L19

Question 1

Fire in high latitudes

Answer 1

• Is a common and natural process in Boreal forests
  
  • Increasingly important in tundra
  • Fire frequency and severity increasing
  • Tundra fires are now occurring much more often
  • Carbon is re-uptook post fire in a natural burn cycle for regrowth
    This balance is lost beyond the natural balance

Question 2

Boreal fire and NBP

Answer 2

-Adding CO2 influence only results in a small carbon gain
-The effect of warming has minimal impact
- Disturbance effects e.g. fires reduces NBP
- Loss of carbon
- Natural fire cycle is beyond balance point
- Carbon loss is 2.5x from fires compared to the 1950s baseline

Question 3

Tundra fire

Answer 3

• Large stores of soil C are thousands of years old
  
  • Post fire plant carbon is completely burnt
  • However some soil carbon is removed (a much larger amount) 20%
  • This 20% equates to a very high carbon loss
  • One fire can cancel entire carbon uptake for the whole year
• Very detrimental

Question 4

Herbivore outbreaks: Insects

Answer 4

• Population spike for summer food
  -* Cold winters kill these yet winters are shifting timing
  
  • Outbreak damage: mild to total defoliation of trees and understorey
  • Loss of photosynthetic capacity - may not recover for more than 70 years
    Large area spread

Question 5

Evidence of outbreaks increasing in frequency

Answer 5

• Winter moth
  
  • Increasing in longitude and latitude
  • outbreaks now occur further north and east
  • Double hit from both moth species
  • Autumnal moth
  • No clear range expansion
  • Has expanded regular outbreaks into coldest areas of its range

Question 6

Pathogens

Answer 6

• Smaller scale than insect outbreaks
  
  • Diseases outbreaks impact ecosystem structure and function
  • Some arctic regions are seeing deeper snow lay which may promote outbreaks
  • Olofsson investigated with snow fences
  • 6 years of increased winter snow depth and longer spring snow-lay
  • Plant growth favoured by the insulating effects of snow
  • After 6 years outbreak killed the majority of empetrum shoots
  • Increased spore production delay prior to release

Question 7

Winter extreme climatic events

Answer 7

High latitudes are warming:
- More than the rest of the world
- More in winter than summer
- With more extreme climatic events
In arctic winter events are of most importance

-Extreme winter warming

• Frost-drought
• Icing

Question 8

Extreme winter warming

Answer 8

-Large scales
- Majority of plants killed
- WinWarm air mass hangs over arctic
- Air temperature can change massively over a short period
- Can melt snow and warm up plants
- Plants no longer protected when temperatures decrease again as no protection from snow
- Ground surveys: 50% loss of live biomass

Question 9

Extreme winter warming: Simulation

Answer 9

• A field simulation reveals the mechanism of damage: mid-winter bud burst
• Plants tricked into thinking it is spring (false early spring)
  -Plants have to lose freeze tolerance to burst buds

Question 10

Frost- drought

Answer 10

Large scales

Majority of plants killed

- Desiccation damage

- Evergreen shrubs are especially vulnerable
- Winter with snow lay exposes canopies to sunshine which can induce stomatal opening and the plan transpires
-Water is frozen in roots so cannot up take it
- Huge reduction in C sink strength
- Photosynthetic carbon decreases….
- Loss of carbon decreases as little going in for photosynthesis
- Decline in ecosystem exchange

Question 11

Icing

Answer 11

• Small patches/ scales
  
  • Ice encased in winter
  • Rain on snow and winter warming
  • This refreezes and causes an ice layer
  • Ice encasement of vegetation
  • Loss of insulation? High CO2? Hypoxia?
  • Photosynthetic carbon gain decreases
  • System is turned carbon neutral/ sink