ISIS Report 02/01/08
Greening the Desert
How Farmers in Sahel Confound Scientists
Scientists are catching up with farmers on how local knowledge and cooperation
can work miracles. Dr. Mae-Wan
Ho and Lim Li Ching
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Scientists catch up with reality
For years, many scientists
have been making dire predictions of widespread irreversible ‘desertification’
in the African Sahel. But recent findings have proven them wrong. Satellite
images consistently show an increase in ‘greenness’ since the 1980s over large
areas, confirming evidence on the ground indicating that the Sahel has recovered
from the great droughts of the 1980s, and that human factors have played a
large role in reclaiming the desert [1].
The African Sahel
is a semi-arid grass and shrubland region situated between the Sahara
desert in the north and the humid tropical savannas in the south, with a steep
north-south gradient in mean annual rainfall. Rainfall is markedly seasonal
and variable. A long dry season alternates with a short humid season during
the northern hemisphere summer. The scarcity of rainfall and its variable,
unpredictable pattern accentuating from south to north, are the most important
factors that shape the Sahel ecosystem. The vegetation cycle closely corresponds
to the seasonality in rainfall, with virtually all the plant growth in the
humid summer months. Overlying the sharp seasonal contrasts in rainfall are
considerable fluctuations from year to year, and from one decade to another.
Although variable
rainfall and droughts are seen as normal in arid and semiarid climates, the
droughts that struck the Sahel in the late 1960s through to
the 1980s were unprecedented in length and severity. Land degradation and
famine during the droughts, exacerbated by political instability and unrest,
prompted the UN to hold a conference on desertification in 1977. This initiated
a debate, still ongoing, on the causes and effects of drought, land degradation
and desertification.
There are two opposing camps
in the debate. Adherents of the desertification hypothesis hold human activities
responsible for ‘irreversible’ declines in vegetation from ‘overuse of resources’
and ‘human mismanagement’. Sceptics, however, see declines in vegetation as
the result of drought, and hence a temporary phenomena, with humans playing
only a minor role, if at all.
Some scientists have stressed
the high potential of adaptation of the Sahel population to
rainfall variability, and they are right.
Greenness correlates
with rainfall
Scientists at the University
of Arizona Tucson, University of Maryland Baltimore and NASA Biospheric Sciences
Branch Greenbelt in the United States investigated the spatial and temporal
patterns of vegetation greenness and rainfall in the African Sahel. For rainfall,
they used available meteorological data. For greenness, they used imaging
data derived from measurements made by the Advanced Very High Resolution Radiometer
instrument on board the National Oceanic and Atmospheric Administration polar-orbiting
satellite series. The measure of greenness, Normalised Differential Vegetation
Index (NDVI), is the normalised ratio of the near-infrared (NIR) and red spectral
reflections:
NDVI = (NIR - red)/(NIR
+ red)
NDVI is sensitive to the
presence, density and condition of vegetation and is correlated with the absorbed
photosynthetically active radiation and growth in vegetation.
For the period
1982-2003, the overall trend in monthly maximum NDVI is positive over a large
portion of the Sahel region, reaching up to 50 percent increase in the average
NDVI in parts of Mali, Mauritania and Chad, though averages are not very meaningful
in this highly dynamic environment with considerable seasonal fluctuations.
This positive trend in NDVI is accompanied by widespread increases in rainfall
over the same period of time, with maximum positive slopes in northern Nigeria.
However, from a longer-term
perspective, the observed increase in rainfall is merely a return to more
or less average conditions that prevailed before the 1960s after an exceptionally
dry period, and does not suffice to cancel out the secular downward trend
in rainfall across the entire region. The early to mid 1980s saw the peak
of desiccation in the Sahel for the century.
