deforestation and forestation (terrestrial lecture 4)

Question 1

What is the state of tropical deforestation?

What percentage of anthropogenic emissions does it account for?

Answer 1

• area the size of South Africa lost between 1990-2015
• the deforestation rate halved in this time
• deforestation rate increased in Brazil for the first time in a decade in 2016 (Nature News, 2016)
• 4-26% anthropogenic emissions comes from tropical deforestation

FAO (2015)

Question 2

Land use change in Crete:

Evidence from Neolithic Period (6000-3000BC)

Evidence from Minoan Period (3000-1000BC)

Answer 2

Neolithic:

• pollen evidence for olive cultivation from ~6000BC
• oak pollen decline at same time
• livestock bones -> farming on crete begins

Minoan:

• olives, figs, cereals, vines, sheep, goats, cattle, pigs
• settlements: villages, towns, places, roads,
• similar population to today

Question 3

What drives tropical deforestation in:

• Amazonia?
• South East Asia?

Answer 3

Amazonia: cattle ranching & soy agriculture

SE Asia: palm oil agriculture

Question 4

How does deforestation release carbon?

Answer 4

• felled tree decay
• disturbance releases soil C
• burning of cleared area

Question 5

How forest cover changes influence regional climate?

• tropical deforestation
• boreal forestation

Answer 5

tropical deforestation:
- cleared land has increased albedo
- cooling effect
BUT
- reduced C sink

boreal forestation:

• dark trees cover light snow
• albedo decreases
• earth surface warms

Question 6

Evapotranspiration in the wet tropics

Answer 6

• convective rainfall, 80% recycling
• transpiration from canopy, evaporation from soil
• decreases w deforestation

Question 7

What is the climate feedback of tropical deforestation?

-albedo/evapotranspiration/net effect

Answer 7

deforestation:

• increases albedo, which reduces surface temp
• reduces evapotranspiration, which increases temperature (more than cooling effect of increased albedo). reduces rainfall

net effect: warming and drying

Question 8

Transpiration & global feedback?

• controls
• effect of rising CO2
• physiological feedback
• structural feedback
• overall effect

Answer 8

CONTROLS

structural: canopy size (leaf area index)
physiological: stomata

EFFECT OF RISING CO2

• greater canopy size
• stomatal closure

PHYSIOLOGICAL FEEDBACK
- stomatal closure: lower transpiration, warming effect

STRUCTURAL FEEDBACK
- increased transpiration, cooling effect

OVERALL COOLING