National Institute of Advanced
Industrial Science and Technology

1. INTRODUCTION
Wildfires frequently occurs in Picea mariana
forests, due mostly to lightning (Engelmark 1999).
Crown fire, incompletely burned the ground-surface
cover, is ordinal and promotes seedling regeneration(Bonan & Shugart 1989). P. mariana develops
aerial seedbank, and disperses seeds mostly after thefires. This strategy adapts to establish on wet,nutrient-poor, unburned ground surface (van Cleve etal. 1986). In discontinuous permafrost regions, thescenarios of succession differ between north andsouth slopes, due mostly to the presence of
permafrost on the north slopes, i.e., P. mariana forests
develop more on the north slopes. Wildfire is likely

to become larger and more intense, i.e., to burn out
the ground surface (Dale et al. 2001). To confirm
the regeneration patterns, annual monitoring has been
conducted on the north slope of Poker Flat, interior
Alaska. We have revealed that the vegetation
composition on the forest floor is a determinant on
seedling emergence of tree species, and thus thevegetation recovery after wildfires should be clarified
to predict forest regeneration.
We have researched the followings from 2005 to2009 after the 2004 wildfire that was large andsevere: 1) Detecting plant community recovery
patterns with different fire severities, and 2)
Characterizing regeneration dynamics after wildfire.

2. STUDY AREA AND METHODS

Figure 1. Picea mariana seeds captured by seed traps, andgerminated in lab-experiment. Mean is shown with SE.
Duration: ■= 2005-2006, ■= 2006-2007, ■ = 2007-2008,
and ■ = 2008-2009. 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.

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 in thesummer of 2004. The field surveys were conductedin May (spring) and July-August (summer) in every
year from 2005 to 2007 and summer 2008 and 2009.
The total censuses were 8 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. H isburned totally, i.e., all stems were killed and > 80%
ground surface was burned out. M was situatedbetween L and H, i.e., most trees were dead but
unburned plant cover remained somehow on the
ground surface. In each plot, we measured heightand diameter at breast height (DBH) for all alive anddead stems  1.3 m in height. Fallen trees were
included on the measurement to reconstruct pre-fireforest structure. Outside the plots, 22 tree cores
were sampled by a borer or clippers in summer 2005.
The locations, aspects and slope gradients were
determined by a portable GPS and lazar compass.
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 (12Table 1. Yearly changes in cover on dominant plant taxa from 2005 to 2008. On each life from, the first three leading species,
except for shrubs that showed five because of high frequencies, are shown, when the number of species is more than five. Eachnumeral shows mean with standard deviation. +: less than 0.1%. Occurrence frequency (%) is shown in parentheses.
Species
Herbs and ferns (13 taxa)
Carex bigelowii
Calamagrostis canadensis
Epilobium angustifolium
Shrubs (12 taxa)
Ledum groenlandicum
Vaccinium vitis-idaea
Vaccinium uliginosum
Betula nana
Oxycoccus microcarpus
Trees (4 taxa)
Picea mariana
Betula neoalaskana
Populus tremuloides
Mosses/lichens (13 taxa)
Polystichum formosum
Sphagnum subsecundum
Ceratodon purpureus
Total number of species
Plot cover (%)
Species richness
Species diversity
Evenness

2005

2006

2007

2008

2009

Total mean

1.7 (49)
0.9 (41)
1.9 (30)

1.8 (49)
1.4 (39)
3.0 (33)

2.5 (50)
6.2 (48)
2.6 (38)

2.9 (51)
7.2 (48)
2.7 (38)

3.0 (51)
7.7 (50)
1.9 (39)

2.4 (50)
4.7 (45)
2.4 (36)

4.3 (91)
1.6 (72)
2.4 (70)
1.6 (51)
0.3 (51)

5.7 (89)
2.2 (70)
3.0 (70)
2.5 (54)
0.4 (50)

8.1 (89)
4.4 (71)
3.8 (71)
4.7 (54)
0.8 (51)

