Deserts: A Very Short Introduction – Nick Middleton

Thoughts: As other Very Short Introduction books have been for their subjects, Deserts is a solid introduction to deserts. No complaints!

The chapter summaries below were made from memory upon finishing each chapter. They may contain misrememberings or other inaccuracies!

Middleton, Nick. 2009. Deserts: A Very Short Introduction. Oxford UP.

Introduction

• deserts can be defined in many ways. One rule-of-thumb approach has to do with water balance - if you left a bucket in a place for a long time, would it fill up? If so: desert. This author states that polar deserts and ocean deserts (many parts of the ocean receive very little rainfall per year) fall outside of the scope of this book.
• it’s difficult to empirically sort areas into desert-or-not by definitions based on climate, because there are so few weather stations in desert areas. It can be easier to define them by vegetation cover, since we have good satellite data for the whole planet. By this definition, deserts have little vegetation cover and much bare soil.
• arid and semi-arid regions are found approximately in bands north and south of the equator - in the northern hemisphere, these include central North America, the Sahara, Middle Eastern deserts, and the inland deserts of Asia. South of the equator are the deserts along the west side of South America, arid areas in the south of Africa, and Australia
• Some deserts have very cold winters; in others, frost is very rare. Some deserts are foggy (e.g., Atacama desert in South America) but receive little actual rain.

1. Desert Climates

• Arid areas tend to be found:
  • in the interiors of continents, far from large bodies of water where evaporation takes place
    • or sometimes on coasts, in places where cool currents mean that not much evaporation takes place
  • downwind from mountains, i.e., in their rain shadows
  • in areas with persistent high-pressure systems - if I recall, these are around 20°N and S
• since deserts tend to have not much moisture (water has a high specific temperature), daily temperature swings can be extreme, especially in continental interiors
• in high-altitude and high-latitude deserts, there can also be dramatic differences between seasons

2. Desert landscapes

• Useful distinctions:
  • shield deserts - ones in the centres of continents, where ancient bedrock is exposed - vs. tectonic deserts - between/within mountain ranges
  • Dunes can be active - moving across the landscape - dormant - immobilized for a time by vegetation, change in sediment supply, etc. - or relict - fully stabilized, usually by well established vegetation.
• in many deserts, crusts form on dunes or other sand surfaces, helping to stabilize them. These crusts can be biological and/or chemical.
• another desert landform: desert pavement, where pebbles on the surface cover finer sediments below. It’s not clear the extent to which pavements are caused by wind erosion, warming/cooling cycles, or other mechanisms

3. Nature in Deserts

• Plants and animals display a range of adaptations to desert conditions. Different clades have arrived at similar solutions, leading to numerous examples of convergent evolution.
• Some plants and animals are adapted to survive stress, whereas others are adapted to avoid stress.
  • In stress-survivors, a key consideration is how to balance water retention with water’s cooling effects as it evaporates.
  • Stress-avoiding plants and animals are often adapted to take full advantage of brief wet periods, hiding and/or going into dormancy during dry spells. Many are adapted to complete their life cycles very quickly when conditions are right, setting seed or laying eggs before harsh conditions return. Some plants of this type have adaptations to prevent seeds from germinating when there has only been a light rain shower.
• Vegetation tends to be patchy in deserts, often occurring in spots or in strips. These patches can form around nurse trees, which create favourable microclimates. Spotty patterns are thought to develop where wind erosion is dominant, whereas stripey patterns are thought to develop where water erosion is more dominant.

4. Desert Peoples

• Groups of people that have lived in deserts for many centuries have found ways of living that local desert ecosystems can sustain. As modern development has occurred in these areas, these peoples have adapted, to varying degrees, their ways of life.
• Some desert cultures have sprung up relatively recently, and depend much more on imports to sustain their ways of life. Imports, desalination of water, etc. are largely paid for with the profits from exploiting these areas’ mineral reserves
• Desertification can be a problem in semi-arid areas. It can be caused by salination due to irrigation, certain agriculture practices (think of the Dust Bowl) overgrazing, changing rainfall patterns, or burning (burning by aboriginal people over tens of thousands of years is thought to have created Australia’s deserts)
• Diversion of water to desert areas often has negative effects in the areas where the water is drawn from
• Culturally, among peoples with long histories of living in deserts, the desert is seen as a place of beauty, whereas in cultures geographically separated from deserts, they are likely to represent hardship, difficulty and harshness

5. Desert Connections

• Dust blown from deserts travels far from its source, enriching soils there
• Deserts are affected by global climate trends - increased aridity leads to the expansion of deserts
• Deserts have a long history of exports, including salt, spices, etc. Some of these traditional resources are still exported today, but the mineral resources of deserts - fossil fuels, uranium, bauxite, etc. - are their most important exports today
• Three of the world’s largest religions - Islam, Judaism, Christianity - had their roots in desert regions
• Domestication had It’s start in desert regions. Desert organisms are adapted to feast-and-famine conditions, and when conditions are favourable, they quickly and efficiently build up biomass and produce plentiful seeds. These traits make them useful for agriculture
  • Some examples: wheat, barley, goats, sheep, cattle, quinoa, potatoes