DESERT AS A REVERSIBLE TRANSITION
Nunes, J., Landscape Architect, PROAP – Landscape Architecture (joao.nunes@proap.pt)
Ribas, C., Landscape Architect, PROAP – Landscape Architecture (carlos.ribas@proap.pt)
Campos, T., Landscape Architect, PROAP – Landscape Architecture (tiago.campos@proap.pt)
Sanz, B., Landscape Architect, PROAP – Landscape Architecture (proap@proap.pt)
In arid countries such as the UAE, characterized by extensive areas of drylands and increasing urban pressure in
territorial and water resources, desertification process has been highly accelerated during last decades. Since
2002, the “Greening the Desert” program has been implementing different projects in order to combat
desertification in the Gulf. Although well intentioned, some of the measures have been criticised for their
unsustainability and high energy demand.
This paper discusses desertification and land degradation and, more specifically, highlights the main causes and
indicators of desertification in the UAE. Among others, hyper-aridity, over-exploitation of water resources, soil
erosion and over-grazing are the most representatives. Throughout the hypothesis that the desert is not a
condition but a state within an ecological process, this reasoning explains the possibility of reversing
desertification process in arid ecosystems, which is graphically demonstrated with a theoretical curve relating
energy input/time ratio.
Along the “de-desertification” process, maximum energy inputs are needed to a reversal phase and a minimum
energy input is needed for a maintenance phase. The less energy input needed during the process, the more
sustainable and efficient the process becomes.
This paper proposes an ecological landscape approach, figuring measures that sustain low energy inputs for
greening the UAE deserts, based on a deep understanding of the desert ecosystem’s dynamics, the identification
and manipulation of the natural limiting factors and the consideration of the interconnection between the site’s
intervention scale and the larger scale of the territorial context, always considering landscape in its most
inclusive conception.
Keywords: reversibility, desertification, de-desertification, energy input-time, ecological succession, resilience
1. Introduction
The present research presents some possible definitions of desertification in arid, semi-arid
and sub-humid climates, identifying its main causes and, ultimately, appointing some
significant landscape strategies to reverse this global process. The paper assumes that desert
is not a condition but a state within an ecological process that can be reversed at the expense
of landscape strategies, which stated between the energy inputs applied to the system and the
time it takes to react.
Desertification was a major global issue during the twentieth century and it will remain on
the international agenda in the present century. According to the International Institute for
Sustainable Development’s (IISD) 1996 report, it affects about one sixth of the world’s
population, seventy per cent of all dry lands and about one quarter of the total world’s land
area (Figure1). According to United Nations Environment Program (UNEP, 1984), about six
million hectares are irretrievably lost or degraded by desertification each year and about one
hundred and thirty five million people are severely affected by this process.
In 1977, the UNEP defined desertification as “the diminution or destruction of biological
potential of land which can lead ultimately to desert-like conditions”. According to this
program “this process leads to reduced productivity of desirable plants, alterations in the
biomass and in the diversity of life forms, accelerated soil degradation and hazards for human
occupancy” (Lal, 1989).
Figure1. World’s desert areas or with tendency to desertification.
Later on, in 1994, the United Nations Convention to Combat Desertification (UNCCD) was
approved in order to provide international guidelines for combating desertification1. From
this convention, desertification was described as “land degradation in arid, semi-arid and dry
sub-humid areas resulting from various factors including climatic variations and human
activities”.
Desertification can be defined as “a dynamic self-accelerating process, resulting from
positive feedback mechanisms driving a downward spiral of land degradation” (Tivy 1990).
Land degradation, a possible synonym for desertification, encompasses soil degradation2, as
well as, the weakening of natural landscapes and vegetation, as it is defined as the reverse of
soil’s development or formation.
Human-induced land degradation includes overgrazing adverse effects, excessive tillage, over
clearing, erosion and sediment deposition, extractive industries, urbanization, disposal of
industrial wastes, road construction, decline of plant communities, the effects of animals and
noxious plants, and pollution of the air with its effect on land (Houghton & Charman, 1986).
