Tuesday, May 29, 2012

Worldbuilding: Creating Geography: Desert, Part 3 – Plant and Animal Species

Photo by Moyan Brenn.
Deserts are not the lifeless expanses that we sometimes think they are. Some are extremely barren, yes, but not all, or even most. Many contain vibrant ecosystems adapted to the little moisture they receive. Desert sand and soil is, often, very rich in nutrients. What it is lacking in, is water. A desert is typically defined as an area which receives less than 10" of precipitation per year. That's not 'no water,' just 'little water.' And when it does rain in the desert, this water can stick around for a while because it soaks in and fills underground hollows. This is how oases form, and the reason why you can have such a fertile area in a dry place. The wet ground can support plant life, and the plant life can provide shade for other plants and animals.

Some oases are lush, green islands in a sea of sand or rock, but there are other types of plant life in other types of deserts. In North America, the deserts of Mexico and the American Southwest feature plants like creosote bushes, sagebrush, the Joshua tree (with found only in the Mojave desert), and—let's not forget—cacti (with one exception, native only to the Americas) and other succulents, and the Lithops ("living rocks," so very cool) which are native to South Africa. As you can see, many desert species find it hard to travel outside of their particular areas, largely due to their high degree of specialization.

There are many ways in which plants learn to live in deserts. In windy deserts, plants typically stay low to the ground. Many desert plants work to limit the amount of sunlight and heat they take in, but there are different ways to do this. Cacti have spines which break up the wind around them and help cool them down. Some plants have leaves that always grow so that the broad sides (which take in light for photosynthesis) face north or east, the directions of least sunlight.

Cacti and other succulents soak up water, storing it in modified stems or leaves, allowing them to go for long periods between 'waterings.' They're basically the camels of the plant world. And, as anyone who has ever forgotten about an aloe for an extended period of time can tell you, you can actually watch these plants turn from brown to green as you water them and the tissues in their leaves (or other storage devices) suck in the water.

Often desert plants go into a dormant phase through the drier seasons (which can be summer or winter, or any other time, depending on the position of the desert and the surrounding weather patterns), waiting for rain to fall in order to seed. They may drop their leaves during this time, not because they're dead, but just as deciduous trees do in the winter. Their dormancy means they cannot divert what energy they have to leaf production and maintenance, so the leaves drop off as the plant focuses its reserves on more vital functions.

Because rain can come on quickly, and dissipate just as quickly, some plants are waiting for the first drops of moisture in order to spring into action. Sometimes literally, as some desert plants have evolved so that their dry tissues expand when they become moist, allowing them to actually fling their seeds out. This gives the seeds a good chance of landing far enough away so that they won't be competing with the parent plant for resources, but still within an area which is likely to have resources and to get rain (because it has for a long enough period for the parent plant to become established). So, areas which get rain, and which have fertile enough ground to support plant life, can be filled with seed-shooting plants, instead of having a cluster of plants which all have to compete for the nutrients in a smaller area.

The insect and animal population of a given desert is also a 'concern' for plants. Plants have a complicated relationship with insects, especially, and this is only truer in many deserts. Some insects require certain types of plants in order to procreate (they will only lay their eggs within a given species) and others require the plants for food, which can be destructive or non-destructive to the plant, depending on what the insect needs. This can lead to very specialized relationships in which certain types of insects will protect plants they need from other more destructive insects. When that's not possible, plants may develop other strategies, such as the Lithops which look exactly like pebbles. Seriously, if you didn't know better, you would think they were just another speckled rock on the ground, except for when they're flowering. They often have very pretty flowers, in various shades, but unless they're flowering, they look like rocks.

In most deserts, mammals play a small role. There generally aren't enough resources to provide for larger mammals, but there are exceptions, such as camels, donkeys and gazelle. Most mammals are small, and many are rodents (moles, mice of varying types) or lagomorphs (rabbits of varying types). There are also canines and cats of various types. Both are generally smaller than their non-desert dwelling counterparts (mountain lions being an exception here), generally they have adaptions like large ears (a way of catching breezes and cooling the blood, which flows close to the surface of the skin when it moves through the ears. Basically, large erect ears are like radiators for desert species), smaller bodies, less or shorter fur, etc.

Reptiles—lizards, snakes, etc.—are very common in deserts. Their cold-blooded natures make them really good at dealing with the heat. Some will burrow down into the sand when it gets too hot or too cold, and then come up to lie in the sun until they're properly warmed up again.

There are many, many different types of creatures that live in deserts, and the adaptations that these species develop can provide a lot of interesting fodder for species you're creating. If you're doing a non-human desert-living species, I highly recommend researching the animal adaptations that have developed and incorporating some of that into not only your species building, but into your culture building as well.

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Which will be the topic of my next desert post!

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