Spruce Budworm (Tordeuse des bourgeons de l'epinette) at Bonanza Creek LTER: A clear case of temperature thresholds in a warming climate Glenn Patrick

Spruce Budworm Spruce Budworm (Tordeuse des bourgeons de l(Tordeuse des bourgeons de l''epinette)epinette)

at Bonanza Creek LTER:at Bonanza Creek LTER: A clear case of A clear case of

temperature thresholds in temperature thresholds in a warming climate a warming climate

Glenn Patrick Juday, Professor of Forest EcologyGlenn Patrick Juday, Professor of Forest EcologySkeeter Werner, USDA FS, PNW Research Station (retired)Skeeter Werner, USDA FS, PNW Research Station (retired)

Robert A. Ott, consultantRobert A. Ott, consultant

? Jim Kruse, USDA Forest Service S&PF? Jim Kruse, USDA Forest Service S&PF

• Large total area burned- early start to fire season- multiple simultaneous fires- large fires- lack of mid-summer “season-ending precipitation event”- active late fire season - continued vigorous spread- some fires extinguished by first snows of season- smouldering through the winter

• • Spruce budworm reproduction/outbreak?Spruce budworm reproduction/outbreak?

• Strong negative tree growth anomaly of “negative responders”- w. spruce on low-elevation productive sites central AK- w. spruce (42%) at treeline

• Decrease in open water/lake surface area

WARM TEMPERATURE ANOMALIES IN BOREAL ALASKA :

• Spruce bark beetle outbreak behavior in southcentral Alaska- shift from 2-yr. to 1-yr. life cycle

Photo: Paul RenschenPhoto: Paul Renschen

Photo: Robert A. OttPhoto: Robert A. Ott

Spruce Budworm, Choristoneura fumiferana

PART 1.PART 1.

IT’S A BIG DEAL.IT’S A BIG DEAL.

IT MATTERS.IT MATTERS.

MacLean, D.A., Porter, K.B., MacKinnon, W.E., Beaton, K.P. 2000. Spruce budworm decision MacLean, D.A., Porter, K.B., MacKinnon, W.E., Beaton, K.P. 2000. Spruce budworm decision support system: lessons learned in development and implementation. support system: lessons learned in development and implementation. Computers and Computers and Electronics in AgricultureElectronics in Agriculture 27: 293 – 314. 27: 293 – 314.

Power, J.M., 1991. National data on forest pest damage. In: Brand, D.G. (Ed.), Canada’s Timber Power, J.M., 1991. National data on forest pest damage. In: Brand, D.G. (Ed.), Canada’s Timber Resources. Can. For. Serv., Petawawa National Forestry Inst., Chalk River, ON. Inf. Rep. PI-X-Resources. Can. For. Serv., Petawawa National Forestry Inst., Chalk River, ON. Inf. Rep. PI-X-101. pp. 119–129.101. pp. 119–129.

Spruce budworm outbreaks:

• Natural disturbance system - especially in NE North America

• Cause large-scale mortality of spruce and balsam fir

- uncertainty in future forest structure and productivity

• • The most destructive forest pest in Canada;The most destructive forest pest in Canada;

- causes ~ 40% of the 81–107 million m- causes ~ 40% of the 81–107 million m33 of timber of timber volume lost to insects and disease each year.volume lost to insects and disease each year.

• Three major spruce budworm outbreaks in the 20th century;

- beginning 1910, 1940, and 1970, - maximum extents of 11, 25, and 58 million hectares- late 20th century in northwest Canada (Alaska)

Budworm populations:

• Usually regulated by combinations of several natural factors

- insect parasites

- vertebrate predators

- invertebrate predators,

- adverse weather conditions.

• During prolonged outbreaks - stands heavily defoliated; eventually budworm starvation becomes important mortality factor.

Explaining spruce budworm outbreak behavior: a popular pastimeTheory 1. The catastrophe theory of budworm outbreaks holds that major infestations occur every 40-60 years, as the result of a cusp-catastrophe event, whereby populations jump suddenly from endemic to epidemic levels.

Theory 2. Outbreaks are the result of spatially synchronized population oscillations that are caused by delayed density-dependent feedback (from various mortality agents) which are synchronized via a process of entrainment, or alignment of period and phase to the period and phase of an external rhythm.

In the far north: spruce budworm reproductive success is clearly heat limited, and sensitive to a variety of temperature controls.