In this regard, the best way to reverse land degradation is early action and prevention, rather
than costly rehabilitation of degraded lands (Shahid, 2007)
Taking the United Arab Emirates (UAE) as a case study, this paper attempts to show an
ecological landscape design approach to reclaim desertifying areas by preventing and/or
reverting the land degradation process.
1
A total of one hundred and ninety one countries had ratified and accepted the guidelines of this convention in 2004: The
UAE became a member in 1999.
2
Soil degradation lowers the current and/or the potential soil’s capability to produce goods or services (FAO-UNEPUNESCO, 1979), causing the loss, or reduction, of soil’s functions and uses (Blum, 1997).
2. Desertification in the UAE
Situated in the Southeast of the Arabian Peninsula in Southwest Asia, on the Persian Gulf, the
UAE3 are located within the arid west continent desert belt and therefore, environmental
conditions are highly sensitive. Sensitivity is due to the delicate balance between numerous
components of the arid natural systems such as climate, water resources, soil, vegetation, and
biodiversity. Despite the little information available in specialized literature proving
desertification in the UAE, there is an evident process of desertification due to both natural
and anthropic stresses, especially enhanced during last decades4. The main causes of
desertification in the UAE are outlined and discussed bellow.
2.1. Hyper arid conditions and climatic change
With extremely hot and dry summers – temperatures rising up to 48ºC in coastal cities and
50ºC in the southern desert regions –, mild to warm winters with sporadic rainfall – with
annual average ranging between 120 and 200 mm per year –, and high evapotranspiration
rates – averaging about 8 mm per day –, climatic conditions within the UAE can be regarded
as hyper-arid. In this regard, the United Nations Environment Programme (UNEP) classifies
the whole of Abu-Dhabi Emirate and most of the surrounding area as hyper-arid, belonging
to one of the most inhospitable regions on earth (Middleton & Thomas, 1997).
Under these extreme conditions, desert areas are a dominant feature of the UAE landscape.
Fully four-fifths of the land area is classified as hyper-arid desert regions, a very fragile series
of ecosystems with unique features such as vast loose sandy deserts, oasis, long coastlines,
islands and rangelands (Figure2) (Ministry of Energy of UAE, 2006).
Figure2. Arid ecosystems in UAE: coastal areas, desert areas and mountainous areas.
3
Bordered by Oman, Saudi Arabia and Qatar, the UAE spans approximately 83,600 square kilometers and is a federation of
seven emirates: Abu Dhabi (the capital), Ajman, Dubai, Fujairah, Ras al-Khaimah, Sharjah and Umm al-Quwain
4 One accepts a great demand of an integrated and coordinated intelligent system between different environmental agencies
and government departments, in order to share information for a better understanding of the desertification problem in the
UAE.
In addition to these harsh environmental conditions in the UAE, it is estimated that climatic
change will affect the near future distribution of the existing dry lands. Expected decreases in
regional soil moisture can induce sub-humid areas to become semi-arid and semi-arid land to
become arid. The Intergovernmental Panel on Climate Change (IPCC) notes that resistance to
degradation and resilience will decrease as aridity increases (TAR, 2001), suggesting that the
vulnerability of the desert ecosystems to arid conditions can increase significantly due to
climate change5.
2.2. Over-exploitation of water resources
The UAE have the highest consumption of water per capita in the world, being eighty per
cent of water consumption used for different greening projects (both agriculture and parks)
and only thirteen per cent for domestic needs (Ouis, 2007). The high rate of water
consumption is exacerbated by increasing population, urbanization and greening projects in
the country. The volume of rainfall the UAE receives annually is not enough to meet the
excessive and growing demands6. As a consequence, the extremely high rate of subsoil water
demand, including non-renewable fossil water resources, is one of the today’s main
environmental problems in the UAE and one of the most important threats for the future
(Environmental Agency of Abu-Dhaby, 2007). Estimates shown by the National Drilling
Company – United States Geological Survey (NDC-USGS) in 1996 revealed that, at the rate
of abstraction estimated at that time, brackish groundwater might last for about two hundred
and fifty years. However, the new abstraction rate in 2002, states that they will last for only
fifty years.
