The Imprinting Foundation: Imprinting is Superior to Other Treatments for Ecological Restoration

This essay is prompted by the report entitled " Rehabilitation Success and Potential of Mojave and Colorado Desert Sites " (1) This report suggests that land imprinting can be adapted to revegetating land disturbed by Off Highway Motor Vehicles (OHV) in the Mojave and Colorado Deserts of California . I agree, but some adaptation of this new technology will be required. To date land imprinting has been successfully tested primarily in the Sonoran Desert region of southern Arizona where average annual precipitation ranges from 150 to 300 mm and is split about equally between summer (July-August) and winter (January - February) rainy seasons. It has not been tested in the deserts of California where precipitation ranges from 100 to 150 mm, most of which occurs during the winter. In fitting land imprinting to this harsher climate its helpful to expand this no-till planting method to the Imprinting Revegetation System (IRS) consisting of three interacting components: Seed, Imprints and Rain (2,3). These are listed in the order in which they impinge upon the soil surface during the land manipulation. Seed is commonly dropped on top of the imprinting roller where it is carried forward to drop on the soil surface, thereupon becoming immediately imbedded in the faces of the imprint. Thus seeding and imprinting, with respect to a given point on the soil surface, occur almost simultaneously, whereas rainfall may be delayed by days, months or even years.

The three keys or criteria to IRS success are:

A. Good Seeds

B. Good Imprints

C. Good Rains

The "good" criteria for the California deserts need to be exhaustively detailed. As a beginning here are a few ideas. The seed that is dropped on top of the imprinting roller should be a mixture of adapted species commonly occurring in local relatively undisturbed areas including early, mid and late seral species. The early or pioneer species serve in cover, nurse, mulch, and green manure roles to help later successional species germinate and become established. As a first approximation, the percent composition of each species in the mix should be similar to that of the relatively undisturbed areas including not only the living plant community, but also the soil seed supply. If possible seeds should be collected from comparable nearby areas to insure climatic adaptation but not necessarily edaphic adaptation because of the usually greater soil degradation of the revegetation site. Because of this degradation late seral species will not be very well adapted edaphically until pioneer plants have had a chance to regrow some topsoil.

Good seed, along with litter mulch, can often be obtained by vacuum sweeping the soil surface especially under late seral shrubs which usually support an understory of desert annuals and short-lived perennials. These seeds are especially abundant during and immediately following above normal rainy seasons like the current winter season in California . The swept seed, although unacceptably trashy and impure by commercial standards, is often much better than commercial seed that is clean and pure but not site adapted. Planting such commercial seed insures failure of IRS unless soil seed or nearby seed sources come to the rescue. Trashy seeds containing plant litter require positive agitation in the bottom of seed boxes to achieve a constant rate of discharge to the soil surface. Hammermill screening may be needed to reduce the litter size (stems and leaves) enough to permit passage through seed discharge ports. Seeds with stiff or fluffy appendages that tend to mat or wad together can be mixed with wheat bran, again with the help of a hammermill. This aggressive mixing action causes the bran to infiltrate the appendages which results in an overall reduction in volume. For example, if one part by volume of purple three-awn grass seed is mixed with one part by volume of bran, the final volume is only about 11/2 parts instead of two as might be expected. Thus, bran gives the seed additional density or ballast which helps in the uniform discharge of seed mixtures by drop seeders. Seeds of each species should possess a range in dormancy so that viability can be maintained through several years of drought.

Good imprints are usually as important to success as good seeds because seeds dropped onto a degraded soil surface which is typically smooth, sealed and barren will seldom germinate, and if they do germinate the chances for seedling survival are very slim. Good imprints are made by forcing angular teeth fully into the soil surface preferably when the soil is moist. Imprinting teeth are usually made from either 6" x 6" or 8" x 8" steel angle cut into about 10-inch lengths. The teeth are welded to the surface of a steel cylinder to form a staggered pattern of disconnected V-shaped troughs in the soil surface. Imprints should have very firm and smooth faces or walls without the presence of loose soil. This means that imprinting should follow a rain of at least one-half inch as closely as possible. In sandy soils imprinting can be done as soon as the rain stops, whereas in clayey soils the soil surface must dry somewhat to prevent soil from sticking to the teeth. Imprints made in dry soil tend to be somewhat loose and unstable especially in degraded desert soils which usually possess little or no structure. Thus, ideally imprinting should follow the first substantial rain of the cool rainy season to maximize the opportunity for establishing a thick cover of winter annuals to, in turn, stabilize imprints and serve in nurse, mulch, and green manure roles for subsequently germinating and establishing later seral species.

If possible large areas should be imprinted to minimize the negative effects of herbivory. Small areas unprotected by screening are often overwhelmed by foraging insects, birds, and rodents. Small areas are also damaged more by the oasis/border effect. The border of a vegetated area is exposed to the harsh external macroclimate which severely retards the rate of secondary succession. Extremely small areas are essentially all border, whereas extremely large areas are mostly interior which can favorably moderate the microclimate. Thus, revegetation of relatively large areas minimizes the damage resulting from herbivory and border effect.

In general, existing vegetation should be imprinter-mulched and imbedded in the faces of the imprint to increase surface stability and suppress evapotranspiration. Desirable perennials should be saved by steering around them, however many desert shrubs will resprout from the crown after the topgrowth has been mulched. Mechanical and chemical weed control prior to imprinting is ecologically regressive and thus counterproductive. However, ripping may be needed to obtain a full-tooth imprint in compacted roads which can be accomplished by attaching ripping shanks to the front side of the tow frame just ahead of the imprinting roller. Then ripping, seeding, and imprinting are accomplished in a rapid-fire sequence.

