Lecture 2 Flashcards
Describe a boreal forest “Tiaga”
- Freezing temps for 6-8 months
- Coniferous forest
- 16 million km2
- 11.5% of terrestrial ecosystem area
- Low tree species diversity
- Make up 30% of global forests
- Responsible for 20% of carbon uptake
Describe the arctic tundra
- Tundra = treeless
- Lands beyond the northern tree limit
- 5.5% of terrestrial land surface
- Above 0 for only 2-6 months of the year
- Grasses and sedges and shrubs dominate
- Light not limiting
What are some commonalities between arctic and boreal ecosystems (6)
- Cold - slow decomposition
- Short growing season (summer) - low nutrients
- Long snow cover duration - freeze tolerant plants
- Environmental extremes - low biodiversity
- Permafrost - slow growth
- High winds, ice abrasion - great longevity
What is GPP
Gross primary productivity
Plant photosynthesis of an ecosystem - positive carbon uptake
What is NPP
Net primary productivity - remove loss from plant respiration (carbon flux in = less)
What is Reco
Ecosystem respiration
Soil respiration and plant respiration
What is NEP
Net ecosystem productivity
Net exchange of carbon GPP-Reco
What is NEB
Net biome exchange
Over longer timescales and landscape scales
What is NPP of tundra vs tropical
1/10 of tropical
What is NPP of boreal vs tropical
1/5
How much more c is held in soil than plant biomass in the boreal ecosystems
2-3 times more c is held in soil than plant biomass in the boreal ecosystems
How much more c is held in soil than plant biomass in the boreal ecosystems in the arctic tundra
5 times more c is held in soil than plant biomass in the boreal ecosystems
What is a carbon turnover rate
The amount of time an atom will stay in an ecosystem once taken up
What ecosystems have the lingers carbon turnover rates
Boreal and mountainous areas
What ecosystem has the longest carbon turnover rates in the world
Tundra
NDVI (normalised difference vegetation index)
NDVI increased by 20% since 1982 Increasing productivity and growing season caused by climate change
What leads to Productivity changes
Plants grow more - warming + growing season longer
Vegetation change caused by climate change
Boreal treeline moving onto tundra - tundra gets warmer so can support more trees - latitudinal treeline advance
Boreal treeline advance - evidence from example in Alaska
Seedlings at the edge
Oldest trees 1930s - new system with active recruitment
Further into the forest back in time - dead trees in middle of forest
Dynamic system
Tundra “shrubification” - greening of the arctic
Increase abundance, size and spread of more productive shrubs
Deciduous shrubs
Bigger and taller
Occurring over greater areas
Name an example of shrubification
Alaska
Increase in shrub abundance 28% (hilltops) to 160% (floodplains)
Explain biomass increase vs soil decomposition
It was believed that increase in C in more biomass = greater removal of CO2 from the atmosphere
Ignored soil
Hartley studied carbon stores and fluxes in adjacent forest and tundra in northern Sweden
- change in c stock = change if forest moves out onto tundra
- less carbon in forest than tundra
- only shrubs in tundra (less carbon) = above ground
- huge amounts of carbon below ground - twice as much in tundra
- overall 1/3 less total carbon stock in boreal forest than tundra = treeline advance = lose 1/3 of carbon
How might C loss happen when treeline advances
Priming of decomposition- see directed reading
Forest trees more productive- more photosynthetically active - take up more carbon
Want nutrients to be able to grow so pump carbon below ground into roots = excrete organic acids and enzymes into soil to breakdown nutrients so they can take it up
Nutrients often bound to carbon so when it’s broken down = release carbon = encourage decomposition of carbon in the soil
=> carbon loss moving from tundra to boreal forest
More productive trees cause soil carbon to decompose faster
