Intense solar radiation, lashing winds, and little moisture i.e. less than 10 inches (25 cm) of rainfall create some of the harshest living condition in the biosphere called hot desert. In hot desert ecosystem generally with cloudless skies, the sun quickly heats the desert by day, producing the highest air temperatures (recorded as 57.8º C in Death Valley, California) in the biosphere.
In contrast, the nights are very cold, as the temperature goes down tremendously due to loss of heat into the atmosphere through radiation. There is little water and temperatures vary widely, one may bake during the day and freeze at night.
High temperatures during daytime and persistent winds accelerate water evaporation and transpiration of water vapour from plants. High evapotranspiration and low rainfall is the chief characteristic of desert ecosystem, thus producing sparse perennial vegetation of widely spaced shrubs. The winters are quite cold, temperatures sometimes below freezing point, while heat during summer is intense and scorching. Scarcity of rain fall in deserts ecosystem can be due to high subtropical pressure (Sahara and Australian deserts), geographical position in the rain shadows (western North American deserts) and due to high altitude (Tibetan, Bolivian or Gobi deserts).
Deserts ecosystem cover about 14 percent of the earth’s land and occur mainly near 30º north and south latitude where global air currents create belts of descending dry air. Some desert ecosystem are also produced in the rain shadows of high mountain ranges, leeward slopes that face away from incoming storms and thereby receive little rainfall. Most deserts ecosystem receives some rain during the year and has at least a sparse cover of vegetation.
Annual net primary productivity of true deserts is less than 2000 kg per hectare. The dominant soils of the arid zone are light-textured and devoid of any significant structural development. These are prone to severe wind erosion. Desert ecosystems have very low water retention capacity – with high infiltration rate and low hydraulic conductivity. Water is hardly retained in deserts soil as it is not soaked into the earth, and rushes off in torrents. The moisture in the arid zones is insufficient to support living beings.
But despite such harsh living conditions, desert ecosystem exhibits a spectacular biological diversity. A large number of plant and animal species thrive in the deserts due to their morphological, anatomical, physiological and behavioural adaptations.
Plant Adaptations
Plants have evolved many adaptions for surviving the rigors of the desert. There are three life-forms of plants that are adapted to desert ecosystem: a) ephemeral annuals, b) succulents, and c) desert shrubs.
Ephemeral annuals are also called as ‘drought evaders’ or ‘drought escapers’. They germinate, grow, flower, and release seeds within the brief period (6-8 weeks) when water is available and temperatures are warm. The seeds remain dormant, resisting drought and heat, until the following spring. Seeds wait out adverse environmental conditions, sometimes for decades, and will germinate and grow only when specific requirements are met. With their small size and large shoots in relation to roots, they are well adapted to dry habitats. They escape dryness in both external and internal environments. Desert sunflower and desert marigold complete their life cycles during brief rainy seasons.
The succulent plants suffer from dryness in only external environment. Their succulent, fleshy stems, leaves and roots serve as water storage organs (water storage region is present in these organs) which accumulate large amount of water during brief rainy seasons. Opuntia, Aloe, Euphorbia, Yucca and Agave have mastered the art of enduring in the desert ecosystem by economizing in their expenditures of moisture.
They rely on their waxy coatings, spongy stem and/or leaf tissues, root structures and their night time stomata openings to carefully regulate their water use. At night the temperatures are lower and humidity higher than during the day, so less water is lost through transpiration. Such plants are sometimes called “drought endures”. In Opuntia spp. (Cactus), the stem modified into a thick, fleshy, green, life-like structure called phylloclade which manufacture food by photosynthesis and conserve water. Their leaves modified into spines which retard transpiration, promote dew formation at their tips, protect from insolation and from thirsty animals. The bulk of the tissue consists of large, round, pitted, parenchymatous water-storing cells. The cell sap is mucilaginous which helps in checking evaporation of water. The extensive shallow root systems are usually radial, allowing for the quick acquisition of large quantities of water during the rainy period.
