Plants Cope with Salt and Heat

Surviving in such a harsh, hot, waterless place demands special adaptations in desert plants. Most have made elaborate adjustments to the lack of water. Many are halophytic, or salt tolerant, having evolved ways to handle loads of salt and minerals that would kill most plants. Many of the low-lying areas into which the wadis drain are former lakebeds, and the soil is laced with the salts and minerals left behind by evaporating water.

Tough seeds of frail annuals and grasses lie scattered in the soil, often waiting for years for a single wet year so they can blossom. Sometimes during a wet spring, the seemingly barren reaches of the desert suddenly sprout a green fuzz of wildflowers. Herders like the Bedouins have relied on such fitful bounty to graze their sheep, camels, and the famed Arabian horse. But centuries of overuse have generally overtaxed the grasses and flowers, leading to a steady expansion in the areas now virtually devoid of plant life.

Other plants have adjusted in surprising ways. The tamarisk tree grows near the scattered oases. It puts roots down deep to reach the water table and sports tough, scratchy threadlike leaves that gather in the Sun’s energy with a minimum loss of moisture. These trees were so tough in a harsh environment that they were imported into the American Southwest to serve as windbreaks to protect railroad tracks. They quickly spread and are now one of the major pest species in the American Southwest, especially in riparian areas already hard hit by cattle grazing, dams, and water pumping. Tamarisks have largely replaced native cottonwoods and willows along thousands of miles of waterways in the American deserts.

Some of the most historically important plants are modest shrubs and trees that produce resins used to make frankincense and myrrh, precious species the wise men reportedly brought as gifts to the newborn Jesus. The fragrance was used extensively for ceremonies, religious rituals, cremations, and royal processions. For centuries, these prized fragrances drove a rich trade network. One recent study using satellite images has mapped the faint shadow of a lost civilization in the Empty Quarter in Oman, using infrared imagery to detect a network of ancient roads beneath hundreds of feet of sand. Scientists believe that the ghostly network of roads and ruins marks the location of the lost civilization of Ad, which grew wealthy and powerful by gathering and then selling frankincense some 5,000 years ago. Brave but frustrated explorers spent years searching for the seemingly mythical civilization of Ad. But the hardships of the Empty Quarter and the massive, shifting sand dunes frustrated every effort. However, the images from the satellites revealed the traces of a 100-yard-wide (91.4 m), hoof-trodden path beneath giant sand dunes, the trade route along which the horse and camel caravans distributed frankincense to the world. The city of Ubar, the Atlantis of the Sands as adventurer T. E. Lawrence dubbed it, was probably the main center in the frankincense trade from about 3000 b.c. to the first century a.d. The Bible, the Koran, and the folktales of the Arabian Nights all mention Ubar.

Another vital plant of the Arabian Desert is the date palm, which grows in the handful of oases where water trapped beneath the surface thousands of years ago bubbles to the surface due to some quirk of the underground rock formations. The date palm and these widely spaced oases formed the basis of life for many desert people. The palm provided wood for building and making well frames, its fronds covered their roofs and its rich, nutritious fruit was a mainstay in their diets. The desert people also grew a variety of other crops close to the oases, including citrus, melons, onions, peaches, grapes, wheat, and even prickly pears, this last an import from North America since the Arabian Desert has no native cactus species.