PART 2.PART 2.

YOU GOTTA KNOW THE BIOLOGYYOU GOTTA KNOW THE BIOLOGY

OF THIS CRITTEROF THIS CRITTER

Several ChoristoneuraChoristoneura actors:

C. fumiferanaC. biennisC. oraeC. occidentalis

Spruce budworm is distributed across the continuous forest zone, but generally is not mapped all the way to northern tree limit.

= 80% to 100% forested

AugustAugust

May/JuneMay/June

The spruce budworm completes its life cycle within a 12-month period, but spread across 2 different years.

First year events

Second year events

startstart

SPRUCE BUDWORM LIFE CYCLE The spruce budworm completes its life cycle within a 12-month period, but spread across 2 different years.

Larval Stage 1The eggs hatch to produce the first instar (LL11) of the budworm.Larval Stage 2The first instar (LL11) caterpillars develop into the second instar (LL22) caterpillars, which move by wind and find sites under bark scales. Here, they will spin silken cocoons for hibernation (overwintering).Larval Stage 3In May, LL22 budworm, which are yellowish with dark brown heads, develop to the next instar (LL33), which either bore into needles or buds or spin silken webbing around new shoots and begin to feed on the needles within.Larval Stages 4, 5, 6The most damage to the foliage normally occurs early to mid-June when the larvae are in their final stage of development (L(L66).). Larger budworms with brown bodies (18-24 mm in length), black heads, and two rows of paired whitish spots down the back, can be spotted on shoots in June.PupaeAfter LL66, the budworms stop feeding and develop into brownish pupae, which in turn become moths.Moths (Adult)

Moths mate and then the female lays eggs.

EggsUp to 300 green eggs per female are laid in masses of about 15-50 eggs on the underside of the needles.

Source: http://www.srd.gov.ab.ca/forests/health/insects/sprucebudworm.aspx

Spruce budworm 2nd instarSpruce budworm 2nd instarSpruce budworm egg massSpruce budworm egg mass

sprucesprucebudbud

““worm”

worm”

Spruce budworm 3rd instarSpruce budworm 3rd instar

sprucesprucebudbud

Spruce budworm 4th instarSpruce budworm 4th instar


Larva stage 6 “… causes most damage to the foliage …”Larva stage 6 “… causes most damage to the foliage …”

“… “… brown body, black head, two rows of paired whitish brown body, black head, two rows of paired whitish spots down the back, … on shoots in June.”spots down the back, … on shoots in June.”


Spruce Spruce budworm budworm

pupa.pupa.

malemale

femalefemale

Spruce budworm pupaeSpruce budworm pupae

Spruce budworm adult mothSpruce budworm adult moth

PART 3.PART 3.

SOME WAY THAT TEMPERATURESOME WAY THAT TEMPERATURE

MIGHT MATTER.MIGHT MATTER.

“Overwintering mortality in the spruce budworm, Choristoneura fumiferana (Clem.), was measured between 1983 and 1990 in several natural stands of balsam fir, Abies balsamea (L.), in Quebec and Ontario. Overwintering losses (disappearance of larvae) averaged 25.2%, occurred mostly in late summer and early fall, ….

We conclude that overwinteringoverwintering mortality does not result from adverse winter weather conditions or from gradual loss of hibernacula.”

Regniere, J. and Duval. P. 1998. Overwintering mortality of spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae), populations under field conditions. Canadian Entomologist 130 (1):13-26.

“Temperature-dependent developmental rate of spruce budworm has been investigated extensively for almost all developmental stages… L1 developmental rate, however, has been overlooked.L1 developmental rate, however, has been overlooked. Here, we divide L1L1 development into subphases based on morphological changes and behavioral events observed during the development of the stadium. We examine the effects of temperature on development time and survival rate for each development phase….L1L1 development time was significantly increased as rearing temperatures decreased…Although it took only a few more days for L1L1 to construct hibernacula at lower temperatures compared with insects reared at higher temperatures, it took a few additional weeks for the larvae to reach the 2nd stadium when they enter diapause. Therefore, temperature could have a significant impact on the timing of diapause initiation.”

Han, E.; Bauce, E.; Trempe-Bertrand, F. 2000. Development of the first-instar spruce budworm (Lepidoptera: Tortricidae). Annals of the Entomological Society of America 93(3): 536-540.

Temperature controlTemperature controlof spruce budworm of spruce budworm

1st instar larva1st instar larvadevelopment ratedevelopment rate

((AugustAugust).).