The leaves are fleshy in Aloe spp. with marginal spines and a large water-storing tissue. The succulent Euphorbia spp. has succulent stem which store large quantities of water during rainy season. It contains toxic milky latex that irritates skin and eyes. The stipules become modified into spines. The toxic substances and spines prevent them from predator animals. The Century plant (Agave spp.) has saw-toothed leaves with waxy coatings that render them nearly waterproof and so prevents loss of water.
The leaves of these plants channel rain water to the plant’s base. It also contains toxic chemicals like oxalate crystals and irritating substances that can irritate the skin and mucous membranes and can cause digestive problems in their predator animals. The Joshua tree (Yucca spp.) is a very tough plant. The leaves are stiff and very pointed. The roots become fleshy to store water in Asparagus spp.
The shrub in desert ecosystem or non-succulent perennials suffers from dryness both in their internal as well as external environments. Their morphological and physiological features include rapid elongation and extensive root system, high osmotic pressure and endurance of desiccation, ability to reduce transpiration and reduction in size of leaf blade. Root system is very extensive i.e. more than 30 m long (Alfalfa spp.) to siphon deep groundwater supplies.
There is waxy coating and sunken type of stomata on leaves, which reduces loss of water during transpiration. Desert grasses have rolled and folded leaves so that the sunken stomata become hidden to minimize the rates of transpiration. In desert ecosystem, individual plants are scattered thinly with large bare areas in between. These spacing reduces competition for a scarce resource; otherwise intense competition for water might result in the death or stunting of all of the plants.
The grasses (bunchgrass) in desert ecosystem also grow in isolated tufts. During extremely hot and dry period, the parts of the plants that are above the land may wither and die, but the root systems remain alive. Desert mariposa and desert lily have bulbs that may remain dormant for several years until a deep soaking rain awakens them. The extensive bare ground in desert ecosystem is not necessarily free of plants. Mosses, algae, and lichens may be present which form a stabilizing crust on sands and soils.
Animal Adaptations
Animals of desert ecosystem are much more affected by extremes of temperature than desert plants because the biological processes of animal tissue function properly within a relatively narrow temperature range. Thus, most of the animals in desert ecosystem rely on their behavioural, physiological and structural adaptations to avoid the desert heat and dryness.
The drought evader animals adopt either a short annual life cycle that revolve around the scanty rains or undergo aestivation (e.g. ground squirrel). During aestivation, the breathing, heartbeat and other body activities slowdown, this in turn decreases the need of water. Many lay eggs that survive until the next rains when they hatch in the transient puddles. On the onset of rains, a variety of animal like grasshoppers, butterflies, bees, beetles, and spider’s and more may be seen in the desert ecosystem. Amphibians like spade foot toad dig burrow with the help of its spade-like feet and goes to sleep till the rains arrive. It can undergo aestivation for 8-10 months. The birds make nest and reproduce during the rainy season when there is abundant food.
The drought resistant animals are active and carry their normal function throughout the year. They circumvent aridity and heat through morphological and physiological adaptations or by modifying their feeding and activity patterns. They remain in cool, humid underground burrows during the day time and search for food only at night when temperatures are lower.
Some xerocole rodents of desert ecosystem, that are active in the day periodically seek burrows and passively lose heat through conduction by pressing their bodies against the burrow walls. The desert toad uses a survival strategy similar to that employed by succulent plants. It stores water in its urinary bladder. The reptiles and some insects are pre-adapted to the hot desert ecosystem. They excrete a dry metabolic waste product in the form of uric acid and guanine so that water loss is minimal. They have thick waterproof skin that also minimizes water loss.
Desert spiders, mites and insects secrete a waxy layer over their cuticles. Wax is impermeable to water thus prevents loss of water from their bodies. Mammals as a group are not well adapted to desert life because they excrete urea, which involves the loss of much water.