9.4 (90)
5.0 (74)
4.3 (70)
6.1 (55)
0.8 (51)

11.3 (90)
5.5 (75)
4.8 (69)
7.0 (56)0.9(51)7.8 (90)
3.8 (72)
3.6 (70)
4.4 (54)
0.6 (51)

0.6 (64)+ (12)+ (8)0.6 (70)
0.1 (20)
0.6 (16)0.7 (68)
0.2 (19)0.5 (19)0.9 (65)
0.5 (22)0.8 (19)0.9 (65)
0.7 (21)1.0 (19)0.7 (66)
0.3 (19)0.6 (16)0.9 (56)29.3 (62)
1.9 (30)
39
47.6
9.8
1.24
0.56

1.0 (46)
29.0 (62)
5.2 (42)
40
56.4
10.1
1.35
0.60

3.2 (65)
26.3 (55)
13.4 (71)
40
75.4
10.9
1.47
0.63

4.7 (65)
21.9 (48)15.3 (75)
41
80.3
11.1
1.56
0.66

6.1 (69)
21.1 (48)14.7(80)
40
82.8
11.3
1.61
0.68

3.2 (60)
25.5 (55)
10.1 (60)
42
68.5
10.7
1.44
0.63

hr/12 hr)] with continuous or 12-hr light.
In each plot, 6 1 m × 1 m quadrats were randomly
set up. Vegetation was annually monitored in all thequadrats. The environments were monitored in fiveof six quadrats, as needed. For examples, canopy
openness was estimated in summer 2005 and 2008
(Frazer et al. 1999), albedo was annually measured(Tsuyuzaki et al. 2009), and duff thickness wasestimated by a steel stake. The cover of eachspecies was recorded on burned (hereafter, i.e., BS)
and unburned (US) ground surfaces, separately, atsummer census. When a tree seedling was observedin the quadrats, the seedling was marked by anumbered flag, and was recorded on height, crownarea 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. In summer 2008,
twenty litterbags that contained dead Sphagnum wasestablished on the slope to estimate litter
decomposition rates.
Of 96 quadrats, 80 quadrats were used forinvestigating relationships between forest-floor
vegetation and the environmental factors, by
non-metric multi-dimensional scaling (NMDS).
Based on vegetation and environmental factors(burned area, canopy openness, elevation, slope
gradient, aspect, and years after wildfire), NMDS
extracted significant environmental factors andrevegetation patterns.

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. By the 2004 wildfire 81% of stems
were burned and dead. The maximum tree heightwas 13.0 m. The age of tree cores was less than175.
The canopy openness ranged from 57% to 95% in2005 and from 45% to 82% in 2008. The plant
cover on the forest floor ranged from 0% to 100%,
indicating that the floor was patchily burned withvarious scales and thus was suitable for this study.
Albedo is positively correlated with total plant coverin quadrats (refer to Kodama’s report and Tsuyuzaki
et al. 2009). Plant cover on the forest floor
decreased down to 40% by the fire even on L. Duff
thickness ranged from 3 cm to 73 cm.
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. The number of seeds
were estimated by:
y = -26700 + 32200·lnx (r2 = 0.715, n = 8),
where y is estimated number of seeds, and x is stemheight.
P. mariana seeds were captured by seed traps until
summer 2008 (Fig. 1). Therefore, even after severe
wildfire, seed immigration from the snags was not
limited for a few years after the wildfire. However,the seeds captured by seed traps decreased abruptly in2009 from everywhere. In addition, the germinationof P. mariana annually decreased, in particular, on H.

