Slash and burn

Overview• Background• Method of “Slash and Burn”• Advantages and Disadvantages • Currently around the World• Future scenario with the

collapse of the Amazon Rainforest

• Alternatives and Obstacles to Overcome

Background• Around 450 million ha of forest

has been lost from 1960 to 1990 alone

• About 90% of the deforestation was for agriculture purposes

• Slash and burn technique had been seen in humans since the Neolithic times– Nomadic lifestyle was given up in favor

of staying in one place and domesticating nature around them

– Slash and burn was an useful technique in maintaining this lifestyle in harsher environments

Background• Estimates of 37-

300 million people around the world involved in slashing and burning• Slash and burn was a viable

technique up to 100 years ago

-However, as the world population grew, forests could no longer keep up with these farmers

Background• Via photosynthesis, plants use CO2

to make energy with O2 as a byproduct– “It’s a neat and self sustaining cycle

that forms the basis of life on Earth”-Tim Flannery

– A trillion tonnes of carbon are tied up in living things alone

• Mature forests don’t need as much CO2 as newer forests– Tropical rainforests as well as Siberia’s

and Canada’s coniferous forests are in balance, as they release CO2 from rotting vegetation in equal amounts to the amount of CO2 they absorb for new plants

Method of Slash and Burn

1. Cut down the selected area of forest

2. Allow time for vegetation to dry out (at least a week)

3. Set the remains on fire

4. Results in Ash Fertilized Fields

In the Short Term…• Burning discharges nutrients into

the ground from the plants• Ward offs competition temporarily,

permitting crops to establish themselves in the earth

• The ash is rich in nitrogen and minerals, as well as increases the pH of the soil, allowing for more nutrients to become available

• Also releases CO2 into the atmosphere, as it is released when living things are burned

Immediate Benefits• Fields are already fertilized, requiring

less work• Cheaper in the short term than using

chemical fertilizers• Clears space for both crop fields and

cattle pasture

In the Long Run…In many cases, by the 4th consecutive

crop planting, soil fertility has decreased by 50%– Field productivity decreases due to

disruption of the equilibrium between erosion and silting

– Soil erosion increases because of the decreased rate of topsoil production

– Erosion leads to nutrient loss, and over time accelerates if balance is not restored

– The soil washes into streams and rivers, potentially blocking transportation routes and harming wildlife

Desertification

Extreme side effect of slashing and burning– Soil becomes incapable of sustaining

most vegetation due to lack of nutrients– Topsoil is further eroded– Seeds and seedlings are unable to take

root with the lack of topsoil

Biodiversity• There is an increased loss of

biodiversity– Slower growing plants are taken

over by faster growing plants – Without the slower growing

plants, the animals dependent on them disappear as well

– Flora and fauna lose much of their habitat, and are forced to live in smaller areas

Currently in the U.S.• In the 19th and 20th centuries

American pioneer culture led to eastern forests being slashed and burned– As the culture began to become less

heavily dependent on agriculture, forests began to recover

• As many of our forests are less than 60 years old, they are able to absorb up to half a billion tonnes of CO2 from the atmosphere– However, as forests grow older they

require less CO2 meaning that even more CO2 will be released into the atmosphere in the future

Currently in Australia• During the 1960’s farmers wanted to

clear a million acres a year and were left with sterile soil, basically sand– They used hydroponics farming

• Put in the wheat, add nutrients and then waited for winter rains

• By 2004 the region moved westward due to the lack of rain– After leaving the lands to waste after

they were no longer useful, the water became much more salty

– Under every square meter there about 70-120kg of salt

– Water became undrinkable and killed vegetation

– The only solution is to bring back vegetation and hope that it can grow in the new conditions

Currently in South America• An area of the Amazon the size of Maryland is cut down every year – 38 million acres of tropical rainforests are lost

each year due to the ever growing numbers of poor farmers

• Tropical rainforests are actually less fertile than temperate forests in the long run

• Chop and mulch alternative being explored, seen with the Kavapo Indians of the eastern Amazon Basin of Brazil– Convert fallow vegetation into mulch, which adds nutrients– CO2 output is five times lower than in the slash and burn

technique

If Global Warming Continues…• The increased temperature would

accelerate the rate of decomposition• Increased decomposition leads to

more CO2 released• More CO2 in the atmosphere

negatively influences the amount of time plants’ stomata are open. – Without open stomata, less water vapor

is lost. Decreased water transpiration leads to less rainfall.