Monthly maximum
NDVI in the Sahel was found to correlate best with rainfall accumulated over
a period 3 months (current plus previous 2 months), which confirmed earlier
findings that vegetation greenness in semi-arid environments is more strongly
related to soil moisture - a function of rainfall accumulated over a period
of time - than to instantaneous rainfall. Correlation coefficients computed
for NDVI and rainfall are highly significant for the entire Sahel
region (P<0.05) with stronger correlations in the southern Sahel than in
the north.
Greenness ‘hotspots’
correlate with human activity
When the main correlation
of NDVI to rainfall is subtracted out, there is a residual pattern of NDVI
in which large areas are without significant trends (over and above that predicted
from the trends in rainfall), and considerable areas of positive residual
trends, i.e., areas in which the vegetation has been greening more than explained
by rainfall alone. These positive ‘hotspots’ are found in parts of Senegal,
Mauritania, Mali, Niger, the Central Plateau of Burkina Faso and large portions
of Chad.
While the greening
in the Niger Delta of Mali might be explained by an expansion of irrigation,
different explanations must be found for the Central Plateau of Burkina Faso,
which had been identified as a prime example of the desertification crisis
some 20 years ago. Here, a recovery of vegetation greenness beyond what would
be expected from the recovery of rainfall alone might be due to increased
investment and improvements in soil and water conservation technique such
as contour bunding, in response to the drought crisis experienced by farmers
[2].
In Niger, the greening hotspots
were observed in Tahoua and Maradi regions, centring around the area of Projet
Keita, an extensive rural development programme with a focus on natural resource
management and soil and water conservation which began in the early 1980s
supported by the FAO and the World Food Programme of the UN as well as the
governments of Niger and Italy. Chris Reij, a soil conservationist who has
worked in the region for decades, has independent corroborated the farmer-managed
natural regeneration in this region of Niger, particularly along
the road between Maradi and Dosso.
In Chad, the
greening hotspot was found, among other places, in the Chari-Baguirmi region.
The West African Pilot Pastoral Programme has managed a few sites there since
1994 to test a participatory approach to holistic rangeland management [3].
Pastoralists have evaluated the outcome as positive.
Areas showing
negative trends in the NDVI residuals cover a considerably smaller area of
the Sahel [1] and are clustered in northern Nigeria and Sudan,
particularly in northern Nigeria. A hypothetical explanation may be human-induced
land degradation due to civil strife and conflict. But overall, the ‘negative’
impacts of human activity are relatively insignificant.
More
supporting satellite evidence
Another study of satellite
images supported the notion that more plants make more rain [4, 5]. Evidence
was found for a positive feedback between vegetation and rainfall at the monthly
time scale, and for a vegetation memory operating at the annual time scale.
That means greater greenness the previous month tends to increase rainfall
a month later, and a green year tends to increase rainfall the next year,
as greater plant growth and deeper root systems tap into more ground water
for making rain.
This positive
interaction between vegetation and rainfall increases the inter-annual variation
in rainfall, accounting for as much as 30 percent of the variability in annual
precipitation in some regions of the Sahel.
As a commentator
stated [4]: “The result adds to the impetus
to preserve green spaces in dry regions, in order to help prevent deserts
from growing and encroaching on agricultural land.”
Evidence
emerging from the ground
Evidence
of recovery has been coming from the ground since at least the beginning of
the present century. Fred Pearce reported in the New Scientist in 2001 on how in Nigeria, Niger, Senegal, Burkina
Faso and Kenya, integrated farming, mixed cropping and traditional soil and
water conservation methods have been increasing per capita food production
several fold, keeping well ahead of population growth [5].
The
use of sheep manure for fertiliser gave increased yields for farmers in Kano, Nigeria. Planting
leguminous crops increased nutrient levels in the soil by fixing nitrogen
from the air. Integration of crops and livestock enhances nutrient cycling;
legumes and manure return to the soil what crops take out. The Kano region
is the most agriculturally productive part of the country, with increased
yields of sorghum, millet, cowpeas and groundnuts.
