Severe forest fire in Alaska and global environmental changes

Vegetation recovery for six years after large-scaled wildfire in Alaska
Team Ecology (Reference#: P4@TSUYUZAKI)
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
Wildfire becomes large and severe and thus burns
out the ground surface (Dale et al. 2001), whilecrown fire, incompletely burned the ground-surface
cover, is common and promotes seedling regenerationin Picea mariana forests (Bonan & Shugart 1989,
Engelmark 1999). Due to the complete removal ofground surface, microenvironments such as albedo,soil moisture and thaw depth of permafrost will be

altered. P. mariana develops aerial seedbank that
disperses seeds mostly after wildfires, and adapts toestablish on wet, nutrient-poor ground surface(Chapin et al. 2006). In discontinuous permafrost
regions, the scenarios of succession differ between
north and south slopes, because of the presence of
permafrost mostly on the north slopes, i.e., P.
mariana forests develop more on the north slopes.
Through changes in microclimate after severe
wildfire, vegetation recovery and successional sere is
likely to be distorted. Therefore, to confirm theregeneration patterns, annual monitoring has been
conducted in a P. mariana forest.
We have researched the followings from 2005 to2010 after the 2004 wildfire that was large andsevere: 1) Detecting plant community recovery
patterns with different fire severities in relation toseed immigration, vegetation composition, and tree
seedling establishment, and 2) Characterizing
regeneration dynamics.

2. STUDY AREA AND METHODS

Figure 1.
Box-whisker plots on Picea mariana seeds
captured by seed traps (top), and germinated in lab-experiment(bottom). In 2005 and 2006, the data were complied withspring and summer. Seed density was not different between
three fire severities (Tukey’s HSD test), and the number ofgerminated seeds was different between years, and is 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. A
wildfire (Boundary Fire) stroke this region in thesummer of 2004. The field surveys were conductedin spring and summer from 2005 to 2007 and insummer from 2008 to 2010. The total censuses
were 9 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 alsomeasured to reconstruct pre-fire forest structure.
Outside the plots, 22 tree cores were sampled by aborer or clippers in summer 2005. The locations,Figure 2. Annual recruitment and mortality of tree species in burned and unburned surfaces on Poker Flat, interior Alaska, after
the 2004 wildfire (Boundary Fire) from 2005 to 2009.

aspects and slope gradients were determined by aportable 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 [15 oC/25oC (12hr/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,
and albedo was annually measured (Tsuyuzaki et al.
2009), and duff thickness was estimated by a steel
stake. The cover of each species was recorded onburned (hereafter, i.e., BS) and unburned (US) groundsurfaces, separately, at summer censuses. When atree seedling was observed in the quadrats, theseedling 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.
Twenty litterbags containing dead Sphagnum were
established on the slope in summer 2008 to estimate
litter decomposition rates. Ten bags were set up on
BS and the remainders were on US. Five bags wererecovered from each habitat in 2009 and 2010,
respectively.
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 severity
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, with the maximum age of 175.
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·ln(x) (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). 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 in 2009
from everywhere. In addition, the germination of 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.
3.3 Plant communities on 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. These two species
are monocotyledons.
Epilobium angustifolium
became dominant in 2006, but thereafter decreased incover.
Shrubs, represented by Ledum groenlandicum,
Vaccinium vitis-idaea, and V. uloginosum, came fromlegacies through the last fire. Since there were few
seedlings on shrubs, vegetative reproduction was
most important for shrub regeneration. Shrubs
annually increased the cover. The most of theseplants survived through the wildfire, and reproduced
vegetatively.
Although P. mariana slightly increased the cover,the cover increase was mostly derived from survived
saplings that showed 0.6% in 2005. the cover ofbroad-leaved trees was less than 0.1% in 2005,
showing that most broad-leaved trees regenerated
from seedlings. The cover of broad-leaved trees
exceeded the cover of P. mariana in 2008.
NMDS indicated that burned area was the mostsignificant determinant on forest-floor vegetation
structures (Fig. 3).
The scores of quadrats
aggregated in the right side of figure 3 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 patterns (Fig. 3).
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 completely

Quadrat score
Species score

Figure 3. 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 cas = 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 4. 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.

dependent on unburned surfaces. In contrast, C.
purpureus and P. formosum established more on
burned surfaces. These facts indicated that moss
communities were differentiated by severity.
3.4 Tree seedling establishment
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. 4).
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 belowground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 5. Sphagnum-litter decomposition rates expressed byweight remaining, N content, and 15N. The relationshipbetween N content and weight remaining is also shown.

than to aboveground, and to stem than to leaf.
Broad-leaved trees allocated aboveground biomass
more to height growth than P. mariana, indicatingthat broad-leaved trees obtained light energy more
effectively than P. mariana, and did not allocate more
to aboveground.
3.6 Litter decomposition
Litter decomposition was faster on burned surface
than unburned surface (Fig. 5), suggesting thatburned surface accelerated litter decomposition. In
addition, N content in litter seemed to become lower
on burned surface. The concentrations of C and13C did not change greatly for the two years, whilethese of N and 15N increased across the time.
However, 13C tended to be higher on BS than on US.

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. Therefore, a trigger on environmental
changes is considered to be in 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 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.
4.4 Conclusions, perspectives and future plans
By monitoring for six years, four findings weresummarized. (1) Seedling regeneration patterns of P.
mariana were determined soon after wildfires,
because of the limitation of seed immigration. (2) P.
mariana established more on unburned and burned
surfaces, and broad-leaved trees were restricted toestablish on burned surface. (3) Broad-leaved trees
grew up faster than P. mariana.
(4) Theregeneration of P. mariana forests is restricted 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 not only
regeneration pattern but also carbon balance, we haveto mention Sphagnum layer more details. The
keystone and umbrella species on the north slopes ofinterior Alaska must be Sphagnum spp.
During 2011 and 2013, the monitoring should becontinued to increase the accuracy. Since seed
immigration and emergence were determined a few
years the wildfire (confirmed by monitoring for 6
years), we focus more on seedling mortality andgrowth. Furthermore, we have a plan to restore P.
mariana regeneration by introducing Sphagnum
propagules that is a key to promote the regeneration.
The restoration through Sphagnum recovery has been
widely used in boreal peatland (Rochefort et al. 2003).
Such restoration techniques should be validated overa wide area, by using remote sensing data. Note that
we are able to assist the other projects, by collecting
vegetation data.

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
005299Chapin III FS, Oswood MW, van Cleve K, Viereck LA,
Verbyla DL. 2006. Alaska’s changing boreal forest. Oxford
University Press, New York.

Dale 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.
Ilisson T, Chen HYH. 2009. Response of six boreal tree
species to stand replacing fire and clearcutting. Ecosystems
12, 820-829
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
Rochefort1 L, Quinty F, Campeau S, Johnson K, Malterer T.
2003. North American approach to the restoration of
Sphagnum dominated peatlands. Wetlands Ecol. Manage.
11, 3-20
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
Wang 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:10.1029/2001JD 000438- Attention Collected data are saved in the ftp server:
ftp://hosho.ees.hokudai.ac.jp/pub/tsuyu/Alaska/
Please use them freely!
Also, voucher specimens are stored in SAPS.

Activities (2008-2011)
Publications
Kimura H, Tsuyuzaki S. (in press) Fire severity affects
vegetation and seed bank in a wetland. Appl. Veg. Sci.
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. 2010. Baidzharakhs (relicmounds) increase plant community diversity byinterrupting zonal vegetation distribution along the Arctic
Sea, northern Siberia. Polar Biol. 33, 565-570