Karen Gogoll, age 12, of Hilton, New York, for her question:
How can cactuses get water in the desert?
Our southwestern deserts are alive with plants and animals and at certain seasons their flowering cactuses make them the most vivid gardens in the land. Yet summer visitors rarely run into a shower and often see only arid wastelands under the scorching azure sky. Obviously, what we see cannot be the whole truth, for neither a cactus nor any other plant can live entirely without water.
Global rainfall is spotty and some regions get more than their share. But there is no spot in the whole world where some rain or snow never fails at all. A region rates as a desert when the average yearly rainfall is about five inches. Even the sandy Sahara gets this much and our western deserts get somewhat more. However, the term average yearly rainfall can be deceptive. It may include a five year drought, followed by a deluge.
All living things are adapted to make do with what nature provides in their home environment. Desert cactuses are adapted to make the very best of their scanty water supply, even though they do not know when to expect it. Most of their water comes from sudden sharp showers. Here and there the ground water lies but a few inches below and sometimes when the summer sun scorches the surface, a little moisture condenses in a morning dew.
None of these sources provide very much water. The rain from desert showers quickly disappears as some dashes down the gullies and the rest soaks into the sandy soil. The cactus plants are ready and waiting to soak it up fast with their roots spread far and wide, just below the surface. Even the tree sized saguaros have shallow roots and every cactus is a water miser.
Warm, dry air evaporates moisture through the pores in leafy foliage. Cactus ancestors gave up leaves ages ago and their greenery is actually modified stems. The desert air cannot steal moisture through its thick, waxy skins. Hence, the cactuses can soak up every unexpected drop of moisture and prevent it from evaporating. These desert misers also have another feature to help them to survive from shower to shower.
Their thick fleshy tissues are riddled with pores that act as inside storage compartments: After a short desert deluge, these pockets are filled with water. The prickly plants become fat and glossy. After a week or so of showers, they gut on new growth and overnight the desert becomes a vivid garden of brilliant cactus flowers.
Numerous smallish animals also live where nature's most precious gift is a drink of water. Certain rodents manage to get their supplies from seeds. Others stay near the stingy ponds and water holes, many suffer through long periods of thirsty drought. All of them know that cactuses contain secret stores of water, but few are tempted to steal it. After all, nature provided her moisture misers with prickles to protect themselves from thirsty bandits.