2.3. Wind erosion
The UAE deserts are dominated by sandy soils and sand dunes of varying heights,
continuously moving at different rates, therefore, aeolian deposits are predominant. Most
parts of the country are subject to violent dust storms causing strong wind erosion (Shahid,
2007). Thus, it is demanding to understand the desert soil’s texture and to determine the
mechanisms of particles movement in order to formulate necessary measures to reduce wind
erosion.
After analyzing the particle movement mechanisms in surface deposits of UAE desert soils, it
was deduced that particles ranging from 5 to 24 percent are displaced in the creep, 70 to 92
per cent in saltation and 2 to 8 percent in suspension (Shahid & Abdelfattah, 2005). This
stresses that saltation moves the main mass of wind-blown particles, what ultimately causes
dust storms and wind erosion in the arid environments of UAE.
2.4. Water erosion
Most of the UAE’s desert environment consists of sandy, sand dune soils, which absorb the
rainwater due to its very high drainage capacity and, therefore, no water erosion occurs in
these areas (Shahid et al., 2004).
5
In their climate simulations, the IPCC has determined that temperatures in the Arabian Peninsula region could increase by
1 ºC to 2 ºC by the 2030-2050 time period while precipitation levels could significantly decline (TAR, 2001; Al
Shindagah, 2001).
6 Current demands in the Emirate of Abu-Dhabi are about 26 times greater than the volume of water which is naturally
recharged within the hydrological system (Environmental Agency of Abu-Dhaby, 2007)
However, more stable and cohesive soils in the highlands have shown signs of combined
effect of wind and water erosion. Water erosion in the UAE occurs only during the intensive
rainy season, mainly concentrated during winter months, from October to March. This
process causes severe run-off flows in the sloppy landscapes in the form of rills and gullies –
surface crusts that obstruct water percolation to root zones. The main consequence of soils
subjected to water (and also wind) erosion is the loss of the organic matter layer and the
nutrient-rich surface (Shahid et al., 2004).
2.5. Over-grazing
Deserts in the UAE are important ecosystems for traditional grazing by domestic animals. As
a result of changes in nomadic practices, these regions have shown vulnerability to chronic
overgrazing (Ministry of Energy of UAE, 2006). The pressure of overgrazing is mainly
concentrated on the rangelands, resulting into a loss or reduction in plant cover beyond its
bearing capacity (Zoebisch and DePauwn, 2004).
Rangelands and forests over-grazing are the main causes for flora’s degradation and
accelerated erosion (Mousavi, 2006). In fact, it has been argued that future trends in human
and livestock practices may have more impact on desert systems than climate change (Al
Shindagah, 2001).
A study made by El-Keblawy, in 2003, shows the difference in number of species, species
diversity, and plant cover density, when comparing in and outside limits of the recently
designated as protected site in the Al Ain-Dubai road region. The dominant species within the
reserve boundaries were the most edible. Outside the reserve boundaries these were absent,
which indicates that they were preferential and overgrazed.
2.6. Salinization, Compaction, Sealing and Crusting
Soil salinization is a widespread natural feature of semi-arid to hyper-arid climates. In the
UAE, soil salinization occurs mostly in coastal areas due to seawater intrusion into
groundwater aquifers (Shahid et al., 2004). It is also verified in inland areas due to the use of
improper irrigation techniques. As a consequence, local plant species that are not used to
saline conditions are being replaced by halophytic ones, inevitably leading to loss of natural
biodiversity.
There are other desertification indicators, namely: surface sealing; crusting and compaction in
heavy, cohesive, flattened soils rich in silt and with dispersible clay contents. In these cases,
dispersible clay in crusted soil at the expense of mechanical energy, such as a rain drop
impact, breaks free of its aggregate and goes into suspension (Southerland et al., 1996). The
clay is, ultimately, accumulated at the surface to form crust or is translocated into the soil as
an internal sealing of pores or clogging. In addition, these processes interact with other soil
degradation processes such as water erosion, decrease soil infiltration, and increase run-off,
aggravating desertification problems (Shahid et al., 2004).
