Appendix G: Techniques for Plant Establishment in Arid Ecosystems
Restoration and Management Notes 13(2): 190-197
1995
David A. Bainbridge
Matthew Fidelibus
Robert MacAller
Reproduced with permission of the publisher.
Recognition of the need for ecosystem restoration is growing in arid lands. Increasing use of deserts has resulted in plant and soil degradation which can be reversed by reestablishing native plants. Without intervention, desert areas disturbed by human activities such as off-road vehicle recreation and mining may take decades or centuries to recover (Bainbridge and Virginia, 1990). Conditions favorable for seed germination and seedling establishment are infrequent and unpredictable in the desert, making direct seeding an ineffective restoration strategy (Cox et al., 1982; Barbour, 1968). Fortunately, many desert shrubs are easy to grow in a nursery and respond well to transplanting. But in harsh desert climates, intense solar radiation, high temperatures, high winds, low rainfall, low soil fertility, and intense herbivore pressure can limit transplant success unless plants are prepared carefully and protected after planting. Our research in the Mojave and Sonoran Deserts of California has identified nursery production techniques and seedling protection methods that improve survival. In this article we provide an overview of successful desert revegetation practices, which should also prove useful to many workers in less severe environments. It begins with a review of containers and soil mixes for transplant preparation, followed by a discussion of strategies for protecting transplants from environmental stress.
Container Types and Soil Mixes
One of the most important choices in developing a planting program on an arid site is understanding the bureaucratic, biological, and physical constraints on the restoration project and, with these in mind, choosing containers that can deliver survivors in the APPENDIX G Restoration and Management Notes 13(2): 190-197 1995 Techniques for Plant Establishment in Arid Ecosystems David A. Bainbridge Matthew Fidelibus Robert MacAller Reproduced with permission of the publisher. field at minimum cost. This overview reflects almost ten years of experience in this area, and concludes with some general recommendations for restorationists working in arid environments.
The primary function of any container is to hold the growing medium, which supplies the roots with water, air, mineral nutrients, and physical support while the seedling is in the nursery. While some container characteristics influence the growth of seedlings in the nursery, others are related to economic and management considerations at the planting site. Although little research has been conducted on the design of containers to meet the special requirements of desert seedlings, a number of practitioners suggest that these plants may benefit from deeper (taller) containers than are commonly used (Smith, 1988; Felker et al., 1988; Bainbridge, 1987, 1994a; Holden, 1992).
Seedlings destined for arid and semiarid sites differ from many ornamental plants because they are basically a root crop, while ornamentals are grown for their flowers, foliage, or shoots. Survival on arid sites, however, often depends on root growth potential and the ability of the root system to gain access to soil moisture and generate new roots.
Containers should be designed to encourage the seedling to form an extensive and vigorous root system that can be protected until the seedling is planted. Plants produced for disturbed arid sites, where growth is commonly limited by water or nutrients, should have a large, active root system because uptake of nutrients and water is increased with greater root biomass (Barbour et al., 1987). The container characteristics described below influence root development and the root-to-shoot ratio of developing plants.
Restoration planners should select, a container that will produce a healthy seedling at the highest practical growing density (in the shortest possible time) to suit the project, the environment of the site, and the project maintenance plan. Economic and administrative factors, such as the likelihood (inevitability?) of delays in delivery, acceptance date, and irrigation and maintenance scheduling should be realistically appraised. The initial cost and availability of containers, soil mixes, irrigation, handling and planting, and the available growing space are important considerations, but the final cost per survivor should be the primary concern. The size of the seed or cutting, growth rate, susceptibility to disease, temperature preferences, and desired outplanting size must all be considered.
Container height (depth) is especially important because it affects the length and biomass of the roots and the water-holding capacity, and aeration of the growth medium. The ratio of width (diameter) to height (W/H) is the aspect ratio. Aspect ratios of commercially available containers vary greatly, from more than 1 to as low as 0.1. For desert work, tall, narrow containers with aspect ratios in the range of 0.12 to 0.20 are usually preferred, both because most desert plants are deep-rooted and because slender containers are less costly to transport and outplant.
