The Desert's Annual Forbs

The Desert Food Chain - Part 8

The annual forbs – short-lived, non-woody, non-grass plants often called “ephemerals” – play colorful but cameo roles on the desert stage.  Like temperamental actors and actresses, these plants sometimes withhold their lively appearances for decades.  Collectively, they complicate every year’s botanical performances because the widely diversified species all have distinctive natural cues, resource needs, life histories, physical attributes and environmental responses.  A particular species may simply wait in the botanical wings until its demands for the order of the seasons, the proper length of daily sunlight, the calibration of daily temperatures, a sufficient amount of rainfall and the condition of the soil – all in the right combination – have been answered.  You can expect a blooming season to be much like a concert in which you do not know the musicians, their instruments or the compositions ahead of time.  You only know that, with good luck and good timing, you will experience a masterful performance. 

For all their differences, the desert’s annual forbs do, however, hold certain characteristics in common.  Given the right confluence of conditions, they will develop, bloom and seed out swiftly, dieing in the end like Shakespeare’s Romeo and Juliet.  In his Flowers of the Southwest Deserts, Natt N. Dodge calls the ephemerals the “desert quickies.”

A Mosaic of Microclimates

As you may recall from the second article in this series (Plants: The Producers), the annual forbs, like all desert plants, live in a landscape of “microclimates,” which change through the days and the seasons in a kind of climatologic kaleidoscope.  This is attributable primarily to the spottiness and randomness of the limited rainfall in the desert.  Rather than receiving general and sustained rainfalls like you might find on, say, the Louisiana Gulf coast, the forbs experience what scientists call rainfall “pulses,” which vary widely over time in terms of location, frequency, intensity and duration.  Moreover, the forbs’ rainfall may run off quickly, in flash floods, before the water can soak into the earth where it would be accessible to the plants’ roots.  It will certainly evaporate swiftly in the face of summer heat, low humidity and frequent winds. 

Arid environments, in which rain occurs sporadically, leading to pulse-interpulse cycles of resource availability and so pulsed opportunities for plant growth and reproduction, provide serious challenges to plants…” according to the article “Resource Pulses, Species Interactions, and Diversity Maintenance in Arid and Semi-arid Environments,” published online by Peter Chesson and eight associates in April of 2004.  “These challenges,” said Chesson and his collaborators, “have caused the evolution of many different adaptations to take advantage of opportunities as they arise and for persistence through harsh times.

Origins and Distribution

Many of the Southwest’s modern ephemerals originated in Mexico, expanding their territory northward as the land grew drier and warmer in the process of desertification that began at the end of the last of the Ice Ages, about 10,000 years ago.  Others – for example, those that develop and bloom after the winter rains of the Sonoran Desert’s Arizona Uplands region – have family connections to the north, where the ephemerals prosper in cooler and wetter weather.

The annual forbs of summer are most abundant across the Chihuahuan Desert and the Arizona Uplands, making their appearances following the rains produced by the monsoon-season storm cells that sweep across the Southwest from the Gulf of Mexico.  Those of winter occur most abundantly across the western Sonoran Desert and the Mojave Desert, developing and blooming in the wake of rains from systems that originate in the Pacific Ocean. 

Opportunists

Unlike the desert plants that have developed structural and behavioral adaptations for surviving prolonged drought, the annual forbs, which range from a few inches to a few feet in height, survive as opportunists.  They capitalize on a coalescence of conditions.  They celebrate the moment with rapid growth and flowers, sometimes leaving alluvial hillsides awash for several days with a painter’s palette of yellow, orange, gold or red.  They purchase their future by covering the soil with the currency of seeds much like New York covers Broadway parades with blizzards of confetti.  Then the plants die.

These ephemerals, it would seem, must live a tenuous life, but William G. McGinnies, in Discovering the Desert, sees them as holding a distinct advantage.  “The restriction of vegetative activity to brief moist periods almost completely relieves the ephemeral plant from the difficulties of water supply that beset the perennial,” he said.  “By speed of germination, rapidity of growth and early flowering, and maturity during favorable periods, the ephemeral escapes the most potent conditions controlling the life and ecological behavior of desert plants” 

Further, McGinnies points out, the ephemerals, as opportunists, “are scarcely affected by the annual or seasonal totals of rain, by the length and severity of drought periods, by the high maximum temperatures of summer, or by the freezing temperatures of the winter.” 

When conditions fall right, the annual forbs (like some other desert plants) typically respond with “explosive production of seeds and vegetative tissue,” according to Richard S. Ostfeld and Felicia Keesing, writing in Tree, Volume 15.  They can put on spectacular shows. 