3. “Greening the Desert” program and the ecological crisis in the UAE
“Combating Desertification” program is the sum of activities leading to land’s integrated
development in arid, semiarid and sub-humid areas for sustainable development. It aims to
prevent and/or decrease land degradation; to rehabilitate partially degraded land; and to
reclaim desertified land. The UAE analyse it from different perspectives based both on their
environmental conditions as the vision of HH Sheikh Zayed Bin Sultan Al Nahyan in
improving UAE’s desert conditions. Therefore, the term “combating desertification” is used
as compromise for the “Greening the Desert” program (FEA-UAE, 2002).
“Greening The Desert” is focused on natural desert environment conversion into productive
agricultural land, guarantying its biodiversity and increasing its economic outcomes.
Traditionally, in the UAE’s area it had only been possible to cultivate land near oasis and
mountains. However, today large areas within the desert have been cultivated at the expense
of intensive irrigation and other technologies that require constant care and high maintenance
costs. This attitude of greening the Emirates, often described as ‘rolling back the desert’, is
being promoted as a source and symbol of national pride, proving the significant scale of the
ecological transformations (Ouis, 2007).
Greening projects are providing positive environmental impacts such as: halting degradation;
sand stabilization and hydrological balance promotion; creeping sand control; microclimatic
comfort improvement; environmental quality enhancement; habitat restoration; and aesthetic
increase of the area.
Furthermore, afforestation was also considered as preventive measure for some of the desert
territories, which with distinct degradation levels7. Nevertheless, well intentioned all these
green development projects might be, they are also threatening desert ecosystems and causing
numerous new environmental problems in the UAE.
With insufficient rainfall to support them, desert ecosystems are entirely dependent on
irrigated water. A substantial proportion of this water is provided by scarce groundwater
reserves, and at present, the subtraction rates far exceed natural recharges. The excessive use
of groundwater will have serious consequences for years to come.
Water demands are also being addressed at the expense of sea water desalination, a process
that requires great amounts of energy and releases great amounts of carbon dioxide (AlRashed & Sherif, 2000).
In addition, aside from water use implications, plantations development cause adverse habitat
effects too. Not only local varieties of shrubs and trees are being planted, but imported ones
from other arid areas as well. These latter have been artificially introduced and have found
optimal conditions. However, it is predicted that these newcomers will oust the local flora
and fauna, in long term.
Habitat fragmentation has also occurred due to great extensions of walls and fences enclosing
plantations and, therefore, restricting the larger animals’ movement.
At this moment, it is also important to acknowledge that the economic costs of the
implementation and maintenance of projects under the purview of “Greening the Desert”
program come mostly from oil exploitation. And, accordingly to Ouis (2007) this is, perhaps,
the major cause for today’s global pollution problems and, which will create severe climatic
changes in future, threatening many environments around the world.
7
“Physical Geography of Abu Dhabi Emirate, United Arab Emirates”. Environment Agency Abu Dhabi, 2008, page 40
4. “Rolling back the desert” 8 in sustainable way
Artificial greening of arid ecosystems is expensive, risky, and the benefits are often shortlived. Ecological restoration is an alternative approach that attempts to minimize management
intervention (and costs) by stimulating natural successional processes in order to develop
stable structural and functional dynamics (Whisenant, 1995).
This paper attempts to demonstrate a vision for combating desertification and greening the
UAE desert, supported by an ecological restoration approach. This reasoning is based on the
idea that the desert is not a condition but a state within a natural process, and can be
graphically demonstrated with the help of the theoretical curve of desertification reversal,
presented below (Figure3).
As shown in the graphic, in order to invert desertification processes (by restoring degraded
arid ecosystems) two sequential phases are needed: a reversal phase, requiring a maximum
energy input and a maintenance phase, requiring a minimum energy input into the system.
Figure3 Curve of Desertification Reversal
This document explores the process of “de-desertification” and, more specifically, the
relation between the energy inputs imposed to a system and the period of time required by it
to react and reverse the process of desertification, therefore giving the possibility to the
ecological succession to evolve towards afforestation (Figure4).