In general, larger seedlings will survive better than small ones. However, increasing size increases cost in four ways: (1) larger containers are more expensive to buy and fill; (2) they take up more growing space, (3) they require longer growing periods for the seedling root system to effectively occupy the container, and (4) they cost more to handle in the nursery, to ship, and to plant.
The optimal container will produce the smallest stock that will survive at acceptable rates in the field. Survival rates can be improved if outplanting is properly timed. We have found that some species, such as honey mesquite (Prosopis glandulosa var. torreyana), survived best when planted in mid-spring to mid-summer (although crew members wilted at temperatures over 40 degrees C (100 degrees F)), while other species prefer early spring planting. Plant ecophysiology is a key consideration, and should be studied before developing a planting program.
The growth and survival of both roots and root symbionts (mycorrhizae and rhizobia) require appropriate soil temperatures. They are strongly affected by the color and insulating properties of the container materials. Dark-colored containers absorb more solar energy and become warmer than lighter ones. Brown (1982) found that changing container color from black to white reduced the temperature of the growing medium by 7 degrees C (11 degrees F) and produced more vigorous plants. Color can be especially important in desert nurseries where air temperatures may reach 43 degrees C (110 degrees F) and black containers may reach surface temperatures above 71 degrees C (160 degrees F).
The best container to use depends on the season, the handling process, the species, and the project goals. Again the prime consideration should be to minimize the cost per survivor. Bigger containers may produce larger plants and higher survival rates, but they can be much more expensive to work with. Since cost and survival are major concerns in desert work, we will review the common container types used by restoration workers.
Systems with individual cells in a holding tray (Ray Leach Conetainers [sic] are desirable because they allow re-sorting of plants. This is especially important when you are working with poorly understood plant species or low-quality seeds because it facilitates removal and replacement of diseased or otherwise undesirable seedlings and empty cells. It also facilitates selection of matched cohorts of plants for experimental work and, of course, replacing empty cells saves space in the greenhouse and during storage and shipping. However, the containers that fit these trays are relatively shallow (12-21 cm).
The 10 in³ cell, commonly referred to as a Supercell, is one of the most commonly used containers for desert plant production, and has been tested with many species. The hard plastic trays that hold the cells are relatively fragile and are likely to be damaged if they are handled repeatedly while loaded with seedlings. They are also heavy, with a rack of 98 plants in sand-based medium weighing almost 22.7 kg (50 lbs).
Seedlings can be removed from these containers by gently squeezing the Supercell or by rapping the top of the cell on a hard surface, using momentum to dislodge the root ball. With the sandy soil-mixes commonly used for desert-plant production the soil usually falls away from the plant as it is removed and the seedling is effectively bare-rooted. Plants with fragile roots can be removed more gently by kneading the cell under water.
An experienced planting crew of three can plant 150- 225 plants per day (50-100 plants per person per day) from Supercells under typical field conditions (Bainbridge and Virginia, 1990). Much of this time is spent hauling water, watering, and installing protective devices. Estimated planting costs run from $0.50 to $3.00 per plant. After one year we have had nearly 90 percent survival for catclaw (Acacia greggii) grown in 164 ml (21 cm deep) Supercells planted on goldmine spoils in the eastern Mojave Desert (Fidelibus and Bainbridge, 1995).
Plant bands are open-ended boxes made of folded and glued plastic or foil-coated cardstock [see figure G1.] Heavy stock with foil on both sides is best, but plastic or wax-coated material is suitable for short rotations. Extreme temperatures can melt the thermoset glue on plant bands, so seams should be faced to the inside of blocks of cells to prevent delamination. Standard sizes are available, but almost any size can be custom-made for larger orders. They have proved very effective in semi-arid and arid sites in California and Texas (Bainbridge, 1994a; Felker et al., 1988).