A four-year
study in eastern Burkina Faso challenged the assumption that
land is degrading largely due to human activities [6]. It found that despite
declining rainfall since the late 1950s and increasing populations, there
was no evidence of land degradation connected to human activities nor a decline
in food productivity. Conversely, yields of many crops have risen, and there
was no decline of
soil fertility over 30 years.
These farmers did not achieve environmental sustainability
through a capital-intensive or high-tech path. In Burkina Faso,
the increased yields of sorghum, millet and groundnuts could hardly be attributable
to increased external inputs, because these crops received little fertilizer
and were cultivated largely with a hand hoe.
The scientists found that farmers have a rich repertoire of
soil and water conservation technologies, such as crop sequencing,
crop rotation, fallowing, weeding, selective clearing, intercropping, appropriate
crop and landrace selection, plant spacing, thinning, mulching, stubble grazing,
weeding mounds, paddocking, household refuse application, manure application,
crop residue application and compost pits. Mechanical practices include perennial
grass strips, stone lines, wood barriers, earth barriers, brick barriers,
stalk barriers, stone bunds, earth bunds and living hedges.
Perhaps more important than the practices is the selective
way they are used, which vary with different field types, allowing
optimal adjustment of limited labour and inputs to the requirements of different
crops and soils. If land becomes limited, farmers do not need to invent new
management systems; they apply these soil and water conservation practices
more intensively. Farmers also
apply land management practices only when and where needed. Using their knowledge
of crops and soils, they treat only the parts of their field that need particular
attention at any one time.
High local
population densities, far from being a liability, are actually essential for
providing the necessary labour to work the land, dig terraces and collect
water in ponds for irrigation, and to control weeds, tend fields, feed animals
and spread manure [5]. As population densities increase, farmers intensify
their cooperation systems, grouping to tend each other’s fields at busy periods,
lending and borrowing land, livestock and equipment, and swapping seed varieties.
People thus invest heavily in creating and maintaining social
networks that share land, labour, seeds, cattle grazing bushland, technologies
and cash [6]. These networks enhance the ability of farmers to farm sustainably
and efficiently by cooperation and reciprocity. They
also allow people to diversify their livelihoods, learn from each other, and
minimize risks, thus avoiding poverty traps.
Furthermore, in Maradi district
of southern Niger, where repeated droughts have wrought environmental
damage, farmers have reversed the damages and reclaimed the desert [5]. This
was also true of Machakos (renamed Makueni) district of Kenya. In the 1930s,
British colonial scientists had condemned the bare eroding hills of the drought-prone
area to environmental oblivion; likewise the local Akamba people were seen
as doomed to a miserable poverty-rife existence. The same narrative was consistently
reproduced in the 1950s and 1970s. Yet researchers found the hills greener,
less eroded and more productive than before, despite a fivefold population
increase. The Akamba had responded to the droughts by switching from herding
cattle to settled farming, giving them incentive to work the land effectively.
Niger a haven of trees
In Niger today,
millions of trees are flourishing, thanks to poor local farmers. There are
at least 3 million tree-covered hectares, not the result of the large-scale
planting or other expensive methods often advocated by African politicians
and aid groups, but by the efforts of individual farmers themselves.
The area is far greener than it was 30 years ago; and these gains have come
at a time when the population of Niger has exploded.
How did all this come about?
Lydia Polgreen told the story in the Herald
Tribune [7]. About 20 years ago, farmers like Ibrahim Danjimo realized
something had to be done. “We look around, all the trees were far from the
village,” he said, “Suddenly, the trees were all gone.”.
Danjima, now
in his 40s, has been working the rocky, sandy soil of his tiny village since
he was a child. He and other farmers in Guidan Bakoye took a small but radical
step of not clearing the saplings from their fields before planting as they
had for generations. Instead, they would protect and nurture the saplings,
carefully ploughing around them when sowing millet, sorghum, peanuts and beans.
