Hot deserts

Geetha Iyer

Deserts are biomes that are dry, arid lands with rainfall that often does not exceed 10 inches (25 cms). They are classified in different ways, but an easy one for beginners is their classification as hot, cold, and coastal deserts. This article is on hot deserts.

The Thar desert or the Great Indian desert is the world’s 9^th largest sub-tropical desert. Nearly 85 per cent of it is in India and the remaining 15 per cent in Pakistan is the western boundary between the two countries. The major part of it falls in the state of Rajasthan in the districts of Jaisalmer, Bikaner, Barmer and to a smaller extent in Jodhpur. It covers an area of 200,000 km² of which 3,162 km² has been declared as the Desert National Park. The desert national park represents the typical desert ecosystem, unlike the parts extending into the states of Gujarat, Punjab, and Haryana which are not typical desert ecosystems. In these three states they are either coastal deserts or arid habitats more typical of scrub ecosystems.

For classroom discussion and debate “If sand dune stabilization programme in these deserts is to succeed, it has to demonstrate that biomass production from the shrub and grass cover on the dunes provides a better financial return to the land owners as compared to the cultivation of any kharif crop.” Use the above statement to examine in detail the desert ecosystem and steps that can be taken to conserve it. You may also discuss whether deserts need to be conserved.

Desert National Park
While the sands of Jaisalmer and Barmer are the gateways to the Desert National Park, the Aravalli hills mark their Eastern boundary. As one leaves these towns and proceeds towards the park, a stark difference in the habitat becomes noticeable, especially the presence of sand and sand dunes. As one moves closer to the National Park, the spectacular dunes along with other landforms typical of desert habitat begin to welcome you. Sand dunes are the predominant landforms with close to 44 per cent of the National Park being claimed by them. Pediments* and structural plains are other landforms seen in the park. The desert habitat may be sandy, gravelly, or rocky. All three habitats may be seen in the park in the Jaisalmer area, but sandy plains and sandy dunes dominate the western landscape. As one enters the national park, the undulating terrain of sand greets us.

Dunes
The sand dunes, forming a kind of dune system are specialized habitat for fauna adapted to survive in them. The dunes are not stationary, the system being governed by several factors, wind being a major one. Thus, the animals living here have to be adapted to not only the scorching temperatures, lack of water, but also the shifting sand. Therefore, mostly grasses and dry shrubs are to be found in these dunes. The grasses and shrubs bind the sands well. As the grass and other indigenous plant species on the dunes help the local economy, locally available shrubs are used to stabilize dunes and help the local communities dependent on them. The large populations of humans living around these deserts have grazing animals that thrive on these plant populations. These days the use of tractors to raise crops has begun which destroys the dunes, in turn affecting the population of the fauna that thrive in these dunes.

All of the desert is not just dunes. The arid, dry hot desert can have soils that are rough and harsh. Some places are rocky while others are a mixture of sand and stones. Temperatures in the deserts fluctuate – hot during the day and cool to cold during the nights. Despite the temperature differences and low water table, a large number of hardy, drought-resistant plant species can be found here. These plants have adapted to the desert conditions by developing deep root systems to tap into low groundwater levels. These species found in arid zones have xeromorphological leaf structures such as highly reduced or no leaves, or modified into thorns to save on water loss through transpiration. The cycle of plant life is best exemplified by grasses. Clumps of grasses, green, sprout immediately after the first rains, soon turning golden brown as the water table goes down and temperatures rise, to slowly dying out, leaving behind their seeds, which will sprout again with the next rains.

Euphorbia caducifolia or the ‘thor cactus’ is seen in the rocky areas of the Thar desert. Prosopis cineraria, the khejri tree, Acacia senegal or kumatiyo as it is locally known, Zizyphus mauritiana or ber, and Commiphora wightii or googal are some of the xerophytic tree species found in the Desert National Park. Capparis decidua or kair is a commonly found shrub.

Did you know that a number of grass species are used to make brooms? Did you also know that there are male and female brooms? Research to write about the grasses found in Rajasthan that are used to make brooms. https://www.arnajharna.org/brooms Reference: The Arna Jharna Museum is a gem of a place that can provide you with a holistic idea of the desert. It is located in the Thar bioregion and is a good source of information for your studies.

Fauna
There are over 141 species of resident and migratory birds to be seen here. This is the place to see vultures. the critically endangered red-headed vulture, the Indian or Long billed vulture, white rumped vulture, Eurasian griffon, Egyptian vulture are all found here. Several species of larks, finches, heatears, sandgrouse, larks and tits can be found here. The most famous bird of this area, (that once roamed in 11 states of our country), highly endangered and not found or seen elsewhere in India is the Great Indian Bustard.

The Asiatic wild cat (Felis silvestris ornata) is not spotted easily unlike the chinkara that is easily spotted and a joy to watch. Bengal desert fox and the Indian fox, black buck, nilgai, and spiny lizard are some of the prominent fauna of this place. The deserts have some unique invertebrate fauna of insects, spiders, and scorpions. The camel spiders are arthropods that are neither true spiders nor scorpions; they are endemic indicators of desert biomes.

The ecological biodiversity of Thar is closely linked to the daily life of the people and forms the basis for traditional knowledge systems. Communities living in this region have passed on their centuries-old experiences gained from their knowledge of agropastoral/livestock husbandry to the next generations, to deal with the adverse effects of climate. For e.g., the woody perennials cultivated in the arid zones not only contribute to their economic stability but serve an important role in conservation.

Write a proposal to the government for a project to save the two birds (mentioned below) from going extinct. Hints: Explore the reasons for birds such as the Great Indian Bustard and Bengal Floricans becoming endangered. What are the threats these birds face and what practical steps can you suggest at the local level to protect them?

Conserving deserts
Why should deserts be conserved? Predominantly because they are habitats for some unique flora and fauna that cannot survive in other habitats. They also need to be conserved because there are several communities that are dependent on them for survival. As in other places across the globe, problems such as availability of water, ground water level, etc., is more acute here. Hence, conservation of flora assumes importance in addition to other measures that need to be put in to conserve ground water. Rain water harvesting therefore assumes greater significance in desert areas.

The Arna Jharna museum is a great place to learn more about the deserts. Not only about the biome, but also about communities and their ways of living, flora and fauna.

*Pediments: An erosional surface. Typically a concave surface sloping down from the base of a steeper desert cliff.

References

1. https://www.sahapedia.org/the-plants-of-the-thar-desert
2. https://www.arnajharna.org/desert-flora-and-fauna

The author is a consultant for science and environment education. She can be reached at scopsowl@gmail.com.