One of the advantages of plant bands is ease of transplanting. With larger sizes (5 cm x 5 cm) and the loose mix used for desert plants, the banded plants can be placed directly in the planting hole and the band can be pulled [up] and over the plant without disturbing the roots. When more cohesive soil mixes are used, it is often necessary to rip or cut open the band to remove the plant.
A wide range of plant-band sizes (up to 3" x 3" x 24" [7.6 x 7.6 x 70 cm]) has been tested, with generally positive results. A 12-16" (30.5-40.6 cm ) tall, 2" (5.1 cm) square cell seems most useful. We have used these extensively in the Mojave and Sonoran Deserts with many species and with excellent results. Bladder-pod (Isomeris arborea, for example, has grown from 15 cm (6 in) at outplanting to over 70 cm (28 in) within one year. Many species have set seed during the first growing season.
Because of their large volume, plant bands allow for greater root development in greenhouse stock than do Supercells. In addition, it is easier and less time-consuming to remove plants from these containers when transplanting. They are our preferred container.
Plants have been grown in plastic pipe sections ranging from ¾" x 30" (1.9 x 76.2 cm) to 6" x 32" (15.2 to 81.3 cm). It has proved necessary to saw smaller diameter pipes open to remove plants, which is very labor intensive and costly. Smooth-walled PVC is desirable, as roots may be entangled in rougher textured plastic (drain pipe, for example) causing root damage during planting. Plants are commonly grown for at least a year to allow roots to fill the rooting volume. They can be maintained in the nursery for several years, if necessary. Before planting the tops are pruned and hardened off to provide a very tough plant with a high root/shoot ratio. Pruning also makes it easier to remove the container by pulling it up and over the shoot during planting, as with a plant band.
Just before planting the screen at the bottom of the container is removed and the container is placed in an augured, prewetted hole (Holden, 1992). The hole is partially back-filled and then, as back-filling continues, the container is pulled out by hand or with hay hooks inserted in two holes drilled in the top rim. The large volume of soil mix protects the roots during and after planting and provides conditions for rapid growth. Tall pot (6" x 32" [15.2 x 81.3 cm]) pipe containers, have been very successful at Joshua Tree National Monument (Holden, 1992), and creosote bush (Larrea divaricata), salt bush (Atriplex canescens), and other species planted from these containers at Red Rock Canyon and Anza Borrego Desert State Park have had very high survival rates. We have also had positive results in a few trials with a mini-tall pot (4" x 24" [10.2 x 61.0 cm]) developed at the California Department of Forestry Reforestation Center in Davis, California. Survival of bursage [Ambrosia dumosa] from these containers planted at Red Rock canyon [sic] was high, and the pots were easier to transport than the larger tall pots, but removal of the seedlings was a little more difficult.
We have found that the large root system has enabled creosote bush and salt-bush transplants to survive even after being gnawed to the root crown by herbivores. In addition, these containers allow rapid growth and fast recovery and are well suited for plantings intended to block trail ends or old roads. However, the size and weight of pipe sections make them costly to transport and plant [see figures G2 and Figure G3].
Although we have not used Styrofoam blocks with planting cells for operational planting, they appear promising for many species. These foam blocks come in a wide variety of cell capacities (16-121 ml [2.3 to 20 cubic inches]), depths up to 23 cm (9 in) and cell densities. They have become the predominant planting container for forest nurseries in many areas because they are easy to handle and provide a good growing environment. The foam is also an excellent insulator, reducing temperature extremes in the rooting zone. Roots of some species grow into the cavity walls making the seedlings difficult to extract and the blocks difficult to clean and sterilize unless copper root-retardant paint is applied to the cells (Landis, 1990). Foam blocks appear most useful for well understood plant species with non-invasive roots when high quality seeds are available.
Standard landscaping pots appear to work reasonably well for shallow-rooted species. Both ocotillo (Fouquieria splendens) and cholla (Opuntia spp) have been planted at highly disturbed sites in Anza Borrego Desert State Park from 1-gallon pots with adequate survival. Plants like ocotillo can be planted deeply, with much of the stem buried, to protect the root mass.
