Boreal forest v Biophysical environments v Biotic interactions v Fire regimes & post-fire succession v Floodplain succession & paludification v Forest clearance and succession v Climate change: natural & anthropogenic
Boreal forest biome ------- Scandinavia 70% Russia 70% Alaska 50% Canada Fairbanks Pr. Albert Chicoutimi Kapuskasing Note latitudinal variation
Mean monthly temperature J F M A M J J A S O N D
Monthly precipitation (mm)
Mean annual snowfall (mm) Bo re al fo re st zo n e
Boreal forest and permafrost distribution -2. 8° Mean annual temperature 0. 6° 0. 7° 3. 0° Discontinuous permafrost limit ~ -2°C
Jan tree growth July 120 150 Mean location Polar Front 30 pollen/seed viability Mean #d >10°C 240 Mean #d <0°C Boreal forest patchy discontinuous Tundra continuous Permafrost
Boreal forest-environment interactions Biota Climate Physical template Soil
The boreal forest biome in Canada “T Bo aig re a a” lf or e st
Trees of the N. American boreal forest Evergreens Deciduous
Boreal forest vegetation types (North America)
Forest structure Boreal forest spruce/birch/pine forest mosaic Taiga spruce-lichen woodland
Boreal forest soils 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. 100 Bf gleysols, cryosols % cover O Ae Underlain by fine-textured deposits / permafrost. Poorlydrained, cold in summer; little microbial activity, slow breakdown of organics, low nutrient availability. Podzols, Cg regosols 0 south boreal forest north taiga O BC
Forest community segregation in the boreal forest black spruce tamarack white spruce birch-aspenbalsam fir jack pine mosses site: wet soil: gleys active: thin (<0. 3 m) layer organic thick layer mesic dry podzols thick (>2 m) (or no permafrost) thin
Biomass and productivity black spruce white spruce paper birch aspen poplar
Nutrient cycling and storage (nitrogen) black spruce white spruce paper birch aspen poplar
Herbivory and boreal forest dynamics Moose population Nitrogen mineralization Browse biomass Wolf population enhancements phytotoxins soil microbiota reductions
Insect outbreaks (e. g. spruce budworm; Siberian silkworm) Climate (early summer drought) Insect populations (larvae) Fire hazard Forest structure* and biomass *suitable host trees (e. g. balsam fir for spruce budworm) enhancements reductions
Fire regime Fire 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).
Forest fire weather zones
Precipitation and wildfire frequency Precip. Fire RI
Fire regime Fire 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 resistance jack pine
Fire regime Post-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 suckers from serotinous cones
Fire succession no
Birch (Betula papyrifera) forest with spruce (Picea sp. ) understorey on mesic site
Fire regime Fire 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) white spruce Balsam poplar herbs
Floodplain succession (climax phase) mature white spruce on scroll bars
Floodplain succession, NE BC
Influence of forest cover on soil temperature
In the absence of disturbance paludification may occur • Moss-organic layers > 5 cm 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 soil water table Sphagnum nutrient uptake Sphagnum moss growth ironpan formation soil acidity enhancements peat development tree growth reductions
Sphagnum bog formation
Effects of successional paludification of boreal forest soils (in western Québec) Data: Simard et al. , 2007. Ecological Applications 17, 1619 -163
Effects of paludification on forest timber production Left: stand opens up over time, and Right: wood production declines (especially in stands >200 -yr old) Data: Simard et al. , 2007. Ecological Applications 17, 1619 -163
Forest clearance in NW Europe
Farm clearance-abandonment cycle (data from New England)
Wood production areas
Effects of harvesting on forest cover in accessed areas of boreal forest poplars % change balsam fir pine spruce birch other
North American vegetation at the Last Glacial Maximum (18 000 14 C 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 green Mixed forest = light green No analogue Overpeck et al. , 1992. Geology 20, 1071 -1074
Ranges, clades and postglacial migrations of New World tree squirrels (T = Tamiasciurus) Douglas squirrel T. douglasii ? eastern clade ? Red squirrel T. hudsonicus SW clade “T. mearnsii” Simplified from data in Abrogast et al. , 2001. J. Mammalogy 82, 302 -319
Range, fossil sites and inferred postglacial migration of American marten Martes americana varieties: americana and caurina • fossils Stone et al. , 2002. Molecular Ecology 11, 2049– 2063
Sphyrapicus (sapsuckers) Dendroica (warblers) Vermivora (warblers) Passerella (warblers) Vireo (vireos) Empidonax (flycatchers) Opopornis (warblers) “Superspecies” complexes of boreal forest birds: note repetitive distribution patterns Poecile (chickadees) Weir and Schluter, 2004. Proc. Roy. Soc. London B, 217, 1881 -1887.
Cladogram of boreal bird superspecies Map shows ice cover at LGM and approximate distribution of boreal forest glacial refugia cold d 18 O Clock for DNA cladogram = 2. 2% change in DNA per Ma palaeotemperature warm Ma (BP) 2. 0 1. 5 1. 0 0. 5 0. 0 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 1250 BC
Global climate change and the boreal forest: growth fire frequency paludification ?
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