20% of Earth’s land is classified as desert (the Desert Biome). Another 20%-25% falls under the category of “semi-arid” or “highly degraded” (Desert, 2011; UNCCD). Every year, 6 million square kilometers, or 2.3 million square miles of this land is added to the desert (Desert, 2011). This happens when the fertile topsoil is degraded or stripped off, making it difficult for most vegetation to take root. While storms can reduce topsoil, most of desertification is anthropogenic. Slash-and-burn agriculture, grazing species, and deforestation all reduce the number of remaining plants. Since the plants’ roots hold the topsoil down in the face of storms, their disappearance causes the soil to be replaced by desert.
In deserts, plants are often spread far apart and must have specific physiologies to survive, such as a thick waxy coating or the ability to shut their stomata during the day to retain moisture. Because only some plants have these desert-survival traits, traditional agriculture is severely hampered (Desert, 2011). Stopping desertification, and reversing it where possible gives a chance to make use of the 40% of the world that is currently unproductive, which would increase food production, and reduce pressure on the land in other areas.
The task is fourfold: stopping desertification, reducing the landmass that the desert covers, and finding ways to promote agriculture in places with low rainfall through the choosing of plants and the pioneer generation of plants.
Stopping the spread of the desert means addressing both anthropogenic and non-anthropogenic causes of desertification. The Ben Gurion University of the Neghev has identified several ways to keep semi-arid lands from becoming deserts, including reducing the amount of ruminating livestock that can be kept in the area. Grazing species can trample the ground, meaning the compaction of earth and death of plants. Furthermore, some species like cattle eat grass by tearing it up from its roots. Plants, and especially their root systems are vital for holding down topsoil, so keeping livestock from grazing on areas at risk can preserve the land.
The roots best suited for the task of holding topsoil are branching systems. Ben Gurion advocates for plants with these systems, such as fruit trees, to be grown on sloped lands rather than plants with taproots, like root vegetables, or shallow roots, like corn. The branching system would hold soil in place to keep it from being carried off during storms.
Figure 1, example of roots, branching versus tap: “Root Systems” NGA’s Learning Garden, National Gardening Association (“Roots as Anchors”)
A key reason deserts are dry is that the evaporation rate may be equal to the already scanty rainfall (Desert), so a large part of reducing desertification is increasing the ground’s capacity for water retention. If enough water is accumulated, plants can take root and cause the desert to recede.
In arid areas, water is found in underground aquifers. In the current state, this is where most water is that does not evaporate. Israel has managed to augment, or even form new aquifers through making impermeable channels that catch runoff during storms and diverting it to underground holdings. This water can then be used for irrigation, particularly drip irrigation, throughout the rest of the year.
Water can also be accumulated above ground by building up bodies of water which do not lend themselves to evaporation as easily as water spread over a large area. Normally during a storm, water becomes runoff, spreads, and then evaporates. However, “agroforestry” uses “Liman” trees to catch the water after a storm (Gurion). The Ben Gurion institute has identified trees that can be planted in such a way that their roots stop the flow of water from runoff areas, which allows it to puddle and grow in the shade of the trees (Mollison, Desertification).
Gabions, cages filled with rocks, provide a similar service in catching water that can later be used for agriculture (Ecofilms). Based on small successes, it has been estimated that 10% of Israel could be irrigated through these artificially grown bodies of water. This number increases when one considers that as the water gathers, channels can be built from the existing bodies of water to new Liman or gabion systems (Mollison).
A more radical approach to turning back deserts was presented by Magnus Larsson in 2008. He suggested using Bacillus pasteurii, a bacterium which turns sand and loose sediments to rock. By burying colonies in the sand, he proposed that the resulting rock structures could be used to store water, provide shade, and create artificial water tables or aquifers (Harmon, 2009; Larsson, 2008).
No matter the method, with access to water, plants can start to grow in the area, which results in a positive feedback loop: the plants shade the ground from the sun, and more water can accumulate; as plants die, they add organic matter to an accumulating topsoil, and their roots hold the topsoil in place, making the desert recede.
Plans to stop or reverse desertification has economic rewards for the countries that implement them. As the desert has spread in India, the direct economic loss associated with desertification has increased sixfold in fewer than fifteen years (UNCCD, 2013). As it is now, the United Nations Committee on Combating Desertification has estimated that 1-10% of countries’ agricultural value is lost because of desertification (UNCCD, 2013), with the numbers as high as 4-12% for Africa, 6% for Paraguay, and 24% in Guatemala. China, for example, loses the equivalent of about 10 billion USD per year because of the desert (UNCCD, 2013). H.E. Dregne and N.T. Chou of Texas Tech considered reversal of desertification 1992, with estimations of the damage considering only the immediate income lost. Their numbers tallied to a USD 42 billion per year loss (Dregne, 1992).
Beyond the direct economic losses associated with desertification, dust storms from the desert can be deposited in reservoirs, the necessary cleaning of which adds another 18.5 billion USD (UNCCD, 2013). There are other losses as well, when one considers the effects from a loss of biodiversity, and from the rising prices of food to compensate for the higher demand and stress on the remaining productive areas (UNCCD, 2013).
In contrast to these price tags, Israel’s projects to reverse desertification have been part of a 17 billion dollar plan with Nigeria. Seemingly high, the long term benefits could have a huge impact both on Israel’s agricultural GDP, and the world’s, and it has already created 2 million jobs (Israel 2010). Dregne and Chou’s estimation for rehabilitation tallies to 213 billion USD over a span of twenty years, while they estimate inactivity to cost 563 billion over the same span. They do note, however, that they are only accounting for 52% of the desertified land by 1992 (Dregne, 1992). While some land is still unlikely to be returned from an arid state, new numbers should consider recent developments in methods to reverse desertification
Within the 52% that Dregne and Chou consider worth rehabilitating, they estimated the land recovery to take five years for land sustaining minimal damage, and fifty years for land severely compromised. Once again, new numbers need to be calculated, but this provides a rule of thumb. When one considers that about 45% of the Earth’s 149 million km2 (Coffey, 2009)of land is semi-arid to arid, then 52% recovery means that 34,866,000 km2 could be made arable fifty years after the start of the project. Considering that half that land is only semi-arid, over 15,000,000 km2 could be at some level of productivity within five years.
Stopping desertification is vital if food production is to outpace population growth, but reclaiming land from the desert is extremely beneficial, both for food production and for the countries that decide to undertake the task. Weighing the gains against the costs, it’s clear that not just stopping desertification, but reversing it where possible is economically advantageous to those countries that do so.
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