Taiga forest of Alaska

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Taiga forest of Alaska
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The taiga as the perfect example to show the
interactions of climate, topography, parent
material, biota, and time since formation. The
climate potential for permafrost Topography
south vs north facing slopes critical Parent
material effects of glacial flour,
permafrost Biota control on microclimate Time
fire and flood set the historical range of
variability (HRV)
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Taiga flood plain example Time Time since
flood scour
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Capillary action causes salt build-up. This
creates a high soil pH. At high soil pH
phosphorus is ________________ N-fixation on
new areas is inhibited by lack of available
phosphorus! (initial successional system is
phosphorus limited!)
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Flooding, capillary rise, phosphorus
precipitation, salt stress Alder
colonization, N fixation, acidification of soil,
decline in P limitation, decline in capillary
activity. Poplars unable to reproduce beneath
closed canopy Feather moss accumulation Insulatio
n of soil, decrease in decomposition increase in
organic mat development of permafrost
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Why does nitrogen fixation lead to soil
acidification? a) b)
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Mammalian herbivores use multiple patches in
landscape Alter ecosystem structure Speed
nutrient cycling
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ALDER WILLOW RATIO
3
2
1
0
B
R
O
W
S
E
D
U
N
B
R
O
W
S
E
D
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Steps in flood plain development Phosphorus
limitation N-fixing alder plants relieve P and
N limitation Light limitation limits deciduous
trees Conifers invade Litterfall greatly
declines Conifers allow for moss development
on soil surface Moss development results in
permafrost development System remains a black
spruce forest/bog until flood scour
reinitiates the process.
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Taiga uplands example Time Time since fire
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Boreal conifer forests are born to burn After
fire are replaced by less flammable deciduous
forests
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Uplands development Fire kicks system into rapid
growth.(no phosphorus limitation) Biota follow
same path as floodplain South-facing slopes
remain as aspen/white spruce North-facing slopes
continue biotic succession to black spruce.
rapid decomposition gt shade gt conifers gt moss
gt permafrost
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The combination of vegetation and topography
create a 4x difference in soil microclimate and
depth of organic matter.
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Fire as a restart mechanism the taiga (boreal
forest)
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Return to black spruce Deciduous sp. shade
forest floor more completely, allowing
shade-tolerant black spruce to incr. More black
spruce more soil shading (spring fall) and
high-lignin litter This decreases soil temps,
decomp, mineralization
Note how permafrost increases (depth to
permafrost decreases) with the presence of moss
and litter
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• Taiga
• Ways that biota control nutrients
• N-fixation by alder changes pH, makes both N and
• P more available!
• Failure of deciduous species to reproduce
  beneath
• the canopy favors conifers, and the reduction
  in
• litterfall favors growth of feather moss.
• Moss functions as blanketsoil becomes cooler
• and wetter, thereby reducing decomposition.
• High lignin content of conifer litter further
  slows decay.

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Climate interacts with topography to favor
permafrost in some areas (north aspects) Fire
can remove organic matter blanket, greatly
stimulate Mineralization, inorganic N and P
availability jump Starts succession favoring
deciduous species. Climate Topography Parent
material (bedrock, loess, glacial flour,
none) Biota (deciduous, coniferous, mosses) Time
(glaciers, fire