– By 2100, 20% decrease in the Amazon’s rainfall by this alone

– Average of 5mm falls to 2mm

The Amazon Forest could Collapse!• Loss of rainforest canopy would no longer

protect the soil from the intense heat. – This would further accelerate the rate of

decomposition, leading to more CO2 released into the atmosphere

• If the Amazon Rainforest does collapse– By 2100, there will be 1000 parts per million of

CO2 in the atmosphere instead of the estimated 710 parts per million of CO2 due to the 78% loss of carbon stored in vegetation and 72% loss of carbon stored underground

– Surface temperature will rise by 10 C instead of 5.5 C

– Rainfall will drop by 64%• Our once vibrant Amazon would

become desert

Alternatives to Slash and Burn• Replace with “Agro-forestry”

– Crops and trees planted together– Tree leaves and branches provide the

fertilizer• “Chop and Mulch”

– Convert fallow vegetation into mulch• Government should take more action

– Increase their regulation of land use– Increase the prices of food crops so that

farmers can make a profit and a sustainable livelihood

– Teach the farmers how to plant different crops that would put back the depleted nutrients the soil needs

Obstacles to Overcome• Cleared land has less taxes than

standing forest in many countries– Encourages deforestation

• Difficult to teach poverty ridden farmers new crops– Unwilling to learn about new crops after

so many years and they are wary of the government

• Government unwilling to lower food prices– Water resources already exhausted,

increasing pressure on land resources to provide nourishment

– Grain prices has doubled in the last 3 decades

SummarySlash and burn, an agriculture method that

involves cutting down forests and setting fire to the remains in order to fertilize fields is a practice that should be outlawed. Previously, slash and burn was a practical solution for our ancestors. However, this practice can no longer be sustained due to the large numbers of farmers that use this method of farming and the amounts of CO2 released into the atmosphere. The impact it has on global warming should also not be discredited, as it may even accelerate the rate of global warming. However, there are several alternatives, such as agro-forestry and cut and mulch, as well as government involvement that could end this practice once and for all.

Works Cited• Benhim JKA (2006) Agriculturee and Deforestation in the

Tropics: A Critical and Empirical Review. AMBIO: A Journal of the Human Environment: Vol. 35, No. 1, pp. 9-16

• Crossette, Barbara (1996, August 4). Report Blames Poor Farmers For Depleting World Forests. New York Times.

• Davidson, E., Deane de Abreu Sa, T., Carvalho, C.J., Figueiredo, R., Kato M., Kato, O.R., Ishida, F.Y. (2008) An integrated greenhouse gas assessment of an alternative to slash-and-burn agriculture in eastern Amazonia. Global Change Biology Vol 14, No. 5, pp.998-1007

• Desertification-a threat to the Sahel (1994) http://www.eden-foundation.org/project/desertif.html (Accessed November 24, 2008)

• Flannery, T. (2005) The Weather Makers: How We are Changing the Climate and What it Means for Life on Earth. Canada: Harper Collins

• Stevens, W.K. (1989, July 18) To Halt Climate change, Scientists Try Trees. New York Times.

Photographs• http://tbn0.google.com/images?q=tbn:4eTcYNA753

ELzM:http://veimages.gsfc.nasa.gov/18627/Brazil.TMOA2003169_lrg.jpg (Accessed Nov. 29, 2008)

• http://virtual.vtt.fi/virtual/space/firealert/images/heinavesi.jpeg (Accessed Nov. 28, 2008)

• http://individual.utoronto.ca/esjones/images/slashburn.jpg (Accessed Nov. 28, 2008)

• http://images.wildmadagascar.org/pictures/hikemadagascar/04/FDSC02159.jpg (Accessed Nov. 30, 2008)

• http://www.eden-foundation.org/project/desertif.html (Accessed November 27, 2008)

• http://jrscience.wcp.muohio.edu/photos/CorcovadoTrail00D.jpg (Accessed November 29, 2008)