8
Synonym to “de-desertification process” extracted from Ouis, O. “Greening the Emirates: the modern construction of
nature in the United Arab Emirates”. Cultural Geographies 2002; 9; page 337.
Figure4 Ecological Succession under arid conditions
In this case, it must be acknowledged that traditional successional concept of vegetation
returning to a predictable, relatively stable state, following disturbance may not be valid in
several arid ecosystems (Westoby and others 1989; Friedel 1991; Laycock 1991). In fact,
most arid ecosystems seem to have multiple and alternative stable-states (Friedel 1991;
Laycock 1991). Besides, and according to Friedel (1991), movement between these steadystates, i.e. ecosystem recovery, requires significant management inputs. Thus, despite the
amount of energy input needed in rehabilitating degraded arid ecosystems – corresponding to
the reversal phase –, there is always a demand for management intervention, providing
minimum energy inputs – corresponding to the maintenance phase.
The idea of combating desertification processes based on ecological restoration strategies that
initiate autogenic succession9 are most appropriate for extensively managed arid ecosystems,
which cannot be completely restored by artificial methods (Whisenant,1995).
5. Strategies for combating desertification. Case study in UAE
The restoration of desertified areas by a “de-desertification” process is based on a thorough
study of the ecological systems in deserts. This process can only be successful through
accurate understanding of the arid ecosystem functioning and identification of the
ecosystem’s natural limiting factors10.
Restoration efforts should be focused on site’s specific attributes and objectives, but always
considering interactions with the surrounding landscape, when understanding it in its most
inclusive conception. Therefore, it is accepted here that the failure to comprehend restoration
sites as integral components of a larger, highly interconnected landscape has often produced
inherently unstable “restored” landscapes (Whisenant,1995).
Unique landscape combinations are formed from interactions of geomorphology, hydrology,
colonization patterns, and local disturbances. The distribution of energy, materials, and
species in relation to sizes, shapes, numbers, types, and configurations of landscape elements
9
Autogenic succession uses are encouraged in this paper, rather than fighting against natural processes.
Ecosystem´s natural limiting factors considered in this research are: water, soil, vegetation, and climatic conditions.
10
is what structures landscape. Landscape functions – or dynamics – are responsible for the
interaction between all the elements concerning energy, materials, water, and species fluxes
(Forman and Godron 1986).
This research introduces a series of strategies that contribute to an ecological restoration
landscape approach, which induces desertification process in arid lands reversal. In order to
obtain credible and systematic data, even if of theoretical character, an application study in
the UAE is presented.
These strategies’ main intention is to manipulate the limiting factors in arid ecosystems, in
order to reverse desertification process. These strategies consider the interrelation between
landscape’s different components and dynamics, considered essential when establishing and
maintaining ecological systems. These different strategies present can be represented by
different profile curves, depending on the energy/time ratios required to reverse the
desertification process (Figure5).
Figure5 Different curves of desertification reversal, according to different ratios energy-time
Once again, it is important to stress the theoretical approach within these graphics. They are
based on realistic reasoning and accurate comparative analysis, even though further research
will be needed to obtain referenced data.
The different strategies are mainly focused on: (1) infiltration enhancement; (2) vegetation
establishment; (3) soil improving processes; and (4) adequate maintenance and resources
conservation.
5.1. Infiltration enhancement
With appropriate techniques, instantaneous infiltration can be substantially increased. On
sites with deeper soil profiles – usually on the lower, less steep sections of hill slopes and in
flat valley bottoms – a large portion of moisture is retained. This moisture improves the in
situ plant development and plant growth on the rangeland. A smaller fraction of the water
will penetrate the soil and enter the substratum to recharge the groundwater. On sites with
shallow soils and high contents of large-size gravel, improved infiltration will directly
increase deep percolation and groundwater recharge in the area. In these cases, the direct
effects on plant development will be less pronounced (Zoebisch and DePauwn, 2004). To
increase instantaneous infiltration, water-conservation measures that improve localized
surface roughness11 – and thus increase infiltration’s opportunity – are recommended:
11
In this regard, Marinez de Azagra (2000) coined the neologism oasification as an antonym of desertification by soil
erosion. This process entails the building of small earth structures to collect and infiltrate as much precipitation and run-off
as possible by modifying a slope´s physiography in a convenient and non aggressive manner. As a result, better soil
moisture conditions will prevail and chances of the establishment and growth of vegetation will improve (Azagra,2004).
