Plants and trees survive by photosynthesis and extracting minerals from water. Without water, photosynthesis does them no good, one is dependent on the other. Water is absorbed to some extent through the leaves, but mainly through its roots.

     Although most plant roots are fairly shallow roots, from a few inches to a few feet.  Some roots, however, can be as deep as 200 or more feet.
soil. These deep roots -- called "tap roots" - are critical to the plant's survival.

     During the wet season, plants can use their shallow roots to absorb water from the soil. But when the upper layers of the soil dry out -- as during a summer drought -- the plant has to go deeper to find water.

      The type of roots a plant or tree has depends a lot on what type of soil they live in. Some plants are more particular than others. Larkspur is a garden flower that has a deep tap root. It is not so choosy about what type of soil it grows in. Roses do not have deep tap roots and so do not do well in very dry soil, unless they are watered by both rain and gardener. Just a quick look at wooded areas and open fields will give you a hint at what types of plants prefer moist or dry soil.

      Desert plants often have the deepest roots. In these areas, almost no moisture can be obtained through shallow roots. Plants and trees rely solely  on very deep tap roots. Most of these plants do not even have a network of shallow roots, but consist mainly of one long tap root with offshoots deeper down. During well drilling in the Kalahari Desert in Botswana, roots of a species of Acacia tree were found about 220 feet underground. This is about the equivalent of an 18 story building! Desert plants must be good at what they do to survive in harsh environments. You won't find an Elm tree growing in a desert. Leafy things like Elm trees lose too much moisture through all those leaves and the roots cannot compensate for that loss no matter how deep they do.

 
   It was once believed that only loose sandy soils could support deep plant
roots. Botanists did not believe roots could make their way successfully through harder soils or rock. But new research shows that roots can penetrate compact clay, rocky soil and even bedrock to reach water. They wind their way through low resistance pathways --highly weathered material, networks of cracks, or tunnels dug by earthworms or previous roots.

     The roots that tap water from the water table are hundreds of times more efficient at absorbing water than shallow roots in dry soil. Again, that is why some plants have a tangled mass of thin shallow roots (daisy's are a good example) which often reach a horizontal distance as wide as the plant, while a single tap root, which is thicker, can absorb more water.

     It is because plants and trees are so adept at what they do with their root systems that they can survive in a wide range of environments. They certainly know how to get to the root of the matter!