Transcript Land and Water Degradation Due to Agriculture

Land Degradation
Due to Agriculture
Part 1: Deforestation
Fall 2012 , Lecture 5
Land Degradation Processes
• Agriculture contributes to land degradation in
two major ways
 Deforestation
 Tilling the soil
2
The
Dust
Bowl
• Intro to Ken Burns “The Dust Bowl” on PBS
3
“A Hundred Dead Cities”
• Walter Lowdermilk describes a region in Syria where invasion
by a Persian Army and later desert nomads during the seventh
century, had turned a thriving region to wasteland
• Soil and water conservation practices used for centuries were
abandoned
• Ancient buildings were still standing in stark isolated relief,
but they were on bare rock
• The soil was gone
4
Lowdermilk’s Work
• Lowdermilk, former Assistant Chief of Soil Conservation
Service of the U.S. Department of Agriculture (USDA),
traveled abroad for 18 months in 1938-39 to look at lands that
had been cultivated for thousands of years, seeking to learn
how these older civilizations had coped with soil erosion
• He found that some had managed their land well, maintaining
its fertility over long stretches of history, and were thriving
• Jared Diamond, in his book Collapse, tells similar stories in
many civilizations
5
History Repeats Itself
• This story is being repeated in many places today
• Lester Brown, in Plan B 3.0, mentions Lesotho and
Syria
• Similar problems are occurring in Haiti, the
Philippines, the Sahel region of Africa, Thailand, and
other regions
6
Government Restrains
• In 1989, Thailand announced a nationwide ban on tree cutting
following severe flooding and the heavy loss of life in landslides
• In August 1998, after weeks of record flooding in the Yangtze River
basin and a staggering $30 billion worth of damage, the Chinese
government banned all tree cutting in the upper reaches of the basin
• In December 2004, Philippine President Gloria Macapagal Arroyo
“ordered the military and police to crack down on illegal logging,
after flash floods and landslides, triggered by rampant deforestation,
killed nearly 340 people”
7
Deforestation Scale
• At the beginning of the 20th century, the earth’s
forested area was estimated at 5 billion hectares
• Since then it has shrunk to just under 4 billion
hectares, with the remaining forests rather evenly
divided between tropical and subtropical forests in
developing countries and temperate/boreal forests in
industrial countries
8
Forest Losses and Gains
• Developing world has lost some 13 million hectares
of forest a year since 1990
• Industrial world has gained an estimated 5.6 million
hectares of forest land each year, principally from
abandoned cropland returning to forests on its own
and from the spread of commercial forestry
plantations
• Net change is a loss of 7 million hectares/year
9
Forest Quality
• The 4 billion hectares remaining is not all high quality forest
• World Resources Institute says that only 40 percent of the
world’s remaining forest cover can be classified as frontier
forest
• WRI says “the vast majority (of remaining forests) are no
more than small or highly disturbed pieces of the fully
functioning ecosystems they once were.”
10
Frontier Forest
• Frontier forest is defined as “large, intact,
natural forest systems relatively undisturbed
and big enough to maintain all of their
biodiversity, including viable populations of
the wide-ranging species associated with each
type”
11
Use of Wood
• In 2011, 1.88 billion cubic meters of wood
were used for fuel worldwide
• This amounted to about 47% of all the wood
consumed worldwide in 2011
12
Wood Use in Developing Countries
• In Haiti, about 89% of the wood produced is
used for fuel in 2011
• Lester Brown said developing countries use
about 75% of their wood for fuel
13
Urban Firewood Demand
• As urban firewood demand surpasses the sustainable
yield of nearby forests, the woods slowly retreat from
the city in an ever larger circle, a process clearly
visible from satellite photographs taken over time.
