Boreal forestBiophysical environmentsBiotic interactionsFire regimes & post-fire successionFloodplain succession & paludificationForest clearance and successionClimate change: natural &

anthropogenic

Boreal forest biome-------

Scandinavia70% Russia70% Alaska50% Canada

Fairbanks

Pr. AlbertKapuskasing

Chicoutimi

Note latitudinal variation

Boreal climate (N.America)

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

1 2 3 4 5 6 7 8 9 10 11 12

FairbanksPrince AlbertKapuskasingChicoutimi

Mean monthly temperature

J F M A M J J A S O N D

J F M A M J J A S O N DFairbanks

Prince AlbertKapuskasing

Chicoutimi0

20

40

60

80

100

120

Monthly precipitation (mm)

FairbanksPrince AlbertKapuskasingChicoutimi

Monthly precipitation (mm)

Mean annual snowfall (mm)

Boreal forest zone

Boreal forest and permafrost distributio

n

Mean annualtemperature

-2.8°

0.6° 0.7° 3.0°

Discontinuous permafrost limit ~ -2°C

Boreal forest Tundra

Permafrostpatchy discontinuous continuous

Mean locationPolar FrontJulyJan

150 240 Mean #d <0°C

treegrowth

pollen/seedviability

120 30 Mean #d >10°C

Boreal forest-environment interactions

Physicaltemplate

Climate

Soil

Biota

The boreal forest biome in Canada

Boreal forest

“Taiga”

Trees of the N. American boreal forest

Evergreens

Deciduous

non-accessed

sprucepinebalsam firpoplarbirchother

Boreal forest vegetation types

(North America)

Forest structure Boreal forest Taiga

spruce/birch/pine forest mosaic spruce-lichen woodland

Boreal forest soils

south north

Podzols,

regosols

gleysols, cryosols

Underlain by coarse-textured deposits or bedrock. Well-drained, warm fairly rapidly in summer, more rapid breakdown of organics, strongly-leached, acidic, low nutrient availability.

Underlain by fine-textured deposits / permafrost. Poorly-drained, cold in summer; little microbial activity, slow breakdown of organics, low nutrient availability.

boreal forest taiga

% c

over

0

100

OAe

Bf

OBC

Cg

Forest community segregation in the boreal

forest

site: wet mesic drysoil: gleys podzolsactive: thin (<0.3m) thick (>2m)layer (or no permafrost)organic thick thin layer

blackspruce tamarack

white spruce -birch-aspen-

balsam fir

jack pine

mosses

Biomass and productivity

black spruce

white spruce

paperbirch

aspen poplar

Nutrient cycling and storage (nitrogen)

black spruce

white spruce

paperbirch

aspen poplar

Herbivory and boreal forest dynamics

enhancements reductions

Browsebiomass

Moosepopulation

phytotoxins soilmicrobiota

Nitrogen mineralization

Wolfpopulation

Insect outbreaks(e.g. spruce budworm; Siberian silkworm)

Climate(early summer drought)

Insect populations(larvae)

Fire hazard

Forest structure* and biomass

enhancements reductions

*suitable host trees (e.g. balsam fir for spruce

budworm)

Fire regimeFire cycle• Natural fire cycle averages 50-200 years• Length of the cycle controlled by moisture

balance• Most fires small (~70% in AK & YK <5 ha).• Severe fires can cover 200,000 ha.• Most boreal forests equally flammable

regardless of age (after first decade).

Forestfire

weather zones

Precipitation and wildfire frequency

Precip.

Fire RI

Fire regimeFire intensity• Most tree species are not fire resistant. Thick

bark protects pines.

• Tendency of fire to crown dependent on tree canopy architecture and understorey vegetation. Crown fires common in spruce and pine forests, rare in deciduous forests.

Fire resistance: protective role of tree bark

paper birch black spruce jack pineresistance

Fire regimePost-fire regeneration• Many trees dependent on recurring fires.• Post-fire reproduction by means of:

light, wind-dispersed seeds (e.g. birches, poplars)serotinous or semiserotinous cones (e.g. jack pine, black spruce)stump sprouting or suckering (aspen, paper birch)

Post-fire regeneration

from serotinous cones

from suckers

Fire succession

no

Birch (Betula papyrifera) forest with spruce (Picea sp.)

understorey on mesic site

Fire regimeFire severity• Removal of the canopy and surface

organic layer increases surface energy receipt. Thickness of active layer may increase substantially for first few years following fire.

• Nutrients in surface mat and soil released by fire (N and P increase most in moderately burned areas).