Desert plants are generally drought-tolerant (up to 50- 60 bars), have high oxygen demands, and are susceptible to many nursery pathogens. They commonly benefit from rapid draining, porous soil mix. While greenhouse plants are commonly produced with a fertile soil mix, which results in a large, green and vigorous shoot, high nutrient levels may inhibit root growth and contribute to a low root-to-shoot ratio (R:S). Increased root biomass appears critical for seedlings, which are less water efficient than mature plants (Rundel and Nobel, 1991).
Additionally, most desert plants form or require symbiotic associations with vesicular arbuscular mycorrhizal fungi (VAM). Inoculating plants with appropriate fungi may increase survival and growth of many species. The fungal association improves phosphorus, water, and nutrient uptake (Allen, 1988; Allen, 1992). Studies have shown that transplants which received VAM inoculations grew faster and outcompeted weedy annuals more effectively than uninoculated plants (Allen and Allen, 1984). Inoculation adds another complication to the task of providing nutrients to young plants. The fungi require nitrogen, but may be inhibited by phosphorus, so it is important to provide these nutrients in ratios that optimize growth of seedlings and mycorrhizae (Hayman, 1982; INVAM Newsletter, 1994). The VAM fungi also require well-aerated soil, in contrast to the rhizobia, which tolerate much lower oxygen levels.
Planting typically costs much more than production. Labor productivity and cost are highly variable depending on environmental conditions such as temperature, wind speed, soil conditions, site characteristics, and the skill of the crew. Obviously, planting rates will go down when temperatures exceed 40 degrees C (100 degrees F). The figures in Table 1 provide estimates of what to expect under ordinary conditions.
| Container | Seedlings/Person/Day |
|---|---|
| Supercell | 50-100 |
| Supercell jellyroll | 100-200 |
| Plant band | 100-120* |
| 1-gallon pot | 40 |
| 2-gallon pt | 30 |
| Tall pot | 10 |
Notice that these rates are much lower than forest planting rates, which may exceed 1,000 seedlings per person per day. Moreover, under the severe conditions of the desert, poor planting techniques and insufficient attention to detail can be dangerous. Planters should be carefully trained and projects should develop a quality control program.
Container stock grown for desert conditions is usually heavy and costly to ship and handle in the field, making outplanting difficult and expensive (Bainbridge and Virginia, 1990). One technique for making handling easier is to remove seedlings from their containers and growth media at the greenhouse and wrap them in moist Kimtex® fabric (a technique known as jellyrolling) prior to shipping to the restoration site (Fidelibus, 1994). An ice chest holding several hundred jellyrolled plants may weight less than 98 plants in Supercells. Physiological and survival data for jellyrolled desert seedlings compares favorably with data for containerized plants (Fidelibus and Bainbridge, 1994). Not all species may be as tolerant of jellyrolling, and some species-specific differences have been noted.
All of the effort and costs associated with researching site characteristics and species physiology, selecting the best containers and soil mixes for a project, and outplanting seedlings may be wasted in a few hours or days unless adequate protection is provided for transplants. Newly transplanted seedling[s] are highly susceptible to grazing pressure, high winds, moisture stress, and extreme temperatures (Bainbridge, 1994b). Protection from these environmental pressures can often be the determining factor in transplant establishment and survival. We provide an overview and recommendations based on out experience in the Sonoran and Mojave Deserts.
Herbivory is increasingly recognized as a critical factor in seedling survival in arid environments (McAuliffe, 1986; Bainbridge and Virginia, 1990). Newly planted seedlings are often the most succulent plants available, and rodents, rabbits, reptiles, domestic livestock and insects find them especially attractive. This herbivory can severely damage and even kill seedlings unless they are protected.
Blacktail jack rabbits (Lepus californicus), other rabbits, and rodents have been the most troublesome herbivores in our trial plantings. We have observed that seedlings of many species can survive heavy browsing if they have access to water, but if they are dry or have a limited root system browsing quickly proves fatal.
