L18

Question 1

Boreal forest (Tiaga)

Answer 1

○ Freezing temperatures for 6 to 8 months
○ Characterised by coniferious forest
○ 16 million km2
○ 11.5% of terrestrial ecosystem area
○ Low tree species diversity
○ Sequesters about 20% of global carbon (not as much as expected for its area)

Question 2

What trees are boreal forest characterized by?

Answer 2

Coniferous forest

Question 3

Does boreal forest sequester the amount of carbon expected for its area?

Answer 3

No - only 20% of global carbon, more is expected

Question 4

Artic Tundra

Answer 4

• Tundra = treeless
  
  • Lands beyond northern tree limit
  • 7.5 million km2
  • 5.5% of terrestrial land surface
  • Greater than 0 degrees only 2-6 months of the year
  • Grasses and sedges , or shrubs dominate
  • Majority is snow covered

Question 5

High Artic

Answer 5

• Features very little grasses, sedges and shrubs
  
  • Light doesn’t limit productivity due to 2 hour days
  • Slow nutrient cycling and cold conditions determine productivity

Question 6

Artic and Boreal ecosystems commonalities

Answer 6

Environmental commonalities:

• Cold
• Short growing season (summer)
• Long snow cover duration
• Permafrost
• High winds, ice abrasion

Ecology commonalities

• Slow decomposition
  -Low nutrients
• Freeze tolerant plants
• Low biodiversity
• Slow growth
• Great longevity

Question 7

GPP

Answer 7

-Plants take up carbon by photosynthesis
-Ecosystem measure

Question 8

NPP

Answer 8

-Losses of CO2 due to respiration
- Photosynthesis - respiration
- GPP- NPP
-Associated with growth

Question 9

Ecosystem respiration R eco

Answer 9

• Plant respiration and soil respiration

Question 10

NEP/NEE

Answer 10

• Overall uptake of carbon for the system
  - Carbon balance

Question 11

Net biome production

Answer 11

-Considers many years
-Whole biome area
- Net balance is easily switched between source and sink

Question 12

High latitude ecosystem NPP

Answer 12

• Based on an equal area basis
  
  • Boreal forest has a poor NPP

-Once carbon is taken up it stays in Boreal forest for long time periods

Question 13

Carbon density

Answer 13

• Same in boreal forests as tropical forest despite a much smaller NPP
• Tundra has large carbon density

Question 14

How much more carbon is there in soil than plant biomass in boreal forest?

Answer 14

2-3 times more

Question 15

How much more carbon is there in soil than plant biomass in tundra?

Answer 15

5 times

Question 16

Carbon turnover rates between tundra, boreal forest and tropical forest

Answer 16

• Carbon taken up to then be release again
  • Tundra takes 65 years for turnover
  • Boreal forest takes 53 years
• Tropical forest take 14.2 years

Question 17

Changing high latitude C

Answer 17

-Growing season summed NDVI = greenness over time (season length)

- Excellent proxy for productivity (biomass production and gross carbon gain)

• High latitude ecosystems are greening-Biomass is increasing = more carbon gain in plants

-Boreal and arctic is increasing its productivity

• NPP is therefore increasing

Question 18

Boreal Treeline advance

Answer 18

• Boreal trees advancing onto tundra

-Extent to this globally evidence is unclear

Question 19

Alaska

Answer 19

• Younger trees
  -No older trees advancing into tundra
• • Younger system on forest tundra transition

Question 20

Tundra shrubification

Answer 20

• Increase in shrub abundance
  
  • 28% hiltops to 160% floodplains
  • NPP increasing
• Models predict increased C in more biomass = greater removal of CO2 from the atmosphere

-But more C in soil than biomass in high latitude ecosystems

-Hartley et al. (2012): C stocks and C fluxes in adjacent forest and tundra

Question 21

Will artic and boreal forest become a greater carbon sink?

Answer 21

• Plants will, but soil processes may combat this
  
  • Models predict increased C in more biomass = greater removal of CO2 from the atmosphere
  • But more C in soil than biomass in high latitude ecosystems
  • Far less carbon in birch forest soil than tundra
  • Birch may be more productive in terms of plant biomass but has half the carbon
  • Boreal forest has ⅔ carbon stored compared to tundra
    
    • As boreal forest moves on to tundra it may cause carbon release

Question 22

Biomass increase vs soil decomposition

Answer 22

• Priming of decomposition
  
  • Stimulate decomposition
  • NEE could end up releasing carbon
  • Tree planting is not a simple a process as previously thought

Question 23

The future? Model projections for arctic and boreal regions

Answer 23

• Models represent increases in soil- warming respiration losses of C
  
  • But priming not properly represented
  • Vegetation carbon will increase
  • Ecosystem carbon storage shall increase over time
  • Runaway climate change will result in lots of co2 release due to warming soils and decomposition
    ○ Tundra shrubification due to warmer temperatures
  • Greater CO2 means more growth for plants however, but less carbon in these than soil in tundra

Question 24

The main issue with artic greening and productivity

Answer 24

-Increase C storage might not occur if greater photosynthesis/growth does not compensate for greater respiration (due to warming or priming).

• So, high latitude ecosystems ‘could’ become a source of C
• Greater photosynthesis must compensate for greater respiration to to priming/warming.