Most of the mammals of desert ecosystem, like kangaroo rat, the pocket mouse and the jerboa have adapted nocturnal habitat. They seal their burrows by day to keep their chamber moist, and can live throughout year without drinking water. They feed on dry seeds and dry plants even when succulent green plants are available. They remain in burrows during the day, and conserve water by excreting very concentrated urine and by hygroscopic water in their food. Thus, adaptation to the desert ecosystem by these rodents is as much behavioural as physiological. Other desert ecosystem mammals like mule, deer and elk avoid the extreme temperatures of the day by limiting activity hours to dawn and dusk. The wood rats survive in parts of the desert by eating dry food as well as succulent cacti or other plants that store water. Jackrabbits and kit fox have large ears that reduce the need of water evaporation to regulate the body temperature. Their ears release heat during their resting periods in a cool, shady place.
The camel in the desert ecosystem can go for long periods without water because their body tissues can tolerate elevation in body temperature and a degree of dehydration. However, it uses water for temperature regulation. The body temperature of camel drops to 33.8ºC over night and rising to 40.6ºC by day when the animal begins to sweat.
Opposed to popular belief, camels do not store water in their hump. Their hump stores fat which yields water after its metabolic oxidation. The kangaroo rat and jerboa have long legs, which help them in jumping and swift running as well as in lifting the body above the ground and thus reducing direct contact with the hot sand.
Desert Gerbils have hairy soles on their feet which allow them excellent traction on sand. The sand rat feeds on plants that have very salty sap which can be toxic in large quantities. Thus, rats simply retain the water and excrete urine that is about four times as salty as sea water. The desert birds utilize a salt gland to help in the maintenance of water balance. They occasionally drink water from dew or other sources.
Thus, these unique natural habitats (desert) with their incredibly diverse flora and fauna have been home to some of the world’s oldest civilizations. The desert ecosystem in California support about 1200 plant species, 200 species of vertebrate animals and numerous insects and other invertebrates. Therefore, the conception of a desert as an uninhabited wasteland is not correct. Besides, we should always remember that the desert is easily damaged and is very, very slow to recover. Thus, fragile beauty and unique heritage of world’s deserts deserve protection.
Endnote-
The general conception about desert, being uninhabited wasteland is not true. This ecosystem which covers 14 percent of earths land surface is actually reservoir of rich and diverse flora and fauna
Recent Posts
The United Nations has shaped so much of global co-operation and regulation that we wouldn’t recognise our world today without the UN’s pervasive role in it. So many small details of our lives – such as postage and copyright laws – are subject to international co-operation nurtured by the UN.
In its 75th year, however, the UN is in a difficult moment as the world faces climate crisis, a global pandemic, great power competition, trade wars, economic depression and a wider breakdown in international co-operation.
Still, the UN has faced tough times before – over many decades during the Cold War, the Security Council was crippled by deep tensions between the US and the Soviet Union. The UN is not as sidelined or divided today as it was then. However, as the relationship between China and the US sours, the achievements of global co-operation are being eroded.
The way in which people speak about the UN often implies a level of coherence and bureaucratic independence that the UN rarely possesses. A failure of the UN is normally better understood as a failure of international co-operation.
We see this recently in the UN’s inability to deal with crises from the ethnic cleansing of the Rohingya Muslims in Myanmar, to civil conflict in Syria, and the failure of the Security Council to adopt a COVID-19 resolution calling for ceasefires in conflict zones and a co-operative international response to the pandemic.
The UN administration is not primarily to blame for these failures; rather, the problem is the great powers – in the case of COVID-19, China and the US – refusing to co-operate.
Where states fail to agree, the UN is powerless to act.
Marking the 75th anniversary of the official formation of the UN, when 50 founding nations signed the UN Charter on June 26, 1945, we look at some of its key triumphs and resounding failures.
Five successes
1. Peacekeeping
The United Nations was created with the goal of being a collective security organisation. The UN Charter establishes that the use of force is only lawful either in self-defence or if authorised by the UN Security Council. The Security Council’s five permanent members, being China, US, UK, Russia and France, can veto any such resolution.
The UN’s consistent role in seeking to manage conflict is one of its greatest successes.
A key component of this role is peacekeeping. The UN under its second secretary-general, the Swedish statesman Dag Hammarskjöld – who was posthumously awarded the Nobel Peace prize after he died in a suspicious plane crash – created the concept of peacekeeping. Hammarskjöld was responding to the 1956 Suez Crisis, in which the US opposed the invasion of Egypt by its allies Israel, France and the UK.
