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Fire Harvest

OUR GUEST WRITER is KIRK ANDERSON FROM THE LIVING DESERT AND ZOO

Palm Springs, California Show 7/1107

FIRE HARVEST

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.

California 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.

California 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.

California 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. 

 

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