INTRODUCTION

Kirk Andersen, Garden Collection Manager from the Living Desert and Zoo in Palm Springs, California, gives us a detailed account of how rainfall brings the desert to life.  Even small amounts of water wake up seeds resting dormant for months, sometimes years.  

Interestingly, not all seeds of a particular species germinate at once.  Some are kept in reserve by Mother Nature, in case a catastrophy hits the growing plants.  Kirk Anderson's vivid recollections of the blooming desert bring the desert alive for us.  Once experienced, the desert in bloom is etched in your mind.  See it through the eyes of someone who has joyfully lived the happening.

WILDFLOWER - Just Add Water (Show 8/1108)

Anyone who has witnessed the stark, sere low-desert landscape will soon forget the transformation into a kaleidoscope of colors by annual wildflowers. Once afflicted, the wildflower ''junkie'' can only count the days, months and, oft times, years that pass between fixes of floral fantasy.  Much of the allure is based in the unpredictability of when wind swept dunes and sun baked bajadas will spring to life once again. 

All the more seductive are years when the oppression of an extended drought is broken – the quiescent, arid soils stirred to life by germination-inducing rains.  The skies delivered .5'' of rain on the last day of November 2007, breaking a 20-month span that saw a total of .72'' fall.  And nearly half of that meager amount (.34'') came pounding down in the form of a July 06 afternoon thunderstorm, much of which was quickly lost to evaporation and run-off.

The mere 3.5'' of rain this season (2008) pales in comparison to the total of 11'' in 2004/05, yet an impressive wildflower season still materialized.  It' not just about how much, but also when and how the moisture comes that determines the magnitude of the flower display. 

Gentle, soaking rains falling between late September and early March have the most influence.  The late summer/early fall rains that come once the brutal heat of the summer has broken, yet while it is still warm, are the most important for a prolonged wildflower season.  Traditionally an initial soaking of at least 1'' is necessary to initiate the massive germination that creates the carpet of color.  The wildflower seed impermeable coat keeps water from reaching the embryo until it is exposed to enough moisture to dissolve through it or is scarified by tumbling across the soil's gravelly surface in flooding waters. 

A substantial rain during moderate temperatures assures seedlings there will be enough soil moisture to support an initial growth spurt. Even if sufficient rain falls, not all of the seeds of any one species will germinate at one time.  This is insurance against crop failure due to a catastrophic event, such as a hard freeze, that prevents the setting of any seed in a given season.  Not all of the mechanisms that promote germination are understood at this time.  I'e seen wonderful displays result from initiating rains much less than an inch in total.

Once germination occurs, each successive well-spaced, growth-sustaining shower adds to the potential scale of bloom.  Stature of plants in years where moisture is just enough to coax germination, and no more, may leave wildflowers barely noticeable, consisting of a single flower on stunted plants.  Whereas in ''et''years they may develop into small shrubs or ground covering mats with each individual plant displaying hundreds of flowers over the course of the season. 

The little belly flower purple mat (Nama demissum) is often easily overlooked due to its diminutive nature.  In 2008, on the bajada at Cottonwood, individual plants of a foot and more across coalesced into show stopping splashes of magenta easily spotted from a moving car. 

Subsequent storms of sufficient intensity and/or duration can alter the scene by creating run-off that may bury or wash away seedlings.  In addition to too much or too little rain affecting the bloom, the same can be said for heat.  Low temperatures can inhibit germination and vegetative growth; if not outright kill plants by freezing them. 

Unseasonably high temperatures can also end a bloom season as wildflowers abruptly cease flower production and push their resources into setting seed, especially in the absence of continuing moisture availability.  I remember leaving town via Monterey Avenue in the middle of March 1988 amidst expanses of dune primrose (Oenothera deltoidea) and sand verbena (Abronia villosa) in peak bloom.  The temperatures jumped into the 90' after I left and I returned a week later to find the flower season finished.  There' a reason they'e called ephemerals.

The temperatures at the time the rains come influences the composition of the upcoming flower season as certain species favor certain temperature ranges for germination.  With potentially tens of thousands of latent seeds in each square yard of desert soil, those plants that germinate first have the best chance to prosper and out-compete late comers. 