• As the circles enlarge, the transport costs of firewood
increase, triggering the development of an industry
for charcoal, a more concentrated form of energy
14
Deforestation in Bolivia
• Images from Bolivia, 1975 through 2000, Satellite Imagine Corporation
15
Papua New Guinea (PNG)
• PNG is losing 362,400 hectares of
rainforest every year, equivalent to 1.4
per cent of its forested land area
• Scientists predict that, in 12 years, more
than 80 percent of the island’s accessible
forests, which represents more
than half of all the remaining rainforests
in Papua New Guinea, will either be
completely cleared or badly degraded and
fragmented
1990
2005
16
Amazon Deforestation in
Rondonia, Brazil, 2000-2010
• The state of Rondonia in western Brazil is observed
by the Moderate Resolution Imaging
Spectroradiometer (MODIS) on NASA's Terra
satellite
• This timelapse on the next slide shows the reduction
of the forest from 2000-2010
17
Amazon Deforestation
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Amazon Deforestation Pattern
• Deforestation follows a fairly predictable pattern in these
images
• The first clearings that appear in the forest are in a fishbone
pattern, arrayed along the edges of roads
• Over time, the fishbones collapse into a mixture of forest
remnants, cleared areas, and settlements
• This pattern follows one of the most common deforestation
trajectories in the Amazon
19
Sequence of Deforestation
• Legal and illegal roads penetrate a remote part of the forest, and
small farmers migrate to the area
• They claim land along the road and clear some of it for crops
• Within a few years, heavy rains and erosion deplete the soil, and
crop yields fall
• Farmers then convert the degraded land to cattle pasture, and clear
more forest for crops
• Eventually the small land holders, having cleared much of their
land, sell it or abandon it to large cattle holders, who consolidate the
plots into large areas of pasture
20
Incoming Radiation
• Some trace gases are known as “greenhouse"
gases because they function like the glass in a
greenhouse
 Incoming radiation strikes the earth and some is
absorbed
 This heats the earth and the earth reradiates in the
infrared portion of the spectrum
21
Infrared Blanket
• If the earth's atmosphere were transparent to infrared
radiation, the earth would lose heat rapidly and would
have a low average temperature
• This temperature would be about 254 K
• Although life might survive at these temperatures, it
would be difficult and life on earth would likely be
much different from life as we know it
• Fortunately, some gases in the earth's atmosphere
absorb some outgoing infrared radiation
22
Greenhouse Gas Properties
• Greenhouse gases absorb infrared radiation
that corresponds to the vibrational and
rotational energy levels of their bonds
• Normally these gases have three or more
atoms
23
Major Atmospheric Gases
• The major gases in the atmosphere, nitrogen,
oxygen, and argon, are either mono- or
diatomic
• They do not have any appreciable absorption
in the infrared
24
Polyatomic Gases
• The most abundant polyatomic gas is water
• Water is the most important greenhouse gas in
the sense that it accounts for the major portion
of the natural greenhouse effect
• Water is followed by carbon dioxide and
methane
25
Absorption of IR
• IR radiation absorbed by polyatomic molecules
excites rotational and vibrational states and raises the
molecules to a higher energy state
• They return to the ground state by radiating IR
radiation in all directions
• IR stands for infrared, light with a wavelength longer
than red light
26
An IR Blanket
• Some of this radiation is directed at the ground
and will likely be reabsorbed by the ground
• Other rays are directed sideways, or upward
• These rays will likely encounter other
greenhouse gas molecules before escaping
from the atmosphere
27
Absorption
• Each gas adsorbs at a discrete set of
wavelengths
• Combinations of gases are more effective at
absorbing across the electromagnetic spectrum
than any single gas
• Some gases are much more effective than
others
28
Natural Greenhouse Effect
• The atmosphere naturally contains carbon
dioxide, methane and nitrous oxide
• These gases--together with water vapor--create
the natural greenhouse effect
• They trap some of the sun's energy and keep
the Earth warm enough to sustain life
29
Carbon Dioxide
• Each year we add more than 30 billion tons of
carbon dioxide to the air mainly by:
 Burning fossil fuels
 Cutting down and burning trees
• Deforestation accounts for about 17 percent of
the carbon dioxide increase from human
activities
30
Global Carbon Flux
31
Effect of
Greenhouse
Gases
• Chart shows how much
warming could be
caused by each of the
gases that human
activities release
32
A Global Problem
• An increase in global temperature would bring
changes to the entire planet, and therefore to
every nation
• This makes it an international issue which