Protection from the wind can be crucial in extreme environments (Virginia and Bainbridge, 1987). In addition to sand blast effects, plants may be damaged or killed by the mechanical action of high winds (Bainbridge and MacAller, 1995). We have observed multiple branching as a common response to wind damage on unprotected catclaw planted on mine spoils in the east Mojave Desert. In these cases, shrub height is restricted to within a few inches of the soil surface and growth can only occur laterally (Fidelibus and Bainbridge, 1994). In other cases young tree seedlings have been blown completely out of the ground.
In addition to lack of available water, the low humidity, high winds, and high temperatures of arid lands create desiccating conditions (Sorensen, 1993). Some protection strategies can reduce evapotranspiration and reduce moisture stress on seedlings. This appears to be most critical in the six to eight weeks after transplanting. Plants usually receive only a few liters of supplemental water, so water conservation is critical.
Protection may also be needed to reduce the adverse effects of extreme heat and cold. Freezing temperatures are not uncommon, and many desert plants (especially young and well hydrated transplants) are easily damaged by freezing (Bowers, 1980). Here is an even more serious problem, with soil temperatures exceeding 60 degrees C (140 degrees F) in the summer. High radiation levels exacerbate the damaging effects of high air temperatures.
Many strategies have been developed to protect plants from environmental pressures. These include tree shelters, rock mulches, plant collars, and animal-repellents [sic]. All of these may be effective when properly used and matched with site conditions and herbivore species. Their advantages and disadvantages should be carefully considered, and alternatives should be tested before they are applied on a large scale.
Almost ten years of testing enables [sic] us to provide a good review of the strengths and weaknesses of some of the more commonly used techniques. These options are listed for use with seedlings of perennial shrubs on a typical exposed site with moderate to high windblast and herbivory, but recent experience indicates that the tree shelters may also be very beneficial for annual plants as well.
Many companies have introduced tree shelters in recent years. These are commonly plastic tubes of various sizes, configurations and materials. Though there are many unanswered questions about tree shelters, many restorationists are finding that they can be very helpful (Windell, 1993; Sorensen, 1993; Bainbridge, 1994; Bainbridge and MacAller, 1995). (See the Proceedings of the June, 1995 Tree Shelter Conference in Harrisburg, Pennsylvania, [USDA Forest Service] for current information on suppliers.) (Editor's note: For information on this conference contact the Center for Urban Forestry at the Morris Arboretum, University of Pennsylvania, 9414 Meadowbrook Ave., Philadelphia, PA 19118; 215-247- 5777.)
Tree shelters have worked well in the desert, but they are not appropriate for all situations and species. To use them effectively it is necessary to have some idea how they work. While this is not completely clear, some things are known: Tree shelters reduce light, decrease wind, increase the relative humidity (depending on the irrigation schedule), protect plants from herbivores, and improve water delivery.
All of these characteristics benefit outplanted seedlings by reducing plant shock and biotic and abiotic stress. However, there are also biological costs. The reduced light, although initially advantageous may, over time, be detrimental to plant health. Lowered light levels may, in some species, for example, creosote bush, decrease photosynthetic activity, reduce the growing season, and limit growth (Sorenson, 1993). Although transpiration often keeps shelter temperatures below ambient air temperature, the leaf temperature may rise far above ambient temperature when protected plants are not irrigated. How plants respond to these conditions will depend on their ability of [sic] to acclimate to, or at least tolerate, the combination of low light and high temperatures.
Tubex® Tree Shelters are translucent, solid-walled 7.5- cm (3-in) diameter cylinders available in a variety of heights (0.2-2 meters). We have mostly used tancolored (which greatly reduces solar radiation), twin walled, polypropylene Tubex shelters ranging in size from 15 to 50 cm in height. There are placed over the plant immediately after transplanting, and the bottom of the cylinder is inserted several (5-10) centimeters into the ground.
