Boreal forest • Biophysical environments • Biotic interactions • Fire regimes & post-fire succession • Floodplain succession & paludification • Forest clearance and succession • Climate change: natural & anthropogenic
Boreal forest biome-------Scandinavia70% Russia70% Alaska50% Canada Fairbanks Chicoutimi Pr. Albert Kapuskasing Note latitudinal variation
Mean monthly temperature J F M A M J J A S O N D
Mean annual snowfall (mm) Boreal forest zone
Boreal forest and permafrost distribution -2.8° Mean annual temperature 0.6° 3.0° 0.7° Discontinuous permafrost limit ~ -2°C
Mean location Polar Front tree growth Jan July 120 30 Mean #d >10°C pollen/seed viability 150 240Mean #d <0°C Boreal forest Tundra Permafrost patchy discontinuous continuous
Boreal forest-environment interactions Biota Climate Physical template Soil
The boreal forest biome in Canada “Taiga” Boreal forest
Trees of the N. American boreal forest Evergreens Deciduous
Forest structureBoreal forest Taiga spruce-lichen woodland spruce/birch/pine forest mosaic
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. Underlain by fine-textured deposits / permafrost. Poorly-drained, cold in summer; little microbial activity, slow breakdown of organics, low nutrient availability. 100 gleysols, cryosols O Ae Bf O BC Cg % cover Podzols, regosols 0 south north boreal forest taiga
Forest community segregation in the boreal forest white spruce - birch-aspen- balsam fir jack pine black spruce tamarack mosses site: wet mesic dry soil: gleys podzols active: thin (<0.3m) thick (>2m) layer (or no permafrost) organic thick thin layer
Biomass and productivity paper birch black spruce white spruce poplar aspen
Nutrient cycling and storage (nitrogen) paper birch black spruce white spruce poplar aspen
Herbivory and boreal forest dynamics Moose population Nitrogen mineralization Browse biomass Wolf population soil microbiota phytotoxins enhancements reductions
Insect outbreaks(e.g. spruce budworm; Siberian silkworm) Climate (early summer drought) Fire hazard Forest structure* and biomass Insect populations (larvae) *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).
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 jack pine resistance
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
Birch (Betula papyrifera) forest with spruce (Picea sp.) understorey on mesic site
Fire regime Fire severity • Removal of thecanopy 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).
Floodplain succession( pioneer phase) Balsam poplar white spruce herbs
Floodplain succession(climax phase) mature white spruce on scroll bars
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 branchesburied 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 peat development Sphagnum moss growth ironpan formation soil acidity tree growth enhancements reductions
Effects of successional paludification of boreal forest soils(in western Québec) Data: Simard et al., 2007. Ecological Applications17, 1619-1637.
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 Applications17, 1619-1637.
Effects of harvesting on forest cover in accessed areas of boreal forest poplars balsam fir birch other % change pine spruce
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 green Mixed forest = light green No analogue Overpeck et al., 1992. Geology20, 1071-1074.
Ranges, clades and postglacial migrations of New World tree squirrels (T = Tamiasciurus) ? Douglas squirrel T. douglasii ? easternclade Red squirrel T. hudsonicus SW clade “T. mearnsii” Simplified from data in Abrogast et al., 2001. J. Mammalogy82, 302-319
Range, fossil sites and inferred postglacial migration of American marten Martes americana varieties: americanaandcaurina • fossils Stone et al., 2002. Molecular Ecology11, 2049–2063
Sphyrapicus (sapsuckers) Dendroica (warblers) Vermivora (warblers) Passerella (warblers) Vireo (vireos) Empidonax (flycatchers) Opopornis (warblers) Poecile (chickadees) “Superspecies” complexes of boreal forest birds: note repetitive distribution patterns Weir and Schluter, 2004. Proc. Roy. Soc. London B, 217, 1881-1887.