This season the rains came to the Coachella Valley during the cooler season, which benefited plants like the mustards (Brassicaceae), and in particular the invasive Sahara mustard (Brassica tournefortii).  This weedy, old world native has spread like wildfire throughout the southwest below 4,000 ft. and prefers the sandy soils favored by dune primrose and sand verbena. 

In many areas the famous vistas of purple, white and yellow that once painted the low desert sands between widely spaced shrubs of creosote (Larrea tridentata) have been replaced by nearly pure stands of Sahara mustard.  Even in locations where this weed fails to inhibit native wildflowers completely, it can so dominate the scene with its weedy aspect that it degrades the whole experience.  Any attempts at biological control of this vegetative scourge may prove challenging due to its close familial relationship with many important food crops such as broccoli, cabbage and cauliflower let alone the risk posed to native members of the mustard family.

Most of the ''nce in a lifetime''wildflower displays are separated by years-long intervals but there doesn' necessarily need to be an extended time gap in order to build up seed stores for the next spectacle.  Actually the odds for producing the grand display are better the year following a grand display when the seed bank is at its fullest and hinge more on  receiving sufficient precipitation in back to back years. 

While the seeds of many desert annuals can lie dormant for years awaiting the right conditions, the march of time inexorably takes its toll.  If the wait alone does not do them in then the host of seedeaters (granivores) that rely on the sand deposited larder surely can have an impact.  Kangaroo rats, pocket mice, antelope ground squirrels, harvester ants, Abert' towhees and black throated sparrows are just a few of the desert dwellers that make regular withdrawals from the sand seed bank. 

Once up and growing, the ultimate wildflower display then faces the plant eaters (herbivores).  Typical low desert scrub of creosote and burro bush (Ambrosia dumosa) generally supports low densities of herbivores like the black-tailed jackrabbit and desert tortoise.  The cottontail is more a denizen of country clubs than open desert.  But there is a group of transient feeders just waiting in the wings for the desert to bloom. 

In wet years, their numbers are hard to ignore.  Episodic explosions in the populations of butterflies and moths, and more importantly their plant-munching larvae, are more than likely tied to the availability of foodstuffs as well as other less understood factors.  Fantastic floral displays can sometimes be hard to focus on amidst the fluttering flotilla of painted lady wings or roadways slickened with the remains of white lined sphinx moth larvae and the fields of frass left in their wake.  Attempts to establish patches of wildflowers in the gardens at The Living Desert over the years have been thwarted by the high numbers of resident herbivores supported by the year round availability of food, water and protection.

Certain species can usually be counted on to appear in their preferred niches: sandy dunes or washes, rocky  slopes, south or north facing slopes, on desert pavement, growing up through shrubs or nestled against boulders.  But even with all things seemingly being equal, no two wildflower seasons are ever alike.  Many times over the years I'e returned to certain spots yearning to re-visit a memorable display only to find it never quite the same.  I rarely come away disappointed as new images nudge their way into the memory bank.  Sometimes a single plant makes an impression. This year it was a lone, pure white Canterbury bell (Phacaelia campanularia) found amongst its deep blue-violet brethren at Cottonwood.

The bajada leading to the Cottonwood entrance to Joshua Tree National Park is one of the local areas known for its potentially spectacular wildflower show.  It delivered once again this year with its ever changing tapestry of Arizona lupine (Lupinus arizonicus), desert gold poppy (Eschscholzia parishii) and desert dandelion (Malacothrix glabrata).  If you had waited to visit when it ''ypically'' is at peak bloom, in mid March, you would have missed the peak by more than a month - well ahead of other valley locations. 

This area benefited from a localized, growth initiating rain event in late summer/early fall that the Coachella Valley didn' receive and was already showing some bloom in November.  It is hard to predict when an area will be at its peak more than a couple of weeks ahead of time and then the peak itself lasts for maybe a couple of weeks.  To stay abreast of current conditions next season, access The Living Desert's wildflower report by phone (760) 346-5694 or on-line: (www.livingdesert.org).  The desert in all its glory is a fleeting moment in time.  One must be ready to head out the door when the time is at hand.  It is an experience not to be missed.