Desert Ecosystems
Jackie Sanchez and Nora Tahbaz
A quick image search of deserts in Google will show pictures of barren landscapes with dunes of sand. However, only about 20% of Earth’s deserts are covered in sand. It is a common misconception to assume all deserts are dry, hot, and empty places. These adjectives do not fully describe all the possible landscapes found in deserts; in fact, there are many different types of deserts that are categorized as coastal deserts, hot deserts, cold deserts, and semi-arid deserts. Deserts are distributed on every continent with the commonality between them all being the amount of rain received.
A desert is defined as an ecosystem receiving less than 10 inches of rain per year. The amount of rain may vary from year to year with some years exceeding – and other years not reaching – the average. Due to the limited amount of precipitation, another characteristic of deserts is the high rate of water loss. Deserts are arid and lose a lot of water through evapotranspiration, which is when water is removed from the land to the atmosphere by evaporation from the soil and plants. In deserts the evapotranspiration rate is greater than the amount of rainfall received.
Desert habitat ranges from mountainous areas to sand or salt flats. Each type of desert offers its own type of animals, plants, food chain, and ecology. Coastal deserts are found adjacent to mountain ranges, lakes, and waterways, and because of this, the soil is less acidic and better at retaining moisture. The temperature in this type of desert does not go through extreme fluctuations, for example summer temperature ranges from 55°F to 75°F (12.78°C to 23.89°C) while winter temperature average is 41°F (5°C). An example of a coastal desert is the Namib Desert in Africa. Hot deserts receive very little precipitation with no more than 28 cm (11 inches) a year. Temperatures reach up to 122°F (50°C). An example of a hot desert is northern Africa’s Sahara.
Cold deserts are found in extreme altitudes, a long way from coastal regions and close to mountain ranges. The annual precipitation does not fall as rain but rather as snow. Winter temperatures range from 28°F to 39°F (-2.22°C to 3.89°C). Summer temperature will reach up to 79°F (26.11°C). The Gobi Desert in Asia and the polar deserts found in Antarctica and the Arctic are examples of cold deserts.
Semi-arid deserts have the greatest amounts of precipitation compared to the others. Temperature does not vary during the time of day and does not see a dramatic change from summer to winter. Australia’s outback and the Nearctic zones in Newfoundland and Greenland are examples of semi-arid deserts.
The Desert Flora and Fauna
The desert fauna has behavioral and physiological adaptations which allow them to survive in these inhospitable conditions. The main adaptation for all living organisms addresses the ability to survive without the access to large water reserves in the environment.
Desert plants are categorized as wildflowers, cacti/succulents, trees, shrubs, and grasses. Because of the variability of precipitation, some desert plants have to go years without water. In order to survive these conditions, many have adapted to grow long roots to receive hydration from deep underground water stores; these types of plants are called phreatophytes. Other plants have adapted their roots to be shallow so water can be quickly absorbed from the topsoil right when rain events occur. Many plants such as cacti have high water retention by altering their physical structure – they have few or no leaves to reduce transpiration. Besides physiological adaptations, plants have behavioral adaptations to adjust to extreme conditions. Desert wildflowers such as the desert lily and California poppies will bloom during periods when there is greatest moisture and during seasons when the temperature is coolest. Desert perennials like agave and African daisies survive by remaining dormant during dry periods.
Extreme weather conditions have also led to a variety of animals that have adaptations to survive the dry, harsh conditions. Adaptations are seen in physical, behavioral, and physiological features that allow them to survive. For example, many species are active only at night when humidity is greater and temperatures are lower. Coloration also helps with living in the desert; many animals have lighter colors to reflect sunlight and avoid overheating. Deserts like the Sonoran Desert surprisingly have a rich variety of species each with their own adaptations that allow them to survive with limited access to water sources. In contrast, the Atacama Desert of Chile and Peru which receives less than 0.6 inches per year lacks diversity and has a limited number of species living in the area. No major vertebrate taxa are limited to only deserts, but many species are well represented. Lizards, snakes, and rodents are well adapted and are the most diverse groups found in the desert habitat. Aquatic animals are limited however and are determined by the persistence of water bodies and how often they are replenished through precipitation. Amphibians are also limited but are seen as long as rainfall is enough for breeding.