For instance, yellow and golden poppies sometimes flow like a brilliantly colored blanket down the alluvial fans at the foot of the Franklin Mountains in far west Texas and the Organ Mountains of southern New Mexico. 

“The spring of 1998,” said Barbara Kingsolver and Steven Hopp in an article, “Desert Blooms,” for the American Museum of Natural History, “was the Halley’s comet of desert wildflower years.  While nearly everyone else on the planet cursed the soggy consequences of El Niño’s downpours, here in southern Arizona we cheered the show: desert hills and valleys colorized in eye-popping schemes of maroon, indigo, tangerine and some hues Crayola hasn’t named yet.” 

In the spring of 2005, the extravagant wildflower bloom in Death Valley – the driest and hottest location in our deserts – drew widespread attention, even making national television news. 

Strategy for Survival

An ephemeral’s strategy for survival rests, not on its short-lived leaves, stems, roots or blooms, but rather on its seeds.  “desert wildflowers have had millennia to come to terms with the inconstant mother,” said Kingsolver and Hopp. “Once a plant rushes through growth and flowering, its seeds wait in the soil—not just until the next time conditions permit germination but often longer.  In any one year, a subset of a species’ seed don’t germinate; they’re programmed for a longer dormancy.  This seed bank is the plant’s protection against a promising rain followed by drought.  If every seed sprouted and died before setting seeds, the species would perish.  Some lie in wait, loading the soil with many separate futures. 

“They stash away a range of competitive possibilities for the future—a strategy made possible by genetic variation (both among and within species) in the schedules for germination, flowering and setting seeds.  Some species even vary seed size: larger seeds make more resilient sprouts, while smaller ones are less costly to produce.  Native desert flowers can hold their own against invaders from greener, more predictable pastures.”

The seeds travel across the landscape on the breath of the desert winds or the rush of  flash flood waters, said McGinnies.  Some find ideal homes at favorable depths in moist sandy soil in a protected location.  In some small depressions, the seeds may accumulate by the thousands within a few square feet, setting the stage for a spectacular bloom in the future.  Other seeds find less favorable homes in rocky soils or on firm smooth soil surfaces, where they struggle to survive.  Under the right conditions, however, an ephemeral’s seeds may retain its viability for years.  “It has been observed,” said McGinnies, “that an exceptionally favorable season will bring forth large crops of species that have been uncommon for ten to fifteen years or more.”  In the end, an ephemeral’s distribution and bloom density reflect the success of its seeds in finding suitable soil and favorable and well-timed conditions.

A Few of the Favorite Annual Forbs

Desert ephemerals hold a special place with the wildflower enthusiast because they paint the desert with unexpected color at unpredictable and often widely separated moments, surprising the eye and delighting the soul.  As Natt N. Dodge said in his 100 Desert Wildflowers, “A great flower year may occur only once in a decade,”  but it can be a memorable experience, an event that lodges in the memory for years.

As far as I can discover, the total number of annual forb species across the Southwestern deserts has not been tallied.  However, according to McGinnies, in southern California alone,  “There are almost one thousand species of annuals, and about half of these are native to the Mojave Desert and adjacent areas.”  The ephemerals sometimes seem like jewels awaiting discovery in the desert sands. 

The Mexican or Desert Goldpoppy, closely related to California’s state flower, the California Goldpoppy, can light up rocky hillsides across the northern Chihuahuan and Sonoran Deserts in the spring and early summer (provided that there has been adequate moisture and warmth during the previous winter).  It produces one- to two-inch diameter cup-shaped blooms with four yellowish to golden (and, occasionally, white) petals, which turn vibrantly orange at the base.  The plant, which has bluish-green stems and leaves, grows one to two feet in height, bearing individual flowers on single stalks.

The Firewheels or Indian Blankets, another of the plants that blooms from spring into early summer, “stand like hundreds of showy Fourth of July pinwheels at the top of slender stalks,” as James A. MacMahon says in his book Deserts.  Spanning a range that runs from the southern Great Plains southwestward across the northern Chihuahuan and Sonoran Deserts, the one- to two-foot greenish-leafed plant bears “showy flower heads with rays red at base, tipped with yellow, each with 3 teeth at the broad end. The well-known flower heads are 1-2 in. across with a red center and a yellow outer band. Occasionally the three-cleft rays are solid orange or yellow. The disk flowers in the center are brownish red,” according to the Lady Bird Johnson Wildflower Center’s Southwest Recommended Native Plant Species List Internet site. 

