The Imprinting Foundation



Robert M. Dixon, Ph.D, Ph.D., Ted St. John, Ph.D., and Mick St. John

Discovery Park, Safford, Arizona, is a non- profit educational facility that serves as the information center for the new Mt. Graham International Observatory. The 125-acre Discovery Park site includes the smaller Gov Aker Observatory with its 20-inch optical telescope, and an open-space area with hiking trails, picnic sites, and a narrow-gauge railroad. Much of the acreage is becoming a wildlife refuge and bird observation area. The three authors have been involved in planning and execution of the habitat restoration that is under way in the wildlife area. The restoration objectives must be accomplished under the constraints typically confronted by non-profits: limited money, water, and time, all in the harsh climate of eastern Arizona.

Funding for the work is primarily state lottery money from the Arizona Game and Fish Heritage Fund. Other help has come from BLM, NRCS, Americorps, and the Arizona National Guard.

A Restoration Pla

The Discovery Park restoration plan began measures to control any continuing disturbance to the site. Some disturbance has come from off-road vehicle use and illegal dumping.

For ten days last fall, the Arizona National Guard deepened the ponds and re-routed the drainage between ponds. Donor sites supplied fill for new berms and stream banks, and previous low areas were filled with dead salt cedar and soil.

Fortunately, Discovery Park is free of any hardpan or caliche layer that would restrict the growth of deep root systems. If caliche had been present, it would have been necessary to break it up by ripping. Soil compaction, a common problem on restoration sites, was likewise absent from Discovery Park.

The biological portion of the plan, prepared in part by the senior author, laid out the requirements and general methods for control of exotics, provided site evaluation, and proposed methods of soil preparation and plant establishment.

A very high priority was removal of the salt cedar ( Tamarix ramosissima ) that had invaded most of the pond and mud flat area. Salt cedar provides little of value for wildlife, and uses much more water than native vegetation. Removal methods included cutting of the stem, followed by herbicide treatment of the stump. Smaller trees were killed by basal bark treatment with the herbicide Garlon 4. Much of the cut material was buried during earthworks.

An important part of the restoration process is evaluation of the restoration site, including groundwater hydrology, soil toxicity and physical state, and microbiological conditions.

Discovery park is situated in a natural drainage, but the historic hydrology has been interrupted by re-channelization, pumping of groundwater, and invasion of salt cedar. Most of the low-lying areas must be restored with vegetation that can withstand, or recover from, possible periods of drought in the future.

The soil was uniformly alkaline. Salinity from previous stands of salt cedar is a legitimate concern, but soil tests have indicated innocuous salinity levels.

To achieve acceptable germination and establishment, the soil must be prepared in a way that provides "safe sites," assures firm seed-soil contact, and overcomes the deleterious effects of soil crusting. Safe sites provide shelter from desiccation, animals, and other dangers. Plant ecologists believe that the final number of plants is best predicted by the number of safe sites, rather than the number of seeds applied. Safe sites are provided by irregularities in the soil surface and features such as rocks and woody debris.

Physical crusting of the soil surface comes from re-sorting surface particles by raindrops into an interlocking layer. The resulting restriction of soil air and water movement is a serious danger to germination and establishment of native plants.

A single seed application method, land imprinting, provides a solution to these problems. The land imprinter is a tractor-drawn roller with angular metal teeth that press the soil into a series of ridges and valleys. Because the seed are dispensed from a bin and fall onto the roller, they are pressed into firm soil contact by the imprinter. Land imprinting was developed and promoted by author Bob Dixon.

Wherever possible, plant introduction was from seed. The restoration plan recommended material of local genetic origin, and much of the seed was collected on and near the site. Other plant material has come from locally collected cuttings and an on-site container nursery.

The plan also suggested monitoring of both above ground and below ground progress as the restoration takes place in phases over future years. Remedial planting is likely to be a continuing part of the program, as at most restoration sites.

Desired Native Vegetation

The wettest areas were believed to have been interior marshlands, and they will be restored to that vegetation type. The drainage includes riparian scrublands, with several species of native shrubs in areas not fully usurped by salt cedar. A grove of large cottonwood trees remains, and enlargement of the grove is an important restoration objective. Willows and other riparian elements are being planted from cuttings taken locally. Some of the mud flats in the drainage are too high for reliable growth of wetland vegetation, and it is those areas that were imprinted with seeds of riparian scrubland species.

Ecosystem Function

Disturbance disrupts the ecosystem, and restoration seeks to restore the array of processes that create "ecosystem function." Most of these processes are below ground, and are mediated by microorganisms. The re-establishment of these properties is the objective of habitat restoration. For example, healthy ecosystems resist weed invasion because of nutrient cycling processes that render the site unsuitable for the rather specific requirements of ruderal (weedy) species. Nutrient retention, the lack of "leakiness" found only in functional ecosystems, is a result of the extensive below ground network of roots and beneficial microorganisms.