-
-
-
Contour stone lines and small
boulder bunds – these measures
increase instantaneous infiltration
and reduce surface run-off. This is
particularly important for highintensity rainfall events, which
usually lead to short-term peak
flows that escape to the sea
through the wadi12 system.
Contour stone lines and boulder
bunds are particularly effective for
soil moisture and water-table
replenishment (Zoebisch and
DePauwn,
2004).They
are
recommended because of their
simplicity, ease of construction,
Fig.6 Small boulder bunds
low maintenance requirements, and
cost-effectiveness (Figure6);
Graded storm water bunds and
diversion channels – these measures intercept run-off at various stages along the slope –
from the steep hillsides to the flatter gravel plains –, in order to slope and facilitate
posterior infiltration. These structures must be developed to provide short-term storage of
overland flow for increased infiltration, always according to sites’ specific features. The
structures must be intermittently graded, so that any excess run-off that could destroy the
structures is safely discharged. (Zoebisch and DePauwn, 2004). The structures should be
made from stone and soil available on site, with minimum interference in the landscape
and minimum cost;
Groundwater-recharge barriers – at wadis level, recharge dams intercept wadi flow to
provide groundwater recharge. Structure should be semi-pervious, such as gabions built
with local materials in wadi branches to reduce the risk of destruction by heavy spate
flows. For the main wadi, a major recharge dam is recommended. This sort of dams
should be designed after all the other measures have been implemented and when their
water-trapping efficiencies have been duly evaluated (Zoebisch and DePauwn, 2004).
5.2. Vegetation’s establishment
Vegetation is re-established by natural regeneration, following the improvement of the soilmoisture’s character. However, this process requires livestock exclusion during rehabilitation
period, from two to five years. Useful seeding and adapted species will speed up the
restoration process on these sites. After establishment and evaluation of the bearing
capacities, both specific and seasonal, a range-use plan may be developed to ensure
sustainable use of the natural resources. This will include irrigated fodder production required
livestock population support during drought periods(Zoebisch and DePauwn, 2004).
Different strategies of plantation can control different erosion problems:
12
Wadi is the Arabic term traditionally referring to a valley. In some cases, it may refer to a dry (ephemeral) riverbed that
contains water only during times of heavy rain or simply an intermittent stream.
-
-
-
13
Trees Contour Ridges – one successful plantation technique to effectively control surface
runoff involves establishing parallel vegetation bands along contour lines. A dense
vegetation belt not only stops or slows down runoff, but also traps soil particles
suspended in the water that have been removed from the more exposed areas between the
strips. Strips spacing depend mainly on slope’s angle and local erosion conditions. The
primary consideration for species selection should include native plants, as contour strips
reduce a percentage of the land out of cultivation, even though they are intended to
increase productivity of the total area. Many different species can be used, often in
combination;
Gullies reclamation – vegetation
can also reduce bank or channel
bottom erosion as long as the
water flow is not too powerful.
Gullies present special problems,
because they often occur on steep
slopes, and even brief peak flows
can cause serious damage. To
prevent gullies formation along
waterways, banks should be lined
with trees and shrubs. Trees,
shrubs, and other mechanical
methods can be combined and
Fig.7 Gully reclamation by contour vegetation
established within the gullies to
further erosion control and to help
rebuild the removed soil layers with
optimal results (Figure7).