needs worldwide study and responses
• Individual countries are each responsible for
their own greenhouse gas production
33
Deforestation
• Until 50 years ago most of the carbon dioxide
from deforestation was released from boreal
and temperate zones
• Now tropical deforestation is the largest source
• Efforts to curb deforestation are seen as a lowcost option for emissions reduction
34
Tropical Deforestation
• Tropical deforestation is especially important
because it releases large amounts of CO2,
because of the carbon stored in the vegetation
and released when tropical forests are cut
down
35
Causes of Tropical Deforestation
• Commercial logging
• Large-scale agriculture (e.g., cattle ranching,
soybean production, oil palm plantations)
• Small-scale permanent or shifting (slash-andburn) agriculture
• Fuelwood removal
36
Images from Google Earth
37
Exacerbation of Deforestation
• These causes combine to exacerbate deforestation
 Commercial logging often includes road construction,
which in turn opens the forest for subsistence farmers
 At times, tropical deforestation results from weak land
tenure and/or weak or corrupt governance to protect the
forests
38
REDD
• Programs called REDD are being considered
by Congress
• REDD stands for Reducing Deforestation and
Forest Degradation
• The primary goal is to reduce carbon
emissions
39
Secondary Benefits
• Preserving biological diversity
• Sustaining livelihoods for the rural poor and
for indigenous communities and culture
40
Implementing REDD
• In the fight against climate change, billions of dollars have
been pledged to save the world's forests
• A scheme called Reducing Emissions from Deforestation and
Forest Degradation - or REDD+ - is being championed as a
possible solution.
• In the Amazon, a team of six researchers linked to the Center
for International Forestry Researchers have been trying to
understand what lessons can be learned from a project called
Bolsa Floresta, which compensates families to safeguard the
forests.
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Bolsa Floresta Project
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Forests Effects on Carbon Dioxide
• Forests are carbon sinks in their natural state
 They store more carbon than they release
• Trees absorb CO2 and convert carbon into leaves, stems, and
roots, while releasing oxygen
• Forests account for more than a quarter of the land area of the
earth, and store more than three-quarters of the carbon in
terrestrial plants and nearly 40% of soil carbon
43
Carbon Dioxide Release
• Forests clearing releases some of their carbon to the
atmosphere
 Slowly through decay
 Quickly through burning
• One estimate shows that land use change, primarily
deforestation, releases about 5.9 Gt CO2 (gigatons or billion
metric tons of CO2) annually, about 17% of all annual
anthropogenic GHG emissions
44
Carbon Storage
• Forests store enormous quantities of carbon,
and contain more biomass per hectare in
vegetation than other biomes
• Carbon sequestration and release vary by
forest type, although generalizations can be
made about the three major forest biomes—
boreal, temperate, and tropical forests
45
Average C Levels Vegetation & Soils
• Table 1 shows global average carbon levels in the vegetation
and soils for major terrestrial biomes, including the forest
biomes
• Quantities shown in Table 1 should be recognized as global
averages, with substantial variation of carbon stocks within
each biome;
 Wetlands can be dominated by trees (a swamp) or by grasses (a marsh)
 Tropical forests can be very wet (rainforests) or quite dry (trees in a
savannah)
46
47
Another GHG
• There has also been some discussion of the
relationship between forests and methane
(CH4), a less prominent but far more potent
GHG than CO2
• On a per molecule basis, methane is at least 21
times as effective at trapping infrared radiation
as carbon dioxide
48
Future Research
• Evidence of the relationship between deforestation
and CH4 release is still limited
• It generally shows forests to be net CH4 sinks, except
in water-saturated soils (i.e., forested wetlands)
• It is unclear whether activities that modify forest
cover (e.g., deforestation) affect CH4 absorption and
release
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Ongoing Research
• Kew, The Royal Botanic Gardens, was founded in 1759, and
declared a UNESCO World Heritage Site in 2003
• Alongside Kew Gardens in London, Kew has a second country
garden based at Wakehurst which is the home of Kew’s Millennium
Seed Bank.
• Kew is a world leader in plant science and conservation. Our work
helps to discover and describe the world’s plant and fungal diversity,
safeguard the world's plant life for our future, promote the
sustainable use of plants and inspire an appreciation of plants and
the environment
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Kew Views on Climate Change
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