Mechanical disturbance, including brushing and disking, removes photosynthetic support and disrupts the key microorganisms in the soil. Grading and earth moving represent complete destruction of even the simplest ecosystem functions. All of these forms of disturbance have taken place on the Discovery Park property at various times.



The most important component of soil microbiology is mycorrhizal fungi. Mycorrhizal fungi form a relationship with the roots of higher plants, and are fundamental to plant survival and growth. A survey indicated that mycorrhizal fungi were present where native vegetation persisted, but were scarce in the disturbed portions of the park. The native fungi would have to be re-introduced before we could hope to create a functional ecosystem.

The effects of mycorrhizae on plant growth are well known: mycorrhizal plants grow faster, survive better, resist drought better, reproduce more, and are less susceptible to root disease than non-mycorrhizal plants. Mycorrhizae increase the availability to the roots of moisture and phosphorus, two resources that are commonly in limited supply in arid regions.

Ecologists are now learning that the benefits of mycorrhizae go far beyond the individual plant. Mycorrhizae lie at the foundation of ecosystem function. They form soil structure, "feed" much of the beneficial soil microflora, and dominate nutrient cycling processes.

Mycorrhizae can link the below ground ecosystem into a functional unit because the fungi are not limited to a single species of plant. A fungus that starts out in partnership with a creosote bush may soon connect to a nearby bunch grass, then a mesquite tree, and then to a cactus as well. As the fungus spreads through the soil and colonizes new roots, it passes nutrients to the interconnected plants.

As the hyphae grow, the soil becomes intricately entangled with mycorrhizal networks. The hyphae "glue" themselves to mineral and organic particles, binding the particles to each other and to the roots. The resulting aggregates, collectively called soil structure, define the soil pore space. Soil structure has a large influence on the capacity of the soil to retain nutrients and moisture.

We know from experimental work that many plant species never appear on a restoration site, even though they were in the seed mix, unless mycorrhizal fungi are available in the soil. The network assures that seedlings of all species can quickly become mycorrhizal. If the network is in place, the seedling need only tap into it.

Functional ecosystems are resistant to invasion by weeds, and the mycorrhizal network is at least partially responsible for this resistance. The presence of nearby mycorrhizal hyphae can suppress the growth of some weedy species that do not normally become mycorrhizal. The roots of at least one species, Russian thistle, may actually be killed by mycorrhizal hyphae.


How to grow a network

The most fundamental challenge is not to make individual plants mycorrhizal, but to build the mycorrhizal network in the soil. The first phase of restoration at Discovery Park concentrated on establishing the network with early successional natives.

Successful production of an active mycorrhizal network requires the simultaneous introduction of both fungi and mycorrhizal host plants. Some plant species are better at supporting mycorrhizal fungi than others, and we made sure that some of these net-builders were in the seed mix. Many of the short-lived native perennial composites and grasses are examples.

Mycorrhizal fungi can be reintroduced by applying topsoil or commercial inoculum. In this case, no topsoil was available, so we incorporated VAM80, a mycorrhizal inoculum produced by the senior author at Tree of Life Nursery in California.

The prospects for successful production of a mycorrhizal network are best near an existing mycorrhizal native plant. The established species can "feed" the network while seedlings of new natives become established. This will enable the new soil network to build much more rapidly than it could using only the energetic input of the new seedlings.

Mycorrhizal inoculum must be placed below ground, in the root zone. In this case it was broadcast by hand and turned under with a disk plow. In other cases, it has been placed at the same time as surface shaping and seed application, with a land imprinter set up for the purpose.


Seed application

Direct seeding is usually the most cost-effective way to introduce plants. Important components of success are good capillary contact with the soil to promote germination, heterogeneity of the soil surface to provide a variety of "safe sites," and low fertility to discourage competing weeds.

It is important that the seed mix include some native species that are aggressive growers as well as good builders of the mycorrhizal network. In this category are many native grasses, composites, and legumes, which should make up half or more of the seed mix.

Seeding rates depend on seed species, seed availability, and application methods. A good method such as imprinting may use half or less the seed of a bad method such as broadcasting. The number of pure live seeds (bulk seed corrected for purity, germination, and seed count) is a more appropriate measure than bulk weight of seed in most cases. Before starting, the seed were mixed with an equal volume of bran to keep the seeds from sorting by size during agitation.

The seed mix at Discovery Park included six-week rye grass, three perennial grasses, six shrubs, and five annual plant species at a total rate of 24 pounds per acre. This provides some non-host shrubs (saltbush species), and some good facultative mycorrhizal host plants.

Land imprinting forms safe sites, good capillary contact, and (with a specially modified machine) allows placement of mycorrhizal inoculum in a single pass. The imprinter is well-suited to the rough terrain typical of restoration sites. It can ride over rocks and debris, and navigate slopes as steep as three to one. A new model, to begin commercial work in California in fall of 1997, can easily imprint 2:1 slopes.

