L18 Flashcards
Boreal forest (Tiaga)
○ 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)
What trees are boreal forest characterized by?
Coniferous forest
Does boreal forest sequester the amount of carbon expected for its area?
No - only 20% of global carbon, more is expected
Artic Tundra
- 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
High Artic
- 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
Artic and Boreal ecosystems commonalities
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
GPP
-Plants take up carbon by photosynthesis
-Ecosystem measure
NPP
-Losses of CO2 due to respiration
- Photosynthesis - respiration
- GPP- NPP
-Associated with growth
Ecosystem respiration R eco
- Plant respiration and soil respiration
NEP/NEE
- Overall uptake of carbon for the system
- Carbon balance
Net biome production
-Considers many years
-Whole biome area
- Net balance is easily switched between source and sink
High latitude ecosystem NPP
- 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
Carbon density
- Same in boreal forests as tropical forest despite a much smaller NPP
- Tundra has large carbon density
How much more carbon is there in soil than plant biomass in boreal forest?
2-3 times more
How much more carbon is there in soil than plant biomass in tundra?
5 times
Carbon turnover rates between tundra, boreal forest and tropical forest
- 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
Changing high latitude C
-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
Boreal Treeline advance
- Boreal trees advancing onto tundra
-Extent to this globally evidence is unclear
Alaska
- Younger trees
-No older trees advancing into tundra - Younger system on forest tundra transition
Tundra shrubification
- 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
Will artic and boreal forest become a greater carbon sink?
- 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
Biomass increase vs soil decomposition
- Priming of decomposition
- Stimulate decomposition
- NEE could end up releasing carbon
- Tree planting is not a simple a process as previously thought
The future? Model projections for arctic and boreal regions
- 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
The main issue with artic greening and productivity
-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.