1313oo 2323oo


gs = green substance gs = green substance

Consolidation ofConsolidation ofgreen substance green substance

(gs) and formation(gs) and formationof hibernaculumof hibernaculum

(hi)(hi)

((August August temperaturetemperaturecontrol).control).


Excretion of greenExcretion of greenpellets in 1st instar.pellets in 1st instar.


“Han and Bauce (1993) reported that the excretion of green substance resulted in a lower super-cooling point as the insect prepared for overwintering. It is also possible that the green substance serves primarily as a camouflage for egg protection as spruce budworm eggs are laid on green needles and may be vulnerable to predation.”


Molt into 2nd instar Molt into 2nd instar larva.larva.



27.2days 27.2days @ 13@ 13oo C C

9.9 days 9.9 days @ 23@ 23oo C C


Mean daily temperature, 01 Aug. to 31 Aug., at Fairbanks

10.0

11.0

12.0

13.0

14.0

15.0

16.0

17.0

18.0

1905 1915 1925 1935 1945 1955 1965 1975 1985 1995 2005

year

Deg. C

2004200419931993

1988198819901990

1977-78?1977-78?

“In Alaska, significant budworm damage was detected in 1978 on white spruce in many residential and park areas of Anchorage.” (Holsten: USDA Forest Service, Alaska Region Leaflet R10-TP-11)

Analysis: G. Juday Analysis: G. Juday

Mean daily minimum temperature, 01 Aug. to 31 Aug., at Fairbanks

3.5

4.5

5.5

6.5

7.5

8.5

9.5

10.5

11.5

1905 1915 1925 1935 1945 1955 1965 1975 1985 1995 2005

year

Deg. C

~3.5~3.5oo C 100yr C 100yr-1-1


“A stochastic model of spruce budworm, Choristoneura fumiferana (Clemens), phenology on balsam fir, Abies balsamea (L.) Miller, and white spruce, Picea glauca (Moench) Voss, in northern Ontario was developed based on relationships between the proportion of budworms in each stage (second instar to adultsecond instar to adult) and accumulated degree-days (DD).

Repeated calculations indicated that 8 degree C (46 F) was a suitable threshold for degree-day calculations. Tests of the model with independent data showed that it simulated spruce budworm development excellently. Model performance was superior compared with a previously published spruce budworm phenology model.”

Lysyk, T.J. 1989. Stochastic model of eastern spruce budworm (Lepidoptera: Tortricidae) phenology on white spruce and balsam fir. Journal of Economic Entomology 82 (4):1161-1168.

Growing Degree-day calculation

DAY 1

Daily High 70 F Daily Low 50 F Mean daily 60 FBase temp. = 46 F

GDD = 14 F

DAY 2

Daily High 60 FDaily Low 40 F Mean daily 50 FBase temp. = 46 F

GDD = 4 F

3-day accumulation = 18 GDD F

DAY 3

Daily High 52 FDaily Low 40 F Mean daily 46 FBase temp. = 46 F

GDD = 0 F

Accumulated degree days associated with peak stages of spruce budworm development

2nd instar 197 GGD(F)3rd instar 217 GGD(F)4th instar 280 GGD(F)5th instar 366 GGD(F)6th instar 492 GGD(F)Pupa 698698 GGD(F)Adult 818818 GGD(F)Base temperature = 46 F.Starting date (Lysyk) = 01 MarchStarting date (Juday -AK) = 01 April

Accumulated degree days associated with peak stages of spruce budworm development

2nd instar 109 GGD(C)3rd instar 121 GGD(C)4th instar 156 GGD(C)5th instar 203 GGD(C)6th instar 273 GGD(C)Pupa 388388 GGD(C)Adult 454454 GGD(C)Base temperature = 8 C.Starting date (Lysyk) = 01 MarchStarting date (Juday -AK) = 01 April

WE TEMPORARILIY INTERRUPTWE TEMPORARILIY INTERRUPT

THIS PRESENTATION IN ORDERTHIS PRESENTATION IN ORDER

TO BRING YOU AN IMPORTANTTO BRING YOU AN IMPORTANT

MESSAGE ABOUT RECENTMESSAGE ABOUT RECENT

TEMPERATURE TRENDS IN TEMPERATURE TRENDS IN

BOREAL ALASKABOREAL ALASKA

Interior Alaska Growth Year Temperature (smoothed)

