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Fall 1993

Revegetating Decomposed Granitic Soils: A Nurseryman's Views

Thomas M. Jopson
Owner-Manager, California Forest Nursery, Etna

Abstract: Revegetation of decomposed granitic soils with long-needled pine species, where appropriate, and using stock types and methods developed by the forest products industry for reforestation of harvest areas offers a great potential for success, at relatively low cost. Reforestation methods used to maximize the probability of success are relatively simple in concept, but often difficult to execute. Success requires: 1) selection of appropriate species; 2) acquisition of good seed or other propagation material; 3) selection of competent growers; 4) understanding production cycles and providing the grower with sufficient lead time; 5) proper stock handling prior to planting; 6) selecting competent and experienced planters; and 7) planting at the optimum time.

Defining "Success"

This paper proposes that revegetation of decomposed granitic soils with long-needled pine species, where appropriate, using stock types and methods developed by the forest products industry for reforestation of harvest areas, offers a great potential for "success", at relatively low cost. Other woody species offer similar benefits on appropriate sites.

"Success" means the establishment of vegetation that re-establishes the natural condition of a deeply penetrating root system and a stable, uninterrupted surface mulch layer. This condition often exists even on formerly disrupted sites, where a sufficient density of long-needled pines has become established.

Benefits of Long-needled Pines

There are three reasons long-needled pine species, especially ponderosa and jeffrey pine, are potentially the best choice for many sites. First, they occur naturally on decomposed granitic soils. Second, the long needles form an effective mulch which resists wind and downslope movement even on quite steep and exposed road cuts. Third, pine seedlings have been produced in large quantities for the forest industry and therefore, the horticulture requirements (from seed collection and storage, to nursery culture, packing, storing, and planting) are well known. This means that the chance of success is much greater with these species than with the host of obscure native plant species which tend to find their way onto the revegetation "wish list" (White and Franks, 1978).

Lessons From Reforestation

Seedlings and methods used by the forest industry tend to be the lowest cost way of getting the most successful possible reforestation of a site, because of the economic restraints placed on company management. For example, foresters for Fruit Growers Supply Company out of Hilt, California decided to revegetate bare decomposed granitic cut and fill slopes along access roads near Etna, California. Using their regular containerized ponderosa pine planting stock and a commercial planting crew, they planted approximately 20,000 ponderosa pine on 4-6 foot spacing. At a cost of $0.13 per seedling, and $0.17 for planting (including administrative costs), this works out to about $0.30 per planted seedling or about $522.00 per acre. The second year survival on this particular planting is around 90%.

The short-term benefits of this planting are limited to a small amount of mechanical stabilization of the slope by the stems of the trees. However, potential long-term benefits are a deeply penetrating root system and a permanent needle mulch cover that will effectively eliminate erosion (Megahan, 1974). This result is in contrast to many grass seed and erosion blanket applications where the short-term benefits are great, but the long-term benefits are essentially nil.

Keys to Success

Reforestation methods used to maximize the probability of success are relatively simple in concept, but often difficult to execute. Success requires:

Selection of Species

Selection of species which will have the highest probability of success can be achieved as follows (Gray and Jopson, 1979). First, choose species which are capable of growing on the actual site. The best way to avoid mistakes is to limit the choices to species which already occur on the site or on very similar sites. Second, choose species which have been grown and planted successfully in meaningful quantities under the conditions found on the site. Third, choose species for which reproductive material (seed or cuttings) is readily available, or can be made available, in suitable quantities. Fourth, choose species which, if they survive and grow, can demonstrably contribute to the long-term stability of the site (Megahan, 1974). What will they look like in ten years?

There are very few species available which can meet all of the criteria. This paper focuses on the conifers, and the long-needled pine species in particular, just because they come closer than any other to meeting all of the criteria. However, there are many sites for which they are not appropriate and suitable alternatives are difficult to find. Species which fail to meet all of these criteria should be considered experimental. The probability of success will be low until more experience with them has been acquired.