Tubex® Tree Shelters protect transplants from many environmental stresses. If transplants are tall or if they are growing rapidly, herbivores can easily graze the foliage growing out of the top. This light grazing has not had a significant adverse effect on most of our transplants (Bainbridge and MacAller, 1995). However, herbivores have been able to pull some plant species out of the ground, leaving only bare, dead, roots in empty shelters. Jack rabbits at one site also learned to kick over the tree shelters even when they were securely buried in the ground. We have also found that Tubex® dramatically reduces light intensity (Sorensen, 1993), and that they very effectively direct water to the root zone when it is poured inside the tree shelter.
The narrow diameter of the tube can have adverse effects on the architecture of shrubs developing in it. Plants left in these tree shelters too long acquire a cylindrical shape. In addition, the reduced light can increase stem elongation, creating a relatively tall, weak stem which branches out at the top of the shelter, creating a mushroom shape. This can make removal difficult unless the shelter is cut with a knife or clippers. This has been a problem especially with bursage (Ambrosia dumosa) and bladder-pod transplants, which are fast growing, bushy shrubs. The odd shape of the plant may also make the shrub susceptible to wind damage; however, most transplants have recovered to a "natural" shape over time. We have had high survival rates with many species, including burrobush (Hymenoclea salsola) and catclaw at Red Rock Canyon and Castle Mountain Gold Mine (Bainbridge and MacAller, 1995; Fidelibus and Bainbridge, 1994). These appear to be best for upright, leader-dominant shrubs and trees.
TreePee® shelters are recycled plastic, translucent-red colored, open-top conical tubes with three integral wire mounting pins. TreePees® have an 8" diameter base (more than twice as large as the Tubex® ) tapered to a 4' diameter top and are 24" in height. These shelters function much like the Tubex® but are much taller and wider, and provide additional protection from herbivory. Although the pins make the shelters easier to anchor, it is harder to force the base of the tree shelters into the soil, so that water applied through the top of the shelter often leaks out around the base reducing delivery to the root zone.
Burrobush have had excellent survival and health when protected by TreePees® (Bainbridge and MacAller 1995). The results were similar to those we got with Tubex®, but no herbivory occurred in TreePee®. These would be a good choice for plants that are sensitive to light grazing and for lower growing, spreading plants. In addition, we have observed that armed senna (Senna armata), bladderpod, and bursage have had good survival and growth (most having had flowers and set seed) after one year at our Red Rock Canyon site. However, they are more expensive than Tubex® and are more easily degraded by sunlight, and so are rarely useful for more than two seasons.
Wire cages provide protection from herbivores, but few physiological benefits, although the cage can be wrapped with bubblepack plastic in a pinch. We usually use wire cages composed of 3.8-cm wire mesh threaded and staked to the ground with pencil rod (7 mm) rebar. Cages can be made with mesh sites ranging from window screen to 6-inch concrete reinforcing mesh (depending on the size of the herbivore) and in any height and diameter desired. Although material costs are low installation and removal is [sic] labor-intensive and costly. Each cage must be cut, threaded with rebar (which also acts as a surface anchor) or fastened with aviary clips (small, flat clips used to clip wire mesh together) and staked to the ground. In addition, cages are bulky and require more space than the easily stackable Tubex® or TreePee® tree shelters.
Burrobush protected by cages at Red Rock Canyon had survival rates comparable to those protected by Tubex® or TreePees®, but were not as healthy (Bainbridge and MacAller, 1995). No plants without protection survived in this rest. Removal can be difficult, and very costly if you wait too long and let the plant grow through the wire mesh.
Other Available Shrub Protection
There are also many other strategies for protecting plants. Our experience with some of the lesser known techniques to protect plants include:
Rock mulch provides good protection from temperature extremes and some protection from herbivory. Three or more medium to large (10-20 cm diameter) rocks are arranged around each seedling. The thermal mass of the rocks provides some thermal buffering, the rocks themselves reduce evaporation from the soil, act as a wind break, and, if properly placed, discourage grazing.