-7.0

-6.0

-5.0

-4.0

-3.0

-2.0

-1.0

190619111916192119261931193619411946195119561961196619711976198119861991199620012006

Year

Sep:Aug temperature (degrees C)

McGrathMcGrath(foothils of Alaska Range)(foothils of Alaska Range)

BettlesBettles(foothills of Brooks Range)(foothills of Brooks Range)


Boreal Alaska Sumer Temperature (smoothed)

10.5

11.5

12.5

13.5

14.5

190619111916192119261931193619411946195119561961196619711976198119861991199620012006

Year

May:Aug Degrees C

TalkeetnaTalkeetna

FairbanksFairbanks

BettlesBettles


Frost date at Fairbanks1905-2007

y = 0.2446x + 231.19

R2 = 0.2496

y = -0.1627x + 149.72

R2 = 0.2091

110

130

150

170

190

210

230

250

270

1905 1915 1925 1935 1945 1955 1965 1975 1985 1995 2005

year

Julian date (day # of year)

cold seasoncold season

cold seasoncold season

growing seasongrowing season

Last spring frostLast spring frost

First fall frost

First fall frost Analysis: G. Juday Analysis: G. Juday

5-factor nWARM index - 15 May-15Sep at Fairbanks

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

19051909191319171921192519291933193719411945194919531957196119651969197319771981198519891993199720012005

year

n index (stdev) Factors Factors • # days 70+F (21.1 C)# days 70+F (21.1 C)• #days grow season#days grow season• mean daily min. Tmean daily min. T• mean daily max. Tmean daily max. T• min. T of coldest 1 daymin. T of coldest 1 day

20072007


WE NOW RESUME OUR WE NOW RESUME OUR

REGULARLY SCHEDULED REGULARLY SCHEDULED

PRESENTATIONPRESENTATION

Spruce budworm abundance in central Alaska

0

50

100

150

200

250

1975 1980 1985 1990 1995 2000 2005

year

Number/m-2

0

50

100

150

200

250

300

acres infested (X 1000)

budworm density ac infested X 1000

Budworm density data: R. Werner, J. Kruse Budworm density data: R. Werner, J. Kruse

no no budwormsbudworms

DataDatastartstart

19901990

19951995

20042004

Budworm area data: AK For. Health Survey Budworm area data: AK For. Health Survey

Date of spruce budworm heat requirement for peak of adult moth stage at Fairbanks, AK

178

182

186

190

194

198

202

206

210

214

218

222

1905 1915 1925 1935 1945 1955 1965 1975 1985 1995 2005

year

Julian date

moth @ 818 F Linear (moth @ 818 F)

July 7 (July 7 (July 6 Leap yr.)July 6 Leap yr.)

2004200420052005

199319931995199519881988

19901990

19131913

19151915

1975?1975?

Mean daily temperature, 01 Aug. to 31 Aug., at Fairbanks

10.0

11.0

12.0

13.0

14.0

15.0

16.0

17.0

18.0

1905 1915 1925 1935 1945 1955 1965 1975 1985 1995 2005

year

Deg. C

Data: National Weather ServiceData: National Weather ServiceAnalysis: G. Juday Analysis: G. Juday

19151915

19131913

19771977

19751975

199419941988-1988-19901990

20042004


Length of time to meet spruce budworm heat requirement from L2 to adult moth at Fairbanks

55

65

75

85

95

105

1905 1915 1925 1935 1945 1955 1965 1975 1985 1995 2005

year

# of days

Larva 2 to moth elapsed Linear (Larva 2 to moth elapsed)

2004-2004-20072007

1993-1993-19951995


Trends of spruce budworm heat requirement at Fairbanks

175

180

185

190

195

200

205

210

215

220

225

1905 1915 1925 1935 1945 1955 1965 1975 1985 1995 2005

year

Julian date

55

65

75

85

95

105

# days

Adult moth done date L2 to moth elapsed

Linear (Adult moth done date) Linear (L2 to moth elapsed)

Date of spruce budworm heat requirement at Fairbanks

170

180

190

200

210

220

230

1905 1915 1925 1935 1945 1955 1965 1975 1985 1995 2005

year

Julian date

0

50

100

150

200

250

300

acres infested (X 1000)

moth @818 F pupa @ 698F ac infested X 1000

19951995

Acreage Data: Alaska Forest Health Survey Acreage Data: Alaska Forest Health Survey Analysis: G. Juday Analysis: G. Juday