If this trend was true, the regeneration success of P.
mariana was mostly determined for a few years after
wildfires. This fate should be confirmed in thissummer. B. neoalaskana was second dominant in
the traps (data not shown).
3.3 Plant communities in forest floor
Although the unburned surface was mostly
covered with Sphagnum spp. soon after the 2004
wildfire (Table 1), the cover declined gradually due
probably to desiccation and fire damage. The cover
increased least in most plots, with a few exceptions.
In contrast, Ceratodon purpureus increased frequency
and now established in 80% of quadrats.
Polystichum formosum followed C. purpureus, i.e.,
showed 45-70% in frequency, and increased annuallyin cover.
Of herbs and ferns, Carex bigeglowii andCalamagrostis canadensis were most common andhad the highest cover of herbs (Table 1). These two
speciesaremonocotyledons.
Epilobium
angustifolium became dominant in 2006, butthereafter decreased in cover.
Shrubs, represented by Ledum groenlandicum,
Vaccinium vitis-idaea, and V. uloginosum, came fromlegacies through the last fire (Table 1). Since there
were few seedlings on shrubs, vegetative
reproduction was most important for shrub
regeneration. Shrubs annually increased the cover.
The most of these plants survived through thewildfire, and reproduced vegetatively.
Although P. mariana slightly increased the cover

Quadrat score(Table 1), the cover increase was mostly derived fromsurvived saplings that showed 0.6% in 2005. thecover of broad-leaved trees was less than 0.1% in
2005, showing that most broad-leaved trees
regenerated from seedlings. In addition, the coverof broad-leaved trees exceeded the cover of P.
mariana in 2008.
3.4 Forest-floor vegetation patterns
NMDS indicated that burned area was the mostsignificant determinant on forest-floor vegetation
structures (Fig. 2).
The scores of quadrats
aggregated in the right side of figure 2 meant thequadrats on less-burned surface, and vice versa. The
scores of less-burned quadrats fluctuated less,indicating that the vegetation structures changed little.
The scores of burned quadrats shown on left-side in
the figure fluctuated greatly along axis II, showingthat the vegetation structures annually changed but
did not go towards the scores of less-burned quadrat.
In total, the vegetation structures changed annually on
burned surface, but did not recover to the pre-burned
vegetation structures.
Species scores supported these facts (Fig. 2).
Broad-leaved trees established more on burned
quadrats, while shrubs established more on unburned
quadrats.
The establishment of mosses had acontrast between Sphagnum and the others. The
establishment of Sphagnum was completelydependent on unburned surfaces. In contrast, C.
purpureus and P. formosum established more on
burned surfaces. These facts indicated that moss

Species score

Figure 2. NMDS ordination diagram. (Quadrat scores) The connected lines show the same quadrats surveyed from 2005 to 2009.
NMDS scores at the first survey, i.e., in 2005, are shown by solid circles, and the others are by open circles. Environmental factors:
Yr = years after wildfire, Brn: burned area (%), Cnp = canopy openness (%), Elv = elevation (m), Slp = slope gradient (o), and Asp =aspect (o). (Species score) Car big = Carex bigelowii, Cal can = Calamagrostis canadensis, Epi ang = Epilobium angustifolium, Led
gro = Ledum groenlandicum, Vac vit = Vaccinium vitis-idaea, Vac uli = Vaccinium uliginosum, Bet nan = Betula nana, Oxy mic =Oxycoccus microcarpus, Pic mar = Picea mariana, Bet neo = Betula neoalaskana, Pop tre = Populus tremuloides, Pol for =Polystichum formosum, Sph sub = Sphagnum subsecundum, and Cer pur = Ceratodon purpureus.

Figure 3. Changes in stem height and crown area on tree seedlings for five years surveyed. 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 andbroad-leaved trees at P < 0.01.

