Boreal forest
description
Transcript of Boreal forest
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)
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FairbanksPrince AlbertKapuskasingChicoutimi
Mean monthly temperature
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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
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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
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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.
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Forest floor thickness (cm)
High severity fireLow severity fire
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Mean ericaceous cover (%)
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Forest floor thickness (cm)
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Effects of paludification on forest timber production
Left: stand opens up over time, and Right: wood production declines (especially in stands
>200-yr old)
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Mean open canopy (%)
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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
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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
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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 ?