lecture 28- land transformation global change Flashcards
What is land use change?
Conversion of existing natural ecosystems to other forms of landscape.
- Generally for anthropocentric use.
What are common changes to natural systems for agriculture?
- Deforestation
- Draining or modifications to wetlands
- Modification of grasslands
How much forest did we have originally? How much forest did we lose?
55%
25%
How is deforestation linked to the carbon cycle?
Atmospheric CO2: trees are a major source of carbon sequestration.
- Carbon is required to build the persistent woody structure of trees.
Trees do not sequester carbon at the same rate throughout their lifecycle:
- Growth slows as the trees reach the maximum height
- So does carbon sequestration
What effects does deforestation have on carbon sequestration?
1- The uptake of atmospheric carbon reduced:
- Annual plants (crops) do not sequester as much carbon as trees
- Lesser permeance than trees
- Animals (pasture land) emit greenhouses gases through respiration
2- Carbon stored in wood is ultimately returned to the atmosphere through decomposition
How is deforestation connected to the hydrological cycle?
1- Trees are a major part of the recycling of green water
- Even more so than other plant groups
2- A large tree population can actually impact local weather patterns through:
- High degree of transpiration
- Cloud-seeding secondary chemicals
3- Influence cloud cover
What is a flying river?
Also known as aerial river.
A system which brings moisture over large areas as a result of wind currents and significant plant transpiration.
Water that comes in from the ocean and falls as rain- but the trees absorb that rain and release it as EV- and release it into the atmosphere- all the plants push out water and continue bringing water in the inside of the continent when it would otherwise be lost as runoff or smt.
So, the density of plant life in the Amazon rainforest impacts weather patterns. Because of its tree density, all that water that enters from the ocean moves its way from the continent to the aerial river.
What is slash-and-burn agriculture?
Farming technique involving the removal or woodland through the use of fire, and the farming of that land using the nutrient-rich ash as fertilizer.
Most common in areas with poor soil fertility (tropical areas), low GDP, and high rates of poverty.
- Primary method for deforestation in the Amazon
How is deforestation connected to nutrient cycling?
Soil nutrients released through burning are quickly lost in the soil.
The area burned becomes unproductive very quickly. Necessitates burning of new virgin forest for continued harvest.
High rates of precipitation in tropical forests: water takes with it minerals and nutrients in the soil- the more it rains the more that the rain washes away the nutrients - high precipitation = low nutrients.
How is deforestation connected to the radiation budget?
Deforestation replaces forests with cropland and pasture.
Cropland and pasture are actually better for albedo than tree cover
- Reflect more solar radiation
How is deforestation connected to biodiversity?
Forests harbor the highest levels of biodiversity for terrestrial species.
Land use change leading to habitat loss or degradation:
- Most significant cause of species extinction risk
Land use change and biodiversity are not equally distributed globally.
What is the most endangered biome on most continents? Why?
Grasslands.
Grasslands biome seized for cropland and pasture:
- Much less effort is required to convert to agriculture than forest or wetlands.
How is grassland involved in the carbon cycle?
Grasslands may be a more reliable form of carbon sequestration than forests under a regime of increased forest fire frequency under climate change.
Grasslands store more carbon in soils than in aboveground biomass. Their roots and soils survive forest fires.
How does agriculture affect wetlands?
1- Wetlands have been drained for agricultural production
- Existing wetlands can be modified for rice production
- Dramatic loss of biodiversity in modern rice cultivation
2- Modification of existing water systems for irrigation
- Change in sedimentation rates can result in loss of landmass
What is the impact of losing wetlands?
1- Conversion of a green and blue water reservoir to a system that holds much less water, for a shorter period of time.
- Loss of water to runoff, or rapid turnover through transpiration
2- Change in GHG cycles:
- Artificial fertilizer increases the production of nitrous oxide
- Changes in the production of methane and CO2
3- Soil degradation
- Loss of soil organic matter
4- Loss in biodiversity
- Most wetland species are obligate to that type of ecosystem
- Cannot live outside of a wetland
5- Ecosystem services such as water filtration and flood prevention