communities were differentiated by severity.
3.5 Tree seedling growth
In total, 1246 tree seedlings were marked for thefive years. P. mariana was most abundant, i.e., 860
seedlings in the quadrats, and germinated more on
unburned surface. Three broad-leaved tree taxa, P.
tremuloides, B. neoalaskana and Salix spp., totaled
386 seedlings.
All of these broad-leaved tree
seedlings established on burned surface with a few
exceptions. Stems  DBH on broad-leaved tree
species were least in the surveyed plots, showing thatthe seeds of broad-leaved trees immigrated from theexternal environments.
On P. mariana seedlings emerged in 2005, seedlingsurvival did not differ greatly between burned andunburned surfaces. On broad-leaved trees on burned
surface, the survival was more than 63% by 2009.
The survivals of P. mariana were 79% on burned
surface and 47% on unburned surface. In total, thesurvival of P. mariana was higher on burned surface
than unburned surface, and was higher thanbroad-leaved trees on burned surface. However,total number of seedlings was more for broad-leaved
trees. Therefore, the density of survived seedlingson burned surface was higher on broad-leaved trees

than on P. mariana.
Stem growth, measured by height and crown area,
was significantly higher on the three broad-leaved
trees than on P. mariana on burned surface (Fig. 3).
In addition, on P. mariana, stem growth wassignificantly slower on unburned surface than on
burned surface.
For estimating carbon fixation by tree seedlings,
the following allometric equations were obtained.
Aboveground biomass (mg) (y) is predicted by stemheight (cm) (x) and aboveground biomass (y)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 burned
and unburned surfaces for P. mariana, and between
species on burned surface (ANCOVA, P < 0.05).
The significant differences in the slopes of allometry
indicated that resource allocation differed between P.
marianaandbroad-leavedtree
species.
Broad-leaved trees allocated more to belowgroundthan to aboveground, and to stem than to leaf.
Broad-leaved trees allocated aboveground biomass
more to height growth than P. mariana, indicatingadditional establishment is not observed after 10
years (Johnstone et al. 2004). Number of seedlingrecruits declined annually on Poker Flat, indicatingthat tree regeneration patterns on P. mariana wasdetermined 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. Therefore, seedsupply will persist for broad-leaved trees.
Furthermore, the intensive forest fire, that removes
duff layer, promotes the seedling establishment of
those broad-leaved trees.

Figure 4. Sphagnum-litter decomposition rates expressed byweight remaining, N content, and 15N. Red and blue circles
indicate litterbags established on burned and unburned surfaces,
respectively. The relationship between N content and weightremaining is also shown.

that broad-leaved trees obtained light energy more
effectively than P. mariana, and did not allocate more
to aboveground. We measured the carbon andnitrogen content in these trees, and will evaluate the
C and N fixation.
3.6 Litter decomposition
Litter decomposition was faster on burned surface
than unburned surface (Fig. 4), suggesting thatburned surface accelerated litter decomposition. In
addition, N content in litter seemed to become lower
on burned surface. This monitoring will be madeagain in 2010.

4. DISCUSSION
4.1 Seed immigration and seedling establishment
P. mariana seeds were captured fluently by seedtraps by 2008 and germinated.
However, thenumbers of dispersed and germinated seeds decreased
in 2009.
Also, number of germinated seeds
gradually decreased in severely-burned sites. P.
mariana provides viable seeds for a few years, byproducing semi-serotinous cones (Bonan & Shugart
1989). Seed production estimated by tree heightsupports this. The seed immigration was unlikely tobe limited for P. mariana regeneration immediately
after wildfire. However, viable seeds decreased
annually, and were lowest in 2009. The decline inviable seeds suggested that more seeds came from theaerial seedbank on the canopy. Between Yukon andBritish Columbia, seedling recruitment on P. mariana
is highest in the first 5 years after fires, while