Windbreaks – windbreaks are barriers planted to reduce wind velocities and to prevent,
or reduce, wind erosion. In addition, they also provide shade; reduce evapotranspiration;
and moderate extreme temperatures. Different from windbreaks, shelterbelts imply a
wider vegetation strip, incorporating more tree and shrub rows than the ones found in
windbreaks. In a shelterbelt planting, three zones can be recognized: the windward zone,
from which the wind blows; the leeward zone, on the side where the wind passes; and the
protected zone, in which the windbreak or shelterbelt effects are experienced). It is
generally accepted that windbreaks or shelterbelts protect areas over a distance up to
their own heights on the windward side and up to twenty times their heights on the
leeward side, depending on the strength of the wind13.In reducing wind speeds, narrow
barriers can be as effective as wide ones, moreover having the advantage of occupying
less land. Is important to make a thorough study of the local winds and to know the
direction and strength of the winds. Barriers should be established perpendicular to the
direction of the prevailing winds for maximum effect. When the prevailing winds are
mainly in one direction a series of parallel shelterbelts perpendicular to that direction
should be established to protect large areas. A checkerboard pattern is required when the
winds are originated from different directions. Windbreaks may be staggered so that they
conform to the established boundaries such as borders of fields, roads, trails, stream, and
other natural or man-made features (Figure8).
“Windbreaks and Shelterbelts”, Arid zone forestry: A guide for field technicians. FAO, 1989
Figure8 Windbreaks and shelterbelts
-
Dune stabilization – shifting and blowing sand causes great damage to entire settlements
in arid zones. Conservation of existing grass and other plant covers is necessary to hold
the sand in place. There are basically two approaches to dune fixation: biological and
physical. Preference should be given to biological control measures whenever possible.
However, some physical constructions are often needed for initial plant establishment.
By breaking the force of the wind, the palisades keep the exposed sand from being
picked up, and the sediment load already carried by the wind is deposited in or behind
the barrier. Sand will become entrapped in such rows and ridges will gradually form.
Plant growth then becomes possible in the protected areas behind the ridges. Project sites
close to or within actual desert zones will require more intensive efforts to stabilize
shifting dunes. In these cases, maintenance inputs will also be higher. The more exposed
a specific location is to the wind, the more difficult it is to establish vegetation (Pytlik,
1989). Physical protection may often be needed and it should be acknowledge that native
occurring trees and shrubs have great resiliency. In this sense, indigenous vegetation
should receive priority over exotics, particularly for large-scale projects.
Figure9 Dune stabilization
5.3. Soil improving processes
Mulching is the practice which maintains soil structure, increase aggregate size and conserve
moisture in soil’s upper layer. It cools plant root areas, reducing the amount of water plants
loss through evapotranspiration. Moreover, this measure reduces weed growth and helps soil
erosion control. In some countries of the Middle East, oil (petroleum) mulch –an oil-extracted
material (hydrocarbon colloid) – is sprayed over sand dunes to assist with re-vegetation. The
hydrocarbon colloid is a by-product of refineries and has no cost for the purpose of sand
stabilization. Iran was the first country in the Middle East to introduce oil mulch for dune
stabilization, a method that has subsequently been adopted in other areas including Abu
Dhabi (Khan, 1983). The mulch, when spread, extends to a depth of about 1 mm, reaching a
maximum of 5 cm after 3 years in higher rainfall areas (Dehdashtian, 2009). According to
recent research, no adverse effects were associated with use of oil mulch in Iran; and positive
effects were noted in some cases in relation to soil organic matter, soil water holding capacity
and the amount and activity of soil organisms (Pouyafar and Moghadam, 2006).
5.4. Adequate maintenance and resources conservation
There are several methods required for accurate maintenance and resources conservation,
namely:
-
-
Aflaj water system – this is an ancient technique by which underground tunnels are dug
to channel water from distant sources to villages where it was needed. It is a tested
method which helps conserve water and is still in use around the world today. Aflaj are
still widespread in Oman, where there are currently more than four thousand channels
with an annual flow of six hundred and eighty million cubic meters. The first aflaj built
in the UAE was discovered in 1985 in Al Ain, and dates back to the Iron Age. Whilst
some Gulf States may believe they have resolved their water scarcity problems through
desalination, there is still a lot to learn from the ancient aflaj system, which not only
supplies clean water, cheaply and effectively, but also transports and conserves large
masses of scarce existing water in arid environments (Aburawa, 2011).
