climatic and biological events in high latitude ecosystems (terrestrial lecture 9)

Question 1

Fire in boreal forests -

are they common?
have they increased?
what are they the biggest factor in reducing?

Answer 1

• common and natural process
• increasing in severity and frequency
• biggest factor reducing net biome productivity (NEP - disturbance)

Question 2

Fire on tundra

what do tundra have in the soil?
have fires increased
how much land did a 2007 alaskan tundra fire burn?
how much carbon was lost?
what percentage of this was from soil?

Answer 2

• tundra have large millenia old C stores
• fires were previously absent from tundra
• 2007 Alaskan tundra fire burned 1039km tundra
• 60% of 2.1Tg C lost was from soil

Question 3

Herbivore outbreaks: insects

• Operophtera brumata - winter moth
• Epirrita autumnata - autumnal moth
• how long are caterpillar outbreak cycles?
• what temperature kills eggs?
• how much damage?
• recovery time

Answer 3

• some high latitude insects have population spikes
• both O. brumata & E. autumnata have caterpillar outbreaks on subarctic birch forest in 9-10 year cycles
• eggs killed in extremely cold temperatures (-35oC)
• outbreak damage varies from mild to complete defoliation of trees and understory
• 70 years for photosynthetic capacity recovery

O. brumata:
- less cold tolerant, is expanding range northward

E. autumnata:

• no clear range shift
• but outbreaks expanding into coldest areas of range

Question 4

Pathogens

-Arwidssonia empetri (Olofsson, 2011 - snow fence study)

what is it?
what does it affect?

what promotes outbreaks?

Answer 4

• disease outbreaks impact ecosystem structure/function

A. empetri is a fungal pathogen (mould) affecting Empetrum shrubs

• snow lay getting deeper/longer
• deeper snow lay promotes fungal outbreak
• insulative snow layer favours plant growth, greater plant growth encourages outbreak

Question 5

Winter extreme climatic events

why are there more at extreme climatic events at high latitudes?

what are types of winter climatic events?

Answer 5

• high latitudes warming at faster rate than everywhere else
• more in winter than summer
• more extreme climatic events

extreme winter climatic events:

• extreme winter warming
• frost-drought
• icing

Question 6

What is extreme winter warming/its effects?

Bokhorst 2009

Answer 6

Bokhorst (2009):

• in dec 2007, in north west scandinavia max temps were 4-12C for 5-10 days
• 50% live biomass loss (ground surveys)
• NDVI 28% loss over 1424km2
• cause: mid winter bud burst
• when it gets cold again buds freeze

Question 7

What is frost-drought and its effects?

Tranquillini (1982)

Answer 7

Tranquillini (1982)

• frost drought is when low/freezing temperatures severely reduce water transport in a plant/ disrupt it to an extent that water lost via transpiration is not replaced
• leads to dessication (frost dessication injury)
• evergreen shrubs v vulnerable
• can affect over hundreds of km
• huge reduction in C strength

Question 8

What is icing and its effects?

Answer 8

• combination of winter warming/rain on snow events
• ice encasement of vegetation
• kills them: hypoxia? lack of insulation? high CO2?
• loss of food accessibility for high latitude herbivores