4.2 Environmental changes and litter deposits
If moss mat, mostly consisting of Sphagnum,
remains on the ground surface after wildfire, soil
temperature keeps low. However, the complete
removal of Sphagnum moss mat promotes soil
temperature increase and melting permafrost(Yoshikawa et al. 2002). Albedo also declines byfire, and is mostly determined by plant cover on the
ground surface in Poker Flat (Tsuyuzaki et al. 2009).
Fire severity, in particular, on the forest floor, must be
mentioned to predict the regeneration. Surface
temperature increases after wildfire in a P. mariana
forest, due to increase in canopy openness anddecrease in albedo (Chambers et al. 2005). In
addition, Sphagnum cover influences permafrost
distribution (see Sawada’s report). Therefore, a
trigger on environmental changes is considered to bein Sphagnum layer. The dominance of Sphagnum
spp. is related to P. mariana forest expansion (Fenton
et al. 2007).
4.3 Regeneration patterns
Although the seedling survival on burned surface
was higher on P. mariana than on broad-leaved trees,
the growth rates were significantly higher on
broad-leaved trees. After disturbances, including
wildfire, in northern Ontario, broad-leaved trees,
represented by Populus tremuloides, trees increased
the relative dominance, and needle-leaved trees,
including P. mariana, decreased it (Ilisson & Chen
2009). Mean annual biomass increment is higher indry sites than in wet sites along a chronosequence on
P. mariana forests in Manitoba, Canada, but carbon
pools in bryophyte, understory and forest floor areless for the dry sites (Wang et al. 2003). The
allometric relationships indicated that P. mariana has
low allocation plasticity, and the growth is reduced 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 ofherbaceous 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.
4.4 Conclusions, perspectives and future plans
By monitoring for five years, four findings weresummarized. (1) Seedling regeneration patterns of P.
mariana might be determined soon after wildfires,
because of seed immigration.
(2) P. mariana
established more on unburned and burned surfaces,
and broad-leaved trees were restricted to establish on
burned surface. (3) Broad-leaved trees grew up
significantly faster than P. mariana.
(4) Theregeneration of P. mariana forests is limited by thedominance of burned surface.
To clarify plant community-climate interactions
with micro-and macro-spatiotemporal changes, weneed further observations on: 1) changes in plantcommunity structures for longer term, and 2) seedlingsurvival and growth related to the determinants on
Sphagnum recovery. To predict carbon balance aswell as regeneration pattern, we have to mention
Sphagnum layer more details. The keystone andumbrella species on the north slopes of interior
Alaska must be Sphagnum spp.
In summer 2010, the monitoring should becontinued to ensure the findings. However, therecovery stages of trees are shifted from seedling tosapling, and became too large to monitor the growththat exceeds to monitor them by using the 1 m × 1 m
quadrat. Therefore, we have to change the survey
design. Since the vegetation changes slowed, it may
be better that the monitoring interval is extended.
Also, if we have a chance, we will make a plan tocompare regeneration patterns after the otherwildfire(s) that recently burned out the groundsurfaces. Another idea is that we assist the otherprojects, by collecting vegetation data. Anyway, we
have to clean up the slope to maintain the plots formonitoring conveniently.

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surface albedo and plant cover after wildfire in a Picea
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517-525
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107, 8148, doi:10.1029/2001JD 000438- Attention Data collected by this team members are stored in the ftp
server:ftp://hosho.ees.hokudai.ac.jp/pub/tsuyu/Alaska/
Please use them freely!

Activities (2008-2010)
Publications
Kushida K., Kim Y., Tsuyuzaki S., Fukuda M. 2009. Spectral
vegetation indices for estimating shrub cover, green
phytomass and leaf turnover in a sedge-shrub tundra. Int. J.
Remote Sensing 30, 1651-1658
Tsuyuzaki S., Kushida K., Kodama Y. 2009. Recovery of
surface albedo and plant cover after wildfire in a Picea
mariana forest in interior Alaska. Climatic Change 93,
517-525
Tsuyuzaki S, Sawada Y, Kushida K, Fukuda, M. 2008. A
preliminary report on the vegetation zonation of palsas in
the Arctic National Wildlife Refuge, northern Alaska, USA.
Ecol. Res. 23, 787-793
Tsuyuzaki S, Sento N, Fukuda M. (in press) Baidzharakhs(relic mounds) increase plant community diversity byinterrupting zonal vegetation distribution along the ArcticSea,northern
Siberia.
Polar
Biol.
DOI:
10.1007/s00300-009-0727-x