Conservation tillage – Tillage aims to create a soil environment favorable to plant growth
(Klute 1982). Appropriate tillage practices are those that avoid the degradation of soil
properties but maintain crop yields as well as ecosystem stability (Lal 1981b, c, 1982,
1984b, 1985a; Greenland 1981). Conservation tillage provides the best opportunity for
halting degradation and for restoring and improving soil productivity (Lal 1983; Parr et
al. 1990). In recent years interest in conservation tillage systems has increased in
response to the need to limit erosion and promote water conservation (Hulugalle et al.
1986; Unger et al. 1988). Conservation tillage includes a number of tilling methods, used
alone or in combination, to control wind and water erosion for minimum loss of the soil’s
surface.
6. Conclusions and considerations
Arid ecosystems within the UAE are suffering serious desertification processes. In order to
combat it, the “Greening the Desert” program has been undertaken at a national level since
2002. Although well intentioned, some measures of this program have also deepened desert
ecosystems causing numerous environmental problems in the country during the last decade.
The proposed methodology, with its most accurate expression in the graphic desertification
reversal curve, demonstrates that most of the projects implemented under this program
actually require high energy inputs into arid ecosystems, normally translated into high
demand of resources, such as water, and high implementation and maintenance costs.
This research is an attempt to highlight the fragility and the high environmental value of
UAE´s desert ecosystems. By extending this reasoning to a wider range of arid climates and
local specificities of many arid regions around the globe, the urgency to adopt new effective
landscape approaches that will lead desertification process reversal towards more sustainable
systems becomes clear.
Landscape approaches based on a series of strategies and measures with ecological
repercussions were presented, considering more efficient uses of the existing natural
resources and lower energy inputs required to achieve the “de-desertification” process.
It is sustained that this approach can only be successful through an accurate understanding of
the arid ecosystem’s functioning and dynamics, the identification and manipulation of the
ecosystem’s natural limiting factors and the consideration of the interconnection between the
site’s intervention scale and the larger scale of the surrounding territorial context. All actions
have territorial consequences and all consequences must be quantified and qualified,
especially when considering landscape in its most inclusive conception.
The strategies presented in this paper are a contribution to landscape ecological restoration
approach towards desertification processes reversal in arid territories, with a specific
application in the UAE context.
7. References
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8. Main author’s biographies
JOÃO NUNES
Lisbon,1960
Founder and CEO of the Landscape Architecture Studio PROAP, which gathers a vast group
of professionals in a cross-disciplinary team, with distinguished levels of expertise in
landscape, in its most inclusive conception.
As International Director is responsible for the strategic, executive and tactical leadership of
the three international offices: Lisbon (Portugal), Luanda (Angola) and Treviso (Italy).
Develops PROAP’s conceptual and creative design and defines the strategic orientation of the
research processes.
Has been lecturing at the Instituto Superior de Agronomia in Lisbon (Agronomics Institute,
Technical University of Lisbon) since 1991. Currently also lectures at the Istituto
Universitario de Architettura de Venezia, Politecnico de Milano, Politécnico di Torino, Roma
La Sapienza, Roma Ludovico Quaroni, Facoltá di Architettura di Alghero.
CARLOS RIBAS DA SILVA
Lisbon, 1966
Partner at the Landscape Architecture Studio PROAP, which gathers a vast group of
landscape architects, architects, designers and plastic artists, part of a core oriented by João
Nunes.
Involved in PROAP’s strategic and financial direction and management, oversees research
and design projects to assure technical coherence.
Frequently participates as guest lecturer in international workshops and conferences,
representing PROAP.
TIAGO TORRES CAMPOS
Lisbon, 1982
Research Manager at the Landscape Architecture Studio PROAP, which gathers a vast group
of landscape architects, architects, designers and plastic artists, part of a core oriented by João
Nunes.
Managing Editor for PROAP’s publications. Jointly runs the international communication
processes, manages graphic and written project information sent to media requests
worldwide.
Participates tactically in the creative processes, review and critique of projects.
Frequently participates in international workshops and conferences, representing PROAP.