Desert Bursts into Flower
The Joshua tree represents one set of adaptations to a place with dry summers and chilling, but still thirsty, winters. Desert creatures have developed many different solutions to those problems. For instance, desert wildflowers seem almost miraculous in their delicate abundance during a rare wet year, when a succession of winter rains or snows yields to the crescendo of spring rain. Suddenly, the seemingly lifeless sand and gravel of the desert soil erupts with a riotous bloom of frail red, blue, purple, and orange flowers.
In fact, this desert soil harbors somewhere between 100 and 2,400 seeds in every square foot. Although harvester ants and their seed-loving neighbors like kangaroo rats consume perhaps 95 percent of these seeds, enough remain dormant and waiting to cause a riot of color in the monochrome desert every five to 10 years when the conditions are just right. Each of the seeds can hold its store of moisture and potential growth through years of barren springs until just the right succession of soaking rains dissolves a coating on the outside that inhibits germination. Each seed has its own carefully programmed instructions in the form of DNA, which include requirements for everything from winter rain to the salt content of the soil. This reluctance to sprout until the conditions are perfect ensures that the seed can give rise to a healthy plant that can last long enough in the face of the short, bittersweet desert spring to release a fresh generation of patient seeds. Some produce seeds exquisitely designed to win that lethal race against the blight of summer. For instance, the seed of the corksbill has a corkscrew tail that coils and uncoils with a change in humidity. The resulting motion effectively screws the seed down into the ground, where it is more likely to avoid the attentions of ants and kangaroo rats.
Oddly enough, the flowers that seem so out of place in a desert help sustain the desert. Certainly, anyone who has witnessed spring in the desert has marveled at the sudden bounty in these normally dry and lifeless soils. How can anything so luminous and delicate as a desert poppy find enough moisture to survive here? So researchers recently did a large-scale study of how much water desert flowers use in such a bountiful spring bloom. They found that the flowers essentially use every bit of excess water that falls in an unusually wet year, so that almost none of this glut of rain makes it past the root zone of the annual plants to reach the water table. In fact, the bloom of the annuals in a good year may actually use up all the moisture that falls, which means that the flowers themselves dry out the soil and help ensure that the area remains a desert by gulping down most of the excess rainfall.