UN peacekeeping missions involve the use of impartial and armed UN forces, drawn from member states, to stabilise fragile situations. “The essence of peacekeeping is the use of soldiers as a catalyst for peace rather than as the instruments of war,” said then UN Secretary-General Javier Pérez de Cuéllar, when the forces won the 1988 Nobel Peace Prize following missions in conflict zones in the Middle East, Africa, Asia, Central America and Europe.
However, peacekeeping also counts among the UN’s major failures.
2. Law of the Sea
Negotiated between 1973 and 1982, the UN Convention on the Law of the Sea (UNCLOS) set up the current international law of the seas. It defines states’ rights and creates concepts such as exclusive economic zones, as well as procedures for the settling of disputes, new arrangements for governing deep sea bed mining, and importantly, new provisions for the protection of marine resources and ocean conservation.
Mostly, countries have abided by the convention. There are various disputes that China has over the East and South China Seas which present a conflict between power and law, in that although UNCLOS creates mechanisms for resolving disputes, a powerful state isn’t necessarily going to submit to those mechanisms.
Secondly, on the conservation front, although UNCLOS is a huge step forward, it has failed to adequately protect oceans that are outside any state’s control. Ocean ecosystems have been dramatically transformed through overfishing. This is an ecological catastrophe that UNCLOS has slowed, but failed to address comprehensively.
3. Decolonisation
The idea of racial equality and of a people’s right to self-determination was discussed in the wake of World War I and rejected. After World War II, however, those principles were endorsed within the UN system, and the Trusteeship Council, which monitored the process of decolonisation, was one of the initial bodies of the UN.
Although many national independence movements only won liberation through bloody conflicts, the UN has overseen a process of decolonisation that has transformed international politics. In 1945, around one third of the world’s population lived under colonial rule. Today, there are less than 2 million people living in colonies.
When it comes to the world’s First Nations, however, the UN generally has done little to address their concerns, aside from the non-binding UN Declaration on the Rights of Indigenous Peoples of 2007.
4. Human rights
The Human Rights Declaration of 1948 for the first time set out fundamental human rights to be universally protected, recognising that the “inherent dignity and of the equal and inalienable rights of all members of the human family is the foundation of freedom, justice and peace in the world”.
Since 1948, 10 human rights treaties have been adopted – including conventions on the rights of children and migrant workers, and against torture and discrimination based on gender and race – each monitored by its own committee of independent experts.
The language of human rights has created a new framework for thinking about the relationship between the individual, the state and the international system. Although some people would prefer that political movements focus on ‘liberation’ rather than ‘rights’, the idea of human rights has made the individual person a focus of national and international attention.
5. Free trade
Depending on your politics, you might view the World Trade Organisation as a huge success, or a huge failure.
The WTO creates a near-binding system of international trade law with a clear and efficient dispute resolution process.
The majority Australian consensus is that the WTO is a success because it has been good for Australian famers especially, through its winding back of subsidies and tariffs.
However, the WTO enabled an era of globalisation which is now politically controversial.
Recently, the US has sought to disrupt the system. In addition to the trade war with China, the Trump Administration has also refused to appoint tribunal members to the WTO’s Appellate Body, so it has crippled the dispute resolution process. Of course, the Trump Administration is not the first to take issue with China’s trade strategies, which include subsidises for ‘State Owned Enterprises’ and demands that foreign firms transfer intellectual property in exchange for market access.
The existence of the UN has created a forum where nations can discuss new problems, and climate change is one of them. The Intergovernmental Panel on Climate Change (IPCC) was set up in 1988 to assess climate science and provide policymakers with assessments and options. In 1992, the UN Framework Convention on Climate Change created a permanent forum for negotiations.
However, despite an international scientific body in the IPCC, and 165 signatory nations to the climate treaty, global greenhouse gas emissions have continued to increase.
Under the Paris Agreement, even if every country meets its greenhouse gas emission targets we are still on track for ‘dangerous warming’. Yet, no major country is even on track to meet its targets; while emissions will probably decline this year as a result of COVID-19, atmospheric concentrations of greenhouse gases will still increase.