Spruce budworm population density vs. heat requirement date at Fairbanks

178

182

186

190

194

198

202

206

210

1970 1975 1980 1985 1990 1995 2000 2005

year

Julian date

0

50

100

150

200

250

insects/sq.M foliage

adult moth @ 818 F GDD budworm density

19951995

19931993

20052005

1988198819901990

20072007

Budworm data: R. Werner, J. Kruse Budworm data: R. Werner, J. Kruse



DataDatastartstart

Spruce budworm population density vs. heat requirement date at Fairbanks

178

182

186

190

194

198

202

206

210

1970 1975 1980 1985 1990 1995 2000 2005

year

Julian date

0

50

100

150

200

250

insects/sq.M foliage

adult moth @ 818 F GDD budworm density

19951995

19931993

20052005

1988198819901990

20072007

Budworm data: R. Werner, J. Kruse Budworm data: R. Werner, J. Kruse



DataDatastartstart

1-yr. lag1-yr. lag

PART 4.PART 4.

OK, SO IT’S HERE, SO WHAT’S OK, SO IT’S HERE, SO WHAT’S

GOING TO HAPPEN?GOING TO HAPPEN?

Spruce budworm damage levels atBNZ 1 Reserve West

(plots 200 & 300; n = 783 trees)

0%

10%

20%

30%

40%

50%

VL L M+damage category

% of trees

2006 2007

(est

imate

d)

Data: G. Juday Data: G. Juday

NE British Columbia - Some useful recent articles:

Alfaro, R.I., Taylor, S.P. R.G. Brown and J.S. Clowater. 2000. Susceptibility of Northern British Columbia forests to spruce budworm defoliation. For. Ecol. and Management. 145: 181-190.

Burleigh, J.S., R.I. Alfaro, J.H. Borden, and S. Taylor. 2002. Historical and spatial characteristics of spruce budworm Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae) outbreaks in northeastern British Columbia. Forest Ecology and Management 168: 301-309.

Magnussen, Paul Boudewyn and René Alfaro. 2004. Spatial prediction of the onset of spruce budworm defoliation. The Forestry Chronicle 80(4): 485-494.

Source: Natural Resources CanadaSource: Natural Resources Canadahttp://cfs.nrcan.gc.ca/subsite/budworm/impact

Cumulative Tree Mortality in white spruceCumulative Tree Mortality in white spruce(39 ecological impact plots in the Fort Nelson, B.C. Forest District)

Mortality from highwater table and windthrow

Budworm

No budworm

“Not known to breed inAlaska.” “Has occurred at Fairbanks, Haines, Pt. Barrow.” Armstrong. 1983. Birds of Alaska.

Cape May Warbler (Dendroica tigrina) :“ … the fortunes of its populations are largely tied to the availability of spruce budworms, its preferred food.”http://www.birds.cornell.edu/AllAboutBirds/BirdGuide/Cape_May_Warbler_dtl.html

Dendron = treeOikein = dwell

Tennessee Warbler (Vermivora peregrina):“A dainty warbler of the Canadian boreal forest, the Tennessee Warbler specializes in eating the spruce budworm. Consequently its population goes up and down with fluctuations in the populations of the budworm.”http://www.birds.cornell.edu/AllAboutBirds/BirdGuide/Tennessee_Warbler_dtl.html

Probable rare breeder in Southeast Alaska, accidental in central Alaska. Armstrong. 1983. Birds of Alaska.

Vermis = worm

Bay-breasted Warbler (Dendroica castanea) :“A large warbler of the northern spruce forests, the Bay-breasted Warbler benefits from spruce budworm outbreaks when the caterpillars provide abundant food.”http://www.birds.cornell.edu/AllAboutBirds/BirdGuide/Bay-breasted_Warbler_dtl.html

Accidental. Fairbanks. Armstrong. 1983. Birds of Alaska.

castanea = chestnut

Fairbanks Summer Temperature and W. Spruce Growth (BNZ LTER - 2PLS; 1902:2007; n = 2 trees)

11.0

11.5

12.0

12.5

13.0

13.5

14.0

14.5

15.0

15.520071997198719771967195719471937192719171907

year

May:Aug T (deg. C)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

mean ring-width (mm)