Succession schematic

Floodplain succession, Alaska

Floodplain succession( pioneer phase)

Floodplain succession( pioneer phase)

Balsam poplarwhite spruce

herbs

Floodplain succession(climax phase)

mature white spruceon scroll bars

Floodplain succession, NE BC

Influence of forest cover on soil temperature

-6

-4

-2

0

2

4

6

8

10

12

14

May June July Aug Sept Oct Nov Dec Jan Feb Mar Apr

white spruceblack sprucebalsam poplar

In the absence of disturbance paludification may occur

• Moss-organic layers > 5cm thick preclude spruce regeneration from seed.

• Spruce stands may reproduce vegetatively by layering (regrowth of low branches buried in the moss-organic mat).

• If moss-organic layer continue to increase in depth, paludification (bog-formation) may occur. In W. Siberia ~1/3 of the taiga is forested bog.

Paludification: a double feedback loop

soilwater table

Sphagnummoss growthironpan

formation

soil acidity

peatdevelopment

Sphagnumnutrient uptake

tree growth

enhancements reductions

Sphagnum bog formation

Effects of successional

paludification of boreal forest soils

(in western Québec)

Data: Simard et al., 2007. Ecological Applications 17, 1619-1637.

0

50

100

150

200

0 50 100 150 200 250 300 350 400Years since fire

Forest floor thickness (cm)

High severity fireLow severity fire

0

20

40

60

80

100

0 50 100 150 200 250 300 350 400Years since fire

Mean ericaceous cover (%)

0

50

100

150

200

0 50 100 150 200 250 300 350 400Years since fire

Forest floor thickness (cm)

High severity fireLow severity fire

Effects of paludification on forest timber production

Left: stand opens up over time, and Right: wood production declines (especially in stands

>200-yr old)

0

20

40

60

80

100

0 50 100 150 200 250 300 350 400Years since fire

Mean open canopy (%)

0

10

20

30

40

50

0 50 100 150 200 250 300 350 400Years since fire

Stem basal area (m^2/ha)

High severity fire

Low severity fire

Data: Simard et al., 2007. Ecological Applications 17, 1619-1637.

Forest clearance in NW Europe

Farm clearance-abandonment cycle (data from New England)

Wood production areas

-20

-15

-10

-5

0

5

10

15

1 2 3 4 5 6

Effects of harvesting on forest cover in accessed areas of boreal forest

spruce

pine

balsamfir

poplars

birch other

% c

hang

e

North American vegetation at the Last

Glacial Maximum

(18 000 14C yr BP

= 20 000 yrs BP)

Postglacial migration

of the boreal forest plant

community from pollen

evidence

Pollen Viewer

http://www.ncdc.noaa.gov/paleo/pollen/viewer/webviewer.html

LGM and Late Glacial distribution of boreal and mixed forest from pollen

evidence

Boreal = dark greenMixed forest = light green

No analogueOverpeck et al., 1992. Geology 20, 1071-1074.

Ranges, clades and postglacial migrations of New World tree squirrels

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Douglas squirrelT. douglasii

Red squirrelT. hudsonicus

“T. mearnsii”

SW clade

(T = Tamiasciurus)

??

Simplified from data in Abrogast et al., 2001. J. Mammalogy 82, 302-319

easternclade

Range, fossil sites and inferred postglacial migration of American

martenMartes americanavarieties: americana and caurina

Stone et al., 2002. Molecular Ecology 11, 2049–2063

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• fossils

“Superspecies” complexes of boreal forest birds: note repetitive

distribution patterns

a

b

Sphyrapicus (sapsuckers)

Dendroica (warblers)

Vermivora (warblers)

Passerella (warblers)

Vireo (vireos)

Empidonax (flycatchers)

Opopornis (warblers)

Poecile (chickadees)

Weir and Schluter, 2004. Proc. Roy. Soc. London B, 217, 1881-1887.

Cladogram of boreal bird superspecies

100

Map shows ice cover at LGM and

approximate distribution of boreal forest glacial refugia

Clock for DNA cladogram = 2.2% change in DNA per

Ma

18O

cold

warmMa (BP) 2.0 1.5 1.0 0.5 0 .0

palaeotemperature

Weir and Schluter, 2004. Proc. Roy. Soc. London B, 217, 1881-1887.

ADVANCE = north;RETREAT = south

Changes in the boreal forest

margin in southern Sweden since

1250BC

Global climate change and the boreal forest:growth fire frequency paludification ?