ECGS-039_ForestTundra_TV.pdf

Boreal Forest (taiga) and Tundra

Forest Boundary

Primarily determined by summer temp conditions (effective temperature sum)

But thereare lots of local and regional variation:

• Moisture conditions:
  • local = slope, drainage
  • regional = climate (evaporation/ppt)
  • Permafrost is very localized - a few rain days can cause massive mud zones
• Soil quality
• Wind
• Herbivory
• Human activities

Impacts of boundary

• Species composition - especially trees, which have massive effects onthe whole ecosystem
  • Shade, snow accumulation, soil effects
• Carbon storage and flows (very affected by trees)
• Radiation balance (darker coniferous trees=low albedo=absorb and emit solar radiation)
• Water circulation and runoff

Location of boundaries

• Location of the boundary has varied historically according to climate conditions
• Climate models predict large changes in the northern region
  • especially due to tree distributions
• Generally tree line follows mean July temperature 10-12 deg, but there are some regional differences
  • Boreal forest begins and ends quite far North in Fennoscandia
  • Canada and Russian far east have quite far south tundra

Boreal Forest

• Largest vegetation entity (?) in the world
• Reaches all through northern hemisphere continents
• bordered by treeless tundra to the north and mixed deciduous forests or steppe to the south (or human-dominanted agriculture etc)
• Important carbon sinks that reduce albedo

Species at the treeline

• In different regions, different species dominate the boreal tree line
  • In more maritime regions, deciduous species like Alnus (Alder), Populus (Alaska), Betula (Nordics), Chosenia (in Yakutia)
  • In most continental regions we have larches dominanting - Siberian and Dachurian larch in Siberia
  • In areas in between like the Canadian arctic and Novosibirsk we have spruces
    • White and black spruce are hard to tell apart at the treeline

Endemism in the Arctic

• As the boreal forests replaces tundra, we are at risk of losing endemic tundra species causing significiant biodiversity loss
• Arctic Biodiversity Assessment

Arctic terrestrial biodiversity

• Monitoring is needed, especially for arthropods and plants

Treeline structure

• Difference between "Forest Line" and "Tree line"
• Concern about forestry at this zone

Forest Development

• It takes between 1000 and 3000 years for forest to develop after the first conifer species appear in the pollen records... why?
  • Intra-species competition
  • Small size of original populations
  • Snow cover thickness
  • Paludification (Peatlands - Introduction) and permafrost dynamics

Controlling factors

Abiotic

• Temperature - direct or indirect
• Precipitation (effective moisture)
  • Snow cover (related to the above two) - loss of snow cover results in decreasing biodiversity
• Wind abrasion - damages trees above the snow line
• Soil properties
  • Porosity
  • Soil maturing rate (nutrient formation) - this is related to migration rate

Tree properties

• Phenology - Timing changes such as bud outbrak, wintering
• Different species have different growth rates
  • Inherited Phenotypic Plasticity
• Inter-annual variation
  • At the northernmost tree line cone production is only successful 1/20 or 1/100 years
  • Under modertately good conditions each individual only produces one viable offpsring in its life on average (Fertility rate)

Biological Interactions

Case studies

• Tundra/forest boundary is a very complex ecosystem - 30m resolution Landsat pixels do not allow for modelling complex mixtures of peatlands, forests, lakes, tundra...