3-yr weighted May:Aug Temperature mean tree 5&8


BA

RK

BA

RK

20052005

2000

2000

2001

2001

2002

2002

2003

2003

2004

2004

2006

2006

1999

1999

1998

1998

1997

1997

1996

1996

1992

1992

1991

1991

1990

1990

1995199519931993

spruce budwormspruce budwormdamagedamage heat/droughtheat/drought

limitationlimitation

Photo: C. AlixPhoto: C. Alix

Summer temperature vs. w. spruce growth(Bonanza Creek LTER -2 Parks Loop South; 1906-2006; n = 12 trees)

r2 = 0.32

0.0

0.2

0.4

0.6

0.8

1.0

1.2

9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0 17.0 18.0 19.0 20.0

previous May:Aug T (deg C)

mean sample ring width (mm)

1912 volcanic 1912 volcanic ash?ash?

1993 & 95 spruce budworm defoliation1993 & 95 spruce budworm defoliation

2004 record hot2004 record hot


KILL ZONEKILL ZONE KILL ZONEKILL ZONE

Fairbanks Summer Temperature and W. Spruce Growth (BNZ LTER - 2PLS; 1902:2007; n = 2 trees)

r2 = 0.31

0.0

0.2

0.4

0.6

0.8

1.0

10.0 11.0 12.0 13.0 14.0 15.0 16.0 17.0

3-yr weighted May:Aug. Temp. (deg. C)

ring width (mm)

2007 spruce 2007 spruce budworm defoliationbudworm defoliation


1968 1968 (1967 flood)(1967 flood)

1984-85 1984-85

19511951

May:Aug mean temperature at Fairbanks

10.0

11.0

12.0

13.0

14.0

15.0

16.0

17.0

18.0

1906191419221930193819461954196219701978198619942002201020182026203420422050205820662074208220902098

year

degrees C

recorded CCC scenario

recordedrecorded

regular occurrenceregular occurrenceof summers of summers warmer thanwarmer than

20042004

20042004

Canadian Climate Center scenario

SUMMARY

• Spruce budworm is a major force shaping the North American boreal forest.

• Climate suitable for spruce budworm outbreaks have generally not been present in boreal Alaska until 1989.

• Seven stages of development (L1 - L6, Pupa) over 2 years.

• Winter cold temperatures do not appear to be a limitation.

• Egg hatch, L1, to L2 must get done in August, faster when warm.

• Greatest amount of damage from L6 feeding.

• L2 to adult must get done by mid-July (818 GDD F).

• Light attacks reduce w. spruce radial growth.

• Moderate attacks reduce growth and height growth points.

• Repeated severe attacks kill w. spruce.

• 3 boreal warblers have been missing from Alaska breeding birds.

PART 5.PART 5.

OK, SO WHAT HAPPENS NEXT?OK, SO WHAT HAPPENS NEXT?

Source: Natural Resources CanadaSource: Natural Resources Canadahttp://cfs.nrcan.gc.ca/subsite/budworm/space-spatiale

NE British ColumbiaWe concluded that timber losses are important in areas with maximum defoliation. Ecological impacts involved transformations of the forest that are likely transitory, considering the time scale of forestry (more than 100 years). Loss of biodiversity habitat is particularly important in areas that have been reserved for their old-growth characteristics. However, a changing climate may alter the long-term effects of budworm on the forest. The current outbreak has been longer and more severe than past outbreaks for which we have historical or tree-ring records. We cannot predict what these future changes will be, but the forest may change in different ways than it has in the past. The spruce budworm may also begin to attack forests where it has not been previously found.

PROBABLE SPRUCE BUDWORM FUTURE IN ALASKA BOREAL FOREST:

• Large outbreaks continue, intensify, and spread west, up, north

• W. spruce experiences high mortality and becomes less abundant

• Spruce budworm becomes limited by lack of contiguous susceptible stands of w. spruce

• W. spruce stabilizes population at lower level and in “refuge” stands in response to repeated outbreak cycles.

• Reduction/bottleneck for old-growth dependent species, esp. insectivorous migratory birds.

• 3 warbler species establish breeding populations in Alaska.

• W. spruce niche in uplands is partially displaced by:

- black spruce

- Alaska birch

- aspen

- lodgepole pine?

From scenario projection to forecasting?

From scenario projection to forecasting?

Documents

Spruce Budworm (Tordeuse des bourgeons de l'epinette) at Bonanza Creek LTER: A clear case of temperature thresholds in a warming climate Glenn Patrick