The lupines, which include several species, some annual and some perennial, rank “among the old dependables of spring display flowers of the desert,” Natt Dodge says.  They grow in a wide variety of environments, ranging from desert floors up into mountain woodlands in the Chihuahuan, Sonoran and Mojave basin and range country.  Two to three feet tall, they produce numerous light blue to purple half-inch-long, three-petal flowers on a single stalk.  “The generic name, Lupinus, is from the Latin lupus, wolf, in popular allusion to the plants’ once supposed greed for soil nutrients,” according to Howard S. Irwin in Roadside Flower of Texas, but it was long ago discovered that the lupines’ roots contain “certain bacteria that combine nitrogen in the air with plant carbohydrates, for nitrogen compounds” that eventually enrich, rather than deplete, the soil for other plants.  A lupine species commonly called the “Bluebonnet” is the state flower of Texas. 

The various paintbrushes, which include both annual and perennial species, are often called “Indian Paintbrushes.”  They hold a place near the top of any list of highly adaptable plants, for they grow in environments ranging from dry sandy basins on the desert floor up to 9000-foot-high wooded slopes of the mountain ranges.  They take their striking color, not from their flowers, which are small and inconspicuous, but from the reddish-tipped leaves, called “bracts,” that embrace the blossom.  They sometimes create solid patches of scarlet in the desert from early spring to mid-summer.  Like other desert ephemerals, the paintbrush, typically several inches in height, calls on the sun’s energy to perform photosynthesis and create foods, but unlike other desert ephemerals, the paintbrush deploys its roots to parasitize other, neighboring plants’ roots, sucking away their nutrients and water.  Some people see an almost mystical symbolism in a flower endowed with stunning beauty on one hand and afflicted with shameless parasitism on the other hand. 

The Consumers

If the desert’s wide diversity of annual forbs offer a visual feast of color for your eyes, they also serve up a welcome variation in the menu for a wide diversity of animals, both invertebrates and the vertebrates.

Ephemerals contribute, for example, nectar for the butterflies, leaf tissue for leaf-cutter ants, and seeds for the harvester ants.  Leaf tissue, chewed up by worker ants, becomes a mulch for a fungus, the food for a colony of the leaf-cutters.  Seeds, cached in labyrinthine chambers perhaps 10 feet or more below ground, help feed colonies of tens of thousands of harvester ants. 

The ephemerals provide substantial, if intermittent, forage for the larger mammals such as pronghorns, mule deer and javelinas and for reptiles such as the desert tortoise and a few lizards.  According to an article by Robert R. Parmenter and Thomas R. Van Devender in The Desert Grassland, the ephemerals also supply a bounty of seeds for rodents such as kangaroo rats, pocket mice, deer mice grasshopper mice, harvest mice and ground squirrels and for birds such as larks, sparrows and wrens.  The seeds gathered and cached by the kangaroo rats often find enhanced opportunities for growth in new areas.

The desert’s annual forbs – producers – serve as diverse and variable food sources, helping shape a diverse and variable animal community – the consumers.  For example, according to Chesson and his associates, “Recent studies suggest that seasonal resource pulses [by ephemerals and other plants] may in part underlie the often high diversity of Granivorous [seed-eating] rodents in deserts…” contributing to a strengthening of the web of life in the desert. 

Next Mavericks of the Desert Plant

 

By Jay W. Sharp

Index

Part 1 Desert Food chain - Introduction
Part 2 Desert Food chain - The Producers
Part 3 Desert Food chain - The Cacti: A Thorny Feast 
Part 4 Desert Food chain - The Yuccas
Part 5 Desert Food chain - The Agave
Part 6 Desert Food chain - Desert Grasslands
Part 7 Desert Food chain - Desert Shrubs
Part 8 Desert Food chain - The annual forbs
Part 9 Desert Food chain - Mavericks of the Desert Plant
Part 10 Desert Food chain - Outlaw desert plants
Part 11 Desert Food chain - Animals: The Consumers
Part 12 Desest Food chain - The Insects
Part 13 Desest Food chain - The Ugly, the Uglier and the Ugliest

Also see: The Desert Food Chain for the young student

Sources you may find interesting include various articles in DesertUSA’s Internet site; James A. MacMahon’s Deserts, part of the Audubon Society Nature Guide series; Ann and Myron Sutton’s The Life of the Desert, part of the McGraw-Hill Book Company Our Living World of Nature series; Peter Chesson’s and associates’ “Resource pulses, species interactions, and diversity maintenance in arid and semi-arid environments,” Oecologia Internet site; Natt N. Dodge’s Flowers of the Southwest; and Matthew W. Fidelibus’ and David A. Bainbridge’s “Microcatchment water harvesting for desertrevegetation,” a research paper prepared for the California Department of Transportation in July 1994

 

 

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