The annual plants that grow as a result of winter rain make up nearly half of our total plant species. The hoped-for displays of showy blooms spreading across the desert are the result of well-spaced winter rains, as well as mild temperatures and windless days. Hardly noticeable in the shadow of the cornflower lupines and persimmon poppies are desert annuals meek and modest. The Desert plantain, buckwheat and fiddleneck are annuals with tiny inconspicuous flowers that bolt to seed without fanfare. Altogether, these plants provide a tasty biomass that is the foundation of food for many animals every year. Annuals seed in the spring but do not germinate until fall. The seeds lie camouflaged in the soil waiting for rain.
During drought winters, the seeds wait the entire year, and longer. In some areas hundreds of thousands of accumulated seeds are contained in a single square meter of desert soil. Critters such as the harvester ant, kangaroo rat and sparrow will survive on these seeds, and themselves become food for insectivores, reptiles, raptors and mammals. The uncertainty of the winter rainfall is mirrored in the reproductive cycles of many desert plants and creatures. Some birds such as the Gambel quail won’t reproduce in very dry years. They instinctively know there will not be enough food for their babies. Other species of birds and mammals will breed less often or not at all during droughts. Although they are unpredictable, the two rainy seasons contribute to a diversity of plant forms in the Sonoran Desert that supports a rich population of wildlife. Rainfall in the different seasons generates two dissimilar crops of blooming plants. In addition, the various methods plants use to deal with limited water and high temperatures provide great variety in plant structures, from annual wildflowers to stately saguaros. Diversity is increased among pollinating insects, nectar-eating birds, bats and small mammals. These creatures may end up as prey for larger birds, reptiles and mammals. In this way, the Sonoran Desert supports a more varied ecosystem than any other desert. Makes one thankful for the winter rains, and we can all be grateful for the lowly unknown annual.
Sources: A Natural History of the Sonoran Desert from Arizona Sonora Desert Museum Press
Desert Wildflowers published by Arizona Highways