Why is the northern hemisphere producing more carbon dioxide than the southern hemisphere?
- It has more land mass and is more industrialised
Why is there correspondence between el nino records and C02 concentrations?
- El Nino caused by climatic oscillations
- C02 spikes in El nino years because tropics become sources rather than sinks
In what ways is carbon lost due to disturbance?
Photosynthesis (respiration)
Fires
Deforestation
What makes a terrestrial sink a terrestrial sink
Carbon sink means photosynthesis has to be > than respiration year after year
The last thing a carbon sink needs means is that the carbon has to be stored with a slow turnover rate (soils,trees etc)
How does demography cause ecosystems to act as carbon sinks?
- young trees grow fast in new forests
- Younger, regenerating forests in mid lats
- Old growth forests in tropic and high lats
How does physiology cause ecosystems to act as carbon sinks?
Hotter weather = increases in productivity, but not in drought
- Evidence of weakening amazon carbon sink, increasing productivity but increased tree turnover
- In African forests there is a net positive trend with increased productivity and no change in mortality
What is helicopter science?
Scientists wouldn’t engage with scientists in the country they were working in
How does C02 fertilisation of growth depend globally on mycorrhizas?
- Mutualistic relationship increases plant C uptake
- High N negatively impacts AMF and good levels of P is needed for AMF to work properly
How do droughts weaken tropical carbon sinks?
- Peak mortality of trees correlate to el nino events
- In the southern, dry amazon, the species adapted to wet climates are at higher risk of mortality
Which processes control carbon sinks in mature tropical forests?
- Rising C02 boosts photosynthesis if there is nutrient bioavailability
- Rising temps and drought limit wood production - could cause saturation of Amazonia C sink
- El Nino increasing tree mortality
- African forests less impacted by heatwaves as they are at higher altitude
When is amazon deforestation aiming to end by?
2030
Why do tropical forests surprisingly remain more intact than other ecosystems?
- They havent yet been transformed
- Savannas are used for pasture land and temperate ecosystems have had much more transformation over a much longer period of time
When did deforestation for agriculture begin and how can we tell?
- intensive land use beginning 3000-1000 BC
- Pollen evidence of olive cultivation from 6000 BC decline of Oak pollen at the same time as well as bones of livestock farming
E.g. Yellow river region in China where there is evidence of land clearance for agriculture 5000-3000 years BC
How is carbon emitted from deforestation?
Decay of felled trees
Disturbance releases soil carbon
Burning to clear the felled area
How much has deforestation been responsible for human C02 emissions?
A third
What are the feedbacks from deforestation mediated via surface energy balance?
The amount of dissipated longwave energy from the sun depends on albedo
High albedo= reflectance (ice)
Low albedo = absorbance (ocean)
Deforestation increases albedo and cools the land
Also a cooling effect as loss of trees=loss of evapotranspiration (significant as convectional rainfall recycles 80% of water over tropical forests)
What is the Bonn Challenge?
to restore 150 million ha of deforested and degraded lands worldwide by 2020
(didn’t happen)
Why is it important that tree restoration is targeted to degraded and not native ecosystems?
-Trees can deplete groundwater reserves
- Most of the C in a savanna is stored in soil and evidence shows that at higher rainfall areas you get a decrease in the amount of soil C after you plantation
How does forest that covers snow warm the earths surface?
- Forest blocks the high albedo of the snow- more light is absorbed
What do we use to fertilise with in the UK?
Ammonium nitrate
- Other places use ammonium or urea
When is N20 released throughout the agricultural process?
- peaks of N20 emission following fertillisation
- after harvest because the plant root is turning over and releasing nitrogen into the system
- tillage also releases N20 as its releasing N20 throughout the soil
What is the natural balancing of N20 emissions
Denitrification produces N20 emissions under anaerobic conditions
The activity of N2O reductase can mitigate its release by converting N2O into N2
N20 reductase is expressed more in anaerobic conditions
- What is effecting this balance is the excessive addition of N through fertilisation
How can fluctuating water systems cause release of N20?
- Through creating anaerobic conditions through water pore-filled spaces
- In anaerobic conditions, organic matter decomposition stops so when the soil is aerated again it can increase
- N20 can accumulate in water saturated soils
How much N added to agriculture is collected by the plant?
30%
