The Imprinting Foundation



Sept 06, 2004

Robert M. Dixon, Ph.D

This essay is a response to all the published interest in desert wildfires, especially the article by Chris Clarke in Earth Island Journal, winter 2006 entitled: The Year We Lost the Deserts . This article suggests that the 4 U.S. deserts are going up in smoke--a terrifying thought to say the least.


I've been interested in land desertification for many years having grown up on a Kansas farm that was washing and blowing away in the Dust Bowl thirties.

I read about W.C. Lowdermilk's global travels in the 1930's in which he observed civilizations that had collapsed or were about to collapse because of uncontrolled land desertification.

Symbolically, the main agents of desertification are the cow and the plow with the cow representing domestic livestock such as cattle, sheep, goats, donkeys, camels, horses, etc. And the plow representing moldboard plows, disc plows, tandem discs, harrows, etc. Both agents of desertification denude the soil surface and seal and smooth it so that rainwater runs off like from the proverbial duck's back, causing soil dehydration, soil erosion and downslope flooding and sedimentation.

Livestock grazing combined with short term droughts is largely responsible for the severe desertification (degradation) of the U.S. deserts-- Chihuahuan, Sonoran, Mojave and Great Basin . Mostly cattle grazing has converted the first 3 deserts to shrublands by removing the perennial grasses, whereas sheep browsing has converted the Great Basin Desert to an annual grassland (mostly cheatgrass) by removing the shrubs and perennial grasses.

Cool-season exotic annual grasses (and some annual forbs) such as red brome and cheatgrass have filled the land niches emptied by the grazing and browsing livestock. The exotic annuals thrive because of these empty niches and the shallow (slow) water infiltration into the desertified soil surface at the expense of native shrubs.


Then come the warm-season fires many of which are sparked by dry monsoonal thunderstorms which work to the advantage of the exotic annuals, but to the detriment of perennial shrubs already suffering from great moisture stress. Eventually desert landscapes are almost totally covered with these cool-season annuals just waiting for another dry lightning strike to eradicate the few remaining perennials.

Are our deserts now doomed to go up in a cloud of smoke? Not necessarily. Albert Einstein said: A problem can't be solved at the same level at which it was created. Thus, more land disturbances such as herbicides will never solve the weed problem. More land disturbances mean more barren land, more empty niches and more exotic annuals colonizing these niches. A higher level of non-destructive technology is now available for weed control. If we act quickly to transfer this new technology to the desert sites colonized by exotic annuals, we can arrest the destructive fire cycle. The strategy is to ecologically displace these exotics with well-adapted native perennials such as saltbush species, etc.


This new technology, called land imprinting, was invented in 1976 and patented by the USDA in 1980. In July 1976 the first imprinter was fabricated in Tombstone , AZ and tested nearby within the transition zone of the Sonoran-Chihuahuan Deserts.

Since that first test, land imprinters have interseeded more than 50,000 acres of degraded rangeland in southern Arizona and southern California for forage production and ecological restoration. To successfully interseed, the land imprinter has to displace exotic winter annuals with seeded perennials which are considered late species in the natural plant succession. This succession process is encouraged by including a cover crop of a cool-season species such as annual ryegrass in the seed mix. The fall season is the best time for seeding, prefereably on an El Nino year when more than normal precipitation is expected. The more the precipitation the quicker will be the desired response.

Imprinter seeding of native perennials to displace cool-season exotic annuals (ecological weed control) will work in all 4 deserts with only minor modifications to make the approach site specific.


For the foregoing approach to work exotic livestock ranching will need to be phased out while native game ranching is phased in with benefits such as hunting, fishing, trapping and ecotourism--benefits that far exceed the current value of livestock production. All feral livestock should also be removed from the rangelands so that all the forage will be available for the native game animals, and other native foragers.


Now to the basics, regarding the origin of the land imprinting concept. Imprinting is scientifically based on 15 years of water infiltration research conducted in four states (WI, MT, NV and AZ) which showed that rainwater infiltration is largely controlled by two soil surface conditions--macroporosity (openness) and microroughness (roughness). The natural (undisturbed) rough open surface infiltrates rainwater (while readily exhausting soil air) very rapidly; whereas, the desertified smooth closed surface infiltrates rainwater (while forcibly exhausting soil air) very slowly. The difference in infiltration between the two surfaces ranges from one to two orders of magnitude.

So imprinting is a simple and efficient way to convert the desertified soil surface into the rough open condition so that the soil can become rehydrated again so that, in turn, seeded perennials can displace the exotic annuals in the natural plant succession.


The land imprinter is simply a heavy steel roller faced with angular teeth that are wedged into the soil surface (without soil inversion) to form V-shaped depressions that, in turn, funnel soil resources (seed, water, plant litter and splash-eroded soil) together where these resources can work in concert to germinate seeds, establish seedlings and grow plants.

The imprinting process works not only to repair surface water hydrology but it works well to establish vegetation, even in rocky soils normally considered to be non-arable. If rocks are too big to push into the ground, the heavy steel imprinting roller merely rolls up and over them.


Finally, while this essay mainly covered the ecological control of exotic cool-season annuals, slightly different strategies can be worked out for controlling exotic perennc">ial plants such as buffelgrass and fountaingrass. Only environmentally benign approaches should be used as land disturbances such as herbicides just lead to more fire-prone annual exotics. An ecology-based strategy is almost always the best approach to weed control.

Desert Wildfire Control
Land imprinting in the Mojave Desert near Pearblossom, CA for enhancing rainwater infiltration
and accelerating vegetation processes.

The Imprinting Foundation
1616 E. Lind Road
Tucson, AZ 85719

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