Bob Dixon arrived with the land imprinter in December, and with Mick St. John got the machine off the trailer and hooked up to the tractor. The machine chosen for this job was a relatively small unit with 10-inch, staggered teeth made from 6-inch angle iron. These newer imprinters are easy to transport and can be pulled over most terrain with a common farm tractor.

The next step was an inspection of the soil, which must not be too hard to get good imprints. Good imprints extend the full depth of the teeth, have relatively sharp rather than rounded ridges between impressions, and have smooth walls with the seed firmly embedded in the soil. If the soil is too hard, it is necessary to either wait for rain or rip it to at least six inches. Author Bob Dixon can tell the condition of the soil by the way his boot heel crunches. If there is no crunch, he calls for ripping first.

The soil was in good condition, with some moisture from fall rains. The work went quickly; within 8 hours the machine had imprinted the full ten acres. The imprints looked very good over most of the area.

Other planting

Early work included container plantings from the on-site nursery and commercial sources. The plantings were grouped into "islands" to facilitate maintenance, give improved survival, and produce a natural appearance. Most islands were set up with a "deep pipe" watering system. This irrigation method has proven far less expensive and less tempting to vandals than conventional irrigation systems. It has the considerable advantage of watering the intended plant rather than surrounding weeds.

Willows, cottonwood, and seep willow have all started readily from cuttings. The cuttings came from a number of individual plants, to increase genetic diversity and to avoid the possibility of producing all male or all female plants. They were cut in winter and early spring, when the stems were without leaves, and were planted within hours of cutting.

A method in wide use in the southwest involves augered holes that break through any hard pan. The cottonwood cuttings were 15-foot poles set in holes ten feet deep. The exposed upper end of each pole was painted with a 50/50 water/latex white paint mixture to help exclude pests and reduce desiccation.

The on-site nursery will provide bare-root stock for future plantings. The stock will be produced in trenches to minimize day-to-day care, and will be outplanted during the appropriate season after containerless transport to the field.

First results

Container plantings around Discovery Park have been doing very well, as have the plants from cuttings. The cottonwood pole cuttings have put on new growth during the spring and promise to nicely enlarge the existing grove in the wildlife viewing area.

Even though only two and one-fourth inches of rain followed imprinting, there was considerable germination of annual and native grasses, and some of the shrubs in the seed mix. Germination took place on the sides of the imprints, but seedling survival was clearly highest in the bottoms. The imprints appeared dry during the afternoon, but each morning they re-wet by capillarity from moisture in the soil below. Capillary re-wetting brought on germination of native seeds that otherwise would have required much more rainfall than was offered by the 1996-1997 season. The imprints trapped wind-borne organic debris, which shaded seedlings and added to the variety of safe sites.

The extremely dry spring would have meant nearly certain death if the seed had been broadcast or hydroseeded, but the imprints protected the plants until a rain event in mid spring. At that point, the seedlings greened up and put on a new spurt of growth. Even though the storm was only one-half inch, the imprints funneled it to the bottoms of the pits and the new seedlings.

It is typical that new plant species move in once the initial vegetation has opened up the soil and built the mycorrhizal network. Below ground dynamics are suggested by the fact that imprinted sites always organize themselves, within a few years, into a patchwork of species associations.


The objective of the Discovery Park restoration effort was to return native vegetation to each physical habitat in the wildlife observation area. The first plantings, especially the imprinting, look promising and economical. The mycorrhizal network should be developing in earnest by late next fall; at that time we should see the first signs of resistance to weed invasion.

Salt cedar is very persistent, and the supply of wind-borne seeds in eastern Arizona is nearly infinite. Therefore, the job of salt cedar control will never be completely finished. However, with healthy functional ecosystems over most of the wildlife area, the mycorrhizal network and vigorous native plants will hold the ground gained by the functional ecosystem.

Sidebar: To learn more:

Desert restoration

Bainbridge, D. A., N. Sorensen, and R. A. Virginia. 1993. Revegetating desert plant communities. P. 21-26 in: T. D. Landis. Proceedings, Western Forest Nursery Association. USDA Forest Service General Technical Report RM-221.

Fidelibus, M. W. 1994. Jellyrolls reduce outplanting costs in arid land restoration (California). Restoration and Management Notes 12(1):87.


St. John, Ted. 1996. Mycorrhizal inoculation: advice for growers and restorationists. Hortus West volume 7, Issue 2.

St. John, Ted. 1996. Specially-modified land imprinter inoculates soil with mycorrhizal fungi (California). Restoration and Management Notes 14:1, p. 874-85.


Dixon, R. M., and A. B. Carr. 1994. Land imprinting for low-cost revegetation of degraded land. Erosion Control 1:38-43.

St. John, Ted, and R. M. Dixon. 1996. Land imprinting: an overview and proposed technical specifications . Tree of Life Nursery, San Juan Capistrano, California.

Tree of Life Nursery
San Juan Capistrano
Tucson, Arizona
Discovery Park, Safford, Arizona

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

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