If rocks are available, the cost is low and the resulting arrangements can be attractive-a consideration in some situations. As the plants grow the rock mulch can be left in place. We have considerable experience with rock mulch in the Coachella Valley, and were pleased with results in years when herbivory was moderate.
Even fairly short collars of plastic, peat, or paper can increase survival rates. These improve watering efficiency and reduce sandblast and evapotranspiration of young seedling. They also provide some protection from grazing and reduce bending and mechanical damage. We used 4-6 inch collars made from 3- to 4-inch diameter PVC pipe before tree shelters became available. Peat collars provided some benefits at Anza-Borrego Desert State Park, but were not as effective as tree shelters. Paper protectors were also marginally effective.
Repellents may provide some protection in the desert. These include both commercial and home-made solutions applied to plants to make them less palatable. We tested three commercially available repellents on bladder-pod transplants at Red Rock Canyon in 1993-1994: Anipel systemic tablets (placed 1 inch below the stem in direct contact with the root), Ropel deterrent spray, and Hinder repellent spray. We found that all three repellents slowed grazing slightly, but long-term damage was comparable to that on untreated controls, and the effects of the repellents were not statistically significant. We suspect that systemics may prove more effective when applied in the nursery at the time of sowing or inserted in the container several weeks before field planting (so the plant has time to assimilate the repellent) or on plants that are irrigated on a regular basis.
Costs are commonly under-estimated in planning and reviewing restoration projects. Full cost-accounting is crucial if the restorationist is to determine the best approach for planting on the basis of cost per survivor. Planting small plants in urban areas may cost more than $15 per survivor if administration and maintenance costs are included, and costs in the desert can be even higher unless plants are well prepared, properly and efficiently planted, and protected from herbivory and environmental stress. Estimates of these costs for small projects on remote sites are shown in Table 2. Experienced planting crews and economies of scale may cut costs in half on larger projects.
Obviously no one container or production system is suitable for all conditions and species. To maximize survival while minimizing cost, it is often best to use a combination of container types and sizes (even for plants of the same species on the same site). This not only allows the restorationist to make a calculated gamble (hedging bets between installation costs and survival) but also results in a more diverse community architecture consisting of multiple size- and age-classes of plants. It also provides a hedge against unusually severe conditions, which may wipe out all but a few of the strongest plants.
Our experience has demonstrated the value of a robust root system, and this is why we feel that plant bands are an excellent choice for difficult sites. They encourage good root development, are relatively easy to transport and can be planted with minimal effort and root disturbance. In addition Tall pots and the new Minitall pots deserve much wider recognition and use as an enrichment planting tool. The fast growth under severe conditions of plants grown in these pots is impressive (see photo).
We have found that the best way to increase the numbers of outplant survivors is to provide them with some form of protection from damaging influences. Although there are still questions about how enclosed tree shelters affect the micro-environment and physiology of many species, it is clear that their use can increase field survival rates dramatically.
The key to success is understanding the plant and the site, working hard to develop a robust root system, and protecting the shoot against excessive grazing and environmental stress. Doing this can yield good survival rates, fast recovery, and minimal cost per acre.
Allen, E. B. and M. F. Allen. 1984. Competition between plants of different successional stages: mycorrhizae as regulators. Canadian Journal of Botany 62: 2625-2629.
Allen, M. F. 1988. Below ground structure a key to reconstructing a practice and ecosystem. Pp. 113-135 in E. B. Allen (ed.) The Reconstruction of Disturbed Lands: An Ecological Approach. Westview Press. Boulder, Colorado.
Allen, M. F. 1992. Mycorrhizal Functioning. Chapman and Hall, NY.
Bainbridge, D. A. 1994 a. Container optimization-field data supports container innovation. in Proceedings Western Forest and Conservation Nursery Association Meeting. U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station, Ft. Collins, (in press).