Seed Collection

Acquisition of seed for woody plants from appropriate sources may require substantial lead times(often years) and in-depth knowledge of seed collection requirements. The standard in the forest industry is plus or minus 500 feet from the site elevation and from the same climatic or seed zone (U.S. Forest Service, 1974). The difficulty is that conifers, and many other woody species, do not produce collectable seeds every year. The average years between good seed crops for ponderosa pine is about 7 years. Thus, advance planning is a must. When seed is collected, it must be collected at the proper time, and handled in the proper way to ensure maximum viability. Trying to grow seed which has been collected too early or badly handled is a nurseryman's nightmare. Many agencies, such as the U.S. Forest Service and state forestry departments, and private seed companies have expertise in these areas and should be at least consulted before seed collection is attempted.

Seedling Production

Seedling production also requires advance planning. The highest probability of obtaining quality seedlings will be achieved by selecting a nursery which has experience in the production of seedlings for wildland plantings. Most likely this will be a reforestation nursery. Too many revegetation plantings fail because the stock is obtained as cast-offs from other projects, grown as a `class project' by the local high school or ROP program, or from other socially meaningful but often horticulturally disastrous sources.

The lead time for a typical containerized seedling includes approximately three to four months prior to the March or April sow for contract finalization, seed shipment, and seed stratification. The seedling would then be available for planting if the Fall of the same year or the Winter or Spring of the following year. Giving the nurseryman sufficient lead time will allow production of the best possible seedling.

Packing and Storage

If seedlings are to be planted in Winter or Spring, they will have to be packed and stored. Appropriate packaging (i.e., vapor barriers in boxes or bags) and storage conditions (either freezer or refrigerator) allow seedlings to be stored for up to four months with little loss of vigor, assuming they were in a dormant condition when packed.

Planting

Proper planting is a crucial step which requires attention to two factors: timing and method. The "right" time to plant a seedling is when the soil is warm enough to allow good root growth (5-10 C), and the moisture content is at field capacity. Of course it is also nice if a warm rain falls every day for the next two weeks and the wind doesn't blow at all. Cold soil means that the seedling will sit in the planting hole and do nothing at all. It may as well still be in storage where it is not subject to desiccating winds and being eaten by animals. Planting outside of the ideal conditions means the probability of success diminishes.

Good planting method is dictated by three factors: good people, good people, and good people. Good means caring about the result of the planting, experienced in planting seedlings, and willing to be flexible to achieve the goal of planting each seedling at the right time and in the right place. Good also means supervision by people who understand the importance of timing, know what constitutes a good planting job, and who are willing to do whatever inspections and enforcement are necessary to ensure the best possible job.

In inland areas, away from the coast, these criteria are most likely to be met in the spring of the year, after the soil have warmed up a little. In coastal areas, the soil temperature criteria may be met almost all year, leaving the moisture criteria as the most important. In areas of reliable summer rainfall, the criteria may be met in the summer.

The quantity of plants on a typical revegetation project tends to be small, so that most of the planting can be accomplished at the right time. This fact, if used to best advantage, will enhance the chance of success of the project.

Conclusions

The lessons learned from many years of wildland reforestation offer significant hope to those who are attempting the more difficult task of revegetating disturbed decomposed granitic sites. Those lessons provide a basis for evaluating the probability of success of a wide range of potential practices and point to specific practices that have a high probability of success if adopted for use by revegetation specialists. The technology is not glamorous, but it does have the advantage of a proven record of success when properly executed.

References
Gray, D.H. and T.M. Jopson. 1979. Vegetative-structural slope protection for rehabilitation of disturbed areas in Redwood National Park. Final report to the National Park Service. University of Michigan, Ann Arbor MI. 204 p.

Megahan, W.F. 1974. Deep-rooted plants for erosion control on granitic road fills in the Idaho Batholith. U.S. For. Serv. Research Paper INT-161. Ogden UT. 18 p.

U.S. Forest Service. 1974. Seeds of woody plants in the United States. USDA Forest Service Agricultural Handbook No. 450. GPO, Wash. D.C. 883 p.

White, C.A. and A.L. Franks. 1978. Demonstration of erosion and sediment control technology, Lake Tahoe Region of California. Calif. State Water Resources Control Bd., Final Report to the U.S. Env. Prot. Agency. Sacramento CA. 393 p.

You can contact Tom at: (916) 467-5211 or by mail at P.O. Box 719, Etna, CA 96027.

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