This illustrates a core conundrum of the UN in that it opens the possibility of global cooperation, but is unable to constrain states from pursuing their narrowly conceived self-interests. Deep co-operation remains challenging.
Five failures of the UN
1. Peacekeeping
During the Bosnian War, Dutch peacekeeping forces stationed in the town of Srebrenica, declared a ‘safe area’ by the UN in 1993, failed in 1995 to stop the massacre of more than 8000 Muslim men and boys by Bosnian Serb forces. This is one of the most widely discussed examples of the failures of international peacekeeping operations.
On the massacre’s 10th anniversary, then UN Secretary General Kofi Annan wrote that the UN had “made serious errors of judgement, rooted in a philosophy of impartiality”, contributing to a mass murder that would “haunt our history forever”.
If you look at some of the other infamous failures of peacekeeping missions – in places such as Rwanda, Somalia and Angola – it is the limited powers given to peacekeeping operations that have resulted in those failures.
2. The invasion of Iraq
The invasion of Iraq by the US in 2003, which was unlawful and without Security Council authorisation, reflects the fact that the UN is has very limited capacity to constrain the actions of great powers.
The Security Council designers created the veto power so that any of the five permanent members could reject a Council resolution, so in that way it is programmed to fail when a great power really wants to do something that the international community generally condemns.
In the case of the Iraq invasion, the US didn’t veto a resolution, but rather sought authorisation that it did not get. The UN, if you go by the idea of collective security, should have responded by defending Iraq against this unlawful use of force.
The invasion proved a humanitarian disaster with the loss of more than 400,000 lives, and many believe that it led to the emergence of the terrorist Islamic State.
3. Refugee crises
The UN brokered the 1951 Refugee Convention to address the plight of people displaced in Europe due to World War II; years later, the 1967 Protocol removed time and geographical restrictions so that the Convention can now apply universally (although many countries in Asia have refused to sign it, owing in part to its Eurocentric origins).
Despite these treaties, and the work of the UN High Commission for Refugees, there is somewhere between 30 and 40 million refugees, many of them, such as many Palestinians, living for decades outside their homelands. This is in addition to more than 40 million people displaced within their own countries.
While for a long time refugee numbers were reducing, in recent years, particularly driven by the Syrian conflict, there have been increases in the number of people being displaced.
During the COVID-19 crisis, boatloads of Rohingya refugees were turned away by port after port. This tragedy has echoes of pre-World War II when ships of Jewish refugees fleeing Nazi Germany were refused entry by multiple countries.
And as a catastrophe of a different kind looms, there is no international framework in place for responding to people who will be displaced by rising seas and other effects of climate change.
4. Conflicts without end
Across the world, there is a shopping list of unresolved civil conflicts and disputed territories.
Palestine and Kashmir are two of the longest-running failures of the UN to resolve disputed lands. More recent, ongoing conflicts include the civil wars in Syria and Yemen.
The common denominator of unresolved conflicts is either division among the great powers, or a lack of international interest due to the geopolitical stakes not being sufficiently high. For instance, the inaction during the Rwandan civil war in the 1990s was not due to a division among great powers, but rather a lack of political will to engage.
In Syria, by contrast, Russia and the US have opposing interests and back opposing sides: Russia backs the government of the Syrian dictator Bashar al-Assad, whereas the US does not.
5. Acting like it’s 1945
The UN is increasingly out of step with the reality of geopolitics today.
The permanent members of the Security Council reflect the division of power internationally at the end of World War II. The continuing exclusion of Germany, Japan, and rising powers such as India and Indonesia, reflects the failure to reflect the changing balance of power.
Also, bodies such as the IMF and the World Bank, which are part of the UN system, continue to be dominated by the West. In response, China has created potential rival institutions such as the Asian Infrastructure Investment Bank.
Western domination of UN institutions undermines their credibility. However, a more fundamental problem is that institutions designed in 1945 are a poor fit with the systemic global challenges – of which climate change is foremost – that we face today.