carbon cycling of high latitude ecosystems (terrestrial lecture 8)

Question 1

What are the characteristics of boreal forest (taiga?)

Answer 1

• freezing temperatures for 6-8 months
• characterised by coniferous needleleaf forest
• ~16 million km^2 = 11.5% terrestrial ecosystem area

Question 2

What are the characteristics of arctic tundra?

Answer 2

• tundra = “treeless”
• lands beyond the northern tree limit
• 7.5 million km^2 = 5.5% terrestrial ecosystem area
• temp above freezing for only 2-6 months
• dominated by grasses/sedges/shrubs

Question 3

What do taiga and tundra have in common?

• environment
• ecology

Answer 3

environment:

• cold
• short GSL (summer)
• long snow cover duration
• environmental extremes
• permafrost
• high winds: ice abrasion

ecology:

• slow decomposition
• low nutrients
• freeze tolerant plants
• low biodiversity
• slow growth
• high longevity

Question 4

What are the carbon stocks in taiga/tundra like?

• amount/density
• soil vs biomass
• carbon turnover rates

Answer 4

• taiga second in amount of C to tropical, comparable in C density (34.2kg/m2 vs 35)
• tundra lower amount of C, but density (20.5kg/m2) comparable to croplands, wetlands, temperate grasslands and forest
• both store more C in soil than biomass
• taiga 2-3x more
• tundra 5x more
• wayyyyy lower C turnover rate than tropical forests
• taiga: 53.3yrs
• tundra: 65.2yrs
• tropical: 14.2yrs

Question 5

How are high latitude systems changing?

• greening
• treeline advance
• shrubification

Answer 5

• greening: phenology changes. biomass is increasing so more C gain
• 20% increase 1982-2014
• boreal treeline advance: moving onto tundra
• younger spruces and higher proportion of seedlings at treeline edge
• shrubification of tundra
• 1950-2000 shrubs increased by 28% (hilltop) to 160% (floodplains)
• Sturm et al., 2005 & Tape et al., 2006

Question 6

High latitude C stocks - biomass increase vs soil respiration?

Answer 6

• models say increased biomass will increase C removed from atmosphere
• but more C in soil than biomass
• greening may prime ground decomposition and release C from soil

Question 7

What is the age of C respired in taiga/tundra through the growing season?

Answer 7

• age of respiring C can be measured through C14 isotope leftover from test bombing in 50s
• tundra gradually increases age of respired C thoughout GS
• taiga has peak in C age respired in middle of GS - peak photosynthesis time
• allocation of C below ground may stimulate decomposition of older recalcitrant C = “priming”