Bainbridge, D. A. 1994 b. Treeshelters improve establishment on dry sites. Tree Planters Notes 45(l):13-16.
Bainbridge, D. A. and R. A. Virginia. 1990. Restoration in the Sonoran Desert. Restoration and Management Notes 8(l):3-14.
Bainbridge, D. A. and R. T. MacAller. 1995. Treeshelters improve desert planting success. in Proceedings of the 1995 Treeshelter Conference. USFS PA. (In press).
Barbour, M. G. 1968. Germination requirements for the desert shrub Larrea divaricata. Ecology 50:679-685.
Barbour, M. G., J. H. Burk, and W. D. Pitts. 1987. Terrestrial Ecology. Benjamin/Cummins, Menlo Park, CA.
Bowen, J. E. 1980. Catastrophic freezes in the Sonoran Desert. Desert Plants 2(4):232- 236.
Brown, W. L. 1982. Temperature in container affects growth of ornamentals. Louisiana Agriculture 26(l):8-9.
Cox, J. R., H. L. Morton, T. N. Johnson, G. L. Jordan, S. C. Martin & L. C. Fierro. 1982. Vegetation restoration in the Chihuahuan and Sonoran Deserts of North America. Agricultural Reviews and Manuals #28. USDA Agricultural Research Service, Tucson, Arizona 37 pp.
Felker, P., Wiesman, and D. Smith. 1988. Comparison of seedling containers on growth and survival of Prosopis alba and Leucaena leueocephala in semi-arid conditions. Forest Ecology and Management 24:177-182.
Fidelibus, M. F. 1994. Jellyrolls reduce outplanting costs in arid land restoration. Restoration and Management Notes 12 (l):87.
Fidelibus, M. F. and D. A. Bainbridge 1994. The effects of containerless transport on desert shrubs. Tree Planters Notes 45 (3):82-85.
Hayman, D. S. 1982. Influence of soils and fertility on activity and survival of vesicular-arbuscular mycorrhizal fungi. Am. Phytopathol. Soc. 72 (8):1119-1125.
Holden, M. 1992. The greening of a desert. American Nurseryman 4 (15):22-29.
INVAM Newsletter. 1994. Culture methods and inoculum production: a reality check. West Virginia University and the National Science Foundation 4(2):4-6.
Landis, T. 1990. The Container Tree Nursery Manual. USDA Handbook 674 Forest Service, 5 vols.
McAuliffe, J. R. 1986. Herbivore-limited establishment of a Sonoran Desert tree, Cercidium microphyllum. Ecology 67(l):276-280.
Rundel, P. W. and P. S. Nobel. 1991. Structure and function in desert root systems. In: D. Atkinson (ed.) Plant Root Growth: an Ecological Perspective. Blackwell Scientific, Boston, MA.
Smith, J. R. S. 1988[1953]. Tree Crops. Island Press, Covelo, CA.
Sorensen, N. 1993. Physiological ecology of the desert shrub Larrea divaricata: implications for arid land revegetation M.S. Thesis. San Diego State University, San Diego, CA.
Virginia, R.A. and D.A. Bainbridge. 1987. Revegetation in the Colorado Desert: lessons from the study of natural systems. Pp. 52-62 In Proceedings of the 2nd Native Plant Revegetation Symposium. Society for Ecological Restoration and Management, Madison, WI.
Windell, K. 1993. Tree shelters for seedling survival and growth. USDA Forest Service Technical Tips 2400. 4 pp.
David A. Bainbridge is a restoration ecologist and teacher in the Biology Department, San Diego State University [SDSU], San Diego, CA 92132, 619-594-4462)[new numbers 858- 635-4616, Fax 858-635-4730.] Matthew Fidelibus 619-594-594-2641 and Roger MacAller 619-594-2641) e-mail: macalle@sunstroke.sdsu.edu) are graduate students in biology at SDSU. All three are members of the Soil Ecology and Restoration Group. MacAller maintains the group's World Wide Web site at http://www.sci.sdsu.edu/SERG/index.html.