Camels are an iconic desert animal found in North Africa, the Middle East, and Central Asia. They have physiological adaptations that allow them to survive temperatures ranging from 20℉ to 120℉ (-6.67°C to 48.89°C). Their iconic humps store fat that is metabolized when food or water is scarce. In order to move around comfortably in the desert, they have thick-soled feet to allow them to walk on the hot sand and have thick eyebrows and long eyelashes to protect their eyes from the sand and sun. Camels also have oval-shaped red blood cells which helps the blood flow when water is limited. Finally, they have extremely long large intestines to absorb as much water from the food they eat. Desert Beetles also have physiological adaptations to minimize water loss. They have cavities under their forewings to trap moisture that would otherwise be lost through respiration. The Namib Desert Beetle has been greatly studied due to the geometric pattern on its shell. The bumps on its shell allow for water droplets to be collected from the air. This facilitates condensation and optimizes water collection.
Some animals use physiological and behavioral adaptations to adjust to the extreme heat found in certain desert ecosystems. The desert tortoise uses both to survive in the desert. Impressively, they can survive one year or more without access to water. Desert tortoises spend 95% of their time underground in burrows they dig to escape the heat. Desert tortoises will also dig catchment basins in the soil to maximize infrequent rainfall. They will remember where these basins are and visit them after rain events. Desert tortoises rely heavily on being able to dig in the soil to avoid extreme temperature variation from hot to cold on the ground level which makes soil suitability critical for desert tortoises. During dry times, water that reaches the bladder can be drawn upon as needed and waste that is produced is a white paste compared to watery urine seen in other tortoises.
Extreme heat is not the only harsh conditions seen in deserts. Many desert types experience freezing temperatures that living organisms have adapted to as well. Emperor penguins live in the Antarctic and breed during the worst weather conditions on earth. They are able to survive due to their thick insulation which consists of several layers of feathers. Emperor penguins are very large which allows them to store body fat as an energy reserve, but to contrast their large body size, they have small bills and flippers to conserve heat. Emperor penguins are also social creatures and they huddle together to keep warm. These behaviors and physiological adaptations are survival mechanisms that allow them to live in Antarctica which is the coldest, driest, and windiest continent on earth.
Issues Within Deserts
Despite deserts only covering 20% of Earth’s surfaces, they have still become a target for habitat destruction caused by human activity which leads to changes in environmental conditions. There is variation in this activity, but it all has negative impacts on desert wildlife and thus it is important to recognize them so changes in our behaviour can be made.
To start off, the rapid growth of the human population has led to multiple negative impacts on deserts. For example, as human communities get larger, the need for more water to support them also increases. As the need to irrigate rises, the salt levels in the soil also rise and this deeply impacts plants’ survivability in the already harsh soil conditions along with removing the small amounts of water from animals that need it. Population growth also means that people need more space for homes, grazing animals or natural resources. Cutting down trees for housing space, collecting firewood, growing low-grade crops to feed cows for meat production, and overgrazing domesticated animals all lead to desertification. Desertification is the process by which fertile land becomes desert, typically as a result of drought, deforestation, or inappropriate agriculture. This means that the size of deserts are increasing across the globe which can lead to a rise in carbon dioxide levels as trees that once sequestered a lot of carbon dioxide have been removed.
Population growth also leads to a rise in waste production and this waste includes human garbage along with nuclear waste. Deserts have been used to dump garbage because they are deemed as an acceptable place, away from people, to dump trash. Secondly, many nuclear testing grounds are also in deserts for the same reason – lack of human populations residing nearby. When trash is dumped, toxic materials can contaminate already harsh soil conditions along with contaminating scarce water sources. This means that all organisms that rely on the soil and water for sustenance and survivability will be at risk. This is considered habitat destruction because waste sites in deserts can no longer support the organisms that originally lived there. Reversing these impacts is nearly impossible especially when nuclear testing is done.
These are just some of the examples that deeply impact the plant and animal life of a desert. On a slightly smaller and more direct form of habitat destruction issues are caused by off-road vehicles and military training. There are some park rangers who are trained to be careful in desert areas with automobiles, but most are not. Off-road vehicles cause irreversible damage to plant life by depositing gas and other chemicals onto the ground and more obviously, by running over plants and animals. This is the same for military training which can also cause habitat destruction by stepping on plants and animals. But also, the disturbances by people in wildlife areas can also impact the daily cycles of desert organisms.
However one of the largest threats deserts face is climate change. The slight changes in temperature or precipitation that come with global warming can dramatically impact the plant life and animals within desert ecosystems. Because we now know that climate change is caused by human activities, we can say that deserts are being most impacted by people. The amount of carbon dioxide in the atmosphere has reached its highest levels in past years and thus has led to rapid increases in average global temperatures and this release of carbon dioxide comes mainly from burning fossil fuels. High amounts of carbon dioxide in our atmosphere has direct links to changes in normal weather patterns which means that as temperatures rise, the weather will continue to become more erratic. In connection to deserts, the slight changes in temperature are having dangerous impacts on wildlife by altering their environments. Because climate change is also directly linked to the size of the human population, the issues deserts face all come together in that the world’s human population has reached a point where the desert’s flora and fauna are in harm’s way.