Another change
was the way trees were regarded by law. From colonial times, all trees in
Niger had been property of the state, which gave farmers little
incentive to protect them, and they were chopped for firewood or construction.
Over time, farmers began
to regard the trees in their fields as their property, and in recent years,
the government has recognized the benefits and allowed individuals to own
trees. Farmers make money off trees by selling branches, pods, fruit and bark.
Mahamane Larwanou, a forestry
expert at the University of Niamey in Niger’s capital, said
the revival of trees had transformed rural life. Farmers can sell the branches
for money, they can feed the pods as fodder to their animals, sell or eat
the leaves and fruits. The tree roots fix the soil in place, preventing it
from being carried off with the fierce Sahel winds. The roots also help hold
water in the ground rather than letting it run off into gullies that flood
villages and destroy crops.
Wrestling subsistence
for 13 million people from Niger’s fragile ecology is something
akin to a puzzle.” Larwanou said, “Less than 12 percent of the country’s land
can be cultivated, and much of that is densely populated. Yet 90 percent of
Niger’s people live off agriculture, cultivating a semiarid strip along the
southern edge of the country.”
Farmers practise mostly
rain-fed agriculture. The return of trees increases the income of rural farmers,
cushioning them against the boom and bust cycle of farming and herding.
Ibrahim Idy, a farmer in
Dahirou, a village in the Zinder region, has 20 baobab trees in his fields.
Selling the leaves and fruit beings him about $300 a year in additional income.
He has used that to buy a motorized pump that draws water from his well to
irrigate his cabbage and lettuce fields, and sends his children to school.
His neighbour, who has fewer baobab trees, cannot send his children to school;
instead they have to draw water from the well. In some regions, swaths of
land that had fallen out of use are being reclaimed with labour-intensive
but inexpensive techniques.
In the village
of Koloma Baba, in the Tahoua region just south of the desert’s edge, a group
of widows has reclaimed fields once thought forever barren. They dug pits
in plots of land as hard as asphalt, placed a shovel of manure in each pit
and wait for rain. The pits held the water and manure stayed in the soil and
regenerated its fertility. In this way, more than 240 000 ha of land have
been reclaimed, according to researchers. But it is still a hand to mouth
existence, the women produce enough to eat, and disaster is always just one
missed rainfall away.
While Niger’s
experience of greening on a vast scale is unique, smaller tracts of land have
been revived in other countries. “It really requires the effort of the whole
community,” said Larwanou. “If farmer don’t take action themselves and the
community doesn’t support it, farmer-managed regeneration cannot work.”
Moussa Bara, the chief of
Dansago, a village in the Aguié region where the regeneration has been a huge
success, said the village had benefited enormously from the revival of trees.
He said not a single child had died of malnutrition in the hunger crisis that
gripped niger in 2005, largely because of extra income from
selling firewood. Still, he said, the village has too many mouths to feed.
Project
Oasis must remain farmer-led
Chris Reij, now at the Free University Amsterdam in the Netherlands,
presented the findings in Niger at the From Desert to Oasis symposium in Niamey.
He wants to spread the success of Niger to neighbouring countries including
Mali, Senegal and Burkina Faso. The programme will form part of the Oasis
initiative to reclaim deserts, which was launched at the symposium in October
2006 by 11 African countries, with support from international research and
government agencies [8].
Let’s hope they will continue to let local
farmers lead the projects, with scientists taking a supporting role. As Fred
Pearce stressed of the Sahel miracle [5], “This is no high-tech
breakthrough, nor a result of Western aid programmes.” A major reason for
the overestimation of land degradation is the underestimation of local farmers’
abilities [6]. Scientists, policy-makers and aid workers must recognize the
overriding importance of local knowledge and ingenuity for innovation, as
well as the cooperative community networks for solving our problems of survival
in times of climate change. The greening of Sahel is a clear example of how the dominant
Western knowledge system had grossly misinformed policy-makers; and it was
the knowledge and initiatives of local farmers that saved the situation.
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