OUR GUEST WRITER is KIRK ANDERSON FROM THE LIVING DESERT AND ZOO
FIRE! No other word in the English language grabs
the attention like this one. It elicits
a dichotomy of visceral reactions tracing back to Man’s earliest
beginnings. Fire is comfort with its
ability to keep us warm, cook our food and hold the threats of darkness at bay,
while at the same time it is terror when experienced unleashed across the
landscape with its hunger to consume everything in its path.
Through slash and burn agriculture, driving game
animals, scorched earth warfare and controlled burns, man has used fire as a
means to his ends. Even in the unlikely
setting of the parched, sparsely vegetated desert of southeastern California, Man was able
to learn from a naturally occurring phenomenon and use fire as a management
tool to his advantage.
Here in the recesses of canyons and washes and along
the fracture zones of fault lines, where water can be found at or near the
surface, the California
fan palm (Washingtonia filifera)
makes its home. In one of the world’s
hottest and driest environments the presence of water is, in essence, a
proclamation of life. The Native
Americans living here learned how to maximize all that could be reaped from
this arid land.
The palm oases were vital to their success and
well-being. They were a source of water
and food derived not only from the plants found growing there but also from the
game animals inexorably drawn to the promise of water and refuge. The oasis itself provided relief from the
relentless desert sun in its deep, deep shade as well as the raw materials for
the construction of shelter.
Palm fronds were used for thatching roofs and
could be counted on to provide a watertight cover for several years. The fibrous leaves were also used for making
footwear, while an assortment of tools and utensils were fashioned from the
leaf stem or petiole.
The black, pea-sized fruits of the California fan palm are
comprised mostly of seed but are covered with a thin sweet-tasting flesh. The potentially bountiful harvest of several
hundred pounds of fruit per tree could be eaten fresh or dried and stored for
grinding, seed, and all, into a meal or mush.
fan palm fruit production can be sporadic from year to year and the Native
Americans must have observed that the palms bore more fruit following
accidental or lightning sparked fires. California’s only native
palm tree is not only fire tolerant but also seems to thrive under a fire
regime. Upon realizing this, the Native
Americans then began to burn the palm groves periodically to improve fruit
yield and tree health.
Fire benefits the palms by removing or drastically
reducing other heavy water-using plants (phreatophytes) that rely on a
permanent supply of ground water, like cottonwood (Populus fremontii) willow (Salix
spp.) sycamore (Platanus racemosa),
tamarisk (Tamarix spp.) and mesquite
(Prosopis glandulosa var. torreyana).
Palms are in a group of plants called monocots
that share the characteristic of having their vascular tissues arranged in
bundles scattered throughout the stem or trunk.
As such, they are pre-adapted to survive trial by fire as outer lying
bundles may be damaged or killed, but those lying further inside the thick
insulating trunk continue to conduct their life support duties.
Dicots, like the trees mentioned above, and
conifers have their vascular tissue in a ring just under the protective layer
of bark and are much more susceptible to damage and death from fire. Removal or reduction of the competing plant
life allows more water to go to the palms.
They respond by producing more flower stalks, spadices, and setting more
fruit – up to several hundred thousand per tree.
Fire also does the job of house cleaning in oases
where deep piles of organic debris accumulate, creating perilous footing and a
haven for rattlesnakes. The removal of
the debris allows clear access and makes harvesting of fruit safer and easier.
fan palms are unique in the retention of their old, dried leaves, which can
form a continuous, highly flammable shaggy skirt from the crown to the
ground. In conjunction with the
reduction of the overgrowth of plants and the removal of fallen palm leaves and
fruit stalks, the burning of the massive skirts opens up the soil in the grove
to more sunlight.
The bare soil, replete with a fresh layer of
fertilizer in the form of ash, increased sunlight, and augmented water supply
makes a perfect bed for germinating new palm seedlings and the successive
generation of palm trees is born. The
increased water flow can also help lower typically high levels of salinity on
the soil surface, which can hamper seedling growth. Young palms are at risk from fire mortality
until they have developed enough trunk thickness to earn some degree of
immunity to fire.
fan palms do not suffer from many maladies.
A few can reduce vigor. In the
1930’s, the USDA conducted tests to determine control measures on palms for red
spider mites and parlatoria date scale.
They concluded that periodic burning offered the best method of
control. Native Americans had been
practicing this form of combustible pest control for hundreds of years.
A more serious threat to this palm is the giant
palm borer (Dinapate wrightii). This large, up to two inches in length,
bostrychid beetle lays its eggs almost exclusively in tunnels chewed into the
leaf bases in the crowns of these palms.
The larvae spend several years or more developing and chewing their way
through the palm’s trunk before emerging as adults. Older trees seem to be particularly attractive
to the beetles and infested palms can be seen with hundreds of dime-sized exit
holes in their trunks. When ready to
pupate, the larva positions itself just inside the trunk’s surface. Fire can kill the pupae at this stage along
with any larvae too close to the trunk exterior.
By finding a niche in an inhospitable land, the California fan palm has endured and even prospered in a
fiery, symbiotic relationship with Man.