The best imprint is often achieved by imprinting a moist soil that has a thick stand of cool-season annual grass. The grass blades stabilize the surface of the imprint whereas the fibrous roots bind the imprint together internally. The bottom of such imprints provide an excellent microenvironment for germinating the seeds and establishing the seedlings of mid and late seral species.

Imprinting pressure should range from about 12 to 48 psi which is achieved by varying the amount of imprinter ballast. To avoid soil compaction, the ballast should be limited to that needed for a full-tooth imprint. With this amount of ballast the imprint is formed by a wedging and embossing action. As the imprinting tooth enters the soil it wedges soil forward and backward, thereby raising the soil surface between adjacent teeth. Thus, there is very little net downward movement of soil during the imprinting process.

Good imprints serve as good seedbeds efficiently concentrating splash-eroded topsoil, plant litter, seed, and rainwater in the trough of the V-shaped imprint where these resources can cooperate in the germination of seeds and the establishment of seedlings. Good imprints also serve as seedling cradles to shield young seedlings from hot sunlight and dry winds, thereby increasing their chances for survival or establishment. Roots of seedlings need to penetrate deeply into the soil before the tops of seedlings grow up into the harsh macroclimate above the imprint. Dormant seeds and stabile imprints can wait years if necessary for adequate rainfall to occur.

The third key to success of IRS is good rain--the factor over which a land manager has minimal control. However, if the criteria for good seeds and good imprints have been fully satisfied, then the rain needed for successful germination and establishment will be somewhat less than it would be otherwise. Imprinter seeding at the onset of the winter rainy season will also increase the likelihood of receiving enough rain to quickly establish a cover of early seral species. Finally, as mentioned earlier the land manager should build as much longevity as possible into seed mixes and soil imprints so that they can wait as long as necessary (up to 5 years) for the good rains to come. Thus the investment made in a good seed mix and good imprints will pay off sooner or later.

In summary the successful adaptation of imprinting for use in the California deserts will depend upon greater effort being directed to meeting the criteria for good seeds and good imprints than required for the imprinting done in Arizona under biseasonal and higher annual rainfall. In other words the harsher desert climates will demand the most rigorous application of high IRS standards. Success will also require greater patience because of the lower and more erratic monoseasonal rainfall. At best its expected that plant communities will respond somewhat more slowly to imprinting in California as compared with Arizona even when the criteria for good seeds and good imprints are fully met. In Arizona, imprinter seeding has been successful about 9 times out of 10 compared with 1 in 10 for drill seeding, the conventional method. Hopefully imprinting, when fully adapted, will also greatly increase the success ratio in California for direct seeding.

Three important IRS standards suggested on the preceding pages for adapting imprinting to the California deserts are:

1. Use a good seed mix collected by vacuum sweeping beneath nearby shrubs following a wetter-than-normal rainy season. Hand picking of seeds from such plant communities can supplement the swept seeds. To provide cover, include winter annual grasses in the seed mix such as barley, annual ryegrass, mediterranean grass, etc. Plantago is often used in Arizona as a pioneer/cover plant.
2. Imprinter seed as soon as possible after the first good rain of the cool rainy season. Imprinting should be done as soon as the soil dries at the surface or as soon as the soil doesn't stick on the imprinting teeth. Imprinter seed large areas (greater than one hectare if possible) to minimize herbivory and the oasis effect, otherwise it will be necessary to fence out the foragers. Add enough ballast to the imprinter to obtain a full-tooth imprint.
3. Be extremely patient as a good vegetative response to the good seed mix and good imprints will require adequate precipitation. Don't set unrealistic temporal criteria for success especially where unpredictable rainfall is the only source of soil moisture.

Now for some possible ways in which the Imprinting Foundation can help expedite the adaptation of land imprinting to the California deserts:

1. Make more land imprinting information available via published articles and papers, newsletters, seminars, workshops, and field tours.

2. Make appropriate imprinters available for testing by:

a. Loaning, renting, and selling existing imprinters.

b. Designing and fabricating new specific and general purpose imprinting devices.

3. Make seeders available for planting trashy seed mixes.

4. Make native seed harvesting devices available.

LITERATURE CITED

(1) Bauder, Ellen T. and Larigauderie, Anne. 1991. Rehabilitation Success and Potential of Mojave and Colorado Desert Sites. Dept. Biology, San Diego State University , San Diego , CA 92182 . Report prepared for: Dept. Parks and Recreation, Off-Highway Motor Vehicle Recreation Division, P.O. Box 942896 , 1416 9th Street , Sacramento , CA 94296 . Contract No. 4-555-0074.

(2) Dixon , R.M. 1989. Air-Earth Interface Model for Ecosystem Restoration and Maintenance. Proc. 1st. Annual Meeting Soc. for Ecological Restoration. Jan. 16-20, Oakland , CA .

(3) Dixon , R.M. 1990. Land Imprinting for Dryland Revegetation and Restoration. IN: Environmental Restoration: Science and Strategies for Restoring the Earth. Editor: John J. Berger, Island Press, Washington , D.C.

Land imprinting for restoring OHV disturbed land. Speep-slope imprinter pictured at Chula Vista , CA .

REVEGETATION OF OFF HIGHWAY VEHICLE DISTURBED LAND IN THE MOJAVE AND COLORADO DESERTS OF CALIFORNIA