Policies Addressing These Issues
There are many policies in place with intent to help protect deserts from human actions that have the potential to cause harm. It is important to recognize that most of these policies are not directly related to protecting deserts alone. In reality, most of them address climate change and carbon emission, but as mentioned above climate change poses a huge risk to deserts and thus such policies are important to recognize.
The first policy is The California Desert Protection Act of 1994, that is directly related to the protection of U.S. deserts. This act establishes the protection of Death Valley and Joshua Tree National Parks and the Mojave National Preserve in the California desert. The U.S. Congress found that the federally owned desert lands of southern California constitute a public wildland resource (based on its historical value, environmental value, ecological value) and that the federal government should begin protecting and managing the challenges that those deserts face.
Additional U.S. policies are related to climate change and decreasing carbon emissions. The first is The Clean Air Act of 1963 which set state-by-state targets for reducing carbon emissions and aimed to lower national electricity sector emissions overall by 32% below 2005 levels by 2050. Similarly to this act, the Paris Agreement, a monumental agreement made by multiple global powers, included member nations who voluntarily committed to reduce GHG emissions by 26%-28% below 2005 levels by 2050. Another policy that moves the U.S. towards more renewable energy in order to limit our reliance on burning fossil fuels is the American Recovery and Reinvestment Act of 2009, which authorizes a $1.6 billion stimulus package that supports new and existing renewable energy and energy efficiency programs.
Moving to reduce emissions and to using renewable energy might seem distant from helping deserts, however in reality the connections are significant. Because one of the largest risks to distablizing desert ecosystems is climate change, any action to help stop climate change is in turn helping deserts. As countries move to renewable energy, less fossil fuels will be burned and thus carbon emissions will drop. This tied to eliminating other forms of emissions will help decrease the effects of climate change and thus decrease all of the negative outcomes.
What Can You Do?
There are many things that you can do on multiple levels of difficulty to help protect deserts. One of the best and easiest things you can do is to educate yourself on agricultural practices that either 1) involve needing large amounts of land for grazing/food grown for cattle, or 2) require a lot of water usage, and then use this information to make better choices about where you get your food from.
There are also many ways to water plants that are better for the environment like drip irrigation which delivers water directly to a plant’s roots and requires much less water. This will decrease the rate of irrigation which would allow for plants to rebalance the soil before it becomes uninhabitable. In California specifically there are dry farmers who rely on soil moisture to produce their crops during dry seasons and this involves special tilling practices and careful attention to microclimates. These practices are just two examples of ways in which farmers around the world are doing their part in helping the plant by reducing the amount of water resources they need.
For individuals who are of voting age, you can use your vote to bring people into office who want to prevent climate change. By bringing these people into policy making positions, we can greatly increase the chance that bills will be passed to help protect the environment (and particularly in the U.S. move towards more conscious practices). The past bills and acts that are in place now really make a difference in making changes because they keep our country and businesses accountable to reducing their carbon footprints.
In terms of limiting waste, you can start to make changes on what you buy and how you get rid of your trash. For example, start buying from grocery stores that don’t use a lot of individual packaging and instead have large containers where people can use reusable bags to pack their food. This can also mean participating in a compost program. Starting a small compost bin near your garbage where you can dispose of food waste is an important renewable way to add nutrients to your own gardens at home and keep food waste out of dumps which only turns into methane and adds to climate change! Many cities even offer community compost programs that residents can participate in. These are all ways to help you decrease the amount of waste that goes to landfills in and near desert ecosystems that can lead to irreversible habitat destruction.
You can also donate to or partner with organizations that help protect wildlife. For example, Defenders of Wildlife is a major national wildlife protection agency that aims to protect all ecosystems and wildlife that live in them. Another great organization is the World Wildlife Fund that preserves and protects the deserts of North America such as the Rio Grande/Rio Bravo River basin. By donating, you can help these groups achieve their goals to protect wildlife and by working with them you can learn about these ecosystems and teach others about them as well which can help motivate them to help.
Sources: The Jungle Jenny Foundation, NPS, National Geographic, Environmental Science, Defenders of Wildlife, Seattle PI, Climate Change News, Desert USA, Live Science, CUESA
