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
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
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
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.